Disulfiram anti-cancer efficacy without copper overload is enhanced by extracellular H2O2 generation: antagonism by tetrathiomolybdate

Abstract

Highlightsexogenous SOD increases apoptosis by sub-toxic disulfiram without copper overloadH2O2 generation from glucose oxidase also potentiates disulfiram toxicityN-acetylcysteine suppresses antitumor potentiation of DSF by H2O2 generationsub-toxic tetrathiomolybdate inhibits potentiation of DSF by SODBackgroundCu/Zn superoxide dismutases (SODs) like the extracellular SOD3 and cytoplasmic SOD1 regulate cell proliferation by generating hydrogen peroxide (H2O2). This pro-oxidant inactivates essential cysteine residues in protein tyrosine phosphatases (PTP) helping receptor tyrosine kinase activation by growth factor signaling, and further promoting downstream MEK/ERK linked cell proliferation. Disulfiram (DSF), currently in clinical cancer trials is activated by copper chelation, being potentially capable of diminishing the copper dependent activation of MEK1/2 and SOD1/SOD3 and promoting reactive oxygen species (ROS) toxicity. However, copper (Cu) overload may occur when co-administered with DSF, resulting in toxicity and mutagenicity against normal tissue, through generation of the hydroxyl radical (•OH) by the Fenton reaction.PurposeTo investigate: a) whether sub-toxic DSF efficacy can be increased without Cu overload against human melanoma cells with unequal BRAF(V600E) mutant status and Her2-overexpressing SKBR3 breast cancer cells, by increasing H2O2from exogenous SOD; b) to compare the anti-tumor efficacy of DSF with that of another clinically used copper chelator, tetrathiomolybdate (TTM)Resultsa) without copper supplementation, exogenous SOD potentiated sub-toxic DSF toxicity antagonized by sub-toxic TTM or by the anti-oxidant N-acetylcysteine; b) exogenous glucose oxidase, another H2O2 generator resembled exogenous SOD in potentiating sub-toxic DSF.Conclusionspotentiation of sub-lethal DSF toxicity by extracellular H2O2 against the human tumor cell lines investigated, only requires basal Cu and increased ROS production, being unrelated to non-specific or TTM copper chelator sequestration.SignificanceThese findings emphasize the relevance of extracellular H2O2 as a novel mechanism to improve disulfiram anticancer effects minimizing copper toxicity.

Neuroprotective effects of ammonium tetrathiomolybdate, a slow-release sulfide donor, in a rodent model of regional stroke

“…It is further notable that sulfide can increase the activities of Mn-SOD and Cu/Zn-SOD, both by upregulating their gene expression and by direct interaction with Cu/Zn-SOD [49]. Conversely, ATTM has been identified as a SOD inhibitor, a mechanism believed partially responsible for its efficacy as an anti-cancer agent [50]. It hence appears contradictory that ATTM-treatment induced an increase in SOD (and catalase) activity after tMCAO.…”

Hydroxycobalamin catalyzes the oxidation of diethyldithiocarbamate and increases its cytotoxicity independently of copper ions

“…It was found that the active metabolite of DSF when it is used in combination with copper is a dithiocarb-copper complex [17] , [34] . Because this complex can damage normal tissues, different ways to increase the DSF toxicity without the use of copper ions and to protect the adjacent tissues by encapsulating the components into micro- and nanoparticles are developed to date [15] , [35] , [36] .…”

Docosahexaenoic acid and disulfiram act in concert to kill cancer cells: a mutual enhancement of their anticancer actions

“…Recently, its potential as an anticancer drug and as an adjuvant therapy has been tested both in preclinical studies and clinical trials [23, 25–27]. The mechanisms of DSF's anticancer effects are versatile.…”