Cell Death-Inducing Activity by Gallic Acid Derivatives

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In this study, the cytotoxic activity of gallic acid derivatives (GDs) was studied using some cancer cell lines.Among them, 3, 4-methylenedioxyphenyl 3, 4, 5-trihydroxybenzoate (GD-1) and S-(3, 4-methylenedioxyphenyl)-3, 4, 5-trihydroxy-thiobenzoate (GD-3) were found to induce cell death in cancer cell lines with IC₅₀s ranging from 2.9 to 114.4 μM, a concentration comparable with or lower than that of gallic acid. On the other hand, although gallic acid did not show any cytotoxicity against primary cultured rat hepatocytes and human keratinocytes, GD-1 and -3 showed slightly higher sensitivity against such normal cells, when compared with gallic acid. The cell death induced by gallic acid and GD-1 was accompanied by internucleosomal DNA fragmentation characteristic of apoptosis, whereas only smear DNA degradation was detected following GD-3 treatment. When the mechanism by which GD-1 and -3 caused cell death in HL-60RG cells was examined, GD-1 and -3-induced cell death was inhibited by the intracellular Ca²⁺ chelator, bis-(o-aminophenoxy)-N, N, N, N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM), calmodulin inhibitor, W-7, and the Ca²⁺/MG²⁺-dependent endonuclease inhibitor zinc sulfate. In contrast, catalase, N-acetylcysteine (NAC), and ascorbic acid inhibited gallic acid-induced apoptosis in HL-60RG cells, whereas they had no effect on GD-1- and -3-induced cell death. This result suggests that GD-1 and -3 induced cell death in a different manner to gallic acid. In conclusion, esterification of gallic acid with a 3, 4-methylenedioxyphenyl group yielded potent agents to treat cancer with a different signaling pathway from gallic acid, although selectivity was lost.