Dominant mutation in mouse cells associated with resistance to Hoechst 33258 dye, but sensitivity to ultraviolet light and DNA base-damaging compounds

Abstract

A spontaneous derivative of murine L tk- cells has been isolated which has gained a resistance to the cytostatic/lethal effects of high concentrations of Hoechst 33258. The resistant clone HoeR-415 was at least 20-fold more resistant to the dye (D10 dose). HoeR-415 cells have a normal response to X-rays and mitomycin-C and colchicine but were found to show a small sensitivity to UV light, 4NQO, and EMS (1.4, 1.6, and 1.6-fold lower D10 doses, respectively). HoeR-415 cells do not show an increased mutability by EMS. The HoeR phenotype was found to be codominant in hybrids. In order to explain these various characteristics, we suggest that the HoeR-415 mutation may result in an altered topoisomerase activity. Consistent with this we find HoeR-415 cells have an increased sensitivity to novobiocin.

DNA topoisomerases and DNA repair

“…Mouse L cells selected for resistance to the intercalating agent Hoechst 33258 have been found to have increased sensitivity to novobiocin and to UV radiation and some chemical agents, though not to Xrays or the crosslinking agent mitomycin C; it is not certain that topoisomerase activity in these cells is in fact altered. 44 Chinese hamster CHO cells selected for sensitivity to the intercalating agent (and topoisomerase inhibitor) adriamycin show mild crosssensitivity to the radiomimetic agent bleomycin, and vice versa;45 however, it is possible that this reflects only the generation of free radicals by both chemicals.4s A human cell line selected for resistance to the crosslinking agent nitrogen mustard has elevated levels of topoisomerase 11, and increased sensitivity to topoisomerase I1 inhibitors ; exactly how the topoisomerase contributes to the resistance is uncertain. 47 And lastly, cells from patients with the hereditary radiosensitive disease ataxia telangiectasia show a hypersensitivity to both n o v o b i o~i n~~ and et~poside,~' which hints at a topoisomerase involvement in repair of radiation damage ; unfortunately, the nature of the repair defect in this syndrome remains obscure.…”

ABCG2‐associated resistance to Hoechst 33342 and topotecan in a murine cell model with constitutive expression of side population characteristics

“…The Hoechst dye 33258-resistant isolate (HoeR415) is a clonal outgrowth of cells from a Hoechst 33258-treated parental culture and its routine maintenance in RPMI medium has been described previously (28,29,33,34). Resistance was confirmed by a single round of reselection in Hoechst 33342 (1 lM Hoechst 33342 for an 8-day exposure) followed by culture maintenance in dye-free medium.…”

“…Here we have exploited an established clonal variant murine cell line, previously derived by one-step selection resulting in resistance to the MGLs Hoechst dye 33258 (28) and the more lipophilic 33,342 (29). This approach allows for a direct assessment of the extent to which the SP phenotype recruits co-resistance to MGLs, specifically TPT, given that these agents share noncovalent DNA minor groove-binding and topoisomerase I inhibitory properties (16,30,31).…”