(481g) Fractal Analysis of Binding and Dissociaition Kinetics of Thrombin on Biosensor Surfaces

A fractal analysis is used to model the binding kinetics of thrombin inhibitors such as Melagatran, CH-248, and Ingotran in solution to human alpha-thrombin immobilized on a surface plasmon resonance (SPR) biosensor surface (Deinum et al., 2002). The prevention of clot formation due to thrombin is an important area of investigation. Drug candidates for thrombin are often selected on the basis of equilibrium constant values obtained for the thrombin-thrombin inhibitor system. The fractal analysis provides physical insights into diffusion-limited thrombin-thrombin inhibitor interactions occurring on biosensor surfaces.

The analysis of both the binding as well as the dissociation steps provide a more complete picture of the reaction occurring on the biosensor surface. In our analysis the lowest equilibrium constant (Ki) value obtained for 24 nM Ch-248 at 15 degrees centigrade is 0.118. The lowest Ki value for Melagatran is 0.108. This occurs at 1.8 nM Melagatran and at 25 degrees centigrade. There is very little difference in these two values, and thus more data needs to be analyzed to clearly define and distinguish which inhibitor needs to be selected as a possible drug candidate.

The fractal dimension value provides a quantitative measure of the degree of heterogeneity that exists on the biosensor chip surface for the thrombin-thrombin interactions. The degree of heterogeneity for the binding and the dissociation phases is, in general, different. Both types of examples are presented wherein either a single- or a dual-fractal analysis is required to describe the binding and/or dissociation kinetics.

This is the first study that links the affinity, K or the inhibitor equilibrium constant (Ki) to the degree of heterogeneity on a biosensor chip surface. This may be of considerable assistance in helping to select a thrombin or other analyte inhibitor.