Cancer Chemotherapy Topics Basic principles: cell cycle, tumor growth kinetics, log kill, recruitment, drug targets Mechanisms of drug action Drug resistance mechanisms Toxicity and new approaches

Cellular Pathways to Malignancy

Tumor Suppressor Genes apc=binds beta catenin p53 = transcription and DNA synthesis WT-1 = zinc finger transcription factor

Cancer Molecular Pathways apoptosis pathway important TGFbeta= anti-growth pathway GPCR= activation of PKA pathway RTK=receptor tyrosine kinases (e.g. EGF receptor)

History of Cancer Chemotherapy Goodman and Gilman: first to use nitrogen mustard (alkylating agent) to treat cancer

Cancer Chemotherapy: Targets for selective toxicity target rapidly dividing cells? cancer cells are not the only replicating cells e.g. intestinal epithelia, bone marrow, mucosal, hair follicle cells are all rapidly dividing as well not all cells in a tumor are replicating not all cancer cells have escaped normal growth control

stem cells, proliferation in the lumen of gut

many tumors are quite slow growing and often more difficult to treat with drugs

Cancer Chemotherapy: Targets for selective toxicity target rapidly dividing cells? cancer cells are not the only replicating cells e.g. intestinal epithelia, bone marrow, mucosal, hair follicle cells are all rapidly dividing as well not all cells in a tumor are replicating altered metabolic enzymes (e.g. L-asparaginase to kill cells that can not synthesize asparagine) cell surface receptors (e.g. trastuzumab (Herceptin) blocks HER2 (ErbB) in breast cancer) ErbB = epidermal growth factor receptors specific hormonal requirements (e.g. steroid receptor antagonists for breast CA, prostate CA) altered intracellular signaling (e.g. imatinib (Gleevec) targets the Abl kinase which is turned on in chronic myelocytic leukemia)

Remissions and complete cures are obtained with specific cancers Hodgkin’s lymphoma choriocarcinoma acute leukemias in children Wilm’s tumor (kidney) testicular cancer breast, prostate CA

The cell cycle G1: growth, protein synthesis, RNA synthesis S: DNA synthesis, replication, RNA & protein synthesis G2: DNA repair, chromosome condensation M: mitosis, nuclear division cell cycle 8hr to 100 days

Restriction point: cells traverse R by expression and activation of cyclin/CDK complexes and then are committed to continue through S phase. cyclin/cdks discovered by Lee Hartwell (Nobel 2001) time in G1 is big variable once past R--tend to complete cycle R regulated by the cyclin cdk complexes

Cell Cycle Specificity of Selected Drugs fluorouracil mercaptopurine methotrexate L-asparaginase paclitaxel vincristine/vinblastine Cycle non-specific alkylating agents: cyclophosphamide, mechlorethamine, nitrosoureas actinomycin D daunorubicin, doxorubicin etoposide, irinotecan cisplatin bleomycin drugs are phase specific as well….mitosis, or S based on mechanism some work better in G2 because there is less time to repair damage (bleomycin)

Tumor growth kinetics Based on Gompertz--German insurance salesman tumors develop from a single cell---clonal the initial tumor cells display stem cell like properties cancer stem cells

Log Kill hypothesis Dr. Howard Skipper 1960s postulated that cell death follows 1st order kinetics with anti cancer drugs experiment: treat mouse leukemia with cytosine arabinose 24 hr of ara-C--mice died 3 treatment every 4 days--mice lived developed concept of Log Kill

log kill = - log fraction surviving

must get last cell (10 to the 0) to cure.

Easy Exam Question As part of your research project you are experimenting with the treatment of mice injected with 1012 leukemia cells. You are using a combination of mechlorethamine and vincristine with a log kill of 4. The leukemia grows at a rate of 1 log per week. If you start treatment immediately and give a treatment every 2 weeks, what is the minimum number of treatments required to theoretically cure your mouse patients? A) 3 B) 4 C) 5 D) 6 E) 7

Harder Exam question The initial tumor burden is 1010 cells and the drug combination used is known to give a log kill of 3. Assuming a 1 log re-growth per week between treatments and that all the cells are sensitive, which of the following treatment schedules would be expected to give a complete cure (ignoring the fact that cancers don’t always behave predictably)? A. 3 treatments at one week intervals B. 8 treatments at two week intervals C. 50 treatments at three week intervals D. 5 treatments at one week intervals E. none of the above

Recruitment non-dividing cells (insensitive to many drugs) rapidly dividing cells (sensitive to drugs) increase nutrient supply increase perfusion reduce crowding: surgery radiation chemo with cycle non-specific drugs (e.g. alkylating agents)

Hypoxia in tumor induces expression of angiogenic genes VEGF and Ang1, Ang2 stimulate angiogenesis diffusion limit for O2 is 100-200um more later bevacizumab (Avastin) antibody to VEGF

Drug Targets in Cancer Chemotherapy 1. DNA a) bondage--alkylating agents (mechlorethamine, cyclophosphamide), cisplatin b) vaporization--bleomycin c) confusion--actinomycin D, doxorubicin, etoposide, irinotecan d) starvation--methotrexate, 6-thioguanine, 5-fluorouracil, cytosine arabinoside,hydroxyurea e) regulation--tamoxifen, aromatase inhibitors 2. Protein synthesis: L-asparaginase DNA is major target (synthesis and function) 3. Mitotic Apparatus: vincristine, vinblastine, paclitaxel 4. Specific antigens: therapeutic antibodies (e.g. Herceptin, Avastin) 5. Protein kinase inhibitors: Gleevec (imatinib) inhibits BCR-ABL which causes CML(chronic myeloid leukemia)