Bosentan is a competitive and dual antagonist of endothelin-1 (ET) for the ETA and ETB receptors with Ki of 4.7 nM and 95 nM in human SMC, respectively.
Bosentan (BOS) competitively and specifically antagonizes binding of 125I-labelled ET-1 to ETA receptors on human smooth muscle cells (SMC) and ETB receptors on human placenta cells. The in vitro binding affinity of Bosentan to ETA receptors on human SMC is 4.7 nM and to ETB receptors on human SMC or placenta cells is 41 or 95 nM. Bosentan has 67-fold greater selectivity for ETA than ETB receptors (mean IC50=7.1 vs 474.8 nM) in an in vitro 125I-labeling assay[1].
Single-dose Bosentan 62.5 mg significantly (p<0.01 vs baseline) plasma ET-1 levels by 2-fold in 7 pts with WHO class II or III idiopathic or CTD-associated PAH, with peak levels achieved at 8 h[1]. In hypertensive rats, Macitentan 30 mg/kg further decreases mean arterial blood pressure (MAP) by 19 mm Hg when given on top of Bosentan 100 mg/kg. Conversely, Bosentan given on top of Macitentan fails to induce an additional MAP decrease. In pulmonary hypertensive rats, Macitentan 30 mg/kg further decreases mean pulmonary artery pressure (MPAP) by 4 mm Hg on top of Bosentan, whereas a maximal effective dose of Bosentan given on top of Macitentan does not cause any additional MPAP decrease[3].
References:
[1]. Dhillon S, et al. Bosentan: a review of its use in the management of mildly symptomatic pulmonary arterial hypertension. Am J Cardiovasc Drugs. 2009;9(5):331-50.
[2]. Akamata K, et al. Bosentan reverses the pro-fibrotic phenotype of systemic sclerosis dermal fibroblasts via increasing DNA binding ability of transcription factor Fli1. Arthritis Res Ther. 2014 Apr 3;16(2):R86.
[3]. Iglarz M, et al. Comparison of pharmacological activity of macitentan and bosentan in preclinical models of systemic and pulmonary hypertension. Life Sci. 2014 Nov 24;118(2):333-9.
[4]. Son GY, et al. Endothelin Regulates Porphyromonas gingivalis-Induced Production of Inflammatory Cytokines. PLoS One. 2016 Dec 28;11(12):e0167713.