Curability of mouse L1210 leukemia by combination of 5-fluorouracil, cis-diamminedichloroplatinum(II), and low doses of gamma-rays.

By combining 5-fluorouracil and cis-diamminedichloro-platinum(II) at drug levels which are ineffective when used alone, we have cured L1210 leukemia in mice in a single treatment session. It was also discovered that the doses of the drugs used in this combination can be decreased, with no corresponding decrease in their effectiveness, if they are administered in conjunction with a very low dose of radiation (gamma-rays), which, when used alone, is ineffective. In the cells, the explanation for the synergic action of radiation, 5-fluorouracil, and cis-diamminedichloroplatinum(II) can be found in the action of each of the cytostatics at different phases of the cell cycle, each cytostatic favoring the action of the others. It is important to emphasize the order in which chemotherapy and radiotherapy are administered, as well as the time lapse between administration of the two treatments, maximum effectiveness having been obtained when radiotherapy was carried out 8 to 24 hr after chemotherapy.