Avanafil, a Potent and Highly Selective Phosphodiesterase-5 Inhibitor for Erectile Dysfunction

Discovery and Optimization of Dihydroquinolin-2(1H)-ones as Novel Highly Selective and Orally Bioavailable Phosphodiesterase 5 Inhibitors for the Treatment of Pulmonary Arterial Hypertension

Phosphodiesterase 5 (PDE5) is a cGMP-specific hydrolytic enzyme and widely distributed in versatile tissues. PDE5 has been identified as a valid therapeutic target for treating erectile dysfunction and pulmonary arterial hypertension (PAH). Herein, a hit-to-lead structural optimizations were performed on the PDE1 inhibitor 10c, leading to compound 14b possessing great potency against PDE5A (IC50 = 3 nM) with high selectivity over PDE1, PDE2, PDE3, PDE4, PDE7, PDE8, PDE9, PDE10, and PDE11 by more than 1125-fold, and remarkable safety properties. Furthermore, oral administration of 14b (5.0 mg/kg) exerted much better pharmacodynamics effects on both mPAP (mean pulmonary artery pressure) and RVHI (index of right ventricle hypertrophy) than sildenafil citrate (10.0 mg/kg) in a monocrotaline-induced PAH rat model. Overall, these results proposed a novel highly selective PDE5 inhibitor 14b which could serve as a potential candidate for treatment of PAH.

Computational analysis of natural compounds as potential phosphodiesterase type 5A inhibitors

Phosphodiesterase type 5 (PDE5) is a cyclic nucleotide-hydrolyzing enzyme that plays essential roles in the regulation of second messenger cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) produced in response to various stimuli. Pharmacological inhibition of PDE5 has been shown to have several therapeutic uses, including treating cardiovascular diseases and erectile dysfunction. In search of PDE5A inhibitors with safer pharmacokinetic properties, computational analyses of the binding propensity of fifty natural compounds comprising flavonoids, polyphenols, and glycosides were conducted. Molecular dynamics simulation coupled with Molecular mechanics with generalized Born and surface area solvation (MM/GBSA) showed that verbascoside may inhibit the activity of PDE5 with a comparative binding energy (ΔG) of -87.8 ± 9.2 kcal/mol to that of the cocrystal ligand (PDB ID: 3BJC), having ΔG = -77.7±4.5 kcal/mol. However, the other top compounds studied were found to have lower binding propensities than the cocrystal ligand WAN: hesperidin (ΔG = -33.8 ± 3.4 kcal/mol), rutin (ΔG = -23.6 ± 26.3 kcal/mol), caftaric acid (ΔG = -21.2 ±3.6 kcal/mol), and chlorogenic acid (ΔG = 6.0 ± 16.5 kcal/mol). Therefore, verbascoside may serve as a potential PDE5A inhibitor while hesperidin, rutin, and caftaric acid may provide templates for further structural optimization for the designs of safer PDE5 inhibitors.

Progress in the Stereoselective Synthesis Methods of Pyrrolidine-Containing Drugs and Their Precursors

The presented review systematizes and summarizes the data on the synthesis of pyrrolidine derivatives, which are precursors for obtaining drugs. Based on the analysis of published data, the most promising directions in the synthesis of biologically active compounds containing a pyrrolidine ring are identified. Stereoselective synthesis methods are classified based on the source of the pyrrolidine ring. The first group includes methods that use a pyrrolidine ring as the starting compound. The second group combines stereoselective methods of cyclization of acyclic starting compounds, which lead to optically pure pyrrolidine derivatives.

Phosphodiesterase-5 inhibitors tadalafil and sildenafil potentiate nitrergic-nerve mediated relaxations in the bladder vasculature

Recent studies suggest that lower urinary tract dysfunction may arise due to changes in local perfusion. Phosphodiesterase-5 inhibitors can improve urinary bladder blood flow, although the local mechanisms have not been fully elucidated. The aim was to pharmacologically characterise the vascular supply to the bladder and determine the mechanisms underlying the effects of the phosphodiesterase-5 inhibitors tadalafil and sildenafil. Responses of isolated rings of porcine superior vesical arteries to electrical field stimulation (EFS) were measured in the absence and presence of inhibitors of key neurotransmitter systems. Vasodilation responses to nitric oxide (NO) donors were also recorded, and the effects of phosphodiesterase-5 inhibitors on all responses determined. EFS caused biphasic responses with an initial vasoconstriction and a slower developing vasodilation. Vasoconstriction was mediated by ATP (55%) and noradrenaline (45%) release, whilst vasodilation was reduced by L-NNA (100 μM) (80%) and propranolol (1 μM) (20%). The nitrergic component was inhibited (81%) by L-NPA, a selective inhibitor of neuronal nitric oxide synthase (nNOS). Endothelial removal did not affect vasodilation. Tadalafil and sildenafil depressed noradrenaline-evoked vasoconstriction (by 26.8% and 35.5% respectively, P < 0.01), enhanced vasodilation to EFS (by 27.8% and 51.8% respectively, p < 0.01) and enhanced responses to NO donors nitroprusside, SIN-1, and SNAP, increasing pIC50 values (P < 0.01), without affecting maximal responses. In conclusion, neuronal NOS has a predominant role in regulating vascular tone of the porcine superior vesical artery and potentiation of nNO-mediated vasodilation is the primary mechanism underlying effects of phosphodiesterase-5 inhibitors in the bladder vasculature.

Zaprinast and avanafil increase the vascular endothelial growth factor, vitamin D3, bone morphogenic proteins 4 and 7 levels in the kidney tissue of male rats applied the glucocorticoid

Objective: This study investigated effect of zaprinast and avanafil on vascular endothelial growth factor (VEGF), bone morphogenic protein (BMP) 4 and 7, and vitamin D₃ levels against the negative effect of dexamethazone.Method: Rats were randomly divided into four groups (n = 6). Control: Empty a syringe was immersed and removed subcutaneously. Dexamethasone (DEX): 120 µg/kg DEX was injected subcutaneously once a day for 28 days. DEX + zaprinast and DEX + avanafil groups: 10 mg/kg zaprinast and avanafil were administrated to rats in addition to the same procedure in the DEX, respectively. VitaminD₃, VEGF, BMP4 and 7 levels by enzyme linked immunosorbent assay (ELISA) and angiogenesis by histopathological/immunohistochemical were evaluated.Results: BMP4 values in the DEX were lower than the other groups (p < .05). DEX + zaprinast and DEX + avanafil exhibited an increase in all the parameters compared to the control and DEX (p < .05). However, these were not significant for the DEX + zaprinast (p > .05). Also, there was a significant increase in angiogenesis in the DEX + zaprinast and DEX + avanafil.Conclusion: Zaprinast and significantly avanafil induced vitamin D₃, BMP4 and 7 levels by increasing angiogenesis in renal.

