Recombinant Human Erythropoietin α Targets Intratumoral Blood Vessels, Improving Chemotherapy in Human Xenograft Models

Abstract

Recombinant human erythropoietin (rHuEPO) is widely used for correction of hemoglobin level in cancer patients. However, apart from hematopoiesis, rHuEPO reportedly has an effect on endothelial cells. We describe here how rHuEPOA can modulate tumor vasculature in human squamous cell (A431) and colorectal carcinoma (HT25) xenograft models. In vivo rHuEPO treatment of xenografts at human-equivalent dose significantly increased the proliferation index of the tumor-associated endothelial cells and the size of CD31-positive intratumoral blood vessels, whereas the pericyte coverage became fragmented. Moreover, rHuEPO administration resulted in decreased expression of vascular endothelial growth factor both by cancer cells and tumor stroma, measured by quantitative PCR. Due to the morphologic alterations in tumoral microvessels, DNA-binding agents (Hoechst and Doxorubicin) labeled significantly larger areas in the tumor mass. Furthermore, rHuEPO treatment led to a significantly improved efficacy of 5-fluorouracil (5-FU) chemotherapy in the case of both tumor xenografts. Meanwhile, rHuEPO had no effect on the in vitro proliferation of erythropoietin receptor-positive tumor cells, and did not interfere with the effects of 5-FU either. These data reveal a new effect of rHuEPO administration: remodeling tumoral microvessels, suppressing vascular endothelial growth factor expression, thereby augmenting antitumor effects of a cancer drug, 5-FU, even in erythropoietin receptor-positive human cancer xenografts. (Cancer Res 2005; 65(16): 7186-93)

A New Mechanism for Pillar Formation during Tumor-Induced Intussusceptive Angiogenesis: Inverse Sprouting

“…In accordance with our previous findings, 16 a tendency toward an increased tumor microvessel surface in mice treated with rHuEPO was also observed. However, when pillar density was calculated for the area of tumor microvessels, the difference in pillar densities between tumors in the rHuEPO- treated and control groups remained statistically nonsignificant (Table 2).…”

“…The s.c. tumors were produced by injecting 2 ϫ 10 6 tumor cells into the back of anesthetized male mice with severe combined immunodeficiency, as previously described. 16 Animals were sacrificed 4 weeks after tumor inoculation.…”

“…To study the effects of angiogenesis-modulating agents on tumor vascularization and pillar formation, groups of six mice bearing C38 tumors received recombinant human erythropoietin ␣ (rHuEPO, epoetinum ␣; JannsenCilag, Shaffhausen, Switzerland), 16 PTK787/ZK22854 (vatalanib; Novartis/Schering AG, Berlin, Germany) 17 (obtained from Selleck Chemicals LLC, Houston, TX), or the vehicle as a control. In mice treated with vatalanib, tumors were allowed to grow for 12 days before treatment.…”

“…from day 1 after tumor inoculation, as previously described. 16 The mice in all groups were sacrificed on day 17, and tumors were removed, weighed, and frozen.…”

Alternative Vascularization Mechanisms in Cancer

“…For instance, rHuEpo administration has recently been shown to be associated with decreased intratumoral VEGF expression, remodeling of tumor capillaries, and increased chemosensitivity to 5-fluorouracil treatment of human tumor xenografts. 69 In a preclinical myeloma model, rHuEpo induced tumor regression and antitumor immune responses. 70 In addition, human kidney carcinoma and myelomonocytic leukemia cell lines treated with rHuEpo exhibited an increase in apoptosis in response to chemotherapy.…”