title: Epidermal growth factor receptor inhibition modulates the microenvironment by vascular normalization to improve chemotherapy and radiotherapy efficacy.
abstract: BACKGROUND
  Epidermal growth factor receptor (EGFR) inhibitors have shown only modest clinical activity when used as single agents to treat cancers. They decrease tumor cell expression of hypoxia-inducible factor 1-alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF). Hypothesizing that this might normalize tumor vasculature, we examined the effects of the EGFR inhibitor erlotinib on tumor vascular function, tumor microenvironment (TME) and chemotherapy and radiotherapy sensitivity.
  
  
  RESULTS
  Erlotinib treatment of human tumor cells in vitro and mice bearing xenografts in vivo led to decreased HIF-1alpha and VEGF expression. Treatment altered xenograft vessel morphology assessed by confocal microscopy (following tomato lectin injection) and decreased vessel permeability (measured by Evan's blue extravasation), suggesting vascular normalization. Erlotinib increased tumor blood flow measured by Power Doppler ultrasound and decreased hypoxia measured by EF5 immunohistochemistry and tumor O(2) saturation measured by optical spectroscopy. Predicting that these changes would improve drug delivery and increase response to chemotherapy and radiation, we performed tumor regrowth studies in nude mice with xenografts treated with erlotinib and either radiotherapy or the chemotherapeutic agent cisplatin. Erlotinib therapy followed by cisplatin led to synergistic inhibition of tumor growth compared with either treatment by itself (p<0.001). Treatment with erlotinib before cisplatin led to greater tumor growth inhibition than did treatment with cisplatin before erlotinib (p = 0.006). Erlotinib followed by radiation inhibited tumor regrowth to a greater degree than did radiation alone, although the interaction between erlotinib and radiation was not synergistic.
  
  
  CONCLUSIONS
  EGFR inhibitors have shown clinical benefit when used in combination with conventional cytotoxic therapy. Our studies show that targeting tumor cells with EGFR inhibitors may modulate the TME via vascular normalization to increase response to chemotherapy and radiotherapy. These studies suggest ways to assess the response of tumors to EGFR inhibition using non-invasive imaging of the TME.
authors: Department of Radiation Oncology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America.
authors: George J
authors: GJ
authors: Cerniglia
authors: Nabendu
authors: N
authors: Pore
authors: Jeff H
authors: JH
authors: Tsai
authors: Susan
authors: S
authors: Schultz
authors: Rosemarie
authors: R
authors: Mick
authors: Regine
authors: R
authors: Choe
authors: Xiaoman
authors: X
authors: Xing
authors: Turgut
authors: T
authors: Durduran
authors: Arjun G
authors: AG
authors: Yodh
authors: Sydney M
authors: SM
authors: Evans
authors: Cameron J
authors: CJ
authors: Koch
authors: Stephen M
authors: SM
authors: Hahn
authors: Harry
authors: H
authors: Quon
authors: Chandra M
authors: CM
authors: Sehgal
authors: William M F
authors: WM
authors: Lee
authors: Amit
authors: A
authors: Maity
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use; D045744:Cell Line, Tumor; D066246:ErbB Receptors / Q000037:antagonists & inhibitors*; D000069347:Erlotinib Hydrochloride; D005260:Female; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000098:blood supply* / Q000188:drug therapy / Q000532:radiotherapy; D010100:Oxygen / Q000378:metabolism; D011799:Quinazolines / Q000494:pharmacology / Q000627:therapeutic use; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011799:Quinazolines; D042461:Vascular Endothelial Growth Factor A; D000069347:Erlotinib Hydrochloride; D066246:ErbB Receptors; D010100:Oxygen