Molecular biology
of the tumor
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Cancer - definition
• name cancer ("cancer") derived from the Latin word
for crab (greek: karkinos = crab, onkos = expense,
burden)
• disease caused by a malignant tumor
• tumor - neoplasia, neoplasm - pathological unit created
in the tissue of a multicellular organism whose growth
is out of control
• affects plants, animals, humans (not a disease of
modern times)
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Historical overview
• 400 B.C. Hippocrates described the cancer as long
extensions (like crayfish feet) jutting into the healthy
tissue:
Gr: karkinos = crayfish; onkos = crab
Lat: cancer = crayfish
• descriptive (epidemiological) findings:
• 1848 - increased incidence of breast cancer among nuns
(associated with childlessness and no breastfeeding)
– 1775 - Scrotal cancer among chimney sweepers (in
connection with the occurrence of harmful substances in
soot; connection with hygiene habits)
– 1902 - connection of x-rays and development of cancer
– begin. 20. cent. - family history of cancer
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Historical overview
• 1909 - Rous - Infectious tumor transmissions in chickens
• study of tumor viruses (oncogene - a fragment of viral genes
which cause tumor) (1961 - Nobel Prize)
• 1976 – Bishop, Varmus – discovered c-src (protooncogenes)
• associated with mitogenic signaling pathways
• slowly transforming viruses
• Henry Harris (cells fusion) – tumor suppressors – recessive
genes (brakes)
• Knudson – retinoblastoma – „two hits hypothesis“
• DNA transfer (transformation, transfection)
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tumor, neoplasm
- It is new and abnormal tissue in a multicellular
organism, which has no physiological function in
this organism and grows in unregulated manner.
- is a genetically conditioned abnormal growth of
cell tissue mass of clonal nature. Its growth is not
coordinated with the growth of surrounding tissue,
and the equilibrium state of the organism.
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Basic characteristics
at the cellular level, genetic disease (a consequence
of mutations that are transmitted to the daughter
cells)
 phenotype of tumor cells is heritable (transmitted
to other cell generations)
 manifests by the change of growth and
differentiation properties of cells and by changing
their viability
 begins at a single cell level
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Danger of cancer
reproduce regardless of the needs of the organism (unresponsive to
conventional cellular signals)
colonize the body areas that are reserved for other cell types
disrupt the function of the affected organs
rapidly dividing tumor cells exhaust the organism
it is difficult for immune system to distinguish from healthy cells
tumor is formed by heterogeneous and continuously further developing
population of cells that exhibit different (and variable) sensitivity to
drugs
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Are tumors hereditary?
• predisposition to tumorigenesis can be inherited: inherited
germline mutations are recorded at rare familial cancer
syndromes (e.g. mutations in the RET proto-oncogene MEN
syndrome causes - "multiple endocrine neoplasia" or thyroid
tumors)
• common are tumors derived from somatic cells, which have
experienced undesirable combination of tumor mutations
• increased frequency of mutations / genomic instability
increase the risk of cancer
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Development of tumors - process of
gradual accumulation of genetic changes
• Incidence of tumors - advanced age
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Three characteristics that describe a
malignant tumor (Richard Klausner 2002)
• genome instability disease
• (Exceptions: leukemia, certain lymphomas, Ewing's
sarcoma)
• altered cell behaviour disease
• modified tissue behaviour disease
Special properties of tumor cells in in vitro cultivation
1. They do not need anchorage
- Most of healthy cells need a substrate and form a monolayer in
culture
- Cancer cells can grow in suspension
2. Reduced sensitivity to contact signals (contact inhibition)
- A healthy cell stops dividing when there is no place (in culture are
only monolayers)
- Cancer cell is further divided, and oppresses the surrounding tissue
(in culture grows into multiple layers, 3D shapes)19_MB-2017 10
Classification of tumors I:
by their ability to infiltrate other tissues
• Benign (noncancerous): remain in their place of origin, they
do not migrate, do not invade other tissues. The similarity
with the original tissue. Usually not life-threatening
• Malignant (cancerous): penetrate into surrounding tissues
through the blood and lymphatic system to the whole body
in new tissues induce the formation of secondary tumors
(metastases). A lower degree of differentiation. High
proliferation (large nuclei, nucleoli, creation polyribosomes).
