Gewirtz David A, Di Xu, Walker Teneille D, Sawyer Stephen T
Department of Pharmacology and Toxicology, Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia, USA.
Clin Cancer Res. 2006 Apr 1;12(7 Pt 1):2232-8. doi: 10.1158/1078-0432.CCR-05-2287.
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.
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.
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-NH(2)-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.
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.
促红细胞生成素（EPO）疗法广泛用于预防和治疗癌症化疗引起的贫血。天然EPO至少部分通过保护红系祖细胞免于凋亡性细胞死亡来调节红细胞生成。最近在癌细胞上发现促红细胞生成素受体（EPOR）引发了人们对EPO疗法可能刺激肿瘤生长和/或保护癌细胞免于药物诱导的凋亡的担忧。因此，在表达EPOR的MCF-7和MDA-MB231乳腺肿瘤细胞以及F-MEL红白血病细胞中，研究了EPO干扰传统化疗药物对增殖、凋亡和衰老诱导作用的能力。
乳腺癌细胞和F-MEL白血病细胞在有或无EPO的情况下培养，然后暴露于抗肿瘤药物。在药物暴露72小时后，通过标准的3-(4,5-二甲基噻唑-2-基)-2,5-二苯基四氮唑溴盐染料还原试验评估细胞增殖。通过克隆形成存活率监测细胞毒性。通过末端脱氧核苷酸转移酶介导的缺口末端标记试验或荧光激活细胞分选分析评估凋亡，并通过β-半乳糖苷酶染色监测衰老。通过监测特定信号蛋白的磷酸化/激活来评估EPO信号传导。
EPO未能刺激MCF-7或MDA-MB231乳腺肿瘤细胞或F-MEL白血病细胞的增殖。EPO治疗也未能干扰阿霉素、紫杉醇和他莫昔芬对乳腺肿瘤细胞的抗增殖和/或细胞毒性作用（或阿糖胞苷和柔红霉素对F-MEL细胞的作用）。EPO未能预防MCF-7细胞中紫杉醇诱导的凋亡或阿霉素诱导的衰老。EPO刺激了MCF-7细胞中细胞外信号调节激酶、p38和c-Jun-NH(2)-激酶的激活，但未激活Akt或信号转导和转录激活因子5（STAT5）。EPO未能在MDA-MB231细胞中激活这些信号通路中的任何一条。阿糖胞苷和柔红霉素干扰了F-MEL细胞中的EPO信号传导。
这些发现表明EPO不太可能直接抵消癌症化疗药物的有效性。这可能是EPOR信号传导无效或药物介导的EPO信号传导抑制的结果。
