Erythropoietin fails to interfere with the antiproliferative and cytotoxic effects of antitumor drugs

Purpose: Erythropoietin (EPO) therapy is widely used for the prevention and treatment of anemia resulting from cancer chemotherapy. Native EPO regulates erythropoiesis, at least in part, by protecting erythroid progenitor cells from apoptotic cell death. The recent discovery of the EPO receptor (EPOR) on cancer cells raises the concern that EPO therapy might stimulate tumor growth and/or protect cancer cells from drug-induced apoptosis. Therefore, the capacity of EPO to interfere with the effects of conventional chemotherapeutic drugs on proliferation, apoptosis, and the induction of senescence was investigated in MCF-7 and MDA-MB231 breast tumor cells, which express the EPOR as well as in F-MEL erythroleukemia cells. Experimental Design: Breast cancer cells and F-MEL leukemic cells were cultured in the presence or absence of EPO and then exposed to antitumor drugs. Cell proliferation was assessed by a standard 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide dye reduction assay 72 hours after drug exposure. Cytotoxicity was monitored by clonogenic survival. Apoptosis was evaluated either by the terminal deoxyribonucleotide transferase - mediated nick-end labeling assay or fluorescence-activated cell sorting analysis, and senescence was monitored by beta-galactosidase staining. EPO signaling was assessed by monitoring the phosphorylation /activation of specific signaling proteins. Results: EPO failed to stimulate the proliferation of MCF-7 or MDA-MB231 breast tumor cells or F-MEL leukemic cells. EPO treatment also failed to interfere with the antiproliferative and/or cytotoxic effects of Adriamycin, Taxol, and tamoxifen in breast tumor cells (or of cytarabine and daunorubicin in F-MEL cells). EPO failed to prevent apoptosis induced by Taxol or senescence induced by Adriamycin in MCF-7 cells. EPO stimulated the activation of extracellular signal-regulated kinase, p38, and c-Jun-NH2-kinase in MCF-7 cells but did not activate Akt or signal transducers and activators of transcription 5 (STAT5). EPO failed to activate any of these signaling pathways in MDA-MB231 cells. Cytarabine and daunorubicin interfered with EPO signaling in F-MEL cells. Conclusions: These findings suggest that EPO is unlikely to directly counteract the effectiveness of cancer chemotherapeutic drugs. This may be a consequence of either ineffective signaling through the EPOR or drug-mediated suppression of EPO signaling.