Pharmacology of the single isomer, esuberaprost (beraprost-314d) on pulmonary vascular tone, IP receptors and human smooth muscle proliferation in pulmonary hypertension

Abstract

Background and purpose: Beraprost is a prostacyclin analogue and IP receptor agonist which is approved to treat pulmonary arterial hypertension (PAH) in Asia. The beraprost-314d isomer (esuberaprost) is one of four stereoisomers contained within the racemic mixture of beraprost. The pharmacological profile of esuberaprost is now evaluated to determine how stereoisomer separation affects its potency and mode of action in functional assays.

Experimental approach: Vascular tone was assessed using wire myography in rat and human distal pulmonary arteries (PAs) pre-contracted with U46619 (100 nM). HEK-293 cells stably expressing the human IP receptor (HEK-293-IP) and pulmonary arterial smooth muscle cells (PASMCs) derived from PAH patients were used to assess cyclic AMP (cAMP) generation and cell proliferation, respectively.

Key results: Esuberaprost relaxed rat PAs with a 5-fold greater potency compared with beraprost, and effects were strongly inhibited by RO3244794 (IP receptor antagonist) or L-NAME (NO synthase inhibitor). Esuberaprost caused EP₃ receptor-dependent vasoconstriction at high concentrations ≥ 1000 nM, but contractions were 50% lower compared to beraprost. In HEK-293-IP cells, esuberaprost was 26-fold more potent (EC₅₀ 0.4 nM) at increasing cAMP than beraprost. In human PASMCs, esuberaprost was 40-fold more potent than beraprost at inhibiting cell proliferation (EC₅₀ 3 nM versus 120 nM), contrasting the 5-fold potency difference for cAMP elevation. Antiproliferative effects of esuberaprost appeared more dependent on NO than on the IP receptor. In PAs from patients with pulmonary hypertension, esuberaprost, caused some relaxation whereas beraprost instead produced a weak contraction.

Conclusions and implications: Stereoisomer separation of beraprost has a significant effect on the pharmacology of the individual isomer, esuberaprost, identified in vitro as a highly potent prostanoid IP receptor agonist.

Keywords: Beraprost optical isomers; Cyclic AMP; Prostanoid IP and EP(3) receptors; Pulmonary hypertension; Smooth muscle cell proliferation; Vascular tone.