43. Neoplasia: The Molecular & Cellular Basis of Tumour Growth Flashcards
With regards to cell growth, what is contact inhibition?
- Regulatory mechanism that functions to keep cells growing into a layer one cell thick
- monolayer
- If a cell has plenty of available substrate space, it replicates rapidly and moves freely
- This process continues until the cells occupy the entire substratum.
What happens during the three stages of interphase?
-
G1
- cell is metabolically active and continuously grows
-
S
- DNA replication, protein synthesis and replication of organelles
-
G2
- during which cell growth continues and the cell synthesizes various proteins in preparation for division
-
M
- During which the duplicated chromosomes (known as the sister chromatids) separate into two daughter nuclei, and the cell divides into two daughter cells, each with a full copy of DNA
What are centrosomes and what do they consist of?
Centrosomes are organelles near the nucleus of a cell, which contain centrioles (mother and daughter), and from which spindle fibres develop in cell division
What happens to the centrosomes during G1 and S?
- The mother and daughter centrioles separate in G1
- Then the mother produces another daughter and the daughter produces another mother, resulting in the formation of 2 centrosomes (the duplication takes place during S phase)
What are the points around the centrosome from which microtubules arise?
Nucleating sites
NOTE: nucleation is the assembly of microtubules
Describe the condensation of chromatin that takes place duringprophase.
- The double helices wrap around histones to form beads-on-a-string
- This is then further compacted to form 30 nm fibres It is then compacted to form a chromosome scaffold and then further wrapped until you get a chromosome (1400 nm)
What is a kinetochore?
Protein complexes that are attached to each sister chromatid – they are important in detecting the attachment of microtubules
Describe the arrangement of centrosomes at the end of prophase.
They are on opposite sides of the nucleus
What is formed when microtubule arrays from the two centrosomes meet in the middle?
Polar microtubules
What happens to the sister chromatids as soon as they are captured by microtubule arrays from both centrosomes?
They slide towards the middle of the cell
What are the three main types of half-spindle?
- Kinetochore microtubule – attached to kinetochores Polar microtubule – attached to a microtubule array from the other centrosome Astral microtubule – microtubule originating from a centrosome that does not connect to a kinetochore
What keeps the sister chromatids stuck together?
Cohesin (protein complex)
What happens in anaphase A?
Cohesin is broken down and the microtubules get shorter so the chromatids start moving towards their respective poles
What happens in anaphase B?
Daughter chromatids continue to migrate towards the poles The centrosomes migrate apart
Describe what happens in telophase.
Daughter chromatids arrive at the pole and the nuclear envelope reassembles Assembly of a contractile ring of actin and myosin filaments where the cells are going to split The contractile ring squeezes the cell so it divides into two daughter cells NOTE: cleavage furrow = where the cell is going to be cleaved
What is the midbody?
The point where the actin-myosin contractile ring is formed
Describe how the spindle assembly checkpoint works.
The kinetochore has proteins that emit a signal when the kinetochore is NOT attached to microtubules When a microtubule attaches to the kinetochore, it stops emitting the signal At the end of metaphase, you want all the kinetochores to stop sending signals before you can proceed to anaphase
Name two proteins that allow the kinetochores to detect spindle attachment.
CENP-E BUB-protein kinase (this dissociates from the kinetochores when the chromatids are properly attached to the spindle – then they go on to signal progression to anaphase)
What can cause aneuploidy?
Mitotic checkpoint defect Mis-attachment of the spindles (so chromatids end up at different poles to the ones that they should be at) Aberrant mitosis (production of an abnormal number of centrosomes leads to abnormal division of the chromatids, and abnormal cytokinesis)
Name four different types of spindle attachment.
Amphitelic – normal spindle attachment Syntelic – both kinetochores of the sister chromatids are attached to spindles from one centrosome Merotelic – one kinetochore of one of the sister chromatids is attached to spindles from both centrosomes Monotelic – one kinetochore of one of the sister chromatids is attached to a spindle, the other is unattached
Broadly speaking, explain how cell cycle checkpoints can be a target for anti-cancer therapy.
By targeting the cell cycle checkpoints, the cancer cells can be arrested in mitosis Cells are very vulnerable when they are in mitosis and are more easily killed
Give an example of anti-cancer drugs that target cell cycle checkpoints.
