Cancer Flashcards
Define metaplasia
A reversible change in which one adult cell type (usually epithelium) is replaced by another cell type - an ADAPTIVE process.
Define dysplasia
An abnormal pattern of growth in which some of the cellular and architectural features of malignancy are present.
Pre-invasive stage: intact basement membrane.
Cells appear darker (hyperchromatic) due to enlarged nuclei which increase the nuclear: cytoplasmic ratio.
What is high grade dysplasia?
More likely to progress and less likely to spontaneously regress than low grade dysplasia.
Define neoplasia
An abnormal, autonomous proliferation of cells unresponsive to normal growth control mechanisms.
Define lesion and tumour.
A lesion is a zone of tissue with impaired function due to damage from disease or wounding. A tumour is any kind of mass-forming lesion.
Give differences between benign and malignant tumours.
Benign tumours do not invade and do not metastasise. This is the key functional difference.
Descriptive (not diagnostic) markers of a benign tumour are that it is encapsulated, well differentiated, slow growing and has normal mitoses.
When might a benign tumour be fatal?
If it is in a dangerous place (pituitary, meninges), secretes something dangerous (insulinoma), gets infected (bladder), bleeds (stomach), ruptures (liver adenoma) or torts (ovarian cyst).
How do we name benign epithelial tumours?
If it is a tumour of surface epithelium, such as skin and the bladder, it is a PAPILLOMA
A benign tumour of glandular epithelium is an ADENOMA.
What is a carcinoma?
A malignant tumour derived from EPITHELIUM.
E.g. squamous cell carcinoma, adenocarcinoma, basal cell carcinoma, transitional cell carcinoma.
What is the nomenclature for benign and malignant tumours of soft tissue (connective tissue).
Benign = add -oma (osteoma) Malignant = SARCOMA, e.g. osteosarcoma.
Contrast rhabdomyosarcoma and leiomyosarcoma.
Rhabdomyosarcoma is a malignant tumour of striated muscles cells.
Leiomyosarcoma is a malignant tumour of smooth muscle cells.
Contrast lymphoma and leukaemia.
Leukaemia is a malignant tumour of bone marrow derived cells circulating in the blood.
Lymphoma is a malignant tumour of lymphocytes in lymph nodes.
Note benign Leukaemias and lymphomas are extremely uncommon and hence the nomenclature.
Define teratoma.
A tumour derived from germ cells, which has the potential to develop into tumours of all 3 germ layers.
Gonadal teratomas in males are all malignant; in females mostly benign.
Define hamartoma.
Localised overgrowth of cells and tissues native to the organ. Cells are mature but architecturally abnormal. Common in children, but usually stop growing when they do.
What is a tumour which performs none of the usual roles of the tissue it is derived from described as?
An anaplastic carcinoma.
What is the assessment of the differentiation of a tumour based on?
Evidence of presence of normal functioning, e.g. production of keratin, bile, mucin, hormones.
How are grade and stage related to prognosis?
Grade (degree of differentiation) correlated with stage (high grade = low differentiation). But stage (TNM) more important in prognosis.
Describe poorly differentiated cells.
They have larger nuclei (and hence a higher nuclear-cytoplasmic ratio) and more mitoses than the normal tissues they are derived from. They may have abnormal mitoses (e.g. tripolar) and marked nuclear pleomorphism (variability in nuclear size and shape).
At what stage of the cell cycle are cells most vulnerable?
M phase (mitosis) - the cells are more easily killed, the DNA damage is irreparable and gene transcription is silenced at this phase.
Describe the centrosome.
An organelle which consists of 2 centrioles at 90 degrees to each other. The centrioles consist of barrels of 9 triple microtubules.
It functions as the microtubule organising centre (MTOC) and forms the mitotic spindle in mitosis.
Describe prophase.
Chromatin condenses - each condensed chromosome consists of 2 sister chromatids. Each chromatid is associated with a kinetochore.
2 sister chromatids linked by a centromere.
Describe late prophase.
Duplicated centrosomes migrate to opposite sides of the nucleus and organise the assembly of spindle microtubules.
Mitotic spindle forms outside the nucleus between the 2 centrosomes.
Radial microtubule arrays (ASTERS) form around each centrosome (MTOC) - the radial arrays meet and form polar microtubules
What happens in prometaphase?
Nuclear membrane breaks down.
Attachment of chromosomes to spindle via kinetochores
Microtubules from opposite pole is captured by sister kinetochore.
Chromosomes attached to each pole congress to the middle. They slide rapidly along microtubules towards the middle.
Describe metaphase.