A change in the morphology, size and shape of cells.
• From this perspective tumors can be classified into primary
and secondary.
(Attention: secondary - therapy-related: the development from other
less serious conditions.) 19_MB-2017 11
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Even benign tumors can be fatal
• overproduction of important biologically active
molecules (e.g. hormones)
Example: glandular tumor cells - Islets of Langerhans
- excessive secretion of insulin - hypoglycemia –
Death
location of the tumor interferes with a vital
function
Example: brain lining - disturbance in the functioning
of vital centers of the brain - death
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Classification of tumors II:
according to cell type (tissues) which they arise from
• Carcinomas - tumors of the epithelial cells (about 90% of human cancers)
• Sarcomas - solid tumors connective tissues - muscles, bones, cartilage
• Leukemia and lymphomas - derived from hematopoietic cells and cells of the
immune system
• Gliomas - tumors derived from neural tissue
name reflects the original tissue where the tumor arose
suffix determines whether the tumor is benign or
malignant
-om (benign)
-karcinoma (malignant epithelial tissue)
-sarkoma (malignant connective tissue or muscle)
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• tumors of epithelial cells (carcinomas) represent the
largest group of human tumors (more than 80% of deaths
from cancers in the Western world)
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Origin Benign Malign
Epithelial/Endothelial
liver adenoma, pancreas, colon,
kidneys etc.
liver adenoma, pancreas, colon,
kidneys etc.
Mesenchymal connective tissue Lipoma Liposarkoma
Fibroma Fibrosarkoma
Chondroma Chondrosarkoma
Neuroblastoma
Retinoblastoma
Germ Teratoma Teratokarcinoma
Embryonal karcinoma
Other Melanoma
Leukemia
Classification of tumors III:
according to the affected organ or tissue
• lung cancer
• colorectal cancer
• breast cancer
• acute myeloid leukemia
• and many others
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Carcinogenesis
- the process of formation and tumor development
- it is a multistep process
- the essence of carcinogenesis is the gradual
accumulation of genetic (and epigenetic) changes
Neoplastic transformation - is transformation of
somatic cell in the tumor cell
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The essence of carcinogenesis is the
gradual accumulation of genetic changes
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Multistage carcinogenesis associated
with clonal expansion steps
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Clonal model of tumor development:
selection, clonal expansion
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How many and which genes are
altered in carcinogenesis?
• Cancer is not a homogenous disease.
• It is estimated that 4-7 targets need to be hit in
carcinogenesis.
• Dozens of particular genes can be targeted during
carcinogenesis.
• Overall there are six (seven?) basic
characteristics to a malignant tumor:
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• https://www.youtube.com/watch?v=MWr20
ZZipNA
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Six acquired characteristics of a
malignant tumor (Robert A. Weinberg
2000)
Self-sufficiency in growth signals H-ras loss
Insensitivity to anti-growth signals RB loss
Evading apoptosis IGF production
Limitless replicative potential telomerase activation
Sustained angiogenesis VEGF production
Activating invasion and metastasis E-cadherine inactivation
characteristic example
Genome instability is a required feature to achieve
these characteristics.
TEST
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Hallmarks of cancer
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Carcinogenesis has individual
progression
Individual – order in which hits occur
- number of hits
- genes that are hit
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(A) Self-sufficiency in growth signals
 healthy cells cannot proliferate without growth signals
 many oncogenes stimulate signal pathways that are usually active only
in the presence of growth factors
 reduced dependency on growth factors is observable also for tumor
cell lines propagated in vitro
alter growth factors or the way they are produced
Healthy cells usually produce growth factors utilized by other cells (heterotypic
signalization), while tumor cells gain the ability to synthesize growth factors to which they
are themselves sensitive (autocrine signaling) e.g.. PDGF – produced by glioblastoma
alter transmembrane receptors
a) Increased expression of receptor gene increases cellular sensitivity to low
concentrations of growth factors (e.g. EGF receptor expression is increased in stomach,
brain and breast cancer),
b) Change to receptor structure: constitutive activity, even without signal
alter intracellular component of signal pathway
Three strategies to sustain proliferative signaling
Main role : Ras-Raf-MAPK cascade
Ras proteins are altered in 25% of human tumors
It is likely that growth factor pathways are somehow deregulated in all tumor types.