Taxanes and Vinca alkaloids These alter microtubule dynamics and produce unattached kinetochores, which leads to long-term microtubule arrest
What can happen to cells that are held up at a checkpoint?
They can undergo DNA repair and then proceed through the cell cycle If the damage is irreparable, they can undergo apoptosis
Where are the main checkpoints within the cell cycle?
During G1 Just before mitosis to check for DNA damage Metaphase-anaphase checkpoint (spindle assembly checkpoint)
State some different types of DNA damage caused by carcinogens.
Base dimers and chemical cross-links Base hydroxylations Abasic sites Single strand breaks Double strand breaks DNA adducts
What are abasic sites?
During the repair process, the entire DNA base has been removed so the sugar backbone is maintained but we have removed the base from the mutagenic molecule During replication, this missing base can cause problems
What are the implications of single strand breaks?
These are common and useful Topoisomerase causes single strand breaks and it is involved in relaxing and unwinding the DNA before replication
What are the implications of double strand breaks?
These are NOT GOOD The two strands have a tendency to drift apart when a double strand break occurs There are repair mechanisms for dealing with this, but sometimes the DNA repair can go wrong and introduce DNA damage
What is the usual type of damage that is caused by chemicals?
DNA adducts
Why is DNA the target for many carcinogens?
Chemical carcinogens are usually metabolically activated and converted into electrophiles (they want electrons) DNA is very electron rich
What are the consequences of bulky DNA adducts?
The electrophiles bind and form a covalent bond The binding of these adducts causes problems, particularly during replication because it interferes with the ability of DNA polymerase to recognise the base (because of the bulky adduct)
What are the six types of Phase II reaction?
Glucuronidation Acetylation Sulphation Methylation Amino acid conjugation Glutathione conjugation
What are polycyclic aromatic hydrocarbons?
They are environmental pollutants formed from the combustion of fossil fuels and tobacco
Describe the two-step oxidation of benzo[a]pyrene.
B[a]P is a substrate for CYP450, which converts it to B[a]P-7,8-oxide (this is an electrophile) The body has a defence mechanism – epoxide hydrolase converts the oxide to a dihydrodiol (B[a]P-7,8-dihydrodiol) This is inactive However, this dihydrodiol is also a substrate for CYP450, which converts it to another oxide (B[a]P-7,8-dihydrodiol-9,10-oxide) This even more reactive than the previous oxide – it goes on to form DNA adducts
State two past components of dyestuff that are potent bladder carcinogens.
Benzidine and 2-naphthylamine
Explain the mechanism by which 2-naphthylamine is a bladder carcinogen.
2-naphthylamine is converted by CYP450 to a hydroxylamine derivative, which is reactive In the liver, this is glucuronidated (thus inactivating it) The inactive metabolite is excreted by the liver and then it goes to the bladder where it mixes with the urine The ACIDITY of the urine causes hydrolysis of the glucuronides – this releases the hydroxylamine derivative, which forms a nitrenium ion This is electrophilic so it leads to the formation of DNA adducts
What does UV radiation lead to the formation of?
Pyrimidine (thymine) dimers – adjacent pyrimidines can covalently link
What does ionising radiation generate?
Free radicals
Name 2 oxygen free radicals.
Superoxide radical (O2.) Hydroxyl radical (HO.)
What are the consequences of oxygen free radical attack on DNA?
Single and Double strand breaks Apurinic and apyrimidic sites Base modifications: Ring-opened guanine and adenine Thymine and cytosine glycols 8-hydroxyadenine and 8-hydroxyguanine
What are the p53 mediated responses to mild and severe physiological stress?
Mild – repair the damage and restore the normal function of the cell Severe – apoptosis
What are the main types of DNA repair?
Direct reversal of DNA damage Base excision repair Nucleotide excision repair During- and post-replication repair
Give two examples of direct reversal of DNA damage.
Photolyase looks for cyclobutane-pyrimidine dimers and cuts them Methyltransferases and alkyltransferases remove alkyl groups from the bases
What comes under during and post replication repair?
Mismatch repair Recombinational repair
Which base is most electron-rich and hence most capable of attracting electrophiles?
Guanine
Describe the process of base excision repair.
DNA glycosylase hydrolyses between the base and the sugar Then AP endonuclease splits the DNA strand so there is a gap in the backbone DNA polymerase then fills in the missing base (using the complementary strand as template) DNA ligase then seals the DNA
Describe the process of nucleotide excision repair.
