Assessment of Inhaled Treprostinil Palmitil, Inhaled and Intravenous Treprostinil, and Oral Selexipag in a Sugen/Hypoxia Rat Model of Pulmonary Arterial Hypertension.

Treprostinil palmitil (TP), a long-acting inhaled pulmonary vasodilator prodrug of treprostinil (TRE), has beneficial effects in a Sugen5416/hypoxia (Su/Hx) rat model of pulmonary arterial hypertension (PAH) that compare favorably to the oral phosphodiesterase 5 inhibitor (PDE5) sildenafil. In this study in male Sprague-Dawley rats, a dry powder formulation of TP (TPIP) was compared with inhaled and intravenous TRE and oral selexipag to evaluate inhibition of hemodynamic and pathologic changes in the lungs and heart induced by Su/Hx challenge. Su (20 mg/kg) was injected subcutaneously followed by 3 weeks of Hx (10% O2/balance N2) and then initiation of test article administration over 5 weeks with room air breathing. Hemodynamics and histopathology were measured at the end of the study. Su/Hx challenge approximately doubled the mean pulmonary arterial blood pressure (mPAP) and the Fulton index, decreased cardiac output (CO), doubled the wall thickness and muscularization of the small (10-50 µm) and medium (51-100 µm) sized pulmonary arteries, and increased the percentage of obliterated pulmonary blood vessels. Even though inhaled TRE (65 µg/kg, 4× daily), intravenous TRE (810 ng/kg/min), and oral selexipag (30 mg/kg, twice daily) provided some beneficial effects against the Su/Hx challenge, the overall benefit was generally greater with TPIP at high dose (117 µg/kg, once daily). These results demonstrate that TPIP compares favorably to inhaled and intravenous TRE and oral selexipag with respect to inhibition of the pathophysiological changes induced by Su/Hx challenge in rats. SIGNIFICANCE STATEMENT: Treprostinil palmitil (TP) is a long-acting pulmonary vasodilator prodrug of treprostinil (TRE) formulated for inhaled administration by dry powder [treprostinil palmitil inhalation powder (TPIP)]. Comparison of the activity of TPIP, inhaled and intravenous TRE, and oral selexipag in a Sugen5416/hypoxia (Su/Hx) rat model of pulmonary arterial hypertension demonstrated that each of these drugs exert protection against the hemodynamic and histopathological changes induced by the Su/Hx challenge, with the greatest effect on these changes produced by TPIP.

Strategies to Overcome Biological Barriers Associated with Pulmonary Drug Delivery.

While the inhalation route has been used for millennia for pharmacologic effect, the biological barriers to treating lung disease created real challenges for the pharmaceutical industry until sophisticated device and formulation technologies emerged over the past fifty years. There are now several inhaled device technologies that enable delivery of therapeutics at high efficiency to the lung and avoid excessive deposition in the oropharyngeal region. Chemistry and formulation technologies have also emerged to prolong retention of drug at the active site by overcoming degradation and clearance mechanisms, or by reducing the rate of systemic absorption. These technologies have also been utilized to improve tolerability or to facilitate uptake within cells when there are intracellular targets. This paper describes the biological barriers and provides recent examples utilizing formulation technologies or drug chemistry modifications to overcome those barriers.

Treprostinil palmitil inhibits the hemodynamic and histopathological changes in the pulmonary vasculature and heart in an animal model of pulmonary arterial hypertension.

