Identification of cytotoxic agents disrupting synovial sarcoma oncoprotein interactions by proximity ligation assay

// Aimée N. Laporte 1, 2 , Jennifer X. Ji 2 , Limin Ma 3 , Torsten O. Nielsen 1, 2 , Bertha A. Brodin 3 1 Department of Pathology and Laboratory Medicine, Vancouver Coastal Health Research Institute and Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada 2 Centre for Translational and Applied Genomics, British Columbia Cancer Agency, Vancouver, BC, Canada 3 Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden Correspondence to: Torsten O. Nielsen, email: torsten@mail.ubc.ca Keywords: synovial sarcoma, proximity ligation assay, drug screening, HDAC inhibitors, protein-protein association Received: September 09, 2015      Accepted: April 02, 2016      Published: April 21, 2016 ABSTRACT Conventional cytotoxic therapies for synovial sarcoma provide limited benefit. Drugs specifically targeting the product of its driver translocation are currently unavailable, in part because the SS18-SSX oncoprotein functions via aberrant interactions within multiprotein complexes. Proximity ligation assay is a recently-developed method that assesses protein-protein interactions in situ . Here we report use of the proximity ligation assay to confirm the oncogenic association of SS18-SSX with its co-factor TLE1 in multiple human synovial sarcoma cell lines and in surgically-excised human tumor tissue. SS18-SSX/TLE1 interactions are disrupted by class I HDAC inhibitors and novel small molecule inhibitors. This assay can be applied in a high-throughput format for drug discovery in fusion-oncoprotein associated cancers where key effector partners are known.