Esonarimod (KE-298) is an antirheumatic drug designed to alleviate symptoms associated with rheumatoid arthritis.

The IC50 of Esonarimod is 117.5 μg/mL. In RAW264.7 cells, Esonarimod (KE-298) (10 to 300 μg/mL) suppresses the production of NO in a dose-dependent manner.

After repeated oral administration of Esonarimod (14C-KE-298), the radioactivity rapidly decreases with no accumulation observed.

To test enzyme activity of NOS, the lysate from RAW264.7 cells (a protein concentration of 37.5 μg/200 μL) is incubated for 3 h at 37°C with 100 mM of L-arginine in the presence of Esonarimod (KE-298) and the conversion of L-arginine to nitrite is monitored.

For in vitro experiment, Esonarimod (KE-298) is dissolved in ethanol and diluted with culture medium or distilled water.RAW264.7 cells are used in this study. For NO production, RAW264.7 cells [2×105/0.2 mL of RPMI-1640 supplemented by 10% heat inactivated fetal bovine serum (FBS), penicillin G (100 U/mL), and streptomycin (100 μg/mL)] are stimulated with 100 ng/mL of Escherichia coli 026:B6 lipopolysaccharide in the presence of Esonarimod (KE-298) (0, 10, 30, 100, 200, 300 μg/mL) in 96 well plates and incubated 24 h at 37°C in an atmosphere of 5% CO2 in air. After incubation, the supernatants are collected and assayed for nitrite (NO2-) instead of NO[1].

Seven-week-old male Wistar rats is administered Esonarimod (5 mg/kg once daily) orally by gastric intubation.