Pentostatin acts by inhibiting –
**Core Concept**
Pentostatin is a potent inhibitor of adenosine deaminase, an enzyme crucial for purine metabolism. This inhibition affects lymphocyte function, particularly in T-cells and B-cells. The **adenosine deaminase** enzyme plays a key role in the breakdown of adenosine and deoxyadenosine.
**Why the Correct Answer is Right**
Pentostatin's mechanism of action involves the inhibition of **adenosine deaminase**, leading to the accumulation of deoxyadenosine triphosphate (dATP), which is toxic to lymphocytes. This results in the suppression of immune function, making it useful in treating certain lymphoproliferative disorders. The inhibition of **adenosine deaminase** by pentostatin disrupts DNA synthesis and repair, particularly affecting activated lymphocytes.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while other mechanisms might be involved in immunosuppression, they are not the primary action of pentostatin.
**Option B:** Incorrect as it does not accurately describe the mechanism of action of pentostatin.
**Option C:** Incorrect because, although relevant to immunosuppression, it is not the specific action of pentostatin.
**Clinical Pearl / High-Yield Fact**
Pentostatin is used in the treatment of **hairy cell leukemia** and has immunosuppressive properties, making it a valuable agent in certain hematological malignancies. Its unique mechanism of action, through **adenosine deaminase inhibition**, sets it apart from other chemotherapeutic agents.
**Correct Answer:** D. Adenosine deaminase.