Treprostinil palmitil (TP) is a long-acting inhaled pulmonary vasodilator prodrug of treprostinil (TRE). In this study, TP was delivered by inhalation (treprostinil palmitil inhalation suspension, TPIS) in a rat Sugen 5416 (Su)/hypoxia (Hx) model of pulmonary arterial hypertension (PAH) to evaluate its effects on hemodynamics, pulmonary vascular remodeling, and cardiac performance and histopathology. Male Sprague-Dawley rats received Su (20 mg/kg, s.c), three weeks of Hx (10% O2) and 5 or 10 weeks of normoxia (Nx). TPIS was given during the 5-10 week Nx period after the Su/Hx challenge. Su/Hx increased the mean pulmonary arterial blood pressure (mPAP) and right heart size (Fulton index), reduced cardiac output (CO), stroke volume (SV) and heart rate (HR), and increased the thickness and muscularization of the pulmonary arteries along with obliteration of small pulmonary vessels. In both the 8- and 13-week experiments, TPIS at inhaled doses ranging from 39.6 to 134.1 µg/kg, QD, dose-dependently improved pulmonary vascular hemodynamics, reduced the increase in right heart size, enhanced cardiac performance, and attenuated most of the histological changes induced by the Su/Hx challenge. The PDE5 inhibitor sildenafil, administered at an oral dose of 50 mg/kg, BID for 10 weeks, was not as effective as TPIS. These results in Su/Hx challenged rats demonstrate that inhaled TPIS may have superior effects to oral sildenafil. We speculate that the improvement of the pathobiology in this PAH model induced by TPIS involves effects on pulmonary vascular remodeling due to the local effects of TRE in the lungs.

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.

Characterisation of cough evoked by inhaled treprostinil and treprostinil palmitil.

Cough is induced by inhaled prostacyclin analogues including treprostinil (TRE), and, at higher doses, treprostinil palmitil (TP), a prodrug of TRE. In this report, we have investigated mechanisms involved in TRE- and TP-induced cough, using a dry powder formulation of TP (TPIP) to supplement previous data obtained with an aqueous suspension formulation of TP (TPIS). Experiments in guinea pigs and rats investigated the prostanoid receptor subtype producing cough and whether it involved activation of sensory nerves in the airways and vasculature. Experiments involved treatment with prostanoid, tachykinin and bradykinin receptor antagonists, a cyclooxygenase inhibitor and TRE administration to the isolated larynx or intravenously. In guinea pigs, cough with inhaled TRE (1.23 µg·kg-1) was not observed with an equivalent dose of TPIP and required higher inhaled doses (12.8 and 35.8 µg·kg-1) to induce cough. TRE cough was blocked with IP and tachykinin NK1 receptor antagonists but not with EP1, EP2, EP3, DP1 or bradykinin B2 antagonists or a cyclooxygenase inhibitor. TRE administered to the isolated larynx or intravenously in rats produced no apnoea or swallowing, whereas citric acid, capsaicin and hypertonic saline had significant effects. The mechanisms inducing cough with inhaled TRE likely involves the activation of prostanoid IP receptors on jugular C-fibres in the tracheobronchial airways. Cough induced by inhaled dry powder and nebulised formulations of TP occurs at higher inhaled doses than TRE, presumably due to the slow, sustained release of TRE from the prodrug resulting in lower concentrations of TRE at the airway sensory nerves.

Development and Characterization of Treprostinil Palmitil Inhalation Aerosol for the Investigational Treatment of Pulmonary Arterial Hypertension.

Treprostinil palmitil (TP) is a prodrug of treprostinil (TRE), a pulmonary vasodilator that has been previously formulated for inhaled administration via a nebulizer. TP demonstrates a sustained presence in the lungs with reduced systemic exposure and prolonged inhibition of hypoxia-induced pulmonary vasoconstriction in vivo. Here, we report on re-formulation efforts to develop a more convenient solution-based metered-dose inhaler (MDI) formulation of TP, a treprostinil palmitil inhalation aerosol (TPIA) that matches the pharmacokinetic (PK) and efficacy profile of a nebulized TP formulation, treprostinil palmitil inhalation suspension (TPIS). MDI canisters were manufactured using a two-stage filling method. Aerosol performance, formulation solubility, and chemical stability assays were utilized for in vitro evaluation. For in vivo studies, TPIA formulations were delivered to rodents using an inhalation tower modified for MDI delivery. Using an iterative process involving evaluation of formulation performance in vitro (TP and excipient solubility, chemical stability, physical stability, and aerosol properties) and confirmatory testing in vivo (rat PK and efficacy, guinea pig cough), a promising formulation was identified. The optimized formulation, TPIA-W, demonstrates uniform in vitro drug delivery, a PK profile suitable for a once-daily administration, efficacy lasting at least 12 h in a hypoxic challenge model, and a significantly higher cough threshold than the parent drug treprostinil.