Endonuclease makes two cuts in the DNA on either side of the site of damage (this demarcates a patch of DNA) Helicase then removes this patch, leaving the double strand with a patch missing DNA polymerase replaces the missing bases DNA ligase joins the DNA up
Describe the possible fates of carcinogen-DNA damage.
Low level of damage –> effective repair –> return to being a normal cell Severe damage –> apoptosis Carcinogen causing altered DNA –> incorrect repair/altered primary sequence –> DNA replication and cell division (fixed mutation) –> transcription and translation giving aberrant proteins + carcinogenesis if critical targets are mutated
Describe the process of testing whether a chemical can cause carcinogenesis.
Look at structure of compound Test in vitro on bacteria Test in vitro on mammalian cells Test in vivo on mammals
Describe the bacterial (Ames) test for mutagenicity of chemicals.
This test usually uses Salmonella typhimurium The bacterium is genetically engineered so that it can’t produce histidine, so it can only survive and grow on a culture medium that has exogenous histidine The compound to be tested is, firstly, incubated with rat liver enzymes containing CYP450 enzymes to metabolise the chemical into an active form that can be carcinogenic The bacteria are mixed with the active chemical and then placed on a culture medium with NO histidine Any colonies that survive will have become mutated by the chemical so that it regains the ability to produce its own histidine and hence cangrow in the absence of histidine Any bacteria that hasn’t been mutated will die on the dish The greater the DNA damaging capability of the chemical, the more colonies will grow in the absence of histidine
Describe the use of in vitro micronucleus assays.
This is trying to measure the ability of a chemical to break up DNA into fragments We need the cell to go through one replication cycle and then stop it when it’s at the binucleus stage – this is when you check for the presence of micronuclei
What is used to block cytokinesis and hold the cell in the binucleate stage in the micronucleus assay?
Cytochalasin-B
What are the two types of chromosomal damage that can be detected by this assay?
Clastogenicity – chromosomal breakage Aneuploidy – chromosomal loss/change in the number of chromosomes
Explain the reasoning behind the use of bone marrow micronucleus assays to test the mutagenicity of a chemical.
Bone marrow is pluripotent The animals are treated with the chemical and their bone marrow cells and peripheral erythrocytes are examined for the presence of micronuclei Erythrocytes normally remove the nucleus during development, but it CANNOT remove small fragments of DNA e.g. a micronucleus So the presence of micronuclei in erythrocytes indicates DNA damage
What are the six hallmarks of cancer?
Disregard of signals to stop proliferating Disregard of signals to differentiate Capacity for sustained proliferation Evasion of apoptosis Ability to invade Ability to promote angiogenesis
What is gene amplification?
Production of multiple gene copies
What are chimeric genes?
Genes that are formed by combinations of portions of one or more coding sequence to produce new genes (e.g. the swapping of tips of chromosomes)
When can the formation of chimeric genes be a problem?
If one of the pieces of translocated DNA is a promoter, it could lead to upregulation of the other gene portion (this occurs in Burkitt’s lymphoma) If the fusion gene codes for an abnormal protein that promotes cancer
What is the Philadelphia Chromosome?
Chromosome produced by the translocation of the ABL gene on chromosome 9 to the BCR gene on chromosome 22 The BCR-ABL fusion gene encodes a protein that promotes the development of cancer
State some important oncogenes in human cancers.
SRC – tyrosine kinase Myc – transcription factor JUN – transcription factor Ha-Ras – membrane bound GTPase Ki-Ras – membrane bound GTPase
What is an example of an inherited cancer?
Retinoblastoma – malignant cancer of the developing retinal cells
What mutation causes retinoblastoma?
RB1 gene 13q14
What are the functional classes of tumour suppressor genes?
Regulate cell proliferation Maintain cellular integrity Regulate cell growth Regulate the cell cycle Nuclear transcription factors DNA repair proteins Cell adhesion molecules Cell death regulators
State some important tumour suppressor genes in human cancers
P53 – cell cycle regulator BRCA1 – cell cycle regulator PTEN – tyrosine and lipid phosphatase APC – cell signalling
In what form is p53 inactive?
When it is bound to MDM2
What is p53 important for?
