Abstract
PURPOSE: Pexidartinib (PLX3397) is a colony-stimulating factor-1 receptor (CSF-1R) inhibitor under clinical evaluation for potential CNS tumor treatment. This study aims to evaluate plasma pharmacokinetic parameters and estimate CNS penetrance of pexidartinib in a non-human primate (NHP) cerebrospinal fluid (CSF) reservoir model. METHODS: Five male rhesus macaques, each with a previously implanted subcutaneous CSF ventricular reservoir and central venous lines, were used. NHPs received a single dose of 40 mg/kg pexidartinib (human equivalent dose of 800 mg/m(2)), administered orally as 200 mg tablets. Serial paired samples of blood and CSF were collected at 0-8, 24, 48, and 72 h. Pexidartinib concentrations were assayed by Integrated Analytical Solutions, Inc. (Berkeley, CA, USA) using HPLC/MS/MS. Pharmacokinetic (PK) analysis was performed using noncompartmental methods. RESULTS: Samples from four NHPs were evaluable. Average (± SD) plasma PK parameters were as follows: C(max) = 16.50 (± 6.67) μg/mL; T(max) = 5.00 (± 2.58) h; AUC(last) = 250.25 (± 103.76) h*μg/mL; CL = 0.18 (± 0.10) L/h/kg. In CSF, pexidartinib was either quantifiable (n = 2), with C(max) values of 16.1 and 10.1 ng/mL achieved 2-4 h after plasma T(max), or undetected at all time points (n = 2, LLOQ(CSF) = 5 ng/mL). CONCLUSION: Pexidartinib was well-tolerated in NHPs, with no Grade 3 or Grade 4 toxicities. The CSF penetration of pexidartinib after single-dose oral administration to NHPs was limited.