10 from each block
Cell biology Block 4
Learn about Cdks, cyclins, CDKI, Wee1 kinase, Cdc25, APC/C and SCF
Cdks
Cyclin-dependent kinases
The progression of the cell cycle through various phases is regulated by
transition through specific “check points”, mediated by specific
phosphorylating enzymes called CDKs
This check point is a type of surveillance system, it allows for
detection of:
An incomplete previous step
Damage to the genome/mitotic spindle
When damage is detected, cells arrest at specific phases
Allow time to repair the damage
Three major regulatory pathways:
Start checkpoint:
The key checkpoint which determines whether or not the
cell will duplicate
Regulated by growth factors, nutrients, and integrity
of DNA
Rb is the primary regulatory protein of this
checkpoint
Rb binds to E2F (blocks transition)
G2/M checkpoint
G2 to Mitosis transition is blocked until all the DNA is
duplicated
Controlled by MPF is blocked until DNA
replicated
Spindle checkpoint
Metaphase to anaphase transition
Makes sure that all chromosomes are properly
attached to microtubules
Anaphase-promoting complex (APC/C) is a key
regulatory factor of this checkpoint
Growth factors
Stimulatory growth factors
Activate Ras pathway
Ras mutations commonly found in pancreatic,
colon, lung, and bladder cancers, and occurs in
about 25-30% of all cancers
Activate the PI3-kinase-Akt pathway
PTEN mutations found in 50% prostate cancer, 35%
uterine cancer and also to varying extent in other
cancers
Inhibitory growth factors act through Cdk inhibitors
TGF-beta causes an increase in CDK inhibitor p15 and
p21
Downstream effects, increase in production of cyclin D
The Cdk inhibitor p21 plays a key role in preventing cells
containing damaged DNA from passing through the G1
checkpoint
Check points
Each CDK phosphorylates and modulates the activity of a subset
of target proteins specific for individual transition within the cell
cycle
Mammalian cells have several CDKs, viz
Cdc2 (CDK1), CDK2, CDK3, CDK4, CDK6, and CDK7
Act at different transitions in the cell cycle
Cyclins
CDK needs to team up with cyclins in order to work
And need to be posttranslationally modified correctly by
phoshporylation at the right residues
Activation of CDKs require their association with another group of
proteins called Cyclins
Cyclin D,H,E,A,B
Contribute to CDK substrate specificity
The levels of different cyclins vary during the cycle
Ex. Cyclin E accumulates in late G1, associates with CDK2 and is
destroyed as cells enter S phase
The activity of cyclin-CDK complex is further subject to positive or
negative regulation
Phosphorylation/dephosphorylation
Inhibitors of CDKs
Proteolysis of cyclins and inhibitors APC/C
Cyclin B levels rise just before mitosis
APC/C marks cyclin B with a ubiquitin for it to be
degraded by proteasomes
The regulation of CDK activity by inhibitory phosphorylation
The active cyclin-cdk complex is turned off when the kinase wee
1 phosphorylated two closely spaced sites above the active site
Removal of these phosphates by the phosphatase cdc25 activates
the cyclin-cdk complex
Cdk activating kinase adds the activating phosphate
–
–
–
–
–
CDK1
The cyclin D/CDK4/CDK6, cyclin E/CDK2, and cyclin A/CDK2 are inhibited
by a group of CDK inhibitor proteins (CDK1) that include p21 and p27
CDK1s also impair CDK activating kinase activity CAK
APC/C and SCF
Anaphase promoting complex or cyclosome (APC/C) is a ubiquitin-ligase that
marks the S and M cyclins for destruction
APC/C activity changes depending on whether it is interacting with the
subunit Cdc20 during anaphase of Cdh1 from late mitosis into G1
APC/C is off most of the cell cycle because it has to team up
with CDC20, which is usually off as well
Following its activation in mid-mitosis, the APC/C remains active in
G1
When the G1/S-Cdks are active in late G1, APC/C is turned off
SCF activity is constant during the cell cycle
Ubiquitylation by SCF is controlled by changes in the phosphorylation
status of its target proteins
Requires the presence of the F-box protein
Cdc25 phosphatase
Removes inhibitory phosphates from Cdks
three family members Cdc25 A, B, and C in mammals
primarily involved in controlling cdk1 activation at the onset of mitosis
Wee 1 kinase
Phosphorylates inhibitory sites in cdks
Primarily involved in suppressing Cdk1 activity before mitosis
P21
Suppresses G1/S-cdk and s-cdk activities following DNA damage
Learn in detail the three key regulatory pathways of the cell cycle
– G1/S
Know the roles of Rb, Cdk4/Cyclin D, Cdk6/Cyclin D and Cdk2/cyclin E,
p21, CAK, E2F, DP1
Restriction point control: G1 to S progression
The transition from G1 to S phase is regulated by a checkpoint called
“restriction point” or start
A very important regulatory step, to ensure repair of genome
damage before initiation of DNA replication.
It is now committed to replicating itself!
The initiation of cycle, ex: entry of cells into G1 phase, is determined
by extra-cellular signals (mutagens, nutrients, and growth factors)
Growth factors induce synthesis of D-type cyclins (D1, D2, D3)
D cyclins associated with CDK4 and CDK6 in G1
Cyclin D/CDK4/CDK6 complexes are activated through
phosphorylation by an enzyme complex called CAK (CDK
activating kinase)
Often upregulation of Cyclin D
Rb controls the G1 to S transition
The retinoblastoma protein, Rb, is phosphorylated by Cyclin
D/CDK4/CDK6, which is necessary to drive the cell past the
restriction point
CDK4 Cyclin e/CDC2 and CDK6 with cyclin D
phosphorylates Rb and turns it off
Once the cell crosses the restriction point, mitogenic
stimulation is no longer needed, and the entry into the S phase
is ensured
Rb is a tumor suppressor, so it halts proliferation and cell
growth
Phosphorylation of Rb dissociates E2F, which then heterodimerizes
with DP family of transcription factors
When Rb binds E2F, it turns off transcription
Rb is active when hypophosphorylated, and turned off
when hyperphosphorylated
The e2f-DP heterodimeric transcription factors bind to sequences in
the regulatory regions of genes important in the control of cell growth
Ex: c-myc, DHFR, c-myb, cdk1, E2F-1, Cyclin A
The synthesis of E2F is upregulated in late G1, presumably through
E2F.