It is important for regulation of p53 target genes (involved in DNA repair, growth arrest, senescence etc.) and protein-protein interactions (e.g. apoptosis)
What is odd about p53 considering it is a tumour suppressor gene?
It acts in a DOMINANT manner –mutation of a single copy is sufficient to achieve dysregulation of activity
What deletion causes loss of the APC gene?
5q21
What is APC involved in?
Cell adhesion Cell signalling
What is the risk of people with this mutation developing colon cancer?
90%
What signalling pathway is APC involved in?
WNT signalling
What is the main role of APC that prevents uncontrolled growth?
It breaks down beta-catenin so that it doesn’t bind to LEF1 and promote uncontrolled proliferation
Describe the step-by-step development of colorectal cancer.
APC mutations –> hyperproliferative epithelium DNA hypomethylation + K-ras mutation will make the polyps –> adenomas P53 mutation will result in the development of carcinoma
What transcription factor is stimulated by growth factor signalling and is vital to starting the cell cycle?
c-Myc
Describe what happens to tyrosine kinase receptors when growthfactors bind to them.
Tyrosine kinase receptors are usually present on membranes as inactive monomers Most growth factors are dimers, so when they bind they bring tyrosine kinase receptors close together This allows the tyrosine kinase receptors to cross-phosphorylate each other (using the gamma phosphate from ATP to phosphorylate tyrosine residues in proteins) The phosphorylated domains on the tyrosine kinase receptors act as docking sites for adaptor proteins
Give an example of an anti-cancer drug that targets tyrosine kinase receptors.
Herceptin – inhibits the Her2 tyrosine kinase receptor (important in many tumours e.g. breast)
Name an important adaptor protein.
Grb2
Describe the structure of this protein.
It is modular It has an SH2 domain, which binds to the docking sites (phosphorylated tyrosine residues on the tyrosine kinase receptors) It has two SH3 domains, which bind to proline-rich regions of proteins
Describe how receptor protein tyrosine kinases can signal to Ras.
Grb2 is bound to an exchange factor called Sos When the tyrosine kinase receptors become active and the dockingsites become available, Grb2 binds to the docking site and it is also attached to Sos This brings Sos close enough to the cell membrane and Ras, to allow it to exchange the GDP on Ras for GTP GTP bound Ras is active
What must the Ras protein be bound to for it to work?
It must be bound to the plasma membrane NOTE: interference with the membrane binding of Ras can make a good anti-cancer drug
How is Ras turned off?
Ras has intrinsic GTP hydrolysis capability This GTPase activity is stimulated by GTPase-activating proteins (GAPs)
Broadly speaking, how might Ras signalling be different in cancer?
Ras could be permanently switched on (in the GTP bound form), thus it constantly signals cell division
Describe two mutations that lead to an increase in the amount of active Ras.
V21Ras – glycine is replaced by valine, which means that a simple hydrogen side chain is replaced by a hydrophobic sidechain. This hydrophobic side chain doesn’t allow GAPs to bind to Ras, thus preventing inactivation of Ras. L61Ras – glutamine is replaced by leucine (in position 61), which means that an amine side chain is replaced by a hydrophobic side chain. This inhibits the GTPase activity of Ras so Ras remains in the active, GTP bound form.
What cascade does Ras activate?
ERK cascade (Extracellular signal-regulated kinase cascade)
What is the family that this cascade belongs to called?
MAPK cascade (Mitogen-activated protein kinase cascade)
What are the three kinases involved in the ERK cascade?
Raf MEK ERK
What does the last kinase in the cascade phosphorylate?
It phosphorylates gene regulatory proteins (transcription factors), which go on to regulate the expression of genes involved in the cell cycle They also phosphorylate other proteins and change their activity
What important gene is turned on by the kinase cascade?
c-Myc
What type of kinase are cyclin-dependent kinases (Cdks)?
Serine-threonine kinases
What conditions do Cdks require to become activated?
Binding to cyclin Phosphorylation (activating phosphorylation and removal of inhibitory phosphorylation) (+ degradation of Cdk inhibitors)
What does the mitosis-promoting factor (MPF) consist of?
Cdk1 + cyclin B
What are the requirements, in terms of phosphorylation, for MPF to become active?
Activating phosphorylation by CAK (Cdk activating kinase) Removal of the inhibitory phosphorylation (that was placed by Wee1)by Cdc25
What activates MPF at the end of interphase?