Chromosomes aligned at equator of spindle - attached by their kinetochores.
Describe anaphase.
Paired chromatids separate to form 2 daughter chromosomes.
Cohesin holds 2 sister chromatids together.
In anaphase A - cohesin breaks down, and daughter chromosomes are pulled towards opposite spindle poles.
In anaphase B - the daughter chromosomes migrate towards poles, and the poles (centrosomes) themselves move apart.
Describe telophase.
Daughter chromosomes arrive at centrosome.
Nuclear envelope reassembles at each pole.
Assembly of contractile ring.
Describe cytokinesis.
Acto-myosin contractile ring contracts.
New membrane inserted.
Midbody begins to form.
Nucellar structures reform, chromatin decondenses
Describe the spindle assembly checkpoint at the transition out of metaphase.
Required CENP-E (centromere protein E) and BUB proteins.
BUBs dissociate from kinetochore when chromosomes are properly attached to the spindle - when all are dissociated, anaphase proceeds.
hence serves to sense completion of chromosome alignment and spindle assembly.
How can the transition out of metaphase lead to aneuploidy?
Misattachment of microtubules to kinetochores.
Syntelic attachment : both microtubules go towards same daughter cell.
Monotelic = only 1 chromatid attached.
Merotelic = multiple microtubules attached to one kinetochore (this chromosome is lost at cytokinesis).
Give another cause of aneuploidy - other than misattachment of microtubules.
Aberrant centrosome/ DNA duplication.
How do checkpoint kinase inhibitors work as anti-cancer therapy?
They induce gross chromosomal mis-segregations by inhibiting attachment error-correction mechanisms.
They target checkpoint kinases (CHEK1 and CHEK2), which work at the G2 phase of the cell cycle to check fidelity of DNA replication.
How do taxanes and vinca alkaloids work as anti-cancer therapy?
They alter microtubule dynamics, producing unattached kinetochores and causing long-term mitotic arrest.
Vinca alkaloids inhibit assembly of mitotic microtubules whereas taxanes inhibit disassembly.
What effect can a tumour have on different checkpoints in the cell cycle?
In the absence of stimulus, a cell enters G0, exits the cell cycle and dismantles its cell cycle apparatus. This can be blocked. Also, G1 checkpoint (growth factors) can be enhanced, G2 checkpoint (DNA damage) can be suppressed Metaphase checkpoint (sister chromatid alignment) can be suppressed.
How are signalling cascades stimulated?
In the presence of a ligand, receptors form dimers. These cause phosphorylation at kinase domains. Activates proteins (causes change in shape or creates docking site for another protein). Amplifies signal.
Briefly describe cytotoxic chemotherapy.
Given i.v. or orally. Systemic. Non-targeted (all rapidly dividing cells affected).
Pre-op = neoadjuvant
Post-op = adjuvant
Can be monotherapy or combination, with curative or palliative intent.
Describe alkylating agents.
A group of drugs given as cytotoxic chemotherapy which add alkyl groups to guanine residues in DNA, leading to cross-linking of DNA strands and prevention of DNA uncoiling at replication.
They trigger apoptosis.
They encourage mis-pairing, and as such are oncogenic and risk secondary malignancy.
Example = chlorambucil.
Describe pseudo-alkylating agents.
A group of drugs given as cytotoxic chemotherapy which add platinum to guanine residues in DNA.
Same mechanism of cell death as alkylating agents.
Example = CISPLATIN!!!!, carboplatin.
Describe anti-metabolites.
A group of drugs given as cytotoxic chemotherapy which masquerade as purine or pyridine residues leading to inhibition of DNA synthesis: DNA double strands breakdown and cells apoptose.
Describe anthracyclines.
A group of drugs given as cytotoxic chemotherapy which inhibit transcription and replication by inserting between nucleotides within DNA/RNA.
They block DNA repair (are mutagenic) and create damaging free radicals.
Examples = doxorubicin.
Describe topoisomerase inhibitors.
A group of drugs given as cytotoxic chemotherapy which induce temporary breaks in the DNA backbone (since topoisomerase needs to prevent DNA torsional strain).
How can tumour cells become resistant to cytotoxic chemotherapy?
Enhanced DNA repair, drug effluxed from the cell by ATP-binding cassette transporters, DNA adducts replaced by Base Excision Repair.
Why are dual-kinase inhibitors used?
Since inactivating one pathway in monogenic cancers can activate parallel pathways or feedback cascades.
Dual-kinase inhibitors prevent feedback loops but increase toxicities
Give 6 hallmarks of cancer cells.
