TISSUE SELECTIVITY OF KMD-3213, AN α 1 -ADRENOCEPTOR ANTAGONIST, IN HUMAN PROSTATE AND VASCULATURE

Understanding the side effects of chronic silodosin administration via untargeted metabolomics approach

BACKGROUND

Precision medicine, which looks for high efficacy and low toxicity in therapies, has increased in popularity with omics technology. This work aims to discover novel and low-toxicity therapy options by examining the complex relationship between silodosin-induced side effects and the metabolomic profiles associated with its administration.

MATERIALS AND METHODS

The plasma samples of the control group and silodosin-treated rats were analyzed by LC-Q-TOF-MS/MS. Employing XCMS and MetaboAnalyst software, MS/MS data processed to detect compounds and investigate metabolic pathways. MATLAB 2019b was used for data categorization and multivariate analysis. A thorough comparison of METLIN and HMDB databases revealed 41m/z values with significant differences between the drug-treated and control groups (p <0.01 and fold analysis≥1.5).

RESULTS

According to multivariate data analysis, 17-β-estradiol, taurocholic acid, L-kynurenine, N-formylkynurenine, D-glutamine, L-arginine, prostaglandin H2, prostaglandine G2, 15-keto-prostaglandin E2, calcidiol, thromboxane A2, 5'-methylthioadenosine, L-methionine and S-adenosylmethionine levels changed significantly compared to the control group. Differences in the metabolisms of glycerophospholipid, tyrosine, phenylalanine, arachidonic acid, cysteine and methionine, and biosynthesis of phenylalanine, tyrosine, and tryptophan, and aminoacyl-tRNA have been successfully demonstrated by metabolic pathway analysis. According to this study, vitamin D, D-glutamine, and L-arginine supplements can be recommended to prevent side effects such as fatigue, intraoperative floppy iris syndrome, blurred vision, and dizziness in the treatment of silodosin. Silodosin treatment negatively affected the immune system by affecting the kynurenine and tryptophan metabolism pathways.

CONCLUSIONS

The study is a guide for silodosin treatments that offer low side effects and high therapeutic effect within the scope of precision medicine.

Evolving Role of Silodosin for the Treatment of Urological Disorders – A Narrative Review

Use of α-androgenic receptor blockers remains a mainstay therapeutic approach for the treatment of urological diseases. Silodosin is recommended over other α-blockers for the treatment of lower urinary tract symptoms (LUTS) and benign prostate hyperplasia (BPH), due to its high α_1A uroselectivity. Current research data suggest that silodosin is efficacious in the management of various urological diseases. Thus, we herein review the current evidence of silodosin related to its efficacy and tolerability and appraise the available literature that might ultimately aid in management of various urological conditions at routine clinical practice. Literature reveals that silodosin is beneficial in improving nocturia events related to LUTS/BPH. Silodosin exerts effect on relaxing muscles involved in detrusor obstruction, therefore prolonging the need for patients undergoing invasive surgery. Silodosin treatment, either as a monotherapy or combination, significantly improves International Prostate Symptom Score (IPSS) including both storage and voiding symptoms in patients with BPH/LUTS. Patients on other treatment therapies such as phosphodiesterase 5 inhibitors or other α-blockers are well managed with this drug. Steadily, silodosin has proved beneficial in the treatment of other urological disorders such as chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), overactive bladder/acute urinary retention (AUR), premature ejaculation (PE), and prostate cancer post brachytherapy-induced progression. In patients with distal ureteral stones, silodosin treatment is beneficial in decreasing stone expulsion time without affecting stone expulsion rate or analgesic need. Moreover, there were significant improvements in intravaginal ejaculation latency time, quality of life scores, and decrease in PE profile among patients with PE. Silodosin has also demonstrated promising results in increasing the likelihood of successful trial without catheter in patients with AUR and those taking antihypertensive drugs. Reports from Phase II studies have shown promising role of silodosin in the treatment of CP/CPPS as well as facilitating ureteral stone passage. From the robust data in this review, further silodosin treatment strategies in the management of different urological conditions need to be focused on.

