hallmarks of cancer

2. What are ‘ hallmarks of cancer ‘ ?
• Biologic capabilities acquired by cancer cells during the
multistep process of development of human tumors
• Essential Alterations In Cell Physiology That Collectively
Lead To Malignant Growth Of A Normal Cells.
• Described by Douglas Hanahan & Robert Weinberg in
2000

4. Originally six hallmarks of cancer proposed :
• Self-sufficiency in growth signals
• Insensitivity to growth-inhibitory (antigrowth) signals.
• Evading apoptosis.
• Limitless replicative potential.
• Sustained angiogenesis.
• Tissue invasion and metastasis.

6. With development in genetics and epigenetics Hanahan and
Weinberg again redefined “Hallmarks of cancer” in 2011.
Two additional hallmarks of cancer are:
• Evading immune destruction.
• Deregulating cellular metabolism or energetics.

9. • Normal cells require growth signals to enter from a
quiescent state into an active proliferative state.
• These signals are transmitted into the cell through
transmembrane receptors that binds to a particular
class of signaling molecules.
• Tumor cells generate their own growth signals and
thereby reducing their dependence on external
stimulation from their normal tissue
microenvironment

10. Cancer cells maintain constant growth through
sustaining proliferative signaling.
Deregulation of cell signaling pathways allows
cancers cells to upregulate growth signals
and downregulate antigrowth signals.

11. The Stages of Cell Signaling
1. Reception: Binding between a ligand molecule
and receptor; highly specific
2. Transduction: conversion of a signal to a form
that can bring about a specific response via
phosphorylation cascade, protein kinases, and
second messengers
3. Response: Regulation of gene expression or
cytoplasmic activities

13. • • Many cancer cells acquire the ability to synthesize abundance
of GFs to which they are responsive, creating a positive
feedback signaling loop
ALTERNATION OF
EXTRACELLULAR GROWTH
SIGNALS
• Receptor overexpression may enable the cancer cell to become
hyperresponsive to ambient levels of GF that normally would
not trigger proliferation
ALTERNATION OF
TRANSCELLULAR
RECEPTOR OF THAT
SIGNAL
• Alterations in components of the downstream cytoplasmic
circuitry that receives and processes the signals emitted by GF
receptors can release aflux of signals into cells, without ongoing
stimulation by their normal upstream regulators
ALTERNATION OF
INTRACELLULAR CIRCUITS
THAT TRANSLATES THAT
SIGNAL

14. Cancer cells acquire growth signal
autonomy in a variety of ways

15. Production of Growth Signals
• Cancer cells produce their own growth signals
• Ability to synthesize growth factors and
signaling molecules to which they are responsive
(Fedi et al., 1997)
• Creates positive feedback loop for cell growth
Example: Production of PDGT and TGF-alpha
by glioblastomas and sarcomas (Fedi et al.,
1997)

16. Overexpression of Receptors
• Cancer cells over-express receptor proteins, in
particular, growth factor receptors
• Causes cancer cells to become hyperresponsive to external
growth signals (Fedi et al., 1997)
• Example:1: Epidermal GF receptor is upregulated in
stomach, brain, and breast tumors (Slamon et al.,1987)
2:HER2/neu receptor over expressed in stomach and
mammary carcinomas

17. Ligand-Independent Signaling
• Over-expression of growth factor receptors induces ligand-
independent signaling (DiFoire et al., 1987)
• No need for signaling molecules to trigger cell division and
growth
• Same result achieved through structural alterations of
receptor proteins
• Example: Modified EGF receptor induces nonstop signaling
(Fedi et al., 1997)

18. Downstream Alterations
• Downstream alterations of intracellular
circuits can trigger proliferative signaling
• SOS-Ras-Raf-MAP Kinase growth pathway
• Example: In 25% of tumors, Ras proteins are
modified to induce mitogenic signals
downstream of the GF receptor (Medema and
Bos, 1993)

19. New Research
• Somatic mutations activate additional downstream
pathways
• About 40% of human melanomas contain
mutations affecting B-Raf proteins in the MAPkinase
pathway (Davies and Samuels, 2010)
• Defects in negative-feedback loops promote
proliferative signaling
• Mutations in Ras oncogenes compromise GTPase
activity, which regulates proliferative signaling
(Hanahan and Weinberg, 2011)

20. Recruitment of Normal Cells
• Cancer cells recruit normal cells neighbors to
supply growth factors and signals
• Cancer cells stimulate normal cells to release
growth factors into the tumor microenvironment
(Cheng et al., 2008; Bhowmick et al., 2004)
• Key role of fibroblasts and endothelial cells

21. The Genetic Basis of Unregulated Growth: Mutation
• Genetic mutation leads to cancer
• Over-expression of oncogenes, under-expression
of tumor suppressor genes
• Mutations in oncogenes mimic growth signaling
(Hanahan and Weinberg,2000)
• About half of human tumors have mutant Ras
oncogenes(Kinzler and Vogelstein,1996)

