Vitro photodynamic induction of a tumor virus

Infectious simian virus 40 (SV40) was induced from SV40-transformed hamster kidney cells by photodynamic treatment of the cells with proflavine and visible light. For photodynamic treatment the cells were incubated with proflavine (2 μm) and exposed to visible light for different times. Following the inducing treatment, the cells were incubated to permit virus expression, and homogenized. Cell extracts were assayed in monkey kidney cells for SV40 plaque forming units. The response curves were compared with those produced with virus induction by 254 nm ultraviolet radiation alone. The maximum stimulation of virus production above background levels (approximately a thousand-fold) that resulted from photodynamic induction was greater than that obtained with induction by ultraviolet radiation. When the visible light exposure time was held constant and proflavine concentration varied, the effective concentrations for induction were found to be 0.5 to 7 μm. No virus induction above background levels was obtained with untreated cells or cells treated with either proflavine or visible light alone