Radiosensitization in vitro by cis-diammine (1,1-cyclobutanedicarboxylato) platinum(II) (carboplatin, JM8) and ethylenediammine-malonatoplatinum(II) (JM40).

The radiosensitizing ability of two analogues of cisplatin have been tested in vitro. The analogues, CBDCA (JM8) and EDMP (JM40), are currently undergoing clinical tests in the search for an active but less toxic cancer chemotherapeutic agent than cisplatin. The compounds were cytotoxic to log phase RIF1 cells in culture, but at higher concentrations than the parent compound. Both analogues were radiosensitizers of oxic cells when given as 1 h exposures beginning either 3 h before, 1 h before or 2 h after irradiation, giving modest enhancements of approximately 1.2. Each drug caused an inhibition of the repair of sublethal damage which was greatest after CBDCA treatment. Although neither analogue was as good a radiosensitizer as cisplatin, CBDCA appears to show promise as a potential radioenhancing platinum compound.