Suppression of Vascular Network Formation by Human Cardiac Endothelial Cells with Low Concentrations of Doxorubicin is Due to the Inhibition of Endothelial Cell Proliferation

Anticancer drug doxorubicin (DOX) is known to cause dilated cardiomyopathy in treated patients. We set out to examine if cardiac endothelial cells present a target of doxorubicin in the heart. Primary human cardiac microvascular endothelial cells (HCMVEC) form vascular network in vitro when co‐cultured with human cardiac fibroblasts (HCFB). DOX suppressed the formation of vascular networks in a co‐culture assay with an IC50 of 8 nM. DOX did not inhibit the production of VEGF by these cells at these low concentrations under both normoxic and hypoxic conditions, but caused moderate inhibition of VEGF release by hypoxic HCFB at concentrations above 250 nM. Similarly, it did not enhance apoptosis in these cells at the concentrations that were shown to completely suppress vascular sprouting in a co‐culture angiogenesis assay. We used Ki67 immunostaining to examine if DOX suppresses proliferation of HCMVEC in a co‐culture angiogenesis assay. Endothelial cell marker CD31 was used to identify HCMVEC. DOX markedly reduced numbers of CD31+ and CD31+Ki67+ cells in co‐cultures at concentrations above 4 nM. We conclude that HCMVEC are exceedingly sensitive to anti‐proliferative effect of DOX, and may present a viable target of this cardiotoxic drug in the heart. Endothelial effects of DOX are likely to contribute to the development of dilated cardiomyopathy. This work was supported by NIH NCRR grant 2P20RR016467‐09A1.