Mouse Macrophage Metalloelastase Gene Transfer into a Murine Melanoma Suppresses Primary Tumor Growth by Halting Angiogenesis

Mouse macrophage metalloelastase (MME) has been associated with the generation of angiostatin, an internal fragment of plasminogen, which inhibits angiogenesis . To clarify whether tumor cells that consistently generate MME can suppress angiogenesis and, therefore, inhibit the growth of primary tumors in vivo , we transfected a cDNA coding for MME into murine B16-BL6 melanoma cells that grow rapidly and are MME deficient . The generation of active MME in MME-transfected clones was confirmed by immunoprecipitation followed by in vitro cleavage of plasminogen. Subcutaneous implantation of these stable clones in C57BL/6 mice inhibited primary tumor growth by an average of 73% ( P = 0.00002), which directly correlated with a significant reduction of blood vessel formation (∼76%) in such tumors. Microangiography revealed massive angiogenesis in control tumors (mock and vector); however, in MME-transfected primary tumors it demonstrated a decreased and disrupted vascular network. Western blot analysis using a specific anti-mouse angiostatin antibody demonstrated a strong 38-kDa immunoreactive band in MME-transfected tumors and in the serum of mice bearing those tumor cells . These results show that placing MME gene directly into B16-BL6 melanoma cells is an effective approach to suppress primary tumor growth in vivo because it halts angiogenesis . Our data provide a feasible and promising strategy for gene therapy of cancer by targeting tumor vasculature.