Multi-Dimensional Screening Strategy for Drug Repurposing with Statistical Framework-A New Road to Influenza Drug discovery.

Influenza virus is known for its intermittent outbreaks affecting billions of people worldwide. Several neuraminidase inhibitors have been used in practice to overcome this situation. However, advent of new resistant mutants has limited its clinical utilization. In the recent years drug repurposing technique has attained the limelight as it is cost effective and reduces the time consumed for drug discovery. Here, we present multi-dimensional repurposing strategy that integrates the results of ligand-, energy-, receptor cavity, and shape-based pharmacophore algorithm to effectively identify novel drug candidate for influenza. The pharmacophore hypotheses were generated by utilizing the PHASE module of Schrödinger. The generated hypotheses such as AADP, AADDD, and DDRRNH, respectively, for ligand-, e-pharmacophore and receptor cavity based approach alongside shape of oseltamivir were successfully utilized to screen the DrugBank database. Subsequently, these models were evaluated for their differentiating ability using Enrichment calculation. Receiver operating curve and enrichment factors from the analysis indicate that the models possess better capability to screen actives from decoy set of molecules. Eventually, the hits retrieved from different hypotheses were subjected to molecular docking using Glide module of Schrödinger Suite. The results of different algorithms were then combined to eliminate false positive hits and to demonstrate reliable prediction performance than existing approaches. Of note, Pearson's correlation coefficients were calculated to examine the extent of correlation between the glide score and IC50 values. Further, the interaction profile, pharmacokinetic, and pharmacodynamics properties were analyzed for the hit compounds. The results from our analysis showed that alprostadil (DB00770) exhibits better binding affinity toward NA protein than the existing drug molecules. The biological activity of the hit was also predicted using PASS algorithm that renders the antiviral activity of the compound. Further, the results were validated using mutation analysis and molecular dynamic simulation studies. Indeed, this integrative filtering is able to exceed accuracy of other state-of-the-art methods for the drug discovery.

Effect of Oxylipins, Terpenoid Precursors and Wounding on Soft Corals' Secondary Metabolism as Analyzed via UPLC/MS and Chemometrics.

The effect of three oxylipin analogues, a terpenoid intermediate and wounding on the secondary metabolism of the soft corals Sarcophyton glaucum and Lobophyton pauciflorum was assessed. Examined oxylipins included prostaglandin (PG-E1), methyl jasmonate (MeJA), and arachidonic acid (AA) in addition to the diterpene precursor geranylgeranylpyrophosphate (GGP). Post-elicitation, metabolites were extracted from coral heads and analyzed via UPLC-MS followed by multivariate data analyses. Both supervised and unsupervised data analyses were used for sample classification. Multivariate data analysis revealed clear segregation of PG-E1 and MeJA elicited S. glaucum at 24 and 48 h post elicitation from other elicitor samples and unelicited control group. PG-E1 was found more effective in upregulating S. glaucum terpene/sterol levels compared to MeJA. Metabolites showing upregulation in S. glaucum include campestene-triol and a cembranoid, detected at ca. 30- and 2-fold higher levels compared to unelicited corals. Such an elicitation effect was less notable in the other coral species L. pauciflorum, suggesting a differential oxylipin response in soft corals. Compared to MeJA and PG, no elicitation effect was observed for GGP, AA or wounding on the metabolism of either coral species.

Stability of Alprostadil in 0.9% Sodium Chloride Stored in Polyvinyl Chloride Containers.

The stability of alprostadil diluted in 0.9% sodium chloride stored in polyvinyl chloride (VIAFLEX) containers at refrigerated temperature, protected from light, is reported. Five solutions of alprostadil 11 mcg/mL were prepared in 250 mL 0.9% sodium chloride polyvinyl chloride (PL146) containers. The final concentration of alcohol was 2%. Samples were stored under refrigeration (2°C to 8°C) with protection from light. Two containers were submitted for potency testing and analyzed in duplicate with the stability-indicating high-performance liquid chromatography assay at specific time points over 14 days. Three containers were submitted for pH and visual testing at specific time points over 14 days. Stability was defined as retention of 90% to 110% of initial alprostadil concentration, with maintenance of the original clear, colorless, and visually particulate-free solution. Study results reported retention of 90% to 110% initial alprostadil concentration at all time points through day 10. One sample exceeded 110% potency at day 14. pH values did not change appreciably over the 14 days. There were no color changes or particle formation detected in the solutions over the study period. This study concluded that during refrigerated, light-protected storage in polyvinyl chloride (VIAFLEX) containers, a commercial alcohol-containing alprostadil formulation diluted to 11 mcg/mL with 0.9% sodium chloride 250 mL was stable for 10 days.

