Abstract LB-269: Anti-RON antibody-drug maytansinoid conjugates (Anti-RON ADC) as potential biotherapeutics for targeted colorectal cancer therapy
Authors: Wang Ming-Hai , Feng Liang , YAO Hang-Ping , Wang Wei , Sharma Sharad , Zhang Ruiwen 
Published: May 2015

The receptor tyrosine kinase RON, a member of the MET family, is critical in epithelial tumorigenesis. RON also is a validated drug target for cancer therapy due to its high levels of expression in cancer cells. At present, monoclonal antibodies (mAb) and tyrosine kinase inhibitors have been developed, preclinically tested, and evaluated under clinical trials. However, accumulated evidences have indicated that the efficacy of RON-targeted therapy alone is weak. Thus, there is an urgent need to develop a strategy to improve the effectiveness of RON-targeted cancer therapy. Here we report the development and therapeutic efficacy of anti-RON mAb Zt/g4-maytansinoid conjugates (Zt/g4-DM1) with enhanced cytotoxicity against colorectal cancer cells (CRC) in mouse xenograft tumor models. Zt/g4 (IgG1a/κ) was selected among several anti-RON mAbs as the drug carrier for its ability to induce RON endocytosis in CRC cells. Zt/g4 was conjugated to DM1 via the thioether link to form anti-RON antibody-drug conjugate Zt/g4-DM1 with an antibody-drug ratio of 1:4 molecules. Using HCT116, HT29, and SW620 cells as the model, we found that Zt/g4-DM1 retains the intrinsic activity that causes rapid RON internalization. Targeted payload delivery significantly induced cell cycle arrest at G2/M phase, reduced cell viability with IC50 values at ∼1.2 μg/ml, which resulted in massive cell death within a period of 72h. The cytotoxic effect of Zt/g4-DM1 was negligible in cancer cells with minimal RON expression. Studies from the mouse CRC xenograft model revealed that Zt/g4-DM1 is highly effective in delaying HT29 cell-mediated tumor growth in athymic nude mice. In a single cycle of q 4 days x 5 with Zt/g4-DM1 at 1, 3, 7, 10, and 15 mg/kg body weight, we observed significant tumor inhibition (&gt;70% tumor growth delay) when Zt/g4-DM1 was used at 7 mg/kg. Significantly, more than 95% of tumor growth was inhibited at 10 mg/kg or 15 mg/kg of Zt/g4-DM1. Continued observation after last treatment showed that the inhibitory effect of Zt/g4-DM1 is long lasting up to 20 days without signs of tumor regrowth. The prepared Zt/g4-DM1 is stable in vitro and has a minimal toxic effect in vivo when Zt/g4-DM1 was used below 40 mg/kg. Zt/g4 has been sequenced and a 3D model of antigen-binding domains in variable regions in both heavy and light chains has been created. Zt/g4 is currently under humanization for potential clinical trials. In conclusion, Zt/g4-DM1 is a highly effective biotherapeutics for inhibition of CRC growth in mouse xenograft models. The therapeutic potential of Zt/g4-DM1 provides a novel strategy for targeted CRC therapy in the future. Moreover, the development of humanized Zt/g4-DM1 opens an avenue for testing its therapeutic effect on various types of cancers harboring aberrant RON expression. (This project is support in part by NIH grant CA91980 to MHW).

Citation Format: Ming-Hai Wang, Liang Feng, Hang-Ping YAO, Wei Wang, Sharad Sharma, Ruiwen Zhang. Anti-RON antibody-drug maytansinoid conjugates (Anti-RON ADC) as potential biotherapeutics for targeted colorectal cancer therapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-269. doi:10.1158/1538-7445.AM2014-LB-269