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An Introduction to:
In Vitro - In Vivo Extrapolation (IVIVE)


                  Masoud Jamei
         Senior Scientific Advisor, Head of M&S
         Honorary Lecturer, University of Sheffield

                  M.Jamei@Simcyp.com


         The University of Greenwich, 29th Oct 2009, UK


                                                          IN CONFIDENCE   © 2001-2009
Acknowledgement: The Team




Current:
Geoff Tucker, Amin Rostami-Hodjegan, Mohsen Aarabi, Khalid Abduljalil, Malidi Ahamadi, Lisa Almond, Steve
Andrews, Adrian Barnett, Zoe Barter, Kim Crewe, Helen Cubitt, Duncan Edwards, Kevin Feng, Cyrus Ghobadi, Matt
Harwood, Phil Hayward, Masoud Jamei, Trevor Johnson, James Kay, Kristin Lacy, Susan Lundie, Steve Marciniak,
Claire Millington, Himanshu Mishra, Chris Musther, Helen Musther, Sibylle Neuhoff, Sebastian Polak, Camilla
Rosenbaum, Karen Rowland-Yeo, Farzaneh Salem, David Turner, Kris Wragg
Previous:
Aurel Allabi, Mark Baker, Kohn Boussery, Hege Christensen, Gemma Dickinson, Eleanor Howgate, Jim Grannell,
Shin-Ichi Inoue, Hisakazu Ohtani, Mahmut Ozdemir, Helen Perrett, Maciej Swat, Linh Van, Hua Wang, Jiansong
Yang & .... Many others

                                                                                         IN CONFIDENCE   © 2001-2009
Grants Received by Simcyp




                            IN CONFIDENCE   © 2001-2009
Simcyp Background

 “Simcyp” stands for simulating CYPs (a super family of
 metabolising enzymes).

 Simcyp is a spin-out company of the University of Sheffield
 founded in 2001.

 Simcyp activities and future developments are guided by a
 consortium of pharmaceutical companies (the Simcyp
 consortium).

 The Simcyp® Population-Based ADME Simulator is a platform
 and database for „bottom-up‟ mechanistic modelling and
 simulation of the ADME processes of drugs and drug
 candidates in healthy and disease populations.


                                                     IN CONFIDENCE   © 2001-2009
Pharmacology, PK and PD

 Pharmacology is the study of how drugs interact with living
 organisms to produce a change in function. The field encompasses
 drug composition and properties, interactions, toxicology, therapy,
 and medical applications and antipathogenic capabilities.

 Pharmacokinetics (PK) is a branch of pharmacology dedicated to
 the determination of the fate of substances administered externally
 to a living organism.
 Or, what the body does to a substance.


 Pharmacodynamics (PD) is the study of the biochemical and
 physiological effects of drugs on the body, the mechanisms of drug
 action and the relationship between drug concentration and effect.
 Or, what the substance does to the body.

                            Source: Wikipedia
                                                          IN CONFIDENCE   © 2001-2009
In Vitro - In Vivo Extrapolation (IVIVE)

 In vitro (Latin: within the glass) refers to the technique of
 performing a given procedure in a controlled environment
 outside of a living organism.

 In vivo (Latin for "within the living") refers to experimentation
 using a whole, living organism as opposed to a partial or dead
 organism.


                   Mechanistic approach


                     Drug fate in body
        in vitro                                   in vivo

                                                        IN CONFIDENCE   © 2001-2009
One Source of the Problem

 PRE-CLINICAL                 CLINICAL




                       Ki
                ED50
                       LogP
            Kinact




                                    IN CONFIDENCE   © 2001-2009
A Timeline of Traditional Drug Discovery and Development




    Hoffman J M et al. Radiology 2007;245:645-660


                                                           IN CONFIDENCE   © 2001-2009
Estimate of the Total Investment required to “launch”




    Hoffman J M et al. Radiology 2007;245:645-660
    Windhover's in vivo: the business and medicine report, Bain drug economics model, Nov 2003



                                                                                      IN CONFIDENCE   © 2001-2009
ADME

PK is often divided into several areas including, but not limited to, the
extent and rate of Absorption, Distribution, Metabolism and Excretion
(ADME).

Absorption is the process of a substance entering the body through mouth.
Distribution is the dispersion or dissemination of substances throughout
the fluids and tissues of the body.
Metabolism is the irreversible transformation of substances and its
daughter metabolites.
Excretion is the elimination of the substances from the body. In rare cases,
some drugs irreversibly accumulate in a tissue in the body.

The biological, physiological, and physicochemical factors influence the
rate and extent of ADME of drugs in the body.

                               Source: Wikipedia
                                                                  IN CONFIDENCE   © 2001-2009
ADME: The Roadmap to Site of Effect
                                         Drug                                  Food, environment,
       Tablet                                              Compliance
     in Faeces
                                       in Tablet
                                                         Comprehension         genetic, race, gender,
       Excretion
                                                                               etc effects!
                                        Drug                                                        Drug
        Drug                       in Tablet in Gut             Release                           Metabolites
     in Faeces

                                     Drug in Gut                Absorption                          Drug
                    Excretion                                                                     Metabolites
                                                                Metabolism

       Drug in                      Drug in Blood               Metabolism
   Urine, Bile, Milk                                                                                Drug
                                                                                                  Metabolites
                   Excretion        Drug in Tissues             Distribution
                                                                Metabolism

                                Drug at Receptor              Metabolite at Receptor



                      NO                            DESIRED                      UNWANTED
                   RESPONSE                        RESPONSE                       RESPONSE




                   NO CHANGE                        THERAPY                            TOXICITY

                                                                                                   IN CONFIDENCE   © 2001-2009
PK Models

 Different PK models:



                               1
        C=Cie-kit




                               2
       Empirical
                           Compartmental   Physiological


 GT Tucker (Basic PK Course)
                                               IN CONFIDENCE   © 2001-2009
Combining Physiological and Drug-dependent Data

                                   Drug
                                   Data
              Systems                            Trial
                Data                            Design

                                 Mechanistic
                                IVIVE & PBPK




                        Population Pharmacokinetics
                                     &
                            Covariates of ADME
 (Jamei et al., 2009)
                                                         IN CONFIDENCE   © 2001-2009
The Challenge of Population Variability


       Environment                        Disease

                                          Genetics




                                                 IN CONFIDENCE   © 2001-2009
Relationships Between Covariates Affecting ADME

                                          Genotypes
                                  (Distribution in Population)            Renal
                                                                         Function
           Body                  Ethnicity         Disease
            Fat                                                            Serum
                                                                         Creatinine

                      Sex                                              Age
           (Distribution in Population)                     (Distribution in Population)



                                           Height                 Brain
  Heart              Body                                        Volume
  Volume            Surface
                      Area
                                            Weight                             MPPGL
                              Cardiac                                          HPGL
            Liver                                     Cardiac
                              Output                   Index                        Enzyme
           Volume                                                                  Abundance
                                           Liver                  Intrinsic
                                          Weight                 Clearance
 (Jamei et al., 2009)
                                                                                           IN CONFIDENCE   © 2001-2009
Covariates of Determining Tissue Volumes




                               Age Sex          Weight         Height

Adipose                                                                               Erythrocytes


          Brain                                                                     Plasma


                  Bone                                                          Spleen


                         Gut   Heart   Kidney   Liver   Lung    Muscle   Skin




                                                                                    IN CONFIDENCE   © 2001-2009
Models to Predict Tissue Volumes
                                                                                                           Price et al., 2003
Volume of Brain (L) for M&F aged 0-19 (including adult F)

                                   Male = (-90.7 * BH(m) + 178.1) * BW(kg) / 1040;
                                   Female = (-97.5 * BH(m) + 181.2) * BW(kg) / 1040;


Volume of Heart (L) in Adults

                                   Male = 9.22 * BW(kg)0.853 / 1040;
                                   Female = 9 * BW(kg)0.855 / 1040;


Volume of Heart (L) for others

                                   Male = (22.81 * BH(m) * BW0.5 - 4.15) / 1040;
                                   Female = (19.99 * BH(m) * BW0.5-1.53) / 1040;

                    1.6 Male                                                        1.6       Female
                    1.4                                                             1.4
 Brain Volume (L)




                    1.2                                          Brain Volume (L)   1.2
                     1                                                               1
                    0.8                                                             0.8
                    0.6                        ICRP                                 0.6                              ICRP
                    0.4                        Predicted                            0.4                             Predicted
                    0.2                                                             0.2
                     0                                                               0
                        0    5     10     15      20       25                             0      5       10     15         20       25
                                 Age (year)                                                            Age (year)
                                                                                                                    IN CONFIDENCE   © 2001-2009
Dosing Regimen and PK Parameters

In many cases, pharmacological action, as well as toxicological action, is
related to plasma concentration of drugs. Consequently, through the study
of PK parameters, we will be able to individualise therapy for patients.

           Dosing regimen: How much?            Dosing regimen: How often?