Self-sufficient (sustains proliferative signalling), insensitive to anti-growth signals, anti-apoptotic, pro-invasive and metastatic, proangiogenic and non-senescent.
How are monoclonal antibodies used as anticancer therapy?
They target extracellular components of receptors and neutralise the ligand, prevent receptor dimerisation and cause receptor internalisation.
How do small molecule inhibitors work as anti-cancer therapy?
Bind to the kinase domain of the tyrosine kinase within the cytoplasm to block autophosphorylation and downstream signalling.
E.g. glivec.
Why are targeted therapies (monoclonal antibodies and small molecule inhibitors) good and how does resistance arise?
By acting on receptors, targeted therapies block cancer hallmarks without the toxicity observed with cytotoxics.
Resistance can arise from mutations in the ATP-kinase domain, intrinsic resistance, intragenic mutations and upregulation of downstream or parallel pathways.
What is a protein domain?
A functional and structural unit copied in many proteins. Some domains are important in molecular recognition: no enzymatic action, simply bring proteins together.
Describe the MAPK (mitogen-activated protein kinase) cascade.
EPG causes epidermal growth receptor dimerization and cross-phosphorylation at the cytoplasmic domain. Adaptor protein, Grb2 binds, associated with sos at SH3 domains. Sos causes RAS to be activated by displacing GDP for GTP. RAS activates Raf (MAPKKK), which activates MEK (MAPKK), which activates ERK (MAPK). ERK activates cMyc, a transcription factor which promotes cyclin D transcription. Cyclin D binds to Cdk4/6: this cyclin/Cdk complex binds to Rb to phosphorylate it (inactivated), releasing E2F (another transcription factor) which is involved in transcribing further cyclin, initially cyclin E.
Give 4 proto-oncogenes in the MAPK pathway.
RAS: can mutate so that GAP (GTPase activating protein) binding is prevented, or so GTP hydrolysis is prevented, resulting in a constitutively active RAS.
cMyc - overexpressed in many tumours.
Cyclin D - overexpressed in 50% of breast tumours.
Epidermal growth factor receptor - can be mutationally active or overexpressed, e.g. HER2.
Describe briefly the cyclin-dependent kinase (Cdk)/ cyclin control of the cell cycle.
Cell cycle control based on cyclically active protein kinases. The Cdks are present all the time: cyclins are transiently expressed at specific points of the cell cycle. They are synthesised then degraded.
Activated (phosphorylated) Cdks phosphorylate proteins drive cell cycle progression.
Cdk 4/6, 2, 2, 1; cyclin D, E, A ,B.
Stimulate synthesis of proteins required for next stage.
Describe the tumour suppressor protein Rb.
pRb binds to transcription factor E2F in G0 of the cell cycle. It inactivates the TF. Cdk4/6-cyclin D phosphorylates pRb, releasing E2F.
It then causes gene transcription, e.g. cyclin E, needed for the next phase of the cell cycle.
Cdks phosphorylate pRb at different sites to cause transcription of different genes.
Describe Cdk inhibitors (CKIs).
CKIs must be degraded to allow cell cycle progression.
INK4 family = G1 phase CKIs. They displace cyclin D.
CIP/KIP family = S phase CKIs. Inhibit all Cdks by binding to whole Cdk/cyclin complex.
CKIs are tumour suppressors.
Give 2 tumour suppressor genes in the MAPK pathway.
pRb - inactivated in many cancers.
KIP - under-expression correlated with poor prognosis in malignancies.
Describe the PI3’K-Akt pathway.
Ligand binds - receptor dimerises. Adapter protein is PI3’k (a lipid) which causes PIP2 to be phosphorylated to PIP3 - resulting in PDK-1 activation which activates PKB/Akt.
PKB/Akt phosphorylates and inactivates caspase 9.
they also phosphorylate and inactive Bad, so Bcl2 is free to bind to Bak and Bax.
they bind to and phosphorylate the transcription factor FOXO, so it is inactivated. FOXO transcribes apoptotic proteins, such as caspase 9, and cell-cycle arresting proteins (KIP).
Describe PTEN.
A tumour suppressor phosphatase which dephosphorylates PIP3 to PIP2, resulting in less activation of PKB/Akt. PTEN promotes cell survival.
How can cytosine be converted to form uracil (the RNA equivalent of thymine)?
Can be deaminated to form uracil relatively easily.
5-methyl cytosine can be deaminated to form thymine directly.
What is an adduct?
A larger molecule attached to DNA.
Describe how radiation in the form of UV light can damage DNA.
UV absorbed by nucleic acids with the resulting influx of energy inducing chemical changes. Most frequently, bonds are formed between pyrimidines, particularly thymine. Results in thymine dimers.