Removal of the inhibitory phosphorylation by Cdc25
Describe the positive feedback loop that is formed by MPF activation.
Removal of the inhibitory phosphorylation by Cdc25 produces active MPF, which then phosphorylates Cdc25 and increases its activity meaning that more MPF can be activated
How does MPF put mitosis on hold before progressing to the next stage?
At the end of metaphase, it phosphorylates a number of key proteins and inhibits their action (thus putting mitosis on hold) until it is signalled to proceed. Then the cyclin B is degraded, Cdk is inactivated and the substrates become dephosphorylated and hence become active.
Which Cdk/cyclin is required for G1/S phase?
Cdk2-cyclin E
Which Cdk/cyclin is required for S phase?
Cdk2-cyclin A
How can the same Cdk be used for two different stages?
Cyclin binding alters the substrate specificity of Cdk Also, different substrates are available at different stages of the cell cycle
What is one of the most important transcription targets of c-Myc?
Cyclin D
What is the first Cdk/cyclin complex that is formed when a cell goes from G0 to G1?
Cdk4/6-cyclin D
This Cdk/cyclin complex then stimulates the expression of the next cyclin in the cell cycle. What properties does this system give to the cell cycle?
This gives the cell cycle direction and timing (because the Cdk-cyclin complexes must reach a certain concentration before they can triggerthe next stage of the cycle)
Give an example of a phosphorylation target of MPF that allows the cell cycle to progress.
Phosphorylation of nuclear lamins allows breakdown of the nuclear envelope
What is start kinase and what is one of its most important targets?
Start kinase = Cdk2-cyclin E Retinoblastoma
Describe the role of retinoblastoma in the quiescent G0 state.
Retinoblastoma is unphosphorylated and binds to and sequesters a group of transcription factors called E2F
What effect does Cdk4/6-cyclin D have on retinoblastoma?
It multiply phosphorylates retinoblastoma – as it becomes phosphorylated it loses its affinity for E2F and releases E2F This means that the E2F transcription factors can regulate gene expression and promote progression of the cell cycle
What is one of the main targets of E2F?
Cyclin E (the next cyclin in the cell cycle)
What type of gene is retinoblastoma?
Tumour suppressor gene (it acts a break on the cell cycle)
State some important genes that are regulated by E2F.
Proto-oncogenes – c-Myc, n-Myc Cell cycle – E2F-1,2,3, pRb, cyclin A, cyclin E, CDK4, CDK2 DNA synthesis – thymidine kinase, thymidine synthetase, dihydrofolate reductase, DNA polymerase
The initial release of E2F allows transcription of cyclin E leading to the formation of Cdk2-cyclin E. What effect does this complex have on retinoblastoma?
Cdk2-cyclin E further phosphorylates retinoblastoma so more E2F is released and the concentration of E2F increases
What is the significance of the increasing concentration of E2F?
This means that E2F can now bind to targets with a lower affinity (e.g. cyclin A gene promoter isn’t activated until the E2F concentration is high enough)
What are the two families of Cdk inhibitors?
NK4 CIP/KIP
During which phase do each of the families act and how do they inhibit Cdk?
INK4 – G1 phase – it displaces cyclin D from the Cdk4/6-cyclin D complex CIP/KIP – S phase – it binds to the Cdk/cyclin complexes and inhibits them NOTE: these inhibitors need to be degraded at various stages for the cell cycle to progress
State some common and important oncogenes.
EGFR/HER2 – mutationally activated or over-expressed in many breast cancers Ras – mutationally activated in many cancers Cyclin D1 – overexpressed in 50% of breast cancers B-Raf – mutationally activated in melanomas c-Myc – overexpressed in many tumours
State some important tumour suppressor genes.
Rb – inactivated in many cancers p27KIP1–under-expression correlates with poor prognosis in many malignancies
Define Metaplasia.
A reversible change in which one adult cell type (usually epithelial) is replaced by another adult cell type
Give two examples of metaplasia, one pathological and one physiological.
Barrett’s Oesophagus – gastro-oesophageal reflux can change the stratified squamous epithelium of the distal oesophagus to simple columnar Cervix during pregnancy – the cervix opens up and the columnar epithelium of the endocervical canal is exposed to the acidic uterine fluids making it squamous
What are the two types of metaplasia that can take place in Barrett’s Oesophagus?
