Potent Phosphodiesterase Research Articles

Protective effect of cilostazol against doxorubicin-induced cardiomyopathy in mice

Doxorubicin (Dox) is an effective anti-cancer drug, but its use is limited because of its adverse effect of inducing irreversible dilated cardiomyopathy. Cilostazol (Cilo), a potent phosphodiesterase III inhibitor, has been reported to have an anti-inflammatory effect. Here, we investigated whether Cilo has a protective effect against Dox-induced cardiomyopathy (DIC). Mice were randomly divided into four groups: saline control, Dox (15mg/kg), Dox (15mg/kg) plus Cilo (50mg/kg), and Cilo (50mg/kg). The results showed that the coadministration of Dox and Cilo significantly enhanced left-ventricular systolic function compared with Dox alone. In addition, Cilo treatment significantly reduced Dox-induced perivascular fibrosis, collagen concentration, and connective growth factor expression in the heart. Also, Cilo administration markedly reduced Dox-induced levels of serum B-type natriuretic peptide, dysferlin, high-mobility group protein B1, Toll-like receptor 4, nuclear factor-κB p65, and cyclooxygenase-2. Furthermore, Cilo treatment significantly reduced Dox-induced oxidative stress by lowering the translocation of Nrf2 into the nucleus and the expression of NQO1, heme oxygenase 1, and superoxide dismutase-1. Our results suggest that Cilo may be a potential antifibrotic, antioxidative, and anti-inflammatory drug for DIC.

The Lipid-Modifying Enzyme SMPDL3B Negatively Regulates Innate Immunity.

SummaryLipid metabolism and receptor-mediated signaling are highly intertwined processes that cooperate to fulfill cellular functions and safeguard cellular homeostasis. Activation of Toll-like receptors (TLRs) leads to a complex cellular response, orchestrating a diverse range of inflammatory events that need to be tightly controlled. Here, we identified the GPI-anchored Sphingomyelin Phosphodiesterase, Acid-Like 3B (SMPDL3B) in a mass spectrometry screening campaign for membrane proteins co-purifying with TLRs. Deficiency of Smpdl3b in macrophages enhanced responsiveness to TLR stimulation and profoundly changed the cellular lipid composition and membrane fluidity. Increased cellular responses could be reverted by re-introducing affected ceramides, functionally linking membrane lipid composition and innate immune signaling. Finally, Smpdl3b-deficient mice displayed an intensified inflammatory response in TLR-dependent peritonitis models, establishing its negative regulatory role in vivo. Taken together, our results identify the membrane-modulating enzyme SMPDL3B as a negative regulator of TLR signaling that functions at the interface of membrane biology and innate immunity.

8-(3-chloro-4-methoxybenzyl)-8H-pyrido[2,3-d]pyrimidin-7-one derivatives as potent and selective phosphodiesterase 5 inhibitors.

A novel series of highly selective phosphodiesterase 5 (PDE5) inhibitors was found. 8H-Pyrido[2,3-d]pyrimidin-7-one derivatives bearing an (S)-2-(hydroxymethyl)pyrrolidin-1-yl group at the 2-position and a 3-chloro-4-methoxybenzyl group at the 8-position exhibited potent PDE5 inhibitory activities and high PDE5 selectivity over PDE6. Among the synthesized compounds, the 5-methyl analogue (5b) showed the most potent relaxant effect on isolated rabbit corpus cavernosum with an EC30 value of 0.85 nM.

Identification of potent phosphodiesterase inhibitors that demonstrate cyclic nucleotide-dependent functions in apicomplexan parasites.

Apicomplexan parasites, including Plasmodium falciparum and Toxoplasma gondii, the causative agents of severe malaria and toxoplasmosis, respectively, undergo several critical developmental transitions during their lifecycle. Most important for human pathogenesis is the asexual cycle, in which parasites undergo rounds of host cell invasion, replication, and egress (exit), destroying host cell tissue in the process. Previous work has identified important roles for Protein Kinase G (PKG) and Protein Kinase A (PKA) in parasite egress and invasion, yet little is understood about the regulation of cyclic nucleotides, cGMP and cAMP, that activate these enzymes. To address this, we have focused upon the development of inhibitors of 3',5'-cyclic nucleotide phosphodiesterases (PDEs) to block the breakdown of cyclic nucleotides. This was done by repurposing human PDE inhibitors noting various similarities of the human and apicomplexan PDE binding sites. The most potent inhibitors blocked the in vitro proliferation of P. falciparum and T. gondii more potently than the benchmark compound zaprinast. 5-Benzyl-3-isopropyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one (BIPPO) was found to be a potent inhibitor of recombinant P. falciparum PfPDEα and activated PKG-dependent egress of T. gondii and P. falciparum, likely by promoting the exocytosis of micronemes, an activity that was reversed by a specific Protein Kinase G inhibitor. BIPPO also promotes cAMP-dependent phosphorylation of a P. falciparum ligand critical for host cell invasion, suggesting that the compound inhibits single or multiple PDE isoforms that regulate both cGMP and cAMP levels. BIPPO is therefore a useful tool for the dissection of signal transduction pathways in apicomplexan parasites.