Preparation and evaluation of radioiodinated avanafil: A novel potential radiopharmaceutical for the diagnostic evaluation of erectile dysfunction

Avanafil, a selective second-generation phosphodiesterase-5 inhibitor, was successfully labeled with iodine-125 via electrophilic and different factors affecting the labeling efficiency were studied. The labeled compound exhibited in-vitro stability of more than 24 h with a maximum labeling yield of up to 98.4 ± 1.9 %. Molecular modeling and in-vitro assessment of tracer inhibitory activity were performed to ensure that radiolabeling did not affect its binding ability to the target. Biodistribution studies were performed in normal rats and models of erectile dysfunction. The tracer specifically accumulated in the penis, and the clearance appeared to take place via the hepatobiliary route. Results suggested the usefulness of radiolabeled avanafil as a promising tracer for erectile dysfunction.

Oral drugs used to treat persistent pulmonary hypertension of the newborn

Introduction:Persistent Pulmonary Hypertension of the Newborn (PPHN) is a life-threatening neonatal condition, mostly treated with inhaled nitric oxide (iNO), intravenous prostaglandins, oral bosentan, sildenafil and tadalafil. However, the utility of non-oral agents is limited in PPHN for their side effects and inconvenient deliveries. Therefore, oral agents such as bosentan, sildenafil and tadalafil are becoming appealing for their satisfactory efficacy, easy mode of administration and acceptable side effects. Areas covered: We conducted a comprehensive search on Pubmed, Scopus, Web of Sciences concerning the use of bosentan, sildenafil and tadalafil to treat PPHN and summarized their efficacy, safety and pharmacokinetics. Expert opinion: Current randomized controlled trials (RCTs) have demonstrated the favorable responses and tolerable side effects of bosentan and sildenafil. Nevertheless, those RCTs are small and only one study has described the pharmacokinetics of sildenafil in neonates. Accordingly, bosentan, sildenafil and tadalafil remain off-label in clinical use. More well-designed RCTs with large samples and long-term follow-up and pharmacometrics studies are needed to demonstrate the efficacy, safety and pharmacokinetics of bosentan, sildenafil and tadalafil in PPHN.

Evaluation of daily avanafil efficacy in improving the endothelial function in Egyptian males with erectile dysfunction

Avanafil is a highly selective and potent oral phosphodiesterase type 5 inhibitor. However, its impact on the soluble markers of endothelial function has not been investigated yet. This study was conducted to assess the effect of daily avanafil on the endothelial markers' serum level and erectile function in patients with erectile dysfunction. In this work, we randomly divided 140 males with erectile dysfunction and other diseases commonly associated with endothelial dysfunction like diabetes mellitus, hypertension and dyslipidaemia into two equal groups: treatment group, treated with 50mg daily oral avanafil, and control group, treated with placebo. The International Index of Erectile Function-5 score and the serum levels of nitric oxide, cyclic guanosine monophosphate and endothelin-1 as markers of endothelial function were measured at baseline and after four weeks of treatment in both groups. At the end of treatment period, those randomised to avanafil achieved statistically significant improvement in erectile function, nitric oxide, cyclic guanosine monophosphate and endothelin-1 levels from baseline versus placebo regardless the type and duration of associated comorbidity as well as the duration and severity of erectile dysfunction. These results permitted us to suggest that daily avanafil can improve the impaired endothelial function associated with the erectile dysfunction.

The Use of Vasoactive Drugs in the Treatment of Male Erectile Dysfunction: Current Concepts

It is widely accepted that disorders of the male (uro)genital tract, such as erectile dysfunction (ED) and benign diseases of the prostate (lower urinary tract symptomatology or benign prostatic hyperplasia), can be approached therapeutically by influencing the function of both the vascular and non-vascular smooth muscle of the penile erectile tissue or the transition zone/periurethral region of the prostate, respectively. As a result of the discovery of nitric oxide (NO) and cyclic guanosine monophosphate (GMP) as central mediators of penile smooth muscle relaxation, the use of drugs known to increase the local production of NO and/or elevate the intracellular level of the second messenger cyclic GMP have attracted broad attention in the treatment of ED of various etiologies. Specifically, the introduction of vasoactive drugs, including orally active inhibitors of the cyclic GMP-specific phosphodiesterase (PDE) 5, has offered great advantage in the pharmacotherapy of ED and other diseases of the genitourinary tract. These drugs have been proven efficacious with a fast on-set of action and an improved profile of side-effects. This review summarizes current strategies for the treatment of ED utilizing the application of vasoactive drugs via the oral, transurethral, topical, or self-injection route.

In Silico Mapping of Essential Residues in the Catalytic Domain of PDE5 Responsible for Stabilization of Its Commercial Inhibitors

Phosphodiesterase type 5 (PDE5) is an important enzyme associated with the hydrolysis of cyclic guanosine monophosphate (cGMP) to guanosine monophosphate (GMP). Due to the relevant role of second messenger cGMP as a mediator in many physiological processes, efforts have been converged to find a safe pharmacological approach, seeking a specific, selective and potent inhibitor of the PDE5 enzyme. There are five commercial drugs with potential for clinical use: tadalafil, sildenafil, avanafil, udenafil and vardenafil. Here, we applied molecular modeling to obtain different profiles of protein–ligand interactions by adopting distinct PDE5 structures, specifically PDBid:1XOZ and two extracted from molecular dynamics (MD) simulations. The results generated by molecular docking showed several possibilities for inhibitor interactions with the catalytic pocket. Tadalafil, sildenafil and vardenafil were clearly stabilized by Gln817 via a well-oriented hydrogen bond. Another set of different interactions, such as polar, hydrophobic, π-stacking, metal–ligand and electrostatic, were responsible for accommodating avanafil and udenafil. All of the ligands are discussed in detail with consideration of the distinct protein structures, and a profile of the probability of residue–ligand contact is suggested, with the most frequently observed being: Tyr612, His613, Ser661, Thr723, Asp724, Asp764, Leu765, Val782 and Phe786. The molecular interactions displayed herein confirm findings achieved by previous authors and also present new contacts. In addition, the discussion can help researchers obtain a molecular basis for planning new selective PDE5 inhibitors, as well as explain an inhibitor’s experimental assays by considering the specific interactions occurring at the catalytic site.

