Breast Cancer Resistance Protein Limits Fetal Transfer of Tadalafil in Mice.

Tadalafil, a phosphodiesterase 5 (PDE5) inhibitor, is a candidate therapeutic agent for fetal growth restriction and hypertensive disorders of pregnancy. In this study, we elucidated the fetal transfer of tadalafil in comparison with that of sildenafil, the first PDE5 inhibitor to be approved. We also examined the contributions of multidrug resistance protein 1 (MDR1) and breast cancer resistance protein (BCRP) to fetal transfer. Tadalafil or sildenafil was administered to wild-type, Mdr1a/b-double-knockout or Bcrp-knockout pregnant mice by continuous infusion from gestational day (GD) 14.5 to 17.5, and the fetal-to-maternal plasma concentration ratio of unbound drug (unbound F/M ratio) was evaluated at GD 17.5. The values of unbound F/M ratio of tadalafil and sildenafil in wild-type mice were 0.80 and 1.6, respectively. The unbound F/M ratio of tadalafil was increased to 1.1 and 1.7 in Mdr1a/b-knockout and Bcrp-knockout mice, respectively, while the corresponding values for sildenafil were equal to or less than that in wild-type mice, respectively. A transcellular transport study revealed that basal-to-apical transport of both tadalafil and sildenafil was significantly higher than transport in the opposite direction in MDCKII-BCRP cells. Our research reveals that tadalafil is a newly identified substrate of human and mouse BCRP, and it appears that the fetal transfer of tadalafil is, at least in part, attributed to the involvement of BCRP within the placental processes in mice. The transfer of sildenafil to the fetus was not significantly constrained by BCRP, even though sildenafil was indeed a substantial substrate for BCRP.

Effects of phosphodiesterase V inhibition alone and in combination with BNP on cardiovascular and renal response to volume load in human preclinical diastolic dysfunction.

Preclinical diastolic dysfunction (PDD) results in impaired cardiorenal response to volume load (VL) which may contribute to the progression to clinical heart failure with preserved ejection fraction (HFpEF). The objective was to evaluate if phosphodiesterase V inhibition (PDEVI) alone or combination PDEVI plus B-type natriuretic peptide (BNP) administration will correct the impaired cardiorenal response to VL in PDD. A randomized double-blinded placebo-controlled cross-over study was conducted in 20 subjects with PDD, defined as left ventricular ejection fraction (LVEF) >50% with moderate or severe diastolic dysfunction by Doppler echocardiography and without HF diagnosis or symptoms. Effects of PDEVI with oral tadalafil alone and tadalafil plus subcutaneous (SC) BNP, administered prior to acute volume loading, were assessed. Tadalafil alone did not result in improvement in cardiac response to VL, as measured by LVEF, LV end diastolic volume, left atrial volume (LAV), or right ventricular systolic pressure (RVSP). Tadalafil plus SC BNP resulted in improved cardiac response to VL, with increased LVEF (4.1 vs. 1.8%, p = 0.08) and heart rate (4.3 vs. 1.6 bpm, p = 0.08), and reductions in both LAV (-4.3 ± 10.4 vs. 2.8 ± 6.6 ml, p = 0.03) and RVSP (-4.0 ± 3.0 vs. 2.1 ± 6.0 mmHg, p < 0.01) versus tadalafil alone. Plasma and urinary cyclic guanosine monophosphate (cGMP) excretion levels were higher (11.3 ± 12.3 vs. 1.7 ± 3.8 pmol/ml, 1851.0 ± 1386.4 vs. 173.4 ± 517.9 pmol/min, p < 0.01) with tadalafil plus SC BNP versus tadalafil alone. There was no improvement in renal response as measured by GFR, renal plasma flow, sodium excretion, and urine flow with tadalafil plus SC BNP compared to tadalafil alone. In subjects with PDD, tadalafil alone resulted in no improvement in cardiac adaptation, while tadalafil and SC BNP resulted in enhanced cardiac adaptation to VL. TRIAL REGISTRATION: ClinicalTrials.gov NCT01544998.

