molecular basis of neo
TRANSCRIPT
MOLECULAR BASIS OF NEOPLASIA
BY MANJIRI JOSHI
REFERRENCE
• Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th
ed. 2007
• Rubin, Strayer. Rubins pathology-clinicopathological
foundation of medicine. 5th ed. 2008.
• Parmus. Essential clinical pathology.1996
• Porth. Pathophysiology concepts of altered health state. 7th
ed. 2005.
• Current Molecular Concept of Oral Carcinogenesis and
Invasion. 2010 Volume 22 Number 01
• Molecular Biology of Oral Cavity Squamous Cell Carcinoma.
Otolaryngol Clin N Am 39 (2006) 229–247
• Medelson, Howley, Gray, Israel, Thompson. The molecular
basis of cancer. 3rd ed. 2008.
SECRET 3- EVASION OF APOPTOSIS
• Just as cell growth is regulated by growth promoting
and growth inhibiting genes, cell survival is
conditioned by genes that promote and inhibit
APOPTOSIS.
• Apoptosis is a pathway of cell death that is
induced by a tightly regulated intracellular
program in which cells destined to die activate
enzymes that degrade the cells' own nuclear DNA
and nuclear and cytoplasmic proteins
5Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
APOPTOTIC PATHWAY
6Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
Genes regulating apoptosis are altered in cancer and these are:
BCL-2 –
– It is a anti-apoptotic gene. Its mutation results in
malignancy.
– For e.g translocation of BCL2 gene from 18q21 to the
immunoglobulin heavy chain locus on 14q32 causes B-cell
lymphomas of the follicular type.
p53 –
– It increases the transcription of pro-apoptotic gene BAX and
BID. Hence mutation of this gene results in decreased
apoptosis.
8Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
SECRET 4- DNA REPAIR DEFECT
• Though humans literally swim in a sea of environmental
carcinogens cancer is relatively rare outcome. This is
fortunate state of affairs results from the ability of normal
cells to repair DNA damage thus preventing mutations.
• a third class of genes in which mutations contribute to
pathogenesis of cancer are genes involved in DNA
mismatch repair., so called mutator genes or caretaker
genes. 10Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
• Normal versions of DNA repair gene exercise surveillance
over the integrity of genetic information by participating in
the cellular response to DNA damage.
• When a strand of DNA is replicating, mismatch repair genes
act as “spell checkers”. E.g if there is an erroneous pairing
of G with T instead of A with T the mismatch repair protein
corrects the defect. Without these proof readers errors
slowly accumulate in several genes.
11Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
• Cells with such defects in DNA repair are said to have the
replication error phenotype readily documented by
examination of microsatellite sequences in the tumor cell
DNA.
• Microsatellites are tandem repeats of one to six nucleotides
scattered throughout the genome.
• Microsatellite instability is hallmark of defective mismatch
repair.12Kumar, Abbas, Fausto, Mitchell. Robbins
Basic Pathology. 7th ed. 2007
• HPNCC-
• Hereditary Nonpolyposis Colonic cancer also known as
Lynch syndrome is a familial predisposition to the
development of colorectal cancer.
• The genes that are mutated in patients with HNPCC have
not yet been completely characterized but include the
genes encoding TGF-B receptor II, the TCF component of
the B-catenin pathway, BAX, and other oncogenes and
tumor suppressor genes.13Kumar, Abbas, Fausto, Mitchell. Robbins
Basic Pathology. 7th ed. 2007
• Xeroderma pigmentosum
• It is an autosomal recessive disease in which increased
sensitivity to sunlight is accomplished by a high incidence
of skin cancer, including basal cell carcinoma, SCC,
malignant melanoma.
• UV light causes cross-linking of pyrimidine residues, thus
preventing normal DNA replication.
14Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
• Ataxia Telangiectasia
• A rare hereditary syndrome that features cerebellar
degenration, immunological abnormalities, occulocutaneous
telangiectasia. And predisposition to cancer.
• Gene ATM on 11q22-q23 codes for a nuclear
phosphoprotein that participates in multiple responses to
DNA damage.
15Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
• Bloom syndrome
• It is an autosomal recessive syndrome.
• Clinical features include small stature, sensitivity to
sun, immunodeficiency, and predisposition to array of
cancers.
• BS gene encodes a protein that has helicase activity
involved in repair of DNA damage.16Kumar, Abbas, Fausto, Mitchell. Robbins
Basic Pathology. 7th ed. 2007
• BRCA-1 & BRCA-2 gene:
• BRCA-1 is located on 17q21 and BRCA-2 is located on
13q12-13.
• Mutation of both the genes causes 80% of familial breast
cancer.
17Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
18Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
SECRET 5- TELOMERASE
• After a fixed number of divisions, normal cells become arrested
in a terminally nondividing state known as replicative
senescence.
• It has been noted that with each cell division there is some
shortening of specialized structures, called telomeres, at the
ends of chromosomes.
• Once the telomeres are shortened beyond a certain point, the
loss of telomere function leads to activation of p53-dependent
cellcycle checkpoints, causing proliferative arrest or apoptosis .
thus, telomere shortening functions as a clock that counts cell
divisions.
19Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
• In germ cells, telomere shortening is prevented by the
sustained function of the enzyme telomerase, thus explaining
the ability of these cells to self-replicate extensively. This
enzyme is absent from most somatic cells,
• and hence they suffer progressive loss of telomeres.
Introduction of telomerase into normal human cells causes
considerable extension of their life span
20Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
• Telomerase activity and maintenance of telomere length
are essential for the maintenance of replicative potential in
cancer cells. Reactivation of telomerase in cells with
abnormal genomes confers an unlimited proliferative
capacity to cells that have tumorigenic potential.
21Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
SECRET- 6 ANGIOGENESIS
• Tumors stimulate the growth of host blood vessels, a
process called angiogenesis, which is essential for
supplying nutrients to the tumor. Even with genetic
abnormalities that dysregulate growth and survival of
individual cells, tumors cannot enlarge beyond 1-2 mm
diameter or thickness unless they are vascularized.
Presumably the 1- to 2-mm zone represents the maximal
distance across which oxygen and nutrients can diffuse
from blood vessels. 22Kumar, Abbas, Fausto, Mitchell. Robbins
Basic Pathology. 7th ed. 2007
AngiogenesisVessel dilation
New TheoryOld Theory
• Beyond this size, the tumor fails to enlarge without
vascularisation because of hypoxia-induced cell death
• Tumor angiogenesis can occur by recruitment of endothelial
cell precursors or by sprouting of existing capillaries, as in
physiologic angiogenesis.
25Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
THE ANGIOGENESIS SIGNALING CASCADE
Genes are activated in cell nucleus
Cancer cell
VEGF (or bFGF)
Endothelial cell surface
Relay proteins
Receptor protein
Proteins stimulate new
endothelial cell growth
ENDOTHELIAL CELL ACTIVATION
SecretesMMPs that
digest surroundin
g matrix
Cell migrates
and divides
Matrix
Activated endothelial cell
Blood vessel
Tumor that can grow and spreadSmall localized tumor
Signaling molecule
Angiogenesis
• However, tumor blood vessels differ from the normal
vasculature by being tortuous and irregularly shape and by
being leaky. The leakiness is attributed largely to the
increased production of VEGF." In contrast to normal mature
vessels, which are quiescent structures, tumor vessels may
grow continuously
29Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
• Tumor growth is controlled by a balance between
angiogenic and anti-angiogenic factors.
• The important angiogenic factors are VEGF and bFGF.
• The anti-angiogenic factors are thrombospondin-1,
angiostatin, endostatin and tumstatin
31Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
SECRET -7 “INVASION AND METASTASIS”
• Invasion and metastasis are biologic hallmarks of malignant
tumors. They are the major cause of cancer-related
morbidity and mortality and hence are the subjects of
intense scrutiny.
• The metastatic cascade will be divided into two phases:
• (1) invasion of the extracellular matrix and
• (2) vascular dissemination and homing of tumor cells.
32Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
• Invasion ofthe ECM is an active process that can be
resolved into several steps
• ■ Detachment ("loosening up") of the tumor cells from
each other
• ■ Attachment to matrix components
• ■ Degradation of ECM
• ■ Migration of tumor cells33Kumar, Abbas, Fausto, Mitchell. Robbins
Basic Pathology. 7th ed. 2007
• Vascular Dissemination and Homing of Tumor Cells
– Once in the circulation, tumor cells are particularly
vulnerable to destruction by innate and adaptive immune
defenses.
– Within the circulation, tumor cells tend to aggregate in
clumps. This is favoured by homotypic adhesions among
tumor cells as well as heterotypic adhesion between tumor
cells and blood cells, particularly platelets.
– Formation of platelet–tumor aggregates may enhance tumor
cell survival and implantability.
34Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
• Arrest and extravasation of tumor emboli at distant sites
involve adhesion to the endothelium, followed by egress
through the basement membrane.
• The site at which circulating tumor cells leave the
capillaries to form secondary deposits is related, in part, to
the anatomic location of the primary tumor.
• Chemokines have a very important role in determining the
target tissues for metastasis
35Kumar, Abbas, Fausto, Mitchell. Robbins Basic Pathology. 7th ed. 2007
36
MICROENVIRONMENT IN CANCER DEVELOPMENT
• Microenvironment of cancer plays a critical role in determining its development.
• Supportive tissues (stroma) of cancer actively collaborate with cancer cells.
• Composition of the stroma- fibroblast- myofibroblast- inflammatory white blood cells- endothelial cells of blood and
lymphatic vessels
• Cancer cells and stromal cells evolve together.
http://www.lbl.gov/LBL-Programs/lifesciences/BissellLab/main.html
EPIGENETICS
• Prior to the middle of the twentieth century, before DNA
was given a special status in biology, the developmental
biologist and evolutionist Conrad H. Waddington (1905-
1975) emphasized that genetics and developmental biology
were related, hypothesizing that patterns of gene
expression, turning genes on and off, and not the genes
themselves, define each cell type, thus linking genes and
gene action to development.
• Waddington coined the term ‘epigenetics’ from the Greek
word epigenesis, referring to embryology and genetics as
“a gradual coming into being of newly formed organs and
tissues out of an initially undifferentiated mass”.
• Epigenetic changes set the stage for alterations in gene
expression and have been identified as important
components of carcinogenesis.
• It has become evident during the past few years that
certain tumor suppressor genes may be inactivated not
because of structural changes but because the gene is
silenced by hypermethylation of promoter sequences
without a change in DNA base sequence’ .
• Methylation also participates in the phenomenon called
genomic imprinting, in which the maternal or paternal allele
of a gene or chromosome is modified by methylation and is
inactivated.
FIELD CANCERIZATION
• Some oral cancer patients develop SCC over a broad
area of the oral mucosa, with multiple lesions arising
simultaneously or over a period of time
• The mechanisms of ‘field cancerization are unkown ,
although three basic hypotheses were proposed
recently by OgdenMolecular Biology of Oral Cavity Squamous Cell Carcinoma. Otolaryngol Clin N Am 39 (2006) 229–247
• Firstly, ‘field changes’ (molecular changes throughout
the oral mucosa of oral cancer patients) may
predispose to the development of multiple primary
cancers.
• In this scenario, a large region of the oral mucosa
may be exposed to the etiological agent(s) which
causes independent transformation of multiple
epithelial cells at separate sites. Molecular Biology of Oral Cavity Squamous Cell Carcinoma. Otolaryngol Clin N Am 39 (2006) 229–247
• A single etiological agent acting at different sites would
cause multiple separate cancers with identical genetic
defects, each arising as a separate clone within the oral
mucosa.
• Subsequent genetic modification (due to spontaneous
mutation or continued exposure to exogenous mutagens)
may render the separate clones genetically distinct.
Molecular Biology of Oral Cavity Squamous Cell Carcinoma. Otolaryngol Clin N Am 39 (2006) 229–247
Different etiological agents acting at different sites
would cause multiple separate cancers with different
genetic defects, each arising as a separate clone within
the oral mucosa.
