Abstract 1705: Cardiac Myocyte Multidrug Resistance Membrane Protein P-Glycoprotein Expression and Anthracycline Resistance is Mediated by Microvascular Endothelial Cell Paracrine Signaling
Objectives: Expression of the ABC-type multidrug resistance membrane protein P-glycoprotein (MDR1) in cardiac myocytes is known to modulate drug responses, including the cardiotoxicity of anthracyclines. However the mechanisms that regulate expression and activity of these transport proteins in the heart is unknown. We therefore examined in vitro and in vivo regulation of cardiac MDR1 expression by the p-glycoprotein substrate Doxorubicin (Dox).
Methods: C57BL/6 mice, isolated adult rat ventricular myocytes (ARVM) and cardiac microvascular endothelial cells (CMEC) were treated with Dox. MDR1 expression was examined by immunoblot, and activity measured by examining Dox uptake into isolated cells.
Results: Untreated mouse heart, and isolated ARVM and CMEC showed only low levels of MDR1 expression. Intraperitoneal injection of Dox (10 mg/kg) induced >10-fold upregulation of mouse cardiac P-glycoprotein expression 48 hours after treatment. Dox (1μM) treatment induced similar upregulation of MDR1 expression in isolated CMEC within 18 hours of treatment. However Dox did not induce MDR1 expression in ARVM, except when ARVM were co-cultured with CMEC using a trans-well system. In co-culture, the media [Dox] 24 hours after treatment was increased by 1.8-fold compared with mono-cultured ARVM at the same cell density, consistent with a more active Dox efflux system under these conditions. Dox-induced protein degradation in cardiac myocytes was also suppressed under co-culture conditions, consistent with paracrine mediated induction of drug-resistance.
Conclusion: These results demonstrate that MDR1 expression and activity in cardiac myocytes is induced by Dox via a CMEC paracrine signal. Elucidation of the molecular mechanisms for this paracrine signal may lead to development of strategies for cardiac protection from anthracyclines.