Oncogenic Variant RON160 Expression in Breast Cancer and its Potential as a Therapeutic Target by Small Molecule Tyrosine Kinase Inhibitor

Aberrant expression of the RON receptor tyrosine kinase contributes to breast cancer malignancy. Although clinical trials of RON targeting are underway, the intriguing issue is the diversity of RON expression as evident by cancer cells expressing different variants including oncogenic RON160. The current study determines aberrant RON160 expression in breast cancer and its potential as a target for breast cancer therapy. Using mouse monoclonal antibody Zt/h12 in immunohistochemical staining of breast cancer tissue microarray, we observed that RON160 was expressed in high frequency in primary invasive ductal (77.2%, 61/79 cases), lobular (42.5%, 34/80 cases), and lymph node-involved (63.9%, 26/36 cases) breast cancer samples. Moreover, RON160 overexpression was predominantly observed in invasive ductal (26.6%, 21/79 cases) and lymph node-involved (33.3%, 12/36) cases. Among a panel of breast cancer cell lines analyzed, Du4475 cells naturally expressed RON160. Silencing RON160 expression by siRNA reduced Du4475 cell viability. Inhibition of RON160 signaling by tyrosine kinase inhibitor PHA665752 also suppressed Du4475 cell anchorage-independent growth and induced apoptotic cell death. Studies in vivo revealed that PHA665752 inhibited 3T3- RON160 and Du4475 cell-mediated tumor growth in mouse mammary fat pad. A 60% reduction in tumor volume compared to controls was achieved after a 13-day treatment. We conclude from these studies that RON160 is highly expressed in breast cancer and its signaling is integrated into cellular signaling network for tumor cell growth and survival. Experimental treatment by PHA665752 in Du4475 breast cancer xenograft model highlights the significance of RON160 as a drug target in molecular-targeted breast cancer therapy.