**Core Concept**
Mechlorethamine is a nitrogen mustard alkylating agent used in chemotherapy. It works by inducing cross-links in DNA, leading to cell death. This mechanism is a result of its ability to alkylate DNA, thereby interfering with DNA replication and transcription.

**Why the Correct Answer is Right**
The correct mechanism of action of mechlorethamine involves the formation of reactive alkyl groups that react with DNA, leading to the cross-linking of DNA strands. This cross-linking prevents the separation of DNA strands during replication, ultimately resulting in cell death. The enzyme topoisomerase II is involved in the repair of DNA damage, but mechlorethamine's mechanism of action bypasses this repair process.

**Why Each Wrong Option is Incorrect**
**Option A:** Mechlorethamine does not work primarily through the inhibition of microtubule formation, which is the mechanism of action of vinca alkaloids.
**Option B:** Mechlorethamine does not act as an antimetabolite, which is the mechanism of action of certain chemotherapeutic agents like methotrexate.
**Option C:** Mechlorethamine does not primarily work through the induction of apoptosis, although it can induce apoptosis in certain situations.

**Clinical Pearl / High-Yield Fact**
Mechlorethamine is a classic example of an alkylating agent, which works by inducing DNA cross-links. This mechanism is shared by other nitrogen mustard compounds, such as cyclophosphamide and chlorambucil.

**Correct Answer: C. Mechlorethamine exerts its cell killing mainly by inducing DNA cross-links.**