Cytotoxic efficacy of reconstituted and stored antitumor agents

The stability of the cell-killing efficacy of 10 antitumor drugs stored at different temperatures and concentrations was evaluated on an established human colon carcinoma cell line using the colony formation technique. Drugs were reconstituted in the appropriate solvent, further diluted in 0.9% NaCl solution to obtain the desired storage concentration, and stored at 4 degrees C, -20 degrees C, and -70 degrees C for periods of up to 3 weeks. Cytotoxic efficacy was tested weekly by exposing the cells to the final drug dilution for 1 h at 37 degrees C. Stability of cytotoxic potency depended on the particular drug, and the duration, concentration, and temperature of storage but, in general, most drugs remained efficacious only within limited periods of time (at most, 2 weeks). These results suggest that the conditions of drug storage following reconstitution are critical factors with respect to lethal efficacy. Therefore, analysis of in vitro cytotoxic efficacy can be meaningful only when storage conditions are specified in order to avoid false-negative results in the human tumor clonogenic assay.