Peptides have emerged as important therapeutics that are being rigorously tested in angiogenesis-dependent diseases due to their low toxicity and high specificity. Since the discovery of endogenous proteins and protein fragments that inhibit microvessel formation (thrombospondin, endostatin) several peptides have shown promise in pre-clinical and clinical studies for cancer. Peptides have been derived from thrombospondin, collagens, chemokines, coagulation cascade proteins, growth factors, and other classes of proteins and target different receptors. Here we survey recent developments for anti-angiogenic peptides with length not exceeding 50 amino acid residues that have shown activity in pre-clinical models of cancer or have been tested in clinical trials; some of the peptides have been modified and optimized, e.g., through L-to-D and non-natural amino acid substitutions. We highlight technological advances in peptide discovery and optimization including computational and bioinformatics tools and novel experimental techniques.

Metastasis is the main cause of mortality in cancer patients. Though there are many anti-cancer drugs targeting primary tumor growth, anti-metastatic agents are rarely developed. Angiogenesis and lymphangiogenesis are crucial for cancer progression, particularly, lymphangiogenesis is pivotal for metastasis in breast cancer. Here we report that a novel collagen IV derived biomimetic peptide inhibits breast cancer growth and metastasis by blocking angiogenesis and lymphangiogenesis. The peptide inhibits blood and lymphatic endothelial cell viability, migration, adhesion, and tube formation by targeting IGF1R and Met signals. The peptide blocks MDA-MB-231 tumor growth by inhibiting tumor angiogenesis in vivo. Moreover, the peptide inhibits lymphangiogenesis in primary tumors. MDA-MB-231 tumor conditioned media (TCM) was employed to accelerate spontaneous metastasis in tumor xenografts, and the anti-metastatic activity of the peptide was tested in this model. The peptide prevents metastasis to the lungs and lymph nodes by inhibiting TCM-induced lymphangiogenesis and angiogenesis in the pre-metastatic organs. In summary, a novel biomimetic peptide inhibits breast cancer growth and metastasis by blocking angiogenesis and lymphangiogenesis in the pre-metastatic organs as well as primary tumors.

Angiogenesis or neovascularization, the process of new blood vessel formation from preexisting microvasculature, involves interactions among several cell types including parenchymal, endothelial cells, and immune cells. The formation of new vessels is tightly regulated by a balance between endogenous proangiogenic and antiangiogenic factors to maintain homeostasis in tissue; tumor progression and metastasis in breast cancer have been shown to be angiogenesis-dependent. We previously introduced a systematic methodology to identify putative endogenous antiangiogenic peptides and validated these predictions in vitro in human umbilical vein endothelial cell proliferation and migration assays. These peptides are derived from several protein families including type IV collagen, CXC chemokines, and thrombospondin-1 domain-containing proteins. On the basis of the results from the in vitro screening, we have evaluated the ability of one peptide selected from each family named pentastatin-1, chemokinostatin-1, and properdistatin, respectively, to suppress angiogenesis in an MDA-MB-231 human breast cancer orthotopic xenograft model in severe combined immunodeficient mice. Peptides were administered intraperitoneally once per day. We have demonstrated significant suppression of tumor growth in vivo and subsequent reductions in microvascular density, indicating the potential of these peptides as therapeutic agents for breast cancer.