Novel small molecule analogs for advancing apelin receptor antagonism with enhanced plasma and microsomal stability

The apelin receptor (APJ), a G protein-coupled receptor, has emerged as a promising therapeutic target in oncology due to its role in tumor growth, angiogenesis, metastasis, and resistance to anti-VEGF therapy. However, ML221, the only reported small-molecule APJ antagonist, exhibits extremely poor plasma (<1 % remaining after 1 h) and liver microsomal (t_1/2 < 1 min) stability, limiting its translational potential. To address this, we designed and synthesized a focused series of ML221 analogs incorporating amide, ether, and sulfonate linkages to block esterase-mediated degradation aiming to improve metabolic stability while maintaining APJ antagonistic activity. Among them, sulfonate-linked analogs 21 and 22 retained strong β-arrestin inhibition (IC₅₀ = 3.1 μM and 3.2 μM; 90.1 % and 80.1 % inhibition, respectively) while exhibiting significantly enhanced metabolic stability (100 % remaining in plasma after 1 h; liver microsomal t_1/2 = 5 min). These compounds selectively inhibited APJ-overexpressing Cancer cells (OVCAR8) and suppressed apelin-induced endothelial cell migration (OVCAR3 and HUVEC), with compound 21 showing the most potent inhibition of cell migration. Overall, this study establishes the sulfonate linkage as a particularly favorable scaffold modification and a metabolically stable ester bioisostere that enhances stability without compromising APJ antagonism. These analogs represent promising candidate for further in-vivo optimization and advancement as next-generation APJ antagonists for Cancer therapy.

APJ antagonist; Apelin receptor (APJ); ML221 analogs; Plasma and liver microsomal stability; Structure-activity relationship (SAR); Sulfonate linkage; β-arrestin inhibition.