Disruption of Gal1-glycan interaction impairs tumor growth and metastasis formation in breast cancer

DALOTTO MORENO T; CROCI DO; CERLIANI JP; DERGAN DYLON SL; MASCANFRONI I; RABINOVICH GA; SALATINO M

Chicago

Congreso; American Association for Cancer Research Annual Meeting 2012; 2012

AACR

Galectin-1 (Gal1) is an endogenous lectin with a pleiotropic function. In the last years there has been substancial progress on the understanding of its immunosupressive role. The effect of Gal1 on the physiology of the immune system places it as a key regulator of immune cell homeostasis and therefore makes it very attractive for the study of many pathologies. Gal1 has recently been identified as a protein associated with tumor escape. The objective of the present work is to investigate whether tumor Gal1 expression contributes to the tumor associated immunosupression, tumor growth and metastasis in breast cancer and can therefore be implicated as a novel therapeutic target. We used the highly metastatic mouse mammary tumor model 4T1 which express high levels of Gal1. We generated Gal1-deficient 4T1 cell line (4T1 KD) by infecting 4T1 cells with a retrovirus encoding a shRNA specific for mouse Gal1. We injected Balb/c mice with 25x103 of either 4T1 WT or 4T1 KD cells and evaluated tumor growth, metastasis formation and tumor associated immunosupression. We observed that Gal1 silencing elicited a reduction in tumor growth  and in 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 previous observation was in fact due to changes in the immune system. The immunohistochemistry of the lungs revealed that the metastasic foci from the 4T1 KD primary tumor were still negative for Gal1 which proves that Gal1 silencing did not affect cell homing to the lung. In regard to the tumor associated immunosupression we observed that 4T1 WT tumor bearing mice presented a higher frequency of CD4+ CD25+ Foxp3+ T regulatory cells (Tregs) in lungs, spleen, tumor draining lymph nodes (TDLN) and in the tumor microenvironment. Silencing of Gal1 expression reverted the generalized immunosupression that characterizes tumor progression and it was partially attributable to a decrease in both Tregs frequency and its immunosuppressive functions as well as to an increase in the proliferation of lymphocytes purified from spleen and TDLN that were reestimulated ex vivo in an antigen specific manner. Concomitantly to a strengthening of the antitumoral immune response, the blockade of tumor Gal1 was accompanied by a reduction of the Th2/Th1 cytokines ratio (IL10/IFNγ). Finally, we demonstrated that i.p. administration of a Gal1 neutralizing monoclonal antibody (F8.G7) to 4T1 WT tumor bearing mice not only induced a reduction in tumor growth and lung metastasis formation but also reverted the tumor associated immunosupression. In conclusion our results indicate that the disruption of Gal1-glycan interactions impaired tumor growth and metastasis formation, in part, through mechanisms involving the reversal of a systemic immunosupression and therefore we postulate Gal1 as an attractive target in the therapeutic treatment of metastasic breast cancer.