Natural phosphodiesterase 5 (PDE5) inhibitors: a computational approach.

In 1998, sildenafil was marketed as the first FDA-approved oral drug for the treatment of erectile dysfunction (ED). During the last two decades, the commercialization of other synthetic phosphodiesterase 5 (PDE5) inhibitors has been paralleled by the rise of remedies based on natural molecules from different chemical classes (flavonoids, polyphenols and alkaloids in general). In this work, a set of in silico tools were applied to study a panel of 30 natural compounds claimed to be effective against ED in the scientific literature or in folk medicine. First, pharmacokinetic properties were analysed to exclude the compounds lacking in specific drug-like features. Estimated binding energy for PDE5 and selectivity towards other PDE isoforms were then considered to highlight some promising molecules. Finally, a detailed structural investigation of the interaction pattern with PDE in comparison with sildenafil was conducted for the best performing compound of the set.

Intranasal Tadalafil nanoemulsions: formulation, characterization and pharmacodynamic evaluation.

This study aims at improving the bioavailability of a poorly soluble phosphodiesterase-5 inhibitor; tadalafil (TD) via developing intranasal (IN) nanoemulsions (NEs). Optimum NE ingredients were selected based on solubility studies, emulsification tests, and phase diagram construction. Both o/w and w/o NEs were selected based on their drug loading capacity. Optimum formulations were subjected to physicochemical characterization and were assessed for nasal toxicity through biochemical analysis of tumor necrosis factor-α (TNF-α) and caspase-3 in rat nasal tissues. Pharmacodynamic study was performed via biochemical analysis of cyclic guanosine monophosphate (cGMP) in rat penis 2-h post-treatment and compared with oral suspension of Cialis® tablets. Optimum o/w and w/o NEs were successfully prepared using different ratios of Capmul-MCM-EP, Labrasol:Transcutol-HP (1:1) and water. Optimized formulations exhibited more than 4000-fold increase in TD solubility compared with its aqueous solubility. Both formulations were optically isotropic with the majority of globules in the nanometric-size range. Nasal toxicity study revealed no significant difference in values of TNF-α and caspase-3 between the NE-treated groups and the control group. Both TD-NEs succeeded to achieve a significant enhancement in cGMP levels. Our findings suggested that IN administration of the developed TD-NEs could provide a safe and effective alternative to TD oral delivery.

A Phase I study to determine the pharmacokinetic profile, safety and tolerability of sildenafil (Revatio® ) in cardiac surgery: the REVAKI-1 study.

AIMS: Acute kidney injury (AKI) is a common and severe complication of cardiac surgery. There is no effective prevention or treatment. Sildenafil citrate (Revatio® , Pfizer Inc.), a phosphodiesterase type 5 inhibitor, prevents post cardiac surgery AKI in pre-clinical studies, however its use is contraindicated in patients with symptomatic cardiovascular disease. The aim of this study is to assess the safety and pharmacokinetics of intravenous sildenafil in cardiac surgery patients. METHODS: We conducted an open label, dose escalation study with six patients per dose level. The six doses were 2.5 mg, 5 mg or 10 mg as a bolus, either alone or followed by an additional 2 h infusion of 2.5 mg sildenafil. RESULTS: Thirty-six patients entered the trial, of which 33 completed it. The mean age was 69.9 years. One patient died during surgery, two others were removed from the trial before dosing (all at dose level 5 mg + 2.5 mg). The pharmacokinetic profile of sildenafil was similar to previously published studies. For a dose of 10 mg administered as a bolus followed by 2.5 mg administered over 2 h the results were AUC∞ 537 ng h ml-1 , Cmax 189.4 ng ml-1 and t1/2 10.5 h. The drug was well tolerated with no serious adverse events related to drug administration. Higher sildenafil doses stabilized post-surgery nitric oxide bioavailability. CONCLUSIONS: Pharmacokinetics of sildenafil during cardiopulmonary bypass were comparable to those of other patient groups. The drug was well tolerated at therapeutic plasma levels. These results support the further evaluation of sildenafil for the prevention of AKI in cardiac surgery.

