All are true about cyclophosphamide except –
**Core Concept**
Cyclophosphamide is a nitrogen mustard alkylating agent used in the treatment of various cancers and autoimmune diseases. It works by inducing cross-linking of DNA strands, thereby inhibiting DNA replication and cell division.
**Why the Correct Answer is Right**
Cyclophosphamide is metabolized by the liver enzyme cytochrome P450 2B6 to its active form, 4-hydroxycyclophosphamide, which is then converted to phosphoramide mustard, the actual alkylating agent responsible for its cytotoxic effects. This process is facilitated by the enzyme aldehyde dehydrogenase. Cyclophosphamide also has a unique side effect profile, including hemorrhagic cystitis, which is due to the formation of acrolein, a toxic metabolite that is also produced during its metabolism.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cyclophosphamide is not primarily used as an immunosuppressant in organ transplantation. While it does have immunosuppressive properties, its use in this context is not as common as other agents like tacrolimus or cyclosporine.
**Option B:** This option is incorrect because cyclophosphamide does not work by inhibiting the enzyme topoisomerase II. Instead, it exerts its effects by alkylating DNA, which leads to DNA strand breaks and inhibition of DNA replication.
**Option C:** This option is incorrect because cyclophosphamide is not a platinum-based chemotherapeutic agent. It belongs to the class of nitrogen mustard alkylating agents, which work by inducing DNA cross-links.
**Option D:** This option is incorrect because cyclophosphamide does not primarily work by inhibiting the enzyme telomerase. While it does have cytotoxic effects, its mechanism of action is distinct from telomerase inhibitors.
**Clinical Pearl / High-Yield Fact**
One notable side effect of cyclophosphamide is its potential to cause hemorrhagic cystitis, which is often due to the formation of acrolein, a toxic metabolite. This can be mitigated by administering mesna, a sulfhydrye compound that helps to neutralize acrolein and reduce the risk of bladder toxicity.
**Correct Answer: A. Cyclophosphamide is not primarily used as an immunosuppressant in organ transplantation.**