MODL-46. RECAPITULATING CELLULAR HETEROGENEITY AND TREATMENT-SPECIFIC EFFECTS THROUGH SINGLE-CELL ANALYSIS OF PATIENT-DERIVED TUMOR SLICE CULTURE MODELS

Abstract

Abstract INTRODUCTION Malignant brain tumors are almost universally fatal despite standard-of-care (SOC) therapy with radiation (XRT) and temozolomide (TMZ). Low Grade Glioma (LGG) is a subclass of malignant glioma that can harbor an R132H mutation in Isocitrate Dehydrogenase 1 (IDH1). Extensive clinical trials have explored the clinical utility of IDH1 R132H mutation small molecule inhibitors such as ivosidenib and vorasidenib; however, the direct intracellular and intercellular effects of IDH1 R132H inhibition relative to SOC remain largely unknown. Objective This study examines these issues by developing a novel patient-specific tumor slice culture model to study the effects of both SOC and IDH1 R132H inhibition on IDH1 mutant glioma. Method En-bloc tumor samples from a patient with IDH mutant LGG undergoing surgery were sectioned into 400 um thick slices using a vibratome and cultured on porous microwell inserts for up to 14 days. Tumor slices were then either left untreated or treated with SOC (XRT/TMZ) or ivosidenib and harvested at various time points. Samples were hashed, and single-cell RNA sequencing was performed and analyzed. Result: Patient-derived tumor slice cultures were able to grow and were observed to contain heterogeneous cell populations, including tumor cells, astrocytes, neurons, oligodendrocytes, and microglia. When slice cultures were treated with SOC and ivosidenib treatment, separate tumor subpopulations were shown to be sensitive to either treatment. Furthermore, scRNA analysis revealed unique subpopulations that were insensitive to either treatment. We further demonstrate that slice cultures treated with Ivosidenib enriched for gene signatures related to protein translation and antigen processing. Intriguingly, we find that tumor cultures treated with ivosidenib abrogated the Notch signaling pathways between tumor-tumor and tumor-immune clusters. CONCLUSION Herein, we demonstrate that patient-derived tumor slice cultures are a viable strategy for understanding drug effects and tumor sensitivity to different therapies.