EXTH-82. TUMOR ORGANOID PREDICTED THERAPEUTIC RESPONSES TO NOVEL EPIGENETIC DRUGS VIA HIGH-THROUGHPUT SCREENING

Abstract INTRODUCTION The treatment choices for pediatric brain tumors are still very limited. Epigenetic therapy emerges as a promising option recently. The lack of in vitro models that represent tumors in vivo and can be scalable for large scale drug screening is major barrier. We have developed tumor organoids from patient-derived orthotopic xenograft and performed a multi-stage high throughput screening for single or combined epigenetic agents and radiation therapy in tumor organoids. METHOD Primary xenograft tumor cells were cultured in matrix and cancer stem cell culture medium in 384-well plates. Radiation sensitivity was examined at 5 different doses. Epigen40 (40 drugs/compounds) targeting various epigenetic modifications was used alone to identify agents with the most cell killing (4 doses for up to 19 days). The drugs that showed partial activity were combined with radiation (at 5 doses) to evaluate additive or synergistic effects. The anti-tumor efficacy of selected drug was then evaluated in vivo. RESULTS The conditions of organoid growth and screen variability were optimized. 7 tumor organoids including 4 glioblastomas and 3 medulloblastomas were successfully established and characterized. The different radio-sensitivities were observed among these models. 7 compounds (JIB-04, SP2509, AS-8351, GSK J4 HCI, 3-Deazaneplanocin A HCL, Chaetocin, TC-E-5003) were shown to effectively suppress organoid growth. Chaetocin, methyltransferase SUV39H inhibitor, demonstrated broadly active and highly potent inhibition across all 7 tested organoids. In addition, bioinformatic analysis identified a subset of epigenetic inhibitors combined with radiation that produced additive anti-tumor activities in vitro. Unfortunately, in vivo treatment of Chaetocin (0.25mg/kg) didn’t convey consistent anti-tumor effects as shown in vitro whereas a high risk of drug toxicity to the mice. CONCLUSION Tumor organoids were successfully developed from primary tumors. With our optimized assay using primary tumor organoids and a multi-stage high throughput drug screening, a novel panel of epigenetic drugs that effective alone or additively with radiation was identified.