Abstract C161: Fsn0503h antibody-mediated blockade of cathepsin S as potential therapeutic strategy for the treatment of solid tumors.
Authors: Vázquez Ramiro , Astorgues-Xerri Lucil , Cvitkovic Esteban , Bekradda Mohamed , Fleck Roman , Gormley Julie , Buick Richard , Kerr Paul , Raymond Eric , D'Incalci Maurizio , Frapolli Roberta , Riveiro María Eugenia 
Published: August 2014

Abstract
Purpose: Cathepsin S (Cat-S) is a lysosomal cysteine protease found overexpressed in many cancers, and it has been associated with tumor aggressiveness. In this sense, increasing evidence indicates that Cat-S is secreted into the tumor environment causing extracellular matrix component degradation, thereby facilitating invasion, angiogenesis and metastasis during tumor progression. The aim of this work was to evaluate the anti-cancer activity of an antagonistic anti-Cat-S monoclonal antibody, Fsn0503h, in several cell lines in vitro and in the Colo-205 colon carcinoma xenograft.
Experimental Procedures: Fsn0503h was provided by Fusion Antibodies Ltd. [Clin Cancer Res 2009;15(19):6042-51]. Cat-S protein expression was studied in a panel of breast, head and neck, hepatocarcinoma, ovarian, pancreas, cholangiocarcinoma, prostate, glioma, renal, and colon cancer cell lines by Western blot. Fsn0503h anti-invasive effects were evaluated in vitro by Matrigel invasion assay in Cat-S-expressing cells. Anti-proliferative effects of Fsn0503h were determined by the MTT assay. Furthermore, subcellular localization of Cat-S was assessed by immunofluorescence. In vivo, Fsn0503h anti-tumor efficacy was evaluated in in nude mice bearing palpable Colo205 tumor xenografts, in different doses and dosing schedules.
Results: Cat-S was found to be expressed in 11 out of 36 cancer cell lines, including renal cancer cells lines Caki-1 and Caki-2. Interestingly, Cat-S expression had not been previously reported in renal cancer cell lines. Furthermore, it was observed for the first time that TNF-γ can induce the expression of Cat-S in the renal cancer cell line 786-0. In vitro, Fsn0503h displayed anti-proliferative effects in some Cat-S-expressing cell lines. In addition, exposure to Fsn0503h (125 nM) for 24 h induced a significant reduction in the invasive capacity of all cell lines expressing Cat-S. Similar results were obtained with another Cat-S inhibitor, Z-FL-COCHO. Subsequent evaluation of the subcellular localization of Cat-S in 786-0 and CAKI-1 cells showed that the protein is mainly expressed in the cytoplasm. Finally, in vivo experiments showed that in this study, 10 mg/kg Fsn0503h administered intravenously in a thrice a week regimen was the most active dose schedule in a Colo205 xenograft model.
Conclusions: Our results indicate that Cat-S is a suitable therapeutic target in some solid tumors. In this regard, Fsn0503h, the first humanized monoclonal antibody against Cat-S, not only inhibits the invasiveness of cancer cell lines in vitro but also displays in vivo anti-tumor effects. These results validate Cat-S as a therapeutic target and encourage further development of the Fsn0503h antibody.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C161.
Citation Format: Ramiro Vázquez, Lucil Astorgues-Xerri, Esteban Cvitkovic, Mohamed Bekradda, Roman Fleck, Julie Gormley, Richard Buick, Paul Kerr, Eric Raymond, Maurizio D'Incalci, Roberta Frapolli, María Eugenia Riveiro. Fsn0503h antibody-mediated blockade of cathepsin S as potential therapeutic strategy for the treatment of solid tumors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C161.