title: EXEL-7647 inhibits mutant forms of ErbB2 associated with lapatinib resistance and neoplastic transformation.
abstract: OBJECTIVE
  Mutations associated with resistance to kinase inhibition are an important mechanism of intrinsic or acquired loss of clinical efficacy for kinase-targeted therapeutics. We report the prospective discovery of ErbB2 mutations that confer resistance to the small-molecule inhibitor lapatinib.
  
  
  METHODS
  We did in vitro screening using a randomly mutagenized ErbB2 expression library in Ba/F3 cells, which were dependent on ErbB2 activity for survival and growth.
  
  
  RESULTS
  Lapatinib resistance screens identified mutations at 16 different ErbB2 amino acid residues, with 12 mutated amino acids mapping to the kinase domain. Mutations conferring the greatest lapatinib resistance cluster in the NH2-terminal kinase lobe and hinge region. Structural computer modeling studies suggest that lapatinib resistance is caused by multiple mechanisms; including direct steric interference and restriction of conformational flexibility (the inactive state required for lapatinib binding is energetically unfavorable). ErbB2 T798I imparts the strongest lapatinib resistance effect and is analogous to the epidermal growth factor receptor T790M, ABL T315I, and cKIT T670I gatekeeper mutations that are associated with clinical drug resistance. ErbB2 mutants associated with lapatinib resistance transformed NIH-3T3 cells, including L755S and T733I mutations known to occur in human breast and gastric carcinomas, supporting a direct mechanism for lapatinib resistance in ErbB2-driven human cancers. The epidermal growth factor receptor/ErbB2/vascular endothelial growth factor receptor inhibitor EXEL-7647 was found to inhibit almost all lapatinib resistance-associated mutations. Furthermore, no ErbB2 mutations were found to be associated with EXEL-7647 resistance and lapatinib sensitivity.
  
  
  CONCLUSIONS
  Taken together, these data suggest potential target-based mechanisms of resistance to lapatinib and suggest that EXEL-7647 may be able to circumvent these effects.
authors.affiliation: Exelixis, Inc., South San Francisco, CA 94083, USA.
authors.forename: Torsten
authors.initials: T
authors.lastname: Trowe
authors.forename: Sotiria
authors.initials: S
authors.lastname: Boukouvala
authors.forename: Keith
authors.initials: K
authors.lastname: Calkins
authors.forename: Richard E
authors.initials: RE
authors.lastname: Cutler
authors.forename: Ryan
authors.initials: R
authors.lastname: Fong
authors.forename: Roel
authors.initials: R
authors.lastname: Funke
authors.forename: Steven B
authors.initials: SB
authors.lastname: Gendreau
authors.forename: Yong D
authors.initials: YD
authors.lastname: Kim
authors.forename: Nicole
authors.initials: N
authors.lastname: Miller
authors.forename: John R
authors.initials: JR
authors.lastname: Woolfrey
authors.forename: Valentina
authors.initials: V
authors.lastname: Vysotskaia
authors.forename: Jing Ping
authors.initials: JP
authors.lastname: Yang
authors.forename: Mary E
authors.initials: ME
authors.lastname: Gerritsen
authors.forename: David J
authors.initials: DJ
authors.lastname: Matthews
authors.forename: Peter
authors.initials: P
authors.lastname: Lamb
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Heuer
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D002470:Cell Survival; D002471:Cell Transformation, Neoplastic; D019008:Drug Resistance, Neoplasm; D006801:Humans; D000077341:Lapatinib; D009154:Mutation; D010766:Phosphorylation; D011487:Protein Conformation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011799:Quinazolines / Q000494:pharmacology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics*
chemical_list: D000970:Antineoplastic Agents; D000077341:Lapatinib; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human