Gastric metaplasia – stratified squamous to simple columnar Intestinal metaplasia – goblet cells begin to appear
State some features of cancer that are seen in dysplasia.
Large nuclei (and hyperchromatic) Increased mitoses Abnormal mitoses Increased nucleo-cytoplasmic ratio Loss of architectural orientation Loss of uniformity of individual cells
What is the difference between low and high-grade dysplasia?
They both show changes of dysplasia but the changes are more severe in high-grade dysplasia High-grade has a high risk of progression to cancer
What are the main features of benign tumours that separate them from malignant tumours?
They do not metastasise They do not invade They also are usually encapsulated (except for fibroids in the uterus), slow growing and have normal mitoses
Under what conditions can benign tumours be dangerous?
If they are in a dangerous location If they secrete something dangerous If they get infected If they bleed If they rupture If they become twisted
What are the features of malignant tumours?
Invade surrounding tissues Spread to distant sites They also have no capsule, can be well or poorly differentiated, rapidly growing and have abnormal mitoses
Define metastasis.
A discontinuous growing colony of tumour cells, at some distance from the primary cancer
What are the two different types of benign epithelial tumour?
Papilloma – of the surface epithelium Adenoma – of glandular epithelium
Define carcinoma.
Malignant tumour derived from the epithelium
What are the different types of carcinoma?
Basal cell carcinoma Squamous cell carcinoma Transitional cell carcinoma (transitional epithelium is found in the bladder) Adenocarcinoma
State some different types of benign soft tissue tumour.
Osteoma –bone Lipoma - fat Leiomyoma – smooth muscle
Define sarcoma.
Malignant tumour derived from connective tissue (mesenchymal) cells
What are the names given to malignant tumours of striated muscle, smooth muscle and the nerve sheath?
Striated muscle – rhabdomyosarcoma Smooth muscle – leiomyosarcoma Nerve sheath – Malignant peripheral nerve sheath tumour
Define leukaemia.
Malignant tumour of bone marrow derived cells, which circulate in the blood
Define lymphoma.
Malignant tumour of lymphocytes (usually) in lymph nodes
Define teratoma.
A tumour derived from germ cells, which has the potential to develop into tumours of all three germ layers
What is an important difference between teratomas in men compared to women?
Gonadal teratomas in men are almost always malignant Gonadal teratomas in women are almost always benign
Define hamartoma.
Localised overgrowth of cells and tissue native to the organ In other words, the cells and tissues present are appropriate for that particular location but their structural organisation is inappropriate
Which group of the population is hamartoma common in?
It is common in children and the hamartoma usually stops growing when the children stop growing
What is the difference between grading and staging?
Grading – how well differentiated the cancer is Staging – how far the cancer has spread Staging > Grading
What is meant by the ‘degree of differentiation’?
How much the tumour cells resemble the cells from which they are derived
What are the grading systems for breast and prostate cancer?
Breast –Nottingham scoring system Prostate – Gleason classification
What is the term given to tumours that show little or no differentiation?
Anaplastic
What are the five most common cancers worldwide?
Lung Breast Bowel Prostate Stomach
What are the four main anti-cancer modalities?
Radiotherapy Chemotherapy Surgery Immunotherapy
List the different types of cytotoxic chemotherapy.
Alkylating agents Pseudoalkylating agents Antimetabolites Anthracyclines Vinca alkaloids and taxanes Topoisomerase inhibitors
What are the main types of targeted therapy for cancer?
Monoclonal antibodies Small molecule inhibitors
hat is the term used to describe chemotherapy that is given: a. Following surgery b. Before surgery
Adjuvant Neoadjuvant
How do alkylating agents work?
They add an alkyl group to the guanine residues in DNA This causes cross-linking of the DNA strands and prevents DNA from uncoiling at replication This then triggers apoptosis (via a DNA checkpoint pathway) It encourages mis-pairing
Name four alkylating agents.
Chlorambucil Cyclophosphamide Dacarbazine Temozolomide
How do pseudoalkylating agents work?
They have the same mechanism as alkylating agents but use platinum instead of alkyl groups
Name three pseudoalkylating agents.
Carboplatin Cisplatin Oxaliplatin
What are some side effects of alkylating and pseudoalkylating agents?
