Abstract
Tissue-nonspecific alkaline phosphatase (TNAP) is an ectoenzyme crucial for bone matrix mineralization via its ability to hydrolyze extracellular inorganic pyrophosphate (ePP(i)), a potent mineralization inhibitor, to phosphate (P(i)). By the controlled hydrolysis of ePP(i), TNAP maintains the correct ratio of P(i) to ePP(i) and therefore enables normal skeletal and dental calcification. In other areas of the body low ePP(i) levels lead to the development of pathological soft-tissue calcification, which can progress to a number of disorders. TNAP inhibitors have been shown to prevent these processes via an increase of ePP(i). Herein we describe the use of a whole blood assay to optimize a previously described series of TNAP inhibitors resulting in 5-((5-chloro-2-methoxyphenyl)sulfonamido)nicotinamide (SBI-425), a potent, selective and oral bioavailable compound that robustly inhibits TNAP in vivo.