Enhancement Effects of High-Energy Neon Particles on the Viral Transformation of Mouse C3H1OT1/2 Cells in Vitro

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Abstract
The enhancement effects of X-rays and high-LET [linear energy transfer] particles on the viral transformation of cultured mammalian cells were studied. Confluent mouse [embryo] C3H1OT1/2 cells, X-irradiated immediately after infection with SV-40, showed a higher frequency of transformation than cells infected only with the virus. The enhancement of viral transformation appeared to be dose-dependent and more than additive. The number of transformations per cell increased with dose and reached a maximum at about 300 rad. The frequency of transformation per survivor was enhanced linearly with the square of the X-ray dose. Compared to X-rays, neon particles with a residual range of 12.7 g/cm2 in water were much more efficient in enhancing the viral transformation of cells. The number of transformants per plated cell reached a peak around 200 rad. The RBE [relative biological effectiveness] for enhancing the frequency of transformation per survivor appeared to vary with dose, being higher at lower dose. For the 50% survival level dose of neon ions, the RBE was about 2.28 compared to about 1.84 for the 10% survival level dose. A decrease in the enhancement effect was found as the interval between the irradiation and viral infection was extended. This suggests that the cells in the G1 phase can repair the radiation-induced lesions that are responsible for the observed increase of transformation. The recovery rate for cells irradiated with neon ions, however, was much slower than that for cells irradiated with X-rays.