Alkylating Agents — MCQs
Which of the following drugs acts by inhibiting DNA synthesis through interference with nucleotide metabolism?
Mutations are due to changes in:
Which compound is not considered as a radiosensitizer?
Leucovorin is used for side effect reduction in which anticancer drug?
Which antineoplastic agent is known to cause hemorrhagic cystitis?
Which of the following drugs is associated with untoward side effect of renal tubular damage?
What is the most appropriate next step in management for a patient with a Stage III ovarian cancer with partial response to platinum-based chemotherapy?
Which of the following is not an alkylating agent?
Secondary leukemias are caused by
Chemotherapeutic Agent of Choice for the treatment of CML?
Alkylating Agents Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following drugs acts by inhibiting DNA synthesis through interference with nucleotide metabolism?
- A. 6-Mercaptopurine (Correct Answer)
- B. Actinomycin D
- C. Asparaginase
- D. Mitomycin C
Explanation: ***6-Mercaptopurine*** - This drug is a **purine analog** that acts as an **antimetabolite** [1]. - It inhibits several enzymes involved in **purine synthesis** and metabolism, ultimately preventing the production of DNA and RNA precursors [1]. - By interfering with **nucleotide metabolism**, it prevents DNA synthesis at the level of building block production [1]. *Asparaginase* - This enzyme depletes **extracellular asparagine**, an amino acid essential for protein synthesis in certain cancer cells. - It primarily inhibits **protein synthesis** rather than targeting nucleotide metabolism or DNA synthesis. *Actinomycin D* - This drug is an **intercalating agent** that inserts itself between DNA base pairs. - Its primary action is to inhibit **RNA synthesis (transcription)** by preventing DNA-dependent RNA polymerase from moving along the DNA template. - Does not affect nucleotide metabolism. *Mitomycin C* - This is an an **alkylating agent** that forms **DNA cross-links**. - While it inhibits DNA replication through direct DNA damage, it does **not act through nucleotide metabolism**. - Its mechanism is DNA alkylation and cross-linking, not interference with purine or pyrimidine synthesis.
Question 2: Mutations are due to changes in:
- A. DNA nucleotide sequence (Correct Answer)
- B. RNA nucleotide sequence
- C. Amino acid sequence of ribonuclease
- D. Cell membrane
Explanation: ***DNA nucleotide sequence*** - **Mutations** are defined as changes in the **genetic material**, which is primarily composed of **DNA**. - These changes in the **nucleotide sequence** of DNA can alter the genetic code, leading to changes in **protein structure and function**. *RNA nucleotide sequence* - While RNA can have its nucleotide sequence altered, these changes are generally not considered true **mutations** in the heritable sense for most organisms. - RNA is typically a temporary molecule, and changes to its sequence are usually not passed down to subsequent generations. *Amino acid sequence of ribonuclease* - An altered **amino acid sequence** in a protein like ribonuclease is a consequence of a **mutation in the DNA**, not the mutation itself. - **Ribonucleases** are enzymes that catalyze the degradation of RNA, and their structure is determined by the **DNA sequence**. *Cell membrane* - The cell membrane is a **lipid bilayer** with embedded proteins that regulates cellular transport and communication. - While its components can be affected by genetic mutations, alterations in the cell membrane itself do not constitute the primary definition of a **mutation**.
Question 3: Which compound is not considered as a radiosensitizer?
- A. Hyperbaric oxygen
- B. Misonidazole
- C. Amifostine (Correct Answer)
- D. Idoxuridine
Explanation: ***Amifostine*** - **Amifostine** is a **radioprotector**, meaning it selectively protects healthy cells from the damaging effects of radiation, rather than enhancing radiation's effect on tumor cells. - It works by being dephosphorylated by alkaline phosphatase in normal tissues to an active thiol metabolite that scavenges **free radicals** generated by radiation. *Hyperbaric oxygen* - **Hyperbaric oxygen** increases the amount of dissolved oxygen in tissues, which is a potent **radiosensitizer**. - **Oxygen** enhances the formation of **free radicals** and fixes radiation-induced DNA damage, making tumor cells more susceptible to radiation. *Misonidazole* - **Misonidazole** is a **hypoxic radiosensitizer** that mimics oxygen, becoming relatively toxic under hypoxic conditions (common in tumors). - It forms **free radicals** and binds to cellular macromolecules when reduced by nitroreductases in hypoxic cells, thereby enhancing the effects of radiation. *Idoxuridine* - **Idoxuridine** is a **halogenated pyrimidine** that acts as a radiosensitizer by being incorporated into DNA in place of thymidine. - This incorporation sensitizes the DNA to radiation by making it more susceptible to **strand breaks** and other damage.
Question 4: Leucovorin is used for side effect reduction in which anticancer drug?
