**Core Concept**
The question is testing the knowledge of enzymes used as anticancer drugs, specifically focusing on the pharmacological principle of targeting cancer cell metabolism. Enzymes play a crucial role in various biochemical pathways, and some have been repurposed as anticancer agents due to their ability to selectively target cancer cells.

**Why the Correct Answer is Right**
The correct answer is an enzyme that is involved in the synthesis of purine nucleotides. In cancer cells, this enzyme is overexpressed, leading to an increased demand for nucleotides. By inhibiting this enzyme, the cancer cells are unable to synthesize the necessary nucleotides for DNA replication and cell division, ultimately leading to cell death. The enzyme in question is **L-asparaginase**, which breaks down the amino acid asparagine into aspartic acid and ammonia. Cancer cells, particularly acute lymphoblastic leukemia (ALL), are unable to synthesize asparagine and rely on external sources. L-asparaginase depletes the available asparagine, starving the cancer cells and inducing cell death.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not relate to the enzyme's mechanism of action as an anticancer agent. While some enzymes may be involved in DNA repair or replication, they are not typically used as anticancer drugs.
* **Option B:** This option is incorrect because it is not a specific enzyme known to be used as an anticancer agent. While some enzymes may have anticancer properties, they are not typically used as targeted therapies.
* **Option C:** This option is incorrect because it is not a correct example of an enzyme used as an anticancer drug. While some enzymes may be involved in cancer metabolism, they are not typically used as targeted therapies.

**Clinical Pearl / High-Yield Fact**
L-asparaginase is a high-yield fact in oncology, particularly in the treatment of acute lymphoblastic leukemia (ALL). It is a targeted therapy that selectively targets cancer cells by depleting the available asparagine, leading to cell death. This enzyme is an important example of how biochemical pathways can be targeted to selectively kill cancer cells.

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