title: Ability of Bruton's Tyrosine Kinase Inhibitors to Sequester Y551 and Prevent Phosphorylation Determines Potency for Inhibition of Fc Receptor but not B-Cell Receptor Signaling.
abstract: Bruton's tyrosine kinase (Btk) is expressed in a variety of hematopoietic cells. Btk has been demonstrated to regulate signaling downstream of the B-cell receptor (BCR), Fc receptors (FcRs), and toll-like receptors. It has become an attractive drug target because its inhibition may provide significant efficacy by simultaneously blocking multiple disease mechanisms. Consequently, a large number of Btk inhibitors have been developed. These compounds have diverse binding modes, and both reversible and irreversible inhibitors have been developed. Reported herein, we have tested nine Btk inhibitors and characterized on a molecular level how their interactions with Btk define their ability to block different signaling pathways. By solving the crystal structures of Btk inhibitors bound to the enzyme, we discovered that the compounds can be classified by their ability to trigger sequestration of Btk residue Y551. In cells, we found that sequestration of Y551 renders it inaccessible for phosphorylation. The ability to sequester Y551 was an important determinant of potency against FcεR signaling as Y551 sequestering compounds were more potent for inhibiting basophils and mast cells. This result was true for the inhibition of FcγR signaling as well. In contrast, Y551 sequestration was less a factor in determining potency against BCR signaling. We also found that Btk activity is regulated differentially in basophils and B cells. These results elucidate important determinants for Btk inhibitor potency against different signaling pathways and provide insight for designing new compounds with a broader inhibitory profile that will likely result in greater efficacy.
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.) andrew.bender@emdserono.com.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Bender
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.).
authors.forename: Anna
authors.initials: A
authors.lastname: Gardberg
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.).
authors.forename: Albertina
authors.initials: A
authors.lastname: Pereira
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.).
authors.forename: Theresa
authors.initials: T
authors.lastname: Johnson
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.).
authors.forename: Yin
authors.initials: Y
authors.lastname: Wu
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.).
authors.forename: Roland
authors.initials: R
authors.lastname: Grenningloh
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.).
authors.forename: Jared
authors.initials: J
authors.lastname: Head
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.).
authors.forename: Federica
authors.initials: F
authors.lastname: Morandi
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.).
authors.forename: Philipp
authors.initials: P
authors.lastname: Haselmayer
authors.affiliation: TIP Immunology (A.T.B., A.P., Y.W., R.G.) and Discovery Technologies (A.G., T.J., J.H., F.M., L.L.-B.), EMD Serono Research and Development Institute, Billerica, Massachusetts; and TIP Immunology, Merck, Darmstadt, Germany (P.H.).
authors.forename: Lesley
authors.initials: L
authors.lastname: Liu-Bujalski
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D045744:Cell Line, Tumor; D016000:Cluster Analysis; D018360:Crystallography, X-Ray; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008958:Models, Molecular; D050505:Mutant Proteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D011961:Receptors, Fc / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D047428:Protein Kinase Inhibitors; D011947:Receptors, Antigen, B-Cell; D011961:Receptors, Fc; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human