Recent advances in prodrug-based nanoparticle therapeutics.

Extensive research into prodrug modification of active pharmaceutical ingredients and nanoparticle drug delivery systems has led to unprecedented levels of control over the pharmacological properties of drugs and resulted in the approval of many prodrug or nanoparticle-based therapies. In recent years, the combination of these two strategies into prodrug-based nanoparticle drug delivery systems (PNDDS) has been explored as a way to further advance nanomedicine and identify novel therapies for difficult-to-treat indications. Many of the PNDDS currently in the clinical development pipeline are expected to enter the market in the coming years, making the rapidly evolving field of PNDDS highly relevant to pharmaceutical scientists. This review paper is intended to introduce PNDDS to the novice reader while also updating those working in the field with a comprehensive summary of recent efforts. To that end, first, an overview of FDA-approved prodrugs is provided to familiarize the reader with their advantages over traditional small molecule drugs and to describe the chemistries that can be used to create them. Because this article is part of a themed issue on nanoparticles, only a brief introduction to nanoparticle-based drug delivery systems is provided summarizing their successful application and unfulfilled opportunities. Finally, the review's centerpiece is a detailed discussion of rationally designed PNDDS formulations in development that successfully leverage the strengths of prodrug and nanoparticle approaches to yield highly effective therapeutic options for the treatment of many diseases.

Development and Preclinical Evaluation of New Inhaled Lipoglycopeptides for the Treatment of Persistent Pulmonary Methicillin-Resistant Staphylococcus aureus Infections.

Chronic pulmonary methicillin-resistant Staphylococcus aureus (MRSA) disease in cystic fibrosis (CF) has a high probability of recurrence following treatment with standard-of-care antibiotics and represents an area of unmet need associated with reduced life expectancy. We developed a lipoglycopeptide therapy customized for pulmonary delivery that not only demonstrates potent activity against planktonic MRSA, but also against protected colonies of MRSA in biofilms and within cells, the latter of which have been linked to clinical antibiotic failure. A library of next-generation potent lipoglycopeptides was synthesized with an emphasis on attaining superior pharmacokinetics (PK) and pharmacodynamics to similar compounds of their class. Our strategy focused on hydrophobic modification of vancomycin, where ester and amide functionality were included with carbonyl configuration and alkyl length as key variables. Candidates representative of each carbonyl attachment chemistry demonstrated potent activity in vitro, with several compounds being 30 to 60 times more potent than vancomycin. Selected compounds were advanced into in vivo nose-only inhalation PK evaluations in rats, where RV94, a potent lipoglycopeptide that utilizes an inverted amide linker to attach a 10-carbon chain to vancomycin, demonstrated the most favorable lung residence time after inhalation. Further in vitro evaluation of RV94 showed superior activity to vancomycin against an expanded panel of Gram-positive organisms, cellular accumulation and efficacy against intracellular MRSA, and MRSA biofilm killing. Moreover, in vivo efficacy of inhaled nebulized RV94 in a 48 h acute model of pulmonary MRSA (USA300) infection in neutropenic rats demonstrated statistically significant antibacterial activity that was superior to inhaled vancomycin.

Modulation of the Cellular Uptake of DNA Origami through Control over Mass and Shape.

Designer nanoparticles with controlled shapes and sizes are increasingly popular vehicles for therapeutic delivery due to their enhanced cell-delivery performance. However, our ability to fashion nanoparticles has offered only limited control over these parameters. Structural DNA nanotechnology has an unparalleled ability to self-assemble three-dimensional nanostructures with near-atomic resolution features, and thus, it offers an attractive platform for the systematic exploration of the parameter space relevant to nanoparticle uptake by living cells. In this study, we examined the cell uptake of a panel of 11 distinct DNA-origami shapes, with the largest dimension ranging from 50-400 nm, in 3 different cell lines. We found that larger particles with a greater compactness were preferentially internalized compared with elongated, high-aspect-ratio particles. Uptake kinetics were also found to be more cell-type-dependent than shape-dependent, with specialized endocytosing dendritic cells failing to saturate over 12 h of study. The knowledge gained in the current study furthers our understanding of how particle shape affects cellular uptake and heralds the development of DNA nanotechnologies toward the improvement of current state-of-the-art cell-delivery vehicles.

Inhaled Treprostinil-Prodrug Lipid Nanoparticle Formulations Provide Long-Acting Pulmonary Vasodilation.

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 Cmax 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 Cmax-associated adverse events which could provide patients with an improved treprostinil therapy.

Inhaled hexadecyl-treprostinil provides pulmonary vasodilator activity at significantly lower plasma concentrations than infused treprostinil.

INS1009 is a long acting pulmonary vasodilator prodrug of treprostinil (TRE) that is formulated in a lipid nanoparticle for inhaled delivery by nebulization. This study examined the ability of INS1009 to inhibit vasoconstriction in the pulmonary vasculature of rats and dogs and the extent to which local activity within the lung contributes to its activity. Rats received a single dose of INS1009 by nose-only inhalation or were given a continuous intravenous (i.v.) infusion of TRE, followed by an i.v. challenge of the thromboxane mimetic pulmonary vasoconstrictor U46619 and the increase in pulmonary arterial pressure (PAP) was measured. In beagle dogs, INS1009 was given by inhalation via face mask and TRE was given by continuous i.v. infusion; vasoconstriction was then induced by inhaled hypoxia with reduction of FIO2 to 0.10. Changes in the dog's right ventricular pulse pressure (RVPP) were measured using implanted telemetry probes. Blood samples were collected in rats and dogs immediately after the challenge to measure the plasma TRE concentration. Exposure of rats to inhaled INS1009 (0.5, 3.0 and 20.9 µg/kg) inhibited the U46619-induced increase in PAP at all doses up to 6 h with statistically significant inhibition up to 24 h with the pooled dose-response data. The concentration of TRE in the plasma at which PAP was reduced by 50% was approximately 60-fold lower for INS1009 (EC50 = 0.08 ng/mL) as compared to i.v. TRE (EC50 = 4.9 ng/mL). In dogs, INS1009 (2.7-80.9 µg/kg) inhibited the hypoxia-induced increase in RVPP at all doses up to 6 h with activity once again observed with the pooled dose-response of 10 µg/kg and higher at 24 h. The concentration of TRE in the plasma at which RVPP was reduced by 50% was approximately 550-fold lower for INS1009 (EC50 = 0.0075 ng/mL) as compared to i.v. TRE (EC50 = 4.1 ng/mL). These studies, in two species and by two different pulmonary vasoconstrictor challenges, demonstrate that inhaled INS1009 not only has long-acting vasodilatory effects but also that the local activity within the lung contributes to this response. Therefore, INS1009 may offer the opportunity to effect pulmonary vasodilation for long periods but with substantially lower systemic exposure than infused TRE.

Preclinical Pharmacology and Pharmacokinetics of Inhaled Hexadecyl-Treprostinil (C16TR), a Pulmonary Vasodilator Prodrug.

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 µM) in receptor binding and enzyme inhibition assays, including binding to prostaglandin E2 receptor 2, prostaglandin D2 receptor 1, prostaglandin I2 receptor, and prostaglandin E2 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 µg/kg), sustained pulmonary vasodilation over 3 hours; inhaled TRE (6 µg/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 Cmax 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 Cmax 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 µg/ml) consistently produced cough, but C16TR-LNP (30 µg/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.