Amidization of doxorubicin alleviates doxorubicin-induced contractile dysfunction and reduced survival in murine cardiomyocytes.

Doxorubicin is an effective anthracycline used for cancer therapy. However, the clinical application of doxorubicin has been largely limited by its irreversible cardiotoxicity, which is mainly induced by the primary amine group. In this study, we structurally modified doxorubicin by converting the primary amine into an acid-labile amide before assessing the acute cardiac effect of doxorubicin (pristine or modified) on cardiomyocyte contractile function. Contractile properties of murine cardiomyocytes were analyzed including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90)) and maximal velocity of shortening/re-lengthening (+/-dL/dt). Cell toxicity and survival rate were evaluated using the MTT assay. The doxorubicin-free base was amidized by reacting with 3,4,5,6-tetrahydophthalic anhydride (THPA) or 3,3,4,4-tetramethylsuccinic anhydride (TMSA) to yield doxorubicin-THPA or -TMSA. Acute exposure of pristine doxorubicin (10(-9)-10(-5)M) for 30 min significantly prolonged TPS and TR(90) without affecting PS and +/-dL/dt. Interestingly, doxorubicin-induced prolongation of TPS and TR(90) was significantly attenuated or abrogated by amidization of doxorubicin. Neither doxorubicin-THPA nor -TMSA affected PS and +/-dL/dt. ROS and MTT assay revealed significantly reduced ROS production and cardiac cell toxicity from amidized doxorubicin compared with the pristine compound. Comparable cytotoxicity in human ovarian cancer SKOV-3 cells was observed between amidized and pristine doxorubicin compounds. These data provide evidence for the first time that structural modification of doxorubicin alleviates its cardiac toxicity.