OBJECTIVETo investigate the correlation between matrix metalloproteinase 9 (MMP-9) expression and tumor invasion and metastasis as well, and to explore the potential application of controlled expression of target gene in tumor gene therapy.

METHODSOne self-contained tetracycline-regulated retroviral vector containing anti-sense cDNA of MMP-9 was constructed and transfected into a metastatic human melanoma cell line WM451 which expressed a high level of MMP-9. Techniques such as growth rate measurment, MTT assay, (3)H-thymidine incorporation, colony forming ability in soft agar, invasion assay in Boyden chamber, as well as zymography and Western blot were applied to analyze the expression of MMPs and behaviors of tumor cells in vitro before and after gene transfection. Tumorigenecity and spontaneous metastasis were tested in nude mice.

RESULTSIn the presence of exogenous tetracycline, the transfected antisense MMP-9 did not affect the endogenous level of MMP-9 in WM451 cells, and showed no significant changes in cell behaviors in comparison with that of the vector-transfected control cells. Nevertheless, withdrawal of tetracycline from the medium caused a significant down-regulation of expression and activity of MMP-9. The capacity of cell growth in vitro, colony forming ability in soft agar, invasion through Matrigel all were inhibited remarkably when compared with the controls. Spontaneous metastasis in nude mice was significantly inhibited.

CONCLUSIONSTransfection of anti-sense MMP-9 can down-regulate the invasion and metastasis of melanoma cells both in vitro and in vivo, further clarifying the important role of MMP-9 in tumor progression.