Paclitaxel is only a weak radiosensitizer of human cervical carcinoma cell lines

Two human squamous cell cervical carcinoma cell lines, C-33A (HTB 31) and MS751 (HTB 34), were exposed to either paclitaxel alone or paclitaxel for 24 hr followed by graded doses of Cs-137 radiation. Each was then analyzed for both clonogenic survival and alterations to cell cycle progression. No radiosensitization or affect on the cell cycle was seen using 1 x 10^-9 M paclitaxel. Each line was equally sensitive to the drug with approximately 50% cell lethality seen after 1 x 10^-8 M of paclitaxel. This concentration of paclitaxel also produced substantial G₂M arrest, seen immediately after drug exposure and lasting up to 2 days. Gamma radiation delivered during the time of G₂M arrest showed only a small degree of radiosensitization by paclitaxel for the relatively radioresistant MS751 line at 4 Gy (SF₄ = 16.0 ± 3.2% → 5.7 ± 1.1%, P = 0.049) but no sensitization using radiation doses of conventional fraction size [sensitizer enhancement ratios 1.1 (0.80-1.40) and 1.3 (0.95-1.65) for the C-33A and MS751 cell lines, respectively]. It is concluded that paclitaxel produces only a modest radiosensitization effect, indicating that this compound will have limited benefit as a radiosensitizer for the treatment of cervical cancer.