Acute exposure to doxorubicin results in increased cardiac P-glycoprotein expression.

Doxorubicin is a frequently used anticancer drug, but its use is restricted due to the occurrence of severe side effects, namely strong cardiotoxicity. It is known from cancer cells that doxorubicin enhanced the expression of its efflux pump P-glycoprotein (P-gp), which may modulate local drug concentrations. We therefore studied the cardiac expression of P-gp in doxorubicin-treated mice. Mice were treated with doxorubicin, and P-gp expression was studied after 1, 3, and 5 days. Thereby, we could show a significant upregulation of abcb1a (162 ± 15% of control) and abcb1b (418 ± 110% of control) mRNA transcripts after 3 days. On protein level, western blot analysis and immunofluorescence staining revealed a similar finding 5 days after doxorubicin administration. In addition, these results could be confirmed by in vitro models using primary rat cardiomyocytes and the murine cardiomyocyte-like HL-1 cells. Besides an enhanced mRNA and protein expression, doxorubicin-treated HL-1 cells also demonstrated an enhanced P-gp function as assessed by a daunorubicin accumulation assay. Our in vivo and in vitro results demonstrate a cardiac upregulation of P-gp in doxorubicin-treated mice on expression and functional level. This finding may be relevant for cardiac tissue concentrations of P-gp substrates and may represent a mechanism in cardiac self-protection against xenobiotics. © 2011 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:3951–3958, 2011