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(B) Insensitivity to anti-growth signals
Healthy tissue
reacts to both pro- and anti-proliferative (e.g. TGFβ) signals that are
dissolved in body fluids and exert
their function through membrane
receptors and intracellular signal
cascades
Tumor cells can loose the sensitivity
to TGFβ by different means:
Lower the expression of TGFβ
receptors, mutate TGFβ receptor,
mutate proteins of intracellular
signal cascade (SMAD proteins)
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(C) Metastasis and
invasion
- primary tumors can be chirurgically
removed
Invasion
Tumor cells penetrate to neighboring
tissue
metastasis
Tumor cells migrate by bloodstream and
create secondary tumors
- requires changes to adhesion
Metastatic cascade
basal membrane disintegrates
cells separate
cells move
invasion
vascular system penetration
Tumor cells circulate
leave bloodstream (TEST) 19_MB-2017
29
tumor cells travel from primary tumor to new locations, that at least at
the early phases have enough room and resources to support tumor growth
enabled by changes in two protein types:
- Proteins that are responsible for cell adhesion to neighboring cells
(CAM) and to matrix (integrins)
- Extracellular proteases (protease overexpression, protease inhibitor
inhibition)
cell detachment
Tumor cells have reduced cohesion as a result
of reduced expression of adhesion genes
(cadherins, catenines)
regular cells of the same type do not
detach from each other inside a tissue
Transfecting invasive cells with
cDNA for E-cadherin decreases their
metastability
(C) Metastasis
E-cadherin
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Metastasis and invasion
- Cancer cells can sustain in secondary tumors in dormant stage, hard to be
discovered by diagnostic tools – causing relapse years after initial treatment
Metastasis cascade
basal membrane disintegration
cells separate
cells migrate
invasion
vascular system penetration
circulation in bloodstream
leaving bloodstream
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(D) Angiogenesis= growth of new capillaries
- capillaries supply (tumor) cells
- tumor needs capillaries to supply nutrients, oxygen and for waste removal,
otherwise it can grow to a max. 1-2 mm
- Controlled by releasing angiogenesis factors (e.g. VEGF and FGF)
- Capillary formation is dependent on balance between angiogenesis inductors
(e.g. FGF, VEGF) and angiogenesis inhibitors (e.g. trombospondine-1)
tumor growth is restricted by capillar availability. Under the lack of oxygen and
other nutrients the cells start to die by necrosis, starting from tumor centre
(furthest from cappilaries).
Tumor cells overproduce angiogenesis inductors and limit angiogenesis inhibitors
Capillary formation under physiological conditions
2 mechanisms:
– angiogenesis – new capillaries start to grow from old ones
- vasculogenesis– capillaries form from „nothing“ – that is by
differentiation of epithelial precursors inside embryo
Oxygen diffuses across 100 micron (0,1 mm)
capillary formation – is regulated by the
needs of metabolism
Tumor cells induce angiogenesis
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Healthy vasculature (right) is more systematically
arranged compared to the tumor vasculature (left)
(E) Limitless replicative potential
Telomeres - repetitive sequences at the end of each chromatid
Mammals: sequence TTAGGG (repeated in humans around 2500x)
During each replication chromatids shorten. Their elongation can be
performed by enzyme - telomerase
Most somatic cells however do not have active telomerase
Active telomerase is a hallmark to tumor and embryonal cells – 90%
immortalization
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(F) Avoiding apoptosis
Apoptosis = programmed cell death
Happens in organogenesis and during growth factor starvation
physiological cell removal without endangering neighboring cells
different than necrosis (result of physical cell injury, when cells
burst, releasing their contents to intercellular space and cause
inflammation)
Apoptosis trademarks:
cytoskelet breaksdown, cell squishes
Nuclear membrane decomposes
nuclear DNA cleaved into fragments
cell disintegrates into apoptotic vesicles
cell surface altered as to induce imminent phagocytosis
Tumor cells are not sensitive to signals inducing cell death
healthy cells can live only in the presence of growth factors, otherwise
they die by apoptosis x tumor cells live on without growth factors
Healthy cells with damaged DNA die by apoptosis x tumor cells do not
Resistance to apoptosis is one of the reasons for increased
survivability of tumor cells
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Molecular basis of cancer
Changes in genes that control cell cycle and DNA repair
1. Proto-oncogenes
- Genes stimulating proliferation
- Mutations causing their hyperactivity are called oncogenic
- "Gain-of-function" mutations
- Often genes of growth signalization cascade
- e.g. Ras, Myc...
