The alcohol aversion
drug disulfiram (DSF) reacts and conjugates with the
protein-bound nucleophilic cysteines and is known to elicit anticancer effects alone or improve the efficacy of many
cancer drugs. We investigated the effects of DSF on human
O(6)-methylguanine-DNA methyltransferase (MGMT),
a DNA repair
protein and
chemotherapy target that removes the mutagenic O(6)-akyl groups from guanines, and thus confers resistance to
alkylating agents in
brain tumors. We used DSF,
copper-chelated DSF or CuCl2-DSF combination and found that all treatments inhibited the MGMT activity in two
brain tumor cell lines in a rapid and dose-dependent manner. The
drug treatments resulted in the loss of MGMT
protein from
tumor cells through the
ubiquitin-
proteasome pathway. Evidence showed that Cys145, a reactive
cysteine, critical for DNA repair was the sole site of DSF modification in the MGMT
protein. DSF was a weaker inhibitor of MGMT, compared with the established O(6)-benzylguanine; nevertheless, the 24-36h suppression of MGMT activity in cell cultures vastly increased the alkylation-induced
DNA interstrand cross-linking, G2/M cell cycle blockade, cytotoxicity and the levels of apoptotic markers. Normal mice treated with DSF showed significantly attenuated levels of MGMT activity and
protein in the liver and brain tissues. In nude mice bearing T98
glioblastoma xenografts, there was a preferential inhibition of
tumor MGMT. Our studies demonstrate a strong and direct inhibition of MGMT by DSF and support the repurposing of this brain penetrating
drug for
glioma therapy. The findings also imply an increased risk for alkylation damage in alcoholic patients taking DSF.