Characterizing Pharmacokinetic-Pharmacodynamic Relationships and Efficacy of PI3K Inhibitors in Respiratory Models of TH2 and TH1 Inflammation.

We leveraged a clinical pharmacokinetic (PK)/pharmacodynamics (PD)/efficacy relationship established with an oral phosphatidylinositol 3-kinase (PI3K) inhibitor (Idelalisib) in a nasal allergen challenge study to determine whether a comparable PK/PD/efficacy relationship with PI3K inhibitors was observed in preclinical respiratory models of type 2 T helper cell (TH2) and type 1 T helper cell (TH1) inflammation. Results from an in vitro rat blood basophil (CD63) activation assay were used as a PD biomarker. IC values for PI3K inhibitors, MSD-496486311, MSD-126796721, Idelalisib, and Duvelisib, were 1.2, 4.8, 0.8, and 0.5 M. In the ovalbumin Brown Norway TH2 pulmonary inflammation model, all PI3K inhibitors produced a dose-dependent inhibition of bronchoalveolar lavage eosinophils (maximum effect between 80% and 99%). In a follow-up experiment designed to investigate PK attributes [maximum (or peak) plasma concentration (Cmax), area under the curve (AUC), time on target (ToT)] that govern PI3K efficacy, MSD-496486311 [3 mg/kg every day (QD) and 100 mg/kg QD] produced 16% and 93% inhibition of eosinophils, whereas doses (20 mg/kg QD, 10 mg/kg twice per day, and 3 mg/kg three times per day) produced 54% to 66% inhibition. Our profiling suggests that impact of PI3K inhibitors on eosinophils is supported by a PK target with a ToT over the course of treatment close to the PD IC rather than strictly driven by AUC, Cmax, or Cmin (minimum blood plasma concentration) coverage. Additional studies in an rat model, a sheep Ascaris-sensitive sheep model, and a TH1-driven rat ozone exposure model did not challenge our hypothesis, suggesting that an IC level of TE (target engagement) sustained for 24 hours is required to produce efficacy in these traditional models. We conclude that the PK/PD observations in our animal models appear to align with clinical results associated with a TH2 airway disease.