Treprostinil palmitil, an inhaled long-acting pulmonary vasodilator, does not show tachyphylaxis with daily dosing in rats.

BACKGROUND: Treprostinil palmitil (TP) is an inhaled long-acting pulmonary vasodilator prodrug of treprostinil (TRE) that has been formulated for delivery as a suspension (treprostinil palmitil inhalation suspension; TPIS) and as a dry powder (treprostinil palmitil inhalation powder; TPIP). In humans, tachyphylaxis is frequently observed with continuous intravenous (IV) or subcutaneous (SC) infusion of TRE and requires dosage escalation to maintain activity. The aim of the present study was to determine whether tachyphylaxis occurs with repeat daily administration of inhaled TPIS. METHODS: Experiments were performed in male Sprague-Dawley rats prepared with a telemetry probe implanted into the right ventricle to measure the change in right ventricular pulse pressure (ΔRVPP) induced by exposure to a 10% oxygen gas mixture. TPIS (6 mL) at concentrations of 0.25, 0.5, and 1 mM was given by nose-only inhalation using an Aeroneb Pro nebulizer, either as a single administration or daily for 16 or 32 consecutive days. In studies involving consecutive daily administrations of TPIS, the delivered TP dosage was 140.3 µg/kg at 1 mM and ranged from 40.2 to 72.2 µg/kg at 0.5 mM. A separate cohort of telemetered rats received continuous IV infusion of TRE via an Alzet mini-pump at a dosage rate of 250 ng/kg/min for 16 days. Blood and lung tissue samples were obtained, and the concentration of TRE in the plasma and TRE and TP in the lungs were measured approximately 1 h after TPIS administration. RESULTS: Dose-response studies with TPIS administered as a single administration inhibited the hypoxia-induced increase in RVPP in both a concentration-dependent (0.25, 0.5, and 1 mM) and time-dependent (1-24 h) manner. TPIS, given QD or BID at inhaled doses ranging from 40.2 to 140.3 µg/kg for 16 or 32 consecutive days, produced statistically significant (P < .05) inhibition of the increase of RVPP due to hypoxia over the full duration of the dosing periods. By contrast, the inhibition of the hypoxia-induced increase in RVPP observed with IV TRE infusion (250 ng/kg/min) disappeared after 16 days of infusion. The plasma concentrations of TRE were significantly higher after IV TRE (range, 2.85-13.35 ng/mL) compared to inhaled TPIS (range, 0.22-0.73 ng/mL) CONCLUSIONS: There was no evidence of tachyphylaxis with repeat daily dosing of TPIS for a period of up to 32 days. The absence of tachyphylaxis with TPIS is likely related to its local vasodilatory effects within the lungs, combined with an absence of sustained high plasma concentrations of TRE.

Prostanoid receptor subtypes involved in treprostinil-mediated vasodilation of rat pulmonary arteries and in treprostinil-mediated inhibition of collagen gene expression of human lung fibroblasts.

Treprostinil (TRE) is a potent pulmonary vasodilator with effects on other pathological aspects of pulmonary arterial hypertension. In this study, the prostanoid receptors involved in TRE-induced relaxation of isolated rat pulmonary arteries and TRE-induced inhibition of increased gene expression in collagen synthesis and contractility of human lung fibroblasts were determined. TRE (0.01-100 µM) relaxed prostaglandin F2α-precontracted rat pulmonary arteries which was attenuated by denudation of the vascular endothelium. TRE-induced relaxation was predominantly blocked by the IP receptor antagonist RO3244194 (1 µM), with slightly greater inhibition in endothelium-denuded tissue. At higher TRE concentrations (> 1 µM), the DP1 receptor antagonist BW A868C (1 µM) also inhibited relaxation reaching significance above 10 µM. In contrast, the EP3 receptor antagonist L798106 (1 µM) accentuated TRE-induced relaxation of pulmonary arteries with intact endothelium. In human lung fibroblasts, the EP2 receptor antagonist PF-04418948 (1 µM) blocked transforming growth factor ß1 (TGF-ß1)-increased expression of collagen synthesis (COL1A1 and COL1A2) and fibroblast contractility (ACTG2) genes in presence of TRE (0.1 µM). In conclusion, the IP receptor located on rat pulmonary vascular smooth muscle and endothelium is the primary receptor mediating vasorelaxation, while the DP1 receptor present on the rat endothelium is involved only at higher TRE concentrations. In human lung fibroblasts, the EP2 receptor is the dominant receptor subtype involved in suppression of increased collagen synthesis and fibroblast contractility gene expression induced by TGF-ß1 in the presence of TRE.

