Discovery of the First Highly Selective 1,4-dihydropyrido[3,4-b]pyrazin-3(2H)-one MKK4 Inhibitor

Due to limited treatment options, liver failure remains a major challenge in modern medicine. With the validation of mitogen-activated protein kinase kinase 4 (MKK4, also known as MEK4 or MAP2K4) as a regulator of hepatocyte regeneration, a promising target for curative treatment of degenerative liver diseases was recently identified via in vivo RNAi experiments. The field of small molecules targeting MKK4 is of growing interest. Several MKK4 inhibitors with differing scaffolds are known, but few have reasonable selectivity profiles and drug-like properties. To further explore the space of drug-like MKK4 scaffolds, we performed a broad screening campaign and identified BI-D1870 as a promising candidate. The dihydropteridinone BI-D1870 is an unselective ribosomal S6 kinase inhibitor with broad off-target activity. In the study presented herein, we report a successful off-to-on target strategy that led to the development of highly selective 1,4-dihydropyrido[3,4-b]pyrazin-3(2H)-one inhibitors of MKK4.