The effect of γ-irradiation on the enzymatic and antitumor activity of papain has been studied. It has been shown that irradiation with a dose of 2.5 kGy does not affect the enzymatic activity of papain. However, irradiation with doses of 5 kGy and higher reduces the efficiency of cleavage of bovine serum albumin. In vivo experiments on mice with lymphocytic leukemia P388 showed no increase in survival when administered either the original papain or its irradiated samples as monotherapy. Combination use of unirradiated or irradiated papain with the cytostatic drug cyclophosphamide, administered at a low subtherapeutic dose, significantly enhanced the antitumor effect. The greatest antitumor effect was obtained with the combined use of cyclophosphamide with nonirradiated papain, the second most effective was the combination with papain irradiated with a dose of 1000 kGy, and the third most effective was the combination with papain irradiated with a dose of 2000 kGy.
Raevskaya et al. (Sun,) studied this question.
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