Plasma and cerebrospinal fluid pharmacokinetics of selumetinib in non-human primates (NHP).

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e14070 Background: Selumetinib (AZD6244 hyd sulfate) is an orally bioavailable agent targeting mitogen-activated protein kinase (MEK) 1/2. Selumetinib has shown activity in children with NF1 plexiform neurofibromas and refractory low-grade gliomas. The central nervous system (CNS) penetration of selumetinib in humans is unknown. Methods: We analyzed selumetinib in the cerebrospinal fluid (CSF) of NHP as a surrogate for CNS penetration. Four adult male rhesus macaques were each given a single dose of selumetinib capsules 2.5 mg/kg (human equivalent dose 50 mg/m2) by mouth on an empty stomach. Selumetinib was quantified in serial paired plasma and CSF samples from 0 to 48 hours after administration by Covance Bioanalytical Services (lower limit of quantification 0.5 ng/mL). Free selumetinib was estimated at 2.3% of total based on reported plasma protein binding of 97.7% in NHP. Pharmacokinetic parameters including area under the concentration x time curve (AUC) of selumetinib were calculated using non-compartmental methods and CSF penetration was calculated from the ratio of AUC (CSF): AUC (plasma). Results: Selumetinib was detected in plasma in all four NHPs, but in the CSF of only one NHP (ZH60). The mean (± SD) AUC0-∞ and half-life (t1/2) in plasma were 3350 ± 489 ng•h/mL and 10.8 ± 2.5 hours, respectively. In ZH60, the CSF AUC0-48 hr was 10.6 ng•h/mL. The CSF penetration of total and free selumetinib in this animal was 0.4%, and 14%, respectively. The mean plasma AUC and t1/2 were comparable to that of children (2842 ng•h/mL and 6.9 hours, respectively) at a similar dose in a phase I trial. However, the average peak concentration in children occurred at approximately 1 hour with a Cmax of 841 ng/mL, while the Cmax in NHP plasma ranged from 1 – 4 hours and averaged 198.8 ng/mL. Conclusions: The CSF penetration of oral selumetinib is limited; in one NHP it was 0.4% and 14% when corrected for plasma protein binding of selumetinib. The fact that plasma AUC0-∞ and half-lives in NHP were similar to previously reported human plasma PK indicates that this model may accurately reflect human CSF penetration as well.