Discovery and SAR study of 2-(4-pyridylamino)thieno[3,2-d]pyrimidin-4(3H)-ones as soluble and highly potent PDE7 inhibitors

The discovery and SAR study of a new series of soluble and highly potent phosphodiesterase (PDE) 7 inhibitors are described herein. We explored a new lead compound with improved solubility, which led to the discovery of a 2-(4-pyridylamino)thieno[3,2-d]pyrimidin-4(3H)-one series. The introduction of 3-piperidines at the 7-position resulted in the significant enhancement of PDE7 activity. In particular, compound 32 also showed strong PDE7 inhibitory activity; good selectivity against PDE3, 4, and 5; and good aqueous solubility.

Discovery of 2-(cyclopentylamino)thieno[3,2-d]pyrimidin-4(3H)-one derivatives as a new series of potent phosphodiesterase 7 inhibitors.

The discovery of a new series of potent phosphodiesterase 7 (PDE7) inhibitors is described. Novel thieno[3,2-d]pyrimidin-4(3H)-one hit compounds were identified from our chemical library. Preliminary modifications of the hit compounds were performed, resulting in the discovery of a fragment-sized compound (10) with highly improved ligand efficiency. Compound design was guided by structure-activity relationships and computational modeling. The 6-substituted derivatives of the thienopyrimidinone showed diminished activity and enzyme selectivity. However, synthesis of the 7-substituted derivatives resulted in the discovery of 28e, a desirable lead compound that selectively inhibits PDE7 with single-digit nanomolar potency while displaying potent cellular efficacy.

In silico-screening of natural products for potential phosphodiesterase (PDE) 5A1 inhibitors

Based on the literature of the traditional herbs used for erectile dysfunction, structural data of compounds from four plants were mined and docked using the Schrödinger Glide interface. In addition to these phytoconstituents, known pharmaceutical PDE5A1 inhibitors and in-house microbial metabolites were included in the docking. The compounds showing the best docking scores were evaluated and validated with in vitro assay method. Four of the seven compounds submitted for bioassay indicated reasonable inhibition potential against PDE5A1 isoform. The exact details of in silico, structural information and in vitro data will be presented.

Synthesis and SAR study of novel tricyclic pyrazoles as potent phosphodiesterase 10A inhibitors

Novel pyrazolo[5,1-f][1,6]naphthyridines, pyrazolo[5,1-a][2,6]naphthyridines, pyrazolo[5,1-a][2,7]naphthyridines and pyrazolo[5,1-a]isoquinolines phenylimidazole/benzimidazole ethylene-linked were designed and synthesized for PDE10A interaction. An AgOTf and proline-cocatalyzed multicomponent methodology based on use of o-alkynylaldehydes, tosylhydrazide and ketones was developed and proved to be a convenient route for assembly of most of the novel tricyclic pyrazoles synthesized. Pyrazolo[5,1-f][1,6]naphthyridine 43 and 59, pyrazolo[5,1-a][2,6]naphthyridine 66, and pyrazolo[5,1-a][2,7]naphthyridine 42 showed the highest affinity for PDE10A enzyme (IC50 = 40, 42, 40, 55 nM, respectively).

Novel quinazolin-4(3H)-one/Schiff base hybrids as antiproliferative and phosphodiesterase 4 inhibitors: design, synthesis, and docking studies.

