Development of a Novel, Proteinase-Activated Toxin Targeting Tumor Neovascularization

Tumor progression and angiogenesis are dependent on the expression and activation of matrix metalloproteinases MMPs. To target invading tumor cells based on their cell-surface expression of active MMPs, a novel bacterial toxin was developed in which the normal furin activation site of the proteolytically activated alpha-toxin of Clostridium septic urn was replaced with a recognition site for the MMPs. Cleavage of either wild-type or mutant alpha-toxin leads its oligomerization into heptameric, pore-forming complexes which insert into the cell membrane, killing the cell. MMP-targeted alpha-toxin was fully effective against HT-1080 fibrosarcoma cells, but significantly less effective against normal fibroblasts that do not constitutively express active MMPs on their surfaces. Similarly, MCF-7 mammary carcinoma cells, which were not significantly susceptible to toxins, became susceptible when transfected with the cell-surface metalloproteinase, MT-MMP-1. MDA-MB-231 mammary carcinoma cells, representing an advanced stage tumor, were subject to toxin-mediated cell death without MMP transfection. These results suggest that an MMP-activated alpha-toxin may be useful as part of an anti-tumor strategy.