Abstract 6069: A bispecific S100A4/TFR antibody to reprogram the GBM tumor microenvironment and target GBM stem cells

Abstract GBM (glioblastoma) is the most common and aggressive primary brain tumor in adults. Despite advances in immunotherapy, current treatment modalities have only provided a modest benefit to GBM patients. We propose that enhancing the efficacy of immunotherapy for GBM requires approaches that increase T cell infiltration and reprogram the myeloid cells to a more pro-inflammatory state. We previously reported that S100A4 is a critical regulator of immune suppressive myeloid and T cell phenotypes and also a major regulator of glioma stem cells in GBM. Our preliminary data show that targeting S100A4 in either glioma cells or stromal cells is sufficient to reprogram the tumor immune landscape and extend survival of glioma bearing mice, indicating that S100A4 is a promising therapeutic target. We recently developed a S100A4 blocking monoclonal antibody; however, this antibody does not cross the blood brain barrier (BBB) efficiently to confer significant therapeutic benefit in glioma bearing mice. To overcome this challenge, we generated a bispecific S100A4-TfR antibody (BsA) that allows robust BBB penetration and accumulation in the brain. We assessed efficacy of BsA treatment in a highly aggressive and therapy-resistant, syngeneic mouse model of GBM (SVP). Using ELISA, confocal immunofluorescent microscopy, flow cytometry, and bulk RNA sequencing, we report that BsA treatment accumulates in the gliomas and reprograms the tumor immune microenvironment to increase T cell infiltration and pro-inflammatory activation. Furthermore, BsA treatment in combination with αPD1 checkpoint blockade significantly extends survival in the SVP mouse glioma model. Combination treated tumors exhibit extensive CD8 T cell infiltration and increased tumor reactive CD4 and CD8 T cells compared to controls. In addition, the BsA is taken up intracellularly within GBM cells and depletes S100A4 and nuclear SOX2 protein. In vitro treatment of GBM stem cell cultures with the BsA reduced self-renewal, as measured by the secondary sphere formation assay. These results indicate that the BsA is a promising agent to reprogram the GBM immune landscape and target GBM cell stemness through inhibition of both extracellular and intracellular S100A4 protein. We are currently performing in vivo efficacy studies in additional murine glioma models, and deeper mechanistic studies using single cell RNA sequencing and functional assays. Citation Format: Thomas Wong, Jia-Shiun Leu, Xuejun Fan, Fransisca Leonard, Maryam Faisal, Reece Kang, Yaqoob Ali, Nourhan Abdelfattah, Ningyan Zhang, Kyuson Yun. A bispecific S100A4/TFR antibody to reprogram the GBM tumor microenvironment and target GBM stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6069.