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T cell activation starts with formation of second messengers that release Ca2+ from the endoplasmic reticulum (ER) and thereby activate store-operated Ca2+ entry (SOCE), one of the essential signals for T cell activation. Recently, the steroidal 2-methoxyestradiol was shown to inhibit nuclear translocation of the nuclear factor of activated T cells (NFAT). We therefore investigated 2-methoxyestradiol for inhibition of Ca2+ entry in T cells, screened a library of 2-methoxyestradiol analogues, and characterized the derivative 2-ethyl-3-sulfamoyloxy-17β-cyanomethylestra-1,3,5(10)-triene (STX564) as a novel, potent and specific SOCE inhibitor. STX564 inhibits Ca2+ entry via SOCE without affecting other ion channels and pumps involved in Ca2+ signaling in T cells. Downstream effects such as cytokine expression and cell proliferation were also inhibited by both 2-methoxyestradiol and STX564, which has potential as a new chemical biology tool., Highlights • 2-Ethyl-3-sulfamoyloxy-17β-cyanomethylestra-1,3,5(10)-triene is a SOCE inhibitor. • novel inhibitor antagonizes SOCE and subsequent signaling events in different T cells • no antagonist effects on IP3 receptor, KV channels or SERCA pumps

d-Glucosamine (GlcNH2) and several of its derivatives are known to possess immunosuppressive activities in various immune cell lines. The novel GlcNH2-containing oligosaccharide Galα1-6GlcNH2 (designated melibiosamine; MelNH2) is expected to be immunosuppressive also. In Jurkat cells (immortalized human T lymphocytes), interleukin 2 (IL-2) production (an index of the T-cell immune response) can be induced by stimulation with a mitogen, such as concanavalin A. Here, we compared the effects of GlcNH2 and MelNH2 on concanavalin A-induced IL-2 production (CIIP) in Jurkat cells and found that GlcNH2 and MelNH2 at millimolar levels both significantly suppressed CIIP without affecting cell viability. When we examined the effects of GlcNH2 and MelNH2 on the activation of the three transcription factors required for CIIP—NFAT (nuclear factor of activated T-cells), NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells), and AP-1 (activator protein 1)—we found that GlcNH2 and MelNH2 both suppressed CIIP by inhibiting the activation of NFAT and NFκB, but, unlike GlcNH2, MelNH2 also promoted the activation of AP-1. These results suggest that MelNH2 may be a potentially useful lead compound for development as an immunosuppressive or anti-inflammatory drug., Highlights • Immunosuppressive effects of MelNH2 (Galα1-6GlcNH2) were examined in Jurkat cells. • Concanavalin A induces IL-2 production in Jurkat cells. • MelNH2 at millimolar levels dose-dependently suppressed ConA-induced IL-2 production. • MelNH2 inhibited the activation of NFAT and NFκB, which control IL-2 expression.