MMP-3 and MMP-9 Gene Transfer Decrease Growth and Angiogenesis in Breast Cancer Xenografts In Vivo

• Matrix metalloproteinases (MMPs) are largely implicated in tumor behaviour due to their extracellular matrix (ECM) remodelling capacities. Although MMP activity generally is discussed in terms of facilitating tumor invasion, MMP inhibition in clinical trials has failed. Increasing amounts of data show that MMPs may inhibit tumor progression by generating anti-angiogenic factors such as endostatin from the tumoral stroma. We have previously shown that intratumoral gene transfer of MMP-9 induced tumor regression and reduced angiogenesis of breast cancer in vivo. Whether MMP activities induce tumor progression or regression may depend on type of MMP and the expression level in the tumor tissue. In this study we treated established breast cancers in nude mice with adenovirus vectors carrying the human genes of MMP-3 or MMP-9 in low or high dose. Microdialysis was used to sample endostatin in situ and tumor growth was monitored for 35 days. Tumors in mice treated with low-dose of either MMP-3 or MMP-9 vectors exhibited tumor stasis throughout the experiment whereas high-dose gene transfer of either MMP-3 or MMP-9 induced significant tumor regression compared to controls treated with empty vectors. The extracellular in vivo levels of endostatin were increased in tumors that received either high or low MMP-3 or MMP-9 gene transfer and these tumors exhibited decreased microvessel area compared to controls. Our results propose that increased expression of MMP-3 and MMP-9 have therapeutic effects of established breast cancer in a dose dependent manner where a slight increase of MMP expression results in tumor stasis and a high expression of either MMP-3 or MMP-9 by gene transfer results in a potent tumor regression.

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