Antibody-Mediated Inhibition of Cathepsin S Blocks Colorectal Tumor Invasion and Angiogenesis

Abstract

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. 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 tumor models (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-T...

Alternative activation of tumor-associated macrophages by IL-4

“…81 Our group and others have identified critical roles for cathepsins in tumor growth, angiogenesis, invasion and metastasis using both genetic and pharmacological strategies in mouse models of cancer. [82][83][84][85][86][87] For example, during sequential stages of tumor development in the RIP1-Tag2 (RT2) model of pancreatic islet carcinogenesis, 88 we found that expression of a subset of cathepsins (B, C, H, L, S, X/Z) progressively increased. 82 Moreover, most of these cathepsins, except cathepsin L, were provided predominantly by infiltrating TAMs in different tumor microenvironments.…”

Effects of novel human cathepsin S inhibitors on cell migration in human cancer cells

“…These indicated that Cat S plays an important role in aspects of angiogenesis both in vitro and in vivo 3 . Furthermore, high Cat S expression has also been observed in a range of tumors such as prostate, astrocytomas, hepatocellular and pancreatic carcinomas [4][5][6][7] . The expression of Cat S together with Cat B was found in neoplastic prostatic cells from pre-invasive to invasive and clinically detectable stage 8 .…”

“…Impaired angiogenesis and tumor growth were found in Cat Sdeficient mice, whereas opposite phenotypes shown in mice lacking of the endogenous inhibitor cystatin C 12 . The invasive and pro-angiogenic effects in preclinical and clinical evaluation were blocked by antibody Fsn0503 against Cat S 6 . The invasive behavior in U251MG glioblastoma cells was disrupted by a peptidic, irreversible Cat S inhibitor, 4-morpholineureaLeu-HomoPhe-vinylsulphone 9 .…”

Antibody research targeting Cathepsin S for cancer therapy

“…In recent years, a panel of monoclonal antibodies was raised to human Cathepsin S [9]. The effects of a selected antibody were successfully determined by cellbased invasion and proteolysis assays.…”