• Secondly, the etiological agent(s) may transform a single
oral epithelial cell.
• The expanding clone of cancer cells may spread through the
oral mucosa via local tissue spread, regional blood vessels,
seeding via the saliva into a mucosal erosion or seeding due
to the trauma of surgery.
• This would give rise to geographically distinct but
genetically identical cancers.
Molecular Biology of Oral Cavity Squamous Cell Carcinoma. Otolaryngol Clin N Am 39 (2006) 229–247
• The clinical significance of p53 mutation within the normal oral
epithelium of oral cancer patients is unclear.
• Some reports suggest an association with the development of
second primary cancers while others find no such association.
• Recent molecular studies have shown that oral cancer is a clonal
proliferation of neoplastic keratinocytes (that is, oral cancers arise
from a single genetically altered cell) and that multiple primary
tumours result from the migration of clonally-related pre-neoplastic
cells through the oral epitheliumMolecular Biology of Oral Cavity Squamous Cell Carcinoma. Otolaryngol Clin N Am 39 (2006) 229–247
• Thirdly, a tumor may have a paracrine effect on the
adjacent oral mucosa. Of great recent interest is that
tumors have been found to secrete tumor inhibitory factors
including inhibitors of neovascularization.
• Removal of the primary tumor would remove these
inhibitors of cancer development and hence promote
second primary tumor formation.
Molecular Biology of Oral Cavity Squamous Cell Carcinoma. Otolaryngol Clin N Am 39 (2006) 229–247
• Alternatively, tumors may secrete promoters of apoptosis.
• Removal of the primary tumors would reduce the level of
apoptosis in adjacent tissue and hence promote second
primary tumor formation.
Molecular Biology of Oral Cavity Squamous Cell Carcinoma. Otolaryngol Clin N Am 39 (2006) 229–
247
GENOMICS AND PROTEOMICS
• The advent of technology and high-throughput analytical tools
has facilitated the dissection of the genetic pathways that
govern tumor biology. One such analytical tool is genomics.
• Genomic is the study of the patterns of gene expression in a
cellular system, which generally refers to the field of biology
that seeks to understand biologic processes from a global view,
evaluating all the transcriptional activity of a particular system
under certain conditions.
Current Molecular Concept of Oral Carcinogenesis and Invasion. 2010 Volume 22 Number 01
• Its counterpart, proteomics, is the evaluation of the entire
network of proteins that contribute to cellular function.
• These two complementary fields brought tremendous
advances in the understanding of tumor biology, primarily
by allowing scientists to study the changes that occur in
thousands of genes or proteins in a single experiment.
Current Molecular Concept of Oral Carcinogenesis and Invasion. 2010 Volume 22 Number
01
• One particular tool, which has identified genomic signatures
of lymphatic metastasis for OCSCC and may allow the early
detection of occult metastases in selected patients.
• The clinical usefulness of these technologies is currently
under evaluation in other tumor systems
GENE THERAPY
• Gene therapy is a technique for correcting defective genes
which are responsible for genetic abnormalities and
diseases. The idea of gene transfer for treating human
diseases was put forward by CUSACK and TARNER in 1998.
The idea envisages the transfer of a therapeutic gene into
cancer cells via a vector. These processes delete the
mutant alleles’ and are replaced by the therapeutic or
functional gene.50Oral & Maxillofacial Pathology Journal [ OMPJ ] Vol 1 No 2 Jul- Dec 2010
51
RATIONAL TREATMENT OF CANCER
• More specific strategies based on genetic instability of cancer cells.
• More specific delivery of anticancer drugs using monoclonal antibodies.
• Development of specific small molecules.
52
RATIONAL TREATMENT OF CANCER
• Cancer treatment by targeting angiogenesis.
• Cancer treatment by inducing immune responses.
• Cocktail approaches to suppress drug resistance.
• Genomic profiling makes specific treatment strategies possible.
• No magic solution. Still a long way to go…