Abstract 4996: Targeting FGFR4 with monoclonal antibodies as therapeutic agents for the treatment of rhabdomyosarcoma
Authors: Baskar Sivasubramanian 
Published: July 2016

Abstract
Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood with two major subtypes, embryonal (ERMS) and alveolar (ARMS), and current treatment modalities have yielded event free 5-year survival in only 30% of the patients with high-risk disease. Therefore, there is a need for novel strategies to identify and validate clinically relevant targets and therapeutics for the treatment of RMS. The fibroblast growth factor receptor 4 (FGFR4) is a very attractive therapeutic target because: 1) the FGFR4 gene is over expressed in RMS, 2) it is directly transcriptionally induced by the PAX3-FOXO1 fusion oncogene found in ARMS, 3) it is crucial for survival, proliferation, metastasis and drug resistance, 4) activating mutations in the kinase domain lead to aggressive growth and poor survival in patients with ERMS and 5) genetic or pharmacologic inhibition of FGFR4 signaling inhibited tumor growth in vitro and in vivo. Most normal human tissues do not express FGFR4 protein as determined by immunohistochemistry and electrochemiluminesence assay. Based these, we hypothesize that monoclonal antibodies (mAbs) targeting FGFR4 and their derivatives can serve as potential therapeutic agents for the treatment of RMS.
We have developed a total of 15 mAbs against human FGFR4 protein from rabbit and mouse (by hybridoma technology), and from human immunoglobulin libraries (by recombinant DNA technology). These mAbs specifically react with human FGFR4 protein in an ELISA and not to the other members of the FGFR family. Flow cytometer analysis demonstrated that they specifically bound to cell surface FGFR4 protein in RMS cell lines although the FGFR4 expression levels was variable in both ARMS and ERMS cell lines. Furthermore, cell surface FGFR4 mediated internalization of the bound antibody upon incubation at 37oC for as little as 30 min and maximum internalization was observed at 2 h. Two of the mouse mAbs tested were able to mediate specific cytotoxicity in FGFR4-expressing cell lines in the presence of an anti-mouse secondary antibody conjugated to cytotoxic drugs (2oADCs), e.g. monomethyl auristatin F (MMAF) or a duocarmycin derivative (DMDM). Dose titration of the anti-FGFR4 mAbs revealed maximum killing at 100 pM indicating their robust activity in vitro, and both ARMS and ERMS cell lines were susceptible to the mAb-mediated cytotoxicity. Ongoing investigations include generation of FGFR4-targeting direct ADCs and evaluation of their efficacy in vivo. Together, these observations support the contention that anti-FGFR4 mAb can be used as a vehicle to deliver a cytotoxic payload in the form of small molecule drugs and toxins. Thus, FGFR-ADCs may serve as potential therapeutic agents for the treatment of patients with RMS, as well other FGFR4-positive cancers including breast, liver, prostate and lung.
Citation Format: Sivasubramanian Baskar. Targeting FGFR4 with monoclonal antibodies as therapeutic agents for the treatment of rhabdomyosarcoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4996.