title: Polyethylenimine/small interfering RNA-mediated knockdown of vascular endothelial growth factor in vivo exerts anti-tumor effects synergistically with Bevacizumab.
abstract: BACKGROUND
  RNA interference is a powerful method for the knockdown of pathologically relevant genes. The in vivo delivery of siRNAs, preferably through systemic, nonviral administration, poses the major challenge in the therapeutic application of RNAi. Small interfering RNA (siRNA) complexation with polyethylenimines (PEI) may represent a promising strategy for siRNA-based therapies and, recently, the novel branched PEI F25-LMW has been introduced in vitro. Vascular endothelial growth factor (VEGF) is frequently overexpressed in tumors and promotes tumor growth, angiogenesis and metastasis and thus represents an attractive target gene in tumor therapy.
  
  
  METHODS
  In subcutaneous tumor xenograft mouse models, we established the therapeutic efficacy and safety of PEI F25-LMW/siRNA-mediated knockdown of VEGF. In biodistribution and siRNA quantification studies, we optimized administration strategies and, employing chemically modified siRNAs, compared the anti-tumorigenic efficacies of: (i) PEI/siRNA-mediated VEGF targeting; (ii) treatment with the monoclonal anti-VEGF antibody Bevacizumab (Avastin); and (iii) a combination of both.
  
  
  RESULTS
  Efficient siRNA delivery is observed upon systemic administration, with the biodistribution being dependent on the mode of injection. Toxicity studies reveal no hepatotoxicity, proinflammatory cytokine induction or other side-effects of PEI F25-LMW/siRNA complexes or polyethylenimine, and tumor analyses show efficient VEGF knockdown upon siRNA delivery, leading to reduced tumor cell proliferation and angiogenesis. The determination of anti-tumor effects reveals that, in pancreas carcinoma xenografts, single treatment with PEI/siRNA complexes or Bevacizumab is already highly efficacious, whereas, in prostate carcinoma, synergistic effects of both treatments are observed.
  
  
  CONCLUSIONS
  PEI F25-LMW/siRNA complexes, which can be stored frozen as opposed to many other carriers, represent an efficient, safe and promising avenue in anti-tumor therapy, and PEI/siRNA-mediated, therapeutic VEGF knockdown exerts anti-tumor effects.
authors.affiliation: Department of Pharmacology and Toxicology, Philipps-University School of Medicine, D-35032 Marburg, Germany.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Höbel
authors.forename: Ivette
authors.initials: I
authors.lastname: Koburger
authors.forename: Matthias
authors.initials: M
authors.lastname: John
authors.forename: Frank
authors.initials: F
authors.lastname: Czubayko
authors.forename: Philipp
authors.initials: P
authors.lastname: Hadwiger
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Vornlocher
authors.forename: Achim
authors.initials: A
authors.lastname: Aigner
mesh_terms: D020533:Angiogenesis Inhibitors / Q000627:therapeutic use*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D000068258:Bevacizumab; D003131:Combined Modality Therapy; D055785:Gene Knockdown Techniques / Q000379:methods; D015316:Genetic Therapy / Q000379:methods*; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000628:therapy*; D011094:Polyethyleneimine / Q000008:administration & dosage* / Q000737:chemistry; D034741:RNA, Small Interfering / Q000008:administration & dosage* / Q000737:chemistry / Q000235:genetics; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors* / Q000235:genetics; D023041:Xenograft Model Antitumor Assays
chemical_list: D020533:Angiogenesis Inhibitors; D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D034741:RNA, Small Interfering; D042461:Vascular Endothelial Growth Factor A; D000068258:Bevacizumab; D011094:Polyethyleneimine