- Activation is dominant – corrupting one allele is enough to start
carcinogenesis
2. Tumor-suppressors
- Genes inhibiting cell cycle
- Often dysfunctional in cancer
- "Loss-of-function" mutations
- e.g. p53, Rb1, BRCA1 a BRCA2...
- Activation is recessive – both alleles must be defective to induce
cancer
TEST
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Proto-oncogenes and tumor suppressors encode genes that regulate
cell proliferation and growth
1. Growth factors
- e.g. PDGF, EGF...
2. Growth factor receptors
- e.g. PDGFR, EGFR...
3. Intracellular carriers
- e.g. Ras, Src...
4. Transcription factors
- e.g. Myc, Fos...
5. Apoptosis regulators
- e.g. Bcl2 protein family
6. Proteins regulating cell cycle
- e.g. Cyclins and cyclin dependent kinases
7. Proteins involved in DNA repair
- e.g. BRCA, ATM, ATR, γH2AX...
TEST19_MB-2017 37
Oncogenes
Proto-oncogene is a structural gene in eukaryotic cell, that is
somehow connected to cellular proliferation and
differentiation
Oncogene is a proto-oncogene altered or activated in a manner
that favors neoplastic cell transformation
Proto-oncogene activation turns proto-oncogene into oncogene.
Proto-oncogene mutations are:
- activating
- dominant
- occur in somatic and rarely also in progenitor cells
pathological oncogene activation
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Tumor suppressors
Tumor suppressors (anti-oncogenes) regulate (inhibit)
proliferation in healthy cells and keep them in non-dividing phase (G0).
Their loss is manifested by uncontrolled proliferation.
Tumor suppressor mutations are:
- inactivating
- recessive (coupled with LOH)
(„recessive oncogenes“)
- occur both in somatic
and progenitor cells
Most tumor suppressors act as
cell cycle negative regulators
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Tumor
suppressors
• cell cycle negative regulators (Rb, p16)
• proliferation signal pathways negative regulators
• (WT-1 inhibits EGR-1; NF-1 inhibits RAS)
• intercellular adhesion negative regulators (APC, DCC)
• DNA damage repair and recognition pathways (p53, MSH2,
MLH1) 19_MB-2017 40
Genes targeted in carcinogenesis
1. Oncogenes
Tumor suppressors
2. Oncogenes
Tumor suppressors
genes for genome stability („stability genes“)
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Types of mutations
a) point mutation, b) gene amplification, c) chromosomal translocation, d)
the local reconstruction of DNA, e) sertional mutagenesis
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DNA repairTEST
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DNA repair
- Homologous recombination (HR) is more accurate than the non-homologous
end joining (NHEJ), but requires the presence of template DNA chain of
sister chromatids appears to the S / G2 phase, less often used as a template
in a second chromosome in G1 – non-sister chromatid)
TEST
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Retinoblastoma protein- tumor suppressor RB
HDAC - Histone deacetylases suppress
the expression (chromatin wraps) - HDAC1, HDAC2, HDAC3...
