Novel phenotypes arising from selection of hamster melanoma cells for resistance to BUdR

Abstract

Pigmented clones of the Syrian hamster melanoma line RPMI 3460 were selected for resistance to high levels of the thymidine analogue 5-bromodeoxyuridine (BUdR). The resistant lines obtained were characterized as to the percentage of thymidine residues in nuclear DNA replaced by BUdR (BUdR substitution), the level of in vitro thymidine kinase (EC 2.7.1.75) (TK) activity the ability to utilize exogenous thymidine for growth, and pigmentation. In contrast to the BUdR resistant cells generally reported in the literature, most of the lines isolated in this study have large amounts of BUdR in their nuclear DNA and/or high levels of TK activity. The ability of the cells to utilize exogenous thymidine was found to correlate well with the level of BUdR substitution. However, there was a definite lack of correlation between the level of in vitro TK activity and the level of BUdR-substitution. Further, the phenotypes of the cells selected in 10 −4 M BUdR appear to be to some extent clonally determined.