CS585, a novel prostacyclin receptor agonist, demonstrates sustained efficacy in vivo in the prevention of thrombosis
Authors: Stanger L , Rickenberg A , Flores M , Dahlof B , Holinstat M 
Published: October 2024

Abstract

Background
Uncontrolled platelet activity resulting from cardiovascular disease can lead to occlusive thrombi, culminating in myocardial infarction or stroke. Despite major advances in anti-platelet therapeutics, many patients remain at risk. Although prostacyclin (IP) receptor agonists are currently used for the treatment of pulmonary arterial hypertension (PAH), activation of the IP receptor has been shown to decrease platelet reactivity. However, engaging the IP receptor as a therapeutic target was previously considered unviable due to the lack of a sustained effect of current IP agonists in the blood. The development of an IP agonist with sustained effects in the blood would represent a novel prevention strategy in targeting platelet hyperreactivity and thrombosis.

Purpose
Assess the stability profile of CS585, an IV and orally bioavailable IP agonist, compared to FDA-approved IP agonists iloprost and selexipag, with regards to sustained activity in vivo in the blood in limiting platelet activation and thrombosis.

Methods
Using ex vivo and in vivo mouse models, we assessed the timeframe of effect of CS585, iloprost and selexipag in blood. Blood was drawn from wild-type mice 24 hours following a single IV dose of CS585, iloprost or selexipag. Platelet adhesion and blood clotting were measured using perfusion flow chamber at arterial shear and total thrombus activation system (T-TAS), respectively. In vivo, platelets and fibrin were labelled 24 hours post IV or oral administration of CS585, iloprost or selexipag, and accumulation at the site of injury was measured using the cremaster arteriole injury thrombosis assay.

Results
Blood drawn from mice administered CS585 was observed to show a decrease in platelet adhesion and clot formation in the perfusion flow chamber and T-TAS assays. The effects of iloprost and selexipag are no longer observed at 24 hours post-administration. Administration of CS585 resulted in sustained inhibition of platelet accumulation and fibrin formation in the laser-induced cremaster arteriole thrombosis assay up to 18 hours post-administration. In mice administered iloprost, a decrease in thrombus formation was observed 10 minutes post-administration, but thrombus size returned to vehicle levels by 4 hours. Selexipag-dosed mice demonstrated inhibition of thrombus formation up to 4 hours, but effects were no longer observed at 18 hours.

Conclusions
CS585, a novel IP agonist, inhibits platelet activation and clot formation up to 24 hours post-administration. In both in vivo and ex vivo models, we demonstrate the sustained effects of CS585. In contrast, current FDA-approved IP agonists do not possess an effect profile sufficient to target the IP receptor in blood. By overcoming the sustainability challenge facing IP agonists, CS585 represents a novel approach to anti-platelet treatment of thrombotic diseases, which could include thrombosis, VTE, secondary prevention after MI and stroke, and PAH.