BACKGROUND AND PURPOSEThe KCa3.1 channel is a potential target for therapy of immune disease. We identified a compound from a new chemical class of KCa3.1 inhibitors and assessed in vitro and in vivo inhibition of immune responses. EXPERIMENTAL APPROACHWe characterized the benzothiazinone NS6180 (4- [[3-(trifluoromethyl)phenyl]methyl]-2H-1,4-benzothiazin-3(4H)-one) with respect to potency and molecular site of action on KCa3.1 channels, selectivity towards other targets, effects on T-cell activation as well as pharmacokinetics and inflammation control in colitis induced by 2,4-dinitrobenzene sulfonic acid, a rat model of inflammatory bowel disease (IBD). KEY RESULTSNS6180 inhibited cloned human KCa3.1 channels (IC50 = 9 nM) via T250 and V275, the same amino acid residues conferring sensitivity to triarylmethanes such as like TRAM-34. NS6180 inhibited endogenously expressed KCa3.1 channels in human, mouse and rat erythrocytes, with similar potencies (15-20 nM). NS6180 suppressed rat and mouse splenocyte proliferation at submicrolar concentrations and potently inhibited IL-2 and IFN-g production, while exerting smaller effects on IL-4 and TNF-a and no effect on IL-17 production. Antibody staining showed KCa3.1 channels in healthy colon and strong up-regulation in association with infiltrating immune cells after induction of colitis. Despite poor plasma exposure, NS6180 (3 and 10 mg·kg -1 b.i.d.) dampened colon inflammation and improved body weight gain as effectively as the standard IBD drug sulfasalazine (300 mg·kg -1 q.d.).

Small-conductance (K Ca 2) and intermediate-conductance (K Ca 3