title: Resistance mechanisms for the Bruton's tyrosine kinase inhibitor ibrutinib.
abstract: BACKGROUND
  Ibrutinib is an irreversible inhibitor of Bruton's tyrosine kinase (BTK) and is effective in chronic lymphocytic leukemia (CLL). Resistance to irreversible kinase inhibitors and resistance associated with BTK inhibition have not been characterized. Although only a small proportion of patients have had a relapse during ibrutinib therapy, an understanding of resistance mechanisms is important. We evaluated patients with relapsed disease to identify mutations that may mediate ibrutinib resistance.
  
  
  METHODS
  We performed whole-exome sequencing at baseline and the time of relapse on samples from six patients with acquired resistance to ibrutinib therapy. We then performed functional analysis of identified mutations. In addition, we performed Ion Torrent sequencing for identified resistance mutations on samples from nine patients with prolonged lymphocytosis.
  
  
  RESULTS
  We identified a cysteine-to-serine mutation in BTK at the binding site of ibrutinib in five patients and identified three distinct mutations in PLCγ2 in two patients. Functional analysis showed that the C481S mutation of BTK results in a protein that is only reversibly inhibited by ibrutinib. The R665W and L845F mutations in PLCγ2 are both potentially gain-of-function mutations that lead to autonomous B-cell-receptor activity. These mutations were not found in any of the patients with prolonged lymphocytosis who were taking ibrutinib.
  
  
  CONCLUSIONS
  Resistance to the irreversible BTK inhibitor ibrutinib often involves mutation of a cysteine residue where ibrutinib binding occurs. This finding, combined with two additional mutations in PLCγ2 that are immediately downstream of BTK, underscores the importance of the B-cell-receptor pathway in the mechanism of action of ibrutinib in CLL. (Funded by the National Cancer Institute and others.).
authors.affiliation: From the Division of Hematology, Department of Internal Medicine (J.A.W., T.-M.L., A.S.R., S.M.J., K.A.B., A.L., A.J.J., J.C. Byrd), the Department of Biomedical Informatics (H.G.O., A.S.Y.), and the Department of Pathology (G.L.), Ohio State University, Columbus; the Department of Medicine, Division of Hematology-Oncology, Weill Cornell Medical College, New York (R.R.F.); the Division of Molecular Genetics, German Cancer Research Center, Heidelberg (M.Z., P.L.), and the Department of Internal Medicine III, University of Ulm, Ulm (S.S.) - both in Germany; Pharmacyclics, Sunnyvale, CA (L.X., D.H.-H.L., S.M.S., D.F.J., J.J.B., B.Y.C.); the Duke Cancer Institute, Duke University, Durham, NC (S.S.D., J.Z.); the Division of Hematology-Oncology, Department of Medicine, Hofstra North Shore-LIJ School of Medicine, New Hyde Park, NY (J.C. Barrientos); and Janssen Research and Development, Beerse, Belgium (M.V.).
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Woyach
authors.forename: Richard R
authors.initials: RR
authors.lastname: Furman
authors.forename: Ta-Ming
authors.initials: TM
authors.lastname: Liu
authors.forename: Hatice Gulcin
authors.initials: HG
authors.lastname: Ozer
authors.forename: Marc
authors.initials: M
authors.lastname: Zapatka
authors.forename: Amy S
authors.initials: AS
authors.lastname: Ruppert
authors.forename: Ling
authors.initials: L
authors.lastname: Xue
authors.forename: Daniel Hsieh-Hsin
authors.initials: DH
authors.lastname: Li
authors.forename: Susanne M
authors.initials: SM
authors.lastname: Steggerda
authors.forename: Matthias
authors.initials: M
authors.lastname: Versele
authors.forename: Sandeep S
authors.initials: SS
authors.lastname: Dave
authors.forename: Jenny
authors.initials: J
authors.lastname: Zhang
authors.forename: Ayse Selen
authors.initials: AS
authors.lastname: Yilmaz
authors.forename: Samantha M
authors.initials: SM
authors.lastname: Jaglowski
authors.forename: Kristie A
authors.initials: KA
authors.lastname: Blum
authors.forename: Arletta
authors.initials: A
authors.lastname: Lozanski
authors.forename: Gerard
authors.initials: G
authors.lastname: Lozanski
authors.forename: Danelle F
authors.initials: DF
authors.lastname: James
authors.forename: Jacqueline C
authors.initials: JC
authors.lastname: Barrientos
authors.forename: Peter
authors.initials: P
authors.lastname: Lichter
authors.forename: Stephan
authors.initials: S
authors.lastname: Stilgenbauer
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Buggy
authors.forename: Betty Y
authors.initials: BY
authors.lastname: Chang
authors.forename: Amy J
authors.initials: AJ
authors.lastname: Johnson
authors.forename: John C
authors.initials: JC
authors.lastname: Byrd
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000368:Aged; D001665:Binding Sites / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D059472:Exome; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy / Q000235:genetics*; D008875:Middle Aged; D051966:Phospholipase C gamma / Q000235:genetics* / Q000378:metabolism; D010880:Piperidines; D017354:Point Mutation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics*; D011720:Pyrazoles / Q000494:pharmacology / Q000627:therapeutic use*; D011743:Pyrimidines / Q000494:pharmacology / Q000627:therapeutic use*; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism; D012008:Recurrence; D017422:Sequence Analysis, DNA
chemical_list: D010880:Piperidines; D011720:Pyrazoles; D011743:Pyrimidines; D011947:Receptors, Antigen, B-Cell; C551803:ibrutinib; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; D051966:Phospholipase C gamma; D000225:Adenine