- Retinoblastoma protein (pRB) inhibit excessive cell division (proliferation) by cell cycle
arrest
- prevents the transition to the S phase of the cell cycle by binding and inhibition of the
transcription factors E2F family
- until Rb bound E2F, the cell remains in the early G1 or G0 phase
- In proliferating cells complex CycD + CDK4,6 pRB is phosphorylated, thereby releasing
E2F → entry into S-phase
- Rb-E2F complex also attracts HDAC to the chromatin,
which reduce transcription factors supporting
transition into S-phase → suppression of DNA synthesis
In tumor cells, pRB often does not work and E2F is
still free → unregulated proliferation
a) mutations in the RB gene - not bind to E2F
b) viral protein E7 displaces pRB
c) the overexpression of cyclin D or CDK 4.6 or
loss of p16 inhibitory → excessive phosphorylation of RB
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Hereditary cancers – RB mutation
- mutation in one allele is already in sexual cell → in all somatic cells of a
descendant
- mutation in the second allele can occur during life
- non-functional RB protein was first described in connection with eye tumors
(retinoblastoma), plays a role in various types of tumors
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Two-hit model
For the formation of retinoblastoma two genetic changes are needed
- in 1971 Alfred Knudson defined "Two-hit" theory based on a comparison of
hereditary and sporadic forms of retinoblastoma
- researchers in the field of cancer initially paid no attention to this theory,
because hereditary cancer is very rare
- This theory, however, was behind the discovery of tumor suppressor genes in
all types of cancer
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Tumor-suppressor p53
The guardian of the genome
- p53 induces transcription of p21 that binds to CDK2 - inhibits the transition to the S phase
- Binding with Mdm2 inhibits its activity
- HATS (eg. P300 / CBP, PCAF) may in response to stress acetylated p53 → increase in activity
- HDAC1, 2 and 3 can reduce the p53 activity by deacetylation
- 50% f tumors have a mutation or deletion of p53
- p53 mutation is mostly negative prognosis for
cancer patients
HDAC - histone deacetylase
suppress the expression of HDAC1, HDAC2, HDAC3...
HAT - Histone acetyl transferase activated
Expression of Gcn5, p300/CBP, PCAF, SRC-1, ACTR, ESA1, MOZ...
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Tumor-suppressor p53
Brake entry into S-phase cell cycle arrest in the G1 phase enables break
necessary to DNA repair
1) damaged mutated cells continuing
the cell cycle
2) allow damaged cells to avoid
apoptosis
3) the emergence of genetic
instability, allowing the accumulation
of mutations
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Li-Fraumeni syndrome
- hereditary
disease
- Mutations or
deletions in one
allele of the p53
gene causing a
hereditary
predisposition to
cancer
- increased
incidence of
cancers of
different tissues
in early age in the
family
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Coordination tumor-suppressors RB and p53
- Two main pathways ensuring cellular
response on potential oncogenic stimuli
- Signals (e.g. DNA damage, oncogene
activation
1. pathway p53
induction of ARF, that separates the
MDM2 - p53
- active p53 regulates a number of
genes, eg..:
- WAF1 → CDK inhibition → cell-cycle
arrest
- BAX → induction of apoptosis
- p21 → CDK inhibition
2. pathway RB
induction of INK4A → CDK inhibition
(4,6) → inhibition of RB
phosphorylation→ complex RB+E2F
arrest cell cycle
RB may also bind to MDM2-p53 and
regulate the activity of p53 19_MB-2017 51
Tumor-suppressors BRCA1 a BRCA2
BReast CAncer 1 and 2 genes - It helps to repair DNA damage, in
particular DSBs (double breaks)
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Tumor-suppressors BRCA1 a BRCA2
- only 5-10% of breast cancer is caused by a mutation in the BRCA
- dangerous mutations in BRCA increases breast cancer and ovarian
cancer (not all mutations are dangerous)
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Proto-oncogenes - signal pathway Wnt
the gradual transformation of healthy cells of colon cancer
1. The loss of the tumor suppressor APC → stabilization of β-catenin → polyp
formation
a) transcription change (increased gene transcription promoting proliferation: cyclin D, c-
myc...)
