In vitro activity: CGI1746 is specific for Btk, with ~1,000-fold selectivity over Tec and Src family kinases. In an ATP-free competition binding assay, the dissociation constant for Btk is 1.5 nM. CGI1746 inhibits Btk activity in a new binding mode that stabilizes an inactive nonphosphorylated enzyme conformation. CGI1746 inhibits both auto- and transphosphorylation steps necessary for enzyme activation. CGI1746 completely inhibits anti-IgM–induced murine and human B cell proliferation, with IC50s of 134 nM and 42 nM, respectively, but had no effect on anti-CD3- and anti-CD28–induced T cell proliferation. CGI1746 potently inhibits the proliferation of CD27+IgG+ B cells isolated from the tonsils of four human donors with an average IC50 of 112 nM. In macrophages, CGI1746 abolishes FcγRIII-induced TNFα, IL-1β and IL-6 production. CGI1746 potently inhibits TNFα, IL-1β and, to a lesser extent, IL-6 (three- to eight-fold higher IC50) production in human monocytes stimulated with immobilized or soluble immune complexes.

Kinase Assay: CGI1746 is specific for Btk, with appr 1,000-fold selectivity over Tec and Src family kinases. In an ATP-free competition binding assay, the dissociation constant for Btk is 1.5 nM. CGI1746 inhibits Btk activity in a new binding mode that stabilizes an inactive nonphosphorylated enzyme conformation. CGI1746 inhibits both auto- and transphosphorylation steps necessary for enzyme activation. CGI1746 completely inhibits anti-IgM-induced murine and human B cell proliferation, with IC50s of 134 nM and 42 nM, respectively, but has no effect on anti-CD3- and anti-CD28-induced T cell proliferation. CGI1746 potently inhibits the proliferation of CD27+IgG+ B cells isolated from the tonsils of four human donors with an average IC50 of 112 nM. In macrophages, CGI1746 abolishes FcγRIII-induced TNFα, IL-1β and IL-6 production. CGI1746 potently inhibits TNFα, IL-1β and, to a lesser extent, IL-6 (three- to eight-fold higher IC50) production in human monocytes stimulated with immobilized or soluble immune complexes[1]. CGI-1746 does not kill cells as well as the irreversible BTK inhibitors at the same drug concentration. CGI-1746 significantly reduces phosphorylation of both the BTK-A and BTK-C proteins, indicating the auto-phosphorylation of the BTK-C isoform is inhibited in a manner similar to BTK-A. CGI-1746 does not kill LNCaP or DU145 prostate cancer cells at the same concentrations as Ibrutinib or AVL-292, but it demonstrates similar inhibition of BTK phosphorylation at tyrosine 233 in the SH3 domain.

Cell Assay: 5×103 DU145 cells or 104 LNCaP cells per well, grown on 96 well plates for 24h, are treated with 1 to 30 μM BTK inhibitors. Cells are fixed after 72h with 2.5% formaldehyde, and stained with Hoechst 33342. Control cells are treated with DMSO. Cell images are acquired using an IN Cell Analyzer 2200 high content imaging system, with a 20X objective. At least 9 fields are imaged per single well of each experiment. Cell numbers are determined and statistics performed using IN Cell Investigator 3.4 high content image analysis software. Each experiment is replicated 3 times, and data are presented as mean±SD. Results are considered significant if p < 0.05.