A novel series of quinazolin-4(3H)-one/Schiff base hybrids was rationally designed and synthesized. The prepared compounds were evaluated for in vitro activity to inhibit phosphodiesterase 4 (PDE4), where several of them showed good-to-moderate activity compared to rolipram. Compound 7 showed potent PDE4 inhibition in this series, with an IC50 of 1.60 µM. Compounds that showed PDE4 inhibition were further assessed for antiproliferative activity using different human tumor cell lines. Compound 10 exhibited significant antiproliferative activity with IC50 values of 140, 79, and 320 nM in breast, lung, and colon tumor cells, respectively. Docking of compound 7 in the active site of PDE4B illustrates its possible binding mode and provides insight for further optimizations of this novel scaffold for inhibiting PDE4.

Determination of ASP3258, a novel phosphodiesterase type 4 inhibitor, in rat plasma by high-performance liquid chromatography with fluorescence detection and its application to pharmacokinetic study.

The potent phosphodiesterase 4 inhibitor ASP3258 contains a carboxylic acid moiety and a naphthyridine ring and is a novel therapeutic agent for asthma and chronic obstructive pulmonary disease. To support the drug development of ASP3258, we developed and validated a simple method for its determination in rat plasma. Following the addition of the analog AS1406604-00 as an internal standard, plasma samples were processed using C18 -bonded solid-phase extraction cartridges under acidic conditions and injected into a high-performance liquid chromatography system with fluorescence detection. Chromatographic separation was achieved on a Shiseido Capcell Pak C18 UG120 column (3.0 × 150 mm, 5 µm) with a mobile phase consisting of acetonitrile-0.5% acetic acid (50:50, v/v). HPLC eluent was monitored with a fluorescence detector set at a wavelength of 315 nm for excitation and 365 nm for emission. The calibration curve was linear over a range of 2.5-250 ng/mL. Validation data demonstrated that the method is selective, sensitive and accurate. In addition, the present method was successfully applied to rat plasma samples from a pharmacokinetic study.

Fluorine-containing 6,7-dialkoxybiaryl-based inhibitors for phosphodiesterase 10 A: synthesis and in vitro evaluation of inhibitory potency, selectivity, and metabolism.

Based on the potent phosphodiesterase 10 A (PDE10A) inhibitor PQ-10, we synthesized 32 derivatives to determine relationships between their molecular structure and binding properties. Their roles as potential positron emission tomography (PET) ligands were evaluated, as well as their inhibitory potency toward PDE10A and other PDEs, and their metabolic stability was determined in vitro. According to our findings, halo-alkyl substituents at position 2 of the quinazoline moiety and/or halo-alkyloxy substituents at positions 6 or 7 affect not only the compounds' affinity, but also their selectivity toward PDE10A. As a result of substituting the methoxy group for a monofluoroethoxy or difluoroethoxy group at position 6 of the quinazoline ring, the selectivity for PDE10A over PDE3A increased. The same result was obtained by 6,7-difluoride substitution on the quinoxaline moiety. Finally, fluorinated compounds (R)-7-(fluoromethoxy)-6-methoxy-4-(3-(quinoxaline-2-yloxy)pyrrolidine-1-yl)quinazoline (16 a), 19 a-d, (R)-tert-butyl-3-(6-fluoroquinoxalin-2-yloxy)pyrrolidine-1-carboxylate (29), and 35 (IC50 PDE10A 11-65 nM) showed the highest inhibitory potential. Further, fluoroethoxy substitution at position 7 of the quinazoline ring improved metabolic stability over that of the lead structure PQ-10.

Novel Class of Benzoic Acid Ester Derivatives as Potent PDE4 Inhibitors for Inhaled Administration in the Treatment of Respiratory Diseases

The first steps in the selection process of a new anti-inflammatory drug for the inhaled treatment of asthma and chronic obstructive pulmonary disease are herein described. A series of novel ester derivatives of 1-(3-(cyclopropylmethoxy)-4-(difluoromethoxy)phenyl)-2-(3,5-dichloropyridin-4-yl) ethanol have been synthesized and evaluated for inhibitory activity toward cAMP-specific phosphodiesterase-4 (PDE4). In particular, esters of variously substituted benzoic acids were extensively explored, and structural modification of the alcoholic and benzoic moieties were performed to maximize the inhibitory potency. Several compounds with high activity in cell-free and cell-based assays were obtained. Through the evaluation of opportune in vitro ADME properties, a potential candidate suitable for inhaled administration in respiratory diseases was identified and tested in an in vivo model of pulmonary inflammation, proving its efficacy.