An overview of the biology of a long-acting inhaled treprostinil prodrug.

Treprostinil (TRE) is a prostanoid analog pulmonary vasodilator drug marketed with subcutaneous, intravenous (i.v.), oral, and inhaled routes of administration for the treatment of pulmonary arterial hypertension (PAH). Due to its short half-life, TRE requires either continuous infusion or multiple dosing, which exacerbates its side effects. Therefore, a long-acting prostanoid analog that maintains the positive attributes of TRE but has fewer TRE-related side effects could be of clinical benefit. In this report, we describe the discovery, preclinical development, and biology of the TRE ester prodrug, treprostinil palmitil (TP), which is formulated in a lipid nanoparticle (LNP) for administration as a nebulized inhaled suspension (TPIS). In screening assays focused on the conversion of prodrug to TRE, TP (16 carbon alkyl chain) had the slowest rate of conversion compared with short-alkyl chain TRE prodrugs (i.e., 2-8 carbon alkyl chain). Furthermore, TP is a pure prodrug and possesses no inherent binding to G-protein coupled receptors including prostanoid receptors. Pharmacokinetic studies in rats and dogs demonstrated that TPIS maintained relatively high concentrations of TP in the lungs yet had a low maximum plasma concentrations (Cmax) of both TP and, more importantly, the active product, TRE. Efficacy studies in rats and dogs demonstrated inhibition of pulmonary vasoconstriction induced by exposure to hypoxic air or i.v.-infused U46619 (thromboxane mimetic) over 24 h with TPIS. Cough was not observed with TPIS at an equivalent dose at which TRE caused cough in guinea pigs and dogs, and there was no evidence of desensitization to the inhibition of pulmonary vasoconstriction in rats with repeat inhaled dosing. TPIS was also more efficacious than i.v.-infused TRE in a sugen/hypoxia rat model of PAH to inhibit pulmonary vascular remodeling, an effect likely driven by local activities of TRE within the lungs. TPIS also demonstrated antifibrotic and anti-inflammatory activity in the lungs in rodent models of pulmonary fibrosis and asthma. In a phase 1 study in healthy human participants, TPIS (referred to as INS1009) had a lower plasma TRE Cmax and fewer respiratory-related side effects at equimolar doses compared with inhaled TRE. We have now formulated TP as an aerosol powder for delivery by a dry powder inhaler (referred to as treprostinil palmitil inhalation powder-TPIP), and as an aerosol solution in a fluorohydrocarbon solvent for delivery by a metered dose inhaler. These options may reduce drug administration time and involve less device maintenance compared with delivery by nebulization.

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.

Therapeutic administration of inhaled INS1009, a treprostinil prodrug formulation, inhibits bleomycin-induced pulmonary fibrosis in rats.

