Radiosensitizers and Biological modifiers in Radiotherapy Dr. Sandeep G

1. RADIOSENSITIZERS
Dr. Sandeep Gedela
PGIMER, Chandigarh

2. • Radiosensitivity
• Relative susceptibility of cells,tissues,organs or organisms to the harmful effect of
ionizing radiation
• Bergonie and Tribondaeu’s law:
Tissues will be more radiosensitive if:
I. The cells are undifferentiated
II. They have greater proliferative capacity
III. They divide more rapidly

3. RADIOSENSITIZATION
• Radiosensitization is a physical, chemical or pharmacological intervention that
increases the lethal effect of radiation when administered in conjunction with it
• To make tumour cells more sensitive to radiotherapy
• Clinical benefit can be expected only if there is differential effect demonstrated
between tumours and normal tissues

4. Mechanisms of radiosensitization
DNA sensitivity direct & indirect Modulate biological response of irradiated cells
• Counteracting tumour hypoxia
• Increase in initial radiation damage
• Cell cycle redistribution
• Inhibition of cellular repair
• Overcoming accelerated repopulation
• Targeting molecular events assosciated with
radiation response

5. Radiosensitive phase of cell cycle

6. M> G2> G1> early S> late S

7. Need of radiosensitizer
• Goal  shrink tumour and kill cancer cells by high energy radiation
• Despite effectiveness, harmful damage caused by such radiation to normal cells is
unavoidable
Radiosensitiser

8. RADIOSENSITISER:
• Radiosensitizer is the agent that increase the lethal effects of radiation when
administered in conjunction to radiotherapy.
• To be clinically effective they should improve the therapeutic ratio ie TCP/NTCP,
because if an intervention equally increases the effect and side effect then it is not
useful.
• A radiosensitizer may or may not have lethal effects against tumor cells when
administered alone without radiation

9. Therapeutic ratio
• Therapeutic ratio: TCP/NTCP
As the separation between these curves increases,
the likelihood increases that treatment will be effective
and without causing unacceptable level of morbidity
• Efficacy and toxicity of radiosensitizing agent
directly effects TR

10. Characterstics of ideal radiosensitiser
• Lack of toxicity
• Potent radiosensitizing effect
• Non-cell cycle specificity
• Amenable to dose intense or prolonged infusion schedules
• Adaptable to convenient out-patient administration

11. Evaluation of radiosensitization effect
• In vitro
• clonogenic assay by measuring no. of colonies formed after irradiation of tumour
cells using several irradiation doses
• Comparing cell survival curves after radiation alone or in presence of
radiosensitiser

12. IN VIVO

13. Types of radiosensitisers
PHYSICAL CHEMICAL
• HYPERTHERMIA
• HYPERBARIC OXYGEN
• CARBOGEN+/- NICOTINAMIDE
• ARCON
• MODIFIERS OF HAEMOGLOBIN
• NON HYPOXIC CELL SENSITISERS
• HYPOXIC CELL SENSITISERS
• HYPOXIC CYTOTOXINS
• BIOLOGICAL MODIFIERS
• CHEMOTHERAPEUTIC DRUGS

14. HYPERTHERMIA
• Tumours are heated using exogenous energy source
• Heat directly kills cancer cells , but also synergises with radiotherapy and/or
chemotherapy to increase therapeutic window
• Temperature 39-45°c
• Mild temperature hypothermia < 40°c
• Thermal ablation > 45°c

15. HISTORY OF HYPERTHERMIA
• Use of heat to cancer is one of the oldest therapies
• First application is quoted in EDWIN SMITH SURGICAL PAPYRUS
where patient with breast cancer is treated with heat 5000yrs back
• 1800’s use of of fever induced treatment to control tumour growth by coley’s
toxin
• 1st real attempt  westermark in 1898
used water circulating cisterns to treat uterine carcinomas with 42-44°c

19. Hyperthermia
• Elevation of temperature to supraphysiological level between 40 and 45 degree C
• Interaction between RT & HT described by – Thermal Enhancement Ratio (TER) – ratio
of doses of radiation with & without heat to produce same biological effects
• Maximum interaction when heat & radiation given simultaneously
• TER ↓es with ↑ing time interval between heat & RT
• When RT precedes HT – sensitization no longer detectable 2-3 hrs after RT
• When HT precedes RT – cells can be sensitized for upto several hrs

