RON Receptor Tyrosine Kinase as a Therapeutic Target for Eradication of Triple-Negative Breast Cancer: Efficacy of Anti-RON ADC Zt/g4-MMAE.

Triple-negative breast cancer (TNBC) is a highly diverse group of malignant neoplasia with poor outcome. Currently, the lack of effective therapy has fostered a major effort to discover new targets to treat this malignant cancer. Here we identified the RON receptor tyrosine kinase as a therapeutic target for potential TNBC treatment. We analyzed RON expression in 168 primary TNBC samples via tissue microarray using anti-RON IHC staining and demonstrated that RON was widely expressed in 76.8% TNBC samples with overexpression in 76 cases (45.2%). These results provide the molecular basis to target RON for TNBC therapy. To this end, anti-RON monoclonal antibody Zt/g4-drug monomethyl auristatin E conjugate (Zt/g4-MMAE) was developed with a drug to antibody ratio of 3.29 and tested in a panel of TNBC cell lines with different phenotypes. In vitro, Zt/g4-MMAE rapidly induced RON internalization, resulted in cell-cycle arrest followed by massive cell death. The calculated IC50 values ranged from 0.06 to 3.46 μg/mL dependent on individual TNBC cell lines tested. Zt/g4-MMAE also effectively killed TNBC stem-like cells with RON+/CD44+/CD24- phenotypes and RON-negative TNBC cells through the bystander effect. In vivo, Zt/g4-MMAE at 10 mg/kg in a Q12 × 2 regimen completely eradicated TNBC xenografts without the regrowth of xenograft tumors. In conclusion, increased RON expression is a pathogenic feature in primary TNBC samples. Zt/g4-MMAE is highly effective in eradicating TNBC xenografts in preclinical models. These findings lay the foundation for using anti-RON Zt/g4-MMAE in clinical trials as a novel strategy for TNBC treatment. ©2018 American Association for Cancer Research.