Adenine-(methoxy)-ethoxy-P_α,α-dithio-triphosphate inhibits pathologic calcium pyrophosphate deposition in osteoarthritic human chondrocytes

Nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) inhibitors have been suggested as a potential treatment for calcium pyrophosphate dihydrate (CPPD) deposition disease. Here, we targeted the development of improved NPP1 inhibitors based on acyclic mimics of P_α,α-phosphorodithioate-substituted adenine nucleotides, 7-10. The latter were obtained in a facile two-step synthesis from adenine-(methoxy)ethanol. Among analogs 7-10, adenine-(methoxy)ethoxy-P_α,α-dithio-triphosphate, 8, was the most potent NPP1 inhibitor both with purified enzyme (IC₅₀ 0.645 μM) and in osteoarthritic human chondrocytes (IC₅₀ 0.033 μM). Furthermore, it efficaciously (10-fold vs. control) inhibited ATP-induced CPPD in human articular chondrocytes. Importantly, 8 was a highly selective NPP1 inhibitor which showed only minor inhibition of NPP3, CD39 and CD73, and did not inhibit TNAP (tissue nonspecific alkaline phosphatase) activity in human chondrocytes. Furthermore, 8 did not activate P2Y_1,2,6 receptors. Analog 8 was not toxic to cultured chondrocytes at 100 μM. Therefore, 8 may be suitable for further development as a drug candidate for the treatment of CPPD arthritis and other NPP1-related diseases.