MLK-IN-2 (Compound 9a) is a potent and selective MLK3 inhibitor (IC50 = 6 nM) based on a 3H-imidazole[4,5-b]pyridine scaffold. This small molecule is a valuable research tool for studying MLK3 signaling in cancer and neurodegenerative disease models, applicable in both in vitro and in vivo experimental contexts.