Abstract C54: In vitro and in vivo anti-tumor activity of the antimacrophage stimulating 1-receptor antibody IMC-RON8 in breast and bladder cancer models.
Authors: Loizos Nick , Bailey Timothy , Topper Michael , Eastman Scott , Pennello Anthony , O'Toole Jennifer 
Published: June 2012

Macrophage stimulating 1-receptor (RON) is a member of the c-Met receptor tyrosine kinase family. RON is normally expressed on macrophages and epithelial cells. However, it is overexpressed and activated in a large number of human tumors. The fully human anti-RON antibody, IMC-RON8, blocks the RON ligand, macrophage-stimulating protein (MSP), from binding to RON and has been demonstrated to have antitumor activity against human colon, lung, and pancreatic xenografts in mice. Overexpression of RON correlates with a worse clinical outcome for patients in at least two human cancer indications, namely breast and bladder. Given this correlation, we investigated the effect of IMC-RON8 in several in vitro and in vivo systems with the RON-positive breast and bladder cancer cell lines JIMT-1 and BFTC-905, respectively. Both of these were found from a screen of breast and bladder cancer cell lines designed to identify those that are RON positive and responsive to MSP through activation of the MAP Kinase signaling pathway. IMC-RON8 inhibited the phosphorylation of MAP Kinase in response to 5nM MSP stimulation for JIMT-1 and BFTC-905. IMC-RON8 also inhibited the MSP-induced cellular migration of JIMT-1 in a wound healing assay, completely preventing progression towards closing of the wound. As measured by flow cytometry, IMC-RON8 at 33.3nM induced the internalization of 38% and 31% cell-surface RON expressed on JIMT-1 and BFTC-905 cells, respectively, following 24 hours of treatment at 37°C. To investigate IMC-RON8-induced RON downmodulation, clonal Hela cells stably expressing a RON-GFP protein were generated. These cells were treated with MSP, a RON agonist antibody (RON2), or IMC-RON8 and the level of RON-GFP was then measured by confocal microscopy in a live-cell time lapse experiment. IMC-RON8 treatment actively induced receptor interalization and caused RON-GFP degradation (reduction of the GFP signal) relative to IgG controls, although to a lesser extent than MSP and RON2. In an in vivo JIMT-1 xenograft model, IMC-RON8 significantly inhibited tumor growth with a %T/C value of 59 when administered at 60 mg/kg twice a week. Combination of IMC-RON8 with the chemotherapeutic agent, docetaxel at 12 mg/kg once per week, significantly improved the anti-tumor effects compared to either monotherapy with a %T/C value of 20. In an in vivo BFTC-905 xenograft model, IMC-RON8 significantly inhibited tumor growth with a %T/C value of 58 when administered at 60 mg/kg twice a week. BFTC-905 tumors removed after the last IMC-RON8 dose (6 total doses over a 3 week study period), showed a decrease in the total level of RON receptor present in tumors relative to controls (p-value of &lt;0.0001). These preclinical results therefore demonstrate that IMC-RON8 possesses antitumor activity in vitro and in vivo and may be effective as a single agent or in combination with a conventional cytotoxic therapy for the treatment of cancer. Taken together, these data suggest the mechanism of action for IMC-RON8 antitumor activity can be both ligand-blocking activity and receptor downmodulation; both leading to a decrease in ligand-induced tumor cell proliferation. IMC-RON8 is presently in Phase I studies to treat patients with advanced solid tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C54.