Restriction point control and S phase
Cyclin E/CDK2 kinase is needed to maintain Rb in its
hyperphosphorylated state
As cyclin E/CDK2 activity decreases, cyclin A synthesis is induced
Accumulation of the cyclin A/CDK2 complexes signals entry into S
phase
In HPV
There are 2 oncogenes:
E6 – compromises p53
E7 – compromises Rb
–
G2/M
Know the roles of MPF (Cdk1/cyclin B)
The mitotic cdk1-cyclin B complex (MPF) controls the G2 checkpoint by
phosphorylating proteins involved in the early stages of mitosis
MPF=maturation-promoting factor
CDK1 with cyclin B
Activated by multistep process
A target: MPF phosphorylates lamin proteins of the nuclear
lamina (causing breakup of nuclear membrane)
A target: MPF phosphorylates condensin complex which may trigger
chromosome condensation
Which triggers mitosis, it is the starting point
– Spindle assembly check point
Know the roles of APC/C, Securin, Separase, Cohesin, Mads, Bubs, Cdc20,
MPF (Cdk1/cyclin B)
The mitotic Cdk-cyclin complex (MPF) controls the spindle assembly
checkpoint by activating the anaphase-promoting complex
Controlled by APC/C
Targets MPF-cyclin B and securin
Anaphase-promoting complex (APC/C) is a ubiquitin ligase that
marks proteins for destruction by proteasomes
MPF and Cdc20 regulate APC/C
APC/C triggers the breakdown of securin
Securin normally binds to and inhibits Separin
When separin (Separase) is release because of lack of securing, it can
target and cleave cohesins, thereby freeing sister chromatids so they
can separate from each other
Anaphase-promoting complex also triggers the breakdown of
MPF cyclin
Degradation of cyclin very important for the end of mitosis
This process is controlled by proteins associated with the kinetochores
Anaphase promoting complex is controlled by kinetochores, which
bind Mad and Bub proteins as long as the kinetochores remain
unattached to spindle microtubules
Mad and Bub proteins inhibits the anaphase-promoting complex
by controlling cdc20 activity, thereby preventing the initiation of
anaphase
Learn about cell cycle arrest in response to DNA damage
– Know the roles of p53, ATM/ATR, Mdm2, p21, Myc, Arf
– In response to DNA damage, ATM and or ATR trigger the activation of a check
point that leads to cell cycle arrest or delay. Checkpoint pathways are
characterized by cascades of protein phosphorylation events (indicated with a P)
that alter the activity, stability, or localization of the modified proteins.
– P53***** (know this pathway)*******
A transcription factor
Levels kept really low in the nucleus, because a protein called MDM2
binds to it, takes it out of nucleus, brings it to cytosol, marks it with
ubiquitin so that it is destroyed
P53 plays a pivotal role in cell cycle arrest in response to DNA damage
When DNA is damaged, ATM and ATR (2 Dna-dependent protein
kinases) leads to the phosphorylation of P53, preventing its
degradation
Thus, DNA strand breaks by UV or ionizing radiation increase
levels of P53 protein
P53 is a transcription factor, when it is phorphorylated, the
levels increase in the nucleus binding to MDM2
P53 then stimulates the expression of p21 (a CDK
inhibitor) that causes cell cycle arrest!!
P21 blocks cdk/cyclin complexes
LEADS TO CELL CYCLE ARREST
So it means the Rb stays in the hyperphosphorylated state
It also prevents DNA synthesis by binding to PCNA (proliferating
cell nuclear antigen), a subunit of DNA polymerase delta enzyme
complex, involved in DNA replication and repair
P53 also induces many other genes such as GADD45 and cyclin G that
contribute to arrest
–
Mdm2
Controls the levels of p53 in the nucleus
Mdm2 controls the level of p53 in the nucleus by binding p53 and
shutting it out of the nucleus where it is destroyed by the ubiquitindependent pathway
If p53 is phosphorylated by the ATM/ATR pathway and is acetylated, it
will no longer interact with mdm2
Thus, the levels of p53 increase in the nucleus
P53 tells the cell to stop, that there is something wrong, either fix it
or go kill yourself
P53 levels also increase if there is excessive stimulation of mitogenic
pathways
Mitogen activated pathways lead to upregulation of transcription
factor Myc
Myc causesArf to be produced
Myc is a transcription factor that promotes proliferation
Arf inactivates mdm2
No mdm2 results in increased p53 levels
Learn about the key differences between Necrosis and Apoptosis (2 types of cell death)
Necrosis
Swelling and rupturing of injured cells
Typically involving many cells at the tissue level as a result of hypoxia,
toxins of physical force
Necrosis is characterized by severe destruction, cytoplasmic organelle
destruction, loss of membrane integrity, heterophagy, accompanying
inflammatory response
Apoptosis
A deliberate genetically controlled cell death (programmed cell death) that
occurs in response to specific environmental, developmental, or other
stimuli
Usually at the single cell level
Apoptosis is a neat and tidy process of cell killing, with minimum
damage to surrounding cells or tissue, autophagy; without
accompanying inflammatory response
Why is it important?
