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S18-01 A QUEST FOR A DISEASE MODIFYING DRUG FOR THE TREATMENT OF OSTEOARTHRITIS-RELATED CALCIUM PYROPHOSPHATE DEPOSITION DISEASE Bilha Fischer, a *Molhm Nassir, a Julie Pelletier, b Uri Arad, c Guillaume Arguin, d Hanoch Senderowich, a Fernand-Pierre Gendron, d Jean Sévigny, b,e Salahuddin Mirza, f and Christa E. Müller f a Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900 Israel b Centre de Recherche du CHU de Québec – Université Laval, Pavillon CHUL, Québec city, QC, Canada c Department of Rheumatology, Tel Aviv Medical Center and the Faculty of Medicine, Tel Aviv University, Tel Aviv, 6997801, Israel d Département d’anatomie et de biologie cellulaire, Faculté de Médecine et des sciences de la santé, Université de Sherbrooke, PRAC, 3201 Jean-Mignault, Sherbrooke, QC, J1E 4K8, Canada e Département de Microbiologie-Infectiologie et d’Immunologie, Faculté de Médecine, Université Laval, Quebec city, QC G1V 4G2, Canada, f PharmaCenter Bonn, Pharmaceutical Institute, Pharmaceutical Chemistry I, University of Bonn, Bonn, Germany, Ecto-nucleotide pyrophosphatase-1 (NPP1) hydrolyzes phosphodiester bonds of ATP resulting mainly in the formation of AMP and pyrophosphate (PP i ). NPP1’s activity plays a deleterious function in osteoarthritis (OA)/calcium pyrophosphate deposition (CPPD) disease. Hence, inhibitors of NPP1 represent a medical need. For this purpose, we developed several generations of potent and selective NPP1 inhibitors based on scaffolds of natural nucleotides. The design of the candidates was based on molecular modeling of NPP1, namely, on the catalytic site which contains two zinc ions, and the catalytic mechanism. The novel nucleotides have been prepared via rather facile syntheses trying to avoid the formation of a new chiral center. Later, the analogs have been evaluated; first as substrates of ecto-nucleotidases, NPP1,-3 and NTPDase1,-2,-3 and -8, and then, for non-substrates, as inhibitors of these enzymes. In addition, we explored the selectivity of the NPP1 inhibitors at relevant purinergic receptors. Promising NPP1 inhibitors effectively inhibited NPPase vs. TNAP activity in whole human cartilage and in human osteoarthritic chondrocytes, and reduced extracellular PP i accumulation. Finally, NPP1 inhibitors were tested for toxicity to human chondrocytes and for stability in culture medium and human plasma. Docking simulations have indicated the origin of the enhanced NPP1 inhibitory activity and selectivity of most promising analogs. Among all tested analogs MN8 was identified as a potent NPP1 inhibitor both in assays using purified enzyme (IC 50 0.645 µM) and in osteoarthritic human chondrocytes (IC 50 0.033 µM). Furthermore, it efficaciously (10-fold vs. control) inhibited ATP-induced CPPD deposition in human chondrocytes. Therefore, we suggest several potent and selective inhibitors of NPP1 for lowering extracellular PP i levels in cartilage for delaying and treating OA/CPPD.