Paclitaxel combined with fractionated radiation in vitro: a study with vulvar squamous cell carcinoma cell lines

Concurrent paclitaxel and radiation has given promising results in the treatment of a variety of solid tumors. We wanted to test the efficacy of this combination for vulvar carcinoma, which currently has a poor outcome in advanced stages. The radiation sensitivity, sublethal damage repair (SLDR) capacity and effect of paclitaxel during fractionated radiation were assessed in our study on 7 vulvar inherently radioresistant squamous cell carcinoma (SCC) cell lines. The 96-well plate clonogenic assay was used. Survival data were fitted to the linear quadratic model. The area under the curve (AUC), equivalent to mean inactivation dose (D), was obtained with numerical integration. AUC ratios between single-dose radiation and fractionated radiation with or without paclitaxel were used to determine the SLDR of the cell lines and the effect of paclitaxel on it. Seven currently tested vulvar SCC cell lines were found to have a limited capacity of repairing sublethal damage (SLD). Only 3 of them presented SLDR of significance. The effect of concurrent radiation and paclitaxel was clearly additive when the radiation dose was fractionated in most of the cell lines. In addition, 2 of the cell lines having SLDR exhibited a trend toward losing the repair capacity when paclitaxel was present during the irradiation. In addition, the survival curve of the UM-SCV-1A cell line gave the impression of a true paclitaxel effect on SLDR. Paclitaxel used concurrently with fractionated radiation showed effectiveness on vulvar carcinoma. The effect was at least additive and could even be expected to abrogate the SLDR during split-dose radiation.