Pu-238 alpha-particle-induced C3H10T1/2 transformants are less tumorigenicthan the X-ray-induced equivalent

Transformation is a complex multistage process in vitro by which benign cel ls gradually acquire characteristics of tumour cells. Transformed C3H10T1/2 cells appear in vitro as multilayers of cells termed foci. A variety of tr ansformed phenotypes are observed in vitro and in this study samples of the se phenotypes were developed as cell lines and assessed for their ability t o induce tumours in C3H mice. It was found that, while a high proportion of X-ray-induced transformants were tumorigenic, most of the alpha-particle-i nduced transformants were non-tumorigenic. Although tumours produced by the X-ray-induced transformants appeared earlier, they grew at similar rates t o the alpha-particle-induced equivalent. Foci were classified as fully or p artially tumorigenic depending on whether the foci produced at least one tu mour in the mice injected (partially tumorigenic) or produced tumours in al l mice injected (fully tumorigenic). It was found that tumours from the par tially tumorigenic foci grew slower or appeared later than those of the ful ly tumorigenic foci. It is hypothesized that the apparent low tumorigenicit y of positively transformed alpha-particle-induced foci is due to an increa se in genomic instability of progeny focus cells compared with Xray-induced foci leading to a larger non-viable population of cells in the alpha-parti cle-induced foci.