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

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.