Idiopathic pulmonary fibrosis is a progressive and lethal disease and while there are now two approved drugs (Esbriet® and Ofev®) additional effective treatments are still needed. Recently, prostacyclin analogs such as iloprost and treprostinil (TRE) have been shown to exert some protection against bleomycin-induced pulmonary fibrosis in mice when administered in a prophylactic regimen. In this study, we evaluated the effect of the inhaled treprostinil prodrug hexadecyl-treprostinil (C16TR) formulated in a lipid nanoparticle (INS1009) administered therapeutically in a fibrotic rat model. Male Fischer 344 rats challenged with intra-tracheal saline instillation were then treated with daily inhaled phosphate buffered saline (PBS) while rats challenged with bleomycin sulfate (3.5-4.0 mg/kg) instillation were treated with either daily inhaled PBS, daily inhaled INS1009 (10, 30, or 100 µg/kg), or twice-daily orally with the anti-fibrotic compound pirfenidone (100 mg/kg). Dosing started on day 10 post-bleomycin challenge and continued until day 27 after bleomycin. Lungs were harvested 24 h after the last dose of treatment for evaluation of lung hydroxyproline content and pulmonary histology. Lung hydroxyproline content increased from 421 µg/lung lobe in saline challenged and PBS treated animals to 673 µg/lung lobe in bleomycin challenged and PBS treated rats. Treatment of bleomycin challenged rats with 10, 30, or 100 µg/kg INS1009 dose-dependently reduced lung hydroxyproline content to 563, 501, and 451 µg/lung lobe, respectively, and pirfenidone decreased hydroxyproline content to 522 µg/lung lobe. Histologically, both INS1009 (100 µg/kg) and pirfenidone (100 mg/kg) reduced the severity of subepithelial fibrosis. Single dose pharmacokinetic (PK) studies of inhaled INS1009 in bleomycin challenged rats showed dose-dependent increases in lung C16TR concentration and plasma TRE on day 10 post-bleomycin challenge. Multiple dose PK studies of inhaled INS1009 showed dose-dependent increases only in lung C16TR concentration on day 27 post-bleomycin challenge. We also investigated the effects of TRE on the cytokine transforming growth factor-ß1 (TGF-ß1)-stimulated collagen gene and protein expressions in cultured human lung fibroblasts, assessed by real-time PCR and Sirius Red staining, respectively. In human fibroblasts, TRE (0.001-10 µM) inhibited TGF-ß1 (20 ng/mL)-induced expression of collagen mRNA and protein in a concentration-dependent manner. These results demonstrated that inhaled INS1009, administered in a therapeutic dosing paradigm, dose-dependently (10-100 µg/kg) inhibited bleomycin-induced pulmonary fibrosis in rats. This effect may involve direct actions of TRE in suppressing collagen expression in lung fibroblasts.

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.

Role of α2-adrenoceptors in electrical field stimulation-induced contraction of pig nasal mucosa and pharmacologic characterization of a novel α2C-adrenoceptor agonist.

BACKGROUND: Blood vessels of the nasal mucosa are richly innervated by sympathetic nerves and neural mechanism is of great interest in upper respiratory tract disorders. This study was designed to determine the role of α2-adrenoceptors and, more specifically, α2C-adrenoceptors, on neurogenic sympathetic vasoconstrictor responses in pig nasal mucosa, and to define the pharmacologic profile of a novel selective α2C-adrenoreceptor agonist. METHODS: Electrical field stimulation (EFS) was applied to nasal mucosa strips placed in an organ bath and attached to force displacement transducers for continuous recording of isometric tension. The affinity and functional activity of compound B for α2C-adrenoceptors were determined by binding analysis and the ability of compound B to stimulate [(35)S]GTPγS binding to the receptors. Compound B was also tested in a postjunctional α2C-adrenoreceptor bioassay. RESULTS: EFS-induced contractions were partly blocked by the α2-adrenoreceptor antagonist yohimbine (41.1%) and the α2C-adrenoreceptor antagonist JP-1302 had no effect. The α2-adrenoreceptor agonist clonidine, but not compound B, exerted a significant blockade (70.6%). Compound B had high affinity (K(i) = 18 nM), produced potent agonist (EC50 = 279 nM) and good efficacy (E(max) = 73%) responses at the α2C-adrenoceptors, and displayed good functional agonist potency in the human saphenous vein α2C-adrenoreceptor bioassay (pD2 = 6.2). CONCLUSION: (1) Neurogenic vasomotor contractility is largely regulated through an α-adrenergic mechanism; (2) pig nasal mucosa possesses post- and prejunctional α2-adrenoceptors; (3) the α2C-adrenoreceptor subtype does not seem to be involved; and (4) compound B is a novel, highly selective, and potent α2C-adrenoreceptor agonist.

Neuromodulation mediated by the tachykinin NK3-receptor agonist [MePhe7]-neurokinin B in the isolated perfused lung of nonsensitized nonchallenged and ovalbumin-sensitized and -challenged guinea pig.

