Effect of PSC 833, verapamil and amiodarone on adriamycin toxicity in cultured rat cardiomyocytes.

Primary cultures of heart myocytes from neonatal rats were used as an in vitro cardiac cell system to study the effects of the p-170kDa glycoprotein (Pgp) blockers PSC 833 [(3'-keto-Bmt1)-(Val2)-cyclosporine], verapamil and amiodarone on adriamycin cardiotoxicity. Immunostaining revealed the presence of Pgp in the cardiomyocytes. Adriamycin induced a concentration-dependent increase in creatine kinase (CK) leakage, a parameter indicating cell death. None of the Pgp blockers was toxic up to 10 microM, but amiodarone markedly increased CK leakage at 25 microM. 1 microM of the Pgp blockers did not increase adriamycin induced CK leakage, whereas 10 microM of the Pgp blockers significantly augmented adriamycin-induced CK leakage. In parallel, cytoplasmic vacuolization and plasma membrane disruptions were observed. Frequency of contraction of cardiomyocytes, as determined by digital image analysis, was concentration-dependently decreased by adriamycin. 1 microM PSC 833 had no additional effect on contractility, only 10 microM PSC 833 enhanced the impairment of contractility induced by adriamycin. Amiodarone and verapamil alone and in combination with adriamycin already at concentrations of 1 microM completely blocked contractility of cardiomyocytes. The results suggest that the increased toxicity of adriamycin in the presence of amiodarone, verapamil and PSC 833 is mediated by an effective blockage of the Pgp efflux pump. The results further indicate that the combination of adriamycin and PSC 833 might be better tolerated with regard to cardiac side-effects, than the combination of adriamycin and verapamil or amiodarone.