tetrathiomolybdate and Melanoma

Cu/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.. To 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 H2O2 from exogenous SOD; b) to compare the anti-tumor efficacy of DSF with that of another clinically used copper chelator, tetrathiomolybdate (TTM).. a) 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.. potentiation 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.. These findings emphasize the relevance of extracellular H2O2 as a novel mechanism to improve disulfiram anticancer effects minimizing copper toxicity.

Topics: Acetylcysteine; Antineoplastic Agents; Blotting, Western; Breast Neoplasms; Cell Line, Tumor; Cell Survival; Chelating Agents; Copper; Disulfiram; Free Radical Scavengers; Humans; Hydrogen Peroxide; MAP Kinase Signaling System; Melanoma; Molybdenum; Mutation, Missense; Proto-Oncogene Proteins B-raf; Reactive Oxygen Species; Receptor, ErbB-2; Superoxide Dismutase

Melanoma cells characteristically produce increased levels of reactive oxygen species (ROS) because of the metal-binding properties of melanin and loss of structural integrity of the melanosome. Agents that deplete gluthathione or inhibit superoxide dismutase, thereby blocking ROS scavenging mechanisms, may be selectively toxic to melanoma. To determine whether the inhibition of ROS scavenging could potentiate alkylator activity, we evaluated the activity of tetrathiomolybdate (ATN-224), a superoxide dismutase inhibitor, alone and in combination with temozolomide, on five melanoma cell lines. We also determined whether the ATN-224 would act synergistically with other agents that interfere with ROS scavenging. We found that the combination of ATN-224 and temozolomide generally exhibited additive cytotoxic effects on the cell lines tested. ATN-224 acted synergistically with buthionine sulfoximine, an agent that causes gluthathione depletion. Combinations of ATN-224 with arsenic trioxide, which may deplete glutathione, or disulfiram, an agent that interferes with recycling of glutathione, were antagonistic. These data suggest that strategically tailoring combination regimens that include ATN-224 and target ROS may be a viable approach to advance the treatment of melanoma.

Topics: Antineoplastic Agents; Apoptosis; Arsenic Trioxide; Arsenicals; Buthionine Sulfoximine; Cell Line, Tumor; Cell Proliferation; Dacarbazine; Disulfiram; Drug Synergism; Enzyme Inhibitors; Glutathione; Humans; Melanins; Melanoma; Molybdenum; Oxidation-Reduction; Oxides; Reactive Oxygen Species; Superoxide Dismutase; Temozolomide

Melanoma is a highly invasive tumor with elevated mortality rates. Progression and aggressiveness appear related to the achievement of an angiogenic phenotype. Melanoma cells express several angiogenic factors, including fibroblast growth factor (FGF)-1 and FGF-2. The autocrine production and release of FGFs and the subsequent activation of FGF receptors, have a central role in melanoma tumor progression. We demonstrated that FGF-1 is secreted from a human melanoma cell line, A375, under conditions of serum deprivation. The release of FGF-1 is inhibited by the copper chelator ammonium tetrathiomolybdate, suggesting a role of copper in the secretory pathway, and is triggered by activation of phosphatidylinositol 3-kinase (PI3K)/Akt intracellular signaling. Interestingly, overexpression or activation of Akt has been correlated with poor prognosis in melanoma patients. Our data indicate a novel role for Akt in supporting the progression of human melanomas and advocate the need for new treatments targeting PI3K/Akt signaling pathway, to control tumor development and progression.

Topics: Cell Line, Tumor; Copper; Culture Media, Serum-Free; Fibroblast Growth Factor 1; Gene Expression Regulation, Neoplastic; Humans; Ions; Melanoma; Molybdenum; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Signal Transduction