Inhibitory effect of vasoactive intestinal polypeptide (VIP) on experimental liver metastasis by murine colon 26-L5 carcinoma cells

We previously reported that vasoactive intestinal polypeptide (VIP) signifi cantly inhibited Matrigel invasion and haptotactic migration of murine colo n 26-L5 carcinoma in vitro. To extend our study, we investigated the inhibi tory mechanisms of VIP on Matrigel invasion of colon 26-L5 carcinoma, and t he effect on metastatic properties of the tumor cells. VIP inhibited the in vasion of the tumor cells in a concentration-dependent manner without affec ting their growth, and achieved approximately 50% reduction at 10(-6) M. VI P also suppressed cell motility with a similar inhibition rate to the invas ion assay. Time course study revealed that the motility was reduced by 40% when the tumor cells were preincubated with 10(-6) M VIP for 3 h. In contra st, 6-h pretreatment with 10(-6) M VIP caused the increased ability of the adhesion to both fibronectin and laminin with a 50% enhancement. A large am ount of VIP, receptor transcripts was expressed in the cells, whereas VIP, receptor was undetectable, by RT-PCR and subsequent Southern blot hybridiza tion. A specific antagonist for VIP1 receptor reversed the suppressed motil ity induced by VIP. Cryostat sections showed that the 3-h pretreatment of t umor cells with VIP caused the reduction of the arrest in the livers at 6 h after the tumor inoculation into a portal vein of mice. VIP could prevent the experimental liver metastasis of the tumor cells in a dose-dependent ma nner. The cells pretreated with 10(-6) M VIP for 3 h also showed the reduce d ability of the liver metastasis. These results suggest that VIP could blo ck the invasion and the metastasis of colon 26-L5 carcinoma through suppres sion of their motility.