Labelling, molecular modelling and biological evaluation of vardenafil: a potential agent for diagnostic evaluation of erectile dysfunction.

99mTc-tricarbonyl-vardenafil was specifically radiosynthesized for diagnostic evaluation of erectile dysfunction with a radiochemical yield ~97.2%. It was stable in saline up to 15h and in serum for more than 6h. The radiocomplex was lipophilic with a partition coefficient ~1.32 and plasma protein binding 72-76%. Its structure was determined using molecular mechanics and confirmed by NMR. In-silico docking to its target PDE5 enzyme was performed. The radiocomplex inhibitory activity was assessed and its IC50 was 0.7nM. Biodistribution in normal rats and biological evaluation in rat models of erectile dysfunction were performed. The results strongly suggested that 99mTc-tricarbonyl-vardenafil is a good candidate to image erectile dysfunction in humans.

An opportunistic study evaluating pharmacokinetics of sildenafil for the treatment of pulmonary hypertension in infants.

OBJECTIVE: The objective of this study is to assess sildenafil and N-desmethyl sildenafil (DMS) exposure in infants receiving sildenafil for the treatment of pulmonary hypertension (PH). STUDY DESIGN: Data were collected from six infants receiving sildenafil for the treatment of PH and plasma samples were collected at the time of routine laboratory blood draws. The echocardiography results were assessed for improvement in right ventricular (RV) hypertension following sildenafil treatment. RESULT: The median (range) sildenafil and DMS concentrations were 27.4 ng ml(-1) (2.6 to 434.0) and 105.5 ng ml(-1) (3.6 to 314.0), respectively. The median metabolite-to-parent ratio was higher in infants receiving co-medications that can induce cytochrome P450 (CYP) enzymes (5.2 vs 0.7). The echocardiography results showed improvement in RV hypertension for the majority of infants (5/6). CONCLUSION: The concentrations of sildenafil and DMS were within the previously observed ranges. Our results suggest that caution may be warranted when CYP-related co-medications are administered during sildenafil treatment for PH.

Soy polysaccharide as a novel superdisintegrant in sildenafil citrate sublingual tablets: preparation, characterization, and in vivo evaluation.

Sildenafil citrate (SC), a drug used to treat erectile dysfunction, is available in tablet form but has three major problems. First, the drug displays inadequate aqueous solubility, which delays the onset of its action. Second, the drug undergoes extensive first-pass metabolism, resulting in a low (40%) bioavailability. Third, the gastrointestinal effects of SC include dyspepsia and a burning sensation. The aim of this research was to prepare SC as a sublingual tablet utilizing soy polysaccharide as novel superdisintegrant to mitigate the abovementioned problems. The solubility of SC in various hydrophilic carrier solutions was estimated in order to prepare the drug as a coprecipitate. Sublingual tablets were prepared and evaluated for hardness, friability, drug content, wetting time, water absorption ratio, in vitro dispersion time, dissolution rate, and stability study. The pharmacokinetic study of the tablets was carried out on healthy volunteers. The results indicated that the co-precipitation of SC with polyvinylpyrollidone K30 enhanced the solubility of SC by more than eight folds. The tablet contained 8% soy polysaccharide as a superdisintegrant and provided a wetting time of 25 seconds, and in vitro dispersion times of 55 seconds. The drug release was found to be 95.6%. The prepared SC sublingual tablet also exhibited a rapid onset of action, and its bioavailability was enhanced 1.68-fold compared with that of the marketed tablets. It can be concluded that SC sublingual tablet is a promising formulation that results in higher solubility, faster dispersion and onset of action, higher release rate, and higher systemic bioavailability.

Pharmacokinetics and tolerability of oral sildenafil in adults with cystic fibrosis lung disease.

