Concentration and time-dependent inter-relationships for antitumour drug cytotoxicities against tumour cells in vitro.

Cryopreserved tumour cells obtained from the ascitic fluid of a patient with an ovarian carcinoma were employed to determine the effect on in vitro drug cytotoxicities of varying both drug concentration and exposure time. Four antitumour drugs, in common clinical usage, were selected for study. Tumour-cell survival following drug treatment was measured by colony-forming ability in the soft-agar developed by Courtenay et al. (1978). Treatment with cis-platinum, adriamycin or vinblastine generated exponential survival curves with increasing cell kill resulting from either increasing drug concentrations or prolonging exposure times. In contrast, no detectable cell kill was elicited by treatment with hydroxyurea for short exposure times of 1 or 6 h, even at concentrations as high as 1 mg/ml, although continuous drug exposure resulted in a steep exponential survival curve. These results, obtained directly from biopsy material, are in close agreement with data from parallel studies employing a continuous human tumour-cell line (COLO 205 derived from a colon carcinoma). Duration of exposure is therefore an important determinant of drug-induced cytotoxicity under these assay conditions. The results with hydroxyurea, however, imply that prolonged incubation times are necessary to evaluate the cytotoxicity of certain agents and so the routinely employed 1 h exposure in most current human tumour drug sensitivity tests is inadequate for such drugs. These data therefore provide evidence that employing a single set of standard conditions of drug exposure to evaluate all antitumour drugs may be inappropriate.