Avanafil Inhibits the Contractility of the Isolated Caprine Detrusor Muscle

Context:

Avanafil is a smooth muscle relaxant that is clinically used to treat erectile dysfunction. It is an inhibitor of phosphodiesterase-5 (PDE5), the enzyme that catalyzes the metabolism of cyclic guanosine monophosphate (cGMP). The inhibitory effect of avanafil on isolated detrusor muscle contractility has not been studied.

Aims:

This study investigated the inhibitory effect of avanafil on isolated caprine (goat) detrusor muscle contractility and the possible mechanisms involved.

Settings and Design:

80 mM potassium chloride (KCl)-induced contractility of the isolated goat detrusor was studied using a physiograph.

Materials and Methods:

Ten caprine detrusor strips were made to contract using 80 mM KCl before and after addition of three concentrations (10, 30, and 60 μM) of avanafil. Three reversal agents, ODQ, a guanylyl cyclase inhibitor; glibenclamide, an adenosine triphosphate (ATP)-sensitive potassium channel blocker; and iberiotoxin, a calcium-sensitive potassium (BKCa) channel blocker, were investigated for their ability to reverse the inhibitory effect of 30 μM avanafil on KCl-induced detrusor contractility.

Statistical Analysis Used:

The nonparametric statistical test, Kruskal–Wallis test, was used for the analysis of the data.

Results:

Avanafil caused a statistically significant inhibition of detrusor contractility at 30 and 60 μM concentrations. The inhibitory effect of 30 μM avanafil on detrusor contractility was significantly reversed by the addition of ODQ, glibenclamide, and iberiotoxin.

Conclusions:

Avanafil inhibits the contractility of the isolated detrusor by inhibiting PDE5, leading to raised cellular levels of cGMP. The raised levels of cGMP could have inhibited detrusor contractility by activating cGMP-dependent protein kinase, by opening ATP-sensitive potassium channels, and by opening BKCa. Avanafil could be evaluated for treating clinical conditions requiring relaxation of the detrusor like overactive bladder.

Design, synthesis and biological evaluation of pyrazolopyrimidinone based potent and selective PDE5 inhibitors for treatment of erectile dysfunction

Our previous discovery of series of pyrazolopyrimidinone based PDE5 inhibitors led to find potent leads but with low aqueous solubility and poor bioavailability, and low selectivity. Now, a new series of same pyrazolopyrimidinone scaffold is designed, synthesized and evaluated for its PDE5 inhibitory potential. In this study, some of the molecules are found more potent and selective PDE5 inhibitors in vitro than sildenafil. The studies revealed that compound 5 is 20 fold selective to PDE5 against PDE6. As PDE6 enzyme is involved in the phototransduction pathway in the retina and creates distortion problem, the selectivity for PDE5 specifically against PDE6 enzyme is preferred for any development candidate and in present study, compound 5 has been found to be devoid of this liability of selectivity issue. Moreover, compound 5 has shown excellent in vivo efficacy in conscious rabbit model, it's almost comparable to sildenafil. The preclinical pharmacology including pharmacokinetic and physicochemical parameter studies were also performed for compound 5, it was found to have good PK properties and other physicochemical parameters. The development of these selective PDE5 inhibitors can further lead to draw strategies for the novel preclinical and/or clinical candidates based on pyrazolopyrimidinone scaffold.

Exploring the binding mechanisms of PDE5 with chromeno[2,3-c]pyrrol-9(2H)-one by theoretical approaches

Cyclic nucleotide phosphodiesterase type 5 (PDE5), exclusively specific for the cyclic guanosine monophosphate (cGMP), is an important drug target for the treatment of erectile dysfunction and pulmonary arterial hypertension (PAH). Although many PDE5 inhibitors have been approved, such as sildenafil, vardenafil, tadalafil and so on, extensive studies have reported some side effects, such as vision disturbance and hearing loss as a result of the amino acid sequence and the secondary structural similarity of other PDEs to the catalytic domain of PDE5. In this study, multiple docking strategies, molecular dynamics (MD) simulations, free energy calculations and decomposition were employed to explore the structural determinants of PDE5 with a series of chromeno[2,3-c]pyrrol-9(2H)-one derivatives. First, reliable docking results were obtained using quantum mechanics/molecular mechanics (QM/MM) docking. Then, MD simulations and MM/GBSA free energy calculations were used to explore the dynamic binding process and characterize the binding modes of the inhibitors with different activities. The predicted binding free energies are in good agreement with the experimental data, and the MM/GBSA free energy decomposition analysis sheds light on the importance of hydrogen bonds with Gln817, π-π stacks against Phe820 and hydrophobic residues for the PDE5 binding of the studied inhibitors. The structural and energetic insights obtained here are useful for understanding the molecular mechanism of ligand binding and designing novel potent and selective PDE5 inhibitors with new scaffolds.

