Understanding CXCR2 antagonism with a dynamic allosteric ternary complex model

Area of Science:

• Pharmacology
• Biochemistry
• Drug Discovery

Background:

• CXC chemokine receptor 2 (CXCR2) antagonists exhibit varied antagonism patterns in vitro and in clinical studies.
• Existing CXCR2 antagonists are allosteric but show inconsistent assay results and clinical efficacy.
• Favorable drug exposures in clinical trials contrast with observed target modulation and efficacy issues.

Purpose of the Study:

• To elucidate the mechanistic basis for inconsistent CXCR2 antagonist behavior using a dynamic allosteric ternary complex model.
• To unify hypotheses explaining variable antagonism patterns observed in different experimental settings.
• To bridge the gap between in vitro pharmacology and clinical outcomes for CXCR2 antagonists.

Main Methods:

• Application of a dynamic allosteric ternary complex model to analyze in vitro binding and cell-based assay data.
• Analysis of clinical neutrophil count data from CXCR2 antagonist studies using the proposed model.
• Development of a unified hypothesis to explain surmountable vs. insurmountable antagonism based on receptor reserve and binding kinetics.

Main Results:

• The dynamic allosteric ternary complex model successfully describes both in vitro and clinical data for CXCR2 antagonists.
• Inconsistent antagonism patterns are attributed to receptor reserve and unsteady-state binding in cell-based assays.
• Suboptimal potency, rather than fast binding kinetics, likely explains the lack of clinical pharmacology effect in some cases.

Conclusions:

• The proposed model provides a unified explanation for the variable pharmacology of CXCR2 antagonists.
• Receptor reserve and binding kinetics are critical factors influencing antagonist behavior in different assay conditions.
• The model offers a framework for predicting clinical responses of allosteric antagonists for CXCR2 and other GPCRs.