b) increased cell adhesion (β-catenin links E-cadherin and α-catenin)
2. "Gain-of-function" mutation of Ras → benign adenoma
3. "Loss-of-function" mutation of p53 → carcinoma
Colon cancer:
p53 mutation in 70%
APC mutation in 70%
APC is negative
regulator of β-catenin
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Proto-oncogenes - receptors for growth factors (GFR)
1. Constitutive activity
- Demonstrate kinase activity in the
absence of ligand
2. Overexpression
- multiplication of receptors
number
EGFR - breast carcinoma, stomach,
colorectum
Her2 – breast carcinoma
c-Kit- role in hematopoiesis
- physiologically expressed mainly on
immature blood progenitors
- skin cancer
Treatment with antibodies or tyrosinkinase
inhibitors
Diagnosis receptors can predict
treatment response
- SCF - stem cell factor; steel factor
- Trastuzumab = Herceptin
- Epidermal growth factor receptor
(EGFR; ErbB-1; HER1)
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3. Biological carcinogenes: oncogenic (tumor) viruses
a) Retroviruses (RNA viruses): single stranded RNA –
uses reverse transcription
- Contain oncogene in their genome (acutely transforming viruses)
- Activate the protooncogene, next to which are integrated (slowly transforming)
Oncoviruses
human lymphotropic virus type I (HTLV-1)
- Adult T-leukemia (lymphoma) (ATTL), latency period of about 30 years
- high proliferative activity of infected cells, mutations are more likely
Lentiviruses
viruses HIV-1 and HIV-2
-tumors associated with their infection lymphomas
and sarcomas
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3. Biological carcinogenes: oncogenic (tumor) viruses
b) DNA tumor viruses
- not contain oncogenes, but encode proteins that interact with tumor suppressor in
host cells
- Pushing the host cell into the S phase → cell cycle acceleration
Inactivation of p53 is one of the key events in the transformation of cells by DNA
viruses
Hepatitis B virus (HBV)
- chronical infection - integration into the chromosome
- hepatocellular carcinoma (HCC) –20-30 years after infection
Herpes viruses - EB (Epstein Barr virus)
- in the cell nucleus in an episomal state (extrachromosomal)
- Lymphomas and carcinomas
Papillomaviruses (HPV xx)
- causes cervical cancer
- in benign tumors - in the form of episomes in malignant integration into the
genome
- Described about 100 different types of papillomaviruses - is divided into "highrisk"
and "low-risk" types according to prognosis
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Human papilloma
virus influences RB
and p53
- virus produces
proteins that
inhibits tumor
suppressors:
- E6 → p53
- E7 → RB
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Selected mutations in tumor diseases:
Ras - 25% of all cancers
active telomerase - 90% tumors
K-Ras - 80% pancreas carcinoma
p53 - the most frequently inactivated in tumors - various tumors, Li-Fraumeni
p16 - melanoma
Rb - retinoblastoma
t(8;14) active Myc - B-cell CLL, ALL, Burkitt lymphoma
N-Myc amplif. - 30% neuroblastoma
β-catenin (WNT) - colorectal carcinoma (mutant catenin insensitive to the APC, transcription of
genes cc)
TGF-β, SMAD4 - resistance against antiproliferative signals
Fas receptor - tumor
Bax - tumors of the digestive tract and leukemia
Bcl-2 translocation - follicular lymphoma
loss chr10, inactive PTEN - glioblastoma
gain chr7, dupl MET - kidney carcinoma
t(9;22) Bcr-Abl - CML, ALL (30%), rarely AML
transl. RAR - acute PML
autocrine TGF - sarcoma
autocrine PDGF - glioblastoma
overexpr EGFR/ERBB – breast carcinoma, stomach, colorectum
overepr HER2 - breast carcinoma (prediction - herceptin Ab against HER2 receptor)
PML/RARA - binds histone deacetylase, which prevent transcription of target genes ATRA
Marker: CD20, CD30, CD33, CD52, CD90
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Hallmarks of cancer
 multistage carcinogenesis  models
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19_MB-2017 61
Models of multistep carcinogenesis
• The development of colorectal cancer
APC is classified as a tumor suppressor gene. The APC protein is a negative
regulator that controls beta-catenin concentrations and interacts with E-cadherin,
which are involved in cell adhesion. Mutations in the APC gene may result in
colorectal cancer.
Transforming of DNA by oncogenic viruses
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Normal
epithelium
Small
adenoma
Medium
adenoma
Large
adenoma Carcinoma
Oncogenic
(tumor)
viruses
Induction of sarkomas in chickens
Peyton Rous was awarded the
Nobel Prize in 1966
evidence of involvement of viruses
in some types of cancers
Rous sarcoma virus is a retrovirus
derived from the avian leukosis
virus ALV
- contains src gene, applies to
development of cancer
- does not have any function for
viruses
19_MB-2017 63
Oncogenic (tumor) viruses
• Retroviruses (RNA viruses): contain in their genome
oncogene (acutely transforming viruses) or activate the
protooncogenes, next to whicg is intergrated (slowly
transforming)
• DNA tumor viruses use another transformation strategy: do
not contain oncogenes, but encode proteins, that can
interact with the tumor suppressors (RB, p53, p300/CBP) of
the host cell and the host cell thus pushed into S-phase:
SV40: large T antigen with different domains interacts with
p53, Rb, p300/CBP
Adenoviruses: E1A interacts with RB and p300/CBP; E1B
interacts with p53
papilomaviruses HPV-16, HPV-18: E6 interacts with p53,
p300/CBP; E7 interacts with RB
19_MB-2017 64
Some methods of inactivation of p53
by viral oncoproteins
Inactivation of p53 is one of the key events in the
transformation of cells DNA viruses.
