Cytotoxicity studies on some novel 2,6-dimethoxyhydroquinone derivatives.

Six synthetic 2,6-dimethoxyhydroquinone derivatives were shown to have different degrees of cytotoxicity to two human tumor cell lines (KB and PC-9) under the synergistic activation of L-ascorbic acid. Two representative compounds displayed very low time-schedule-independent index, showing that the cytotoxic action is independent of time of drug treatment. The addition of catalase produced a significant inhibitory effect on the cytotoxicity of two representative compounds, indicating that the cytotoxic action is mediated by the generation of H2O2, which may yield hydroxyl radicals via various mechanisms. ESR studies employing the spin-trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) showed that massive hydroxyl radicals were generated from four of these drugs as a non-linear function of L-ascorbic acid concentration. The results indicate the possible involvement of hydroxyl radicals in the cytotoxic action of these novel drugs.