title: Chronic exposure of colorectal cancer cells to bevacizumab promotes compensatory pathways that mediate tumour cell migration.
abstract: BACKGROUND
  Bevacizumab (Bev), a monoclonal antibody to vascular endothelial growth factor (VEGF), is used in combination with chemotherapy for the treatment of metastatic colorectal cancer (CRC). The effects of Bev on angiogenesis have been well described, but the direct effect of Bev on tumour cells is unknown. This study was carried out to determine the molecular and phenotypic changes in CRC cells after chronic Bev exposure in vitro.
  
  
  METHODS
  Human CRC cell lines were chronically exposed (3 months) to Bev in vitro to develop Bev-adapted (Bev-A) cell lines. Vascular endothelial growth factor family members were determined by reverse transcription-polymerase chain reaction and western blotting. Migration and invasion was determined using standard in vitro assays. Intravenous injection of tumour cells was carried out to evaluate metastatic potential in mice.
  
  
  RESULTS
  Bevacizumab-adapted cells were found to be more migratory and invasive than control cells (P<0.001). Bevacizumab-adapted cells showed higher levels of VEGF-A, -B, -C, placental growth factor (PlGF), VEGF receptor-1 (VEGFR-1) and phosphorylation of VEGFR-1. Furthermore, treatment with SU5416, a VEGFR protein tyrosine kinase inhibitor, led to significantly decreased cell migration in vitro (P<0.001). Bevacizumab-adapted cells were more metastatic in vivo (P<0.05).
  
  
  CONCLUSIONS
  Chronic exposure of CRC cells to Bev (1) increased expression of VEGF-A, -B, -C, PlGF, VEGFR-1 and VEGFR-1 phosphorylation, (2) increased tumour cell migration and invasion, and (3) metastatic potential in vivo. Our study shows the functional significance of autocrine VEGF signalling in CRC cells.
authors.affiliation: Department of Cancer Biology, The University of Texas MD Anderson Cancer Center, Unit 173, PO Box 301402, Houston, TX 77030-1402, USA.
authors.forename: F
authors.initials: F
authors.lastname: Fan
authors.forename: S
authors.initials: S
authors.lastname: Samuel
authors.forename: P
authors.initials: P
authors.lastname: Gaur
authors.forename: J
authors.initials: J
authors.lastname: Lu
authors.forename: N A
authors.initials: NA
authors.lastname: Dallas
authors.forename: L
authors.initials: L
authors.lastname: Xia
authors.forename: D
authors.initials: D
authors.lastname: Bose
authors.forename: V
authors.initials: V
authors.lastname: Ramachandran
authors.forename: L M
authors.initials: LM
authors.lastname: Ellis
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000494:pharmacology; D000068258:Bevacizumab; D002277:Carcinoma / Q000473:pathology*; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects*; D015179:Colorectal Neoplasms / Q000473:pathology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000502:physiology*; D045325:HCT116 Cells; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009362:Neoplasm Metastasis; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D014183:Transplantation, Heterologous
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D000068258:Bevacizumab