Cancer Therapy: Preclinical Antibody-Mediated Inhibition of Cathepsin S Blocks Colorectal Tumor Invasion and Angiogenesis

Purpose: Cathepsin S is a cysteine protease that promotes the invasion of tumor and endothelial cells during cancer progression. Here we investigated the potential to target cathepsin S using an antagonistic antibody, Fsn0503, to block these tumorigenic effects. Experimental Design: A panel of monoclonal antibodies was raised to human cathepsin S. The effects of a selected antibody were subsequently determined using invasion and proteolysis assays. Endothelial cell tube formation and aorta sprouting assays were done to examine antiangiogenic effects. In vivo effects were also evaluated using HCT116 xenograft studies. Results: A selected cathepsin S antibody, Fsn0503, significantly blocked invasion of a range of tumor cell lines, most significantly HCT116 colorectal carcinoma cells, through inhibition of extracellular cathepsin S–mediated proteolysis. We subsequently found enhanced expression of cathepsin S in colorectal adenocarcinoma biopsies when compared with normal colon tissue. Moreover, Fsn0503 blocked endothelial cell capillary tube formation and aortic microvascular sprouting. We further showed that administration of Fsn0503 resulted in inhibition of tumor growth and neovascularization of HCT116 xenograft tumors. Conclusions: These results show that blocking the invasive and proangiogenic effects of cathepsin S with antibody inhibitors may have therapeutic utility upon further preclinical and clinical evaluation. (Clin Cancer Res 2009;15(19):6042–51) The lysosomal cysteine cathepsins encompass a family of closely related cysteine proteases, mediating a diverse range of proteolytic effects (1–4). However, an increasing body of evidence has shown the overexpression of a number of cysteine cathepsins in cancer (5–7). Significantly, these proteases are secreted into the tumor extracellular milieu, producing potent degradative effects on a broad range of extracellular matrix (ECM) components, including collagen and laminins (8–10). Further confirmation of these effects were provided in a murine model of sporadic pancreatic carcinogenesis (RIP1-Tag2), in which the genetic ablation of either cathepsin B or cathepsin S severally attenuated tumor invasion and angiogenesis, and cathepsin L or cathepsin B deficiency inhibited tumor proliferation (11). These observations highlight their potential as therapeutic targets in cancer treatment. Indeed, the application of synthetic broad-spectrum probes and combination therapies has successfully shown efficacy in vivo using various tumormodels (12–15). However, given the roles that these proteases play in normal cellular homeostasis, an approach that selectively targets a specific cathepsin with limited normal tissue distribution may be more therapeutically attractive. Cathepsin S, unlike the ubiquitous cathepsin B and cathepsin L, exhibits a restricted tissue expression. It is found predominantly in lymphatic tissue, macrophages, and other professional antigenpresenting cells (16); mediating key steps in antigen presentation through cleavage of the invariant chain (17, 18). However, the inappropriate expression of cathepsin S has also been observed in a range of tumors such as astrocytomas (19–21), prostate (22), hepatocellular (23), and pancreatic carcinomas (11). Crucially, evidence from the RIP1-Tag2 model and other studies (11, 23–25) also suggests a pivotal role for endothelium-derived cathepsin S in neovasularization. In this current investigation we describe the development of an antibody to specifically bind and attenuate cathepsin S over other closely related cathepsins. We show that application of this antibody, Fsn0503, blocks tumor cell invasion through ablation of cathepsin S–mediated ECM remodeling. Furthermore, Fsn0503 also inhibits endothelial tube formation and Authors' Affiliations: School of Pharmacy, Centre for Infection and Immunity, and Institute of Pathology, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, and Fusion Antibodies Ltd., Springbank Industrial Estate, Belfast, United Kingdom Received 5/18/09; revised 6/19/09; accepted 6/23/09; published OnlineFirst 9/29/09. The costs of publication of this article were defrayed in part by the payment of page charges. This articlemust therefore be herebymarked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Requests for reprints: Christopher J. Scott, School of Pharmacy, Queen's University Belfast, 97 LisburnRoad, Belfast, BT9 7BLUnited Kingdom. Phone: 0044-2890972350; Fax: 0044-2890227794; E-mail: [email protected]. F 2009 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-09-1262 6042 Clin Cancer Res 2009;15(19) October 1, 2009 www.aacrjournals.org Published Online First on September 29, 2009 as 10.1158/1078-0432.CCR-09-1262 Research. on April 12, 2017. © 2009 American Association for Cancer clincancerres.aacrjournals.org Downloaded from Published OnlineFirst September 29, 2009; DOI: 10.1158/1078-0432.CCR-09-1262