Abstract 2685: Tumor hypoxia drives immunosuppression via upregulation of galectin-1 in recurrent Glioblastoma
Authors: Glore Wayne , Das Arabinda , Lindhorst Scott M. , Varma Abhay K. , Vandergrift William A. , Patel Sunil J. , Cachia David 
Published: July 2021

Abstract
Background: Glioblastoma (GB) recurrence is associated with a highly immunosuppressive tumor microenvironment. Previous research in our lab has illustrated that the carbohydrate-binding protein Galectin-1 (Gal-1) has high expression in GB patient samples and plays vital pro-tumorigenic roles within the tumor microenvironment, regulated by hypoxia-inducible factor-1 (HIF-1). However, since Gal-1 displays many different activities by binding to a number of diverse N- or O-glycan modified target proteins, it has been difficult to fully understand how Gal–1 supports tumor growth and promotes resistance to anti-VEGF mAb. Thus, our aim is to elucidate the role of tumor hypoxia which may in turn increase tumor aggressiveness by up-regulating the expression of Gal-1 in relevant GB in vitro and in vivo model.
Methods and Results: GB cells were cultured in a hypoxic environment simulated by cobalt chloride (CoCl2), which is a chemical inducer of hypoxia-inducible factor-1α (HIF-1α). HIF-1α is a transcription factor that has an important role in tumor cell adaptation to hypoxia and controls the expression of several genes. Various CoCl2 concentrations were used to simulate degrees of hypoxia in GB cells. Following treatment with 250 µM CoCl2, an MTT assay was conducted to determine the growth and anti-VEGF mAb (+/- Radiation + Temozolomide) sensitivity of GB cells. We observed that CoCl2(chemical activator of HIF-1α)-treatment simulated hypoxia and induced resistance to anti-VEGF mAb treatment via upregulation of HIF-1α, MDR1/P-gp and MRP protein levels. In addition, proapoptotic members of the Bcl-2 protein family, Bax and Bad, were downregulated. The anti-apoptotic member Bcl-2 exhibited no significant change in expression, whereas the ratio of Bcl-2/Bax was increased. We observed that hypoxia induced Gal-1 through mechanisms that are independent of HIF 1α and HIF-2α but involved reactive oxygen species-dependent activation of the transcription factor nuclear factor κB. Since upregulation of hypoxia inducible transcription factors (HIFs) via Gal-1 is the primary adaptive cellular response to a hypoxic environment, we analyzed the effects of Gal-1 inhibition treatment in vivo. We observed significant alteration of hypoxic tumor microenvironment (TME) in recurrent GB by alteration of tumor associate microglia phenotypes from M2 to. M1, suppression of CD4+CD25+Foxp3+ regulatory T cells and activation of CD 8+ T cells in in vivo GB models.
Conclusion: The present study revealed that a CoCl2-simulated hypoxic microenvironment was able to effectively induce resistance to anti-VEGF mAb treatment in GB cells. The results demonstrate the inhibitory effect of Gal-1 in the tumor hypoxia microenvironment and inhibition may be a viable therapeutic target for recurrent GB treatment.
Citation Format: Wayne Glore, Arabinda Das, Scott M. Lindhorst, Abhay K. Varma, William A. Vandergrift, Sunil J. Patel, David Cachia. Tumor hypoxia drives immunosuppression via upregulation of galectin-1 in recurrent Glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2685.