Ensures homeostasis of all tissues
each individual will produce and eradicate a mass of cells
equal to its body weight
helps prevent tumor growth
destroys obsolete or old cells
vital control mechanisum in maintaining the immune system
death of neutrophils during acute inflammatory response
death of B and T lymphocytes after cytokine depletion
cell death induced by cytotoxic T cells
cell death following certain viral infection (ex. Viral
hepatitis)
physiological, adaptive, or pathological causes
programmed cell death during embryogenesis
implantation, organogenesis, involution
removal of webbing in between digits, resorption of tadpole
tail, pruning of neurons in infant brain development
hormone-dependent involution in the adult
endometrial breakdown during menstrual cycle
regression of lactating breast after weaning
cell death following injuries
radiation, cytotoxic drugs, hypoxia
Stages of apoptosis
Morphological characteristics: cell shrinkage, chromatin condensation,
surface blebbing, followed by formation of membrane-bound apoptotic
bodies containing cytoplasm and tightly packed organelles. Often
phagocytosis of apoptotic bodies by adjacent healthy cells and
macrophages occurs
DNA segregates to nuclear periphery and cytoplasmic volume
decreases
Cell produces blebs, organelle fragments
DNases digest chromatin
Cell is dismantled in apoptotic bodies
A hallmark of apoptosis: DNA ladder
Biochemical characteristics:
Protein cross-linking
Mediated by transglutaminase
Convert cytoplasmic proteins into covalently linked
shrunken shells for packaging into apoptotic bodies
Protein cleavage mediated by “caspases”
Cleavage of nuclear scaffold, cytoskeletal proteins
Fragmentation of genomic DNA
Mediated by calcium and magnesium dependent
endonucleases
Triggered by caspases
Intracellular zymogens critical for apoptosis
Needs to be cleaved in order to be active
Genomic DNA is cleaved at internucleosomal sites, into
DNA fragments
Loss of membrane asymmetry: appearance of
phosphotidylserine (a phospholipid), thrombospondin, on
outer plasma membrane help recognition of apoptotic cells by
macrophages
In normal cells, the phosphatidylserines are facing the
cytosol
During apoptosis, flippases are turned off, so
phosphatidylserine is now facing the outside of the cell,
so it is just asking to be killed
Learn about the role of caspases during apoptosis (Initiator vs effector caspases )
– Caspases
Cytosolic aspartate-specific cysteine proteases
Caspases are zymogens
Need to cleave in order to become active
They remain inactive until an apoptosis signal initiates the activation of
one (initiator caspase) which will cause a cascade leading to activation of
other caspases (effectors)
3 classes of caspases
Intiator caspases
Caspase 8, 9, 10, and 12
Caspase 8** and 10– death receptor
induced apoptosis
Caspase 9** – mitochondrial pathway
Effector (executioner) caspases
Caspase 3, 6, and 7
Inflammatory response mediators
Initiators are activated first, and then they go after the effectors
Learn about IAPs and anti-IAPs
Caspases are regulated by inhibitors (IAPs)
The inhibitor of apoptosis proteins (IAPs), XIAP, cIAP-1, c1AP-2 and
Survivin, can prevent proteolytic processing of procaspases 3, 6, 7 and 9
Bind to caspases and prevent them from being activated
Role of IAPs and anti-IAPs in the control of apoptosis
In the absence of an apoptotic stimulus, IAPs prevent accidental apoptosis
caused by the spontaneous activation of procaspases
The IAPs are located in the cytosol and bind to and inhibit any
caspases
Some IAPs are also ubiquitin ligases
When the intrinsic apoptotic pathway is stimulated, proteins including
anti-IAPs are released
Anti-IAPs bind and block the inhibitory activity of IAPs are
released
Now apoptosis can be induced
Learn about the 3 classes of BCL-2 family of proteins
Bcl2 on outer surface of mitochondria
Their job is to tell the cell to stay alive
About 30 Bcl2 family members
These proteins play tissue-specific as well as signal pathway-specific roles in
regulating apoptosis
The tissue specificity is overlapping
For example, BCL2 is expressed in hair follicles, kidney, small intestines,
neurons, and the lymphoid system
Whereas Bcl-x is expressed in the nervous system and hematopoetic cells
3 classes:
Anti-apoptotic
Bcl-2
Bcl-x
Bcl-w
Proapoptotic – channel-forming
Bax
Bak
Bok
Pro-apoptotic BH3 only
Bad
Bid
Bim
Roles of Bcl2 family members in apoptosis
Bcl-2 which is antiapoptotic, binds bid and blocks formation of
channels that allow cytochrome c release from the mitochondria
Death signals result in activation of BH3-only protein such as bid,
which can lead to mitochondrial pore formation, swelling, and
release of cytochrome c
Bid binds to and activates the membrane ion-channeled
protein Bax, activating cytochrome c release, which binds
to Apaf (APF1)and lead to formation of apoptosme
Recruits procaspase 9, activate caspase 9, etc.
APAF1 is the adaptor this time!!!!
Apoptosis triggered by DNA damage**
P53 activates/increases production of Bax and PUMA and other
factors when the cell has extreme DNA damage
Bax and PUMA (death promoting genes) interact with
mitochondria
Cytochrome C and other factors are released into the cytosol
Cytochrome C recruits Apaf1, procaspase 9 and ATP or dATP into
a complex (apoptosome)
Caspase 9 then stimulates caspase 3
Apoptosis activated
Learn in detail two examples of death receptor pathway of apoptosis (TNF and Fas
ligand)
– Death receptor pathway of apoptosis
Activation-induced cell death
Has cytotoxic t cells
Involves tumor necrosis factor receptor super-family and ligands.
Examples:
Fas ligand-fas receptor (CD95)
TNF-TNFRI
TRAIL
Pathway:
The apoptosis is induced by certain transmembrane or intracellular
stimuli
Positive induction involving ligands related to TNF binding to
their receptors
TNF with TNFR1
FasL with FAS/APO-1
Ligand interacts with receptors, the death receptors oligomerizes
and recruit adaptor proteins and initiator caspases to a complex,
death-inducing complex, which results in activation of initiator
caspases. The active initiator caspase will then cleave and activate
effector/exevutioner caspases
The ligand (either a free ligand or a cell surface-associated protein
from another cell) binds to the death receptor, which makes a
scaffold for autocatalytic activation of caspases 8 or 10.
Active caspases 8 or 10 cleave apoptotic execution caspases
directylu
However, the pathway also activates Bid, which acts on
mitochondrial membrane integrity
Apoptosis is induced
Cell death receptors binding of ligand to the Fas receptor induces
apoptosis by direct activation of caspase-8. Fas ligand consists of 3
polypeptide chains, so its binding induces receptor trimerization. Caspase8 bound to the receptor via adaptor molecules is then activated by
autocleavage, leading to activation of downstream caspases and cell death
Fas signaling *** (death receptor pathway)
Cytotoxic t cell binds to ligand, death receptor ligand
Killer lymphocyte interacts with infected cell via CD95/Fas
receptors
Receptors aggregate and recruit FADD
FADD recruits procaspase-8 to complex
Interaction inhibited by FLIP
FADD is the adaptor protein
Procaspase-8 activates each other by cleavage
Caspase -8 (initiator caspase) activates caspase-3 via
cleavage
In some cells, caspase 8 activates Bid, which interacts with
mitochondria which induces death
Result: Amplify apoptotoic signaling
TNF-alpha-TNFR1 induced signals*** (death receptor
pathway)
TNFR1 can either initiate apoptosis if associated with adaptor
proteins TRADD and FADD
Stimulate caspase-8 pathway
FLIP inhibits apoptosis by blocking the interaction
between FADD(it’s in both pathways) and capase-8
and also by activating survival signals
Result: amplify apoptotic signaling. Death.
-ORInitiate survival response if TRADD is associated with TRAF2
and RIP(no FADD)
**
not that the adaptor proteins are different!!!!!!
Stimulate NF-kappaB pathway
RIP interferes with TRADD interacting with FADD
Result: promotes cell survival
How these two differ: they differ at the adaptor protein!!
Learn in detail two examples of mitochondrial pathway of apoptosis
– Mitochondrial pathway of apoptosis (innate pathway)
Very important: BCL2 is associated with outer membrane of
mitochondria!