The neuromodulatory action of the tachykinin NK(3)-receptor agonist [MePhe(7)]-neurokinin B ([MePhe(7)]-NKB) was evaluated on vagal stimulation-induced bronchoconstriction in nonsensitized nonchallenged and ovalbumin (OVA)-sensitized and -challenged guinea pig using the isolated perfused lung preparation. Lungs were placed inside a warmed (37°C) glass chamber and suspended from a force displacement transducer (Grass FT-03) with both vagi connected to a stimulating electrode. Isolated lungs were stimulated at a constant voltage (20 V) and pulse duration (5 ms) with electrical stimulation frequencies ranging from 1 to 128 Hz. The authors demonstrated that vagal stimulation produced frequency-dependent bronchoconstriction and [MePhe(7)]-NKB, at a dose (0.1 µM) that does not produce bronchoconstriction by itself, potentiated the vagally induced bronchoconstriction at all frequencies in nonsensitized nonchallenged animals and to a greater extent in OVA-sensitized and -challenged guinea pigs; the potentiations were totally inhibited by the tachykinin NK(3)-receptor antagonist SR 142801 (1 µM). In a second set of experiments, [MePhe(7)]-NKB produced bronchoconstriction in a dose-dependent (1 to 300 µg/mL) manner with similar potencies and maximum responses in nonsensitized nonchallenged (EC(50) = 8.6 ± 1.1 µM; E(Max) = 61.1 ± 3.5 mm Hg) and OVA-sensitized and -challenged (EC(50) = 8.5 ± 1.3 µM; E(Max) = 63.5 ± 3.7 mm Hg) animals. In conclusion, these results demonstrated that [MePhe(7)]-NKB potentiated vagal stimulation-induced bronchoconstriction via the tachykinin NK(3)-receptors and OVA sensitization caused development of airway hyperresponsiveness in these potentiations. However, OVA sensitization had no effect on airway responsiveness of vagal stimulation-and [MePhe(7)]-NKB-induced bronchoconstrictions.

Pharmacological characterization of a novel α2C-adrenoceptor agonist N-[3,4-dihydro-4-(1H-imidazol-4-ylmethyl)-2H-1, 4-benzoxazin-6-yl]-N-ethyl-N'-methylurea (compound A).

We define the pharmacological and pharmacokinetic profiles of a novel α(2C)-adrenoceptor agonist, compound A [N-[3,4-dihydro-4-(1H-imidazol-4-ylmethyl)-2H-1,4-benzoxazin-6-yl]-N-ethyl-N'-methylurea]. This compound has high affinity (K(i)) for the human α(2C)-adrenoceptor (K(i) = 12 nM), and 190- to 260-fold selectivity over the α(2A)- and α(2B)-adrenoceptor subtypes. In cell-based functional assays, compound A produced good agonist (EC(50) = 166 nM) and efficacy (E(max) = 64%) responses at the α(2C)-adrenoceptor, much lower potency and efficacy at the α(2A)-adrenoceptor (EC(50) = 1525 nM; E(max) = 8%) and α(2B)-adrenoceptor (EC(50) = 5814 nM; E(max) = 21%) subtypes, and low or no affinity and functional activity at the α(1A)-, α(1B)-, and α(1D)-adrenoceptor subtypes. In the human saphenous vein postjunctional α(2C)-adrenoceptor bioassay, compound A functions as a potent agonist (pD(2) = 6.3). In a real-time contraction bioassay of pig nasal mucosa, compound A preferentially constricted the veins (EC(50) = 108 nM), and the magnitude of arteriolar contraction reached only 50% of the maximum venular responses. Compound A exhibited no effect on locomotor activity, sedation, and body temperature in mice (up to 100 mg/kg) and did not cause hypertension and mydriasis (30 mg/kg) in conscious rats. Compound A is orally bioavailable (24%) with good plasma exposure. This compound is a substrate for the efflux P-glycoprotein transporter, resulting in very low central nervous system (CNS) penetration. In summary, compound A is a highly selective, orally active, and non-CNS-penetrating α(2C)-adrenoceptor agonist with desirable in vitro and in vivo pharmacological properties suitable for the treatment of nasal congestion.

Bronchoconstrictor effect of the tachykinin NK3-receptor agonists [MePhe7]-neurokinin B and senktide in the isolated guinea pig lung.

