title: Suppression of HER2/HER3-mediated growth of breast cancer cells with combinations of GDC-0941 PI3K inhibitor, trastuzumab, and pertuzumab.
abstract: OBJECTIVE
  Oncogenic activation of the phosphatidylinositol 3-kinase (PI3K) signaling pathway is prevalent in breast cancer and has been associated with resistance to HER2 inhibitors in the clinic. We therefore investigated the combinatorial activity of GDC-0941, a novel class I PI3K inhibitor, with standard-of-care therapies for HER2-amplified breast cancer.
  
  
  METHODS
  Three-dimensional laminin-rich extracellular matrix cultures of human breast cancer cells were utilized to provide a physiologically relevant approach to analyze the efficacy and molecular mechanism of combination therapies ex vivo. Combination studies were done using GDC-0941 with trastuzumab (Herceptin), pertuzumab, lapatinib (Tykerb), and docetaxel, the principal therapeutic agents that are either approved or being evaluated for treatment of early HER2-positive breast cancer.
  
  
  RESULTS
  Significant GDC-0941 activity (EC(50) <1 micromol/L) was observed for >70% of breast cancer cell lines that were examined in three-dimensional laminin-rich extracellular matrix culture. Differential responsiveness to GDC-0941 as a single agent was observed for luminal breast cancer cells upon stimulation with the HER3 ligand, heregulin. Combined treatment of GDC-0941, trastuzumab, and pertuzumab resulted in growth inhibition, altered acinar morphology, and suppression of AKT mitogen-activated protein kinase (MAPK) / extracellular signed-regulated kinase (ERK) kinase and MEK effector signaling pathways for HER2-amplified cells in both normal and heregulin-supplemented media. The GDC-0941 and lapatinib combination further showed that inhibition of HER2 activity was essential for maximum combinatorial efficacy. PI3K inhibition also rendered HER2-amplified BT-474M1 cells and tumor xenografts more sensitive to docetaxel.
  
  
  CONCLUSIONS
  GDC-0941 is efficacious in preclinical models of breast cancer. The addition of GDC-0941 to HER2-directed treatment could augment clinical benefit in breast cancer patients.
authors.affiliation: Department of Cancer Signaling, Genentech, Inc, South San Francisco, California, USA.
authors.forename: Evelyn
authors.initials: E
authors.lastname: Yao
authors.forename: Wei
authors.initials: W
authors.lastname: Zhou
authors.forename: Si Tuen
authors.initials: ST
authors.lastname: Lee-Hoeflich
authors.forename: Tom
authors.initials: T
authors.lastname: Truong
authors.forename: Peter M
authors.initials: PM
authors.lastname: Haverty
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Eastham-Anderson
authors.forename: Nicholas
authors.initials: N
authors.lastname: Lewin-Koh
authors.forename: Bert
authors.initials: B
authors.lastname: Gunter
authors.forename: Marcia
authors.initials: M
authors.lastname: Belvin
authors.forename: Lesley J
authors.initials: LJ
authors.lastname: Murray
authors.forename: Lori S
authors.initials: LS
authors.lastname: Friedman
authors.forename: Mark X
authors.initials: MX
authors.lastname: Sliwkowski
authors.forename: Klaus P
authors.initials: KP
authors.lastname: Hoeflich
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology; D045744:Cell Line, Tumor; D000077143:Docetaxel; D004791:Enzyme Inhibitors / Q000627:therapeutic use*; D006801:Humans; D007191:Indazoles / Q000627:therapeutic use*; D000077341:Lapatinib; D051379:Mice; D008819:Mice, Nude; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011799:Quinazolines / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors*; D020893:Receptor, ErbB-3 / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013449:Sulfonamides / Q000627:therapeutic use*; D043823:Taxoids / Q000494:pharmacology; D000068878:Trastuzumab; D023041:Xenograft Model Antitumor Assays
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D000077143:Docetaxel; D004791:Enzyme Inhibitors; D007191:Indazoles; D000077341:Lapatinib; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011799:Quinazolines; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3; D013449:Sulfonamides; D043823:Taxoids; D000068878:Trastuzumab; C532162:2-(1H-indazol-4-yl)-6-(4-methanesulfonylpiperazin-1-ylmethyl)-4-morpholin-4-ylthieno(3,2-d)pyrimidine; C485206:pertuzumab