                           Oral
                                                          Half-life
                       bioavailability




                                                                      Volume of
          Absorption                     Clearance
                                                                      distribution




                 van de Waterbeemd and Gifford 2003, Drug Discovery
                                                                                IN CONFIDENCE   © 2001-2009
Oral Absorption and the GI Tract




                       From Moore & Dalley, 5th Ed
                                                     IN CONFIDENCE   © 2001-2009
Factors Affecting Solid Drug Absorption

 Physicochemical &             Physiological issues
 Pharmaceutical issues
   Disintegration                Gastric emptying
   De-aggregation                Intestinal mobility
   Dissolution                   pH
   Solubility                    Intestinal metabolism
   Precipitation                 Disease state
   Permeability                  P-gp and other transporters
   Intra-gut degradation         Intestinal blood flow
                                  Food effects
                                  GI-tract fluid secretion, re-
                                   absorption and motility


                                                        IN CONFIDENCE   © 2001-2009
Oral Absorption and First-Pass Effect

           Gut Lumen
                                                Portal Vein


                       Gut Wall
                                                           Liver



                  Fa              FG                        FH              To Site
                                                                              of
                                                                            Action




                                                            Metabolism
                              Metabolism




                         To Faeces

                                  Rowland and Tozer 1995

                                                                         IN CONFIDENCE   © 2001-2009
Oral Bioavailability

                                Fraction escaped metabolism
Fraction of dose released
                                in enterocytes
from formulation and                                Fraction escaped
permeates through gut wall                          metabolism in
                                                    hepatocytes




Foral = fa . FG . FH
                 Release
                 Solubility
                                        Metabolism     Metabolism
                 Stability
                                        Permeability   Transport
                 Transit
                                        Binding        Binding
                 Permeability
                                        Blood Flow     Blood Flow

                                                        IN CONFIDENCE   © 2001-2009
Solid Drug Absorption


                       dissolution
                                                     Solution              Absorption




                                                                precipitation

                                                 dissolution
      disintegration



                                     deaggregation


                                     reaggregation




                                                                                IN CONFIDENCE   © 2001-2009
Breakdown / Dissolution Stages
                                                    kf,n-1AF,n-1                 Drug in              kf,nAF,n
 AF,n : the amount of solid mass trapped                                       formulation
 in the formulation and not available for
 dissolution
                                                                                           Release
                                                                                            Rate

                                                    kt,n-1AS,n-1                                        kt,nAS,n
 AS : the amount of solid mass available                                       Solid drug
 for dissolution

                                                            Precipitation           Dissolution Rate
                                                                Rate
                                                    kt,n-1AD,n-1                                         kt,nAD,n
 AD : dissolved drug                                                           Dissolved
                                                                                 drug

                                                                   Transport         Absorption Rate
                                       Luminal                       Rate
                                     Degradation

                                                                            Absorbed drug



                                        Gut Wall                                      To portal vein
Jamei et al. (2009) AAPSJ
                                       Metabolism
                                                                                                     IN CONFIDENCE   © 2001-2009
Some Differential Equations

 dAS ,n          dAdiss,n                                               dAF, n
                               kt ,n AS ,n  kt ,n  1 AS ,n  1 
   dt                 dt                                                  dt


                            k deg,n  kan  kt ,n AD,n  kt ,n1 AD,n1   nCLuintT , n fu gutCent, n
 dAD,n        dAdiss,n
          
   dt            dt

 dCent, n
   dt
            
                  1
                Vent, n
                           ka An   diss, n    Qent, nCent, n  CLuintG , n  CLuintT ,n  fu gutCent, n 


 dAdiss,n                   1       1                                   AD ,n 
               4πr ( t )D2
                                                            C S ,n                 
    dt                      r( t ) h                                 Vlumen,n ( t ) 
                                    eff                                             

 Jamei et al. (2009) AAPSJ 11:225


                                                                                               IN CONFIDENCE   © 2001-2009
Advanced Dissolution Absorption & Metabolism
  Stomach            Duodenum     Jejunum I & II       Ileum I    Ileum II       Ileum III   Ileum IV      Colon

   Solid
  Dosage

                                                      Release

    Fine
  Particles


                                Dissolution / Precipitation         / Super-Saturation


 Dissolved
   Drug
       Degradation
                Pgp                      Absorption / Efflux
                                                                                                                     Faeces

Enterocytes
                                                                                                        Metabolism


R distribution
pH distribution
                                                                                                          PBPK Distribution
Permeability distribution                          Portal Vein               Liver                             Model
CYPs+Pgp distribution
Blood flow distribution            After Agoram 2001             Jamei et al. 2009
                                                                                                         IN CONFIDENCE   © 2001-2009
Fluid Dynamics in the GI-tract

                                 Rsec, j

                        Ktj-1 Vj-1
                                                                Ktj Vj
                                             Vj

                                                         KRe-Abs, j

 Rsec, j:   Fluid secretion rate into jth gut segment (1/h)
 KRe-Abs, j: Fluid re-absorption rate constant from jth segment (1/h)
 Vj:        Volume of fluid in jth segment (mL)
 Ktj:       Transit rate constant in jth segment (1/h)

dV j
      Kt j 1V j 1  Rsec, j  K Re  Abs, jV j  Kt jV j
 dt
                                                                         IN CONFIDENCE   © 2001-2009
Inter-individual Variability & fa


                                                                                        fa vs Peff and Tsi (R=1.7 cm)
             250                                              120%

                                                              100%
             200                                                               100
                                                              80%
             150




                                                                     fa (%)
                                                              60%               50
 Frequency




             100
                                                              40%

             50                                                                 0
                                                              20%
                                                                                    4
              0                                               0%                                                                     10
                   52    135   207   288   365    447   570                                 2                       5
                                                                          Peff (cm/h)
                  Intestinal Transit Time (min)                                                     0 0                 Tsi (h)

   Yu et al. (1998)                                                           M Jamei et al, 2009




              Probability distribution fitting                                                Sensitivity Analysis



                                                                                                              IN CONFIDENCE       © 2001-2009
Clearance (CL)

 The Clearance (Cl) of a drug is the volume of plasma from
 which the drug is completely removed per unit time. The
 amount eliminated is proportional to the concentration of
 the drug in the blood.
                       Mass Balance
          Q x CA                             Q x CV



 Rate of Extraction=
 E = (CA-CV)/CA
                       Q(CA - CV)
 Clearance = QE

                                                    IN CONFIDENCE   © 2001-2009
Metabolism in the liver

 Metabolism mainly happens in the liver but it can happen in
 the gut and to much lesser degree in the kidney.
 Intrinsic hepatic (gut) clearance (CLint): The ability of the liver
 (gut) to remove xenobiotic from the blood in the absence of
 other confounding factors (e.g., QH).
                                      fuB.CLuint
                             EH   =
                                    QH + fuB.CLuint

                                       QH.fuB.CLuint
                            CLH     =
                                      QH + fuB.CLuint

               Can we find Cluint from in vitro assays?
               How?
                                                         IN CONFIDENCE   © 2001-2009
Scaling Factors for Hepatic Clearance

             In vitro                  CLuint per
               CLuint                   g Liver

 In vitro                   Scaling             Scaling CLu per
                                                           int
 system                     Factor 1            Factor 2 Liver


HLM       µL.min-1
                                       MPPGL
       mg mic protein X

HHEP        µL.min-1                                               Liver
                        X              HPGL                 X
            106 cells                                             Weight


rhCYP      µL.min-1      pmol P450 isoformX MPPGL
                       X  mg mic protein
      pmol P450 isoform
                                                       IN CONFIDENCE   © 2001-2009
IVIVE - Metabolism

   CLint per         CYP/mg x MPPGL           Overall CYPs                                     fuB
  Specific CYP                               (pmol/g liver)
                                                                Liver Weight
 CLint per mg of        MPPGL          Microsomal Protein
                                          (mg/g liver)                                  CLint Liver
Microsomal Protein

    CLint per             HPGL             Hepatocellularity
   Hepatocyte                                (106/g liver)                           Liver Blood Flow


                                                                      CLH
                                                      CLpo
                                                                     fa, FG
   Genetic/Environmental/rac
      e/age/sex/disease
        considerations
                                                                               Gut Blood Flow

                                                                              Gut Surface Area

                        Total CYP in gut          Overal CYPs
    CLint per CYP                                    in gut
                                                                                   CLint Gut

                                                                        Gut Wall Permeability

                                                                                          IN CONFIDENCE   © 2001-2009
Rate per pmol of “Each Enzyme”

Knowing:
 the abundance of each CYP isoform per mg of microsomal
  protein
 the isoform(s) responsible for specific metabolic routes
                       n  m Vmax (rhCYPj )i  CYP jabundance 
CLuint [ L / h]                                             MPPGL Liver Weig ht
                       j1  i 1
                                    K m (rhCYPj )i           
                                                               
 Proctor et al. Xenobiotica 2004                                                Vmax
                                                Americans/Europeans    CLint 
CYP1A2
                                                                               Km  [ S ]
CYP2A6

CYP2B6

CYP2C8

CYP2C9

CYP2C18

CYP2C19

CYP2D6

CYP2E1

CYP2J2

CYP3A4

CYP3A5
                                             Japanese/Chinese

                                                                           IN CONFIDENCE   © 2001-2009
Mechanistic Model for Expressing Enzyme Pool

                                   [S]               [P]

                                          [E·S]
                          Rsys
                                   [E]
      Induction
                         kdegrad          [E·I]

                                   [I]       kinact [PI]

                                         [E·MI]

   Accelerated Deactivation


                                                       IN CONFIDENCE   © 2001-2009
Mutual Interactions:       Drugs/Metabolites/Self-Induction/Inhibition


                                       Comp, MBI, Ind



                                                                         Comp, MBI, Ind
        Comp, MBI, Ind




 Sub       Sub Met             Inh 1           Inh1 Met          Inh 2        Inh 3




                     Comp, MBI, Ind


                            Comp, MBI, Ind


                                       Comp, MBI, Ind

                                                                         IN CONFIDENCE   © 2001-2009
Predicting Volume of Distribution (Vss)

Vss knowing distribution into individual tissues is (Sawada et al.,
1984):

     Vss  Vp  Ve  E : P   Vt  Pt:p
                                             t

Vp = volume of plasma; Vt = tissue (t) volume
                                                                    Ce, ss
Erythrocyte : Plasma partition coefficient              E:P
                                                                    C p , ss
                                                                        Ct ,ss
Tissue : Plasma partition coefficient                   K p  Pt: p 
                                                                        C p ,ss