Key anti-apoptotic protein
It’s telling the cell to stay alive
Induced by intracellular damage, DNA damage or growth factor
withdrawal
Release of key mitochondrial proteins into the cytosol from
intermembrane space leads to activation of apoptosis
A number of stimuli, including chemotherapeutic agents, UV radiation,
stress molecules (reactive oxygen and reactive nitrogen species), and
growth factor withdrawal appear to mediate apoptosis via the
mitochondrial pathway, a death receptor-independent pathway
The outer mitochondrial membrane is the target of apoptotic factors
Normally cell survival is ensured by balanced expression of survival
(=antiapoptotic) and apoptotic factors on the mitochondrial membrane
Apoptotic threshold is established, when the level of expression of
apoptotic factors (Bak, Bax, Bad, Bcl-xs) exceed the level of expression of
survival factors (Bcl2, Bcl-xl, bclw, mcl1) leading to activation of
caspases
Note: that the survival or apoptotic factors indicated above are
members of the bcl2 proto-oncogene family
Once the apoptotic threshold is reached, the physiology of the
mitochondria changes which leads to the release of calcium and key
mitochondrial proteins found in the intermembrane space
Cytochrome C, Diablo/Smac, apoptosis inducing factor AIF, endo
g, Htra2/Omi
– DNA damage and deprivation of survival factor
Apoptosis induced by loss of growth factor/survival factor
Loss of cytokine binding to receptor initiates second messenger signaling
pathway which causes loss of AKT kinase activity
Growth factors/hormones are normal survival factors, assumed to
suppress preexisting death program
Bad and related pro-apoptotic factors are dephosphorylated
Bad is a death promoting protein,
Phosphorylated bad is usually sequestered in the cytosol bound
to 14-3-3 protein, and keeps it away from the mitochondria
This occurs when the cell is “wanted”
Bad translocates to mitochondria and interacts with bcl2 or bclx
Loss of normal mitochondrial physiology
Release of cytochrome c and other factors
Activation of caspase 9 pathway
The 3 ways that extracellular survival factors can inhibit apoptosis
– The middle one – what was just discussed above is a MUST KNOW
Know the roles of SMAC/Diablo, HtrA2/Omi, AIF and Endonuclease G (Other factors
released by mitochondria)
FOUND ON outer membrane of mitochondria
Calcium
Can lead to activation of caspases associated with ER
Usually kept very low in the cytosol
SMAC/Diablo (anti-IAPs)
Directly interacts with IAPs (XIAP, cIAP1 and cIAP2) and block their
activity
Lead to apoptosis occurring (inhibiting an inhibitor of apoptosis)
HtrA2/Omi (anti-IAPs)
Blocks IAPs
Can cleave IAPs
Promotes caspase-independent apoptosis via its serine protease activity
Apoptosis inducing factors AIF
Transported to nucleus where it stimulates large DNA fragmentation and
condensation of chromatin
Also involved in electron transport (FAD binding and oxidoreductase
activity)
Endonuclease G
Considered to directly mediate nuclear DNA fragmentation
Cytochrome c
Learn about cytolytic granule mediated apoptosis
Can circumvent the requirement of FAS or TNF receptors
Granzymes (A,B,H,K, and M) and porins released by cytotoxic T cells or natural
killer cells activate effector caspases inside the cell
These enzymes also target other proteins
Mcl1 and Bid
Leads to activation of mitochondrial apoptotic pathway
Lamins
Histones
Apoptosis and cancer
Nearly all have a defect in cell cycle regulation
Follicular B-cell lymphoma: chromosomal translocation leads to up-regulation of
Bcl-2
Presentation 2- cancer
Learn about the role of cell proliferation & differentiation in the genesis of tumors
Cell division and differentiation
Tumors are produced by uncontrolled cell proliferation in which the
balance between cell division and differentiation is disrupted. This is
usually coupled with loss of regulated cell death (apoptosis)
Cell differentiation is the process by which cells acquire specialized
properties that distinguish different cell types from each other
As cells acquire traits, they often lose the capacity to divide
Normal differentiation process in balanced with cell proliferation so that
no net accumulation of dividing cells occur
In tumors, this finely balanced arrangement is disrupted and cell division
is uncoupled from cell differentiation
Consequence: increase in number of proliferating cells which lead
to disruption of normal tissue structure and function
Cells may require two types of signals to proliferate
One signal drives cell cycle progression (mitogens)
The other signal promotes cell growth
Ex: pi-3 kinase pathway
Learn the three main forms of cancer (carcinomas, sarcomas, leukemia)
Sarcomas
Tumors originating in mesenchymal tissue, such as bone, muscle or CT
Rare types
Carcinomas
Originate in epithelial tissues, such as the cells lining the intestines,
bronchi, or mammary ducts
Account for 90% of all cancers
Leukemia and lymphomas
Lekeumia: cancer cells reside and proliferate mainly in the bloodstream
rather than growing as a solid mass
Often see translocation
Within each of the major groups, tumors are classified by site, tissue type,
histological appearance, and degree of malignancy
Learn the differences between benign and malignant tumors
Tumors
A disease process characterized by uncontrolled cellular proliferation
leading to a mass or tumor (neoplasm)
Malignant tumors
For a neoplasm to be cancer, it must be malignant which means its
growth is no longer controlled and the tumor is capable of invading
neighboring tissues or spreading (metastasizing)
Cancer is a general term for malignant tumor
Benign tumors
Tumors that do not metastasize
Instead they tend to grow in a confined local area
Learn the importance of PI3-K/PTEN in growth signaling
PTEN tumor suppressor important in controlling AKT growth signaling pathway
The role of PTEN is to dephosphosphorylate PIP3, acting as a
negative control on PKB/Akt activation
Under normal growth conditions, stimulatory signals from the insulin
receptor activate the enzyme phosphoinositide kinase (PI3-kinase) which
phosphorylates PIP2 to generate PIP3, a lipid signaling molecule
If a mutation in PTEN renders it unable to carry out its phosphatase
function, PIP3 can no longer be deactivated, so continues to propagate its
signal downstream
Learn that cancer cells are anchorage-independent and Insensitive to population density
Most normal cells need a surface in order to proliferate and survive. Tumor cells
do not.
