Potentiation of anti-cancer drug activity at low intratumoral pH induced by the mitochondrial inhibitor m-iodobenzylguanidine (MIBG) and its analogue benzylguanidine (BG)
The quinone antitumor agent mitomycin C is preferentially toxic to some cells under hypoxic and acidic conditions. The two-electron reducing enzyme DT-diaphorase may be a major contributor to mitomycin C activation under aerobic conditions, but its role in drug activation under hypoxic and acidic conditions is unclear. In this study, we observed that mitomycin C produced increased DNA cross-linking and cytotoxicity in Chinese hamster ovary cells at pH 6.6, compared with pH 7.2, under aerobic conditions, but drug activity was similar at these pH values under hypoxic conditions. The DT-diaphorase inhibitor dicoumarol completely inhibited the enhanced activity of mitomycin C at acidic pH under aerobic conditions but had no effect on DNA cross-linking or cytotoxicity under hypoxic conditions. These finding suggest that the enhanced activity of mitomycin C at acidic pH, in air, is due to increased drug activation by DT-diaphorase. However, the role of DT-diaphorase in activating mitomycin C under hypoxic conditions appears to be limited, even at acidic pH.