Increased invasiveness and expression of matrix metalloproteinase-9 in a human bile duct cancer cell line resistant to heating

Background - Recent studies have reported that intraluminal hyperthermia may be a useful therapy for some malignant tumors. In Japan, intraluminal hyperthermia is considered to be a useful therapy for bile duct carcinoma, However, fee have seen cases which recur after intraluminal hyperthermia, with rapid development of distant metastases. Several previous studies have demonstrated that matrix metalloproteinase-9 (MMP-9) plays an important role in tumor invasion and metastasis. We have examined the invasiveness of cells surviving after hyperthermia in tissue culture. Methods - A human bile duct cancer cell line (HuCCT1) was treated at 43 degrees C for 1 hour, Viable cells, which were defined as heat-resistant HuCCT1 cells (sh-HuCCT1), were harvested and examined in an invasion assay using a Boyden chamber, Supernatant from untreated-HuCCT1 cells (ut-HuCCT1), sh-HuCCT1 and a control cell line were analyzed by Western blotting using a mouse monoclonal anti-MMP-9 antibody and by gelatin zymogram. Results - In the invasion assay, the invasiveness was higher in sh-HuCCT1 than in ut-HuCCT1, Moreover, the expression and activity of MMP-9 in the supernatant, which were not detectable in the control cell line, also increased in sh-HuCCT1 more than in ut-HuCCT1. Conclusions - These results suggest that MMP-9 may play an important role in the invasiveness of HuCCT1, and that heat stress may increase the expression and activity of MMP-9 in cells surviving after hyperthermia. Further studies are needed to understand the regulation of MMP-9 protein in cells surviving after hyperthermia and develop adjuvant therapy to inhibit MMP-9 protein overexpression.