Normal cells undergo apoptosis if not attached
Safeguard that prevents normal cells from floating away and
colonizing other tissues
Cancer cells therefore exhibit anchorage-independent growth
(hallmarks of cancer)
Ex: E-cadherin (normally abnormally expressed in cancers) and
Beta-catenin (linker protein)
Cancer cells also exhibit a reduced sensitivity to density-dependent inhibition of
growth
Normal cells in tissue culture will usual grow until a single layer of cells is
formed, then cell division stops
Cancer cells grow unrestrained on top of each other
Learn how cancer cells become immortalized by reactivating telomerase
Normal cells divide about 50-60 times when placed in culture
Stop dividing and undergo degenerative changes
Cellular senescence may be due to loss of telomerase activity
Cancer cells seem to proliferate indefinitely
Cancer cells have telomerase activity reactivated and can maintain their
telomeres. By maintaining telomere length above a critical threshold, cancer cells
retain the ability to proliferate indefinitely
Telomerase expression reappears in transformed cells and in many tumors
An alternative mechanism for maintaining telomere length employs enzymes that
exchange DNA information between chromosomes
Learn about the importance of angiogenesis during oncogenesis
– The roles of VEGF and matrix metalloproteinases in the process
– The hazards posed by cancer cells come from uncontrolled proliferation combined
with the ability to spread throughout the body
– Angiogenesis (growth of blood vessels) is required for tumors to grow beyond a
few millimeters in diameter
– Blood vessel growth is controlled by a balance between angiogenesis activators
and inhibitors
Activators: VEGF, FGF
These cause endothelial cells to proliferate and produce matrix
metalloproteinases which breakdown extracellular matrix allowing
endothelial cells to migrate
MMPs are upregulated!
Inhibitors: angiostatin, endostatin and thrombospondin
Tumors increase production of activators and decrease inhibitors
Avastin works by targeting VEGF and angiogenesis.
– Tumors
Increase production of activators
Decrease production of inhibitors
Learn about invasion and metastasis
– Spreading of cancer by invasion and metastasis is a complex multistep process
– Invasion
Refers to the direct migration and penetration of cancer cells into
neighboring tissues
Take over fibroblasts and blood vessels
Changes in cell adhesion, motility, and protease production allow cancer
cells to invade surrounding tissues and vessels
Mechanisms that allow for invasion
Alteration in cell surface proteins that cause cells to adhere
E-cadherin levels lower in epithelial cancers
Increased motility of cancer cells
Production of proteases which compromise barriers of cell
movement and degrade extracellular matrix (ECM)
Breaching the basal lamina in epithelial cancers
Ex: plasminogen activator which converts plasminogen into
plasmin
Plasmin degrades ECM and basal lamina proteins
Activates matrix metalloptoteinases
Facilitate cell migration into blood vessel
– Metastasis
Able to set up colonies elsewhere in the body – very rare, which is good!
Involves the ability of cancer cells to enter body fluids (blood) and travel
to distant sites, where they form tumors
Relatively few cancer cells survive the voyage through the bloodstream
and establish metastases
Either directly or indirectly through the lymph system, cancer cells
arrive in the blood stream
Most do not survive
Those that do, usually have additional changes which make them
well suited for metastasizing
Blood flow patterns and organ specific factors determine where cancer
cells metastasize
Often metastasize the first capillary bed encountered
Usually the lungs or liver
Seed and soil hypothesis: some sites provide optimal growth
conditions for a particular cancer cells, other sites do not
Prostate cancer commonly metastasizes to bone
Bone cells produce specific growth factors that
stimulate prostate cells
– Learn about the importance of matrix metalloproteinases in the process
– Learn why metastasis occur more frequently with certain organs
Learn about causes of cancer and tumor progression
Cancers are caused mainly by environmental agents and lifestyle factors, most of
which act by triggering DNA mutations
Carcinogens
Carcinogens are cancer causing agents
Ex: tobacco and nasal cancer, scrotum cancer in chimney sweepers
Many chemicals can cause cancer, often after metabolic activation in the
liver
Cytochrome p450 enzyme (Reside in SMOOTH ER) family
responsible (highly polymorphic)
2 napithylamine and bladder cancer
Requires conversion in active form in liver
Aryl hydrocarbon hydroxylase AHH converts hydrocarbons into
epoxide form that can be carcinogenic
High inducibility vs low inducibility of CYPA1A1 )AHH
gene) in response to smoking. Low inducibilty – less likely
to develop cancer, high inducibility more likely to develop
cancer
The dose and the length of time exposed, increases risk
Usually work by altering the DNA
DNA mutations triggered by chemical carcinogens lead to cancer – how
do scientists figure out if something is a carcinogen?
Ames test
Detect mutations that cause bacteria to regain the ability to
produce histadine and grow
Strain of bacteria that can’t grow in absence of
histadine!
Must pre-incubate the test subject with liver extract
(Since it contains cytochrome p450)
Cigarette smoking & lung cancer
Radiation
Ionization radiation increases the risk of cancer
Risk is age dependent (greatest for those under 10 and elderly)
Significant risk for individuals with inborn defects of DNA repair
Ionizing and ultraviolet radiation also cause DNA mutations that
lead to cancer
UV causes thymine dimers
Hepatocellular carcinoma & Aflatoxin B1
Hepatocellular carcinoma (liver cancer)
The 5th most common cancer world wide
In many parts of the world, hepatocellular carcinoma
occurs at increased frequency because of ingestion of
aflatoxin B1, a potent carcinogen produced by mold
found on peanuts
Aflatoxin has been shown to modify a particular
base in the TP53, causing a G to T transversion in
codon 249, converting an arginine codon to serine
in the critically important p53 protein
This mutation is found in nearly half of all
hepatocellular carcinomas in patients in parts of the
world in which there is a high frequency of
contamination of food by aflatoxin, but it isn’t
found in similar cancers in patients whose exposure
to aflatoxin is low
The Arg249Ser mutation in p53 enhances
hepatocyte growth and interferes with the growth
control and apoptosis associated with wild-type p53
LOH of TP53 in hepatocellular carcinoma is associated
with a more malignant appearance of the cancer
Although aflatoxin B1 alone is capable of causing
hepatocellular carcinoma, it also acts synergistically with
chronic hepatitis B and C infections
Pathogens
Viruses and other infectious agents are responsible for some
cancers
Oncogenic viruses
2 ways pathogens trigger cancer
Virus stimulates proliferation by either introducing
a viral gene or modifying host gene expression
EBV, retroviruses, papillomavirus
Those that cause tissue destruction and chronic
inflammation. Immune response leads to the
generation of free radicals and DNA damage
H pylori, parasitic flatworm, hepatis B and
C viruses
HPV E6 & E7
Initiators vs promoters
Cancer arises through a multi-step process involving initiation,
promotion and tumor progression
Successive rounds of random inherited change followed by
natural selection
During initiation, normal cells are converted to a precancerous
state.
