Abstract 3547: Disruption of Galectin1-glycan interaction impairs tumor growth and metastasis in breast cancer by disarming the immunosuppressive capacity of regulatory T cells

Abstract

Abstract Galectin-1 (Gal1) is an endogenous lectin that emerged as a key regulator of immune cell homeostasis. By binding to surface glycoconjugates, Gal1 modulates diverse physiological processes and also shapes the immune response during cancer progression to a suppressive phenotype. For that reason Gal1 has become a molecule with a profound impact in the tumor microenvironment biology. In the present work we investigated whether tumor Gal1 expression contributes to immunosuppression, tumor growth and metastasis in breast cancer in order to validate the Gal-1-glycan axis as a novel therapeutic target in these tumors. We used the highly metastatic mouse mammary tumor model 4T1 which expresses high levels of Gal1. We generated Gal1-deficient 4T1 cell line (4T1 KD) using a retrovirus encoding a shRNA specific for mouse Gal1. After injecting Balb/c mice with either 4T1 WT or KD cells we studied tumor growth, metastasis formation and analyzed tumor-associated immune compartments. Silencing of Gal-1 induced a marked reduction in both tumor growth and the number of lung metastases. This effect was abrogated if a 4T1 WT tumor was inoculated in the contralateral flank of these mice, suggesting that the antitumor effect involves modulation of the immune system. In regard to the latter we observed that 4T1 WT tumor-bearing mice exhibited a higher frequency of CD4+CD25+Foxp3+ regulatory T cells (Tregs) in the lungs, spleen, tumor draining lymph nodes (TDLN) and tumor microenvironment. Remarkably, knocking down Gal1 reverted the systemic immune tolerance that characterizes tumor progression, and decreased the frequency and immunosuppressive function of Tregs as evidenced by a suppression assay and expression of Tregs tolerogenic molecular markers as Foxp3, TGF-β and LAT. In this sense, mice bearing Gal-1 KD tumors were able to reject an allogeneic B16 tumor similarly to tumor free mice. In addition, antigen-specific proliferation of lymphocytes purified from 4T1 KD-bearing mice was increased when reestimulated ex vivo. Concomitantly, blockade of tumor Gal1 was accompanied by a reduction of the IL-10/IFNγ cytokines ratio. Finally, therapeutic administration of a Gal1 neutralizing mAb (F8.G7) to 4T1 WT tumor bearing mice not only induced a reduction in tumor growth and lung metastasis formation but also reverted tumor associated immunosuppression. These results are strengthened by the observation that in human breast cancer biopsies Gal1 expression correlates with tumor grade (Bloom-Richardson histopathological grade I vs II-III). In conclusion our results indicate that disruption of Gal1 impairs tumor growth and metastasis via mechanisms involving reversal of systemic immunosuppression and further validate the Gal1-glycan axis as an attractive target in the therapeutic treatment of metastasic breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3547. doi:1538-7445.AM2012-3547