Neflamapimod (VX-745) , a specific and effective inhibitor of p38α(IC50=10 nM), is 22-fold greater specificity against p38β and no inhibition activity to p38γ.

VX-745 selectively inhibits p38α and p38β MAPK with IC50 of 10 nM and 220 nM, respectively, but not p38γ MAPK and a large panel of other kinases, with IC50 larger than 20 μM. In a human peripheral blood mononuclear cell (PBMC) assay, VX-745 provides IC50 of 56 and 52 nM for IL-1β and TNFα, respectively. VX-745 blocks IL-6 and IL-8 production induced by IL-1 and TNFα, and COX-2 synthesis mediated by LPS and IL-1β. [1-3] VX-745 (60 nM-20 μM) inhibits IL-6 and VEGF secretion in bone marrow stromal cells (BMSCs), without affecting their viability. VX-745 also inhibits TNF-α-induced IL-6 secretion in BMSCs. VX-745 inhibits both multiple myeloma (MM) cell proliferation and IL-6 secretion in BMSCs triggered by adherence of MM cells to BMSCs, suggesting that VX-745 can inhibit paracrine multiple myeloma (MM) cell growth in the BM milieu and overcome cell adhesion-related drug resistance. [4]

VX-745 is effective against adjuvant-induced arthritis (AA) in the rat with ED50 of 5 mg/kg. Histological scores for VX-745 in AA rats are 93% inhibition of bone resorption and 56% inhibition of inflammation. In the classical cartilage-induced arthritis model, VX-745 exhibits a dose-responsive decrease in severity score. [1-3] In a type II collagen-induced arthritis (CIA) mice model, VX-745 (2.5, 5, and 10 mg/kg) has 27%, 31%, and 44% improvement in the inflammatory scores, respectively, when compared to vehicle-treated mice. In addition, histological scores show a 32-39% protection of bone and cartilage erosion by VX-745. [5]

Spectrophotometric coupled-enzyme assay: The IC50 for the inhibition of p38α and p38β homologs are obtained by a spectrophotometric coupled-enzyme assay. A fixed concentration of enzyme (15 nM of p38α or p38β) is incubated with VX-745 in DMSO for 10 min. at 30 °C in 0.1 M HEPES buffer, pH 7.5, containing 10% glycerol, 10 mM MgCl2, 2.5 mM phosphoenolpyruvate, 200 μM NADH, 150 μg/mL pyruvate kinase, 50 μg/mL lactate dehydrogenase, and 200 μM EGF receptor peptide (KRELVEPLTPSGEAPNQALLR). The reaction is initiated with 100 μM and 70 μM ATP for p38α and p38β assays, respectively. The decrease of absorbance at 340 nm is monitored to follow the rate of the reaction. IC50 is evaluated from the rate data as a function of the inhibitor concentration.

BMSCs (5 × 104 cells/well) or MM cells (3 × 104 cells/well) are incubated in 96-well culture plates in the presence or absence of VX-745 for 48 hours at 37 °C. DNA synthesis is measured by [3H]-thymidine ([3H]TdR) uptake. Cells are pulsed with [3H]TdR (0.5 μCi/well [.0185 MBq]) during the last 8 hours of 48-hour cultures. Growth inhibition of both MM cells and BMSCs by VX-745 is also assessed by measuring 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) dye absorbance.(Only for Reference)