Abstract 2742: Cerebral microdialysis for simultaneous sampling of crenolanib (PDGFR inhibitor) and erlotinib (EGFR inhibitor) in mouse models of glioma
Authors: Elmeliegy Mohamed , Throm Stacy L. , Wang Fan , Bai Feng , Ramachandran Abhijit , Stewart Clinton F. 
Published: August 2012

Abstract
Cerebral microdialysis, a technique used to monitor anticancer drug disposition in the central nervous system (CNS), is commonly used to sample extracellular fluid (ECF) for analysis of a single anticancer agent. However, combining anticancer drugs represents a promising strategy to overcome the highly resistant nature of some CNS tumors, such as malignant glioma. To date, the feasibility of simultaneous sampling multiple anti-cancer agents via cerebral microdialysis has not been reported. Given the role of PDGFRα and EGFR in providing multiple inputs for sustaining PI3K signaling, critical for glioma cell survival and proliferation, combining PDGFRα and EGFR inhibitors represents a valid treatment strategy for these tumors. The goals of the current study are to 1) to optimize microdialysis conditions to sample crenolanib and erlotinib as single agents or in combination from brain ECF (CbECF) and tumor ECF (CtECF) and 2) to characterize CNS penetration of crenolanib as a single agent and in combination with erlotinib. In vitro microdialysis experiments to sample crenolanib and erlotinib from aCSF determined that addition of 10% hydroxylpropyl betacyclodextrin increased the recovery of crenolanib and erlotinib by 16.1 and 2.6 fold, respectively. Zero-flow rate recovery method estimated stock concentrations with &gt;85% accuracy. Sensitive LC-MS/MS methods will allow us to detect very low concentrations in the CNS (LLOQ for crenolanib and erlotinib is 0.1 and 0.5ng/mL, respectively). Unbound crenolanib concentrations in brain and tumor ECF were determined in a spontaneous glioma model under steady-state conditions achieved by using a miniosmotic pump loaded with crenolanib which administered a dose of 300 mg/kg/day. Plasma steady-state levels (Cpss) were 516.8±92.9ng/mL, mean ± SD. Crenolanib penetration into tumors [PTumor = CtECF/Cpss] was 3-fold higher than in normal brain [PBrain = CbECF/Cpss] (1.0±0.5 and 0.3±0.02, respectively). In a murine orthotopic xenograft model bearing SJG2 pediatric glioma tumors, crenolanib (300 mg/kg/day via miniosmotic pumps) inhibited PDGFRα phosphorylation (in vitro IC50 =8.1ng/mL) in 75% (3/4) of SJG2 tumors but failed to inhibit AKT phosphorylation or to induce apoptosis. We subsequently treated these animals with an EGFR inhibitor, erlotinib, and tried to determine whether co-administration of erlotinib affected the CNS penetration of crenolanib. Administration of 200 mg/kg/day crenolanib and erlotinib simultaneously via a miniosmotic pump resulted in a crenolanib Cpss of 210.1± 57 ng/mL and an erlotinib Cpss of 634±208 ng/mL. To conclude, optimizing microdialysis technique enhances the ability to simultaneously dialyze crenolanib and erlotinib in vitro. Studies to determine the effect of co-administration of erlotinib on crenolanib CNS penetration are ongoing.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2742. doi:1538-7445.AM2012-2742