Development of Validated and Stability-Indicating LC-DAD and LC-MS/MS Methods for Determination of Avanafil in Pharmaceutical Preparations and Identification of a Novel Degradation Product by LCMS-IT-TOF

Avanafil (AVA), one of the most effective drugs prescribed for erectile dysfunction, is a pyrimidine-derivative PDE5 inhibitor. In the current work, new LC methods were developed and validated for quantitative determination of avanafil and qualitative determination of its degradation products. The quantitative determination of avanafil was carried out using liquid chromatography with photodiode array detection (LC-DAD) and liquid chromatography-tandem mass spectrometry LC-MS/MS methods, and fully validated according to the ICH Q2 (R1) guideline, while qualitative determination was performed using a liquid chromatography mass spectrometry-ion trap-time of flight (LCMS-IT-TOF) instrument. The separation of avanafil and its degradation products was carried out using the same reversed-phase chromatographic conditions, in which a second-generation C₁₈-bonded monolithic silica column (Chromolith^® High Resolution RP-18e, 100 × 4.6 mm, Merck KGaA) was used as stationary phase. Briefly, the methods enable quantitation of avanafil with high accuracy (recovery > 95%) and precision (RSD% < 2.0), within the ranges of 0.5–20 μg/mL for LC-DAD and 150–6000 ng/mL for LC-MS/MS. In the forced degradation studies, over and above currently existing data, a new oxidation-based degradation product, whose predicted m/z is 367.1168, was identified and its structure was confirmed by high-resolution mass spectrometric analysis. As the main advantage, either an LC-DAD or LC-MS/MS instrument can be chosen for interference-free quantitation of AVA, according to the facilities in quality-control laboratories.

PDE5 inhibitors - pharmacology and clinical applications 20 years after sildenafil discovery

The discovery of the nitric oxide/cGMP pathway was the basis for our understanding of many normal physiological functions and the pathophysiology of several diseases. Since the discovery and introduction of sildenafil, inhibitors of PDE5 have been the first-line therapy for erectile dysfunction (ED). The success of sildenafil in the treatment of ED stimulated research in the field of PDE5 inhibition and led to many new applications, such as treatment of lower urinary symptoms, and pulmonary arterial hypertension, which are now approved indications. However, PDE5 inhibitors have also been used in several other disorders not discussed in this review, and the fields of clinical use are increasing. In the present review, the pharmacological basis of the NO/cGMP pathway and the rationale and clinical use of PDE5 inhibitors in different diseases are discussed.

Effects of the Phosphodiesterase-5 (PDE-5) Inhibitors, Avanafil and Zaprinast, on Bone Remodeling and Oxidative Damage in a Rat Model of Glucocorticoid-Induced Osteoporosis

Background

The aim of this study was to evaluate the effects of the phosphodiesterase-5 (PDE-5) inhibitors, zaprinast and avanafil, on NO signalling pathway, bone mineral density (BMD), epiphyseal bone width, bone marrow angiogenesis, and parameters of oxidative stress in a rat model of glucocorticoid-induced osteoporosis (GIOP).

Material/Methods

Twenty-four 8-month-old male rats in four groups were given a single daily treatment during a 30-day period: an (untreated) control group (n=6): a dexamethasone-treated group (120 μ/kg) (n=6); a group treated with dexamethasone (120 μ/kg) and zaprinast (10 mg/kg) (n=6): and a group treated with dexamethasone (120 μ/kg) and avanafil (10 mg/kg) (n=6). Rat whole body bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DEXA), and bone histology was performed. Also, selected oxidative stress parameters by HPLC method and the other biochemical parameters by ELISA method were measured.

Results

The GIOP model rats treated with zaprinast and avanafil showed a significant increase in NO, cyclic guanosine monophosphate (cGMP), and protein kinase G (PKG) (NO/cGMP/PKG) signaling-pathway components, and in C-terminal telopeptide of type I collagen (CTX-1), bone marrow angiogenesis, BMD, and epiphyseal bone width, compared with the (untreated) control rats (p<0.05). Levels of pyridinoline (PD) and deoxypyridinoline (DPD) were significantly reduced in the dexamethasone + zaprinast, and dexamethasone + avanafil treatment groups (p<0.05). Malondialdehyde (MDA), ubiquinone-10 (CoQ10), ubiquinol CoQ10 (CoQ10H), and 8-hydroxy-2′-deoxyguanosine (8-OHdG) were significantly increased in the dexamethasone-treated group, compared with the (untreated) controls (p<0.05).

Conclusions

In the GIOP rat model, markers of oxidative stress and bone atrophy were significantly reduced by treatment with the PDE-5 inhibitors, zaprinast and avanafil.

Phosphodiesterase (PDE5) inhibition assay for rapid detection of erectile dysfunction drugs and analogs in sexual enhancement products

Products marketed as dietary supplements for sexual enhancement are frequently adulterated with phosphodiesterase-5 (PDE5) inhibitors, which are erectile dysfunction drugs or their analogs that can cause adverse health effects. Due to widespread adulteration, a rapid screening assay was developed to detect PDE5 inhibitors in adulterated products. The assay employs fluorescence detection and is based on measuring inhibition of PDE5 activity, the pharmacological mechanism shared among the adulterants. Initially, the assay reaction scheme was established and characterized, followed by analysis of 9 representative PDE5 inhibitors (IC50 , 0.4-4.0 ng mL-1 ), demonstrating sensitive detection in matrix-free solutions. Next, dietary supplements serving as matrix blanks (n = 25) were analyzed to determine matrix interference and establish a threshold value; there were no false positives. Finally, matrix blanks were spiked with 9 individual PDE5 inhibitors, along with several mixtures. All 9 adulterants were successfully detected (≤ 5 % false negative rate; n = 20) at a concentration of 1.00 mg g-1 , which is over 5 times lower than concentrations commonly encountered in adulterated products. A major distinction of the PDE5 inhibition assay is the ability to detect adulterants without prior knowledge of their chemical structures, demonstrating a broad-based detection capability that can address a continuously evolving threat of new adulterants. The PDE5 inhibition assay can analyze over 40 samples simultaneously within 15 minutes and involves a single incubation step and simple data analysis, all of which are advantageous for combating the widespread adulteration of sex-enhancement products.

Phosphodiesterase type 5 and cancers: progress and challenges

Cancers are an extraordinarily heterogeneous collection of diseases with distinct genetic profiles and biological features that directly influence response patterns to various treatment strategies as well as clinical outcomes. Nevertheless, our growing understanding of cancer cell biology and tumor progression is gradually leading towards rational, tailored medical treatments designed to destroy cancer cells by exploiting the unique cellular pathways that distinguish them from normal healthy counterparts. Recently, inhibition of the activity of phosphodiesterase type 5 (PDE5) is emerging as a promising approach to restore normal intracellular cyclic guanosine monophosphate (cGMP) signalling, and thereby resulting into the activation of various downstream molecules to inhibit proliferation, motility and invasion of certain cancer cells. In this review, we present an overview of the experimental and clinical evidences highlighting the role of PDE5 in the pathogenesis and prevention of various malignancies. Current data are still not sufficient to draw conclusive statements for cancer patient management, but could provide further rational for testing PDE5-targeting drugs as anticancer agents in clinical settings.