                                                               IN CONFIDENCE      © 2001-2009
Minimal Physiologically-Based PK Model

                                            1-fa
    PO                  Gut Lumen                    Faeces
                                  fa        1-FG
                           Gut Wall                Gut Metabolism

                        Portal Vein

                   FG
                        QPV          QPV
                               QHA

                               FH            Systemic
           Liver                                                         IV
                              QPV+HA       Compartment
         CLH   Hepatic
                                            CLR    Renal
               Clearance
                                                   Clearance
                                                         IN CONFIDENCE    © 2001-2009
Whole Body Physiologically-based PK Parameters

 Physiologically-based pharmacokinetics (PBPK) models need different
 sets of parameters which can be divided into:

 Physiological parameters including:
  •   tissue volumes,
  •   tissue compositions,
  •   blood flow to each organ/tissue,
  •   Enzyme abundances and distributions,
  •   Transporters abundances and distributions

 Drug-dependent parameters including:
  • Physicochemical and blood/plasma binding data (MW, LogP, pKa, fu,
    B:P, etc),
  • Absorption data (fa, ka, permeability, solubility, particle size, etc),
  • Metabolism data (CL, CLint, etc),
  • Distribution data (tissue:plasma ratios (Kp))
  • Transport data (Jmax, Km, REF, CLPD, etc)


                                                                  IN CONFIDENCE   © 2001-2009
Full PBPK Model with Time-Dependent Volume

                        Lung

                       Adipose
                        Bone
                        Brain
                        Heart
   Venous                                         Arterial
                        Kidney                     Blood
    Blood
                       Muscle
                         Skin
                         Liver
                                      Spleen
                      Portal Vein
                                       Gut
            IV Dose                            PO Dose

                                                IN CONFIDENCE   © 2001-2009
Multicompartment Mammillary Model
           Plasma Water                                                     KKtP-off
                                                                             P-on
                                                           P                                              +ve
             P                                                               KP-off                      pH=7.4
                                      KtEW-in             KtEW-out
                                                                 KtP-off
                             +ve
                                                                                       P
                                                               KtP-on            +ve
                 EW                                                                               pH=7.4
                                           KtIW-in             KtIW-out

                           KtNP-on
                                                                                            +ve

                                KtNP-off                                   KtAP-on          KtAP-off
                      NP

    Ktel                                   KtNL-on          KtNL-off                                +ve


                                                                                       AP
                                                                                                  -ve
                                                     NL
                 IW                                                                                     pH=7

EW: Extracellular Water         NL: Neutral Lipids        AP: Acidic Phospholipids
IW: Intracellular Water         NP: Neutral Phospholipids
                                                                                                               IN CONFIDENCE   © 2001-2009
Prediction of Tissue to Plasma Partition Coefficients

 Strong bases (pKa ≥ 7) and Zwitterions (pKa ≥ 7)

      K pu  f EW
                      X
                      f IW                               
                                                                          
                               P  f NL  0.3P  0.7 f NP   Ka AP AP T  a 
                                                                          
                                                                                 
                                                                                
                      Y                     Y                      Y        


 Other compounds (Zwitterions pKa < 7, neutrals, acids and weak
 bases)
                      X       P  f NL  0.3P  0.7 f NP 
      K pu  f EW     f IW                                 KaPR PR T 
                      Y                     Y              


                             Rodgers and Rowland 2006, 2007

                                                                         IN CONFIDENCE   © 2001-2009
Active and Passive Transport
  QT                                                                                   QT
              Capillary blood

              Extracellular fluid


              Phospholipid bilayer

              Intracellular fluid

 For most drugs the capillary membrane is very permeable and diffusion to
 the interstitial fluid is very fast (Gibaldi and Perrier 1975).
 The drug movement across the cell membrane can be either passive
 or/and active.

   Perfusion-limited penetration (permeability is NOT rate limiting)
   Permeability-limited penetration (permeability is rate limiting)

             http://cellbiology.med.unsw.edu.au/units/science/lecture0803.htm

                                                                                IN CONFIDENCE   © 2001-2009
Known Human Transporters!


                                             > 50
           human ABC transporters are identified;
                   7 sub-families (A-G)


                                             > 360
                          human SLC transporters;
                             48 sub-families

  http://www.bioparadigms.org/slc/menu.asp           http://www.humanabc.bio.titech.ac.jp/

                                                                            IN CONFIDENCE   © 2001-2009
Tissues Transporters




                       Ho and Kim, 2005
                                          IN CONFIDENCE   © 2001-2009
Permeability-limited Liver Model - Hepatobiliary Transporters


                     Capillary blood                                                 KP-on
                                                                                      KtP-off
                                                                    P                                                +ve
                          P                                                           KP-off              pH=7.4
                                                   KtEW-in              KtEW-out
                                                                            KtP-off
                                           +ve
                                                                                                      P
                                                                           KtP-on               +ve
                      EW                                                                                      pH=7.4
    Sinusoidal            OATP1B1           OATP1B3                           OCT1                        MRP3
                                                 KtIW-in            KtIW-out
    membrane
                                                                                                                                Tight junction
                                         KtNP-on
                                                                                                          P-gp
                                                                                                          +ve

                                             KtNP-off                                  KtAP-on            KtAP-off
                              NP                                                                          MRP2
                                                        KtNL-on           KtNL-off                                         Bile
          Ktel
                                                                                                             +ve
                                                                                                          BCRP
                                                                                                 AP
                                                                                                             -ve
                                                                   NL
                      IW                                                                                           pH=7

EW: Extracellular Water       NL: Neutral Lipids                  AP: Acidic Phospholipids                           Canalicular
IW: Intracellular Water       NP: Neutral Phospholipids                                                              membrane
                                                                                                                           IN CONFIDENCE   © 2001-2009
Parameter Estimation Module


                              Tune design parameters
                                 to fit observations
                    Simcyp simulation



                     Trial and Error



             Parameter Estimation (PE) Module




                                                 IN CONFIDENCE   © 2001-2009
Parameter Estimation Process

During a parameter estimation process the design parameters are changed,
according to a specific algorithm, to get the model outputs as close as possible to
the observed DVs.
Design parameters: Vss, CL, fu, BP, …
Model: one-compartment absorption and/or PBPK model
DVs: plasma concentrations

                    3


                    2

          C(t)
                    1


                    0
                            t1            t2            t3



                                                                       IN CONFIDENCE   © 2001-2009
Least Squares (LS) Objective Function
                  3


                  2                   e (t1)                  e (t2)
     C(θ, t)

                  1                                                                     e (t3)


                  0
                      0        t1           20           t2      40             t3       60            80
                                    i n                                         i n
    WLS  min  w i e( t i )  min  w i y( t i )  C, t i 
    ˆ                        2                                   2

                                    i 1                                         i 1



  in
         yi  f (, t i )2        in
                                           yi  f (, t i )2        in
                                                                              yi  f (, t i )2   in
                                                                                                           yi  f (, t i )2
  
  i 1           yi
                                    
                                    i 1           yi2
                                                                      i 1          f (, t i )
                                                                                                    
                                                                                                    i 1       f (, t i ) 2

                                                                                                                IN CONFIDENCE    © 2001-2009
Optimisation Algorithms

  Direct/random search methods (Hooke-Jeeves,
   Nelder-Mead, …);

  Genetic Algorithms (GA);

  Combined Algorithms:

     Begin with a global optimisation method (GA) and
     then switch to a local optimisation method; e.g.,
     HJ or NM.

                                              IN CONFIDENCE   © 2001-2009
Genetic Algorithms
                                            Evaluate Candidates

  Randomly Assigned      Set of Candidate
     Candidates            Parameters




   Select a New Set of
                                                Rank Candidates
       Candidates




   Recombination and                             Reproduce New
       Mutation                                    Candidates



                                                        IN CONFIDENCE   © 2001-2009
Maximum Likelihood (ML) Estimation

 In a population, the model parameters and observations are different for different
 subjects and we are interested in predicting individual as well as population
 parameters.                               l(θ|y2)

                         3       l(θ|y1)


                         2                                l(θ|y3)
               C(θ, t)

                         1


                         0
                             0     t1      20   t2   40     t3      60           80

 Assuming normal distribution of parameters N(C(θ, t1), σ12)
                                                         y i  C  , ti 2              
                              | y   
                                              1
 Likelihood function:                             exp                                       
                                            i 2              2 i2                        
                                                                                            

                                                                         IN CONFIDENCE   © 2001-2009
Maximum a Posterior (MAP) Objective Function

 MAP estimation is a Bayesian approach in the sense that it can exploit an
 additional information on the supplied experimental data.
 Consequently if the user has prior knowledge regarding the experimental data
 then the MAP should in theory provide more accurate estimations of the design
 parameters than the Maximum Likelihood which only requires experimental
 measurements.

 MAP differs from ML in that MAP assumes the parameter θ is also a random
 variable which has a prior distribution p(θ)


                    ( yi  f (, t i )) 2                                          P  ( j   j ) 2           
                                                                                  
                  N
  O MAP ()                                  ln (b 0  b1f (, t i ) b 2 ) 2                     ln( j )
                                                                                                                2

              i 1  ( b 0  b1f (, t i ) )                                        j  j
                                          b2 2                                                  2
                                                                                                                 
                                                                                                                  

 Where β={b0, b1, b2} vector defines the variance model:

 Additive                 β={b0, 0, 1}
 Proportional             β={0, b1, 1}
 Combined                 β={b0, b1, 1}

                                                                                                     IN CONFIDENCE   © 2001-2009
Expectation-Maximisation (EM) Algorithm

 In order to determine the ML or MAP estimations we need to use an optimisation
 algorithm.