20. Hyperthermia…
• Clinical hyperthermia achieved by exposing tissues to –
a)Conductive heat sources
b)Non – ionizing radiation – e.g. electromagnetic or ultrasonic
• Deposit energy in tissues by different mechanisms
• Sensitive to heterogeneity of tissue properties, geometry of blood flow
• Can be administered using –
Invasive sources –– designed for direct application into tissue or for intracavitary use --
include radiofrequency antennas, RF electrodes, hot water tubes, ferromagnetic metals &
US transducers
Noninvasive - using externally applied power

21. Magnetic hyperthermia therapy
• Heat generation using magnetic nanoparticles
in response to an externally applied
alternating magnetic field
• MNPs are specifically targeted to tumour site for homogenous heating
• Localised and controlled heating
• Repeated and intracellular heating possible with single injection
• Efficient targeting of resistant tumour cells

22. Prospective randomized trials
Trial n CR for RT CR for RT +HT p value
Advanced H & N cancer
Datta et al 52 13% 46% <0.05
Valdagni et al 40 41% 83% 0.016
ESHO-2 et al 62 53% 50% NS
Advanced Breast Cancer
MRC et al 143 64% 71% NS

23. Prospective randomized trials
Trial n CR for RT CR for RT +
HT
p value
Advanced Cervix/Rectal/Bladder Cancers
DDHG 143(rectal)
114(cervix)
101(bladder)
15%
57%
51%
21%
83%
73%
NS
0.003
0.01
Harima 40 50% 80% 0.048

24. HYPOXIA
• Tumour vasculature
• Slow rate of proliferation  decreased sensitivity to chemotherapy and
radiotherapy
• concentration of anticancer drugs lesser in cells away from blood vessels leads to
less killing of hypoxic cells

25. Hypoxia  tumour progression

28. Oxygen effect
• Oxygen acts at the level of free radicals
• Oxygen sensitization occurred as late as 0.01 msec after irradiation
• Rapidly growing cells have OER 2.5
• Phase of cell cycle

29. H & N tumor oxygenation

30. Methods to Sensitize or Eliminate Hypoxic Cells
1. Physical
 Overcoming hypoxia by eliminating it with treatment that increases
delivery of oxygen to tumor i.e. increases the oxygen carrying capacity of
blood and increasing the tumor blood flow
a) Hyperbaric oxygen
b) Carbogen with or without nicotinamide

31. Hyperbaric oxygen
• An increase in barometric pressure of the gas breathed by the patient during
radiotherapy is termed as hyperbaric oxygen therapy
• Pioneered by Churchill and Davidson in 1968 at st. Thomas hospital in London
• Increases plasma and tissue oxygen 10times  maintain tissue viability
• Increases VEGF secretion as well as secretion of matrix by fibroblasts

32. • Placing the patient in a compression chamber, increasing the environmental pressure
within the chamber, and administering 100% oxygen for respiration
• Tumour o2 sensitisation involves pressurisation to between 2 to 4 atmospheres absolute
for periods of 20 to 30 minutes, following which radiation therapy is delivered

33. Meta analysis

34. Advantages
• Stimulates oxygenation  increasing radiosensitivity
• Promotes growth of new capillaries and blood vessels boosts the
efficacy of chemptherapeutic drugs
• Treatment of radiation induced bone and soft tissue necrosis in head
and neck region
• Used along with anti coagulation therapy in treatment of cerebral
radionecrosis
• Boosts circulating stem cells
• Supports faster wound healing

35. Problems
• Feeling of claustrophobia being sealed in closed narrow tube
• Cumbersome logistics assosciated with delivery, use of non
conventional hypofractionated regimens
• Side effects
• Barotruma  ears ,sinuses and lungs
• Temporary worsening of myopia
• Oxygen toxicity seizures
• With the advent of better chemical radiosensitisers that would
acheueve same end by the simpler means

