AZD-7624

Inhaled drugs generally aim to drive a local pharmacological effect in lung, at the same time minimizing systemic exposure, in order to obtain efficacy in lung disease without unwanted systemic effects. Here, we demonstrate that inhaled delivery of a p38 inhibitor (AZD7624) can provide superior pharmacokinetic exposure and superior pharmacodynamic lung effects. In rats, inhaled AZD7624 had a five times higher dose-adjusted lung exposure compared with intravenous dosing. In healthy volunteers, lipopolysaccharide (LPS)-induced tumor necrosis factor α (TNFα) in sputum has been shown to be significantly reduced (85%) by means of inhaled AZD7624. Here, we demonstrate that this effect is associated with a mean unbound plasma concentration, gained from in vitro and ex vivo LPS-challenge protocols, significantly below potencies obtained for AZD7624, suggesting that lung exposure is probably much higher than systemic exposure. This assessment was made for the unbound potency (pIC₅₀u), e.g., the potency remaining after adjustment for plasma protein binding and blood plasma ratio. Hence, the unbound potency of AZD7624 to inhibit LPS-induced TNFα in human mononuclear cells, in whole blood as well as in alveolar macrophages in vitro, was 8.4, 8.7 (full inhibition), and 9.0 (partial inhibition), respectively. The pIC₅₀u in whole blood ex vivo was 8.8, showing good in vitro/in vivo potency correlations. Thus, a mean unbound AZD7624 plasma concentration of 0.3 nmol/l, which was associated with a decrease in LPS-induced sputum TNFα by 85%, is much lower than the pIC₅₀u. This demonstrates that AZD7624 can achieve significant local lung pharmacodynamic effects with concomitant sub-pharmacological systemic exposure.

The p38 protein kinases, in particular p38α and p38β, regulate the production of multiple inflammatory mediators. Consequentially, considerable effort has been focused on trying to develop p38 inhibitors for the treatment of inflammatory diseases. Some 20 p38 inhibitors have progressed to clinical development, mostly for the treatment of rheumatoid arthritis, but with little success. Increasingly, interest has turned to their use in other indications and notably chronic obstructive pulmonary disease (COPD).

In this review, the author discusses the eight p38 inhibitors that have been clinically evaluated. Acumapimod is the only one of four orally delivered inhibitors that remains in active development while Phase II results of PH-797804 and losmapimod are compared. The activity of two inhibitors designed for inhaled delivery, RV-568 and PF-03715455, is compared but little is known about AZD-7624 or the discontinued GSK-610677.

Results from animal models provide a clear rationale for developing p38 inhibitors for COPD, and appear to be (partially) validated by the efficacy seen with PH-797804 and losmapimod. Inhaled delivery provides the opportunity to enhance p38 inhibition in the lung while reducing unwanted systemic effects of p38 inhibition. Validation of this hypothesis should come from the results of the recently completed Phase II study with RV-568.