Usually is a change in the DNA mutationj
Promotion then stimulates the altered cells to proliferate and form
tumors
Then a change in behavior
Chemicals that act as initiators often cause DNA damage
Chemicals that act as promoters stimulate cell proliferation
Natural selection will then favor cells with the fastest
growth rates
Tumor progression
Initiation and promotion are followed by a 3rd stage, tumor
progression
Cancers evolve – one thing goes wrong, then another thing goes
wrong, etc. Most cancers have the same origin
During tumor progression, tumor cell properties gradually change
as cells acquire more aberrant traits and become increasingly
aggressive
Any new trait which encourages growth, survival and
invasiveness, usually results in those cells dominating
New aberrant traits can result from epigenetic changes during
tumor progression
Human cancer cells are genetically unstable and frequently
changing
Ames test
Learn that most cancers are clonal, somatic and sporadic in origin
All cancers are genetic diseases
The vast majority are sporadic and somatic in origin
In most cancers, the mutations occur in a single somatic cell that then
divides and proceeds to develop into cancer
However, a single mutation is not enough to cause cancer
Cancer evolves by accumulating additional genetic damage
Only a small % of cancers occur as part of a hereditary cancer mutation
inherited through the germ line
Mutations in genes controlling proliferation and death are responsible for cancer
Two distinct categories of genes involved in cancer
Oncogenes (gain of function)
Tumor-suppressor genes (loss of function)
Learn about cancer stem cells
Cancer stem cells are defined as those cancer cells that can self-renew to produce
additional malignant stem cells, and at the same time generate non-tumorigenic
cells such as transit amplifying cells
Cancer stem cells can arise from normal stem cells that have sustained
mutations to make them cancerous
Cancer stem cells may arise from more differentiated cells that have
undergone mutations or epigenetic changes that give them stem cell
properties
A small population of cancer stem cells maintain many tumors
Cancer stem cells are often difficult to eradicate by conventional
treatments because they replicate more slowly
To cure cancer we need to find better ways to target and kill cancer stem
cells
Learn about the roles of oncogenes and tumor suppressors during tumorgenesis
Oncogenes – are genes whose presence can trigger the development of cancer
Often encode for proteins that stimulate excessive cell proliferation and or
promote cell survival
Nonviral oncogenesis determined by the oncogene transfection assay
Oncogene transfection assay is used to analyze the ability of DNA
to transform a cell
Most common oncogene mutated: Ras
Most oncogenes code for components of growth factor signaling pathways
Tumor suppressors are genes whose loss of inactivation can lead to cancer
Most common tumor suppressor mutated: p53
People who inherit one bad allele of a tumor suppressor gene are at
significantly increased risk of developing cancer
Require both alleles of the tumor suppressor gene to become
inactivated
MUST LOSE BOTH ALLELES – 2 HIT HYPOTHESIS
Learn the five mechanism of converting a proto-oncogene into an oncogene
Protooncogenes are normal cellular genes that can become mutated into
oncogenes
5 mechanism of converting a proto-oncogene into an oncogene
1. Point mutation
Ex: Ras point mutations keep it in the active form
2. Gene amplification: extra copies of genes leads to excess of protein
product
3. Chromosomal translocation
Ex: Burkitt’s lymphomas, CML, follicular B-cell lymphoma
4. Local DNA rearrangements
Insertional mutations: retrovirus integrates in the wrong location
Must know translocations cancers CML, Burkitt lymphoma & Follicular B-cell
lymphoma
Chronic myelogenous leukemia CML:
T(9;22) (q34;q11)
Philadelphia chromosome(9;22) Ph1: a translocation between
chromosomes 9 and 22
Creates a fusion BCR-ABL gene at 9q and 22q
Abnormal tyrosine kinase activity
So treat it with a tyrosine-kinase inhibitor - Gleevac
A cancer of blood cells characterized by replacement of bone marrow with
malignant, leukemic cells. Many of these leukemic cells can be found
circulating in the blood and can cause enlargement of the spleen, liver, and
other organs.
Burkitt Lymphoma
T(8;14)!!!!!!!!!!!!!!!(q24;q32)
Immunoglobulin put in front of the MYC gene on chromosome 8
Common tumor of children in equatorial Africa
Seems to be associated with Epstein Barr Virus
Translocation puts the MYC gene under the influence of an enhancer from
the immunoglobulin genes
Lesser likely causes: 2 with 8 lighter chains
Follicular B-cell lymphoma
T(14;18)(q32;q21)
BCL2, an antiapoptotic gene is upregulated by a translocation which
brings an immunoglobulin promoter and enhancer in proximity to the
BCL2 gene
Differences between gatekeeper and caretaker tumor suppressors
Gatekeeper
Some truly suppress tumors by regulating the cell cycle or causing growth
inhibition by cell-cell contact; tumor suppressors genes of this type are
gatekeepers because they regulate cell growth directly
Rb and P53 (master regulators)
Caretakers
involved in repairing DNA damage and maintaining genomic stability
Loss of both alleles of genes that are involved in repairing DNA damage
or chromosome breakage leads to cancer indirectly by allowing
additional secondary mutations to accumulate either in
protooncogenes or in other tumor suppressors genes.
