Abstract B130: Monoclonal antibody (mAb)-induced down-regulation of the RON receptor tyrosine kinase impairs malignant phenotypes of colon cancer cells

Abstract

Abstract Targeting receptor tyrosine kinases (RTK) with specific mAbs disrupts oncogenic signals and diminishes tumorigenic activities. The RON receptor tyrosine kinase is a member of the MET proto-oncogene family and contributes to motile/invasive phenotypes of colon cancer cells. Here, we studied mAb-induced down-regulation of RON in modulating tumorigenic phenotypes of colon cancer cells. Three mAbs (Zt/g4, Zt/c9 and Zt/f2), recognizing different epitopes in the RON extracellular sequences, were used in various in vitro experiments. Colon cancer SW620 and other cells were used as the model. Treatment of SW620 cells individual mAbs results in transient RON phosphorylation within minutes. However, persistent treatment of cells with Zt/g4 or other mAb causes the down-regulation RON expression as evident by Western blot and cell surface fluorescent analyses. The effect of mAb was in both concentration and time-dependent manners. These activities were not related to antigenic epitopes recognized by individual mAb but highly specific to RON because MET or EGFR expression was not affected. Down regulation of RON impairs intracellular signaling events. Phosphorylation of Erk1/2 and AKT was dramatically reduced after Zt/g4 and other mAb treatment, indicating that the anti-RON mAb has the ability to disrupt downstream signal cascades. Functional studies showed that treatment of SW620 cells with anti-RON mAb affects tumor cell growth in soft agar. It also increases the sensitivity of colon cancer SW620 cells towards chemoagent gemcitabine. In this case, the cytotoxicity of SW620 cells treated with mAbs was significantly increased with reduced IC50 of gemcitabine. In conclusion, our results demonstrated that the persistent treatment of cancer cells with antibodies specific to the RON extracellular domains results in down-regulation of RON expression in colon cancer cells. The reduced RON expression is accompanied with the impaired signaling events and diminished tumorigenic activities. Thus, anti-RON mAb directed targeting could have therapeutic implication for controlling malignant phenotypes of cancer cells (*supported in part by NIH R01 grant Ca91980 and Amarillo Area Foundation of Texas) Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B130.