EXTH-73. TARGETING THE CELL ADHESION CLUSTER OF DIFFERENTIATION 44 TRANSMEMBRANE GLYCOPROTEIN SENSITIZES CRANIOPHARYNGIOMAS TO IMMUNOTHERAPY

Abstract BACKGROUND Craniopharyngiomas are categorized as an adamantinomatous craniopharyngioma (ACP) or papillary craniopharyngioma (PCP) subtype with distinct histological, pathological and genetic differences. Studies propose the potential therapeutic benefit of targeting PD-L1 and/or PD-1 in both ACP and PCP subtypes using immune checkpoint inhibitors (ICI). The alternative mRNA splice variant of CD44, CD44v9, is expressed on cancer stem cells and plays multiple key roles including drug resistance and tumor cell invasiveness. CD44 positively regulates PD-L1, but the role of this transmembrane glycoprotein in craniopharyngioma tumorigenesis is unknown. Objectives: To replicate the complexity of the craniopharyngioma tumor microenvironment (TME) by developing a novel patient tissue-generated craniopharyngioma in vitro organoid preclinical model for the development of therapeutic strategies. Approach: NanoString CosMx™ Spatial Molecular Imager (SMI) was performed using FFPE tissue sections prepared from patient craniopharyngiomas. Quantification of PD-L1, and stem cell transmembrane glycoproteins CD44v9 and TROP2 was performed using multiplex immunofluorescence (MxIF). Craniopharyngioma patient-derived organoids (CranioPDOs) were generated and co-cultured with autologous immune cells (IMM) generated from patient peripheral blood mononuclear cells. CranioPDO/IMM co-cultures were used to predict the potential therapeutic benefit in response to tyrosine kinase inhibitor cabozantinib (Cabo) plus pembrolizumab (Pembro) or atezolizumab (Atezo) combinatorial therapy. RESULTS SMI analysis showed expression of CD44 and TROP2 positive cells, cancer-associated fibroblasts and myeloid-derived suppressor cells (MDSCs) consistent with the staining pattern of PD-L1. MxIF of matched tissues showed expression of CD44v9 and TROP2 within the same CD44 positive spatially mapped cell populations. Combinatorial treatment of CranioPDO/IMM co-cultures with Cabo plus Pembro or Atezo led to depletion of MDSCs correlating with decreased expression of CD44v9 and a significant increase in cytotoxic T lymphocyte proliferation and tumor cell death. CONCLUSION Our preclinical in vitro organoid data support the potential therapeutic benefit of ICI in combination with cabozantinib for the treatment of craniopharyngiomas.