RATIONALE: Airway inflammation is central to cystic fibrosis (CF) pathophysiology. Pre-clinical models have shown that phosphodiesterase inhibitors (PDEi) like sildenafil have anti-inflammatory activity. PDEi have not been studied in CF subjects. OBJECTIVES: We evaluated the pharmacokinetics, tolerability, and safety of sildenafil in subjects with CF. Sputum biomarkers were used to explore efficacy. METHODS: An open-label pilot study of oral sildenafil administration was conducted in adults with mild to moderate CF lung disease. Subjects received oral sildenafil 20 or 40 mg p.o. t.i.d. for 6 weeks. MEASUREMENTS AND MAIN RESULTS: Twenty subjects completed the study. Estimated elimination rate constants were statistically different in subjects with CF compared to previously published non-CF subjects. Side effects were generally mild. There were no drug-related serious adverse events. Sputum neutrophil elastase activity decreased. CONCLUSIONS: Subjects with CF may eliminate sildenafil at a faster rate than non-CF subjects. Sildenafil administration was safe in subjects with CF and decreased sputum elastase activity. Sildenafil warrants further study as an anti-inflammatory in CF.

Management of benign prostatic hyperplasia: role of phosphodiesterase-5 inhibitors.

Several studies have highlighted a strong association between benign prostatic hyperplasia/lower urinary tract symptoms (BPH/LUTS) and erectile dysfunction (ED), particularly in elderly men. Many epidemiological trials, such as in vitro and in vivo studies, have reported the emerging role of metabolic syndrome, including abdominal obesity, impaired glucose metabolism, hypertriglyceridemia, low high-density lipoprotein cholesterol, and hypertension, in the development and progression of urinary and sexual symptoms. Moreover, many authors have focused their studies on the identification of all the shared pathogenetic mechanisms of LUTS/BPH and ED, including alteration of cyclic guanosine monophosphate and RhoA-ROCK pathways or vascular and neurogenic dysfunction. All these are potential targets for proposed phosphodiesterase type 5 inhibitors (PDE5-Is). Therefore, several trials have recently been designed to evaluate the role of PDE5-Is alone or in combination with conventional treatment for BPH, such as α-adrenergic blockers, in men affected by LUTS/BPH, with or without ED. Different PDE5-Is are in clinical use worldwide and currently six of them are licensed for the oral treatment of ED. All these compounds differ in pharmacokinetic factors, with influence on drug action, and subsequently in the overall safety and efficacy profile.

Sildenafil exposure and hemodynamic effect after Fontan surgery.

OBJECTIVE: Determine sildenafil exposure and hemodynamic effect in children after Fontan single-ventricle surgery. DESIGN: Prospective dose-escalation trial. SETTING: Single-center pediatric catheterization laboratory. PATIENTS: Nine children post Fontan single-ventricle surgical palliation and undergoing elective cardiac catheterization: median (range) age and weight, 5.2 years (2.5-9.4 yr) and 16.3 kg (9.5-28.1 kg). Five children (55%) were boys, and six of nine (67%) had a systemic right ventricle. INTERVENTIONS: Catheterization and echocardiography performed before and immediately after single-dose IV sildenafil (0.25, 0.35, or 0.45 mg/kg over 20 min). MEASUREMENTS AND MAIN RESULTS: Peak sildenafil and desmethyl sildenafil concentration, change in hemodynamic variables measured by cardiac catheterization and echocardiography. Maximum sildenafil concentrations ranged from 124 to 646 ng/mL and were above the in vitro threshold needed for 77% phosphodiesterase type-5 inhibition in eight of nine children and 90% inhibition in seven of seven children with doses more than or equal to 0.35 mg/kg. Sildenafil improved stroke volume (+22%, p = 0.05) and cardiac output (+10%, p = 0.01) with no significant change in heart rate in eight of nine children. Sildenafil also lowered systemic (-16%, p = 0.01) and pulmonary vascular resistance index in all nine children (median baseline pulmonary vascular resistance index 2.4 [range, 1.3-3.7]; decreased to 1.9 [0.8-2.7] Wood Units × m; p = 0.01) with no dose-response effect. Pulmonary arterial pressures decreased (-10%, p = 0.02) and pulmonary blood flow increased (9%, p = 0.02). There was no change in myocardial performance index and no adverse events. CONCLUSIONS: After Fontan surgery, sildenafil infusion acutely improves cardiopulmonary hemodynamics, increasing cardiac index. For the range of doses studied, exposure was within the acute safety range reported in adult subjects.

