Vector-based RNA interference against vascular endothelial growth factor-C inhibits tumor lymphangiogenesis and growth of colorectal cancer in vivo in mice.

BACKGROUND: RNA interference (RNAi) technology is emerging as a very potent tool to generate a cellular knockdown of a desired gene. The aim of this study was to explore whether RNAi targeting vascular endothelial growth factor-C (VEGF-C) could inhibit colorectal tumor lymphangiogenesis and tumor growth.

METHODS: We used vector-based RNAi to inhibit VEGF-C expression in colon cancer in vitro and in vivo. VEGF-C expression was quantified by real-time polymerase chain reaction and Westen blotting. To establish LoVo cell tumor xenografts in mice, we subcutaneously inoculated 1.0 x 10(6) LoVo cells in nude mice; after injection, tumors were allowed to grow for 4 weeks until the volume reached (75.8+/-55.8) mm(3). The mice were then randomly divided into two groups: (1) the VEGF-C-siRNA group (n=10) received direct injection of "therapeutic" plasmid 50 microg of LoVo-VEGF-C-siRNA into the tumor mass; (2) the control group (n=10) were injected with LoVo-control in 20 microl of sterile 0.9% NaCl solution into the tumor mass. Tumor growth, microlymphatics and microvessels were compared for mice administered either systemic VEGF-C-siRNA or control over 4 weeks.

RESULTS: The mRNA and protein expression of VEGF-C in the colon tumor cell line, LoVo, stably transfected with a VEGF-C-siRNA vector, were significantly downregulated 45.3% and 35.3% respectively. In vivo, four weeks after injection, the tumor volume were significantly smaller in VEGF-C-siRNA group than in LoVo-control group ((314.8+/-54.8) mm(3) vs (553.9+/-90.1) mm(3)); the incidences of lymph node metastasis (30%) in VEGF-C-siRNA were significantly inhibited compared with LoVo-control group (70%); in VEGF-C-siRNA group, the number of microlymphatics per microscopic field was (5.3+/-0.7) and the number of microvessels per microscopic field was (24.2+/-6.5) decreased compared with LoVo-control group (12.5+/-6.9) and (42.1+/-7.4) (all P<0.001).

CONCLUSION: Inhibition of VEGF-C expression using siRNA-mediated gene silencing vectors reduced lymphangiogenesis and lymph node metastasis and enhanced survival.