Paclitaxel: a radiation sensitizer of human cervical cancer cells

Paclitaxel is an exciting chemotherapeutic agent active in a variety of malignant tumors. This study was designed to explore the radiosensitizing potential of paclitaxel in human cervical cancer cell lines. The cell lines ME180, SiHa, and MS751 were evaluated. Experiments were performed in the proliferative phase of growth. Paclitaxel doses were treated at 0.01x, 0.02x, 0.03x, 0.04x, and 0.05x peak plasma concentration (PPC) in ME180 and 0.001x, 0.002x, 0.003x, 0.004x, and 0.005x PPC in SiHa and MS751. Radiation (RT) doses of cobalt-60 were 0, 2, 4, 6, 8, and 10 Gy. In the combination group RT was given 48 hr after paclitaxel treatment. To allow for median effect analyses, combination doses were kept at a fixed ratio: 0.01x/2 Gy, 0.02x/4 Gy, 0.03x/6 Gy, 0.04x/8 Gy, and 0.05x/10 Gy for ME180 and 0.001x/2 Gy, 0.002x/4 Gy, 0.003x/6 Gy, 0.004x/8 Gy, and 0.005x/10 Gy in MS-751 and SiHa. Adenosine triphosphate bioluminescence was performed on Day 7 after treatment and compared to untreated controls. Dose-response data were fit to the linear quadratic model and mean inactivation dose D was calculated. Data analysis with t test was performed. The median effect principle was used to evaluate the nature of the interaction between the two therapeutic modalities. Paclitaxel increased radiation cytotoxicity in all three cell lines. Mean inactivation D values for RT versus combination were 6.70 (+/- 0.15) and 4.33 (+/- 0.43) (P = 0.004) in ME180, 6.08 (+/- 0.70) and 4.54 (+/- 0.093) (P = 0.033) in MS751, and 7.03 (+/- 0.46) and 5.97 (+/- 0.51) (P = 0.034) in SiHa. The interaction of paclitaxel and RT was found to be supraadditive in ME180 and SiHa and subadditive in MS751. We conclude that paclitaxel has modest radiation-sensitizing effects in cervical cancer cell lines and that further clinical trials should be considered.