Prodrug Strategy to Address Impaired Oral Absorption of a Weakly Basic TYK2 Inhibitor Caused by a Gastric Acid-Reducing Agent

The pH-dependent solubility of the weakly basic TYK2 inhibitor 1 posed a risk to its advancement, given that drugs with such profiles have exhibited drug–drug interaction (DDI) with stomach acid-reducing agents in humans. In a rat model of pH dependence, preadministration of famotidine caused a 2.4-fold lower exposure of 1 when compared to control rats, implying that pH-dependent oral absorption can reduce the active drug's exposure and translate to subtherapeutic treatment. As part of risk mitigation, a prodrug strategy was explored by synthesizing solubility-enhancing prodrugs, resulting in the identification of lead prodrug 3c with acceptable stability and solubility profiles. In rats, the prodrug eliminated the significant difference in AUC and Cmax between pentagastrin and famotidine arms, thereby effectively mitigating the impaired drug absorption at the elevated pH relevant for absorption and DDI with famotidine. The prodrug also facilitated dose-proportional systemic exposure of 1 following dose escalation in rats and monkeys.