Synthesis and in vitro evaluation of polyethylene glycol-treprostinil conjugates for sustained local delivery in pulmonary arterial hypertension

Treprostinil (TRE) is a prostacyclin analogue approved for the treatment of pulmonary arterial hypertension (PAH). Despite its effectiveness, TRE has a short half-life, necessitating frequent or continuous administration to maintain therapeutic levels while minimizing adverse effects. To improve pharmacokinetics and pulmonary targeting of TRE, we designed a series of polyethylene glycol (PEG) ester conjugates for inhalation. The increase in molecular size achieved through polymer conjugation prevents the passive diffusion of TRE across the alveolar-capillary barrier, a common drawback of small, lipophilic drugs delivered to the lungs. The ester bond between TRE and PEG enables a gradual release of the active compound within the alveolar space. TRE was chemically modified with seven different alkyne-bearing linkers and subsequently conjugated to PEG-azide 6 kDa via click chemistry. These linkers were strategically designed to modulate the chemical environment around the cleavable ester bond, allowing for the systematic evaluation of the steric and electronic effects on the stability of the PEG-TRE conjugates. Drug release studies in bronchoalveolar lavage from healthy rats demonstrated that sterically hindered and electronically stabilized linkers significantly slowed the release of TRE. Moreover, conjugate stability was dependent on the enzymes availability, with a higher conjugate-enzyme ratio leading to slower release, suggesting enzyme saturation as a potential mechanism for controlled drug release. Overall, these findings demonstrate a tunable strategy for releasing drugs from polymer-drug conjugates in biological media.