The Cheng-Prusoff relationship: something lost in the translation

Area of Science:

• Pharmacology
• Receptor binding assays
• Drug discovery

Background:

• Pharmacologists frequently use 'inhibition curves' to assess antagonists due to practical considerations.
• A common misconception suggests that determining antagonist affinity (Kb) from inhibition curves necessitates the Cheng-Prusoff equation, which requires prior knowledge of agonist affinity.
• This reliance on agonist affinity can be a limitation in experimental design and data interpretation.

Purpose of the Study:

• To critically examine the methodology of 'inhibition curve' construction in pharmacology.
• To demonstrate a theoretically sound method for estimating antagonist Kb values from inhibition curves without needing to know the agonist affinity.
• To provide a practical alternative to the Cheng-Prusoff equation for antagonist characterization.

Main Methods:

• Analysis of 'inhibition curve' data.
• Comparison of different mathematical models for data fitting.
• Theoretical derivation of an alternative equation for Kb estimation.

Main Results:

• The study identifies a specific equation, distinct from the Cheng-Prusoff equation, that is suitable for analyzing inhibition curves.
• This alternative equation allows for the reliable estimation of antagonist Kb values.
• Crucially, this method does not require prior knowledge of the agonist's affinity for the receptor.

Conclusions:

• Inhibition curves can be practically and theoretically utilized to derive valid antagonist Kb values.
• A specific, related equation enables Kb estimation without requiring knowledge of agonist affinity.
• This finding offers a more accessible and versatile approach for pharmacologists evaluating antagonists.