A human antibody against human endothelin receptor type A that exhibits antitumor potency

Endothelin receptor A (ET(A)), a class A G-protein-coupled receptor (GPCR), is involved in the progression and metastasis of colorectal, breast, lung, ovarian, and prostate cancer. We overexpressed and purified human endothelin receptor type A in Escherichia coli and reconstituted it with lipid and membrane scaffold proteins to prepare an ET(A) nanodisc as a functional antigen with a structure similar to that of native GPCR. By screening a human naive immune single-chain variable fragment phage library constructed in-house, we successfully isolated a human anti-ET(A) antibody (AG8) exhibiting high specificity for ET(A) in the β-arrestin Tango assay and effective inhibitory activity against the ET-1-induced signaling cascade via ET(A) using either a CHO-K1 cell line stably expressing human ET(A) or HT-29 colorectal cancer cells, in which AG8 exhibited IC(50) values of 56 and 51 nM, respectively. In addition, AG8 treatment repressed the transcription of inhibin βA and reduced the ET(A)-induced phosphorylation of protein kinase B and extracellular regulated kinase. Furthermore, tumor growth was effectively inhibited by AG8 in a colorectal cancer mouse xenograft model. The human anti-ET(A) antibody isolated in this study could be used as a potential therapeutic for cancers, including colorectal cancer.