Nicotinamide phosphoribosyltransferase is a molecular target of potent anticancer agents identified from phenotype-based drug screening.

Phenotypic screening in drug discovery has been revived with the expectation of providing promising lead compounds and drug targets and improving the success rate of drug approval. However, target identification remains a major bottleneck in phenotype-based drug discovery. We identified the lead compounds K542 and K405 with a selective inhibition of cell viability against sphingosine-1-phosphate lyase 1 (SGPL1)-transduced ES-2 cells by phenotypic screening. We therefore performed an in vivo pharmacological examination and observed the antitumor activity of K542 in an HT-1080 tumor-bearing mouse xenograft model. SGPL1 was expected to be a therapeutic target in some cancers, suggesting that these lead molecules might be promising candidates; however, their mechanisms of action still remain unexplained. We therefore synthesized the affinity probe Ind-tag derived from K542 and identified the proteins binding to Ind-tag via a pull-down experiment. Proteomics and biochemical analyses revealed that the target molecule of these lead compounds was Nicotinamide phosphoribosyltransferase (NAMPT). We established K542-resistant DLD-1 and HT-1080 cells, and genetic analyses of these cells identified a missense mutation in the NAMPT-encoding gene. This enzymatic experiment clearly showed that K393 exerts enzymatic inhibition against NAMPT. These proteomics, genetics and biochemical analyses clarified that compounds K542 and K405 were NAMPT inhibitors.

The orally-active and selective c-Fms tyrosine kinase inhibitor Ki20227 inhibits disease progression in a collagen-induced arthritis mouse model.

Macrophage colony-stimulating factor (M-CSF) is important in the development of macrophages and osteoclasts. Previous studies have also shown that CD11b(+) myeloblasts and osteoclasts play key roles during inflammation and bone destruction in arthritic lesions. In this study, we investigated whether N-{4-[(6,7-dimethoxy-4-quinolyl)oxy]-2-methoxyphenyl}-N'-[1-(1,3-thiazole-2-yl)ethyl] urea (Ki20227), an inhibitor of the M-CSF receptor (c-Fms), suppressed disease progression in a type II collagen (CII)-induced arthritis (CIA) mouse model. We found that Ki20227 inhibited M-CSF-dependent reactions, such as lipopolysaccharide-induced tumor necrosis factor-alpha production, which were enhanced by M-CSF in vitro. Oral administration of Ki20227 in vivo prevented inflammatory cell infiltration and bone destruction, and consequently suppressed disease progression. In addition, the number of CD11b(+), Gr-1(+), and Ly-6G(+) cells in the spleen decreased in the Ki20227-treated mice, and the CII-induced cytokine production in splenocytes isolated from the Ki20227-treated arthritic mice was also reduced. These observations indicate that Ki20227 might exert its therapeutic effects in the CIA mouse model by suppressing the M-CSF-dependent accumulation of both inflammatory and osteoclast cells, as well as by inhibiting inflammatory cytokine production. Hence, inhibitors of the c-Fms tyrosine kinase might act as anti-inflammatory or anti-osteolytic agents against arthritis.