A Receptor Model With Binding Affinity, Activation Efficacy, and Signal Amplification Parameters for Complex...

Area of Science:

• Quantitative Pharmacology
• Receptor Theory
• Biophysics

Background:

• Complex nonlinear relationships between fractional receptor occupancy and response necessitate multi-parameter models.
• Existing models like the operational and del Castillo-Katz models have limitations in parameter intuitiveness and fitting complex data.
• Understanding receptor-ligand interactions requires accounting for binding, activation, and post-activation signal transduction.

Purpose of the Study:

• To propose a general two-state receptor model unifying receptor binding, activation, and signal amplification.
• To introduce a model with intuitive parameters (Kd, ε, γ, εR0) suitable for nonlinear regression.
• To provide a unified framework for fitting complex pharmacological data, including biased agonism and constitutive activity.

Main Methods:

• Development of a general two-state receptor model incorporating equilibrium dissociation constant (Kd), intrinsic efficacy (ε), signal gain (γ), and constitutive activity (εR0).
• Utilizing two-state receptor theory where receptors exist in active/inactive states, with ligand binding influencing activation likelihood (induced fit).
• Demonstrating the model's ability to simplify to established models (e.g., Emax, Clark) under specific parameter conditions.

Main Results:

• The proposed model successfully unifies distinct processes: receptor binding, activation, and post-activation signal transduction.
• Parameters are more intuitive and better suited for nonlinear regression compared to the operational or del Castillo-Katz models.
• The model accommodates complex data including mismatched fractional responses/occupancies, receptor reserve, biased agonism, and constitutive activity.

Conclusions:

• The general two-state receptor model provides a unified and more intuitive framework for quantitative pharmacology.
• This model enhances the analysis of complex receptor-ligand interactions and downstream signaling.
• Its flexibility allows for application to diverse pharmacological scenarios and simplification to known models.