Effect of ultraviolet irradiation on the antitumor activity of bleomycin.

The effect of bleomycin (BLM) on the growth of the tumor, murine B16 melanoma, implanted onto the chorioallantoic membrane of chick embryo was examined. The inhibition ratio of BLM was about 30% at 3 micrograms/egg. This inhibitory effect of BLM on the growth of the tumor was enhanced by an appropriate dose of ultraviolet (UV) irradiation. The inhibition ratios of BLM irradiated for 10, 30 and 60 min were in order of about 50, 30 and 30% at 3 micrograms/egg. However, when these BLMs pretreated with 1 mM 1,2-benzenediol (catechol) were administrated, the inhibition ratios of BLM irradiated for 0, 10, 30 and 60 min were about 30, 20, 10 and 10%, respectively. On the other hand, the direct cytotoxicity of BLM to cultured murine B16 melanoma cells was depressed with UV irradiation and its toxic activity was further decreased by treatment with catechol after irradiation. These findings show that, although the antitumor activity of BLM is enhanced by UV irradiation, the activity of UV-irradiated BLM is inhibited by catechol. Moreover, it seems to show that the present results may provide a useful manner for the in vivo activation of BLM.