<i>In Vivo</i> Hemin Conditioning Targets the Vascular and Immunologic Compartments and Restrains Prostate Tumor Development.

Abstract

<b>Purpose:</b> Conditioning strategies constitute a relatively unexplored and exciting opportunity to shape tumor fate by targeting the tumor microenvironment. In this study, we assessed how hemin, a pharmacologic inducer of heme oxygenase-1 (HO-1), has an impact on prostate cancer development in an <i>in vivo</i> conditioning model.<b>Experimental Design:</b> The stroma of C57BL/6 mice was conditioned by subcutaneous administration of hemin prior to TRAMP-C1 tumor challenge. Complementary <i>in vitro</i> and <i>in vivo</i> assays were performed to evaluate hemin effect on both angiogenesis and the immune response. To gain clinical insight, we used prostate cancer patient-derived samples in our studies to assess the expression of HO-1 and other relevant genes.<b>Results:</b> Conditioning resulted in increased tumor latency and decreased initial growth rate. Histologic analysis of tumors grown in conditioned mice revealed impaired vascularization. Hemin-treated human umbilical vein endothelial cells (HUVEC) exhibited decreased tubulogenesis <i>in vitro</i> only in the presence of TRAMP-C1-conditioned media. Subcutaneous hemin conditioning hindered tumor-associated neovascularization in an <i>in vivo</i> Matrigel plug assay. In addition, hemin boosted CD8⁺ T-cell proliferation and degranulation <i>in vitro</i> and antigen-specific cytotoxicity <i>in vivo</i> A significant systemic increase in CD8⁺ T-cell frequency was observed in preconditioned tumor-bearing mice. Tumors from hemin-conditioned mice showed reduced expression of galectin-1 (Gal-1), key modulator of tumor angiogenesis and immunity, evidencing persistent remodeling of the microenvironment. We also found a subset of prostate cancer patient-derived xenografts and prostate cancer patient samples with mild HO-1 and low Gal-1 expression levels.<b>Conclusions:</b> These results highlight a novel function of a human-used drug as a means of boosting the antitumor response. <i>Clin Cancer Res; 23(17); 5135-48. ©2017 AACR</i>.