Which of the following antiumor agents works by impairing de novo purine synthesis?
**Core Concept**
Impairing de novo purine synthesis is a key mechanism by which certain antitumor agents exert their effects. This process involves the inhibition of enzymes responsible for purine nucleotide synthesis, ultimately leading to the disruption of DNA replication and cell division.
**Why the Correct Answer is Right**
The correct answer works by inhibiting the enzyme IMP dehydrogenase (IMPDH), which is crucial for the synthesis of guanine nucleotides from inosine monophosphate (IMP). IMPDH is particularly important in rapidly dividing cells, such as cancer cells. By inhibiting IMPDH, the correct answer disrupts the de novo purine synthesis pathway, leading to a decrease in guanine nucleotide levels and subsequently inhibiting DNA synthesis and cell proliferation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specifically target de novo purine synthesis. Instead, it may interfere with other cellular processes.
* **Option B:** This option is incorrect because it is not directly related to the impairment of de novo purine synthesis. Its mechanism of action may involve other cellular targets.
* **Option C:** This option is incorrect because, although it may affect DNA synthesis, its primary mechanism of action is not through the impairment of de novo purine synthesis.
**Clinical Pearl / High-Yield Fact**
The inhibition of IMPDH has been shown to have a significant impact on rapidly dividing cells, making it a valuable target for cancer therapy. This mechanism of action is particularly relevant in the treatment of hematological malignancies and certain solid tumors.
**Correct Answer: C. Methotrexate.**