A primary purpose of a radiosensitizer like Cisplatin is to:

Radiosensitizers like Cisplatin are specifically designed to increase the sensitivity of cancer cells to radiation therapy. When employed in conjunction with radiation treatments, these agents can enhance the effects of the radiation, making cancer cells more likely to be killed. This increased sensitivity is achieved because the radiosensitizer interferes with cellular processes that repair the damage inflicted by the radiation, leading to a more significant reduction in tumor viability.

The mechanism behind Cisplatin's action involves its ability to form DNA crosslinks, which can hinder the cell's ability to reproduce and repair itself after radiation exposure. By doing so, it primes the cancer cells for further damage when they are subsequently exposed to radiation, ultimately enhancing the overall therapeutic effect of the treatment.

Other choices present alternative concepts that do not align with the primary role of a radiosensitizer. For example, reducing cell exposure to radiation would be counterproductive to its purpose, and speeding up the repair of damaged DNA contradicts the objective of increasing sensitivity to radiation. Enhancing the immune response is also unrelated to the function of a radiosensitizer in the context of radiation therapy.