Alpha-particle-induced neoplastic transformation in synchronized hybrid cells of HeLa and human skin fibroblasts

Abstract

Abstract. Survival and oncogenic transformation frequencies were determined through the cell cycle in hybrid cells (HeLa human skin fibroblasts), exposed to 0.30 and 0.15 Gy 4.3 MeV (LET 101 keV/ mu m) alpha -particles. The cells were synchronized by mitotic collection and irradiated at times ranging from 2 to 10 h after collection, corresponding to G1 and early S. At 0.30 Gy the highest value in the transformation frequency (1.6 0.3)*10 -4 transformants/survivor, occurred 4 h after mitotic collection, corresponding to mid-G1 and was about twice as high as that for the asynchronous population (0.7 0.1)*10 -4 transformants/survivor. A similar pattern was seen at 0.15 Gy albeit less marked. The results are similar to previous findings with C3H10T1/2 exposed to 0.30 Gy where (1.8 0.4)*10 -4 and (0.8 0.4)*10 -4 transformants/survivor were found in mid-G1 and in the asynchronous population respectively. The results of both these studies with 101 keV/ mu m alpha particles indicate that mid-G1 cells may be more sensitive than asynchronous cells by up to a factor of two. However, it is unlikely that such a factor is sufficient to represent the cell cycle 'hot spot' for transformation postulated to explain the inverse dose-rate effect.