The key residue within the second extracellular loop of human EP3 involved in selectively turning down PGE2- and retaining PGE1-mediated signaling in live cells.

Key residues and binding mechanisms of PGE1 and PGE2 on prostanoid receptors are poorly understood due to the lack of X-ray structures for the receptors. We constructed a human EP3 (hEP3) model through integrative homology modeling using the X-ray structure of the ß2-adrenergic receptor transmembrane domain and NMR structures of the thromboxane A2 receptor extracellular loops. PGE1 and PGE2 docking into the hEP3 model showed differing configurations within the extracellular ligand recognition site. While PGE2 could form possible binding contact with S211, PGE1 is unable to form similar contacts. Therefore, S211 could be the critical residue for PGE2 recognition, but is not a significant for PGE1. This prediction was confirmed using HEK293 cells transfected with hEP3 S211L cDNA. The S211L cells lost PGE2 binding and signaling. Interestingly, the S211L cells retained PGE1-mediated signaling. It indicates that S211 within the second extracellular loop is a key residue involved in turning down PGE2 signaling. Our study provided information that S211L within EP3 is the key residue to distinguish PGE1 and PGE2 binding to mediate diverse biological functions at the initial recognition step. The S211L mutant could be used as a model for studying the binding mechanism and signaling pathway specifically mediated by PGE1.

Effects of alprostadil and iloprost on renal, lung, and skeletal muscle injury following hindlimb ischemia-reperfusion injury in rats.

OBJECTIVES: To evaluate the effects of alprostadil (prostaglandin [PGE1] analog) and iloprost (prostacyclin [PGI2] analog) on renal, lung, and skeletal muscle tissues after ischemia reperfusion (I/R) injury in an experimental rat model. MATERIALS AND METHODS: Wistar albino rats underwent 2 hours of ischemia via infrarenal aorta clamping with subsequent 2 hours of reperfusion. Alprostadil and iloprost were given starting simultaneously with the reperfusion period. Effects of agents on renal, lung, and skeletal muscle (gastrocnemius) tissue specimens were examined. RESULTS: Renal medullary congestion, cytoplasmic swelling, and mean tubular dilatation scores were significantly lower in the alprostadil-treated group than those found in the I/R-only group (P<0.0001, P=0.015, and P<0.01, respectively). Polymorphonuclear leukocyte infiltration, pulmonary partial destruction, consolidation, alveolar edema, and hemorrhage scores were significantly lower in alprostadil- and iloprost-treated groups (P=0.017 and P=0.001; P<0.01 and P<0.0001). Polymorphonuclear leukocyte infiltration scores in skeletal muscle tissue were significantly lower in the iloprost-treated group than the scores found in the nontreated I/R group (P<0.0001). CONCLUSION: Alprostadil and iloprost significantly reduce lung tissue I/R injury. Alprostadil has more prominent protective effects against renal I/R injury, while iloprost is superior in terms of protecting the skeletal muscle tissue against I/R injury.

Ternary inclusion complex formation and stabilization of limaprost, a prostaglandin E1 derivative, in the presence of α- and ß-cyclodextrins in the solid state.

Limaprost/α-cyclodextrin (CD)/ß-CD ternary inclusion complex was prepared by freeze-drying a solution containing all three components. Under humid conditions, limaprost was more stable in the ternary α-/ß-CD inclusion complex than in the binary α- or ß-CD complex. Specifically, during storage at 30°C/75% relative humidity (R.H.) for 4 weeks, about 19% of limaprost degraded into 17S,20-dimethyl-trans-Δ(2)-prostaglandin A1 (referred as 11-deoxy-Δ(10)) in the ß-CD complex, 8.1% degraded in the α-CD complex, and only 2.2% degraded in the α-/ß-CD complex. The mechanism of limaprost stabilization in the presence of both CDs was investigated by Raman and solid-state NMR spectroscopy and powder X-ray diffractometry. The fast degradation of limaprost to 11-deoxy-Δ(10) in the ß-CD complex was due to the rapid crystallization of ß-CD from the complex, liberating the free amorphous drug, which is susceptible to degradation. The dissociation and crystallization of ß-CD from the inclusion complex were suppressed by freeze-drying limaprost in the presence of both α- and ß-CDs. In addition, the interaction between limaprost and the two CDs was reinforced by inclusion of different moieties of limaprost: α-CD predominantly included the alkyl ω-chain, whereas ß-CD included the five-membered ring. Thus, a stable ternary inclusion complex was formed that included limaprost, maintaining the amorphous state of the complex and dramatically stabilizing the drug under humid conditions.

