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 targleting 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 1.0×1 06LoVo cells in nude mice;after injection,tumors were allowed to grow for 4 weeks until the volume reached (75.8±55.8)mm3.The mice were then randomly divided into two groups:(1)the VEGF-C-siRNA group(n=10)received direct injection of"therapeutic"plasmid 50 μg of LoVo-VEGF-C-siRNA into the tumor mass;(2)the control group(n=10)were injected with LoVo-control in 20 μl 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)mm3vs (553.9±90.1)mm3);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 suwival.