Abstract 453: Engineering the tumor microenvironment: Hemin conditioning in vivo impairs tumor growth and reprograms the immune-modulatory response in prostate cancer
Authors: Felipe M. Jaworski, Geraldine G. Gueron, Lucas D. Gentilini, Daiana B. Leonardi, Ignacio González Pérez, Geraldine Contrufo, Gabriel A. Rabinovich, Daniel G. Compagno, Diego J. Laderach, Elba S. Vazquez
Journal: Cancer Research (2015)

Abstract Prostate cancer (PCa) is the second leading cause of cancer death in men in the United States, and inflammation is recognized as a risk factor. In this regard we have previously shown that Heme Oxygenase-1 (HO-1) over-expression plays a critical role in prostate tumor cells per se by impairing cell proliferation, invasion and migration in vitro and tumor growth in vivo. In the present study, we aimed to assess the role of stromal HO-1 in PCa. The stroma was conditioned by subcutaneously (s.c.) injecting C57BL/6 mice with 200μl of hemin (30μM; HO-1 pharmacological inducer) or its vehicle PBS on days 8, 5 and 1 prior to tumor challenge. TRAMP-C1 cells (T-C1; 2×106 isogenic murine PCa cells) were s.c. injected on the same flank in Matrigel®. Hemin pre-treated animals showed a significant increase in tumor latency (12-day delay when compared to control mice; Mantel-Cox test, P&amp;lt;0.01) and a significant decrease in tumor growth rate (Student t test, P &amp;lt;0.05). In vitro lymphocyte proliferation assays showed that hemin was able to enhance αCD3-mediated T cell proliferation and its administration was sufficient to revert T-C1-mediated immunosuppresion. Immunophenotyping of the tumor infiltrate, draining and contralateral lymph nodes and spleen samples obtained from mice after euthanasia was carried out using flow cytometry. Significant differences were detected in the frequency and activation state of both CD8+ T lymphocytes (P&amp;lt;0.05) and myeloid Gr-1+ cells (P &amp;lt;0.01). These phenomena were observed not only in the tumor infiltrate but also in other organs, suggesting hemin treatment had systemic effects on the immune compartment. The expression levels of several neovascularization-related genes was assessed by RT-q-PCR, and no significant differences were observed for VEGF, FGFβ, TIMP-1, CD142, uPA and TSP-1. Collectively, these data suggest that hemin does not affect vascularization and acts through an immune-based mechanism. Interestingly, tumors from hemin-conditioned mice showed reduced Galectin-1 (Gal-1) expression (2.6 fold; Student t test, P &amp;lt;0.01), evidencing a clear and long-term effect on lectin/glycan interactions on tumor cells. This in turn, may impact upon host immunosurveillance, as Gal-1 has been widely recognized as a central tumor escape mechanism. Altogether, these results showcase how HO-1 pharmacological modulation in the stroma dramatically affects PCa tumor progression in vivo and postulate lectin/glycan interactions as potential mediators of these observations. Citation Format: Felipe M. Jaworski, Geraldine G. Gueron, Lucas D. Gentilini, Daiana B. Leonardi, Ignacio González Pérez, Geraldine Contrufo, Gabriel A. Rabinovich, Daniel G. Compagno, Diego J. Laderach, Elba S. Vazquez. Engineering the tumor microenvironment: Hemin conditioning in vivo impairs tumor growth and reprograms the immune-modulatory response in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 453. doi:10.1158/1538-7445.AM2015-453