 The Expectation-Maximisation (EM) algorithm is one of the most popular
 algorithms for the iterative calculation of the likelihood estimates.

 The EM algorithm was first introduced by Dempster et al (Dempster, Laird et al.
 1977) and was applied to a variety of incomplete-data problems and has two steps
 which are the E-step and the M-step.
 E-step:

 Determining the conditional expectation using Monte Carlo (MC) sampling and
 updating MC pool for each individual after each iteration

 M-step:

 Maximise this expectation with respect to θ and updating population parameters
 and variance model parameters


                                                                    IN CONFIDENCE   © 2001-2009
Useful Simulations vs Accurate Predictions




              Rostami-Hodjegan & Tucker, Drug Discovery Today:
                        Technologies, V4, Dec 2004               IN CONFIDENCE   © 2001-2009
3 Pillars of Successful Knowledge Management
- Intelligent Workforce - Reliable Data - Enabling Tools

Regular Hands-on Workshops to give update on
latest IVIVE activities applied to ADME to ALL key
players in the drug development scene (e.g.
scientists in regulatory agencies, different sections of
industry)




                                                              Amount of CYP3A4 in the Gut
                                                                                            8.10 4



Gathering Data / Reaching Consensus on Common
                                                                                            6.10 4                                                50 mg




                                                                      (Pmol/gut)
                                                                                                                                                  100 mg

IVIVE & ADME Parameters / Identifying Areas of                                              4.10 4                                                200 mg
                                                                                                                                                  400 mg
                                                                                                                                                  600 mg

Further Research (defining specific projects in the form of                                 2.10 4                                                800 mg


focus groups)                                                                                0
                                                                                                     0   50   100      150    200   250   300

                                                                                                                    Time (hour)




 Continuous Development and Update of a user
 friendly and mechanistic platform for easier
 integration of ADME models & databases
 (simulation of candidate drugs in virtual populations)

                                                                                                                             IN CONFIDENCE      © 2001-2009
Organising IVIVE Workshops
Washington – April
                      Leiden - May
                                     Sheffield – September
                                                      La Jolla – November




                                                             IN CONFIDENCE   © 2001-2009
Annual Simcyp IVIVE Awards Academic (Research & Teaching)


   For academic and research institutions leading the field of
   IVIVE, ADME, Pharmaceutics and Modelling and Simulation


   ‘Most Informative Scientific Report’
   • Awarded to lead author
   • Receives bursary towards scientific meeting / sabbatical at Simcyp


   ‘Most Innovative Teaching Application’

   • Awarded to course leader
   • Receives contribution towards computer hardware or software /
     sabbatical at Simcyp




                                                                IN CONFIDENCE   © 2001-2009
Publications: Peer Reviewed Articles

 Research Articles Published/In Press
 1. Johnson TN, Boussery K, Tucker GT, Rostami-Hodjegan A. Prediction of the increased exposure to drugs in liver cirrhosis: A
    systems biology approach integrating prior information on disease with in vitro data on drug disposition, Clin Pharmacokin
    2009 (in press)
 2. Johnson TN, Kerbusch T, Jones B, Tucker GT, Rostami-Hodjegan A, Milligan P. Assessing the efficiency of mixed effects
    modelling in quantifying metabolism based drug-drug interactions: Using in vitro data as an aid to assess study power,
    Pharm Stats 2009 (Epub ahead of print)
 3. Van LM, Sarda S, Hargreaves JA and Rostami-Hodjegan A. Metabolism of Dextrorphan by CYP2D6 in Different
    Recombinantly Expressed Systems and its Implications for the In Vitro Assessment of Dextromethorphan Metabolism, J
    Pharm Sci 2009, 98(2): 763-71
 4. O‟Mahoney B, Farre Albaladejo M, Rostami-Hodjegan A, Yang J, Cuyas Navarro E, Torrens Melich M, Pardo Lozano R,
    Abanades S, Maluf S, Tucker GT and De La Torre Fornell R. The consequences of 3,4-methylenedioxymethamphetamine
    (MDMA, Ecstasy) induced CYP2D6 inhibition in humans, J Clin Psychopharm 2008, 28(5): 523-9
 5. Barter Z, Chowdry J, Harlow JR, Snawder JE, Lipscomb JC and Rostami-Hodjegan A. Co variation of human microsomal
    protein per gram of liver with age: Absence of influence of operator and sample storage may justify inter laboratory data
    pooling, Drug Metab Dispos. 2008, 36(12): 2405-9

 Review Articles Published/In Press
 1. Almond LM, Yang J, Jamei M, Tucker GT, Rostami-Hodjegan A. Towards a quantitative framework for the prediction of DDI‟s
    arising from Cytochrome P450 induction, Curr Drug Metab 2009, 10(4): 420-432
 2. Jamei M, Turner D, Yang J, Neuhoff S, Polak S, Rostami-Hodjegan A, Tucker GT. Population-based Mechanistic Prediction of
    Oral Drug Absorption, The AAPS Journal 2009, 11(2): 225-237
 3. Jamei M, Dickinson GL, Rostami-Hodjegan A. A framework for assessing inter-individual variability in pharmacokinetics using
    virtual human populations and integrating general knowledge of physical chemistry, biology, anatomy, physiology and
    genetics: A tale of „bottom-up‟ vs „top-down‟ recognition of covariates, DMPK 2009, 24(1): 53-75
 4. Jamei M, Marciniak S, Feng K, Barnett A, Tucker G, Rostami-Hodjegan A. The Simcyp population-based ADME simulator,
    Expert Opinion on Drug Metabolism & Toxicology 2009, 5(2): 211-223

                                                                                                        IN CONFIDENCE   © 2001-2009
Publications: Others

    Book Chapters in Press


1. Rostami-Hodjegan A. Translation of in vitro metabolic data to predict in vivo drug-drug
   interactions: IVIVE and modeling and simulations, in “Enzymatic- and Transporter-Based
   Drug-Drug Interactions: Progress and Future Challenges” (Eds. Sandy K. Pang, David A.
   Rodrigues and Raimund M. Peter), Springer, 2009, In press

2. Rostami-Hodjegan A. Predicting Inter-individual Variability of Metabolic Drug-Drug
   Interactions: Identifying the Causes and Accounting for them Using Systems Approach, in
   “Enzyme Inhibition in Drug Discovery and Development: The Good and the Bad” (Eds.
   Chuang Lu and Albert P. Li), Wiley, 2009, In press

3. Yang J. Simulation of population variability in pharmacokinetics, in “Systems Biology in
   Drug Discovery and Development” (Eds. Daniel L. Young and S. Michelson), Wiley, In
   press



      Commentary Articles


    1. Toon S, „Model Making – Virtual Reality‟, International Clinical Trials, November 2008

    2. Toon S, „R&D in a Virtual World‟, Applied Clinical Trials, 17(10):82, October 2008




                                                                                                IN CONFIDENCE   © 2001-2009
Publications: Growing Independent Research
Applications of Simcyp
1. Wong H, Chen JZ, Chou B, Halladay JS, Kenny JR, La H, Marsters JC, Plise E, Rudewicz PJ, Robarge K, Shin Y, Wong S, Zhang C, Khojasteh SC.
    Preclinical assessment of the absorption, distribution, metabolism and excretion of GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2-
    yl)phenyl)-4-(methylsulfonyl)benzamide), an orally bioavailable systemic Hedgehog signalling pathway inhibitor. Xenobiotica. 2009 Sep 2.
    [Epub ahead of print]
2. Polasek TM, Polak S, Doogue MP, Rostami-Hodjegan A, Miners JO. Assessment of inter-individual variability in predicted phenytoin
    clearance, Eu J Clin Pharm, 2009 (in press)
3. Gibson CR, Bergman A, Lu P, Kesisoglou F, Denney WS, Mulrooney E. Prediction of Phase I single-dose pharmacokinetics using
    recombinant cytochromes P450 and physiologically based modelling, Xenobiotica 2009, 39(9): 637-648
4. Foti RS, Pearson JT, Rock DA, Wahlstrom JL, Wienkers LC. In vitro inhibition of multiple cytochrome P450 isoforms by xanthone derivatives
    from mangosteen extract, Drug Metabolism & Disposition 2009, 37(9): 1848-55
5. Fahmi OA, Hurst S, Plowchalk D, Cook J, Guo F, Youdim K, Dickins M, Phipps A, Darekar A, Hyland R, Obach RS. Comparison of different
    algorithms for predicting clinical drug-drug interactions, based on the use of CYP3A4 in vitro data: predictions of compounds as
    precipitants of interaction, Drug Metabolism & Disposition 2009, 37(8): 1658-1666
6. Thelingwani RS, Zvada SP, Hughes D, Ungell AL, Masimirembwa CM. In vitro and in silico identification and characterisation of
    thiabendazole as a mechanism-based inhibitor of CYP1A2 and simulation of possible pharmacokinetic drug-drug interactions, Drug
    Metabolism & Disposition 2009, 37(6): 1286-1294
7. Hyland R, Osborne T, Payne A, Kempshall S, Logan YR, Ezzeddine K, Jones B. In vitro and in vivo glucuronidation of midazolam in humans,
    British Journal of Clinical Pharmacology 2009, 67(4): 445-454
8. Ping Z, Ragueneau-Majlessi I, Zhang L, Strong JM, Reynolds KS, Levy RH, Thummel KE, Huang SM. Quantitative Evaluation of
    Pharmacokinetic Inhibition of CYP3A Substrates by Ketoconazole: A Simulation Study, J Clin Pharmacol 2009, 49: 351-359
9. Emoto C, Murayama N, Rostami-Hodjegan A, Yamazaki H. Utilization of estimated physicochemical properties as an integrated part of
    predicting hepatic clearance in the early drug-discovery stage: Impact of plasma and microsomal binding, Xenobiotica 2009, 39(3): 227-235
10. Badwan A, Remawi M, Qinna N, Elsayed A, Arafat T, Melhim M, Hijleh OA, Idkaidek NM. Enhancement of oral bioavailability of insulin in
    humans, Neuro Endocrinology Letters, 30(1): 74-78
11. Grime KH, Bird J, Ferguson D, Riley RJ. Mechanism-based inhibition of cytochrome P450 enzymes: an evaluation of early decision making
    in vitro approaches and drug-drug interaction prediction methods, European Journal of Pharmaceutical Sciences 2009, 36(2-3): 175-191


