P10.23.A A PATIENT-DERIVED FUNCTIONAL GBM DRUG SCREEN OFFERS A TOOL TO PREDICT TMZ RESPONSE AND ASSESS SENSITIVITY TO CANDIDATE TREATMENTS ON A PER PATIENT BASIS
Authors: Ntafoulis I , Kleijn A , Posthoorn-Verheul C , Koolen S , Jimenez-Cowell K , Kers T , Klein M , den Hollander C , Ju J , Li Y , Stubbs A , Dirven C , Leenstra S , Lamfers M 
Published: September 2023

Abstract

BACKGROUND
Major obstacles that have impeded the development of effective new therapies for GBM include inter- and intratumoral heterogeneity, the blood-brain-barrier and use of sub-optimal cell line-based preclinical models. Taking these hurdles into account, we have set up a patient-derived GBM drug-screening platform. Molecular similarities and dissimilarities between tumors and derived cultures were investigated and the predictive power of our assay for patient response to TMZ was assessed. A large panel of GBM cells was screened for sensitivity to available oncological agents with the aim of deriving a set of drugs with favorable physicochemical properties for BBB crossing and potent activity in (a subset of) GBM cultures. Finally, we determined the success rate of performing a small-scale screen with 20 selected agents within 4 weeks post-surgery.

MATERIAL AND METHODS
Tissue samples as well as ultrasonic surgical aspirates (USA) were received from GBM surgeries and utilized to establish glioma stem cell (GSC) cultures. Correspondence of GSCs to parental tumors was assessed by DNA/RNA-sequencing. In vitro sensitivity to temozolomide was screened across 55 GSC cultures. Cell viability readouts were related to clinical parameters of corresponding patients. FDA-approved anticancer agents (n=107) were screened on 45 GBM cultures by dose-response testing and viability was assessed using Cell Titer-Glo. Twenty selected agents were screened on 24 fresh tumor samples within 4 weeks of receiving the tissue.

RESULTS
By combining both USA and tissue piece-derived dissociation protocols, culture success increased to 95%, ensuring representation of the near-complete spectrum of GBM subtypes. Tumor DNA and RNA sequences revealed strong similarities to corresponding GSC cultures although differences related to neuronal signaling, immune interactions, and cell cycle were observed. Tumor expression profiles of hallmark genes of GBM were faithfully retained in derived cell cultures. In vitro screening of TMZ on a large cohort identified 3 response categories (responders/intermediates/non-responders) for which Cox regression analysis revealed significantly different overall survival curves of corresponding patients. Screening of approved anticancer agents on 45 GBM cultures underscored the tremendous intertumoral heterogeneity in drug sensitivities. We identified 20 potent agents each effective at clinically-achievable concentrations in (a subset of) GBM cultures with favorable BBB penetration properties (CNS-MPO score). Screening of these agents on a per patient basis within 4 weeks of receiving tissue was successful in 18 out of 24 (75%) tested tumors.

CONCLUSION
Patient-derived functional drug screening offers a tool to predict TMZ response in GBM patients and assess tumor sensitivity to candidate treatments, either for GBM subsets or on a per patient basis.