Inhibitory effect of pheophorbide a, a chlorophyll-related compound, on skin tumor promotion in ICR mouse

Anti-tumor-promoting activity of pheophorbide a (PPBa), a chlorophyll-related compound, was examined in a two-stage carcinogenesis experiment in ICR mouse skin by 7,12-dimethylbenz[a]anthracene (DMBA, 0.19 mu mol) and 12-O-tetradecanoylphorbol-13-acetate (TPA, 1.6 nmol). Topical application of PPBa (160 nmol) markedly reduced the average number of tumors per mouse and the ratio of tumor-bearing mice (inhibitory ratio: IR = 56%, P < 0.01 and 31%, P < 0.005, respectively). PPBa exhibited potent anti-inflammatory activity in ICR mouse ears and moderate inhibitory activity toward TPA-induced superoxide (O-2(-)) generation in differentiated HL-60 cells. While CuPPBa, a synthetic copper complex of PPBa, exhibited higher anti-inflammatory activity than that of indomethacin, it showed little antioxidative effect against formation of lipid hydroperoxides (LOOHs) and malondialdehyde (MDA), suggesting that the antioxidative effect of PPBa might not be important for anti-inflammatory activity. These results imply that the active mechanism of PPBa for anti-tumor promotion might be partly involved in inhibition of TPA-induced inflammatory responses by suppressing leukocyte activation.