                                                                                                                   IN CONFIDENCE   © 2001-2009
Publications: Growing Awareness

 Referring to Simcyp

   Espie P, Tytgat D, Sargentini-Maier Maria-Laura, Pogessi I, Watelet JB. Physiologically based pharmacokinetics (PBPK),
   Drug Metabolism Reviews 2009, 41(3): 391-407
   Peters SA, Ungell AL, Dolgos H. Physiologically based pharmacokinetic (PBPK) modeling and simulation: Applications in
   lead optimization, Current Opinion in Drug Discovery & Development 2009, 12(4): 509-518
   Grimm SW, Einolf HJ, Hall SD, He K, Lim HK, Ling KH, Lu C, Nomeir AA, Seibert E, Skordos KW, Tonn GR, Van Horn R,
   Wang RW, Wong YN, Tang TJ, Obach RS. The conduct of in vitro studies to address time-dependent inhibition of drug-
   metabolizing enzymes: a perspective of the Pharmaceutical Research and Manufacturers of America (PhRMA), Drug
   Metabolism & Disposition, 37(7): 1355-1370
   Chu V, Einolf HJ, Evers R, Kumar G, Moore D, Ripp S, Silva J, Sinha V, Sinz M. In vitro and in vivo induction of cytochrome
   p450: a survey of the current practices and recommendations: a Pharmaceutical Research and Manufacturers of America
   (PhRMA) perspective, Drug Metabolism & Disposition 2009, 37(7): 1339-1354
   Summerfield S, Jeffrey P. Discovery DMPK: changing paradigms in the eighties, nineties and noughties. Expert Opinion on
   Drug Discovery 2009, 4(3): 207-218
   Bouzom F, Walther B. Pharmacokinetic predictions in children by using the physiologically based pharmacokinetic
   modelling, Fundamentals of Clinical Pharmacology 2008, 22(6): 579-587



 Book Chapters

  Zhao P, Zhang L and Huang SM, Complex Drug Interactions: Significance and Evaluation, in “Enzyme and Transporter
  Based Drug-Drug Interactions” Eds. Sandy K. Pang, David A. Rodrigues and Raimund M. Peter) , Springer, 2009, In press
  Prakash C and Vaz ADN, Drug Metabolism: Significance and Challenges, in “Nuclear Receptors in Drug Metabolism” (Ed.
  W Xie), John Wiley & Sons, 2009, 1-42




                                                                                                        IN CONFIDENCE   © 2001-2009
Thanks for Your Attention


     Any Questions?


                      IN CONFIDENCE   © 2001-2009

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An Introduction to:In Vitro-In VivoExtrapolation (IVIVE)

