title: Simultaneous inhibition of EGFR and PI3K enhances radiosensitivity in human breast cancer.
abstract: OBJECTIVE
  Mutations in the epidermal growth factor receptor (EGFR)/phosphoinositide 3-kinase (PI3K)/Akt signaling transduction pathway are common in cancer. This pathway is imperative to the radiosensitivity of cancer cells. We aimed to investigate the radiosensitizing effects of the simultaneous inhibition of EGFR and PI3K in breast cancer cells.
  
  
  METHODS
  MCF-7 cell lines with low expression of EGFR and wild-type PTEN and MDA-MB-468 cell lines with high expression of EGFR and mutant PTEN were used. The radiosensitizing effects by the inhibition of EGFR with AG1478 and/or PI3K with Ly294002 were determined by colony formation assay, Western blot was used to investigate the effects on downstream signaling. Flow cytometry was used for apoptosis and cell cycle analysis. Mice-bearing xenografts of MDA-MB-468 breast cancer cells were also used to observe the radiosensitizing effect.
  
  
  RESULTS
  Simultaneous inhibition of EGFR and PI3K greatly enhanced radiosensitizing effect in MDA-MB-468 in terms of apoptosis and mitotic death, either inhibition of EGFR or PI3K alone could enhance radiosensitivity with a dose-modifying factor (DMF(SF2)) of 1.311 and 1.437, radiosensitizing effect was further enhanced by simultaneous inhibition of EGFR and PI3K with a DMF(SF2) at 2.698. DNA flow cytometric analysis indicated that dual inhibition combined with irradiation significantly induced G0/G1 phase arrest in MDA-MB-468 cells. The expression of phosphor-Akt and phosphor-Erk1/2 (induced by irradiation and PI3K inhibitor) were fully attenuated by simultaneous treatment with both inhibitors in combination with irradiation. In addition, dual inhibition combined with irradiation induced dramatic tumor growth delay in MDA-MB-468 xenografts.
  
  
  CONCLUSIONS
  Our study indicated that simultaneous inhibition of EGFR and PI3K could further sensitize the cancer cells to irradiation compared to the single inhibitor with irradiation in vitro and in vivo. The approach may have important therapeutic implication in the treatment of a subset of breast cancer patients with high expression of EGFR and deficient function of PTEN.
authors.affiliation: Department of Radiation Oncology, 6th People's Hospital of Jiao Tong University, Shanghai 200233, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Li
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhang
authors.forename: Artour
authors.initials: A
authors.lastname: Torossian
authors.forename: Zhao-bin
authors.initials: ZB
authors.lastname: Li
authors.forename: Wen-cai
authors.initials: WC
authors.lastname: Xu
authors.forename: Bo
authors.initials: B
authors.lastname: Lu
authors.forename: Shen
authors.initials: S
authors.lastname: Fu
mesh_terms: D000818:Animals; D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000235:genetics; D005260:Female; D016193:G1 Phase / Q000502:physiology / Q000528:radiation effects; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009025:Morpholines / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors*; D051059:PTEN Phosphohydrolase / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D011799:Quinazolines / Q000494:pharmacology; D011836:Radiation Tolerance; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D011897:Random Allocation; D016192:Resting Phase, Cell Cycle / Q000502:physiology / Q000528:radiation effects; D020032:Tyrphostins / Q000494:pharmacology
chemical_list: D002867:Chromones; D066246:ErbB Receptors; D009025:Morpholines; D009363:Neoplasm Proteins; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D011799:Quinazolines; D011838:Radiation-Sensitizing Agents; D020032:Tyrphostins; C101044:RTKI cpd; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494929:PTEN protein, human