Alopecia (except carboplatin) Nephrotoxicity Neurotoxicity Ototoxicity (platins) Nausea, Vomiting, Diarrhoea, Immunosuppression, Tiredness
How do anti-metabolites work?
They masquerade as purine or pyrimidines leading to inhibition of DNA replication and transcription They can also be folate antagonists (dihydrofolate reductase inhibitors) This blocks DNA replication and transcription
Give six examples of anti-metabolites.
Methotrexate Capecitabine Gemcitabine 5-fluorouracil 6-mercaptopurine Fludarabine
State some side effects of anti-metabolites.
Alopecia (not 5-fluorouracil or capecitabine) Bone marrow suppression Increased risk of neutropenic sepsis Nausea, Vomiting, Mucositis, Diarrhoea, Fatigue Palmar-plantar erythrodysesthesia (PPE)
How do anthracyclines work?
They intercalate into DNA or RNA sequences and inhibit transcription and replication It also blocks DNA repair They create DNA damaging and cell membrane damaging oxygen free radicals
Give two examples of anthracyclines.
Doxorubicin Epirubicin
State some side effects of anthracyclines.
Cardiac toxicity (probably due to the free radicals) Alopecia Neutropenia Nausea, Vomiting, Fatigue Red urine (doxorubicin –‘the red devil’)
How do vinca alkaloids and taxanes work?
Vinca alkaloids inhibit assembly of microtubules Taxanes inhibit disassembly of microtubules This forces the cells into mitotic arrest
State some side effects of these drugs.
Nerve damage (peripheral neuropathy and autonomic neuropathy) Hair loss Nausea, Vomiting Bone marrow suppression Arthralgia (severe joint pain without swelling or signs of arthritis) Allergy
How do topoisomerase inhibitors work?
Topoisomerase is responsible for the unwinding of DNA and they induce temporary single and double strand breaks in the phosphodiester backbone Topoisomerase inhibitors alter the binding of topoisomerase to DNA and allow permanent breaks in the DNA
Give three examples of topoisomerase inhibitors.
Topotecan Irinotecan Etoposide
State some side effects of topoisomerase inhibitors.
Irinotecan = acute cholinergic type syndrome (diarrhoea, abdominal cramps, diaphoresis – so they are given atropine) Hair loss Nausea, Vomiting, Fatigue Bone marrow suppression
What are the six hallmarks of cancer?
SPINAP Self-sufficient Pro-invasive and metastatic Insensitive to anti-growth signals Non-senescent Anti-apoptotic Pro-angiogenic
What are the four hallmarks of cancer that have recently been added?
DIE U Dysregulated metabolism Inflammation Evades the immune system Unstable DNA
Give three examples of receptors that are over-expressed in cancer.
EGFR – over-expressed in many breast and colorectal cancers HER2 – breast PDGFR – glioma (brain)
Give an example of a ligand that is over-expressed in some cancers.
VEGF – prostate, kidney and breast cancer
Give two examples of constitutive (ligand independent) receptor activation in cancer.
EGFR – lung cancer FGFR – head and neck cancers, myeloma
What do each of the following suffixes mean in relation to monoclonal antibodies: a. -momab b. -ximab c. -zumab d. -mumab
a.–momab Derived from mouse antibodies b.–ximab Chimeric antibody c.–zumab Humanised antibody d.–mumab Fully human antibody
Describe the structure of humanised monoclonal antibodies.
Murine regions are interspersed within the with the light and heavy chains of the Fab portion
Describe the structure of chimeric monoclonal antibodies.
The murine component of the variable region of the Fab section is maintained integrally
What effect can monoclonal antibodies have on receptors and their activation?
They target the extracellular component of receptors and can prevent receptor dimerization, neutralise the ligand and cause internalisation of the receptor NOTE: they also activate Fc-receptor-dependent phagocytosis or cytolysis induced complement-dependent cytotoxicity or antibody-dependent cellular cytotoxicity (ADCC)
Give two examples of monoclonal antibodies used in oncology.
Bevacizumab (avastin) – binds and neutralises VEGF Cetuximab – targets EGFR
How do small molecule inhibitors work?
They bind to the kinase domain of tyrosine kinase receptors within the cytoplasm and block autophosphorylation and downstream signalling
What was the first targeted treatment for cancer and how did it work?
Glivec (imatinib) – it is a small molecule inhibitor that targets the ATP binding region within the kinase domain of BCR-ABL1 This inhibits the kinase activity of ABL1
Give four examples of small molecule inhibitors that inhibit receptors.