Discovery of Phosphodiesterase-4 Inhibitors: Serendipity and Rational Drug Design

Phosphodiesterase 4 (PDE4), the primary cyclic AMP-hydrolysing enzyme in cells, is a promising drug target for a wide range of mental disorders including Alzheimer's and Huntington's diseases, schizophrenia, and depression, plus a range of inflammatory diseases including chronic obstructive pulmonary disease, asthma, and rheumatoid arthritis. However, targeting PDE4 is complicated by the fact that the enzyme is encoded by four very closely related genes, together with 20 distinct isoforms as a result of mRNA splicing, and inhibition of some of these isoforms leads to intolerable side effects in clinical trials. With almost identical active sites between the isoforms, X-ray crystallography has played a critical role in the discovery and development of safer PDE4 inhibitors. Here we describe our discovery of a novel class of highly potent PDE4 via a ‘virtuous’ cycle of structure-based drug design and serendipity.

Phosphodiesterase 5 Inhibitors Enhance Chemotherapy Killing in Gastrointestinal/Genitourinary Cancer Cells

The present studies determined whether clinically relevant phosphodiesterase 5 (PDE5) inhibitors interacted with clinically relevant chemotherapies to kill gastrointestinal/genitourinary cancer cells. In bladder cancer cells, regardless of H-RAS mutational status, at clinically achievable doses, PDE5 inhibitors interacted in a greater than additive fashion with doxorubicin/mitomycin C/gemcitabine/cisplatin/paclitaxel to cause cell death. In pancreatic tumor cells expressing mutant active K-RAS, PDE5 inhibitors interacted in a greater than additive fashion with doxorubicin/gemcitabine/paclitaxel to cause cell death. The most potent PDE5 inhibitor was sildenafil. Knock down of PDE5 expression recapitulated the combination effects of PDE5 inhibitor drugs with chemotherapy drugs. Expression of cellular FLICE-like inhibitory protein-short did not significantly inhibit chemotherapy lethality but did significantly reduce enhanced killing in combination with sildenafil. Overexpression of B-cell lymphoma-extra large suppressed individual and combination drug toxicities. Knock down of CD95 or Fas-associated death domain protein suppressed drug combination toxicity. Combination toxicity was also abolished by necrostatin or receptor interacting protein 1 knock down. Treatment with PDE5 inhibitors and chemotherapy drugs promoted autophagy, which was maximal at ∼24 hour posttreatment, and 3-methyl adenine or knock down of Beclin1 suppressed drug combination lethality by ∼50%. PDE5 inhibitors enhanced and prolonged the induction of DNA damage as judged by Comet assays and γhistone 2AX (γH2AX) and checkpoint kinase 2 (CHK2) phosphorylation. Knock down of ataxia telangiectasia mutated suppressed γH2AX and CHK2 phosphorylation and enhanced drug combination lethality. Collectively our data demonstrate that the combination of PDE5 inhibitors with standard of care chemotherapy agents for gastrointestinal/genitourinary cancers represents a novel modality.

Inhibitory Effects of Vinpocetine on the Progression of Atherosclerosis Are Mediated by Akt/NF-κB Dependent Mechanisms in apoE-/- Mice

BackgroundRecent studies have found additional roles for vinpocetine, a potent phosphodiesterase type I inhibitor, in anti-proliferation and anti-inflammation of vascular smooth muscle cells and cancer cells via different mechanisms. In this study, we attempted to investigate whether vinpocetine protected against atherosclerotic development in apoE-/- mice and explore the underlying anti-atherogenic mechanisms in macrophages.Methodology/Principal FindingsVinpocetine markedly decreased atherosclerotic lesion size in apoE-/- mice measured by oil red O. Masson’s trichrome staining and immunohistochemical analyses revealed that vinpocetine significantly increased the thickness of fibrous cap, reduced the size of lipid-rich necrotic core and attenuated inflammation. In vitro experiments exhibited a significant decrease in monocyte adhesion treated with vinpocetine. Further, active TNF-α, IL-6, monocyte chemoattractant protein-1and matrix metalloproteinase-9 expression induced by ox-LDL were attenuated by vinpocetine in a dose-dependent manner. Similarly, ox-LDL-induced reactive oxygen species were significantly repressed by vinpocetine. Both western blot and luciferase activity assay showed that vinpocetine inhibited the enhanced Akt, IKKα/β, IκBα phosphorylation and NF-κB activity induced by ox-LDL, and the inhibition of NF-κB activity was partly caused by Akt dephosphorylation. However, knockdown of PDE1B did not affect Akt, IKKα/β and IκBα phosphorylation.ConclusionsThese results suggest that vinpocetine exerts anti-atherogenic effects through inhibition of monocyte adhesion, oxidative stress and inflammatory response, which are mediated by Akt/NF-κB dependent pathway but independent of PDE1 blockade in macrophages.