Development, Optimization, and Characterization of PEGylated Nanoemulsion of Prostaglandin E1 for Long Circulation.

Lipo-PGE1 is the most widely used formulation of PGE1 in clinic. However, PGE1 is easier to leak out from lipo-PGE1 and this will lead to the phlebophlogosis when intravenous injection. The stability of lipo-PGE1 in storage and in vivo is also discounted. The aim of this study is to develop a long-circulating prostaglandin E1-loaded nanoemulsion modified with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG) to improve the stability and pharmacokinetics profiles of lipo-PGE1. PEGylated PGE1 nanoemulsion was prepared using a dispersing-homogenized method. The stability of nanoemulsion in 1 month was investigated. Pharmacokinetic studies were employed to evaluate the in vivo profile of the optimized nanoemulsion. The optimized nanoemulsion PGE1-PEG2000(1%)-NE showed an oil droplet size <100 nm with a surface charge of -14 mV. Approximately, 97% of the PGE1 was encapsulated in the nanoemulsion. The particle size, zeta potential, and drug loading of PGE1-PEG2000(1%)-NE were stable in 1 month. After PGE1-PEG2000(1%)-NE was intravenously administered to rats, the area under curve (AUC) and half-life of PGE1 were, respectively, 1.47-fold and 5.98-fold higher than those of lipo-PGE1 (commercial formulation). PGE1-PEG2000(1%)-NE was an ideal formulation for prolonging the elimination time of PGE1. This novel parenteral colloidal delivery system of PGE1 has a promising potential in clinic use.

Utilizing immunoaffinity chromatography (IAC) cross-reactivity in GC-MS/MS exemplified at the measurement of prostaglandin E1 in human plasma using prostaglandin E2-specific IAC columns.

Immunoaffinity chromatography (IAC) is an elegant and highly efficient method to isolate a particular compound from biological samples for measurement by mass spectrometry coupled to GC, CE, or LC. The utility of IAC for the quantitative determination of several prostaglandins including prostaglandin E2 (PGE2) by GC-MS/MS and LC-MS/MS has been demonstrated. The aim of the present work was to test whether the cross-reactivity of the antibody immobilized on an insoluble support can be utilized for the quantitative determination of biomolecules by stable-isotope dilution mass spectrometry. In this communication, we provide evidence that this is indeed possible for prostaglandin E1 (PGE1) in human plasma by GC-MS/MS using commercially available Sepharose 4-based IAC columns with immobilized mouse anti-PGE2 monoclonal antibody with a declared cross-reactivity of about 19% toward PGE1. Endogenous PGE1 and the internal standard [3,3',4,4'-(2)H4]-PGE1 (d4-PGE1) externally added to human plasma samples were extracted by IAC, converted to their pentafluorobenzyl ester-methoxime-trimethylsilyl ether derivatives and analyzed by GC-MS/MS in the electron-capture negative-ion chemical ionization mode. Quantification was performed by selected-reaction monitoring of the mass transition m/z 526→m/z 258 for PGE1 and m/z 530→m/z 262 for d4-PGE1. By this method we measured PGE1 concentrations in EDTA plasma samples (1mL) of six healthy volunteers in the range 10-25pg/mL (29-72pM). PGE1 plasma concentration showed a trend for positive correlation with plasma parameters such as low density lipoprotein (LDL)-cholesterol, total cholesterol and glucose. The method described here provides a novel tool to study the potential link of PGE1 formation to dyslipidemia, insulin resistance and related metabolic disorders.

Formation of the ternary inclusion complex of limaprost with α- and ß-cyclodextrins in aqueous solution.

