01. Make a diagram illustrating the stages of the cell cycle.

02. Briefly describe the rationale for using combination chemotherapy.

Combination chemotherapy is used because multiple drugs may have a synergistic effect in killing a given type of neoplastic cell. Therefore, multiple drugs would decrease the likelihood of neoplastic cells to develop resistance. Also, combination chemotherapy may be able to destroy the multiple types of neoplastic cells found in a given tumor.

03. What are the four actions of alklyating agents on nucleic acids? Which of the four is most important for the cytotoxicity of alkylating agents? How does this last action affect DNA replication and transcription?

Alkylating agents have four actions on nucleic acids. First of all, the agent may cause crosslinking of DNA strands which interferes with DNA and RNA synthesis. This is thought to be the most important reason for the cytotoxic effect of alkylating agents. Secondly, the agent may alter the "side chain groups" of the nucleotide base ring which would lead to abnormal base pairing and point mutations in the synthesized DNA and RNA chains. Thirdly, the alkylating agent may split the base ring from the nucleotide which again interrupts proper DNA and RNA synthesis. Finally, the alkylating agent may break the ring structure of a nucleotide base which would prevent base pairing during DNA and RNA synthesis.

04. Name three prototypes for the nitrogen mustards. Which are effective when given orally? Which drug must be metabolized by cytochrome P450 to an active alkylating agent?

The nitrogen mustards are a group of alkylating agents. This group includes mechlorethamine, cyclophosphamide, melphalan and chlorambucil. Of the nitrogen mustard prototypes mentioned above, only mechlorethamine is not orally effective and must be administered intravenously. Ifosamide is an analog of cyclophosphamide which must be metabolized by cytochrome P450 in the liver in order to be an active alkylating agent.

05. Name the prototype for the alkyl sulfonates. What is the only significant side-effect of this agent?

Alkyl sulfonates are another group of alkylating agents. The prototypical alkyl sulfonate is busulfan. Since it is used for myelosuppression only, its major side effect is not bone marrow suppression. Instead, the major side effect is pulmonary fibrosis.

06. Name two prototypes for the nitrosoureas. What are the abbreviations of their chemical names?

The nitrosoureas are a third group of alkylating agents. Two prototypical nitrosoureas are carmustine (BCNU) and lomustine (CCNU).

07. Provide a concise, detailed explanation of the mechanism of action of each of the following drugs: vinca alkaloids; etoposide; dactinomycin; doxorubicin; bleomycin; L-asparaginase; cisplatin.

Another large catagory of chemotherapeutic agents are the natural products. One group of the natural products catagory is the vinca alkaloids. The two vinca alkaloids, vinblastine and vincristine, work by preventing microtubule spindle formation. Therefore, they block mitosis. A second group of the natural products catagory is the epipodophyllotoxins of which etoposide is the prototypical agent. Etoposide seems to block DNA synthesis by inhibiting DNA Topoisomerase II in eukaryotic cells. The third group of the natural products catagory is the antibiotics. This group includes dactinomycin, doxorubicin, bleomycin and L-asparaginase. Dactinomycin works by blocking RNA synthesis. Doxorubicin seems to work by blocking DNA synthesis. Bleomycin works by fragmenting DNA and inhibiting DNA repair. Finally, L-asparagine works by hydrolyzing asparagine, an essential amino acid in certain types of tumor cells.

Cisplatin is a platinum compound that belongs in the "other agents" catagory of anti- neoplastic agents. Like the alkylating agents, cisplatin works by forming DNA crosslinks.

08. What is the mechanism of action of methotrexate? What drug can be given immediately after methotrexate in order to reduce the toxicity of methotrexate?

Methotrexate is the prototypic antitherapeutic drug of the antimetabolite catagory. It works by inhibiting the enzyme, folate reductase which prevents the conversion of dihydropteroate to tetrahydrofolate. Tetrahydrofolate is an important metabolite in the one-carbon transfer reactions which are essential for purine and pyrimidine synthesis. In order to reduce the toxicity of methotrexate on normal cells, leucovorin (ie folinic acid) is given. It is a metabolite further along the folate pathway and allows for normal cells to carry on purine and pyrimidine synthesis.

09. Name two pyrimidine analogs. Name two purine analogs.

Pyrimidine analogs are compounds with similar structures to thymidine, uracil, and cytosine. Two pyrimidine analogs used as anti-neoplastic agents are 5-fluorouracil (which inhibits thymidine synthetase) and cytosine arabinoside (which is added into a growing DNA chain and terminates its synthesis).

Purine analogs are compounds with similar structures to adenosine and guanine. Two purine analogs used as anti-neoplastic agents are 6-mercaptopurine and thioguanine. Both agents inhibit the synthesis of purine nucleotides.

10. Briefly define "lethal synthesis."

"Lethal synthesis" is the process by which a chemotherapeutic agent must be converted into an active (ie toxic) metabolite utilizing chemical reaction pathways found in the neoplastic cell. [NOTE: Usually, these pathways also exist in normal cells which leads to the low chemotherapeutic index for compounds requiring "lethal synthesis."]

