0015 : Epac signalling in doxorubicin-induced cardiotoxicity: a novel implication in death pathways

The main mechanisms underlying doxorubicin (Dox)-induced cardiotoxicity involve classically reactive oxygen species generation, DNA intercalation and topoisomerase II (TopII) inhibition which lead ultimately to cardiomyocyte death. However, new signalling pathways are now emerging. β-adrenergic signalling with Epac (exchange protein directly activated by cAMP) implication could be worth investigating as Epac activates small G proteins (Rac1, Rho) known to be involved in dox-induced cardiotoxicity. Therefore, we have investigated the Epac role in Dox cardiotoxicity in both in vivo (C57Bl63/ Knock-out Epac1 mice, iv injections, 12mg/kg cumulative dose) and in vitro model (primary culture of neonatal rat cardiomyocytes (NRVM), 24h, Dox 1μM). In vivo, long-term follow up showed the development of dilated cardiomyopathy (DCM) 15 weeks post treatment associated with Ca2+ homeostasis dysfunction in Dox-treated mice. We also observed a time-dependent modulation of Epac1, Epac2, Rho A and Rac1 expression with alterated, compensated and final decompensated phase at, 2, 6 and 15 weeks respectively. In vitro, Dox treatments led to a global alteration of Epac signalling: Dox treatment led to a reduced Epac 1 / 2 expressions while Epac1 activity is increased. Dox also decreased Rap1 and Rac1 expression and activities. Moreover, the inhibition of Epac1 (ESI09, CE3F4, shEpac1), but not Epac2, prevented Doxinduced DNA-TopIIβ cleavable complex/DNA damage in part by TopIIβ downregulation. We also reported that Dox induces cell death in cardiomyocytes through activation of the mitochondrial caspase dependent apoptotic pathway which as again prevented by specific EPAC1 inhibition. These results were confirmed in vivo as Dox-induced cardiotoxicity was prevented in Epac1 KO as evidenced by lack of DCM, alteration of cardiac function and calcium homeostasis (15 weeks). In conclusion, Epac could be a valuable therapeutic target to prevent Anthacyclines-induced cardiomyopathy. The author hereby declares no conflict of interest