Dissimilar effects of stereoisomers and racemic hydroxychloroquine on Ca(2+) oscillations in human induced pluripotent stem cell‐derived cardiomyocytes

All currently employed pharmaceutical formulations of hydroxychloroquine (HCQ) sulfate are a racemate, consisting of equal parts mixture of two stereoisomers: R(−)HCQ and S(+)HCQ sulfates. The aims of the current study were first, to obtain and characterize pure HCQ enantiomers. The separation and purification of free base HCQ enantiomers from the racemate form were performed using semi‐preparative chiral high‐performance liquid chromatography. Second, we compared the pharmacological properties of both optical isomers and racemic mixture on the intracellular Ca(2+) oscillations employing an in vitro model of human cardiomyocytes derived from induced pluripotent stem cells (iPSCs). The results of the pharmacological investigations indicate that the racemic and pure stereoisomer forms of HCQ sulfate exhibited a dose‐dependent inhibition of spontaneous Ca(2+) oscillations (as measured from their frequency and Ca(2+) peak widths) in cardiomyocytes 5–45 min following exposure. In addition, the concentration‐response relationships for all three compounds indicated that the rank order of potency (IC(50)) was R(−)HCQ >racemic HCQ >S(+)HCQ for the frequency of the Ca(2+) oscillations and width of Ca(2+) peaks for all time points examined. These studies indicate that both R(−) and S(+) stereoisomers exhibit differing pharmacological actions on hiPSC cardiomyocytes, with the former effecting a greater potency on cell Ca(2+) handling.