Specificity of a new approach to anti-angiogenesis therapy: Anti-denatured collagen antibodies selectively target tumor neovascularization but not normal tissue

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The extracellular matrix (ECM) is a molecular network that was originally thought to function mainly as mechanical support to cells and tissues. This concept has dramatically changed in the past few years with the findings that the ECM contains a wealth of biochemical information that plays important roles in cellular processes such as cell proliferation, adhesion, and migration. Collagen, one of the most abundant components of the ECM, is composed of three chains organized in a triple helical structure. Proteolytic degradation of collagen by matrix metalloproteases (MMPs) secreted by both tumor and endothelial cells during angiogenesis, changes collagen structure, revealing cryptic binding sites. These sites play an essential role in the initiation and progression of new blood vessel formation, signaling through members of the integrin family (Xu et. al., J Cell Biol. 154, 1069-79, 2001). Murine monoclonal antibodies that bind to cryptic epitopes on denatured (dn) collagen have been shown to inhibit tumor cell adhesion, migration, and bFGF-induced angiogenesis in chick embryos, as well as human melanoma growth in SCID mice. In this report, humanized anti dn-collagen antibodies D93 and H8 were shown to retain preferential binding to dn collagens I and IV compared to native collagens. Importantly, the anti-dn collagen antibodies were shown to bind with similar affinity to dn collagens of different species, such as mouse, chicken, and human, indicating that the collagen epitopes are conserved across species. In preclinical studies, the anti-dn collagen antibodies D93 and H8 exhibited specific binding to sites juxtaposed to blood vessels by immunohistochemistry (IHC) in several xenograft human tumor models, consistent with the exposure of cryptic epitopes on dn collagen during angiogenesis. In addition, IHC evaluation of surgically removed tissues from patients with different types of malignancies (breast, colon) revealed that the murine and humanized-biotinylated anti-dn collagen antibodies D93 and H8 specifically bind to the subendothelial basement membrane of blood vessels in tumor tissue, but not to adjacent normal tissues. This observation underscores the high specificity of these antibodies for sites of angiogenesis in human tumor tissues and suggests that these antibodies may be less likely to cause adverse/toxic effects associated with non-specific binding in normal tissues. These findings, taken together, support continuing investigations of the therapeutic potential of humanized anti-dn collagen antibodies for the treatment of cancer.