The Molecular Basis for the Selectivity of Tadalafil toward Phosphodiesterase 5 and 6: A Modeling Study

Great attention has been paid to the clinical significance of phosphodiesterase 5 (PDE5) inhibitors, such as sildenafil, tadalafil, and vardenafil widely used for erectile dysfunction. However, sildenafil causes side effects on visual functions since it shows similar potencies to inhibit PDE5 and PDE6, whereas tadalafil gives a high selectivity of 1020-fold against PDE6. Till now, their molecular mechanisms of selectivity of PDE5 versus PDE6 have remained unknown in the absence of the crystal structure of PDE6. In order to elucidate its isoform-selective inhibitory mechanism, a 3D model of PDE6 was constructed by homology modeling, and its interaction patterns with tadalafil plus sildenafil were exploited by molecular docking, molecular dynamics (MD) simulations, and binding free energy calculations. The present work reveals that tadalafil exhibits a less negative predicted binding free energy of -35.21 kcal/mol with PDE6 compared with the value of -41.12 kcal/mol for PDE5, which suggests that tadalafil prefers PDE5 rather than PDE6 and confers a high selectivity for PDE5 versus PDE6. The binding free energy results for tadalafil were consistent with external bioassay studies (IC50 = 5100 and 5 nM toward PDE6 and PDE5, respectively). Two important residues from the Q2 pockets (Val782 and Leu804 in PDE5 and their corresponding Val738 and Met760 in PDE6) were further identified to account for the high selectivity of tadalafil for PDE5 versus PDE6. These findings have shed light on the continuous puzzle of why sildenafil (IC50 = 74 and 6 nM toward PDE6 and PDE5, respectively) causes visual disorders because of its poor selectivity but tadalafil does not. In addition, the homology model of PDE6 can be used to design more potent and selective second-generation PDE5 inhibitors with less inhibitory potency against PDE6.

N-Phenyl-3-Pyridin-2-yl Imino Derivatives as Vascular Smooth Muscle Relaxants: Potential Phosphodiesterase V Inhibitors

The present communication deals with development of ten novel N-Phenyl-3-Pyridin-2-yl imino derivatives as vascular smooth muscle relaxants. The derivatives were prepared and optimized using pocket modelling and pharmacophore modelling. The 4 hydroxy substituted derivatives are showed potent activity comparable to the sildenafil. native ligand surface were marked. The marked pocket of the protein was used for optimizing structural requirements of designed molecules and further studies. Docking Studies. To explore the interactions of the com- pounds, we carried out binding simulations using biopredicta module of Vlife MDS 4.3 suite. We used the crystal structure of the Phosphodiesterase V PDB ID 2H42, to perform dock- ing simulations and potential H-bonding, π-stacking, VDW, Hydrophobic interactions with the designed compounds were recorded. The structure of 3,4-thiadiazol-2-yl)-3-((5- nitropyridin-2-yl)imino)butanamide was used as the tem- plate to built the molecules in the dataset in builder module of Vlife MDS 4.3. Prior to docking studies a systematic conformational search was performed to obtain the low energy conformations of the ligands. The low energy confor- mations thus obtained, were optimized till they reached rms gradient energy of 0.001 kcal/mol A. In order to define ligand-receptor interactions, docking of all the low energy conformations within a range of 5 kcal/mol A from the lowest energy conformation of each molecule. Molecular Alignment. 13 The molecules of the dataset

Synthesis and biological evaluation of 5-carbamoyl-2-phenylpyrimidine derivatives as novel and potent PDE4 inhibitors