36. carbogen
• Pure oxygen if breathed – vasoconstriction - closing down of some blood
vessels – defeats the object
• Carbogen – 95% O2 +5% CO2
• Rationale – addition of CO2 to gas breathing mixture - shift the oxyHb
association curve to right – facilitate unloading of oxygen into most hypoxic
tissues
• Simple attempt to overcome chronic hypoxia
• Can be given with or without concurrent administration of nicotinamide

37. Nicotinamide
• Vitamin B3 or niacinamide
• Co factor of NADPH oxidase2  angiogenesisprevent fluctuations
in tumour blood flow increases prevents acute hypoxia
• Inhibition of PARP  inhibition of DNA repair
• 60-80mg/kg, 1to 1 1/2hr before radiation

38. • Phase II study by Hoskin et al
• 335 patients with locally advanced bladder cancer randomly assigned
to RT alone versus RT with carbogen and nicotinamide
• 55Gy in 20#/4weeks are given
• OS  59% vs 46%
• RFS  54% vs 43%

39. ARCON
• Use of acclererated radiotherapy with carbogen and nicotinamide
tested in head and neck cancer patients

41. Phase III study in head and neck cancer
patients

42. ARCON in GBM

44. Blood transfusion
• Anemia – adverse prognostic factor in pts of Ca Cervix, H& N cancers & lung cancer
• Haemoglobin is the first investigation in cervical cancer patients
• Transfusion to pts with low Hb levels - ↑ed oxygen tension within tumor
• Transfusion to Hb level of 11g/dl or higher – improved survival
• H & N Cancer pts – 2 phase II trials from DAHANCA study group – failed to demonstrate
any benefit

45. Erythropoetin
• Recombinant human erythropoietin : alternative means of raising haemoglobin during
radiotherapy
• Two studies conducted in H & N cancers failed to show any benefit
• Dose : 200u/kg/day x 5 days/week  increase in Hb by 1-3gm/dl
• Induces prompt reticulocyte response from 2.4 to 4.9%
• Expensive than BT
• In one of the studies – pts who received erythropoetin showed significantly poor
outcome than those who did not
• ? Erythropoietin may stimulate tumor growth STUDY

46. perfluorocarbons
• Artificial blood substances
• Small particles capable of carrying more oxygen or manipulating the oxygen
unloading capacity of blood
• Potential usefulness uncertain

47. Non hypoxic cell sensitiser
• Halogenated pyrimidines
• Non hypoxic cell sensitizer ( Halogenated pyrimidines)
• Sensitizes cell to degree dependent on amount of analogue incorporated
Differential effects --Tumor cells cycles faster and therefore incorporates more drug than
normal tissue
• 5- bromodeoxyuridine
• 5-iododeoxyuridine
• Incorporated into DNA in place of thymidine
• Cell cycle specific radiosensitisers

48. • Extended exposure must be required for incorporation into DNA
• Tumour responses are good but tissue damage is unacceptable

49. Budr & iudr

50. Hypoxic radiosensitisers
• Instead of forcing oxygen into hypoxic cells by use of high pressure
tanks, the approach shifted to oxygen substitutes
• These compounds selectively activated in the hypoxic environment of
tumour cells
• Electronisc affinic compounds oxidise radiation induced free redical
damage in the cell to produce increased kill
• Useful in hypoxic tumour microenvironment

51. Properties of clinically useful hypoxic cell sensitizer
1. Selectively sensitize hypoxic cells at concentration that would result
in acceptable normal tissue toxicity
2. Chemically stable & not subject to rapid metabolic break down
3. Highly soluble in water or lipids & must be capable of diffusing a
considerable distance through a nonvascularized cell mass to reach
the hypoxic cell
4. It should be effective at relatively low daily dose /# used in
conventional fractionated radiotherapy

53. Development of nitroimidazoles
Metronidazole
Misonidazole
more active, toxic,
benefit in
subgroup
Etanidazole less
toxic, not active
Nimorazole less
active, much
less toxic,
benefit in H& N
cancer

54. Metronidazole
• 1st generation 5-nitroimidazole
• Sensitizer Enhancement ratio - 1.2
• Formulations - 500 mg tablets or 500mg /100 ml solution
• Half life – 9.8 hrs
• Total cumulative dose not to exceed 54 gm/m2
• Multiple doses 6gm/m2 3 times/wk for 3- 4week
• Optimal time for administration - 4 hour before radiation
• Dose limiting toxicity –
• Gastrointestinal

