The potency-insolubility conundrum in pharmaceuticals: Mechanism and solution for hepatitis C protease inhibitors
As compounds are optimized for greater potency during pharmaceutical discovery, their aqueous solubility often decreases, making them less viable as orally-administered drugs. To investigate whether potency and insolubility share a common origin, we examined the structural and thermodynamic properties of telaprevir, a sparingly soluble inhibitor of hepatitis C virus protease. Comparison of the hydrogen bond motifs in crystalline telaprevir with those present in the protease–telaprevir complex revealed striking similarities. Additionally, the thermodynamics of telaprevir dissolution closely resembles those of protein–ligand dissociation. Together, these findings point to a common origin of potency and insolubility rooted in particular amide–amide hydrogen bond patterns. The insolubility of telaprevir is shown by computational analysis to be caused by interactions in the crystal, not unfavorable hydrophobic hydration. Accordingly, competing out the particular amide–amide hydrogen bond motifs in crystalline telaprevir with 4-hydroxybenzoic acid yielded a co-crystalline solid with excellent aqueous dissolution and oral absorption. The analysis suggests a generalizable approach for identifying drug candidate compounds that either can or cannot be rendered orally bioavailable by alteration of their crystalline solid phases, in an approach that provides a pragmatic way to attain substantial enhancements in the success rate of drug discovery and development.