Murine L5178Y cells resulting in altered drug sensitivities from fractionated radiation exposure in vitro.

Exposure of murine L5178Y cells in vitro to fractionated X-irradiation (DXR) produced a subline that exhibited significantly altered responses to the cytotoxic effects of a range of antitumor drugs. A DXR schedule of 2 Gy per fraction for 10 fractions (total dose, 20 Gy) was used. Characterization of this subline revealed no marked differences when compared with the parent line in terms of growth rate, cloning efficiency, cell volume, chromosome number, macromolecular content, cell cycle distribution, or response to acute DXR exposure. Drug sensitivities were assessed following 24-hour exposures by colony formation in soft agar. Three distinct patterns of response were found: increased sensitivity of DXR-pretreated cells to bleomycin, cis-diamminedichloroplatinum (II), or dibromodulcitol; comparable responses in both lines to doxorubicin, 5-fluorouracil, or hydroxyurea; and decreased sensitivity of DXR-pretreated cells to vincristine or VP 16213.