  • 1. An Introduction to: In Vitro - In Vivo Extrapolation (IVIVE) Masoud Jamei Senior Scientific Advisor, Head of M&S Honorary Lecturer, University of Sheffield M.Jamei@Simcyp.com The University of Greenwich, 29th Oct 2009, UK IN CONFIDENCE © 2001-2009
  • 2. Acknowledgement: The Team Current: Geoff Tucker, Amin Rostami-Hodjegan, Mohsen Aarabi, Khalid Abduljalil, Malidi Ahamadi, Lisa Almond, Steve Andrews, Adrian Barnett, Zoe Barter, Kim Crewe, Helen Cubitt, Duncan Edwards, Kevin Feng, Cyrus Ghobadi, Matt Harwood, Phil Hayward, Masoud Jamei, Trevor Johnson, James Kay, Kristin Lacy, Susan Lundie, Steve Marciniak, Claire Millington, Himanshu Mishra, Chris Musther, Helen Musther, Sibylle Neuhoff, Sebastian Polak, Camilla Rosenbaum, Karen Rowland-Yeo, Farzaneh Salem, David Turner, Kris Wragg Previous: Aurel Allabi, Mark Baker, Kohn Boussery, Hege Christensen, Gemma Dickinson, Eleanor Howgate, Jim Grannell, Shin-Ichi Inoue, Hisakazu Ohtani, Mahmut Ozdemir, Helen Perrett, Maciej Swat, Linh Van, Hua Wang, Jiansong Yang & .... Many others IN CONFIDENCE © 2001-2009
  • 3. Grants Received by Simcyp IN CONFIDENCE © 2001-2009
  • 4. Simcyp Background “Simcyp” stands for simulating CYPs (a super family of metabolising enzymes). Simcyp is a spin-out company of the University of Sheffield founded in 2001. Simcyp activities and future developments are guided by a consortium of pharmaceutical companies (the Simcyp consortium). The Simcyp® Population-Based ADME Simulator is a platform and database for „bottom-up‟ mechanistic modelling and simulation of the ADME processes of drugs and drug candidates in healthy and disease populations. IN CONFIDENCE © 2001-2009
  • 5. Pharmacology, PK and PD Pharmacology is the study of how drugs interact with living organisms to produce a change in function. The field encompasses drug composition and properties, interactions, toxicology, therapy, and medical applications and antipathogenic capabilities. Pharmacokinetics (PK) is a branch of pharmacology dedicated to the determination of the fate of substances administered externally to a living organism. Or, what the body does to a substance. Pharmacodynamics (PD) is the study of the biochemical and physiological effects of drugs on the body, the mechanisms of drug action and the relationship between drug concentration and effect. Or, what the substance does to the body. Source: Wikipedia IN CONFIDENCE © 2001-2009
  • 6. In Vitro - In Vivo Extrapolation (IVIVE) In vitro (Latin: within the glass) refers to the technique of performing a given procedure in a controlled environment outside of a living organism. In vivo (Latin for "within the living") refers to experimentation using a whole, living organism as opposed to a partial or dead organism. Mechanistic approach Drug fate in body in vitro in vivo IN CONFIDENCE © 2001-2009
  • 7. One Source of the Problem PRE-CLINICAL CLINICAL Ki ED50 LogP Kinact IN CONFIDENCE © 2001-2009
  • 8. A Timeline of Traditional Drug Discovery and Development Hoffman J M et al. Radiology 2007;245:645-660 IN CONFIDENCE © 2001-2009
  • 9. Estimate of the Total Investment required to “launch” Hoffman J M et al. Radiology 2007;245:645-660 Windhover's in vivo: the business and medicine report, Bain drug economics model, Nov 2003 IN CONFIDENCE © 2001-2009
  • 10. ADME PK is often divided into several areas including, but not limited to, the extent and rate of Absorption, Distribution, Metabolism and Excretion (ADME). Absorption is the process of a substance entering the body through mouth. Distribution is the dispersion or dissemination of substances throughout the fluids and tissues of the body. Metabolism is the irreversible transformation of substances and its daughter metabolites. Excretion is the elimination of the substances from the body. In rare cases, some drugs irreversibly accumulate in a tissue in the body. The biological, physiological, and physicochemical factors influence the rate and extent of ADME of drugs in the body. Source: Wikipedia IN CONFIDENCE © 2001-2009
  • 11. ADME: The Roadmap to Site of Effect Drug Food, environment, Tablet Compliance in Faeces in Tablet Comprehension genetic, race, gender, Excretion etc effects! Drug Drug Drug in Tablet in Gut Release Metabolites in Faeces Drug in Gut Absorption Drug Excretion Metabolites Metabolism Drug in Drug in Blood Metabolism Urine, Bile, Milk Drug Metabolites Excretion Drug in Tissues Distribution Metabolism Drug at Receptor Metabolite at Receptor NO DESIRED UNWANTED RESPONSE RESPONSE RESPONSE NO CHANGE THERAPY TOXICITY IN CONFIDENCE © 2001-2009
  • 12. PK Models Different PK models: 1 C=Cie-kit 2 Empirical Compartmental Physiological GT Tucker (Basic PK Course) IN CONFIDENCE © 2001-2009
  • 13. Combining Physiological and Drug-dependent Data Drug Data Systems Trial Data Design Mechanistic IVIVE & PBPK Population Pharmacokinetics & Covariates of ADME (Jamei et al., 2009) IN CONFIDENCE © 2001-2009
  • 14. The Challenge of Population Variability Environment Disease Genetics IN CONFIDENCE © 2001-2009
  • 15. Relationships Between Covariates Affecting ADME Genotypes (Distribution in Population) Renal Function Body Ethnicity Disease Fat Serum Creatinine Sex Age (Distribution in Population) (Distribution in Population) Height Brain Heart Body Volume Volume Surface Area Weight MPPGL Cardiac HPGL Liver Cardiac Output Index Enzyme Volume Abundance Liver Intrinsic Weight Clearance (Jamei et al., 2009) IN CONFIDENCE © 2001-2009
  • 16. Covariates of Determining Tissue Volumes Age Sex Weight Height Adipose Erythrocytes Brain Plasma Bone Spleen Gut Heart Kidney Liver Lung Muscle Skin IN CONFIDENCE © 2001-2009
  • 17. Models to Predict Tissue Volumes Price et al., 2003 Volume of Brain (L) for M&F aged 0-19 (including adult F)  Male = (-90.7 * BH(m) + 178.1) * BW(kg) / 1040;  Female = (-97.5 * BH(m) + 181.2) * BW(kg) / 1040; Volume of Heart (L) in Adults  Male = 9.22 * BW(kg)0.853 / 1040;  Female = 9 * BW(kg)0.855 / 1040; Volume of Heart (L) for others  Male = (22.81 * BH(m) * BW0.5 - 4.15) / 1040;  Female = (19.99 * BH(m) * BW0.5-1.53) / 1040; 1.6 Male 1.6 Female 1.4 1.4 Brain Volume (L) 1.2 Brain Volume (L) 1.2 1 1 0.8 0.8 0.6 ICRP 0.6 ICRP 0.4 Predicted 0.4 Predicted 0.2 0.2 0 0 0 5 10 15 20 25 0 5 10 15 20 25 Age (year) Age (year) IN CONFIDENCE © 2001-2009
  • 18. Dosing Regimen and PK Parameters In many cases, pharmacological action, as well as toxicological action, is related to plasma concentration of drugs. Consequently, through the study of PK parameters, we will be able to individualise therapy for patients. Dosing regimen: How much? Dosing regimen: How often? Oral Half-life bioavailability Volume of Absorption Clearance distribution van de Waterbeemd and Gifford 2003, Drug Discovery IN CONFIDENCE © 2001-2009
  • 19. Oral Absorption and the GI Tract From Moore & Dalley, 5th Ed IN CONFIDENCE © 2001-2009
  • 20. Factors Affecting Solid Drug Absorption  Physicochemical &  Physiological issues Pharmaceutical issues  Disintegration  Gastric emptying  De-aggregation  Intestinal mobility  Dissolution  pH  Solubility  Intestinal metabolism  Precipitation  Disease state  Permeability  P-gp and other transporters  Intra-gut degradation  Intestinal blood flow  Food effects  GI-tract fluid secretion, re- absorption and motility IN CONFIDENCE © 2001-2009
  • 21. Oral Absorption and First-Pass Effect Gut Lumen Portal Vein Gut Wall Liver Fa FG FH To Site of Action Metabolism Metabolism To Faeces Rowland and Tozer 1995 IN CONFIDENCE © 2001-2009
  • 22. Oral Bioavailability Fraction escaped metabolism Fraction of dose released in enterocytes from formulation and Fraction escaped permeates through gut wall metabolism in hepatocytes Foral = fa . FG . FH Release Solubility Metabolism Metabolism Stability Permeability Transport Transit Binding Binding Permeability Blood Flow Blood Flow IN CONFIDENCE © 2001-2009
  • 23. Solid Drug Absorption dissolution Solution Absorption precipitation dissolution disintegration deaggregation reaggregation IN CONFIDENCE © 2001-2009
  • 24. Breakdown / Dissolution Stages kf,n-1AF,n-1 Drug in kf,nAF,n AF,n : the amount of solid mass trapped formulation in the formulation and not available for dissolution Release Rate kt,n-1AS,n-1 kt,nAS,n AS : the amount of solid mass available Solid drug for dissolution Precipitation Dissolution Rate Rate kt,n-1AD,n-1 kt,nAD,n AD : dissolved drug Dissolved drug Transport Absorption Rate Luminal Rate Degradation Absorbed drug Gut Wall To portal vein Jamei et al. (2009) AAPSJ Metabolism IN CONFIDENCE © 2001-2009
  • 25. Some Differential Equations dAS ,n dAdiss,n dAF, n   kt ,n AS ,n  kt ,n  1 AS ,n  1  dt dt dt  k deg,n  kan  kt ,n AD,n  kt ,n1 AD,n1   nCLuintT , n fu gutCent, n dAD,n dAdiss,n  dt dt dCent, n dt  1 Vent, n ka An diss, n  Qent, nCent, n  CLuintG , n  CLuintT ,n  fu gutCent, n  dAdiss,n  1 1  AD ,n   4πr ( t )D2   C S ,n   dt  r( t ) h  Vlumen,n ( t )   eff   Jamei et al. (2009) AAPSJ 11:225 IN CONFIDENCE © 2001-2009
  • 26. Advanced Dissolution Absorption & Metabolism Stomach Duodenum Jejunum I & II Ileum I Ileum II Ileum III Ileum IV Colon Solid Dosage Release Fine Particles Dissolution / Precipitation / Super-Saturation Dissolved Drug Degradation Pgp Absorption / Efflux Faeces Enterocytes Metabolism R distribution pH distribution PBPK Distribution Permeability distribution Portal Vein Liver Model CYPs+Pgp distribution Blood flow distribution After Agoram 2001 Jamei et al. 2009 IN CONFIDENCE © 2001-2009
  • 27. Fluid Dynamics in the GI-tract Rsec, j Ktj-1 Vj-1 Ktj Vj Vj KRe-Abs, j Rsec, j: Fluid secretion rate into jth gut segment (1/h) KRe-Abs, j: Fluid re-absorption rate constant from jth segment (1/h) Vj: Volume of fluid in jth segment (mL) Ktj: Transit rate constant in jth segment (1/h) dV j  Kt j 1V j 1  Rsec, j  K Re  Abs, jV j  Kt jV j dt IN CONFIDENCE © 2001-2009