• LT (SV40) – binds to the DNA binding domain of p53 and
prevents binding of p53 to DNA
• E1B (adenoviruses) – binds to the transactivation domain of
p53 and prevents transactivation of target genes
• E4orf6 (adenoviruses) – causes degraduation of p53
• HBV X (hepatitis B virus) – retains p53 in cytoplasm
• E6 (papillomavirus) – induces degradation of p53 using
ubiquitin ligase E6AP; E6 also directly inhibits the
transactivation ability of p53
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The proportion of proteins E6 and E7 of
papillomaviruses to transformation of the
cells
Viral oncoproteins: stimulate proliferation, inhibit apoptosis, increase
the replicative potential, change the morphology of the cells, induce
the malignant phenotype 19_MB-2017 66
Proliferation Unlimited
replication
capacity
Apoptosis
Bloc of the cell cycle
Loss of
polarity
Loss of
intercellular
adhesion
Invasion
The proportion of E6 protein of
papillomaviruses to cell
transformation
E6 – inactivate p53 (G1 block, dependent apptosis, genetic
stability)
- interact with p300/CBP (disruption of homeostasis)
- activate the expression of hTERT (telomerase activation)
- inactivate p16ink (disruption of maintain rest stage)
- interact with Bak (inhibition of apoptosis)
- interact with E6BP/ERC-55 (inhibition of terminal
differentiation)
- induce degradation of hDlg (and other interactions with
proteins containing PDZ binding structure) (change in
morphology, obtaining of invasive nature)
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The proportion of E7 protein of
papillomaviruses to cell
transformation
E7 – bind to RB (release TF E2F)
- inactivation of p21Cip and p27Kip (disconnection:
differentiation - proliferation)
- cancel the inhibitory effect of TGF- on cell
growth
- lead to the formation of multiple centrosome
19_MB-2017 68
The proportion of proteins E6 and E7 of
papillomaviruses to transformation of the
cells
19_MB-2017 69
Proliferation Unlimited
replication
capacity
Apoptosis
Bloc of the cell cycle
Loss of
polarity
Loss of
intercellular
adhesion
Invasion
The clinical significance of
papillomaviruses
• Described more than 100 different types of papillomaviruses.
• They are divided into „high-risk“ and „low-risk“ types according to
the prognosis which they are associated with. „Low-risk“ viruses
induce the formation of bening tumors, „high-risk“ viruses are
associated with malignant progression.
• About 30 types of HPV preferentially infect the anogenital area,
infection with „high-risk“ viruses are associated with almost all
cervical cancer.
• About 20 % of all cancers of the oral cavity, which are not
associated with a history of smoking and alcohol consumption is
associated with HPV infection.
