Production of altered cell foci by 3-methylcholanthrene in mouse cells infected with AKR leukemia virus.

This report describes altered cell foci observed 9-14 days after treatment with 3-methylcholanthrene of mouse-embryo tissue cultures that had previously been infected with wild-type AKR (RNA tumor) virus. The foci consisted of randomly oriented, piled-up, spindle-shaped cells. When heavily stained with Giemsa, the colonies of transformed cells were grossly visible and countable. Under the same experimental conditions, such changes of morphology were not detectable in the uninfected cells treated with 3-methylcholanthrene or in untreated cells infected with virus. The procedure may provide a rapid, quantitative test system for measurement of the oncogenic potential of certain carcinogens. As in similar previous studies in rat and hamster cells, the results suggest that the infectious, but nontransforming, RNA tumor viruses provided nascent oncogenic information, which when activated by 3-methylcholanthrene served as the specific genetic determinants of transformation.