title: EGFR-targeted plasmonic magnetic nanoparticles suppress lung tumor growth by abrogating G2/M cell-cycle arrest and inducing DNA damage.
abstract: BACKGROUND
  We have previously demonstrated the epidermal growth factor receptor (EGFR)-targeted hybrid plasmonic magnetic nanoparticles (225-NP) produce a therapeutic effect in human lung cancer cell lines in vitro. In the present study, we investigated the molecular mechanism of 225-NP-mediated antitumor activity both in vitro and in vivo using the EGFR-mutant HCC827 cell line.
  
  
  METHODS
  The growth inhibitory effect of 225-NP on lung tumor cells was determined by cell viability and cell-cycle analysis. Protein expression related to autophagy, apoptosis, and DNA-damage were determined by Western blotting and immunofluorescence. An in vivo efficacy study was conducted using a human lung tumor xenograft mouse model.
  
  
  RESULTS
  The 225-NP treatment markedly reduced tumor cell viability at 72 hours compared with the cell viability in control treatment groups. Cell-cycle analysis showed the percentage of cells in the G2/M phase was reduced when treated with 225-NP, with a concomitant increase in the number of cells in Sub-G1 phase, indicative of cell death. Western blotting showed LC3B and PARP cleavage, indicating 225-NP-treatment activated both autophagy- and apoptosis-mediated cell death. The 225-NP strongly induced γH2AX and phosphorylated histone H3, markers indicative of DNA damage and mitosis, respectively. Additionally, significant γH2AX foci formation was observed in 225-NP-treated cells compared with control treatment groups, suggesting 225-NP induced cell death by triggering DNA damage. The 225-NP-mediated DNA damage involved abrogation of the G2/M checkpoint by inhibiting BRCA1, Chk1, and phospho-Cdc2/CDK1 protein expression. In vivo therapy studies showed 225-NP treatment reduced EGFR phosphorylation, increased γH2AX foci, and induced tumor cell apoptosis, resulting in suppression of tumor growth.
  
  
  CONCLUSIONS
  The 225-NP treatment induces DNA damage and abrogates G2/M phase of the cell cycle, leading to cellular apoptosis and suppression of lung tumor growth both in vitro and in vivo. Our findings provide a rationale for combining 225-NP with other DNA-damaging agents for achieving enhanced anticancer activity.
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Shinji
authors.initials: S
authors.lastname: Kuroda
authors.affiliation: Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Justina
authors.initials: J
authors.lastname: Tam
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Jack A
authors.initials: JA
authors.lastname: Roth
authors.affiliation: Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Sokolov
authors.affiliation: Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA ; Graduate Program in Biomedical Sciences, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA ; Stephenson Cancer Center, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
authors.forename: Rajagopal
authors.initials: R
authors.lastname: Ramesh
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology* / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage / Q000187:drug effects*; D066246:ErbB Receptors / Q000378:metabolism*; D005260:Female; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects*; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism*; D058185:Magnetite Nanoparticles / Q000737:chemistry* / Q000633:toxicity; D051379:Mice; D008819:Mice, Nude; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D058185:Magnetite Nanoparticles; C541485:EGFR protein, mouse; D066246:ErbB Receptors
keywords: autophagy; epidermal growth factor receptor; lung cancer