Targeting pediatric sarcoma with a bispecific ligand immunotoxin targeting urokinase and epidermal growth factor receptors

// Kristy Pilbeam 1 , Hongbo Wang 1 , Elizabeth Taras 2 , Rachel J. Bergerson 1 , Brianna Ettestad 1 , Todd DeFor 3 , Antonella Borgatti 4 , Daniel A. Vallera 2, * and Michael R. Verneris 1, * 1 Pediatric Blood and Marrow Transplantation, University of Minnesota, Minneapolis, MN 55345, USA 2 Radiation Oncology, University of Minnesota, Minneapolis, MN 55345, USA 3 Biomedical Statistics, University of Minnesota, Minneapolis, MN 55345, USA 4 Veterinary Medicine, University of Minnesota, Minneapolis, MN 55345, USA * These authors have contributed equally to this work Correspondence to: Michael R. Verneris, email: Michael.Verneris@ucdenver.edu Keywords: Ewing’s sarcoma, rhabdomyosarcoma, urokinase-type plasminogen activator receptor (uPAR), epidermal growth factor receptor (EGFR), immunotherapy Received: May 04, 2017      Accepted: August 07, 2017      Published: September 23, 2017 ABSTRACT Children with high risk sarcoma have a poor prognosis despite surgical resection, irradiation and chemotherapy. Alternative therapies are urgently needed. Urokinase-type plasminogen activator receptor (uPAR) and epidermal growth factor receptor (EGFR) are surface proteins expressed by some pediatric sarcomas. We show for the first time that a de-immunized bispecific ligand toxin, EGFATFKDEL, directed against EGFR and uPAR, successfully targets pediatric sarcoma. Using flow cytometry, we identified a rhabdomyosarcoma (RMS) cell line, RH30, that expresses both uPAR and EGFR, and a Ewing sarcoma (EWS) cell line, TC-71, that expresses only uPAR. We tested the differential sensitivity of these two sarcoma cell lines to toxin-induced killing, using both in vitro assays and an in vivo murine model. We show that pediatric sarcomas are highly sensitive to EGFATFKDEL (at subnanomolar concentrations) in vitro . In vivo , tumor growth was significantly attenuated after treatment with EGFTFKDEL, compared to untreated controls, in both RH30 and TC-71 tumor bearing mice. In addition, we found that simultaneously targeting both receptors in a dual positive cell line was more effective than targeting a single receptor or antigen, resulting in a greater tumor response, including complete tumor regression in an animal model of bulky disease. Our findings provide support for further exploration of bispecific targeting of pediatric sarcomas with bispecific ligand toxins, such as EGFATFKDEL.