Erlotinib (EGFR) Gefitinib (EGFR) Lapatinib (EGFR/HER2) Sorafenib (VEGFR)
Give three examples of small molecule inhibitors that inhibit intracellular kinases.
Sorafenib (Raf kinase) – this is in addition to its anti-VEGFR effects Dasatinib (Src kinase) Torcinibs (mTOR inhibitors)
State some advantages and disadvantages of monoclonal antibodies.
Advantages: High target specificity Cause ADCC, complement-mediated cytotoxicity and apoptosis induction Can be radiolabelled Long half-life Good for haematological malignancies Disadvantages: Large and complex structure Less useful against bulky tumours Only useful against targets with extracellular domains Not useful for constitutively activated tumours Cause immunogenicity and allergy IV administration Expensive
State some advantages and disadvantages of small molecule inhibitors.
Advantages: Can target tyrosine kinases without an extracellular domain or which are constitutively activated Pleiotropic targets (useful in heterogenic tumours/cross-talk) Oral administration Good tissue penetration Cheap Disadvantages: Shorter half-life, more frequent administration Pleiotropic targets (more unexpected toxicity)
State some resistance mechanisms to targeted therapies.
Mutations in ATP binding domain Intrinsic resistance Intragenic mutations Upregulation of downstream signalling pathways
Explain how anti-sense oligonucleotides work.
These are short single-stranded DNA-like molecules They bind to the complementary sequence on mRNA and hinder its translation It then recruits RNase H to cleave the target mRNA Mechanism: anti-sense oligonucleotides
Name a successful B-Raf inhibitor.
Vemurafenib NOTE: side effects include arthralgia, skin rash and photosensitivity
Explain how the PD-1 receptor-PDL1 ligand system works.
PD-1 receptor is on the cell membrane When the ligand (PDL-1) binds to the PD-1 receptor, the body’s T cells can no longer recognise tumours as foreign So blocking the PD-1 receptor will stimulate the immune system
Name a drug that inhibiting PD-1.
Nivolumab (anti-PD1 antibody)
What type of carcinoma are most colon cancers?
Adenocarcinoma
What is the rate of turnover of cells in the colon?
2-5 million cells per minute
What is a polyp?
Any projection from a mucosal surface into a hollow viscus
What is an adenoma?
Benign neoplasm of the mucosal epithelial cells
What are the different types of colonic polyp?
Metaplastic/hyperplastic Adenoma
State some characteristics of hyperplastic polyps.
These are VERY COMMON 90% of all colonic polyps They have NO malignant potential 15% have K-ras mutations
What are the different types of colonic adenoma?
Tubular Tubulovillous Villous NOTE: the more villous it is the worse it is
What are the different shapes of colonic adenomas?
Pedunculated – looks like a tree Sessile – looks like a hedge
What is the difference between tubular and villous adenomas?
Tubular– COLUMNAR cells with nuclear enlargement, elongation, multi-layering and loss of polarity + increased proliferative activity + reduced differentiation Villous– MUCINOUS cells with nuclear enlargement, elongation, multi-layering and loss of polarity. May be exophytic.
What is the most famous condition that causes an increasednumber of colonic polyps?
Familial Adenomatous Polyposis
What gene mutation is FAP caused by?
5q21
What are the two genetic pathways in colorectal cancer?
Adenoma-carcinoma sequence = presence of adenomas will increase the risk of colorectal cancer Microsatellite instability
What are microsatellites?
Repeat sequences of DNA that are prone to misalignment Some microsatellites are found in coding sequences of genes which inhibit growth or are involved in apoptosis
State two genetic diseases that predispose to colorectal cancer.
Familial adenomatous polyposis – inactivation of the APC tumour suppressor gene HNPCC – microsatellite instability (affects mismatch repair genes)
State some dietary factors that can increase the risk of colorectal cancer.
High fat Low fibre High red meat Refined carbohydrates
State two dietary deficiencies that can increase the risk ofcolorectal cancer.
Folates– important for nucleotide synthesis and DNA methylation MTHFR– deficiency leads to disruption of DNA synthesis and DNA instability (this leads to mutation). It also causes decreased methionine synthesis leading to genomic hypomethylation and focal hypermethylation – this can have gene activating and silencing effects