The inclusion mode of Limaprost in the presence of α- and ß-cyclodextrins (CDs) was investigated to gain insight into the stabilization mechanism of Limaprost-alfadex upon the addition of ß-CD in the solid state. The inclusion sites of α- and ß-CDs were studied by NMR spectroscopic and kinetic methods. With the addition of α- and ß-CDs, displacements in (13)C chemical shifts of prostaglandin F2α (PGF2α) were observed in the ω-chain and the five-membered ring, respectively, of the drug. Similar shift changes were observed with the addition of both α- and ß-CDs. In two-dimensional (2D) (1)H-NMR spectra, intermolecular correlation peaks were observed between protons of PGF2α and protons of both α- and ß-CDs, suggesting that PGF2α interacts with α- and ß-CDs to form a ternary complex by including the ω-chain with the former CD and the five-membered ring with the latter. In kinetic studies in aqueous solution, Limaprost was degraded to 17S,20-dimethyl-trans-Δ(2)-PGA1 (11-deoxy-Δ(10)) and 17S,20-dimethyl-trans-Δ(2)-8-iso-PGE1 (8-iso). The addition of α-CD promoted the dehydration to 11-deoxy-Δ(10), while ß-CD promoted the isomerization to 8-iso, under these conditions. In the presence of both α- and ß-CDs, dehydration and isomerization were also accelerated, supporting the formation of the ternary Limaprost/α-CD/ß-CD complex.

New therapeutic approach to heart failure due to myocardial infarction based on targeting growth hormone-releasing hormone receptor.

BACKGROUND: We previously showed that growth hormone-releasing hormone (GHRH) agonists are cardioprotective following myocardial infarction (MI). Here, our aim was to evaluate the in vitro and in vivo activities of highly potent new GHRH agonists, and elucidate their mechanisms of action in promoting cardiac repair. METHODS AND RESULTS: H9c2 cells were cultured in serum-free medium, mimicking nutritional deprivation. GHRH agonists decreased calcium influx and significantly improved cell survival. Rats with cardiac infarction were treated with GHRH agonists or placebo for four weeks. MI size was reduced by selected GHRH agonists (JI-38, MR-356, MR-409); this accompanied an increased number of cardiac c-kit+ cells, cellular mitotic divisions, and vascular density. One week post-MI, MR-409 significantly reduced plasma levels of IL-2, IL-6, IL-10 and TNF-α compared to placebo. Gene expression studies revealed favorable outcomes of MR-409 treatment partially result from inhibitory activity on pro-apoptotic molecules and pro-fibrotic systems, and by elevation of bone morphogenetic proteins. CONCLUSIONS: Treatment with GHRH agonists appears to reduce the inflammatory responses post-MI and may consequently improve mechanisms of healing and cardiac remodeling by regulating pathways involved in fibrosis, apoptosis and cardiac repair. Patients with cardiac dysfunction could benefit from treatment with novel GHRH agonists.

Stabilizing effect of ß-cyclodextrin on Limaprost, a PGE1 derivative, in Limaprost alfadex tablets (Opalmon) in highly humid conditions.

Stabilization against humidity of Limaprost (a prostaglandin E1 derivative), which is currently marketed as Opalmon, was undertaken using ß-cyclodextrin (ß-CD). Aqueous solutions of Limaprost alfadex/dextran 40 were lyophilized with and without ß-CD. Limaprost alfadex lyophilized with ß-CD was more chemically stable in humid conditions than that without ß-CD. Moreover, the addition of ß-CD as an excipient to tablets of these lyophilized composites remarkably improved the stability of Limaprost, and Limaprost in this moisture-resistant formulation was chemically stable for 19 weeks at 30°C, 75% relative humidity (R.H.). Chemical analysis of Limaprost and its degradation products indicated that degradation proceeded in the inclusion form (i.e., within the CD cavity). Solid (2)H-NMR spectroscopic studies showed that ß-CD constrained the molecular mobility of water in the solid state. These results suggested that the stabilization of Limaprost by ß-CD was at least partly due to the restricted molecular mobility of water, which acted as a catalytic species for the degradation, and also to the protection of the five-membered ring of Limaprost from water catalytic dehydration through inclusion complex formation with ß-CD.

Determination of Prostaglandin E1 in dog plasma using liquid chromatography-tandem mass spectrometry and its application to a pharmacokinetic study.

The determination of Prostaglandin (PG) E1 in plasma is challenged by its low concentration (pg/mL) and endogenous interference. An LC-MS/MS method for the determination of PGE1 in dog plasma has been developed and validated. Plasma being sampled at 4°C and treated with indomethacin effectively inhibited interferents synthesized post-sampling. Samples were subjected to one-step extraction and separated by reversed phase HPLC with a short cycle time of 3min. An LLOQ of 10pg/mL was achieved with 500µl plasma. The method was applied to a pharmacokinetic study in beagle dogs involving an intravenous infusion of 3.2µg/kg PGE1. The half-life was recovered at 7min. The simple, sensitive and rapid method was suitable to be applied to pharmacokinetic studies of PGE1 at clinically relevant doses.