  • 28. Inter-individual Variability & fa fa vs Peff and Tsi (R=1.7 cm) 250 120% 100% 200 100 80% 150 fa (%) 60% 50 Frequency 100 40% 50 0 20% 4 0 0% 10 52 135 207 288 365 447 570 2 5 Peff (cm/h) Intestinal Transit Time (min) 0 0 Tsi (h) Yu et al. (1998) M Jamei et al, 2009 Probability distribution fitting Sensitivity Analysis IN CONFIDENCE © 2001-2009
  • 29. Clearance (CL) The Clearance (Cl) of a drug is the volume of plasma from which the drug is completely removed per unit time. The amount eliminated is proportional to the concentration of the drug in the blood. Mass Balance Q x CA Q x CV Rate of Extraction= E = (CA-CV)/CA Q(CA - CV) Clearance = QE IN CONFIDENCE © 2001-2009
  • 30. Metabolism in the liver Metabolism mainly happens in the liver but it can happen in the gut and to much lesser degree in the kidney. Intrinsic hepatic (gut) clearance (CLint): The ability of the liver (gut) to remove xenobiotic from the blood in the absence of other confounding factors (e.g., QH). fuB.CLuint EH = QH + fuB.CLuint QH.fuB.CLuint CLH = QH + fuB.CLuint Can we find Cluint from in vitro assays? How? IN CONFIDENCE © 2001-2009
  • 31. Scaling Factors for Hepatic Clearance In vitro CLuint per CLuint g Liver In vitro Scaling Scaling CLu per int system Factor 1 Factor 2 Liver HLM µL.min-1 MPPGL mg mic protein X HHEP µL.min-1 Liver X HPGL X 106 cells Weight rhCYP µL.min-1 pmol P450 isoformX MPPGL X mg mic protein pmol P450 isoform IN CONFIDENCE © 2001-2009
  • 32. IVIVE - Metabolism CLint per CYP/mg x MPPGL Overall CYPs fuB Specific CYP (pmol/g liver) Liver Weight CLint per mg of MPPGL Microsomal Protein (mg/g liver) CLint Liver Microsomal Protein CLint per HPGL Hepatocellularity Hepatocyte (106/g liver) Liver Blood Flow CLH CLpo fa, FG Genetic/Environmental/rac e/age/sex/disease considerations Gut Blood Flow Gut Surface Area Total CYP in gut Overal CYPs CLint per CYP in gut CLint Gut Gut Wall Permeability IN CONFIDENCE © 2001-2009
  • 33. Rate per pmol of “Each Enzyme” Knowing:  the abundance of each CYP isoform per mg of microsomal protein  the isoform(s) responsible for specific metabolic routes  n  m Vmax (rhCYPj )i  CYP jabundance  CLuint [ L / h]       MPPGL Liver Weig ht  j1  i 1   K m (rhCYPj )i   Proctor et al. Xenobiotica 2004 Vmax Americans/Europeans CLint  CYP1A2 Km  [ S ] CYP2A6 CYP2B6 CYP2C8 CYP2C9 CYP2C18 CYP2C19 CYP2D6 CYP2E1 CYP2J2 CYP3A4 CYP3A5 Japanese/Chinese IN CONFIDENCE © 2001-2009
  • 34. Mechanistic Model for Expressing Enzyme Pool [S] [P] [E·S] Rsys [E] Induction kdegrad [E·I] [I] kinact [PI] [E·MI] Accelerated Deactivation IN CONFIDENCE © 2001-2009
  • 35. Mutual Interactions: Drugs/Metabolites/Self-Induction/Inhibition Comp, MBI, Ind Comp, MBI, Ind Comp, MBI, Ind Sub Sub Met Inh 1 Inh1 Met Inh 2 Inh 3 Comp, MBI, Ind Comp, MBI, Ind Comp, MBI, Ind IN CONFIDENCE © 2001-2009
  • 36. Predicting Volume of Distribution (Vss) Vss knowing distribution into individual tissues is (Sawada et al., 1984): Vss  Vp  Ve  E : P   Vt  Pt:p t Vp = volume of plasma; Vt = tissue (t) volume Ce, ss Erythrocyte : Plasma partition coefficient E:P C p , ss Ct ,ss Tissue : Plasma partition coefficient K p  Pt: p  C p ,ss IN CONFIDENCE © 2001-2009
  • 37. Minimal Physiologically-Based PK Model 1-fa PO Gut Lumen Faeces fa 1-FG Gut Wall Gut Metabolism Portal Vein FG QPV QPV QHA FH Systemic Liver IV QPV+HA Compartment CLH Hepatic CLR Renal Clearance Clearance IN CONFIDENCE © 2001-2009
  • 38. Whole Body Physiologically-based PK Parameters Physiologically-based pharmacokinetics (PBPK) models need different sets of parameters which can be divided into: Physiological parameters including: • tissue volumes, • tissue compositions, • blood flow to each organ/tissue, • Enzyme abundances and distributions, • Transporters abundances and distributions Drug-dependent parameters including: • Physicochemical and blood/plasma binding data (MW, LogP, pKa, fu, B:P, etc), • Absorption data (fa, ka, permeability, solubility, particle size, etc), • Metabolism data (CL, CLint, etc), • Distribution data (tissue:plasma ratios (Kp)) • Transport data (Jmax, Km, REF, CLPD, etc) IN CONFIDENCE © 2001-2009
  • 39. Full PBPK Model with Time-Dependent Volume Lung Adipose Bone Brain Heart Venous Arterial Kidney Blood Blood Muscle Skin Liver Spleen Portal Vein Gut IV Dose PO Dose IN CONFIDENCE © 2001-2009
  • 40. Multicompartment Mammillary Model Plasma Water KKtP-off P-on P +ve P KP-off pH=7.4 KtEW-in KtEW-out KtP-off +ve P KtP-on +ve EW pH=7.4 KtIW-in KtIW-out KtNP-on +ve KtNP-off KtAP-on KtAP-off NP Ktel KtNL-on KtNL-off +ve AP -ve NL IW pH=7 EW: Extracellular Water NL: Neutral Lipids AP: Acidic Phospholipids IW: Intracellular Water NP: Neutral Phospholipids IN CONFIDENCE © 2001-2009
  • 41. Prediction of Tissue to Plasma Partition Coefficients Strong bases (pKa ≥ 7) and Zwitterions (pKa ≥ 7) K pu  f EW X   f IW         P  f NL  0.3P  0.7 f NP   Ka AP AP T  a      Y   Y   Y  Other compounds (Zwitterions pKa < 7, neutrals, acids and weak bases) X   P  f NL  0.3P  0.7 f NP  K pu  f EW   f IW      KaPR PR T  Y   Y  Rodgers and Rowland 2006, 2007 IN CONFIDENCE © 2001-2009
  • 42. Active and Passive Transport QT QT Capillary blood Extracellular fluid Phospholipid bilayer Intracellular fluid For most drugs the capillary membrane is very permeable and diffusion to the interstitial fluid is very fast (Gibaldi and Perrier 1975). The drug movement across the cell membrane can be either passive or/and active.  Perfusion-limited penetration (permeability is NOT rate limiting)  Permeability-limited penetration (permeability is rate limiting) http://cellbiology.med.unsw.edu.au/units/science/lecture0803.htm IN CONFIDENCE © 2001-2009
  • 43. Known Human Transporters! > 50 human ABC transporters are identified; 7 sub-families (A-G) > 360 human SLC transporters; 48 sub-families http://www.bioparadigms.org/slc/menu.asp http://www.humanabc.bio.titech.ac.jp/ IN CONFIDENCE © 2001-2009
  • 44. Tissues Transporters Ho and Kim, 2005 IN CONFIDENCE © 2001-2009
  • 45. Permeability-limited Liver Model - Hepatobiliary Transporters Capillary blood KP-on KtP-off P +ve P KP-off pH=7.4 KtEW-in KtEW-out KtP-off +ve P KtP-on +ve EW pH=7.4 Sinusoidal OATP1B1 OATP1B3 OCT1 MRP3 KtIW-in KtIW-out membrane Tight junction KtNP-on P-gp +ve KtNP-off KtAP-on KtAP-off NP MRP2 KtNL-on KtNL-off Bile Ktel +ve BCRP AP -ve NL IW pH=7 EW: Extracellular Water NL: Neutral Lipids AP: Acidic Phospholipids Canalicular IW: Intracellular Water NP: Neutral Phospholipids membrane IN CONFIDENCE © 2001-2009
  • 46. Parameter Estimation Module Tune design parameters to fit observations Simcyp simulation Trial and Error Parameter Estimation (PE) Module IN CONFIDENCE © 2001-2009
  • 47. Parameter Estimation Process During a parameter estimation process the design parameters are changed, according to a specific algorithm, to get the model outputs as close as possible to the observed DVs. Design parameters: Vss, CL, fu, BP, … Model: one-compartment absorption and/or PBPK model DVs: plasma concentrations 3 2 C(t) 1 0 t1 t2 t3 IN CONFIDENCE © 2001-2009
  • 48. Least Squares (LS) Objective Function 3 2 e (t1) e (t2) C(θ, t) 1 e (t3) 0 0 t1 20 t2 40 t3 60 80 i n i n WLS  min  w i e( t i )  min  w i y( t i )  C, t i  ˆ 2 2 i 1 i 1 in yi  f (, t i )2 in yi  f (, t i )2 in yi  f (, t i )2 in yi  f (, t i )2  i 1 yi  i 1 yi2 i 1 f (, t i )  i 1 f (, t i ) 2 IN CONFIDENCE © 2001-2009
  • 49. Optimisation Algorithms  Direct/random search methods (Hooke-Jeeves, Nelder-Mead, …);  Genetic Algorithms (GA);  Combined Algorithms: Begin with a global optimisation method (GA) and then switch to a local optimisation method; e.g., HJ or NM. IN CONFIDENCE © 2001-2009
  • 50. Genetic Algorithms Evaluate Candidates Randomly Assigned Set of Candidate Candidates Parameters Select a New Set of Rank Candidates Candidates Recombination and Reproduce New Mutation Candidates IN CONFIDENCE © 2001-2009
  • 51. Maximum Likelihood (ML) Estimation In a population, the model parameters and observations are different for different subjects and we are interested in predicting individual as well as population parameters. l(θ|y2) 3 l(θ|y1) 2 l(θ|y3) C(θ, t) 1 0 0 t1 20 t2 40 t3 60 80 Assuming normal distribution of parameters N(C(θ, t1), σ12)    y i  C  , ti 2   | y    1 Likelihood function: exp    i 2  2 i2    IN CONFIDENCE © 2001-2009
  • 52. Maximum a Posterior (MAP) Objective Function MAP estimation is a Bayesian approach in the sense that it can exploit an additional information on the supplied experimental data. Consequently if the user has prior knowledge regarding the experimental data then the MAP should in theory provide more accurate estimations of the design parameters than the Maximum Likelihood which only requires experimental measurements. MAP differs from ML in that MAP assumes the parameter θ is also a random variable which has a prior distribution p(θ)  ( yi  f (, t i )) 2  P  ( j   j ) 2    N O MAP ()     ln (b 0  b1f (, t i ) b 2 ) 2     ln( j ) 2 i 1  ( b 0  b1f (, t i ) )  j  j b2 2 2    Where β={b0, b1, b2} vector defines the variance model: Additive β={b0, 0, 1} Proportional β={0, b1, 1} Combined β={b0, b1, 1} IN CONFIDENCE © 2001-2009
  • 53. Expectation-Maximisation (EM) Algorithm In order to determine the ML or MAP estimations we need to use an optimisation algorithm. The Expectation-Maximisation (EM) algorithm is one of the most popular algorithms for the iterative calculation of the likelihood estimates. The EM algorithm was first introduced by Dempster et al (Dempster, Laird et al. 1977) and was applied to a variety of incomplete-data problems and has two steps which are the E-step and the M-step. E-step: Determining the conditional expectation using Monte Carlo (MC) sampling and updating MC pool for each individual after each iteration M-step: Maximise this expectation with respect to θ and updating population parameters and variance model parameters IN CONFIDENCE © 2001-2009
  • 54. Useful Simulations vs Accurate Predictions Rostami-Hodjegan & Tucker, Drug Discovery Today: Technologies, V4, Dec 2004 IN CONFIDENCE © 2001-2009