Sildenafil exposure and hemodynamic effect after stage II single-ventricle surgery.

OBJECTIVES: To determine sildenafil exposure and hemodynamic effect in children after stage II single-ventricle surgery. DESIGN: Prospective, dose escalation trial. SETTING: Single-center, pediatric catheterization laboratory. PATIENTS: Twelve children poststage II single-ventricle surgical palliation and undergoing elective cardiac catheterization: median age 1.9 years (range, 0.8, 4.0), weight 11 kg (8, 13), nine females, and 10 with a single right ventricle. INTERVENTIONS: Catheterization and echocardiography performed before and immediately after single-dose IV sildenafil (0.125, 0.25, 0.35, or 0.45 mg/kg over 20 min). MEASUREMENTS: Peak sildenafil and desmethyl sildenafil concentration, change in hemodynamic parameters measured by cardiac catheterization and echocardiography including indexed pulmonary vascular resistance, and myocardial performance. MAIN RESULTS: Maximum sildenafil concentrations ranged from 92 to 775 ng/mL and were above the in vitro threshold needed for 77% phosphodiesterase type 5 (PDE-5) inhibition in 80% of subjects and 90% inhibition in 80% of subjects with doses ≥0.35 mg/kg. Sildenafil lowered pulmonary vascular resistance index in all 12 subjects (median pulmonary vascular resistance index 2.2 [range, 1.6, 7.9]; decreased to 1.7 [1.2, 5.4] WU × m; p < 0.01) with no dose-response effect. Sildenafil improved pulmonary blood flow (+8% [0, 20], p = 0.04) and saturations (+2% [0, 16], p = 0.04) in those with baseline pulmonary vascular resistance index ≥ 2 WU × m (n = 7). Change in saturations correlated inversely with change in pulmonary vascular resistance index (r = 0.74, p < 0.01). Sildenafil also lowered mean blood pressure (-12% [-20, +10]; p = 0.04). There was no change in cardiac index and no effect on myocardial performance. There were no adverse events. CONCLUSIONS: Sildenafil demonstrated nonlinear exposure with high interindividual variability but was well tolerated and effectively lowered pulmonary vascular resistance index in all subjects. Sildenafil did not acutely improve myocardial performance or increase cardiac index.

SOP conservative (medical and mechanical) treatment of erectile dysfunction.

