P10.28.B INTERMODEL VARIATION OF BBB PERMEABILITY AFFECTS CNS DRUG DELIVERY IN PDX MODELS OF GBM

Abstract

Abstract BACKGROUND Little progress has been made in the development of effective new therapies for glioblastoma (GBM) the past decades. One of the major obstacles in identifying novel candidate drugs against GBM remains the blood-brain barrier (BBB) and the efflux transporters. Therefore, it is crucial to select drugs able to cross BBB and reach the tumor tissue in therapeutically effective concentrations. In current study, we evaluated the anti-glioma effect of the protein synthesis inhibitor omacetaxine mepesuccinate (OMA) in vitro and its CNS penetrating properties in vivo. MATERIAL AND METHODS The FDA-approved Oncology Drug Set II library was tested on 55 patient-derived GBM cell cultures. We designed a drug shortlisting pipeline combining efficacy data with pharmacodynamic and pharmacokinetic characteristics of each compound. We developed and characterized 3 orthotopic mouse PDX models in terms of brain vascular integrity, BBB permeability and expression of ABC transporters. The PK profile of omacetaxine was assessed in these orthotopic mouse PDX models. RESULTS In vitro, OMA revealed anti-tumor activity at IC50 values well-below reported Cmax plasma value (Cmax=43nM) in approximately 80% of GBM cultures. Unexpectedly, OMA does not downregulate the expression of its acknowledged target, ribosomal protein 3 (RPL3). In glioma cells while activation of caspase 3/7 activity is linked to its anti-tumor effect. OMA is a substrate for ABCB1 (P-glycoprotein) but not for ABCG2 (BCRP). In vivo, dose escalation showed safety of the drug and OMA was found to reach the brain tumor tissue in concentrations similar or higher to the reported IC50 values in vitro, depending on the PDX model used. No adverse reactions were noted. CONCLUSION OMA is a CNS penetrant drug that reaches the brain tumor tissue in all tested concentrations. The inter-model variation in accumulation of OMA is associated to the extent of BBB disruption of each PDX model. Additional in vivo experiments are ongoing to investigate the therapeutic effect of OMA and longer exposure using in vivo models.