Radiation survival of two human cervical carcinoma cell lines after multifraction irradiation

Abstract

Purpose : Multifraction irradiation may contribute to radiation therapy treatment failure is selection of radiation resistant subpopulations occurs. We sought to determined whether surviving cells following daily fraction irradiation of two human cervical squamous cell carcinoma lines would express different radiation survival characteristics compared to the unirradiated parent. Methods and Materials : A late-passage line (HTB35) and an early-passage line 9RECA) received daily 2 Gy x-irradiation. Two stable HTB35 cell lines were extablished after 40 and 60 Gy (HTB3540 and HTB3560). A single line was established from RECA after 30 Gy (RECA-30). High dose rate (74 cGy/min) acute radiation survival curves were prepared from the three nre lines and the unirradiated parents. Potentially lethal damage repair (PLDR) and sublethal damage repair (SLDR) responses were detailed for HTB35, HTB3540 and HTB3560. Low dose rate (1.27 cGy/min) survival was measured dfor HTB35 and HTB3560. Clones were derived from HTB35 and from HTB3560 and the survivung fraction at 2 Gy (SF 2) values were determined. Results : The two parent lines (HTB35 and RECA) differed in acute radiation survival. The surviving lines following multifraction irradiation (HTB3540, HTB3560, and RECA) showed no change in acute radiation response compared to the appropriate parent. HTB3540 and HTB3560 were repair proficient, demonstrating similar PLDR anmd SLDR recovery ratios as the parent. Likewise, low dose rate survival of HTB35 and HTB3560 was similar. Nine clones derived deom HTB35 lacked a consistent difference in SF 2 compared to the original culture. A single clone of seven derived from HTB3560 was consistently radiation resistant (SF 2 = 0.81 ± 0.06 compared to the original culture (SF 2 = 0.50 ± 0.09). Conclusion : No evidence was obtained that cell lines generated following multiple daily fractions of x-irradiation in vitro possessed acute radiation survival or repair characteristics that were different from the unirradiated parent.