Osteopontin (OPN) has been implicated in various stages of cancer progression such as malignant transformation, invasion and metastasis. Several groups independently demonstrated that plasma OPN level is a potential diagnostic and prognostic marker for several human malignancies (Bellahcene A et al, Nat Rev Cancer 8:212, 2008 and Anborgh PH, et al Clin Chem 55:895, 2009). Interestingly, a human breast cancer cell with an aggressive lymph node metastatic ability has been established, which demonstrated strong expression of α9β1 integrin and OPN (Vantyghem SA et al Clin & Exp Meta 22:351, 2005). Of note, α9β1 integrin is a receptor for not only OPN, but also VEGF-C and -D, known lymphatic vessel growth factors. To address whether and how α9β1 integrin is involved in tumorigenesis, growth, invasion and lymph node metastasis, we took advantage of using an inhibitory anti-human α9 integrin antibody (clone: K33N), which does not cross react with murine α9 integrin and an α9β1 integrin-positive human breast cancer cell line, MDA-MB-231 luc-D3H2LN (D3H2LN), in in vitro functional assays and an in vivo orthotopic xenotransplantation model.

We found that K33N inhibited in vitro migration and invasion of D3H2LN cells, indicating that the interaction of α9β1 integrin with its ligands was involved in the breast cancer cells motility. Next, we inoculated D3H2LN cells into the mammary fat pad of nude mice at day 0, and K33N or control IgG was given to them twice per week from day 15 to day 50 after tumor inoculation. K33N significantly reduced both primary tumor growth and draining lymph node metastasis. To gain an understanding of the mechanism by which K33N suppressed the primary tumor growth and lymph node metastasis, we examined the expression of various molecules which are associated with the cancer progression. We found significant matrix metalloproteinase (MMP) up-regulation in K33N-treated primary tumor tissues, consistent with a recent report demonstrating an indirect involvement of MMPs involved in tumor growth. Of note, upon orthotopic injection of human D3H2LN cells, plasma level of host-derived murine OPN, but not tumor-derived human OPN was significantly elevated. Surprisingly, host-derived murine OPN was significantly reduced in the mice treated with K33N. These results suggest that the interaction between α9β1 integrin on breast cancer cells and its ligands favors the generation of tissue microenvironments which contribute to primary tumor growth and lymph node metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 417. doi:10.1158/1538-7445.AM2011-417