Biochemical mechanism of acetylsalicylic acid (Aspirin) selective toxicity toward melanoma cell lines.

In the current work, we investigated the biochemical toxicity of acetylsalicylic acid (ASA; Aspirin) in human melanoma cell lines using tyrosinase enzyme as a molecular cancer therapeutic target. At 2 h, ASA was oxidized 88% by tyrosinase. Ascorbic acid and NADH, quinone reducing agents, were significantly depleted during the enzymatic oxidation of ASA by tyrosinase to quinone. The 50% inhibitory concentration (48 h) of ASA and salicylic acid toward SK-MEL-28 cells were 100 micromol/l and 5.2 mmol/l, respectively. ASA at 100 micromol/l was selectively toxic toward human melanocytic SK-MEL-28, MeWo, and SK-MEL-5 and murine melanocytic B16-F0 and B16-F10 melanoma cell lines. However, ASA was not significantly toxic to human amelanotic C32 melanoma cell line, which does not express tyrosinase enzyme, and human nonmelanoma BJ, SW-620, Saos, and PC-3 cells. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, increased ASA toxicity toward SK-MEL-28 cells indicating quinone formation and intracellular GSH depletion played important mechanistic roles in ASA-induced melanoma toxicity. Ascorbic acid, a quinone reducing agent, and GSH, an antioxidant and quinone trap substrate, prevented ASA cell toxicity. Trifluoperazine, inhibitor of permeability transition pore in mitochondria, prevented ASA toxicity. ASA led to significant intracellular GSH depletion in melanocytic SK-MEL-28 melanoma cells but not in amelanotic C32 melanoma cells. ASA also led to significant reactive oxygen species (ROS) formation in melanocytic SK-MEL-28 melanoma cells but not in amelanotic C32 melanoma cells. ROS formation was exacerbated by dicoumarol and 1-bromoheptane in SK-MEL-28. Our investigation suggests that quinone species, intracellular GSH depletion, ROS formation, and mitochondrial toxicity significantly contributed toward ASA selective toxicity in melanocytic SK-MEL-28 melanoma cells.