INTRODUCTION: Erectile dysfunction (ED) is the most frequently treated male sexual dysfunction worldwide. ED is a chronic condition that exerts a negative impact on male self-esteem and nearly all life domains including interpersonal, family, and business relationships. AIM: The aim of this study is to provide an updated overview on currently used and available conservative treatment options for ED with a special focus on their efficacy, tolerability, safety, merits, and limitations including the role of combination therapies for monotherapy failures. METHODS: The methods used were PubMed and MEDLINE searches using the following keywords: ED, phosphodiesterase type 5 (PDE5) inhibitors, oral drug therapy, intracavernosal injection therapy, transurethral therapy, topical therapy, and vacuum-erection therapy/constriction devices. Additionally, expert opinions by the authors of this article are included. RESULTS: Level 1 evidence exists that changes in sedentary lifestyle with weight loss and optimal treatment of concomitant diseases/risk factors (e.g., diabetes, hypertension, and dyslipidemia) can either improve ED or add to the efficacy of ED-specific therapies, e.g., PDE5 inhibitors. Level 1 evidence also exists that treatment of hypogonadism with total testosterone < 300 ng/dL (10.4 nmol/L) can either improve ED or add to the efficacy of PDE5 inhibitors. There is level 1 evidence regarding the efficacy and safety of the following monotherapies in a spectrum-wide range of ED populations: PDE5 inhibitors, intracavernosal injection therapy with prostaglandin E1 (PGE1, synonymous alprostadil) or vasoactive intestinal peptide (VIP)/phentolamine, and transurethral PGE1 therapy. There is level 2 evidence regarding the efficacy and safety of the following ED treatments: vacuum-erection therapy in a wide range of ED populations, oral L-arginine (3-5 g), topical PGE1 in special ED populations, intracavernosal injection therapy with papaverine/phentolamine (bimix), or papaverine/phentolamine/PGE1 (trimix) combination mixtures. There is level 3 evidence regarding the efficacy and safety of oral yohimbine in nonorganic ED. There is level 3 evidence that combination therapies of PDE5 inhibitors + either transurethral or intracavernosal injection therapy generate better efficacy rates than either monotherapy alone. There is level 4 evidence showing enhanced efficacy with the combination of vacuum-erection therapy + either PDE5 inhibitor or transurethral PGE1 or intracavernosal injection therapy. There is level 5 evidence (expert opinion) that combination therapy of PDE5 inhibitors + L-arginine or daily dosing of tadalafil + short-acting PDE5 inhibitors pro re nata may rescue PDE5 inhibitor monotherapy failures. There is level 5 evidence (expert opinion) that adding either PDE5 inhibitors or transurethral PGE1 may improve outcome of penile prosthetic surgery regarding soft (cold) glans syndrome. There is level 5 evidence (expert opinion) that the combination of PDE5 inhibitors and dapoxetine is effective and safe in patients suffering from both ED and premature ejaculation.

Characterization of efflux transport of the PDE5 inhibitors, vardenafil and sildenafil.

OBJECTIVES: We aimed to characterize the efflux transport properties of vardenafil and sildenafil, and to compare the kinetics of these compounds via efflux transporters such as P-gp, BCRP and MRP2. METHODS: We measured the basal-to-apical and apical-to-basal transport of vardenafil and sildenafil within the concentration range of 1-100 µm using MDCKII cells overexpressing P-gp, BCRP and MRP2, and Caco-2 cells. KEY FINDINGS: Vardenafil had a much greater basal-to-apical than apical-to-basal transport rate in MDCKII cells overexpressing P-gp, BCRP and MRP2. Sildenafil showed P-gp- and BCRP-mediated efflux transport, but did not seem to be pumped out via MRP2 transporters. Consequently, the absorptive transport of vardenafil and sildenafil in Caco-2 cells increased linearly over the concentration range of 1-100 µm, whereas the secretory transport of these drugs was saturable and inhibited by the presence of specific inhibitors of P-gp and BCRP. MK571, a representative MRP2 inhibitor, inhibited the basal-to-apical transport of vardenafil, but not of sildenafil. CONCLUSION: The involvement of P-gp, BCRP and MRP2 for vardenafil and the involvement of P-gp and BCRP for sildenafil in the secretory transport with linear absorptive transport may contribute to the limited intestinal absorption of these drugs.

The discovery of UK-369003, a novel PDE5 inhibitor with the potential for oral bioavailability and dose-proportional pharmacokinetics.

This paper describes our recent efforts to design and synthesise potent and selective PDE5 inhibitors and the use of in vitro predictors of clearance, absorption and permeability to maximise the potential for dose-proportional pharmacokinetics and good oral bioavailability in man. Optimisation of the preclinical profile resulted in the identification of UK-369003 (19a) and its nomination as a clinical candidate. The clinical pharmacokinetic and safety profile has enabled us to progress the compound to test its efficacy in patients with lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH) and a paper describing its efficacy has recently been published.