**Core Concept**
The question is testing knowledge of enzymes used in cancer treatment, specifically those that have been repurposed as anti-cancer agents. This involves understanding the role of enzymes in cancer metabolism and their potential as therapeutic targets.

**Why the Correct Answer is Right**
L-asparaginase is an enzyme used in the treatment of acute lymphoblastic leukemia (ALL). It works by depleting the amino acid asparagine, which is essential for the growth and survival of lymphoblasts. Lymphoblasts are unable to synthesize asparagine due to a deficiency in the enzyme asparagine synthetase, making them dependent on the host's supply of asparagine. By administering L-asparaginase, the level of asparagine in the blood is reduced, leading to the death of lymphoblasts and a reduction in tumor size.

**Why Each Wrong Option is Incorrect**
* **Option A:** Not applicable, as no information is provided about this option.
* **Option B:** Not a correct answer, as no information is provided about this option.
* **Option C:** Not a correct answer, as no information is provided about this option.

**Clinical Pearl / High-Yield Fact**
L-asparaginase is a classic example of an enzyme-based cancer therapy, and it is essential to remember that it is primarily used in the treatment of acute lymphoblastic leukemia. It is also worth noting that L-asparaginase can cause hyperglycemia, pancreatitis, and thrombosis as side effects.

**Correct Answer: D. L-asparaginase**