Learn the two-hit origin of cancer for tumor suppressors
– Both alleles of the gene need to be mutated
1st hit can be inherited
2nd hit can arise spontaneously (but once first is gone, likelihood of
second being contaminated is extremely high)
Epigenetic origin: gene silencing such as x inactivation and
imprinting
– Learn the mechanisms leading to loss of heterozygosity
Individuals who have heterozygous alleles in normal tissue but have
tumors that contained allels from only one of their two chromosomes
LOH is the common mutational mechanism by which the remaining
normal RB1 allele is lost in heterozygotes (chromosome 13 region)
LOH is a feature of a number of other tumors, both sporadic and heritable,
and is often considered evidence for the existence of a tumor-suppressor
gene
Occurs by
Nondisjunction
Mitotic recombination
Deletion/point mutations
Learn the role of epigenetics in oncogenesis
Epigenetic changes that accumulate in cancer cells involve inherited chromatin
structures and DNA methylation
Epigenetic changes are important during the process of oncogenesis
A mechanism by which developing tumor cells can inactivate tumor suppressor
genes
Methylation
Chromatin packaging
MUST know Retinoblastoma and Rb
Disease caused by a mutation in a tumor suppressor gene (Rb)
Diagnosis of a retinoblastoma must usually be followed by removal of the
affected eye
The disorder is inherited as a dominant trait, because the large number of
primordial retinoblasts and their rapid rate of proliferation make it very likely that
a somatic mutation will occur
Penetrance is not complete. Second hit is a matter of change
60% are nonheritable (sporadic)
Sporadic cases average age of onset is later than in infants with heritable
form and usually develops tumor in one eye
Infant with heritable retinoblastoma 400xs more likely to developing
mesenchymal tumors. The risk is much higher if child received radiotherapy
Get tumors in their eyeball
Need to be very concerned with exposing someone to x-rays
Because it causes DNA damage
The sporadic version usually occurs later in life
The Rb gene
Involved in causing hereditary retinoblastoma
Found mutated in several common adult nonhereditary cancers
Lung, breast, and bladder cancer
Regulates G1 to S phase transition
Retinoblast protein
A 110 kilodalton phosphoprotein found in many tissues
The RB1 gene is a prototypical gatekeeper tumor suppressor gene
Loss of Rb allows the cell to proliferate uncontrollably
Rb regulates G1 to S transition
It blocks cell cycle progression (G1/S phase) when it is in the
hypophosphorylated state. It interacts and modifies the behavior of
nuclear proteins (E2F)
Dephosphorylated Rb interacts with transcription factor
E2F. This prevent E2F from stimulating transcription
When it is hyperphosphorylated it allows the cell to enter S phase
G1 cdk-cyclin phosphorylates Rb causing it to be released
from E2f and allowing e2f to stimulate transcription
Must know Li Fraumeni and p53 (transcription factor)
P53 is guardian of the genome
A transcription factor, tumor suppressor, which influences:
Cell cycle arrest – p21
Lead to apoptosis – bAX an d puma
The most frequently mutated gene associated with cancer
Levels usually kept really low in nucleus, with DNA damage, levels
increase
P21 increases
A DNA-binding protein froms a tetramer
Important in the cellular response to DNA damage
Activates genes that stop cell division and allow DNA repair
P53 also is involved with inducing apoptosis in cells that have
irreparable DNA damage
Loss of p53 function, allows cells with damaged DNA to survive and
divide, thereby propagating potentially oncogenic mutations
Li-fraumeni syndrome results from p53 mutation
P53 is the most common sporadic gene associated with cancer
(over half)
Early onset of cancers
Every generation, someone is getting affected, runs autosomal
dominant in the family
Inactivation of the Rb and p53 proteins is involved in the action of certain
cancer viruses
Human papillomavirus contains an oncogene called E7 which binds to
and inactivates Rb, and another oncogene E6 which inactivates p53!!!
Learn about BRCA1 & 2 in inherited breast cancer
DNA repair pathway involved with: repairing double stranded DNA breaks via
homologous recombination
Strong genetic component
Increased risk if first degree relative afflicted. More so if onset occurred prior to
the age of 40
Frequent bilateral disease
Less than 5% of all breast cancer
BRCA1 gene: chromosome 17q21 (50% of autosomal dominant familial
breast cancer)
BRCA2 gene: chromosome 13q12.3 (33% of autosomal dominant familial
breast cancer)
Increased chance of male breast cancer (10-20% of all)
Men who inherit BRCA also need to worry about breast cancer
MUST KNOW Familial polyposis coli
–
–
Colorectoal cancer: 150,000 people/year, 15% of all cancer
More than one tumor –
Symptoms:
Little polyps on colon
– Autosomal dominant
– Small protion due to autosomal dominant familial polyposis coli (familial
adenomatous polyposis) FAP
Gardner variant is a subvariant (develop osteomas of the jaw and
desmoids (tumors in the muscles of the abdominal wall)
– FAP heterozygotes can have numerous benign growths by the age of 20
Usually one or more polyps become malignant
Colectomy (removal of colon) prevents development of malignancies
– What is wrong here? Mutation in APC
– The role of APC and b-catenin
Adenomatous polyposis coli = APC
In wnt pathway, it’s job is to destruct b-catenin to keep levels
low
Linker protein with e-cadherin
APC gene loci is responsible located on chromosome 5q
APC encodes a cytoplasmic protein that regulates B-catenin (key target
of APC)
Two roles of regulates b-catenin
Link the cytoplasmic portion of transmembrane cell adhesion
molecules and actin cytoskeleton
Activate transcription
Wnt pathway
Loss of APC leads to accumulation of free regulates b-catenin that is
translocated to the nucleus and activates transcription
Tumor suppressor APC gene mutations are common in nonhereditary
forms of colon cancer
Learn HNPCC and mismatch repair
MICROSATELLITE INSTABILITY
2-4% of colon cancers due to HNPCC (less than 5%)
An autosomal dominant disease onset during early adulthood without the
adenomatous polyps of FAP
Heterozygous males have 90% lifetime risk of developing cancer
Female heterozygotes have 70% chance, 40% risk of endometrial cancer and 1020% risk for cancer of bilary or urinary tract, and the ovary
DNA isolated from tumors display microsatellite instability
Symptoms
Abdominal pain
Anemic
Blood in stool
Diarrhea, trouble going to the bathroom
HNPCC is caused by mutations in DNA repair genes
HNPCC is a group of 5 similar syndromes caused by mutations in 1 of 5
distinct DNA repair genes
Inherited defects in genes required for mismatch repair are responsible
for HNPCC
The genes: MLH1, MSH2, PMSL1, PMSL2, and MSH6
MLH1 and MSH2 together account for 60-70% of HNPCC
The HNPCC genes are prototypical caretaker tumor-suppressor genes
Multi hit model of colon cancer induction
Usually more than one pathway is disrupted
Colon cancer evolves through distinct, well-characterized morphological
stages
Intermediate stages: polyps, benign adenomas, and carcinomas can be
isolated
Mutations in each of the morphological stages can be identified
Resulting in a series of mutations that commonly arise in a well-defined
order, hence multi-hit model
Learn about microRNAs (miRNAs) and cancer
The catalogue of genes involved in cancer also includes genes that are transcribed
into noncoding RNAs from which regulatory microRNAs (miRNAs) are
generated
There are at least 250 miRNAs in the human genome that carry out RNAmediated inhibition of the expression of their target protein-coding genes,
either by inducing the degradation of their targets’ mRNA or by blocking
their translation
Approx. 10% of mRNAs have been found to be either greatly overexpressed
of down-regulated in various tumors, sometimes strikingly so, and are
referred to as ONCOMIRS
One example is the 100-fold overexpression of the miRNA miR-21 in
glioblastoma multiforme, a highly malignant form of brain cancer
Oncomir = oncogenic micro RNA
Overexpression of some miRNAs can suppress the expression of tumorsuppressor gene targets
Whereas loss of function of other miRNAs may allow overexpression of the
oncogenes they regulate
Since each miRNA may regulate as many as 200 different gene targets,
overexpression or loss of function of miRNAs may have widespread ocogenic
effects because many genes will be dysregulated
RB and Oncomir miR-106a
The retinoblastoma gene RB1 is frequently mutated in many cancers,
including breast cancer
Ex. 13q14 LOH observed in human breast cancers is associated
with loss of RB1 mRNA in the tumor tissues
In still other cancers, the RB1gene is intact and its mRNA appears to be at
or near normal levels, and yet the p110 Rb1 protein is deficient
This anomaly has now been explained by the recognition that
RB1 can be down-regulated in association with overexpression of
the oncomir mi-RNA 106a, which targets RB1 mRNA and blocks
its translation
Thus, miR-106a might be considered an oncogene that
exerts its effect by reducing the expression of the TSG
encoding the p11- Rb1 protein
One group blocks tumor suppressors
Too much of them
Other group target protooncogenes
Learn about genetic instability and gene amplification
Genetic instability
Trait of cancer cells in which abnormally high mutation rates are caused
by defects in DNA repair and/or chromosomes sorting mechanisms
Inherited defects in genes required for mismatch repair are responsible for
HNPCC
Xeroderma pigmentosum caused by inherited defects in UV damage
excision repair pathway
Hereditary breast cancers involves mutated forms of BRCA1 or
BRCA2, which are involved in repairing double-strand breaks within
DNA
Genetic instability can cause defects in mitosis and aneuploidy
Some cancer cells have an extra chromosome
Tumors generally have chromosome and genome mutations that reflect
defects either in double-stranded break repair (generate chromosomal
translocations) or maintenance of the fidelity of how chromosomes align
on the mitotic spindle during mitosis (lead to nondisjunction and
aneuploidy)
Gene amplification
What are usually amplified?