5-Carbamoyl-2-phenylpyrimidine derivative 2 has been identified as a phosphodiesterase 4 (PDE4) inhibitor with moderate PDE4B inhibitory activity (IC50=200nM). Modification of the carboxylic acid moiety of 2 gave N-neopentylacetamide derivative 10f, which had high in vitro PDE4B inhibitory activity (IC50=8.3nM) and in vivo efficacy against lipopolysaccharide (LPS)-induced pulmonary neutrophilia in mice (ID50=16mg/kg, ip). Furthermore, based on the X-ray crystallography of 10f bound to the human PDE4B catalytic domain, we designed 7,8-dihydro-6H-pyrido[4,3-d]pyrimidin-5-one derivative 39 which has a fused bicyclic lactam scaffold. Compound 39 exhibited excellent inhibitory activity against LPS-induced tumor necrosis factor alpha (TNF-α) production in mouse splenocytes (IC50=0.21nM) and in vivo anti-inflammatory activity against LPS-induced pulmonary neutrophilia in mice (41% inhibition at a dose of 1.0mg/kg, i.t.).

Effects of Sildenafil on the Gastrocnemius and Cardiac Muscles of Rats in a Model of Prolonged Moderate Exercise Training

Moderate exercise training improves energetic metabolism, tissue perfusion and induces cardiac and skeletal muscle remodeling. Sildenafil, a potent phosphodiesterase-5 inhibitor used to treat erectile dysfunction, reduces infarct size and increases tissue oxygenation in experimental models of cardiovascular disease. We have evaluated the effects of prolonged moderate exercise training and a repeat administration of sildenafil on the rat gastrocnemius and cardiac muscles. Animals were divided into two groups: sedentary and trained. Each group was subdivided into animals treated with vehicle or with two doses of sildenafil (10 or 15 mg/kg/day) during the last week of training. Physical exercise did not induce cardiac hypertrophy, whereas it increased mRNA levels of the PGC-1α, HIF-1α and VEGF genes, which are involved in mitochondrial biogenesis and angiogenesis, and reduced mRNA levels of FoxO3a, MuRF-1 and Atrogin-1. Sildenafil dose-dependently promoted both angiogenesis, as shown by increased capillary density, and muscle atrophy, as shown by muscle fibre size. These effects were more pronounced in trained animals. Our data confirm the beneficial effects of a moderate and prolonged training on cardiovascular and skeletal systems and document the positive and negative effects of sildenafil on these tissues at doses higher than those used in clinical practice. This report may impact on the use of sildenafil as a substance able to influence sports performance.

Efficacy and tolerability of udenafil in Turkish men with erectile dysfunction of psychogenic and organic aetiology: a randomized, double‐blind, placebo‐controlled study

Udenafil is a potent phosphodiesterase type-5 inhibitor (PDE5) previously shown in studies conducted in populations of Eastern-Asian ethnicity, to significantly improve sexual function, in addition to a favourable safety profile. The purpose of this study was to evaluate the efficacy and safety of udenafil for the treatment of erectile dysfunction (ED), for the first time in a non-Eastern-Asian population. In this multicentre, randomized, double-blind, parallel, placebo-controlled study conducted in five centres in Turkey, 118 eligible subjects were randomized to receive udenafil 100 mg taken as on-demand or matching placebo for an 8-week treatment period. The primary efficacy variable was the change from baseline of the International Index of Erectile Function Questionnaire-Erectile Function Domain (IIEF-EFD) score, secondary efficacy variables were changes from baseline in IIEF Questionnaire Domains' 2-5 scores (Intercourse Satisfaction, Orgasmic Function, Sexual Desire, Overall Sexual Satisfaction) and IIEF Questionnaire Grand Total score, changes from baseline in penetration success rates (SEP2) and intercourse completion rates (SEP3) and evaluation of responses to the global assessment question (GAQ). Patients treated with udenafil demonstrated significantly higher increase in the IIEF-EFD scores compared with placebo-treated subjects [4.0 (95% CI: 1.3-6.6; p = 0.003)]. Similarly, greater improvements were observed in the scores for SEP2 [0.65 (95% CI: 0.02-1.3, p = 0.043)], SEP3 [0.9 (95% CI: 0.3-1.5, p = 0.003)] and two other IIEF Questionnaire Domains (Domain 4: Sexual Desire, Domain 5: Overall Sexual Satisfaction). The proportion of positive responses to the GAQ was greater in the udenafil compared to the placebo group (72.2% vs. 49.1%, p = 0.014). The most frequent treatment-emergent adverse events were headache, flushing and rhinorrhea, all of mild or moderate severity. This is the first study to demonstrate in a non-Eastern-Asian population that udenafil 100 mg taken as on-demand can effectively improve erectile function and is well tolerated.