title: Lapatinib, a dual EGFR and HER2 tyrosine kinase inhibitor, downregulates thymidylate synthase by inhibiting the nuclear translocation of EGFR and HER2.
abstract: BACKGROUND
  Epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) has been shown to exert a synergistic antitumor effect when combined with fluoropyrimidine. This synergy may be attributable to the downregulation of thymidylate synthase (TS), which is frequently overexpressed in fluoropyrimidine-resistant cancer cells. However, the molecular mechanism underlying the downregulation of TS has yet to be clearly elucidated.
  
  
  RESULTS
  In this study, we demonstrate that lapatinib, a dual TKI of EGFR and HER2 downregulates TS via inhibition of the nuclear translocation of EGFR and HER2. From our cDNA microarray experiments, we determined that a variety of nucleotide synthesis-related genes, including TS, were downregulated with lapatinib, and this was apparent in HER2-amplified cells. Targeted and pharmacologic inhibition assays confirmed that the dual inhibition of EGFR and HER2 is required for the more effective reduction of TS as compared to what was observed with gefitinib or trasutuzumab alone. Additionally, we determined that co-transfected EGFR and HER2 activate the TS gene promoter more profoundly than do either EGFR or HER2 alone. The translocation of EGFR and HER2 into the nucleus and the subsequent activation of the TS promoter were inhibited by lapatinib.
  
  
  CONCLUSIONS
  These results demonstrate that lapatinib inhibits the nuclear translocation of EGFR and HER2 and downregulates TS, thus sensitizing cancer cells to fluoropyrimidine.
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Hwang-Phill
authors.initials: HP
authors.lastname: Kim
authors.forename: Young-Kwang
authors.initials: YK
authors.lastname: Yoon
authors.forename: Jin-Won
authors.initials: JW
authors.lastname: Kim
authors.forename: Sae-Won
authors.initials: SW
authors.lastname: Han
authors.forename: Hyung-Seok
authors.initials: HS
authors.lastname: Hur
authors.forename: Jinah
authors.initials: J
authors.lastname: Park
authors.forename: Ju-Hee
authors.initials: JH
authors.lastname: Lee
authors.forename: Do-Youn
authors.initials: DY
authors.lastname: Oh
authors.forename: Seock-Ah
authors.initials: SA
authors.lastname: Im
authors.forename: Yung-Jue
authors.initials: YJ
authors.lastname: Bang
authors.forename: Tae-You
authors.initials: TY
authors.lastname: Kim
mesh_terms: D021581:Active Transport, Cell Nucleus; D000911:Antibodies, Monoclonal / Q000008:administration & dosage; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000008:administration & dosage; D045744:Cell Line, Tumor; D015536:Down-Regulation; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000096:biosynthesis*; D000077156:Gefitinib; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000077341:Lapatinib; D009368:Neoplasm Transplantation; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology; D011799:Quinazolines / Q000008:administration & dosage / Q000494:pharmacology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis*; D000068878:Trastuzumab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D066246:ErbB Receptors; D000077156:Gefitinib; D000077341:Lapatinib; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D011799:Quinazolines; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C508053:ERBB2 protein, human