Neuropilin-binding tumor-penetrating peptides increase vascular and tissue permeability in tumors, allowing drugs conjugated to the peptide and even free drugs co-injected with the peptide to widely distribute within the tumor tissue (Sugahara KN et al, Cancer Cell 16:510, 2009; Science 328:1031, 2010). Thus, the peptides provide an elegant way to enhance therapeutic index of anti-cancer drugs. However, the ability of the peptides to increase vascular permeability has raised concerns that the peptides might enhance metastasis by promoting cell seeding from the primary tumor. Here, we show a recent unexpected finding that a prototypic tumor-penetrating peptide, iRGD (amino acid sequence: CRGDK/RGPD/EC), is a potent metastasis inhibitor. iRGD did not cause systemic tumor cell dissemination or metastasis in mice bearing breast tumors with low metastatic potential. iRGD treatment of mice bearing aggressive orthotopic pancreatic tumors resulted in significant decrease in spontaneous metastasis formation. Primary tumor growth was not affected by the treatment. Another tumor-penetrating peptide, iNGR, also inhibited metastasis, while conventional RGD peptides or a scrambled iRGD peptide that lack neuropilin affinity failed to do. These results indicate that the anti-metastatic effect of iRGD was dependent on its neuropilin-binding peptide motif. In vitro migration assays demonstrated that iRGD potently inhibits tumor cell migration and serves as a chemorepellent of tumor cells in a neuropilin-dependent manner. Chemorepulsion assays based on live cell imaging confirmed the findings, and further demonstrated that iRGD dramatically collapses tumor cell protrusions leading to an instantaneous retraction of tumor cells from iRGD-bound surfaces.

Our finding refutes the hypothesis that iRGD may cause enhanced metastasis. The mechanism of the anti-metastatic effect may involve neuropilin-mediated chemorepulsion of tumor cells. Collectively, iRGD may simultaneously achieve tumor-specific drug delivery and metastasis inhibition when utilized for cancer treatment.

Citation Format: Kazuki N. Sugahara, Gary B. Braun, Tatiana H. de Mendoza, Venkata R. Kotamraju, Tambet Teesalu, Erkki Ruoslahti, Randall P. French, Andrew M. Lowy. A tumor-specific tissue penetrating peptide inhibits metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-102. doi:10.1158/1538-7445.AM2014-LB-102