The devil is in the details: an analysis of the subtleties between phosphodiesterase inhibitors for erectile dysfunction

Erectile dysfunction (ED) is a common sexual disorder with numerous etiologies involving multiple organ systems that leads to significant distress and decreased quality of life for the affected men. Fortunately, there are several modalities and interventions for treating ED. Oral medications, intra-urethral compounds, intracorporeal injections, vacuum-assist devices and surgically implanted prostheses are all part of the treatment algorithm. One of the first-lines and certainly the most widely used options for treating ED is the family of oral phosphodiesterase type 5 inhibitors (PDE5I). The introduction of these medications in the late 1990s revolutionized the field of sexual medicine. Currently there are no guidelines and minimal literature to help providers choose among drugs in this class. This review will address differences in efficacy and side effects between various members of the oral selective phosphodiesterase-5 inhibitor class of drugs.

Plasma concentrations of tadalafil in children with pulmonary arterial hypertension

BACKGROUND

There is no report documenting the plasma concentrations of tadalafil in children. This study was performed to evaluate the variability in the pharmacokinetics of tadalafil in children with pulmonary arterial hypertension (PAH) treated routinely with the drug.

METHODS

Plasma samples were taken twice (post- and predose) after repetitive oral administration, and the pharmacokinetic parameters (CL/F and V/F) in individual patients were estimated by the Bayesian method using the nonlinear mixed effects model. We also determined the unbound concentration of tadalafil using ultrafiltration.

RESULTS

Tadalafil was administered to 23 children aged between 0.25 and 17.4 years, with a mean age of 3.58 years. The mean (±SD) daily dose of tadalafil was 0.97 ± 0.41 mg/kg. Sixteen of the 23 children received bosentan concomitantly. The mean CL/F and V/F values of tadalafil were 0.149 L·h-1·kg-1 and 1.87 L/kg, respectively, which were higher than those reported in adults. No effects of age, bosentan, or the estimated glomerular filtration rate were observed on the CL/F value, indicating that other residual factors might account for the interindividual variability among children with PAH. The unbound tadalafil concentrations of the postdose samples ranged from 5.9 to 146 (46.9 ± 37.1) nmol/L, higher than the reported IC50 value of this phosphodiesterase-5 drug for humans (2-4 nmol/L, corresponding to 0.8-1.6 ng/mL).

CONCLUSIONS

We demonstrated variability in the total and unbound plasma concentrations of tadalafil in children. However, all children received the empirical doses of the drug; a mean dose of 0.97 mg·kg-1·d-1 showed sufficient unbound concentrations needed for half-maximal inhibition of human phosphodiesterase-5 in vitro. These observations may provide information for the proper use of tadalafil to treat children with PAH.

Efficacy of Avanafil 15 Minutes after Dosing in Men with Erectile Dysfunction: A Randomized, Double-Blind, Placebo Controlled Study

PURPOSE

We examined the therapeutic effects of avanafil 15 minutes after dosing in men with mild to severe erectile dysfunction.

MATERIALS AND METHODS

This randomized, double-blind, placebo controlled, 12-week study (4-week run-in and 8-week treatment) randomized 145 men to placebo, 147 to avanafil 100 mg and 148 to avanafil 200 mg on demand. The primary efficacy variable was the per subject proportion of sexual attempts during the treatment period in which subjects achieved erection sufficient for vaginal penetration within approximately 15 minutes after dosing as measured by a stopwatch. The attempt had to enable successful completion of sexual intercourse according to SEP question 3.

RESULTS

Significantly greater mean per subject percentages of successful intercourse attempts within approximately 15 minutes after dosing were observed for avanafil 100 mg (mean 25.9%, LS mean ± SE 24.7% ± 2.9%) and 200 mg (mean 29.1%, LS mean 28.2% ± 2.9%) vs placebo (mean 14.9%, LS mean 13.8% ± 2.9%, p = 0.001 and <0.001, respectively). After treatment we noted a statistically significant difference between avanafil and placebo in the average per subject proportion of successful intercourse attempts according to SEP question 3 as early as 10 minutes in the 200 mg group and 12 minutes in the 100 mg group. Treatment emergent adverse events included headache, upper respiratory tract infection and nasal congestion, and most such events were mild or moderate in severity.

CONCLUSIONS

Avanafil was efficacious within approximately 15 minutes of dosing compared to placebo. A statistically significant treatment difference in the percentage of successful sexual attempts was demonstrated as early as 10 minutes after treatment.

Avanafil for male erectile dysfunction: a systematic review and meta-analysis

Avanafil, a potent new selective phosphodiesterase type 5 (PDE5) inhibitor, has been developed for the treatment of erectile dysfunction (ED). We carried out a systematic review and meta-analysis to assess the efficacy and safety of this drug for the treatment of ED. A literature review was performed to identify all published randomized, double-blind, placebo-controlled trials of avanafil for the treatment of ED. The search included the following databases: MEDLINE, EMBASE and the Cochrane Controlled Trials Register. The reference lists of the retrieved studies were also investigated. Four publications, involving a total of 1381 patients, were used in the analysis, including four randomized controlled trials (RCTs) that compared avanafil with a placebo. Among the co-primary efficacy end points indicating that avanafil 100 mg was more effective than a placebo were successful vaginal penetration (SEP2) (the odds ratio (OR) =5.06, 95% confidence interval (CI) =3.29–7.78, P< 0.00001) and successful intercourse (SEP3) (OR = 3.99, 95% CI = 2.80–5.67, P< 0.00001). Men randomized to receive avanafil were less likely than those receiving the placebo to drop out due to an adverse event (AE) (OR = 1.48, 95% CI = 0.54–4.08, P = 0.44). Specific AEs with avanafil included headache and flushing, which were significantly less likely to occur with placebo. This meta-analysis indicates that avanafil 100 or 200 mg is an effective and well-tolerated treatment for ED. Compared with avanafil 100 mg, patients who take avanafil 200 mg are more likely to experience headaches.

