Evaluation of cytotoxicity of vesnarinone causing drug-induced agranulocytosis by a myeloperoxidase-like nonenzymatic metabolic approach using hypochlorous acid and application of the constructed assay method

The involvement of metabolism by myeloperoxidase (MPO) has been reported in drug-induced agranulocytosis (AG). In this study, we investigated whether MPO metabolic reactions could be nonenzymatically mimicked using hypochlorous acid (HClO) and HL-60 cells to generate the reactive metabolite of vesnarinone, a drug known to cause AG, and to detect its cytotoxicity. First, HClO is a strong radical agent and has a direct cytotoxic effect on cells. We tried to reduce its cytotoxicity by using dimethyl sulfoxide (DMSO), which is a solvent but also has the characteristics of a radical scavenger. Thus, the cytotoxicity disappeared when ≥ 20% DMSO was added against HClO. When vesnarinone was reacted under this condition, we observed its concentration-dependent cytotoxicity and converting vesnarinone into two metabolites (metabolite 1 and 2). Next, the presence of reduced glutathione protected its cytotoxicity and converted metabolite 2 into metabolite 1, which were consistent with the MPO reaction. Furthermore, we performed the assessment using this assay system utilizing 12 drugs with different AG incidences. The correlation diagram created between the clinical maximum plasma/serum concentration (Cmax) and the reciprocal concentration of 50% cell viability (1/CV50) was suggested that drugs with high Cmax (≥ 0.062 μg/mL) and strong cytotoxicity (CV50 ≤ 40.9 µM) were related to a clear probability incidence of AG. In conclusion, it was suggested that the constructed HClO test system can be applied to drugs with a clear probability incidence of AG.