Pharmacokinetic characterization of amrubicin cardiac safety in an ex vivo human myocardial strip model. I. Amrubicin accumulates to a lower level than doxorubicin or epirubicin.

Antitumor anthracyclines such as doxorubicin and epirubicin are known to cause cardiotoxicity that correlates with anthracycline accumulation in the heart. The anthracycline amrubicin [(7S,9S)-9-acetyl-9-amino-7-[(2-deoxy-β-d-erythro-pentopyranosyl)oxy]-7,8,9,10-tetrahydro-6,11-dihydroxy-5,12-napthacenedione hydrochloride] has not shown cardiotoxicity in laboratory animals or patients in approved or investigational settings; therefore, we conducted preclinical work to characterize whether amrubicin attained lower levels than doxorubicin or epirubicin in the heart. Anthracyclines were evaluated in ex vivo human myocardial strips incubated in plasma to which anthracycline concentrations of 3 or 10 μM were added. Four-hour incubations were performed to characterize myocardial anthracycline accumulation derived from anthracycline uptake in equilibrium with anthracycline clearance. Short-term incubations followed by multiple washouts were performed to obtain independent measurements of anthracycline uptake or clearance. In comparison with doxorubicin or epirubicin, amrubicin attained very low levels in the soluble and membrane fractions of human myocardial strips. This occurred at both 3 and 10 μM anthracycline concentrations and was caused primarily by a highly favorable clearance of amrubicin. Amrubicin clearance was facilitated by formation and elimination of sizeable levels of 9-deaminoamrubicin and 9-deaminoamrubicinol. Amrubicin clearance was not mediated by P glycoprotein or other drug efflux pumps, as judged from the lack of effect of verapamil on the partitioning of amrubicin and its deaminated metabolites across myocardial strips and plasma. Limited accumulation of amrubicin in an ex vivo human myocardial strip model may therefore correlate with the improved cardiac tolerability observed with the use of amrubicin in preclinical or clinical settings.