Prediction of the antitumor activity of new platinum analogs based on their ex vivo pharmacodynamics as determined by bioassay.

We report the predictive model for the clinical response of new platinum analogs against lung cancer by a bioassay using human lung-cancer cell lines including small-cell (SCLC) and non-small-cell lung cancer (NSCLC). Exponentially growing cells of six different SCLC and six NSCLC lines were exposed to different concentrations of the three platinum compounds, cisplatin, carboplatin, and 254-S in a double-agar colony-forming cell assay. The concentrations inhibiting 50% of colony formation (IC50 value) for cisplatin, carboplatin and 254-S in SCLC cell lines were significantly lower than those in NSCLC cell lines. A total of 15 patients entered the pharmacological study. In all, 80 mg/m2 cisplatin, 450 mg/m2 carboplatin, and 100 mg/m2 254-S were each given to five patients by intravenous drip infusion. Bioassay as well as chemical assay was achieved by clonogenic techniques using NCI-H-69 (SCLC cell line) and PC-9 (NSCLC cell line) as target cells. Biological comparison of antitumor activity was performed on the basis of the antitumor activity of patients' plasma using the antitumor index (ATI), which was defined as the area under the percentage of colony suppression versus time curve obtained by bioassay and calculated by the trapezoidal rule. When NCI-H-69 and PC-9 were used as target cells for bioassay, colony-inhibitory activity was revealed by the ATIs. The ATIs obtained by bioassay showed better correlation than the AUCs obtained by chemical assay with the clinical response for cisplatin and carboplatin against SCLC and NSCLC, according to the following equation: [Reported Response (%)] = 11.5668 + 0.0014 x [ATI] (r = 0.97). The response rates for 254-S against SCLC and NSCLC were predicted by this formula to be 40%-65% and 14%-16%, respectively. 254-S is prospectively suspected of having the same, if not more, activity then carboplatin against SCLC and of having almost the same activity as cisplatin against NSCLC.