Avanafil for erectile dysfunction in elderly and younger adults: differential pharmacology and clinical utility

The treatment modalities of erectile dysfunction range from oral pharmacotherapy to intracavernosal injections, intraurethral pellets, vacuum erectile devices, and the surgical option of penile prosthesis insertion. Oral phosphodiesterase 5 inhibitors still remain the preferred treatment for patients since they are the least invasive, not to mention that they can be prescribed by non-urologists. Due to these factors, there has been development of newer drugs with fewer side effects. This is a review of the second generation phosphodiesterase 5 inhibitor, avanafil, looking into its pharmacology as well as its clinical utility. Avanafil’s faster onset and shorter duration of action has made it preferred as compared to other PDE5 inhibitors for patients with multiple comorbidities.

Advances in targeting cyclic nucleotide phosphodiesterases

Cyclic nucleotide phosphodiesterases (PDEs) catalyse the hydrolysis of cyclic AMP and cyclic GMP, thereby regulating the intracellular concentrations of these cyclic nucleotides, their signalling pathways and, consequently, myriad biological responses in health and disease. Currently, a small number of PDE inhibitors are used clinically for treating the pathophysiological dysregulation of cyclic nucleotide signalling in several disorders, including erectile dysfunction, pulmonary hypertension, acute refractory cardiac failure, intermittent claudication and chronic obstructive pulmonary disease. However, pharmaceutical interest in PDEs has been reignited by the increasing understanding of the roles of individual PDEs in regulating the subcellular compartmentalization of specific cyclic nucleotide signalling pathways, by the structure-based design of novel specific inhibitors and by the development of more sophisticated strategies to target individual PDE variants.

Discovery of 3-(4-hydroxybenzyl)-1-(thiophen-2-yl)chromeno[2,3-c]pyrrol-9(2H)-one as a phosphodiesterase-5 inhibitor and its complex crystal structure

Phosphodiesterase-5 (PDE5) inhibitors have been approved for the treatment of erectile dysfunction and pulmonary hypertension, but enthusiasm on discovery of PDE5 inhibitors continues for their potential new applications. Reported here is discovery of a series of new PDE5 inhibitors by structure-based design, molecular docking, chemical synthesis, and enzymatic characterization. The best compound, 3-(4-hydroxybenzyl)-1-(thiophen-2-yl)chromeno[2,3-c]pyrrol-9(2H)-one (57), has an IC₅₀ of 17 nM against the PDE5 catalytic domain and good selectivity over other PDE families. The crystal structure of the PDE5 catalytic domain in complex with 57 was determined at 2Å resolution and showed that 57 occupies the same pocket as other PDE5 inhibitors, but has a different binding pattern in detail. On the basis of the binding pattern of 57, a novel scaffold can be proposed as a candidate of PDE inhibitors.

The selectivity and potency of the new PDE5 inhibitor TPN729MA

INTRODUCTION

TPN729MA is a newly developed phosphodiesterase type 5 inhibitor (PDE5i) for the treatment of erectile dysfunction, which offers potential for greater selectivity and longer duration of action than PDE5i in current clinical use.

AIM

We investigated the in vitro inhibitory potency and selectivity of TPN729MA on PDE isozymes, and its efficacy in animal models.

METHODS

The inhibition of 11 human recombinant PDEs by TPN729MA, sildenafil, and tadalafil were determined using radioimmunoassay. The effect of TPN729MA and sildenafil on intracavernous pressure (ICP), blood pressure (BP), and ICP/BP ratio were determined in a rat model of erection induced by electric stimulation and in a dog model of erection induced by sodium nitroprusside injection.

MAIN OUTCOME MEASURES

The main outcome measures were IC50 of TPN729MA, sildenafil, and tadalafil for PDE1-PDE11; maximum ICP; BP and ICP/BP ratio.

RESULTS

The IC50 of TPN729MA, sildenafil, and tadalafil for PDE5 was 2.28, 5.22, and 2.35 nM, respectively. TPN729MA showed 248, 366, 20, and 2671-fold selectivity against PDE1, PDE4, PDE6, and PDE11, respectively. TPN729MA showed excellent selectivity against PDE2, 3, 7, 8, 9, and 10 (>10,000-fold). In the rat model of erection, TPN729MA (5.0 and 2.5 mg/kg), but not sildenafil, significantly increased the maximum ICP compared with vehicle. Significantly increased ICP/BP was observed in the TPN729MA (5.0 mg/kg) group at all time points, in the TPN729MA (2.5 mg/kg) group at 75, 90, 105, and 120 minutes time points, and in sildenafil group at 75 and 90 minutes time points compared with vehicle. In the dog model of erection, TPN729MA and sildenafil significantly increased ICP and ICP/BP but showed no significant effect on BP compared with vehicle.

CONCLUSIONS

TPN729MA is a potent PDE5i with a balanced selectivity profile. TPN729MA shows excellent in vitro and in vivo potency, and a longer effect on erectile function than sildenafil in animal model.

PDE5 inhibitors: considerations for preference and long-term adherence

INTRODUCTION

Erectile dysfunction (ED) is a highly prevalent condition affecting nearly one in five men worldwide. The advent of phosphodiesterase type 5 inhibitors (PDE5i) has revolutionised the ED treatment landscape and provided effective, minimally invasive therapies to restore male sexual function.

MATERIALS AND METHODS

A pubmed search was performed of all English language articles from 1996 to present reviewing PDE5i, including pharmacokinetics, efficacy profiles and comparisons, where available.

RESULTS

Currently available PDE5i in the United States include sildenafil, vardenafil, tadalafil and avanafil, each of which has unique side effect, pharmacokinetic and outcome profiles. Sildenafil is associated with increased rate of visual changes, vardenafil with QT prolongation and tadalafil with lower back pain. Avanafil and vardenafil orodispersible tablet rapidly achieve peak plasma concentration, which results in faster onset of action, whereas tadalafil exhibits the longest half-life. First time response to PDE5i is approximately 60-70%, with no significant differences in efficacy noted among therapies. The literature does not clearly demonstrate a preference for one drug. High-treatment success rates (89%) were reported when patients were prescribed all available PDE5i. Daily dosing with tadalafil is associated with improved erectile function (EF) over time. Finally, novel modes of patient-provider interaction, including internet-based education, communication and prescribing, may also improve long-term adherence.

