RADIATION SURVIVAL OF 2 HUMAN CERVICAL-CARCINOMA CELL-LINES AFTER MULTIFRACTION IRRADIATION

Purpose: Multifraction irradiation may contribute to radiation therapy treatment failure if selection of radiation resistant subpopulations occurs. We sought to determine whether surviving cells following daily fraction irradiation of two human cervical squamous cell carcinoma li nes would express different radiation survival characteristics compare d to the unirradiated parent. Methods and Materials: A late-passage li ne (HTB35) and an early-passage line (RECA) received daily 2 Gy x-irra diation. Two new stable HTB35 cell lines were established after 40 and 60 Gy (HTB35-40 and HTB35-60). A single line was established from REC A after 30 Gy (RECA-30). High dose rate (74 cGy/min) acute radiation s urvival curves were prepared from the three new lines and the unirradi ated parents. Potentially lethal damage repair (PLDR) and sublethal da mage repair (SLDR) responses were detailed for HTB35, HTB35-40 and HTB 35-60. Low dose rate (1.27 cGy/min) survival was measured for HTB35 an d HTB35-60. Clones were derived from HTB35 and from HTB35-60 and the s urviving fraction at 2 Gy (SF2) values were determined. Results: The t wo parent lines (HTB35 and RECA) differed in acute radiation survival. The surviving lines following multifraction irradiation (HTB35-40, HT B35-60, and RECA-30) showed no change in acute radiation response comp ared to the appropriate parent. HTB35-40 and HTB35-60 were repair prof icient, demonstrating similar PLDR and SLDR recovery ratios as the par ent. Likewise, acute, low dose rate survival of HTB35 and HTB35-60 was similar. Nine clones derived from HTB35 lacked a consistent differenc e in SF2 compared to the original culture. A single clone of seven der ived from HTB35-60 was consistently radiation resistant (SF2 = 0.81 +/ - 0.06) compared to the original culture (SF2 = 0.50 +/- 0.09). Conclu sion: No evidence was obtained that cell lines generated following mul tiple daily fractions of x-irradiation in vitro possessed acute radiat ion survival or repair characteristics that were different from the un irradiated parent.