S-methyl-KE-298 is an active metabolite of KE-298. KE-298 inhibits matrix metalloproteinase (MMP-1) production from rheumatoid arthritis (RA) synovial cells. S-methyl-KE-298 is a methyl conjugate of deacetyl-KE-298 is plasma. In vitro protein binding of KE-298 and its plasma metabolites, deacetyl-KE-298 (M-1) and S-methyl-KE-298 (M-2), is high in rat (>97%), dog (>89%) and human plasma (>99%), respectively. KE-298 blocks this IL-1β-induced pro-MMP-2 activation and MT1-MMP expression, but does not affect IL-1β-induced tissue inhibitor of metalloproteinase-2 (TIMP-2) secretion from rheumatoid synovial cells. KE-298 inhibits MMP-1 production from rheumatoid arthritis (RA) synovial cells by affecting a transcription factor, AP-1. KE-298 inhibits the basal levels of MT1-MMP expression of unstimulated rheumatoid synovial cells.