Suppression of the radiation-induced expression of a tumor-associated antigen in human cell hybrids by the protease inhibitor antipain

The effect of the protease inhibitor antipain (1.25 μg/ml) on the radiation-induced expression of a tumor-associated antigen in human cell hybrids has been investigated. A variety of treatment protocols have been studied where antipain was present before, during and at various times post-irradiation. It was found that antipain suppressed the radiation-induced expression of the tumor-associated antigen in all treatment protocols. The most effective suppression was obtained in those protocols where the protease inhibitor was present for the first 4 h post-irradiation. A possible explanation for this observation is that antipain may inhibit an error-prone DNA repair process. However, it is clear that this is not the only mechanism whereby the inhibitor can exert its effect since suppression was obtained even when antipain was added 10 days post-irradiation, a time when any DNA repair processes would be expected to be over.