- A. Cisplatin
- B. 5-FU
- C. Adriamycin
- D. Methotrexate (Correct Answer)
Explanation: ***Methotrexate*** - **Leucovorin rescue** is a critical adjunct therapy for **methotrexate** to prevent severe toxicity. - Methotrexate is a **folate antagonist**, and leucovorin (folinic acid) provides a reduced folate form that bypasses the blocked enzyme, restoring normal cellular function and protecting healthy cells. - This is true **"rescue therapy"** - leucovorin protects normal cells from methotrexate toxicity. *Cisplatin* - **Cisplatin** is a platinum-based chemotherapy drug primarily associated with **nephrotoxicity** and **ototoxicity**. - Its side effects are managed with **hydration, amifostine**, and antiemetics, not leucovorin. *5-FU* - **5-FU (5-fluorouracil)** is a pyrimidine analog that can cause severe **myelosuppression** and **gastrointestinal toxicity**. - While leucovorin is used WITH 5-FU (e.g., in colorectal cancer regimens), it serves to **enhance/potentiate** 5-FU's cytotoxic effect through biochemical modulation, NOT to rescue from toxicity. - This is the key distinction: leucovorin + 5-FU = **potentiation**; leucovorin + methotrexate = **rescue**. *Adriamycin* - **Adriamycin (doxorubicin)** is an **anthracycline antibiotic** known for causing **cardiotoxicity** and **myelosuppression**. - **Dexrazoxane** is used to prevent Adriamycin-induced cardiotoxicity, not leucovorin.
Question 5: Which antineoplastic agent is known to cause hemorrhagic cystitis?
- A. Cyclophosphamide (Correct Answer)
- B. Methotrexate
- C. Cisplatin
- D. Vincristine
Explanation: ***Cyclophosphamide*** - Cyclophosphamide is an **alkylating agent** that forms highly reactive metabolites, such as **acrolein**, which is excreted in the urine and causes direct irritation and damage to the bladder urothelium, leading to **hemorrhagic cystitis**. - This toxicity can be mitigated by co-administration of **mesna** (2-mercaptoethane sulfonate sodium), which inactivates acrolein in the bladder, and aggressive intravenous hydration. *Methotrexate* - Methotrexate is a **folate antagonist** primarily known for causing **myelosuppression**, **mucositis**, and **hepatotoxicity**. - While it can cause renal toxicity at high doses due to precipitation in renal tubules, it is not typically associated with hemorrhagic cystitis. *Cisplatin* - Cisplatin is a **platinum-based chemotherapy agent** with significant **nephrotoxicity** and **ototoxicity** as its dose-limiting toxicities. - It also commonly causes profound nausea and vomiting but is not a primary cause of hemorrhagic cystitis. *Vincristine* - Vincristine is a **vinca alkaloid** that interferes with microtubule formation, primarily known for causing **peripheral neuropathy** (e.g., foot drop, paresthesias, constipation due to autonomic neuropathy) and is a vesicant. - It does not typically cause hemorrhagic cystitis; its bone marrow toxicity is generally less severe compared to other chemotherapeutic agents.
Question 6: Which of the following drugs is associated with untoward side effect of renal tubular damage?
- A. Streptozotocin
- B. Methysergide
- C. Cyclophosphamide
- D. Cisplatin (Correct Answer)
Explanation: ***Cisplatin*** - **Cisplatin** is a platinum-based chemotherapy drug well-known for its dose-limiting nephrotoxicity, primarily causing **renal tubular damage**. - Its mechanism involves direct DNA damage within renal tubular cells, leading to **acute tubular necrosis** if not managed with aggressive hydration and other protective measures. *Streptozotocin* - **Streptozotocin** is an alkylating agent primarily used in treating **pancreatic neuroendocrine tumors**; its main toxicity is typically to pancreatic beta cells (leading to hypoglycemia) and to the liver. - While it can be nephrotoxic, its predominant and most recognized untoward side effect is not renal tubular damage, but rather **pancreatic beta-cell destruction**. *Methysergide* - **Methysergide** is an ergot alkaloid used for **migraine prophylaxis** but is largely discontinued due to severe side effects like **retroperitoneal fibrosis**. - Renal damage in the context of methysergide is typically due to this fibrosis compressing the ureters, rather than direct tubular toxicity. *Cyclophosphamide* - **Cyclophosphamide** is an alkylating agent known for its immunosuppressive and chemotherapeutic effects; its major side effects include **hemorrhagic cystitis** and myelosuppression. - While high doses can cause nephrotoxicity, its primary and most feared renal-related toxicity is hemorrhagic cystitis, not direct tubular damage as seen with cisplatin.
Question 7: What is the most appropriate next step in management for a patient with a Stage III ovarian cancer with partial response to platinum-based chemotherapy?
