Engineered Human Antibody with Improved Endothelin Receptor Type A Binding Affinity, Developability, and Serum Persistence Exhibits Excellent Antitumor Potency

Endothelin receptor A (ET_A), a class A G protein-coupled receptor (GPCR), is a promising tumor-associated antigen due to its close association with the progression and metastasis of many types of cancer, such as colorectal, breast, lung, ovarian, and prostate cancer. However, only small-molecule drugs have been developed as ET_A antagonists with anticancer effects. In a previous study, we identified an antibody (AG8) with highly selective binding to human ET_A through screening of a human naïve immune antibody library. Although both in vitro and in vivo experiments indicated that the identified AG8 had anticancer effects, there is a need for improvement in biochemical and physicochemical properties such as the ET_A binding affinity, thermostability, and productivity. In this study, we engineered the framework regions of AG8 and isolated an anti-ET_A antibody (MJF1) exhibiting significantly improved thermostability and ET_A binding affinity. Subsequently, our previously isolated PFc29, an Fc variant with an enhanced pH-dependent human FcRn binding profile, was introduced to MJF1, and the resulting Fc-engineered anti-ET_A antibody (MJF1-PFc29) inhibited the proliferation of tumor cells comparably to MJF1 and showed a 4.2-fold increased serum half-life in human FcRn transgenic mice. Moreover, MJF1-PFc29 elicited higher tumor growth inhibition in colorectal cancer xenograft mice compared to MJF1. Our results demonstrate that the engineered human anti-ET_A antibody MJF1-PFc29 has great therapeutic potential and high antitumor potency against various types of cancers including colorectal cancer.