What sort of changes do oxygen free radicals cause on DNA?
They cause double and single strand breaks, leading to apurinic and apyrimidic sites: “nicks” or “gaps”.
What is p53?
A tumour suppressor gene which is the “guardian of the genome”. It regulates cell cycle and conserves genomic stability by preventing mutation.
It responds to a wide variety of insults.
Regulates target genes, including DNA repair pathways.
Describe direct repair of DNA.
Direct repairs involve the reversal of the damage, e.g. photolyases repair thymine dimers.
Compare base excision repair (BER) and nucleotide excision repair (NER).
In BER, the base has been damaged by a mutagen. The base is removed by DNA-glycolase.
Endonucelase splits the phosphodiester backbone.
Polymerase adds a new base.
The backbone is ligated by DNA ligase.
In NER, a larger molecule, an adduct, has been added. The endonuclease makes a nick. Helicase removes the area. Polymerase adds new nucleotides, before ligase connects the backbone.
What are the consequences of DNA damage?
3 outcomes:
Efficient repair –> normal cell
Apoptosis –> cell death.
Incorrect repair –> DNA replication with fixed mutations leading to aberrant proteins or, if crucial targets mutated, carcinogenesis.
When would programmed cell death (PCD) be required?
Harmful cells (viral infection, DNA damage).
Developmentally defective (B-lymphocytes expressing self-antibodies).
Excess/unnecessary cells.
Obsolete cells (mamillary epithelium at the end of lactation).
Exploitation - chemotherapeutic killing of cells.
Contrast necrosis and apoptosis.
Necrosis is unregulated cell death, associated with trauma, cellular disruption and an inflammatory response.
Apoptosis is PCD - controlled disassembly of cell contents without disruption and with no inflammatory response.
Describe necrosis.
Plasma membrane becomes permeable, e.g. trauma. Cell swelling and rupture of cellular membranes releases proteases leading to autodigestion and dissolution of the cell.
Localised inflammation.
Describe apoptosis.
Latent phase: death pathways are activated, but cells appear morphologically the same.
Execution phase: loss of microvilli and intercellular junctions, cell shrinkage, loss of plasma membrane and asymmetry, formation of membrane blebs.
Fragmentation into membrane-enclosed apoptotic bodies.
Plasma membrane remains intact: no inflammation
Apoptotic bodies are phagocytosed by neighbouring cells and roving macrophages.
Describe the role of cysteine-dependent aspartate-directed proteases (caspases) in apoptosis.
Caspases divided into initiator and effector caspases. Form homotypic protein-protein interactions be activate each other.
Initiator caspases cleave and activate effector caspases, which carry out apoptosis. Effector caspases cleave and inactivate proteins or complexes and activate enzymes.
Describe the extrinsic (“death by design”) pathway of caspase activation in apoptosis.
Death receptors, e.g. Fas, present on cell surface. Ligand binds to receptors - cause TRIMERISATION. Adapter protein FADD binds to cytoplasmic domain of Fas via death domain (DD).
Procaspase 8 binds to each FADD via death effector domain (DED) - forming the death-inducing signalling complex (DISC). This oligomerisation of procaspase 8 leads to activation to caspase 8, which in turn activates caspase 3 (an effector caspase).
Describe the role of FLIP as a cytoprotective molecule.
FLIP competes with procaspase 8 for the DED domain of FADD. If prevents transcleavage of procaspase 8, preventing activation.
Describe the intrinsic (“death by default”) pathway of caspase activation in apoptosis.
Cellular stresses lead to loss of mitochondrial membrane potential. Cytochrome C released.
Apoptotic activating factor-1 (Apaf-1) forms a heptamer. Cytochrome C can bind to each of the WD-40 domains of Apaf-1. Caspase recruitment domain (CARD) recruits and oligomerises procaspase 9 - cleaves and activated and released as caspase 9 - this is the APOPTOSOME.
How are the extrinsic and intrinsic apoptotic pathways linked?
Caspase 8 cleaves Bid, which enhances release of mitochondrial proteins, thus augmenting apoptosome formation.
Which members of the Bcl-2 family are pro- and anti-apoptotic?
Bcl-2 and Bcl-xL are anti-apoptotic. They bind to Bax and Bak (pro-apoptotic) on the mitochondrial membrane, preventing them from forming pores.
Bad (pro-apoptotic) binds to Bcl-2 to displace it from Bax and Bak.
Bid is also proapoptotic.
PKB/Akt phosphorylates Bad, inactivating it to preventing it from binding to Bcl-2.