Modular enantioselective synthesis of 8-aza-prostaglandin E1.

We report herein for the first time the enantioselective synthesis of 8-aza-PGE1. The synthesis used the cross olefin metathesis reaction to connect the 5-vinyl-γ-lactam subunit, prepared from (R)-malic acid via the Ley's sulfone-based α-amidalkylation protocol (dr = 6.8:1), with the chiral pre-ω-chain. The latter was synthesized in high enantioselectivity from (E)-2-octenol by the Sharpless asymmetric epoxidation and the titanocene-mediated epoxide opening. This modular approach is quite concise and flexible, and requires only eight steps from commercially available reagents.

Efficiency of high molecular weight backbone degradable HPMA copolymer-prostaglandin E1 conjugate in promotion of bone formation in ovariectomized rats.

Multiblock, high molecular weight, linear, backbone degradable HPMA copolymer-prostaglandin E1 (PGE1) conjugate has been synthesized by RAFT polymerization mediated by a new bifunctional chain transfer agent (CTA), which contains an enzymatically degradable oligopeptide sequence flanked by two dithiobenzoate groups, followed by postpolymerization aminolysis and thiol-ene chain extension. The multiblock conjugate contains Asp8 as the bone targeting moiety and enzymatically degradable bonds in the polymer backbone; in vivo degradation produces cleavage products that are below the renal threshold. Using an ovariectomized (OVX) rat model, the accumulation in bone and efficacy to promote bone formation was evaluated; low molecular weight conjugates served as control. The results indicated a higher accumulation in bone, greater enhancement of bone density, and higher plasma osteocalcin levels for the backbone degradable conjugate.

Formulation optimization of prostaglandin E1-loaded lipid emulsion: enhanced stability and reduced biodegradation.

The purpose of this study is to develop a new formulation for prostaglandin E1 (PGE1)-loaded lipid emulsion (Lipo-PGE1) with improved stability and reduced biodegradation. High-pressure homogenization was used to prepare the Lipo-PGE1, and high-performance liquid chromatography and accelerated test were used to evaluate its physicochemical stability. A tissue homogenate incubation test was firstly established and validated to assess its biodegradation. The factors influencing the stability of Lipo-PGE1, including oil phase, emulsifier, pH value, and drug concentration were systematically investigated. The optimized formulation consisting of poloxamer188 1.5% (w/v), egg lecithin 0.5% (w/v), soybean oil 10.0% (w/v), oleic acid 0.24% (w/v), and glycerol 2.2% (w/v), with the pH value at 4.0, was defined and characterized. When compared with the currently available commercial product of Lipo-PGE1, the degradation percentage of this optimized Lipo-PGE1 reduced by 47.1% after sterilization, the drug remaining percentage increased by 13.9% after storage at 4°C over 6 months. Also, a significant reduction in biodegradation of the optimized Lipo-PGE1 in comparison with the commercial Lipo-PGE1 was observed by a tissue homogenate incubation test. Overall, we provided a novel formulation for Lipo-PGE1 with a better physicochemical stability and a less biodegradation than the currently available commercial product of Lipo-PGE1, indicating its potential superiority in clinical application.

Alprostadil liposome microsphere preparation stabilizes vascular plaques and inhibits intra-plaque inflammation.

