EPEN-34. HIGH-THROUGHPUT DRUG SCREENING OF PRIMARY CULTURES REVEALS IRREVERSIBLE ERBB2 INHIBITION AS NOVEL THERAPEUTIC VULNERABILITY OF EPENDYMOMAS

Ependymoma is the third most common brain tumor in children. Subsets of ependymomas, in particular RELA fusion-positive supratentorial ependymomas and posterior fossa type A ependymomas, are associated with frequent recurrence and dismal outcome. Neurosurgical resection and radiotherapy are the main therapeutic options, while response to conventional chemotherapy is limited. We aimed to establish a high-throughput drug screening (HTS) pipeline for comprehensive individualized testing of patient-derived primary cultures to identify novel therapeutic targets for ependymomas. Ependymoma primary cultures (n=6) were established following tumor resection and underwent HTS in 1536-well plates to allow large-scale drug screening despite limited cell numbers. We generated dose-response data with 9 dilution steps (dose range 32.5nM to 25µM) for a clinical inhibitor library (n=196) comprising established chemotherapeutic agents and novel anti-cancer compounds currently in phase III and IV studies. The Infinium MethylationEPIC Array was used to characterize primary tumors and matched primary cultures genomically and epigenetically. DNA methylation and copy number profiles revealed that short-term primary cultures faithfully recapitulate the genomic and epigenetic landscape of the corresponding primary tumors. Comparison of drug response data from ependymomas, other pediatric brain tumors (n=25) and controls (i.e. non-neoplastic neural progenitor cells) confirmed extraordinary chemoresistance of ependymomas but also revealed promising selectively active drugs, such as neratinib, an irreversible ERBB2 inhibitor. Thus, our data demonstrate the feasibility of HTS in primary cultures derived from pediatric brain tumors and provide preclinical evidence suggesting inhibition of ERBB2 as a promising therapeutic option in a subset of otherwise highly chemoresistant ependymomas.