55. Misonidazole• 2nd generation 2- nitroimidazole
• Higher electron affinity
• Sensitizer Enhancement ratio –
• 1.4 with multiple dose of 2 gm/m2
• 1.15 with 0.5mg/m2
• Formulations 500 and 100 mg tablets and capsules
• once or twice/wk for 5-6 wks
• Total cumulative dose not to exceed 12 gm/m2
• Optimal time for administration -- 4 hour before radiation
• Dose limiting toxicity-
• gastrointestinal
• Sensory peripheral neuropathy that progress to central nervous system toxicity

56. Radiation Sensitization by Misonidazole

57. Reasons for Failure of
Misonidazole Clinically
1. Dose limiting toxicity – peripheral neuropathy
2. If drug not stopped – progression to CNS toxicity
3. Toxicity prevented use of drug at adequate dose levels throughout
multifraction regimens

58. Etanidazole (SR2508)
• 3rd generation, analog of Misonidazole
• SER- 2.5-3 with dose of 12 g/m2
• Shorter half life
• Lower lipid solubility, less neurotoxicity
• Arthralgia seen more often with 48 hr continuous infusion
• 1000mg/19.4 ml saline solution
• Total dose - 40.8 g/m2 at 1.7-2g/m2 3 times/wk for 6 wks
• 30 min before radiation

59. pimonidazole
• 4- nitroimidazole
• More potent than Misonidazole
• Several – fold ↑ in tumor concentration
• Maximum tolerated dose – 750 mg/m2
• Dose limiting toxicity – CNS manifesting as disorientation & malaise
• Randomized trial conducted in advanced Ca Cervix –showed no benefit

60. Nimorazole
• A 5-nitroimidazole of same structural class as metronidazole
• Administered in form of gelatin-coated capsules containing 500 mg active
drug
• Given orally 90 min prior to irradiation.
• Daily dose 1200 mg/m2 body surface given in connection with first 30
radiation treatment fractions.
• Total dose should not exceed 40g/m2 or 75 g in total.
• Less effective radio sensitizer then Misonidazole or Etanidazole
• Less toxic, no cumulative neuropathy

62. Etanidazole
• RTOG phase III study with Etanidazole in head and neck tumors
n- 521 patients
Conventionally fractionated RT RT
with Etanidazole 2mg/m2 with out Etanidazole
three times wk
• No grade III or IV central nervous system or peripheral neuropathy was
observed.
No overall benefit when
Etanidazole added to
conventional radiotherapy

63. Nimorazole

64. Nimorazole – dahanca 5
Significant improvement in terms
of LRC & OS
Nimorazole significantly improves the effect of radiotherapeutic
management of supraglottic and pharynx tumors and can be given
without major side-effects

65. Head & neck CA
TRIALS No. of
pts
Sensitizer RT &
Sensitizer
RT alone
DAHANCA 2 (1989) 626 Miso 41% 34%
MRC (1984) 267 Miso 40% 365
EORTC (1986) 163 Miso 52% 44%
RTOG (1987) 306 Miso 19% 24%
RTOG 79-04 (1987) 42 Miso 17% 10%
DAHANCA 5 (1992) 414 Nim 49% 34%
RTOG 85-27 (1995) 500 Eta 39% 38%

66. Ca cervix
TRIALS No. of
pts
Sensitizer RT &
Sensitizer
RT alone
Scandinavian (1989) 331 Miso 50% 54%
MRC (1984) 153 Miso 59% 58%
RTOG (1987) 119 Miso 53% 54%
MRC (1993) 183 Pim 64% 80%

67. GBM & BRONCHOGENIC CA
TRIALS No. of pts Sensitizer RT &
Sensitizer
RT alone
GLIOBLASTOMA
MRC (1983) 384 Miso 8 mths 9 mths
EORTC (1983) 163 Miso 11 mths 12 mths
BRONCHOGENIC CA
RTOG (1987) 117 Miso 7 mths 7 mths
RTOG (1989) 268 Miso 7 mths 8 mths