- A. Bevacizumab
- B. Perform surgery (Correct Answer)
- C. Switch to radiotherapy
- D. Continue regimen
Explanation: ***Perform surgery (Interval Debulking Surgery)*** - In **Stage III ovarian cancer**, after an initial partial response to **platinum-based chemotherapy**, **interval debulking surgery** is the standard next step to remove residual disease. - This approach aims to reduce tumor burden to an optimal level (< 1 cm residual disease), which has been shown to improve overall survival in multiple trials (EORTC 55971, GOG-152). - Performed after 3-4 cycles of neoadjuvant chemotherapy when the patient has demonstrated response and is medically fit for surgery. *Bevacizumab* - **Bevacizumab** is an **anti-angiogenic agent** used in ovarian cancer, typically as part of frontline maintenance therapy or for recurrent disease, not as the immediate next step after partial response to primary chemotherapy when surgery is feasible. - While it can be incorporated into maintenance treatment post-surgery, it's not the primary next step after partial response when interval debulking surgery is indicated. *Switch to radiotherapy* - **Radiotherapy** has a limited role in the primary treatment of advanced ovarian cancer due to its widespread peritoneal nature. - It is sometimes used for localized recurrence or symptom palliation, but not as a standard next step after partial response to chemotherapy in Stage III disease. *Continue regimen* - Continuing the same regimen after only a **partial response** is generally not the most effective strategy when further tumor reduction via surgery is possible. - The goal in advanced ovarian cancer is **maximal cytoreduction**, and if residual disease is present after neoadjuvant chemotherapy, interval debulking surgery is preferred over continued chemotherapy alone.
Question 8: Which of the following is not an alkylating agent?
- A. Cyclophosphamide
- B. Busulfan
- C. 5-Fluorouracil (Correct Answer)
- D. Melphalan
Explanation: ***5-Fluorouracil*** - **5-Fluorouracil** is an **antimetabolite**, specifically a **pyrimidine analog**, that inhibits DNA synthesis by interfering with **thymidylate synthase**. - It does not function by directly **alkylating DNA** as other options do. *Cyclophosphamide* - **Cyclophosphamide** is a **nitrogen mustard alkylating agent** that forms **DNA cross-links**, leading to cell death. - It requires **hepatic activation** into its active form to exert its cytotoxic effects. *Busulfan* - **Busulfan** is an **alkylating agent** that cross-links DNA strands, primarily affecting **myeloid stem cells**. - It is often used in **hematopoietic stem cell transplantation** as a conditioning agent. *Melphalan* - **Melphalan** is a **phenylalanine mustard alkylating agent** that forms DNA cross-links, particularly effective against **multiple myeloma**. - Its mechanism involves directly damaging DNA to prevent cell replication.
Question 9: Secondary leukemias are caused by
- A. Antimetabolites
- B. Vinca alkaloids
- C. Actinomycin D
- D. Alkylating agents (Correct Answer)
Explanation: ***Alkylating agents*** - **Alkylating agents**, such as **cyclophosphamide**, **chlorambucil**, **melphalan**, and **busulfan**, are highly associated with the development of secondary leukemias, particularly **acute myeloid leukemia (AML)** and **myelodysplastic syndrome (MDS)**. - They cause **DNA damage** by forming covalent bonds with DNA, leading to mutations and chromosomal aberrations (especially deletions of chromosomes 5 and 7) that can promote leukemogenesis. - The latency period is typically **5-7 years** after exposure, and the risk is dose-dependent. *Antimetabolites* - **Antimetabolites**, like **methotrexate** and **5-fluorouracil**, interfere with **DNA replication** and repair but are less frequently linked to secondary leukemias compared to alkylating agents. - While they can cause bone marrow suppression, their mechanism of action typically involves disrupting nucleotide synthesis rather than directly inducing the specific chromosomal changes seen in secondary leukemias. *Vinca alkaloids* - **Vinca alkaloids**, such as **vincristine** and **vinblastine**, primarily target **microtubule formation** and inhibit cell division, often used in cancer chemotherapy. - They are not a significant cause of secondary leukemias; instead, they primarily cause **neurotoxicity** and bone marrow suppression as side effects. *Actinomycin D* - **Actinomycin D** (dactinomycin) acts by intercalating into **DNA** and inhibiting RNA synthesis, making it an **antitumor antibiotic**. - While it is a potent chemotherapy agent with various side effects, it is not a primary cause of **secondary leukemias**, which are predominantly associated with alkylating agents and topoisomerase II inhibitors.
Question 10: Chemotherapeutic Agent of Choice for the treatment of CML?
- A. Imatinib (Correct Answer)
- B. Vincristine
- C. Cyclophosphamide
- D. Methotrexate
Explanation: ***Imatinib*** - **Imatinib** is a **tyrosine kinase inhibitor** specifically targeting the **BCR-ABL fusion protein**, which is the hallmark of CML [1][2]. - It dramatically improved the prognosis of CML patients, making it the **first-line therapy** and agent of choice due to its high efficacy and relatively low toxicity compared to conventional chemotherapy [2]. *Vincristine* - **Vincristine** is a **vinca alkaloid** that inhibits microtubule formation, primarily used in acute leukemias and lymphomas. - It is not the agent of choice for CML due to its different mechanism of action and the availability of more targeted therapies for CML. *Cyclophosphamide* - **Cyclophosphamide** is an **alkylating agent** that causes DNA damage, used in various cancers and autoimmune diseases. - While it can be used in some hematologic malignancies, it is not the preferred or most effective treatment for CML, especially given the success of targeted therapies. *Methotrexate* - **Methotrexate** is an **antimetabolite** that interferes with DNA synthesis, commonly used in acute leukemias, lymphomas, and autoimmune conditions. - It is not considered the chemotherapeutic agent of choice for CML, as its mechanism of action is not specific to the BCR-ABL anomaly characteristic of CML.
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