Neoplasia Flashcards
Three phases of cancer formation?
1) preneoplastic epigenetic changes
2) cancer transformation (initiation)
3) Progression
Mass of detectable tumors? Mass of fatal tumors?
- At least 1 gram
- Usually 1 kg
What three major classes of genes are usually mutated in cancer?
- DNA repair genes
- Tumor suppressor genes
- Protoncogenes
What are three different ways oncogenes can stimulate cells?
- overexpression
- expression at the wrong place/time
- unresponsive to negative regulation
What receptor is overexpressed by KSHV (Kaposi’s)?
G protein receptor that signals without ligand
With HTLV-1 (human T cell lymphotrophic virus), which growth factor receptor is overexpressed? in which cells?
IL-2 receptor in infected T cells
Which EGF receptor is overexpressed in breast cancer, ovarian cancer, etc? Consequence?
ERBB2 (Her-2-Neu)
Hypersensitivity to EGF signaling
What drug targets ERBB2?
Herceptin
In CML, a chromosome translocation produces what hybrid oncogene product? Consequence?
Bcr-Abl – Abl inhibitory domain is lost and cell is constitutively activated
What drug inhibits Abl kinase?
imatinib (Gleevec)
What is B-Raf? In melanomas, colorectal cancers, and thyroid cancers, what mutation is observed in B-Raf? Consequence?
- protoncogene; member of Raf threonine/serine protein kinase family
- Regulator downstream of Ras
- V600E
- signals on its own bypassing upstream receptors
What drug/drug type is used to treat melanomas with the BRAF V600E mutation?
protein kinase inhibitor = VEMURAFENIB
What pathway is regulated by PTEN (phosphatase and tensin homolog)?
What is the function of this pathway?
- phosphatidylinositol-3-kinase (PI3K)/Akt pathway
- PTEN phosphatase protein is a tumor suppressor
- important for cell activation and apoptosis resistance
What fusion gene can be formed by translocation with the ALK (anaplastic lymphoma kinase) gene? How does this fusion gene product function and in what cancers is it often found?
- ALK gene codes for tyrosine kinase receptor of insulin super family
- EML4-ALK fusion gene
- Dimerizes without the need for a ligand and constitutively signals
- Lung cancers, particularly NSC adenocarcinomas in young, non-smokers
What protein kinase inhibitor can be used to treat EML4-ALK positive lung cancers?
crizotinib
What is an example of a common GAP (GTPase activating protein)?
NF-1
What gene regulates B-catenin? What is the function of B-catenin?
- APC (adenomatous polyposis coli) = tumor suppressor protein that acts as antagonist in the Wnt pathway
- APC docks on B-cat that isn’t bound to E cadherin and B-cat is degraded
- Wnt frees B-cat from APC to act as TF to activate various proliferating genes (wound healing)
- TF involved in cell-cell contact signaling
Defective APC is most commonly found in what cancers?
colorectal cancers and benign intestinal polyps
What is the normal function of let7 miRNA? Deleted/underexpressed in what cancer type?
- Targets 3’ UTR of Ras and downregulates Ras protein expression
- lung cancer
What 4 types of cancer respond only occasionally to chemotherapy?
- Non-small lung cancer
- melanoma
- pancreatic and hepatocellular carcinoma
- renal and prostate cancer
What are two anti-mitotic drugs?
- paclitaxel
- vincristine
How does paclitaxel work?
- Promotes tubulin polymerization and blocks disassembly required for mitosis
- Cells are arrested in mitosis
Three unusual side effects of paclitaxel?
neuropathy, hypersensitivity, arrhythmias
How does vincristine work?
Binds tubulin and inhibits microtubule formation (opposite of paclitaxel)
Unusual vincristine side effect? Cause?
neurotoxicity because microtubules are important in neuronal transport
What drugs are substrates for CYP450?
paclitaxel (anti-mitotic) - inactivated
doxorubicin (antibiotic)
cyclophosphamide (pro-drug, alkylating agent)
ondansetron (anti-emetic)
Two antibiotics used in chemotherapy? Natural source?
doxorubicin
dactinomycin
Soil microbe Streptomyces
What cancers are often treated with doxorubicin?
hematologic cancers and solid tumors
How does doxorubicin work?
Inhibits topoisomerase II, intercalates DNA, binds cell membranes, and generates free radicals
How does dactinomycin work?
Binds dsDNA by intercalating between G-C bp – inhibits RNA synthesis (RNA needed all the time)
Unusual side effects of doxorubicin? Treatment for more severe side effect?
- Cardiotoxicity, red urine
- dezroxane = iron chelator
How is doxorubicin eliminated?
Biphasic - peak half-lives at 3 and 30 hours (CYP450 in liver)
What is one alkylating agent used in cancer treatment?
Cyclophosphamide (nitrogen mustard)
How does cyclophosphamide work?
- transfers alkyl groups to cellular constituents
- Damages and cross-links DNA
- Targets REPLICATION - fork stops at alkyl groups
Secondary use for cyclophosphamide?
immunosuppression in transplant patients
How is cyclophosphamide metabolized?
Pro-drug activated by P450 proteins in liver
Two anti-metabolites used in cancer treatment?
Methotrexate and 5-fluorouracil, also 6-MP
Methotrexate inhibits which enzyme and synthesis of which products?
Dihydrofolate reductase - THF, thymidylate, nucleotides, amino acids
Dual functions of 5-FU?
- incorporated into RNA/DNA – inhibits RNA functioning/processing
- inhibits thymidylate synthase – inhibits biosynthesis of pyrimidines
Two things to consider with methotrexate?
- can accumulate in ascetic, pleural, peritoneal fluid
- significant interactions with drugs that bind to plasma proteins (salicylate, sulfonamides, phenytoin), which can displace metho from normal binding proteins and cause increased tox