title: Rapamycin synergizes with the epidermal growth factor receptor inhibitor erlotinib in non-small-cell lung, pancreatic, colon, and breast tumors.
abstract: The receptor for epidermal growth factor (EGFR) is overexpressed in many cancers. One important signaling pathway regulated by EGFR is the phosphatidylinositol 3'-kinase (PI3K)-phosphoinositide-dependent kinase 1-Akt pathway. Activation of Akt leads to the stimulation of antiapoptotic pathways, promoting cell survival. Akt also regulates the mammalian target of rapamycin (mTOR)-S6K-S6 pathway to control cell growth in response to growth factors and nutrients. Recent reports have shown that the sensitivity of non-small-cell lung cancer cell lines to EGFR inhibitors such as erlotinib (Tarceva, OSI Pharmaceuticals) is dependent on inhibition of the phosphatidylinositol 3'-kinase-phosphoinositide-dependent kinase 1-Akt-mTOR pathway. There can be multiple inputs to this pathway as activity can be regulated by other receptors or upstream mutations. Therefore, inhibiting EGFR alone may not be sufficient for substantial inhibition of all tumor cells, highlighting the need for multipoint intervention. Herein, we sought to determine if rapamycin, an inhibitor of mTOR, could enhance erlotinib sensitivity for cell lines derived from a variety of tissue types (non-small-cell lung, pancreatic, colon, and breast). Erlotinib could inhibit extracellular signal-regulated kinase, Akt, and S6 only in cell lines that were the most sensitive. Rapamycin could fully inhibit S6 in all cell lines, but this was accompanied by activation of Akt phosphorylation. However, combination with erlotinib could down-modulate rapamycin-stimulated Akt activity. Therefore, in select cell lines, inhibition of both S6 and Akt was achieved only with the combination of erlotinib and rapamycin. This produced a synergistic effect on cell growth inhibition, observations that extended in vivo using xenograft models. These results suggest that combining rapamycin with erlotinib might be clinically useful to enhance response to erlotinib.
authors.affiliation: OSI Pharmaceuticals, 1 Bioscience Park Drive, Farmingdale, NY 11787, USA. ebuck@osip.com
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Buck
authors.forename: Alexandra
authors.initials: A
authors.lastname: Eyzaguirre
authors.forename: Eric
authors.initials: E
authors.lastname: Brown
authors.forename: Filippo
authors.initials: F
authors.lastname: Petti
authors.forename: Siobhan
authors.initials: S
authors.lastname: McCormack
authors.forename: John D
authors.initials: JD
authors.lastname: Haley
authors.forename: Kenneth K
authors.initials: KK
authors.lastname: Iwata
authors.forename: Neil W
authors.initials: NW
authors.lastname: Gibson
authors.forename: Graeme
authors.initials: G
authors.lastname: Griffin
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000069347:Erlotinib Hydrochloride; D005260:Female; D045325:HCT116 Cells; D019073:HT29 Cells; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D011799:Quinazolines / Q000494:pharmacology / Q000627:therapeutic use*; D020123:Sirolimus / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D000069347:Erlotinib Hydrochloride; D066246:ErbB Receptors; D020123:Sirolimus