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Oncogenic viruses and human
tumors
RNA viruses:
• human lymphotropic virus type I (HTLV-1) - T-leukemia
(lymphoma) adults (ATTL)
DNA viruses:
• Epstein-Barr virus (EBV) - Burkitt lymphoma (BL), Hodgkin´s
lymphoma (HD), lymphomas, nasopharyngeal carcinomas
(NPC)
• Hepatitis B virus (HBV) – hepatocellular carcinoma (HCC)
• Human papillomaviruses (HPV 16, 18,..) – anogenital tumors,
tumors of oral cavity, verruca
• Human herpes virus type 8 (HHV8) – Kaposi´s sarcoma (KS)
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Cancer treatment
1. Conventional chemotherapy
Target is proliferating cells, non-specific, always the same % of proliferating cells
Target:
- damage tumor DNA
- stop of the proliferation
- apoptosis induction of p53 or massive damage (p53 independent)
tumor more susceptible to general pro-apoptotic stimulus (genotoxic substanceslátky, mitotic
poisons, antimetabolites)
Disadvantages: huge side effects (removal of healthy tissues – can lead to the formation of
secondary cancers)
2. Target therapy
Selective for tumor cells (specific for particular cell process), low toxicity toward healthy cells
Disadvantages:
- is not 100% specific for molecules
- target molecule is larger and also fill up the physiological function (partial exception for fusion
gene)
- requires the identification of the molecular basis - individualized medicine (tailored medicine)
In oncology, chemotherapy = cytostatic drug with a cytotoxic effect (synthetic or plant/fungi)
cytostatic: lsubstance moderating growth and cell reproduction epecially the tumor tissue
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Mechanism of action of conventional
cytostatics
1. Alkylating agents
Attacking the negative charge of the DNA and cause breaks in DNA - prevent replication
- can induce formation of secondary leukemia
- Chlorambucil (lymphoma, CLL)
- Cyclophosphamide – the most common
- Busulfan – pre-transplantation myeloablation, CML
- Cisplatina - DNA damage, intercalation, active intracellularly, nephrotoxicity
2. Antimetabolites
- interfere with synthesis of nucleic acids
- Targeting mainly on proliferating cells
- Methotrexate - block of purine synthesis with inhibition of dihydrofolatereductase
(osteosarkoma)
- Fludarabine - block purines – substitution of adenosine – DNA fragmentation, (AML, CLL)
- 5-fluoruracil – integration into RNA
- Hydroxyurea - block of ribonucleotide reductase, inhibition of pyrimidine, CML
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Mechanism of action of conventional
cytostatics
3. Antitumor antibiotics*
- Doxorubicin
- intercalates between DNA strands
- induce formation of free radicals
- blocking topoisomerase II
4. Herbal alkaloids
Block the formation of the mitotic spindle
by binding to microtubules
- Vinca alkaloids (from Vinca rosea) –
depolymerization of microtubules – desintegration
of the spindle
Camphothecin- block of topoisomerase I
- Taxanes - (yew needles),
- Paclitaxel - blokc of depolymerization
microtubules (breast carcinoma or ovarial)
*antitumor antibiotics in this context do
not indicate antibacterial substances
topoisomerase: unwinding the DNA during
replication
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Targeted therapy - examples
Monoclonal antibodies
- Specific antibody (Ab) agains selected antigens on the cell surface
a) Naked: after binding can block the receptor, or activate immune cells
b) Conjugated: with a toxin, radioisotope, cytokine
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Targeted therapy - examples
Monoclonal antibodies
- Herceptin - anti-HER-2 (breast cancer 30% amplification of the gene for the receptor
HER-2)
- Rituximab - anti-CD20, malignant B-cell lymphomas, B-lymphatic CLL, follicular
lymphoma
- Gemtuzimab - anti-CD33 (on larger leukemia cells), AML, conjugation with ATB
colcheamicine
- Cetuximab - anti-EGFR, conjugation with toxin, internalization into cells, colorectal
carcinoma
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Targeted therapy - examplexs
Tyrosine kinase inhibitors (TKIs)
- occupying the ATP binding site
- high structural variability allows for the specific binding
- Do not lead to complete cure :(
- Gefitinib – lung and kidney carcinoma, solid tumors
- Erlotinib – ovary carcinoma
- Imatinib, Dasatinib, Nilotinib – cure of CML
Farnezyltransferase inhibitors (FTIs)
Inhibition of Ras function (permanently switched on in tumors)
- Lonafarnib
Targeted therapy of chronic Myelogenous Leukemia (CML)
Over-expression of tyrosine kinase Bcr-Abl in CML caused:
• cytokine-independent growth and survival of the cells demonstrated oncogenic adiction
• protects cells from apoptosis in response to growth factors, or DNA damage * ,
Tipifarnib, BMS-214662
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Targeted therapy of chronic Myelogenous Leukemia (CML)
Over-expression of the tyrosine kinase Bcr-Abl in CML caused:
• cytokin-independent growth and survival of the cells demonstrated oncogenic adiction
• protects cells from apoptosis in response to growth factors, or DNA damage * ,
Tipifarnib, BMS-214662
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Inhibition
MEK
TKI targeted in Bcr-Abl