Susceptibility of Cells Transformed by Polyoma Virus and Simian Virus 40 to the Cytotoxic Effect of the Carcinogenic Hydrocarbon Benzo[a]pyrene

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Abstract
Clones of hamster cells transformed by polyoma virus (PV) tested at an early time after transformation are susceptible, or have various degrees of resistance, to the cytotoxic effect of benzo[a]pyrene (BP). The frequency of transformed clones with a considerable degree of resistance was similar to that of resistant clones after BP treatment of cloned normal cells. The study of PV-transformed clones at different times after transformation indicates that resistance to the cytotoxic effect of BP increased in the later cell passages. No such increase in resistance was found in subcultures of normal cells. Although the degree of resistance in transformed cells tested at an early time after transformation was not correlated with the cloning efficiency of the cells in liquid and agar medium or the rate of tumor growth after subcutaneous inoculation into adult animals, the increased resistance found at later times after transformation was correlated with an increase in these three properties. The results indicate: 1) Susceptible normal cells remain susceptible when tested at an early time after transformation; 2) transformed cells can be resistant as a result of transformation of cells already resistant as normal cells; and 3) susceptible transformed cells as a secondary change after transformation can give rise to resistant cell variants with a selective advantage in vitro and in vivo. Results obtained with cells transformed by simian virus 40 also indicate the existence of susceptible transformed cells and the selection of more resistant cells at later times after transformation. Resistance to the cytotoxic effect of a carcinogenic hydrocarbon thus doesnot seem to be a good marker for transformation.

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