Pharmacokinetic and pharmacodynamic profiling of a P2X7 receptor allosteric modulator GSK1482160 in healthy human subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • P2X7 receptors are involved in the production of pro-inflammatory cytokines, such as Il-1β, by central and peripheral immune cells. Il-1β has been implicated as an important mediator of inflammation. Therefore, the P2X7 receptor is an attractive therapeutic target for inflammatory diseases. WHAT THIS STUDY ADDS • Findings in pharmacokinetics, pharmacodynamics, safety and tolerability of a P2X7 receptor modulator, GSK1482160, from the first human study for the molecule are described. A pharmacokinetic/pharmacodynamic model for LPS-stimulated ATP-induced Il-1β production in blood allowed the integration of all relevant data and provided in vivo evidence of the nature of the drug–receptor interaction. The model has the potential to be used to simulate future trials. AIMS This paper describes findings from the first-in-human study for GSK1482160, an orally available allosteric P2X7 receptor modulator. The study aimed to assess the pharmacokinetics (PK), pharmacodynamics (PD), safety and tolerability of the compound in healthy subjects. METHODS Escalating single doses of up to 1 g were administered to healthy subjects in a single-blind and placebo-controlled fashion. Safety, tolerability, blood drug concentrations and ex vivo Il-1β production in blood were evaluated. RESULTS Drug concentration peaked within 3.5 h of dosing under fasting conditions and declined thereafter with a relatively short half-life of less than 4.5 h. Exposure was proportional to dose with between subject variability of less than 60%. A PK/PD model quantified Il-1β as a function of drug exposure. The model allowed simulation of in vivo pharmacology for various untested dose levels and regimens. Furthermore, the mechanistic model supported the hypothesis that the compound reduces the efficacy of ATP at the P2X7 receptor without affecting its affinity. No major safety or tolerability concerns were identified in this small study (n= 29), except for one case of asymptomatic accelerated idioventricular rhythm at the top dose. CONCLUSION The model-based approach maximized analysis power by integrating all biomarker data and revealed mechanistic insight into the pharmacology of P2X7 modulation by GSK1482160. Simulations by this model ultimately led to the discontinuation of the development of this compound. The therapeutic relevance of the P2X7 receptor remains to be tested in patients. The mechanistic-model-based approach can be applied widely to drug development.