A quantitative mechanistic PK/PD model directly connects Btk target engagement and in vivo efficacy

Correlating target engagement with <i>in vivo</i> drug activity remains a central challenge in efforts to improve the efficiency of drug discovery. Previously we described a mechanistic pharmacokinetic-pharmacodynamic (PK/PD) model that used drug-target binding kinetics to successfully predict the <i>in vivo</i> efficacy of antibacterial compounds in models of <i>Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i> infection. In the present work we extend this model to quantitatively correlate the engagement of Bruton's tyrosine kinase (Btk) by the covalent inhibitor CC-292 with the ability of this compound to reduce ankle swelling in an animal model of arthritis. The modeling studies include the rate of Btk turnover and reveal the vulnerability of Btk to engagement by CC-292.