22. Somatic Mutations activate additional downstream pathways
that promote sustained growth
• RAS-RAF-MAPK PATHWAY
• 90% Pancreatic adenocarcinomas carry mutant K-RAS
alleles
• 40% melanomas contain activating mutations affecting B-
RAF

23. Excessive Proliferative Signaling Can Trigger Cell
Senescence
• Excessively elevated signaling by oncoproteins, such
as RAS, MYC, and RAF in a normal cell provoke
protective response such as induction of cell death.
• Alternatively, cancer cells expressing high levels of
these oncoproteins may be forced to enter into the
nonproliferative but viable state called senescence.
• Whenever these tumor cells get the favorable
microenvironment they enter into proliferative phase

26. The most prominent brakes:
Retinoblastoma protein (pRb) (Gatekeeper)
• Direct regulator of the cell division cycle.
• RB transduces growth-inhibitory signals and
decides whether or not a cell should proceed
through its growth-and-division cycle.
• Defects in the RB pathway function
persistent cell proliferation.

27. p53 pathways : Guardian of the genome
• TP53 receives inputs from stress and abnormality
sensors that function within the cell’s intracellular
operating systems.
• TP53 can
– halt further cell-cycle progression
– trigger apoptosis
Inactivation of TP53 leads to inappropriate replication
of cells

28. Mechanisms of Contact Inhibition and Its Evasion –
• Healthy cell stops dividing when comes in contact with
other cells but cancer cell does not.
Contact inhibition is abolished in various types of cancer
through many mechanisms

29. • Merlin, the cytoplasmic NF2 gene product, activate contact
inhibition by coupling cell-surface adhesion molecules like
Ecadherin to transmembrane receptor tyrosine kinases.
• Merlin strengthens the adhesiveness of cadherin-mediated
cell-to-cell attachments and thus inhibits the mitogenic
signals.
• Thus, the mutation of NF-2 gene results in loss of this
property and thus grow in uncontrolled manner.

31. Role of TGF-B
• In normal cells, its exposure blocks their progression
through the G1 phase of cell cycle; in many late stage
tumors, however, its signalling is redirected away from
suppression to activation of a cellular program termed
“epithelial to mesenchymal transition”

33. Normally when cells become old or damaged they are
programmed to die in a process called apoptosis.
• But cancer cells escapes normal cell death and
continue to accumulate in the body.
• Tumor cells develops a variety of strategies to escape
apoptosis.

34. Cancer cells acquires anti apoptotic regulators:-
• Most common is the loss of P53 tumor suppressor
function, which eliminates this critical damage sensor
from the apoptosis-inducing circuit.
• Alternatively, tumors may escape apoptosis by
increasing the expression of antiapoptotic regulators
(Bcl-2, Bcl-XL Mcl1).
• By downregulating proapoptotic Bcl-2–related factors
(Bax,Bim,Apaf-1 ).

35. Autophagy Mediates Both Tumor Cell Survival and Death –
• Nutrient starvation, radiotherapy, and certain cytotoxic drugs can
induce elevated levels of autophagy that apparently protect cancer
cells via resistance to apoptosis.
• Moreover, severely stressed cancer cells have been shown to
shrink
via autophagy to a state of reversible dormancy.
• This particular survival response may enable the cancer cells to
survive during anticancer therapy or during shortage of nutrition.

36. Necrosis has proinflammatory & tumor promoting potential
• Necrotic cells can release bioactive regulatory factors which
can directly stimulate viable neighbouring cells to proliferate

38. In normal cell division, a small portion at the end of
each chromosome composed of multiple tandem
hexanucleotide called telomere, is shortened every
time DNA is copied.
• Loss of telomere reaches a critical point and cell will
no longer divide and replicate and undergo p53
dependent cell cycle arrest or apoptosis. In this way
healthy cells self limit their replication.
• But in cancer cells activation of an enzyme called
telomerase can maintain telomeres and allow cells to
replicate limitlessly.

39. • Enzyme TOLEMERASE …maintain chromosome length (adds
telomeres to the ends of telomeric DNA)
• Cancer cells have unlimited replicative potential.
• All cancer cells maintain their telomeres.
90% of them do so by increasing the production of telomerase
enzyme.
• Acquire the unlimited replicative potential—termed cellular
immortality

43. ANGIOGENIC SWITCH OF TUMORS INVOLVES :
Sprouting
Splitting
Remodeling of the existing vessels
WHY IT IS IMPORTANT?
Supply of oxygen and nutrients
Removal of waste products

48. Pericytes
• They provide important mechanical and physiologic support to
the endothelial cells
• Pericyte also secrete PDGF which helps in recruitment of
pericytes and smooth muscle cells.
A Variety of Bone Marrow-Derived Cells Contribute to
tumor Angiogenesis-
• These include cells of the innate immune system including
macrophages, neutrophils, mast cells, and myeloid progenitor.
• This tumor associated inflammatory cells can help to trigger the
angiogenic switch by providing tumor microenvironment and
secrete various growth factors.