Protooncogenes and tumor suppressors
Many additional copies of a segment of genome present in cell
Common in many cancers – more amplification that you see, the worse the
prognosis
Amplified segments detect by CGH typically as 2 types of cytogenetic
changes
Double minutes; very small accessory chromosomes
Homologous staining regions (HSR) that do not band normally and
contain multiple, amplified copies of a particular DNA segment
Amplified regions are known to contain extra copies of proto-oncogenes
(myc, Ras, EGFR)
Ex. Amplification of mycn proto-oncogene for n-myc is a clinical
indicator for prognosis in the childhood cancer, neuroblatoma
Myc-n is amplified more than 200xs in 40% of advanced stages of
neuroblastoma
Learn about the hallmarks of cancer
1. Self sufficiency in growth signals
Do not need to be stimulated to grow
Ras mutation
2. Insensitivity to antigrowth signals
Mutations involving RB or TGFbeta/smad pathway
3. Evasion of apoptosis
Mutations in p53 or bcl2 which promote cell survival
4. Limitless replicative potential
Mutation allows cell to maintain telomere length
5. Sustained angiogenesis
Blood supply and nutrients re vital for tumor growth
6. Tissue invasion and metastasis
Decrease in cell adhesion (E-cadherin mutation) and/or increase in
protease production
7. Cancers induce help from normal stromal cells in their local environment
8. They are defective in the intercellular control mechanisms that normally
stop cell divisions permanently in response to stress (such as hypoxia) or
DNA damage
An enabling trait: genetic instability
Allows for generation of genetic mutations to occur
Introduction about diagnosis, screening and treatment of cancer
– Know Herceptin & breast/ovarian cancer, Gleevec & CML, and Avastin
– Diagnosis
Cancer is diagnosed by microscopic examination of tissue specimens
Biopsy of tumor for microscopic analysis
Is a sufficient numver of these traits are observed, it can be
concluded that cancer is present, even if invasion and metastasis
have not yet occurred
Tumor grading: numerical grade based on microscopic appearance
Lower numerical grades are assigned to tumors who cells exhibit
normal differentiated features and display modest abnormalities
The highest grade are anaplastic: poorly differentiated, abnormal in
appearance. They bear no resemblance to the cells of the tissue
they arose from
– Screening techniques for cancer
Higher cure rates when cancer is treated before it spreads
Important to screen and detect cancers as early as possible
Pap smear: technique for early detection of cervical cancer. Analyze
sample of vaginal secretions for abnormal cells
Large irregular nuclei or prominent variations in cell size or shape
Can detect before metastasis
Prevent many cancer deaths
Mammography for detecting breast cancer
Colonoscopy for detecting colon cancer
PSA test: measure prostate-specific antigen in the blood
High PSA indicates prostate problem
Proteomic analysis of protein in the blood
Utilize mass spectrometry
–
Used for detecting ovarian cancer
Screens for 5 protein markers of ovarian cancer
Treatments for cancer
Surgery radiation, and chemotherapy
Radiation therapy employs x-rays or other types of radiation to kill cancer
cells by 2 mechanisms
Radiation activates p53 pathway leading to apoptosis
Severly destroys DNA and prevent progression through mitosis
Chemotherapy to kill dividing cells, four categories
Antimetabolites
Inhibit DNA synthesis
Methotrexate, fluorouracil, and mercaptourine
Alkylating agents
Inhibit DNA function by crosslink DNA double helix
Cyclophosphamide, cholrambucil, and cysplatin
Antibiotics
Inhibit DNA function by binding DNA or topoisomerases
Bleomycin, docorubicin
Plant-derived drugs
Either inhibit topoisomerase or disrupt microtubules
Ectoposide and taxol-binds and stabilizes
(vinlblastin, vinchristin)
Block action of hormone require growth: tamoxifen for breast cancer
Magic bullet strategy: selectively destroy the cancer cells and not the
normal cells
Immunotherapies explot the ability of the immune system to recognize
cancer cells
Tumors occasionally regress in people who develop bacterial
infections because infections trigger immune response
Bacilis calmette-guerin bacteria is inserted into the bladdter after
primary tumor is removed
Drugs: interferon alpha and interleukin 2
Herceptin and gleevec are cancer drugs that act through molecular
targeting
Gleevec (imatinib) is a small molecule that binds to and inhibits
the tyrosine kinase activity or BCR-ABL in chronic
myelogenous leukemia CML (Philadelphia chromosome)
How gleevac blocks the activity of bcr-abl protein and halts
CML -Sits in the ATP-binding pocket of the tyrosine
residue in a substrate protein
This blocks onward transmission of a signal for cell
proliferation and survival
Herceptin is an antibody which recognizes the ERBB2 growth
factor receptor
Breast and ovarian cancers
–
Anti angiogenic therapies act by attacking a tumor’s blood supply. Block
blood vessel formation in tumors.
Avastin – is a monoclonal antibody that binds to and inactivates
VEGF
Best way to treat cancer and aids
Multiprong attack
Personalized medicine