CONCLUSIONS

PDE5i represent first line therapy for ED with excellent overall efficacy and satisfactory side effect profiles. Enhanced communciation, coupled with increased knowledge of drug characteristics, comparative treatment regimens and optimal prescribing patterns, offer compelling tools to improve long-term treatment success.

An open-label, long-term evaluation of the safety, efficacy and tolerability of avanafil in male patients with mild to severe erectile dysfunction

AIM

Determine the long-term efficacy, safety and tolerability of avanafil, a highly specific, rapidly absorbed phosphodiesterase type 5 inhibitor in male patients with mild to severe erectile dysfunction (ED), with or without diabetes.

METHODS

This was a 52-week, open-label extension of two 12-week, randomised, placebo-controlled, phase 3 trials. Patients were assigned to avanafil 100 mg, but could request 200 mg (for increased efficacy; '100/200-mg' group) or 50 mg (for improved tolerability). Primary end points included percentage of sexual attempts ending in successful vaginal penetration [Sexual Encounter Profile 2 (SEP2)] and intercourse (SEP3) and erectile function domain score per the International Index of Erectile Function (IIEF-EF).

RESULTS

Some 712 patients enrolled; 686 were included in the intent to treat population and contributed to the data. All primary end points showed sustained improvement. SEP2 and SEP3 success rates improved from 44% to 83% and from 13% to 68% (100-mg group) and from 43% to 79% and from 11% to 66% (100/200-mg group), respectively. Mean IIEF-EF domain scores improved from 13.6 to 22.2 (100-mg group) and from 11.9 to 22.7 (100/200-mg group). Avanafil was effective in some patients ≤ 15 min and > 6 h postdose. Sixty-five per cent (112/172) of 'nonresponders' to avanafil 100 mg responded to the 200-mg dose. The most common (≥ 2%) treatment-emergent adverse events were headache, flushing, nasopharyngitis and nasal congestion; < 3% of patients discontinued therapy because of adverse events.

CONCLUSIONS

The long-term tolerability and improvement in sexual function, coupled with rapid onset, suggest that avanafil is well suited for the on-demand treatment of ED.

[Male sexuality in the elderly]

Male sexuality in the elderly is an important issue with a growing relevance. In contrast to the assumption of an asexual state when becoming older, recent representative surveys show that the majority of men maintain sexual desires and fantasies into old age. Sexual activity primarily depends on the availability of a partner and on maintaining intimacy and sexuality in the face of changes in the sexual response cycle and increasing comorbidity. This review aims to clarify the normal aging process, the sexual behavior of aging males and the prevalence of sexual dysfunction.

Hemodynamic effect of avanafil and glyceryl trinitrate coadministration

A Phase I, double-blind, randomized, crossover study in healthy males (N=106) was conducted between March 21, 2004, and May 17, 2004, to determine the magnitude and duration of the hemodynamic interaction of avanafil (a phosphodiesterase type-5 inhibitor for treating males with erectile dysfunction) when coadministered with glyceryl trinitrate (NTG) compared with sildenafil and placebo. Subjects received avanafil (200 mg), sildenafil (100 mg), and placebo (on separate days) via the oral route followed by NTG (0.4 mg) 12, 8, 4, 1, or 0.5 hours post-dose via the sublingual route. Blood pressure (BP) and heart rate (HR) were assessed at defined intervals.

Throughout the study (after administration of the study drug, and including the period after NTG administration), the effects of avanafil and sildenafil on BP and HR were significantly greatest overall, at the shortest (0.5-hour) time interval compared with placebo. By the 8- and 12-hour time intervals, no significant difference in BP or HR was observed for avanafil (8 and 12 hours) or sildenafil (12 hours) (p>0.05, compared with placebo). Compared with avanafil, sildenafil had a significantly greater effect when dosed 0.5 hours before NTG on standing HR (p=0.05); 1 hour before NTG on standing systolic blood pressure (SBP) (p<0.05), sitting SBP (p=0.01) and standing HR (p<0.01); and 12 hours before NTG on standing SBP (p=0.05). Throughout the study, symptomatic hypotension adverse events occurred in 27%, 29%, and 12%, and clinically significant reductions in standing SBP (≥30 mmHg) occurred in 15%, 29%, and 12% of subjects dosed with avanafil, sildenafil, and placebo, respectively (overall treatment differences: p<0.01 and p<0.05, respectively).

These data show that avanafil and sildenafil have no significant effect on BP and HR if administered to healthy males ≥8 hours (avanafil) or ≥12 hours (sildenafil) before a sublingual dose of NTG. However, results may differ in populations with known vascular disease, especially those using other concurrent pharmacotherapy. These findings may be of interest to clinicians who treat patients with erectile dysfunction and who also have a cardiovascular condition. Of note, the applicability of these results in such patients may be limited because the enrollment comprised healthy, normal subjects.

Avanafil for the treatment of erectile dysfunction: initial data and clinical key properties

Orally active, selective inhibitors of phosphodiesterase type 5 (PDE 5, cyclic GMP PDE), such as sildenafil, tadalafil and vardenafil, are currently the first-choice treatment options for the clinical management of erectile dysfunction (ED) of various etiologies and severities. However, a significant number of patients remain dissatisfied with the available therapies due a lack of efficacy or discomfort arising from adverse events. Several new PDE5 inhibitors, among which are avanafil (TA-1790), lodenafil, mirodenafil, udenafil, SLX-2101, JNJ-10280205 and JNJ-10287069, have recently been approved and introduced into the market or are in the final stages of their clinical development. Avanafil (marketed in the US under the brand name STENDRA(™)) has been developed by VIVUS Inc. (Mountain View, CA, USA) and has recently received approval from the US Food and Drug Administration (FDA) for use in the treatment of male ED. The drug has demonstrated improved selectivity for PDE5, is rapidly absorbed after oral administration with a fast onset of action and a plasma half-life that is comparable to sildenfil and vardenafil. In phase II and phase III clinical trials that included a large number of patients, avanafil has been shown to be effective and well tolerated. Owing to its favorable pharmacodynamic and pharmacokinetic profile, avanafil is considered as a promising new option in the treatment of ED. The present article summarizes the initial data and clinical key properties of avanafil.