68. Summary of efficacy of clinical trials with
nitroimidazoles
Compounds Trials (n) Significant
benefit
No benefit
Metronidazole 1 1 _
Misonidazole /
Nimorazole
38 5 33
Etanidazole 7 _ 7
Pimonidazole 1 _ 1

69. Hypoxic cytotoxins…
3 categories
Quinone
antibiotics
Nitroaromatic
compounds
Benzotriazine di-
N-oxides

70. Quinone antibiotic - Mitomycin C
• Prototype bioreductive drug
• Used as chemotherapy agent for many years
• Cytotoxic to relative radio resistant hypoxic cells
• But the differential cytotoxicity between hypoxic and oxygenated cells , however is small
• Acts as an alkylating agent after intracellular activation & inhibits DNA – DNA cross
linking, DNA depolymerization
• Dose limiting toxicity – cumulative myelosuppression
• Mitomycin C plays an important role in conjunction with radiotherapy and 5FU, the
definitive, chemoradiation squamous cell carcinoma of the anal canal

71. Porfiromycin
• A mitomycin C derivative
• Provides greater differential cytotoxicity between hypoxic and oxygenated cells in vitro
Phase III study
• Compared patients treated with conventionally fractionated radiation plus mitomycin C
versus radiation plus porfiromycin
• The median follow-up - >6 years. Hematologic and non-hematologic toxicity was
equivalent in the two treatment arms
• Mitomycin C was superior to porfiromycin with respect to 5-year local relapse-free
survival (91.6% vs. 72.7%; p = 0.01)

72. • Local-regional relapse-free survival (82% vs. 65.3%; p = 0.05)
• Disease-free survival (72.8% vs. 52.9%; p = 0.03)
• There were no significant differences between the two arms with respect to
overall survival (49% vs. 54%) or distant metastasis-free rate (80% vs. 76%)
• Their data supported the continuing use of mitomycin C as an adjunct to radiation
therapy in advanced head and neck cancer and will become the control arm for
future studies
Porfiromycin…

73. Tirapazemine (sr 4233)
• Highly selective toxicity against hypoxic cells both in vivo and vitro
• This bioreductive agent is itself cytotoxic to hypoxic tissues
• MOA- Drug is reduced by intracellular reductases to form highly reactive radical -
produces both double & single strand breaks in DNA
• Analysis of DNA and chromosomal breaks after hypoxic exposure to Tirapazemine
suggests that DNA double-strand breaks are the primary lesion causing cell death
• Efficacy depends on no. of effective doses that can be administered during course of RT
& presence of hypoxic tumor cells
• S/E – nausea & muscle cramping

74. Tirapazemine
• Hypoxic/cytotoxicity ratio – ratio of drug
concentration under aerated and hypoxic condition
required to produce same cell survival
• Unlike the oxygen-mimetic sensitizers, tirapazamine-
mediated therapeutic enhancement occurs both when
the drug is given before or after irradiation.
• Tirapazamine can also enhance the cytotoxicity of
cisplatin

76. N= 121 stage III/IV SCC of the head and neck
randomized to receive definitive radiotherapy (70 Gy in 7 weeks)
Tirapazamine On day 2 of weeks 1, 4, and 7,
290 mg/m2 was administered for 2 hours,
followed 1 hour later by cisplatin 75 mg/m2 for 1 hr
followed immediately by radiotherapy
In addition, tirapazamine 160 mg/m2 was given
before radiation three times/week in weeks 2 and 3
Cisplatin 50 mg/m2 was given
before radiotherapy on day 1 of
weeks 6 and 7 of radiotherapy
and
Fluorouracil 360 mg/m2/d was
given by continuous infusion from
day 1 - 5 (120-hour infusion) of
weeks 6 and 7 of radiotherapy
Arm 2. n-58Arm 1,n-62

77. • Three-year failure-free survival rates were 55% with TPZ/CIS and 44% with chemo RT( p
.16)
• Three-year locoregional failure-free rates were 84% in the TPZ/CIS arm and 66% in the
chemo RT arm (p .069)
 Toxicity
• More febrile neutropenia and grade 3 or 4 late mucous membrane toxicity were observed
with TPZ/CIS
• Compliance with protocol treatment was satisfactory on both arms

