Treprostinil (TRE), a prostanoid analogue approved in the USA for the treatment of pulmonary arterial hypertension, requires continuous infusion or multiple dosing sessions per day for inhaled and oral routes of administration due to its short half-life. The inhaled drug is known to induce adverse systemic and local effects including headache, nausea, cough, and throat irritation which may be due at least in part to transiently high drug concentrations in the lungs and plasma immediately following administration [1]. To ameliorate these side effects and reduce dosing frequency we designed an inhaled slow-release TRE formulation. TRE was chemically modified to be an alkyl prodrug (TPD) which was then packaged into a lipid nanoparticle (LNP) carrier. Preclinical screening in a rat model of hypoxia-induced pulmonary vasoconstriction led to selection of a 16-carbon alkyl ester derivative of TRE. The TPD-LNP demonstrated approximately 10-fold lower TRE plasma C compared to inhaled TRE solution while maintaining an extended vasodilatory effect. The favorable PK profile is attributed to gradual dissociation of TPD from the LNP and subsequent conversion to TRE. Together, this sustained presentation of TRE to the lungs and plasma is consistent with a once- or twice-daily dosing schedule in the absence of high C-associated adverse events which could provide patients with an improved treprostinil therapy.

This article describes the preclinical pharmacology and pharmacokinetics (PK) of hexadecyl-treprostinil (C16TR), a prodrug of treprostinil (TRE), formulated in a lipid nanoparticle (LNP) for inhalation as a pulmonary vasodilator. C16TR showed no activity (>10 M) in receptor binding and enzyme inhibition assays, including binding to prostaglandin E receptor 2, prostaglandin D receptor 1, prostaglandin I receptor, and prostaglandin E receptor 4; TRE potently bound to each of these prostanoid receptors. C16TR had no effect (up to 200 nM) on platelet aggregation induced by ADP in rat blood. In hypoxia-challenged rats, inhaled C16TR-LNP produced dose-dependent (0.06-6 g/kg), sustained pulmonary vasodilation over 3 hours; inhaled TRE (6g/kg) was active at earlier times but lost its effect by 3 hours. Single- and multiple-dose PK studies of inhaled C16TR-LNP in rats showed proportionate dose-dependent increases in TRE and area under the curve (AUC) for both plasma and lung; similar results were observed for dog plasma levels in single-dose PK studies. In both species, inhaled C16TR-LNP yielded prolonged plasma TRE levels and a lower plasma TRE compared with inhaled TRE. Inhaled C16TR-LNP was well tolerated in rats and dogs; TRE-related side effects included cough, respiratory tract irritation, and emesis and were seen only after high inhaled doses of C16TR-LNP in dogs. In guinea pigs, inhaled TRE (30 g/ml) consistently produced cough, but C16TR-LNP (30g/ml) elicited no effect. These results demonstrate that C16TR-LNP provides long-acting pulmonary vasodilation, is well tolerated in animal studies, and may necessitate less frequent dosing than inhaled TRE with possibly fewer side effects.