BACKGROUND: Vulnerable plaques play an important role in the onset of sudden cardiac events and strokes. How to stabilize vulnerable plaques is still a challenge to medical science. Alprostadil is a biologically active substance with strong activity on vessel. Our study assessed the stabilizing effects of an alprostadil liposome microsphere preparation (ALMP) on vulnerable plaques in the brachiocephalic artery of apolipoprotein E (Apo E) knockout mice. METHODS: Seventy-two male Apo E-knockout mice were fed a high-fat diet beginning at eight weeks of age. At week 17, they were divided randomly into groups for treatment with a high dose (3.6 µg×kg(-1)×d(-1)) or low dose (1.8 µg×kg(-1)×d(-1)) of an ALMP, or 0.2 ml/d normal saline (control group). The drug was administered using a micro-capsule pump. Twenty weeks after drug administration, pathological changes in the vulnerable plaques within the brachiocephalic artery were assessed, and levels of anti-mouse monocyte/macrophage monoclonal antibody (MOMA-2) and superoxide anions in the plaques were detected using immunofluorescence. The soluble intercellular adhesion molecule-1 (ICAM-1) expression was measured by ELISA, and the expression of matrix metalloproteinase-9 (MMP-9) and CD40 mRNA was measured using RT-PCR. Thrombospindin-1 (TSP-1) expression was detected using Western blotting. RESULTS: Compared with the control group, ALMP treatment significantly reduced the plaque area in the brachiocephalic artery (P < 0.01), significantly lowered the contents of the lipid core (P < 0.01), significantly reduced the number of ruptured fibrous caps (P < 0.05), and increased the thickness of the fibrous cap and significantly reduced the incidence of intra-plaque hemorrhage (P < 0.05). ALMP treatment significantly reduced the expression of MOMA-2, superoxide anion, MMP-9, ICAM-1 and CD40 in the plaques (P < 0.01), decreased plasma ICAM-1 expression (P < 0.01), and increased the expression of TSP-1. CONCLUSIONS: Treatment with ALMP can stabilize vulnerable plaques by inhibiting inflammation.

Discovery of an 8-aza-5-thiaProstaglandin E1 analog as a highly selective EP4 receptor agonist.

For the purpose of discovering an orally available EP4 subtype-selective agonist, a series of 8-aza prostaglandin E(1) (PGE(1)) analogs were synthesized and evaluated for their affinity for PGE(2) receptor subtypes. Additionally, the structure-activity relationships of these compounds were studied. Among the tested compounds, the 8-aza PGE(1) analog 6 and 8-aza-5-thiaPGE(1) analog 12 had highly potent EP4 receptor affinity, good functional activity, and excellent subtype-selectivity. Furthermore, these analogs demonstrated good stability in human liver microsomes. As a result, we concluded that these two series of 8-aza PGE(1) analogs could be promising chemical leads for an orally available EP4 subtype-selective agonist.

Discovery of orally available 8-aza-5-thiaProstaglandin E1 analogs as highly selective EP4 agonists.

Analogs 8-aza-16-aryl prostaglandin E(1) (PGE(1)) and 8-aza-5-thia-16-arylPGE(1) were synthesized and evaluated with respect to their subtype receptor affinity and EP4 agonist activity for the purposes of identifying subtype-selective EP4 agonists that demonstrate oral efficacy. Using an inhibition assay of lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)-α production in rats, representative compounds were evaluated for their pharmacokinetic profiles and in vivo efficacy. Structure-activity relationships (SARs) were characterized and presented. Of the compounds tested, several demonstrated better oral exposure and/or in vivo efficacy compared with the previously reported analog 2a.

Influence of PEI as a core modifying agent on PLGA microspheres of PGE1, a pulmonary selective vasodilator.

This study tests the hypothesis that large porous poly (lactic-co-glycolic acid) (PLGA) microparticles modified with polyethyleneimine (PEI) are viable carriers for pulmonary delivery of prostaglandin E(1) (PGE(1)) used in the treatment of pulmonary arterial hypertension (PAH), a pulmonary vascular disorder. The particles were prepared by a double-emulsion solvent evaporation method with PEI-25 kDa in the internal aqueous phase to produce an osmotic pressure gradient. Polyvinyl alcohol (PVA) was used for external coating of the particles. The particles were examined for morphology, size, aerodynamic diameter, surface area, pore volume and in-vitro release profiles. Particles with optimal properties for inhalation were tested for in-vivo pulmonary absorption, metabolic stability in rat lung homogenates, and acute toxicity in rat bronchoalveolar lavage fluid and respiratory epithelial cells, Calu-3. The micromeritic data indicated that the PEI-modified particles of PGE(1) are optimal for inhalation. Incorporation of PEI in the formulations resulted in an increased entrapment efficiency - 83.26 ± 3.04% for particles with 1% PVA and 95.48 ± 0.46% for particles with 2% PVA. The amount of cumulative drug released into the simulated interstitial lung fluid was between 50.8 ± 0.76% and 55.36 ± 0.06%. A remarkable extension of the circulation half-life up to 6.0-6.5h was observed when the formulations were administered via the lungs. The metabolic stability and toxicity studies showed that the optimized formulations were stable at physiological conditions and relatively safe to the lungs and respiratory epithelium. Overall, this study demonstrates that large porous inhalable polymeric microparticles can be a feasible option for non-invasive and controlled release of PGE(1) for treatment of PAH.