Radiation and platinum drug interaction.

Platinum drugs have chemical as well as biochemical and biological effects on cells, all of which may interact with radiation effects. They inhibit recovery from sublethal and potentially lethal radiation damage. They produce a pattern of chromosome aberrations analogous to that from alkylating agents. Cellular sensitivity to platinum is increased when glutathione levels are reduced, just as is radiosensitivity. There is a pattern of drug sensitivity throughout the phases of the cell cycle which is different from that for radiosensitivity. The ideal platinum drug-radiation interaction would achieve radiosensitization of hypoxic tumour cells with the use of a dose of drug which is completely non-toxic to normal tissues. Electron-affinic agents are employed with this aim, but the commoner platinum drugs are only weakly electron-affinic. They do have a quasi-alkylating action however, and this DNA targeting may account for the radiosensitizing effect which occurs with both pre- and post-radiation treatments. Because toxic drug dosage is usually required for this, the evidence of the biological responses to the drug and to the radiation, as well as to the combination, requires critical analysis before any claim of true enhancement, rather than simple additivity, can be accepted. The amount of enhancement will vary with both the platinum drug dose and the time interval between drug administration and radiation. Clinical schedules may produce an increase in tumour response and/or morbidity, depending upon such dose and time relationships.