52. Invasion–metastasis cascade, which include: local invasion,
intravasation into blood and lymph vessels, transit through
the vasculature, extravasation from the vessels, formation
of micrometastases, and growth of micrometastases into
macroscopic tumors.
1.Invasion of extracellular matrix
ECM is made of collagens, glycoproteins, and involves the
basement membrane and the interstitial connecting tissue.

53. Tumour cell must first penetrate the bm and then the
interstitial ct in the following sequence
Detachment of tumour cells from each other
-Cells are adhered to each other by adhesion molecules like
E-cadherins. These are down regulated in cancer cells and
the cells become loose.
Attachment to matrix components
-Tumour cells bind to laminin and fibronectin through
receptors.
Degradation of ECM
-Tumour cells secrete proteolytic enzymes that degrade the
matrix and create passage ways.
Migration of tumour cells

54. 2) Vascular dissemination and homing
Tumour cells form emboli in circulation by
aggregation and by adhering to lymphoid cells and
Platelets
This tumour emboli adhere to the endothelium, then
extravasates and forms a metastatic deposit

59. Cancer metabolism is different than normal tissue metabolism.
First time it was noted in 1920 by biochemist Otto Warburg that
when cancer cells are provided with glucose , they generate large
amount of lactate regardless of whether oxygen is present or not.
• This metabolic difference is referred as THE WARBURG
EFFECT……
The normal cells utilize aerobic respiration to completely
catabolize glucose and generate cellular energy.
• Cancer cells rely primarily on glycolysis for their metabolism
to make lactate and it is called aerobic glycolysis.

60. Aerobic glycolysis also generates ATP but less than aerobic
respiration.
• Cancer cells metabolize glucose for purpose other than
generating ATPs.
• Lactate produced from aerobic glycolysis causes
acidification of tumor cell which has been shown to promote
invasion and metastasis.
• Lactate can also act as a nutrient for some cells in the
tumor.

61. Mutation in metabolic enzymes causing cancer
• FH[fumarate hydratase]– metabolizes fumarate in
TCA…mutation leads to RCC ,leiomyomas.
• IDH [ isocitrate dehydrogenase]– in glioma, glioblastoma,
AML, myelodysplastic syndrome,ALL, prostate, colorectal
cancer.

63. Mechanisms by which tumor cells escape immune
recognization and destruction:
• Low immunogenicity of tumor cells – Failure to produce
tumor antigen
• Mutation in MHC gene needed for antigen processing.
• Inability to recognize tumor cells by immune system.

64. Tumor induced immune supression-
• Factors secreted by tumor cells eg. TGF-b inhibit T cells
directly.
Tumor induced privileged site-
• Factors secreted by tumor cells create a physical barrier to
the immune system.
Tumor treated as self antigen-
• Tumor antigens are taken up and presented by APCs in
absence of co-stimulation taken as self antigens and escape
from immune destruction

67. • DNA damage or mutation in a normal cell results in cell
cycle arrest followed by DNA repair or apoptosis.
• Interference in this process may occur either by lack of
recognizing and repair of damaged DNA or abnormal
gatekeeping of cell cycle.
• Genomic instability and mutation acts as enabling hallmark
of cancer ie facilitator of hallmark capabilities.

68. • These mutations can include change in nucleic acid
sequence, chromosomal rearrangements or aneuploidy.
• DNA damage from external cause or impaired DNA
repair mechanism due to epigenetic mechanism such
as DNA methylation and histone modifications.
• Cancer cells generally have severe chromosomal
abnormalities

69. Based on the level of disruption types of gene instablity are-
• Nucleotide instablity-
Include nucleotide substitution, deletion or insertion
E.g. xeroderma pigmentosum, MYH associated polyposis
• Microsatellite instablity-
Include defect in mismatch repair leads to contraction or
expansion of microsatellite
E.g. Lynch syndrome
•

70. • Chromosomal instablity-
Most prominent form
90% of human cancer exhibiting chromosomal abnormalities
It include chromosomal aneuploidy, amplifications, deletions,
translocations and inversions.
E.g. Breast, prostate, non small cell lung cancer, leukemia,
neuroblastoma etc.

71. Defects in these caretaker genes results in-
• DNA damage and inactivation of repair machinery
• Inability to inactivate mutagenic molecules resulting in
DNA damage.
• CGH (comparative genomic hybridization)- one method of
molecular genetic analysis to compare patient DNA to
reference DNA to check the gains and losses of gene copies
in the patients cell genome by using florescent dye .

73. Virtually every tumor contains immune cells present at
varying densities.
• Such immune responses are largely thought to reflect an
attempt by the immune system to eradicate tumors
• However, tumor-associated inflammatory response is
shown to have paradoxical effect of enhancing tumorigenesis
and progression.

74. • Inflammation can contribute to multiple hallmark
capabilities by supplying bioactive molecules for favourable
tumor microenvironment including:
• Growth factors that sustain proliferative signaling
• Survival factors that limit cell death
• Proangiogenic factors
• Extracellular matrix-modifying enzymes that facilitate
angiogenesis, invasion and metastasis