A displacement approach for competitive drug-protein binding studies usingthe potentiometric 1-anilino-8-naphthalene-sulfonate probe technique

A displacement approach for competitive binding studies was developed. The method utilizes the potentiometric 1-anilino-8-naphthalene-sulfonate (ANS) probe technique and is applied to the binding study of several non-steroida l anti-inflammatory drugs (NSADs) to bovine serum albumin (BSA). A home-mad e ANS electrode was used to monitor the displaced free ANS probe from its b inding sites on the protein molecule by the stepwise addition of the studie d drug. To assess and compare quantitatively the displacing ability of the various drugs, the 'ANS Displacement Index' is used. The possible interfere nce of 19 ionizable drugs (NSADs, sulfonamides, etc.) to the ANS selective electrode at pH 7.4 was studied and their potentiometric selectivity coeffi cients (K-ANS,D(pot)) were determined. Correction procedures for the determ ination of the free ANS concentration are proposed in the case of interferi ng ionic drugs. A blank binding experiment in conjunction with the incorpor ation of K-ANS,D(pot) values in the 'general competitive site oriented mode l' allows one to derive estimates for the drug binding parameters, i.e. the number of binding sites and association constants. (C) 1999 Elsevier Scien ce B.V. All rights reserved.