Thermodynamic characterization of pyrazole and azaindole derivatives binding to p38 mitogen-activated protein kinase using Biacore T100 technology and van’t Hoff analysis

Biacore T100 technology was used in conjunction with a van’t Hoff analysis to characterize the thermodynamic binding parameters of 85 small-molecule inhibitors of adenosine triphosphate (ATP) binding to p38 mitogen-activated protein (MAP) kinase. The compounds were selected from a large panel of azaindole and pyrazole derivatives for which IC50 data exist. We showed a strong relationship between the KD and IC50 of a compound, but only a modest relationship between koff and IC50 was detected and an apparent relationship between a compound’s kon and its IC50 could not be discerned. Similarly, a correlation between a compound’s IC50 and its thermodynamic parameters ΔH° and ΔS° could not be established. The lack of a predominant kinetic or thermodynamic signature associated with the inhibitory potential of these compounds demonstrates that there exists, even within a single well-defined system, a library of kinetic routes or, alternatively, a library of initial and final enthalpic and entropic states from which to effect inhibition. As a complement to these studies, selected double mutant thermodynamic cycles were performed to probe the energetic coupling, if any, between common sites of fluorination in both the azaindole and pyrazole classes and two different substituents. Although both cycles indicated negligible coupling free energies, both revealed significant coupling enthalpies, an observation made in other similarly dissected systems. The possible significance and caveats associated with these findings along with the advantages of using Biacore technology to derive thermodynamic parameters in drug discovery efforts are discussed.