78. Tirapazemine……
• A phase III trial has been conducted to validate the concept of targeting of hypoxic cells
in head and neck cancer
• Concurrent chemoradiation with standard fractionation RT (70 Gy) and
tirapazamine/cisplatin was tested against conventional chemoradiation with standard
single agent cisplatin
• This trial enrolled 880 patients and is in a follow-up phase

80. Biologic Modifiers of Radiation Response
• The EGFR system represents a promising therapeutic target because it is commonly over
expressed in H & N tumor
• Tumor levels of EGFR and its ligand -significant predictors of tumor staging and clinical
outcome.
• In addition, several studies have reported that repopulation of epithelial tumor cells after
exposure to radiation is related to the activation and expression of EGFR
• These findings suggest that EGFR blockade may be important in reducing tumor cell
repopulation by modulation of cellular proliferation and enhancement of tumor
radioresponse

82. Cetuximab
• Specifically targets EGFR with high affinity & blocks
ligand binding
• Enhances antitumor activity of cisplatin
• Enhances antitumor activity of radiotherapy
• Showed activity in pts with SCCHN & documented
platinum resistance
• EGFR inhibition is a promising new approach for
radiosensitization
• Need to drive predictive biomarkers to assess response
to molecular therapies
• Optimize radiotherapy fractionation schemes to
complement targeted agents

83. Dose, schedule & toxicity
• Intravenous cetuximab given one week before radiotherapy
• Loading dose of 400 mg per square meter of BSA over a period of 120 minutes,
followed by weekly 60-minute infusions of 250 mg per square meter for the duration
of radiotherapy
• Premedication to be given
• Before the initial dose , a test dose of 20 mg should be infused over a 10-minute
period, followed by a 30-minute observation period
Side effects
• Infusion reaction -angioedema, urticaria, hypotension ,bronchospasm

84. Results
Bonner , Harari, Giralt etal N Engl J Med 354;567-78. 2006

85. Results contd…
Bonner , Harari, Giralt etal N Engl J Med 354;567-78. 2006

86. Drug Radiation Interactions : Mechanisms
1. Enhancement of tumour Radioresponse
Denotes interaction between drugs & radiation at molecular, cellular or metabolic level
Increasing initial Radiation damage
• Acts through DNA damage------Cell Death
• Drugs make DNA more susceptible to radiation
•eg Halogenated pyrimidines
2. Inhibition of repair of Sublethal radiation damage or recovery from Potentially lethal
damage
• Chemotherapeutic agents interact with cellular repair mechanisms & inhibit repair----
enhance response to radiation

87. Drug Radiation Interactions : Mechanisms
3. Cell cycle redistribution & synchronization
Cells in G2-M phase - thrice as sensitive as S phase cells
Agents may block transition of cells thru mitosis – accumulates in G2-
M phase – enhanced radiosensitivity.
E.g.. Taxanes
Elimination of radioresistant S phase cells.
E.g.. Gemcitabine – gets incorporated in S phase – induce
apoptosis

88. 5-fluorouracil (Anti-metabolite)
• Incorporation into RNA----disruption of RNA function
• Inhibition of Thymidylate Synthetase function – inhibits DNA synthesis and results in
accumulation of cells in early S phase
• Combination of these effects underlie its radio sensitizing effect
• The combination of FU and radiation is a mainstay of treatment for GI tumors, where it
has a proven role in improving locoregional control and survival

89. Cisplatinum (cis diamminedichloroplatinumII)
• Cell cycle non specific
• More toxic to hypoxic then aerated cell i.e hypoxic cell sensitizer though not powerful as
nitroimidazole
• Also, radiation induces increased cellular Cisplatin uptake
• When used concurrently with radiation, substantial enhancement of cell kill observed
• Coughlin and Richmond and Douple suggested two mechanisms of radiation
enhancement by platinum:
(a) in hypoxic or oxygenated cells, free radicals with altered binding of platinum to DNA
are formed at the time of irradiation
(b) interaction inhibits repair of radiotherapy induced potentially lethal or sub lethal
damage

90. taxanes
• Taxanes (Mitotic spindle Inhibitors)
• Cellular arrest in G2/M phase – highly radiosensitive
• Induction of apoptosis
• Reoxygenation

91. Mechanisms of Radiosensitization
for Antimetabolites