Disulfiram, An Old Drug with New Potential Therapeutic Uses for Human Haematological Malignancies

Proteasome is a novel, interesting target in cancer drug therapy, and the proteasome inhibitor Bortezomib has been used for its antitumor activity in multiple myeloma and other lymphoid malignancies. The commonly used thiocarbamate alcohol-abuse deterrent disulfiram (DSF) is an aldehyde dehydrogenase (ALDH) inhibitor with documented proteasome-inhibiting activity. Recent reports indicate that DSF and other dithiocarbamates may have a significant potential in the treatment of human cancer without significant side effects. It was previously shown that this compound is able to block the P-glycoprotein extrusion pump, to inhibit the transcription factor nuclear factor-kappaB (NF-kB), to sensitize tumors to chemotherapy, to reduce angiogenesis, and to inhibit tumor growth in mice. In addition a recent work has described several compounds with proteasome-inhibiting activity, among which in the hit was DSF. Here we show that MM (18 samples), AML (14 samples) and ALL (5 samples) primary cells from newly diagnosed and relapsed/resistant patients were significantly sensitive to DSF at doses < 5 mM (dose achievable in vivo). Median IC50 was DSF 0,5 mM for MM and DSF 0,35 mM for AML and r ALL samples after 48 hours of incubation. These cells are ALDH weakly positive and we did not find any difference in the sensitivity to DFS on the basis of amount of ALDH expression or status of disease (diagnosis vs relapse). Conversely, DSF, at the dose of 0,5 mM had only a weak effect on normal CD34 and peripheral blood mononuclear cells (<30% of cell death). We next exposed the cells to the combination of low dose DCF (0,5 mM) plus CuSO4 (another commonly used herbal medicinal product, that makes complex with DCF and reduces the superoxide dismutase, an enzyme involved in the mitochondrial depolarization) and we found that this combination was able to induce about 80–90% of cell death after 48 hours of treatment. The apoptotic effect of the combination (DSF plus CuSO4 0,5 mM) was comparable to that exert by therapy with Bortezomib plus Desametazone for MM samples, Cytarabine, Etoposide, Daunorubicine alone or in combination for AML samples or Vincristine, Desametazone and Daunorubicine alone or in combination for ALL samples. All these drugs were used in vitro at doses compatible with the levels reached in vivo during cancer treatment. In addition we show that DSF plus CuSO4 induce loss of mithocondrial membrane potential thus suggesting the involvement of mitochondrial apoptotic pathway. These results may suggest a novel strategy for treating multiple myeloma and acute leukemias by employing an old drug, with known and mild side-effect, toward a new therapeutic use, probably in combination with other agents.