11. What drug-drug interaction occurs between allopurinol and 6-mercaptopurine? What enzyme is inhibited by allopurinol?

Allopurinol is an anti-gout treatment which blocks the production of uric acid by inhibiting the enzyme, xanthine oxidase. However, xanthine oxidase is a key enzyme in the metabolism of 6-mercaptopurine. Therefore, if a patient is being treated with both allopurinol and 6-mercaptopurine, the serum level of 6-mercaptopurine will be higher than usual and may lead to increased normal cell cytotoxicity.

12. What is the mechanism of action of each of the following as chemotherapeutic agents? Provide at least one primary indication for each drug: prednisone; progesterone; estrogen; tamoxifen; and aminoglutethimide.

Another catagory of the antineoplastic agents is the hormones. Prednisone, progesterone, estrogen, tamoxifen and aminoglutethimide all belong to this catagory.

Prednisone is a glucocorticoid analog which has a high amount of anti-inflammatory activity and a low amount of salt retention activity. Its mechanism of action is the dissolution and the prevention of mitotic activity in lymphocytes. As a result, it is commonly used to induce remission in children with acute lymphocytic lymphoma.

Progesterone is a natural sex steroid. Its mechanism of antineoplastic action is the inhibition of LH release from the anterior pituitary which causes a reduction in estrogen production by the ovary. It is commonly used in estrogen-"induced" tumors such as endometrial cancer.

Estrogen is a natural sex steroid. Its mechanism of antineoplastic action is the antagonism of androgens such as 5-dihydroxytestosterone. As a result, it is commonly used in the treatment of prostatic cancer after castration.

Tamoxifen is an antagonist of estrogen. Therefore, it works by blocking estrogen-dependent tumor growth. It is used mainly in the treatment of breast cancer.

Finally, aminoglutethimide inhibits cortisol synthesis. Therefore, it is used to control adrenocortical carcinoma which results in Cushing's syndrome.

13. Briefly define what is meant by the terms cell-cycle specific (CCS) and cell-cycle nonspecific (CCNS).

Cell-cycle specific and cell-cycle non-specific are terms used to generally describe where in the cell cycle the anti-neoplastic agent has the greatest effect. Cell-cycle specific agents act at a particular stage (ie microtubule spindle blocking agents act during the M phase). Cell-cycle nonspecific agents do not work at a specific stage. Instead, they work at multiple stages of the cell-cycle.

14. For each chemotherapeutic agent, indicate whether the drug is CCS or CCNS. If the drug is CCS, then indicate in step of the cycle it is most active. Mechlorethamine; cyclophosphamide; carmustine; cisplatin; doxorubicin; mitomycin; dactinomycin; methotrexate; vinblastine; bleomycin; 5-fluorouracil; 6-mercaptopurine.

Mechlorethamine, cyclophosphamide, carmustine, mitomycin and cisplatin all cause the cross-linking of DNA. Therefore, they effect DNA, RNA and protein synthesis during the various stage of the cell-cycle. As a result, they are CCNS.

Methotrexate, 5-fluorouracil,and 6-mercaptopurine are different types of antimetabolites.

Although all these agents can affect both DNA and RNA synthesis, they mainly act during the S phase of the cell cycle and are therefore CCS.

Vinblastine, doxorubicin, dactinomycin, and bleomycin are members of the natural products catagory. Vinblastine blocks microtubular formation required to produce the mitotic spindle during mitosis. Therefore, it is CCS and works at the M stage. Of the antibiotic group, all are CCNS except bleomycin. Bleomycin seems to have its main effect at the S stage of the cell cycle.

15. Nearly all cancer chemotherapeutic agents (increase/decrease) the susceptibility of the patient to infection. Also they predominantly effect (rapidly/slowly) proliferating tissue such as __________, __________, and __________. Hence they almost all cause __________, __________, and __________.

Nearly all cancer chemotherapeutic agents increase the susceptibility of the patient to infection. Also they predominantly effect rapidly proliferating tissue such as gastrointestinal cells, blood cell precursors, and hair cells. Hence they almost all cause vomiting, bone marrow suppression, and alopecia (hair loss).

16. The following drugs produce toxicities for specific organs: doxorubicin; bleomycin; cyclophosphamide; L-asparaginase; vincristine; cisplatin; and vinblastine. Identify the organ specific toxicity associated with each drug.

Of the natural product anti-neoplastic agents, doxorubicin causes cardiotoxicity, bleomycin causes pulmonary fibrosis, L-asparaginase causes hepatic and clotting factor toxicity, vincristine causes neurotoxicity, and vinblastine causes bone marrow suppression. Cyclophosphamide mainly causes bone marrow suppression and hemorrhagic cystitis. Finally, cisplatin mainly causes nephrotoxicity.

17. What is the major difference in the toxicities of vincristine and vinblastine?

Although vincristine and vinblastine structurally are very similar, they are effective on different neoplasms and have different toxicities. Vincristine's major side effect is neurotoxity while vinblastine's major side effect is bone marrow suppression.