A phase 3, placebo controlled study of the safety and efficacy of avanafil for the treatment of erectile dysfunction after nerve sparing radical prostatectomy

PURPOSE

We evaluated the safety and efficacy of 100 and 200 mg avanafil for the treatment of adult males with erectile dysfunction after bilateral nerve sparing radical prostatectomy.

MATERIALS AND METHODS

This was a double-blind, placebo controlled, parallel group, phase 3 study in males age 18 to 70 years with a history of erectile dysfunction of 6 months or more after bilateral nerve sparing radical prostatectomy. Patients were randomized to 100 or 200 mg avanafil or placebo (taken 30 minutes before sexual activity) for 12 weeks. Primary end points included successful vaginal insertion (Sexual Encounter Profile [SEP] question 2), successful intercourse (SEP3) and change in score on the erectile function domain of the International Index of Erectile Function (IIEF-EF) questionnaire.

RESULTS

A total of 298 patients were randomized and 84.6% completed the study. At baseline 16.1% were age 65 years or older and 71.5% had severe erectile dysfunction (mean overall IIEF-EF domain score 9.2). After 12 weeks there were significantly greater increases in SEP2 and SEP3 and change in mean IIEF-EF domain score with 100 and 200 mg avanafil vs placebo (p <0.01). Following dosing with avanafil 36.4% (28 of 77) of sexual attempts (SEP3) at 15 minutes or less were successful vs 4.5% (2 of 44) for placebo (p <0.01). Avanafil was generally well tolerated. No serious adverse events were reported and fewer than 2% of patients discontinued the study due to an adverse event.

CONCLUSIONS

Avanafil in 100 and 200 mg doses was effective and well tolerated in improving erectile function after prostatectomy. Results suggest a rapid onset of action and sustained duration of effect, with all 3 primary end points being achieved at both dose levels.

A phase II, single-blind, randomized, crossover evaluation of the safety and efficacy of avanafil using visual sexual stimulation in patients with mild to moderate erectile dysfunction

OBJECTIVE

To evaluate the safety, efficacy and time course of three doses of avanafil (50 mg, 100 mg and 200 mg) compared with sildenafil 50 mg or placebo, given in conjunction with visual sexual stimulation (VSS) videos in men with mild to moderate erectile dysfunction (ED).

PATIENTS AND METHODS

Male patients, 35-70 years of age, with mild to moderate ED of ≥6 months duration, were included in the study. During the course of the study, each patient received placebo, active control (sildenafil 50 mg), and one dose of avanafil (50 mg, 100 mg or 200 mg), all administered in random order at least 72 h apart. RigiScan® (Dacomed Corp., Minneapolis, MN, USA) monitoring was used in conjunction with 20-min VSS videos (20, 60, and 100 min after dosing) to determine the duration of and time to ≥60% penile rigidity, maximum rigidity, tumescent activity units (TAUs), rigidity activity units (RAUs), and responses to the five-point Erection Assessment Scale. Safety assessments included adverse events (AEs), vital sign changes in response to dosing, laboratory results (complete blood counts, chemistry panel, prostate-specific antigen, serum testosterone, prothrombin time and urine analysis) and physical examination findings.

RESULTS

Eighty-three patients were randomized and received at least one dose of study medication; 82 patients completed the study. Peak response to avanafil occurred in the early interval (20-40 min after dosing), while peak response to sildenafil occurred either in the middle (60-80 min) or late (100-120 min) intervals after dosing. Results were qualitatively similar for all other efficacy endpoints. During the 20-40-min interval, the majority of values for TAUs and RAUs with the avanafil 50-mg, 100-mg and 200-mg treatments were significantly superior to placebo (P < 0.05). Avanafil treatment was generally well tolerated; facial flushing (7-15%) was the most commonly observed AE, and no visual disturbances were reported.

CONCLUSION

A favourable safety profile and improvement in sexual function, coupled with rapid onset of action and durability of effect, make avanafil an attractive option for males with ED, especially in the setting of on-demand treatment.

Selectivity of avanafil, a PDE5 inhibitor for the treatment of erectile dysfunction: implications for clinical safety and improved tolerability

INTRODUCTION

Phosphodiesterase type 5 (PDE5) inhibitors are indicated for the treatment of erectile dysfunction (ED); however, they can also inhibit other PDE isozymes, affecting their target tissues (e.g., PDE1: heart; PDE6: retina; and PDE11: skeletal muscle), which in some cases can cause unwanted side effects and therapy discontinuation. Data from in vitro studies showed that avanafil, a PDE5 inhibitor for the treatment of ED, exhibited strong selectivity toward PDE5 and against all other PDE isozymes.

AIM

To review the inhibitory effects of avanafil for PDE isozymes compared with those of sildenafil, tadalafil, and vardenafil and to discuss these results within the context of clinical trial safety observations.

METHODS

Review of in vitro selectivity data for avanafil (published primary data from a peer-reviewed journal and scientific congress abstracts); PubMed search for pertinent publications on PDE5 inhibitor safety data; and review of published articles and abstracts from avanafil phase 1, 2, and 3 clinical trials.

MAIN OUTCOME MEASURES

A low incidence of some PDE-related adverse events may be reflected by the high selectivity of avanafil against non-PDE5 isozymes.

RESULTS

Avanafil is highly selective toward PDE5 and against all other PDE isozymes tested. Lower selectivity against PDE1, PDE6, and PDE11 is consistent with results from randomized, placebo-controlled, phase 3 trials in which musculoskeletal and hemodynamic adverse events were reported in <2% of patients and no color vision-related abnormalities were reported with avanafil doses up to 200 mg once daily.

CONCLUSIONS

Data suggest that avanafil may confer a safety benefit, in terms of a lower incidence of specific adverse events, by virtue of its high specificity to PDE5 and its overall selectivity against other PDE isozymes.