Development of Selective Pyrido[2,3-d]pyrimidin-7(8H)-one-Based Mammalian STE20-Like (MST3/4) Kinase Inhibitors.

Mammalian STE20-like (MST) kinases 1-4 play key roles in regulating the Hippo and autophagy pathways, and their dysregulation has been implicated in cancer development. In contrast to the well-studied MST1/2, the roles of MST3/4 are less clear, in part due to the lack of potent and selective inhibitors. Here, we re-evaluated literature compounds, and used structure-guided design to optimize the p21-activated kinase (PAK) inhibitor G-5555 (8) to selectively target MST3/4. These efforts resulted in the development of MR24 (24) and MR30 (27) with good kinome-wide selectivity and high cellular potency. The distinct cellular functions of closely related MST kinases can now be elucidated with subfamily-selective chemical tool compounds using a combination of the MST1/2 inhibitor PF-06447475 (2) and the two MST3/4 inhibitors developed. We found that MST3/4-selective inhibition caused a cell-cycle arrest in the G1 phase, whereas MST1/2 inhibition resulted in accumulation of cells in the G2/M phase.

Structure-Based Design of Selective Salt-Inducible Kinase Inhibitors.

Salt-inducible kinases (SIKs) are key metabolic regulators. The imbalance in SIK function is associated with the development of diverse cancers, including breast, gastric, and ovarian cancers. Chemical tools to clarify the roles of SIK in different diseases are, however, sparse and are generally characterized by poor kinome-wide selectivity. Here, we have adapted the pyrido[2,3-d]pyrimidin-7-one-based p21-activated kinase (PAK) inhibitor G-5555 for the targeting of SIK, by exploiting differences in the back-pocket region of these kinases. Optimization was supported by high-resolution crystal structures of G-5555 bound to the known off-targets, MST3 and MST4, leading to a chemical probe, MRIA9, with dual SIK/PAK activity and excellent selectivity over other kinases. Furthermore, we show that MRIA9 sensitizes ovarian cancer cells to treatment with the mitotic agent paclitaxel, confirming earlier data from genetic knockdown studies and suggesting a combination therapy with SIK inhibitors and paclitaxel for the treatment of paclitaxel-resistant ovarian cancer.

A Highly Selective Chemical Probe for Activin Receptor-like Kinases ALK4 and ALK5.

The transforming growth factor beta-receptor I/activin receptor-like kinase 5 (TGFBR1/ALK5) and its close homologue ALK4 are receptor protein kinases associated with the development of diverse diseases, including cancer, fibrosis, heart diseases, and dysfunctional immune response. Therefore, ALK4/5 are among the most studied kinases, and several inhibitors have been developed. However, current commercially available inhibitors either lack selectivity or have not been comprehensively characterized, limiting their value for studying ALK4/5 function in cellular systems. To this end, we report the characterization of the 2-oxo-imidazopyridine, TP-008, a potent chemical probe with dual activity for ALK4 and ALK5 as well as the development of a matching negative control compound. TP-008 has excellent cellular potency and strongly abrogates phosphorylation of the substrate SMAD2 (mothers against decapentaplegic homologue 2). Thus, this chemical probe offers an excellent tool for mechanistic studies on the ALK4/5 signaling pathway and the contribution of these targets to disease.

Fenofibrate oral absorption from SNEDDS and super-SNEDDS is not significantly affected by lipase inhibition in rats.

The effect of drug load and digestion on the solubilization and absorption of fenofibrate in self-nanoemulsifying drug delivery system (SNEDDS) was assessed in a pharmacokinetic study in rats and in an in vitro lipolysis model. SNEDDS containing fenofibrate at 75% of equilibrium solubility (Seq), a super-saturated SNEDDS (super-SNEDDS) containing fenofibrate at 150% of Seq and a super-SNEDDS suspension containing fenofibrate at 100% of Seq and an additional 50% Seq fenofibrate suspended (150% of Seq in total) were used. To assess the effect of lipid digestion on fenofibrate absorption in rats and fenofibrate solubilization during in vitro lipolysis, the lipase inhibitor orlistat was added at 1% (w/w) to the SNEDDS, resulting in six different SNEDDS: SNEDDS, super-SNEDDS and super-SNEDDS suspension with and without orlistat 1% (w/w). In vivo, super-SNEDDS had a higher Cmax and AUC0-30h compared to SNEDDS and super-SNEDDS suspension, both with and without orlistat. While orlistat did not affect fenofibrate absorption in SNEDDS and super-SNEDDS, an increase of Tmax and AUC0-30h for super-SNEDDS suspension was found when orlistat was present. During in vitro lipolysis, the addition of orlistat decreased digestion and lowered drug precipitation. Super-SNEDDS showed significantly increased absorption in rats compared to SNEDDS and super-SNEDDS suspension and the inhibition of digestion resulted in prolonged and increased absorption for the super-SNEDDS suspension.