869 Discovery and Therapeutic Potential of FGFR2 Gene Amplification in Diffuse Gastric Cancer

Abstract

Background & Aims: VEGF is a key stimulator of angiogenesis and promotes the growth colon tumors via increased nutrient and oxygen supply. A recent study demonstrated that colorectal cancer (CRC) cells have increased expression of VEGF and its receptors VEGFR1 & VEGF-R2, which indicates a possibility of direct stimulation of CRC cell growth by VEGF. However, the role of VEGF in CRC cell proliferation by an autocrine mechanism has not been fully explored in depth. We hypothesized that VEGF secreted by CRC cells binds to VEGF-R1 & VEGF-R2 on CRC cells and: 1) promotes proliferation of these cells through an autocrine pathway, 2) inhibits CRC apoptosis. Methods: We used: (1) human CRC cell lines HCT116 & HT29 and (2) normal colonic epithelial cells NCM356 & NCM460 cultured in nutrient media. Studies: 1) VEGF, VEGF-R1 & VEGF-R2 mRNA and protein expression of by Real-Time RT-PCR and immunoblotting; 2) VEGF165 secretion into the culture media by ELISA; 3) cell proliferation by BrdU assay; 4) apoptosis by TUNEL staining and assessment of activated caspases 3 and 9; 5) Inhibition of VEGF receptor function using AAL993 inhibitor, which blocks function of VEGF-R1 and VEGF-R2; 6) assessment of phosphorylation of EGF receptor (EGF-R) to test its transactivation by VEGF. Results: 1) Normal colonic cells do not secrete VEGF (< 35 pg/ml culture media) while CRC cells express and secrete high levels of VEGF (840 1500 pg/ml culture media); 2) Normal colonic epithelial cell lines expressed no or minimal VEGF-R1 & VEGF-R2 mRNA and protein while CRC cell lines exhibit strong expression of VEGF-R1 & VEGF-R2 vs. normal colonic epithelial cells by 14and 24-fold, respectively (all p < 0.001); 3) CRC cell lines have significantly increased cell proliferation by 31% (p < 0.01) and decreased apoptosis vs. normal colonic epithelial cells; 3) Inhibition of both VEGF-R1 & VEGF-R2 receptors using AAL-993 significantly decreased CRC cell proliferation by (2.2-fold) ; 4) Treatment of CRC cells with AAL-993 decreased phosphorylation of EGF-R by 1.9-fold (p < 0.01). Conclusions: 1) VEGF and its VEGF-R1 & VEGF-R2 receptors are increased in CRC cell lines; 2) CRC cells secrete VEGF, which stimulates CRC cell proliferation via an autocrine mechanism by its VEGF-R1 & VEGF-R2 receptors and also inhibits apoptosis; 3) VEGF receptor signaling pathway is critical for activating EGF-R in CRC cells; 4) These studies suggest a cross-talk between VEGF receptor and EGF-R signaling in CRC cells, which promotes these cells' proliferation.