Supra-additive effect with concurrent paclitaxel and cisplatin in vulvar squamous cell carcinoma in vitro

The effect of concurrent paclitaxel and cisplatin was tested in vitro in 5 vulvar squamous cell carcinoma (SCC) cell lines (UM-SCV-1A, -2, -4 and -7 and UT-SCV-3). Chemosensitivity was tested using the 96-well plate clonogenic assay. Paclitaxel concentrations used varied between 0.4 and 1.6 nM, and cisplatin concentrations varied between 0.1 and 0.9 microg/ml. These drug concentrations are clinically achievable. Survival data were fitted to the LQ model, and the area under the curve (AUC) value was obtained with numerical integration. The type of interaction was determined by comparing the AUC ratio of the 2 drugs with the survival fraction (SF) of paclitaxel alone. With all cell lines tested the growth-inhibitory effect of simultaneous paclitaxel and cisplatin was at least additive. The effect of the tested combination on the UM-SCV-1A and UT-SCV-3 cell lines was clearly supra-additive with all paclitaxel concentrations tested, and the UM-SCV-4 and UM-SCV-7 cell lines exhibited a supra-additive effect with increasing paclitaxel concentrations. The degree of supra-additivity was dose-dependent in the UM-SCV-7 cell line with increasing synergy at higher paclitaxel doses. In the current study the combination of paclitaxel and cisplatin had a clear additive or supra-additive cytotoxic effect on the vulvar SCC cell lines, and it has been successfully used in other gynecologic malignancies; therefore concurrent paclitaxel and cisplatin also deserves further testing in clinical settings in advanced-stage vulvar carcinoma, which has a poor prognosis.