To determine whether bronchoconstriction can be mediated via the tachykinin NK3 receptors, isolated guinea pig lungs were challenged with the exogenous tachykinin NK3-receptor agonists [MePhe7]-neurokinin B ([MePhe7]-NKB) and senktide. [MePhe7]-NKB induced bronchoconstriction (EC50 = 11.8 ± 1.7 µM) that was significantly inhibited by the tachykinin NK3-receptor antagonist SB 223412 at 10 µM (EC50 = 24.4 ± 4.5 µM). Senktide also induced bronchoconstriction (EC50 = 96.2 ± 20.3 µM) and the bronchoconstriction was significantly reduced by SB 223412 at 1 and 10 µM (EC50 = 270.8 ± 78.9 µM and 388.3 ± 105.5 µM, respectively). Although the authors demonstrated that SB 223412, [MePhe7]-NKB, and senktide are potent and selective for the tachykinin NK3 receptors in binding and functional (Ca(2+) mobilization) assays, the tachykinin NK1-receptor antagonist CP 99,994 at 1 µM (EC50 = 32.7 ± 8.5 µM) produced inhibition of [MePhe7]-NKB-induced bronchoconstriction, whereas the tachykinin NK2-receptor antagonist SR 48968 at 0.1 µM (EC50 = 213.2 ± 42.9 µM) blocked senktide-induced bronchoconstriction. These data suggest that [MePhe7]-NKB and senktide caused bronchoconstriction in guinea pig through activation of the tachykinin NK3-receptors but the tachykinin NK1- and/or NK2-receptors are also involved in the response.

The synthesis and structure-activity relationship of 4-benzimidazolyl-piperidinylcarbonyl-piperidine analogs as histamine H3 antagonists.

A structure-activity relationship study of the lead piperazinylcarbonylpiperidine compound 3 resulted in the identification of 4-benzimidazolyl-piperidinylcarbonyl-piperidine 6h as a histamine-3 (H(3)) receptor antagonist. Additional optimization of 6h led to the identification of compounds 11i-k with K(i)

Alpha-2c-adrenergic receptors contribute to basal nasal patency in the anesthetized cat.

BACKGROUND: Nasal congestion is the most troublesome symptom associated with a variety of upper airway diseases, including allergic rhinitis and the common cold. A better understanding of the mechanisms that regulate nasal cavity caliber may engender the development of novel treatment strategies. It is well accepted that alpha-adrenergic (both alpha(1) and alpha(2)) mechanisms play a fundamental role in the control and maintenance of basal nasal patency. JP-1302 is a selective alpha(2c)-subtype antagonist that has been recently described in the scientific literature. Thus, we sought to examine the potential effects of this new pharmacological tool on basal nasal patency. METHODS: Using acoustic rhinometry, we studied the activity of the selective alpha(2c)-antagonist JP-1302 on nasal cavity volumes in an anesthetized cat. Cumulative concentrations of JP-1302 were applied directly into the right nasal cavity. Changes in the nasal cavity geometry of the drug-treated naris relative to the untreated left nasal cavity were determined. In separate studies, the nonselective alpha(2)-antagonist yohimbine and the nonselective alpha(1)-antagonist prazosin were run as comparators. Systolic blood pressure was measured at the hind leg, using an ultrasonic Doppler flow detector. RESULTS: JP-1302 (0.03, 0.1, 0.3 and 1.0%) administered by the intranasal route decreased nasal cavity volumes from baseline values by 17, 25, 40 and 40%, respectively. Yohimbine (0.03, 0.1, 0.3 and 1.0%) decreased volumes by 19, 36, 46 and 53%, and topical administration of the nonselective alpha(1)-antagonist prazosin (0.001, 0.003, 0.01, 0.03 and 0.1%) decreased volumes by 6, 47, 56, 64 and 71%, respectively. JP-1302, yohimbine and prazosin, at the dose level tested, did not alter the blood pressure. CONCLUSIONS: The present set of experiments indicates that both alpha(1)- and alpha(2)-adrenergic receptors are involved in the maintenance of basal nasal patency in the cat. Moreover, alpha(2c)-receptors may play a significant role in the sympathetic control of upper airway function.