Abstract 5287: Ex vivo pharmacologic inhibition of STAT3 effectively targets tumor and tumor associated suppressor cells in high-grade glioma 3D spheroids
Authors: Lassahn Katy A. , Elrod Ashley K. , DesRochers Teresa M. , Appleton Kathryn M. 
Published: March 2024

Abstract
Gliomas, a type of brain tumor originating from glial cells, comprise a heterogenous group of neoplasms. High-grade gliomas, in particular, present significant therapeutic challenges in the clinic. Unlike other solid tumors, the heterogenous glioma microenvironment is heavily enriched with tumor associated suppressor cells including myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs), which can account for 30-40% of the cellular composition1. These pro-tumorigenic myeloid cells are thought to contribute to the resistance of glioma to immunotherapy. Efforts to target the suppressive nature of these dominating cell types are in development to yield more therapeutic options for patients with these devastating diseases. Constitutive activation of STAT3 in gliomas has been associated with increased tumor progression and reduced immune response. We have observed in other cancer models that a phenotypic switch occurs from STAT3 pathway activation in 3D spheroid culture to STAT3 inactivation when cultured in 2D. Therefore, we sought to determine the role of STAT3 activation and its role in the interplay between glioma and their immune suppressive environment using a 3D spheroid model. We modified our commercially available test platform, 3D-Predict™ Glioma, such that it is conducive to monitoring immune cell function. Newly diagnosed treatment naive primary samples from HGG patients were dissociated and cryogenically preserved and banked. Samples were profiled for the abundance of tumor associated suppressive myeloid cells using flow cytometry. We determined that relative proportions of tumor suppressor cells were detectable and varied across HGG primary patient samples with TAMs being the predominate immune cell type identified. Pro-tumorigenic TAM markers including CD163 and CD206 were correlated with temozolomide response and were associated with poor patient prognosis. When we evaluated the role of p-STAT in HGG primary samples, p-STAT was detected at baseline and abundance was related back to the presence of tumor associated immune suppressor cells. The impact of STAT3 signaling blockade by the inhibitor WP1066 was determined ex vivo, and efficacy was related back to MGMT promotor methylation status and patient clinical outcome. We detected shifts in cytokine signatures following treatment of HGG 3D spheroid models with WP1066 which are known to target tumor associated suppressor cell functions. This work demonstrates the critical role suppressive immune cells play in HGG clinical response. Given p-STAT can be altered in 2D culture compared to 3D culture, ex vivo therapeutic response profiling of HGG samples is necessary using the more physiologically relevant spheroid culture model.
1.Hambardzumyan et al. The role of microglia and macrophages in glioma maintenance and progression. Nat. Neurosci. 19, 20-27 (2016).
Citation Format: Katy A. Lassahn, Ashley K. Elrod, Teresa M. DesRochers, Kathryn M. Appleton. Ex vivo pharmacologic inhibition of STAT3 effectively targets tumor and tumor associated suppressor cells in high-grade glioma 3D spheroids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5287.