Generating CAR-macrophages to target endothelin B receptor-positive tumors

The endothelin axis is highly involved and overexpressed in many tumors, making it an interesting therapeutic target. However, except for strategies based on small molecule antagonists, this axis is poorly targeted by immunotherapy approaches. Although cell-based therapies, in particular CAR-T cells, have produced impressive results in treating hematological tumors, they remain challenging for solid tumors. CAR-macrophages represent a promising alternative, but only a few therapeutic targets have been evaluated thus far. Having developed antibodies targeting ET1R, our laboratory proposes this axis as a target for CAR-macrophages development. This study investigated the efficacy of CAR-macrophages directed against the endothelin B receptor (ET_B), expressed by melanoma cells developed from Rendomab B4 (RB4), an antibody targeting ET_B. Before assembling the CAR against ET_B, the scFv RB4 fragment, derived from the full-length RB4 antibody, was characterized. It exhibited properties similar to those of the original antibody and displayed exclusive recognition of ET_B-positive melanoma cell lines. CAR RB4 evaluation showed remarkable antitumor activity against the high ET_B-expressing WM266 cell line, but no activity on the low ET_B-expressing A375 cell line. We show the first proof of concept for CAR therapy targeting the endothelin axis and establish CAR RB4 as a promising candidate for the treatment of ET_B-positive solid tumors.