  • 55. 3 Pillars of Successful Knowledge Management - Intelligent Workforce - Reliable Data - Enabling Tools Regular Hands-on Workshops to give update on latest IVIVE activities applied to ADME to ALL key players in the drug development scene (e.g. scientists in regulatory agencies, different sections of industry) Amount of CYP3A4 in the Gut 8.10 4 Gathering Data / Reaching Consensus on Common 6.10 4 50 mg (Pmol/gut) 100 mg IVIVE & ADME Parameters / Identifying Areas of 4.10 4 200 mg 400 mg 600 mg Further Research (defining specific projects in the form of 2.10 4 800 mg focus groups) 0 0 50 100 150 200 250 300 Time (hour) Continuous Development and Update of a user friendly and mechanistic platform for easier integration of ADME models & databases (simulation of candidate drugs in virtual populations) IN CONFIDENCE © 2001-2009
  • 56. Organising IVIVE Workshops Washington – April Leiden - May Sheffield – September La Jolla – November IN CONFIDENCE © 2001-2009
  • 57. Annual Simcyp IVIVE Awards Academic (Research & Teaching) For academic and research institutions leading the field of IVIVE, ADME, Pharmaceutics and Modelling and Simulation ‘Most Informative Scientific Report’ • Awarded to lead author • Receives bursary towards scientific meeting / sabbatical at Simcyp ‘Most Innovative Teaching Application’ • Awarded to course leader • Receives contribution towards computer hardware or software / sabbatical at Simcyp IN CONFIDENCE © 2001-2009
  • 58. Publications: Peer Reviewed Articles Research Articles Published/In Press 1. Johnson TN, Boussery K, Tucker GT, Rostami-Hodjegan A. Prediction of the increased exposure to drugs in liver cirrhosis: A systems biology approach integrating prior information on disease with in vitro data on drug disposition, Clin Pharmacokin 2009 (in press) 2. Johnson TN, Kerbusch T, Jones B, Tucker GT, Rostami-Hodjegan A, Milligan P. Assessing the efficiency of mixed effects modelling in quantifying metabolism based drug-drug interactions: Using in vitro data as an aid to assess study power, Pharm Stats 2009 (Epub ahead of print) 3. Van LM, Sarda S, Hargreaves JA and Rostami-Hodjegan A. Metabolism of Dextrorphan by CYP2D6 in Different Recombinantly Expressed Systems and its Implications for the In Vitro Assessment of Dextromethorphan Metabolism, J Pharm Sci 2009, 98(2): 763-71 4. O‟Mahoney B, Farre Albaladejo M, Rostami-Hodjegan A, Yang J, Cuyas Navarro E, Torrens Melich M, Pardo Lozano R, Abanades S, Maluf S, Tucker GT and De La Torre Fornell R. The consequences of 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) induced CYP2D6 inhibition in humans, J Clin Psychopharm 2008, 28(5): 523-9 5. Barter Z, Chowdry J, Harlow JR, Snawder JE, Lipscomb JC and Rostami-Hodjegan A. Co variation of human microsomal protein per gram of liver with age: Absence of influence of operator and sample storage may justify inter laboratory data pooling, Drug Metab Dispos. 2008, 36(12): 2405-9 Review Articles Published/In Press 1. Almond LM, Yang J, Jamei M, Tucker GT, Rostami-Hodjegan A. Towards a quantitative framework for the prediction of DDI‟s arising from Cytochrome P450 induction, Curr Drug Metab 2009, 10(4): 420-432 2. Jamei M, Turner D, Yang J, Neuhoff S, Polak S, Rostami-Hodjegan A, Tucker GT. Population-based Mechanistic Prediction of Oral Drug Absorption, The AAPS Journal 2009, 11(2): 225-237 3. Jamei M, Dickinson GL, Rostami-Hodjegan A. A framework for assessing inter-individual variability in pharmacokinetics using virtual human populations and integrating general knowledge of physical chemistry, biology, anatomy, physiology and genetics: A tale of „bottom-up‟ vs „top-down‟ recognition of covariates, DMPK 2009, 24(1): 53-75 4. Jamei M, Marciniak S, Feng K, Barnett A, Tucker G, Rostami-Hodjegan A. The Simcyp population-based ADME simulator, Expert Opinion on Drug Metabolism & Toxicology 2009, 5(2): 211-223 IN CONFIDENCE © 2001-2009
  • 59. Publications: Others Book Chapters in Press 1. Rostami-Hodjegan A. Translation of in vitro metabolic data to predict in vivo drug-drug interactions: IVIVE and modeling and simulations, in “Enzymatic- and Transporter-Based Drug-Drug Interactions: Progress and Future Challenges” (Eds. Sandy K. Pang, David A. Rodrigues and Raimund M. Peter), Springer, 2009, In press 2. Rostami-Hodjegan A. Predicting Inter-individual Variability of Metabolic Drug-Drug Interactions: Identifying the Causes and Accounting for them Using Systems Approach, in “Enzyme Inhibition in Drug Discovery and Development: The Good and the Bad” (Eds. Chuang Lu and Albert P. Li), Wiley, 2009, In press 3. Yang J. Simulation of population variability in pharmacokinetics, in “Systems Biology in Drug Discovery and Development” (Eds. Daniel L. Young and S. Michelson), Wiley, In press Commentary Articles 1. Toon S, „Model Making – Virtual Reality‟, International Clinical Trials, November 2008 2. Toon S, „R&D in a Virtual World‟, Applied Clinical Trials, 17(10):82, October 2008 IN CONFIDENCE © 2001-2009
  • 60. Publications: Growing Independent Research Applications of Simcyp 1. Wong H, Chen JZ, Chou B, Halladay JS, Kenny JR, La H, Marsters JC, Plise E, Rudewicz PJ, Robarge K, Shin Y, Wong S, Zhang C, Khojasteh SC. Preclinical assessment of the absorption, distribution, metabolism and excretion of GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2- yl)phenyl)-4-(methylsulfonyl)benzamide), an orally bioavailable systemic Hedgehog signalling pathway inhibitor. Xenobiotica. 2009 Sep 2. [Epub ahead of print] 2. Polasek TM, Polak S, Doogue MP, Rostami-Hodjegan A, Miners JO. Assessment of inter-individual variability in predicted phenytoin clearance, Eu J Clin Pharm, 2009 (in press) 3. Gibson CR, Bergman A, Lu P, Kesisoglou F, Denney WS, Mulrooney E. Prediction of Phase I single-dose pharmacokinetics using recombinant cytochromes P450 and physiologically based modelling, Xenobiotica 2009, 39(9): 637-648 4. Foti RS, Pearson JT, Rock DA, Wahlstrom JL, Wienkers LC. In vitro inhibition of multiple cytochrome P450 isoforms by xanthone derivatives from mangosteen extract, Drug Metabolism & Disposition 2009, 37(9): 1848-55 5. Fahmi OA, Hurst S, Plowchalk D, Cook J, Guo F, Youdim K, Dickins M, Phipps A, Darekar A, Hyland R, Obach RS. Comparison of different algorithms for predicting clinical drug-drug interactions, based on the use of CYP3A4 in vitro data: predictions of compounds as precipitants of interaction, Drug Metabolism & Disposition 2009, 37(8): 1658-1666 6. Thelingwani RS, Zvada SP, Hughes D, Ungell AL, Masimirembwa CM. In vitro and in silico identification and characterisation of thiabendazole as a mechanism-based inhibitor of CYP1A2 and simulation of possible pharmacokinetic drug-drug interactions, Drug Metabolism & Disposition 2009, 37(6): 1286-1294 7. Hyland R, Osborne T, Payne A, Kempshall S, Logan YR, Ezzeddine K, Jones B. In vitro and in vivo glucuronidation of midazolam in humans, British Journal of Clinical Pharmacology 2009, 67(4): 445-454 8. Ping Z, Ragueneau-Majlessi I, Zhang L, Strong JM, Reynolds KS, Levy RH, Thummel KE, Huang SM. Quantitative Evaluation of Pharmacokinetic Inhibition of CYP3A Substrates by Ketoconazole: A Simulation Study, J Clin Pharmacol 2009, 49: 351-359 9. Emoto C, Murayama N, Rostami-Hodjegan A, Yamazaki H. Utilization of estimated physicochemical properties as an integrated part of predicting hepatic clearance in the early drug-discovery stage: Impact of plasma and microsomal binding, Xenobiotica 2009, 39(3): 227-235 10. Badwan A, Remawi M, Qinna N, Elsayed A, Arafat T, Melhim M, Hijleh OA, Idkaidek NM. Enhancement of oral bioavailability of insulin in humans, Neuro Endocrinology Letters, 30(1): 74-78 11. Grime KH, Bird J, Ferguson D, Riley RJ. Mechanism-based inhibition of cytochrome P450 enzymes: an evaluation of early decision making in vitro approaches and drug-drug interaction prediction methods, European Journal of Pharmaceutical Sciences 2009, 36(2-3): 175-191 IN CONFIDENCE © 2001-2009
  • 61. Publications: Growing Awareness Referring to Simcyp  Espie P, Tytgat D, Sargentini-Maier Maria-Laura, Pogessi I, Watelet JB. Physiologically based pharmacokinetics (PBPK), Drug Metabolism Reviews 2009, 41(3): 391-407  Peters SA, Ungell AL, Dolgos H. Physiologically based pharmacokinetic (PBPK) modeling and simulation: Applications in lead optimization, Current Opinion in Drug Discovery & Development 2009, 12(4): 509-518  Grimm SW, Einolf HJ, Hall SD, He K, Lim HK, Ling KH, Lu C, Nomeir AA, Seibert E, Skordos KW, Tonn GR, Van Horn R, Wang RW, Wong YN, Tang TJ, Obach RS. The conduct of in vitro studies to address time-dependent inhibition of drug- metabolizing enzymes: a perspective of the Pharmaceutical Research and Manufacturers of America (PhRMA), Drug Metabolism & Disposition, 37(7): 1355-1370  Chu V, Einolf HJ, Evers R, Kumar G, Moore D, Ripp S, Silva J, Sinha V, Sinz M. In vitro and in vivo induction of cytochrome p450: a survey of the current practices and recommendations: a Pharmaceutical Research and Manufacturers of America (PhRMA) perspective, Drug Metabolism & Disposition 2009, 37(7): 1339-1354  Summerfield S, Jeffrey P. Discovery DMPK: changing paradigms in the eighties, nineties and noughties. Expert Opinion on Drug Discovery 2009, 4(3): 207-218  Bouzom F, Walther B. Pharmacokinetic predictions in children by using the physiologically based pharmacokinetic modelling, Fundamentals of Clinical Pharmacology 2008, 22(6): 579-587 Book Chapters  Zhao P, Zhang L and Huang SM, Complex Drug Interactions: Significance and Evaluation, in “Enzyme and Transporter Based Drug-Drug Interactions” Eds. Sandy K. Pang, David A. Rodrigues and Raimund M. Peter) , Springer, 2009, In press  Prakash C and Vaz ADN, Drug Metabolism: Significance and Challenges, in “Nuclear Receptors in Drug Metabolism” (Ed. W Xie), John Wiley & Sons, 2009, 1-42 IN CONFIDENCE © 2001-2009
  • 62. Thanks for Your Attention Any Questions? IN CONFIDENCE © 2001-2009