Extra- and intracranial blood flow regulation during the cold pressor test: influence of age

We determined how the extra- and intracranial circulations respond to generalized sympathetic activation evoked by a cold pressor test (CPT) and whether this is affected by healthy aging. Ten young [23 ± 2 yr (means ± SD)] and nine older (66 ± 3 yr) individuals performed a 3-min CPT by immersing the left foot into 0.8 ± 0.3°C water. Common carotid artery (CCA) and internal carotid artery (ICA) diameter, velocity, and flow were simultaneously measured (duplex ultrasound) along with middle cerebral artery and posterior cerebral artery mean blood velocity (MCAv_mean and PCAv_mean) and cardiorespiratory variables. The increases in heart rate (~6 beats/min) and mean arterial blood pressure (~14 mmHg) were similar in young and older groups during the CPT (P < 0.01 vs. baseline). In the young group, the CPT elicited an ~5% increase in CCA diameter (P < 0.01 vs. baseline) and a tendency for an increase in CCA flow (~12%, P = 0.08); in contrast, both diameter and flow remained unchanged in the older group. Although ICA diameter was not changed during the CPT in either group, ICA flow increased (~8%, P = 0.02) during the first minute of the CPT in both groups. Whereas the CPT elicited an increase in MCAv_mean and PCAv_mean in the young group (by ~20 and ~10%, respectively, P < 0.01 vs. baseline), these intracranial velocities were unchanged in the older group. Collectively, during the CPT, these findings suggest a differential mechanism(s) of regulation between the ICA compared with the CCA in young individuals and a blunting of the CCA and intracranial responses in older individuals.NEW & NOTEWORTHY Sympathetic activation evoked by a cold pressor test elicits heterogeneous extra- and intracranial blood vessel responses in young individuals that may serve an important protective role. The extra- and intracranial responses to the cold pressor test are blunted in older individuals.

A Randomized, Open-Label, Comparative Study of Efficacy and Safety of Tolterodine Combined with Tamsulosin or Doxazosin in Patients with Benign Prostatic Hyperplasia

Background

Benign prostatic hyperplasia (BPH), a common disease in men over age 50 years, often causes bladder outlet obstruction and lower urinary tract symptoms (LUTS). Alpha blockers in combination with muscarinic receptor antagonists may have the potential to improve symptoms. This study aimed to assess the efficacy and safety of doxazosin or tamsulosin combined with tolterodine extend release (ER) in patients with BPH and LUTS.

Material/Methods

In a prospective, randomized, open-label study (ChiCTR-IPR-15005763), 220 consecutive men with BPH and LUTS were allocated to receive doxazosin 4 mg and tolterodine ER 4 mg per day (doxazosin group) or tamsulosin 0.2 mg and tolterodine ER 4 mg per day (tamsulosin group). Treatment lasted 12 weeks. The primary endpoint was the international prostatic symptom score (IPSS). Secondary endpoints were quality of life (QoL) and maximum flow rate (Q_max), which were evaluated at 0, 6, and 12 weeks, and urodynamic parameters assessed at 0 and 12 weeks.

Results

A total of 192 patients completed the trial. Baseline measurements showed no differences between the groups. After 6 weeks, IPSS improved in both groups and QoL was significantly better in the doxazosin group (P=0.01). After 12 weeks, Q_max, IPSS, QoL, intravesical pressure (Pves), and bladder compliance (BC) in the doxazosin group were significantly better than in the tamsulosin group (P=0.03, P<0.001, P<0.001, P=0.027, and P=0.044, respectively).

Conclusions

Administration of alpha blockers combined with muscarinic receptor blocker for 12 weeks improved LUTS in men with BPH.

Agonist pharmacology at recombinant α1A - and α1L -adrenoceptors and in lower urinary tract α1 -adrenoceptors

BACKGROUND AND PURPOSE

Two distinct α1 -adrenoceptor phenotypes (α1A and α1L ) have recently been demonstrated to originate from a single α1A -adrenoceptor gene. Here, we examined the agonist profiles of recombinant α1A and α1L phenotypes and of lower urinary tract (LUT) α1 -adrenoceptors.

EXPERIMENTAL APPROACH

A series of drugs (A61603, Ro 115-1240, NS-49 , MK017 and ESR1150) originally developed for stress urinary incontinence (SUI) therapy were used to stimulate recombinant α1A - and α1L -adrenoceptor phenotypes, and their potencies and intrinsic activity estimated from Ca(2+) responses. Agonist-induced contractions were also examined in LUT tissues of rats and humans and in human mesenteric artery and rat tail artery.

KEY RESULTS

All the drugs were potent agonists of the α1A -adrenoceptor compared with the α1L -adrenoceptor phenotype. Among them, Ro 115-1240 was shown to be an α1A -specific partial agonist that produced partial contractions through α1A -adrenoceptors in rat prostate and tail artery, but not in the other LUT tissues and human mesenteric artery. In contrast, P-come 102 showed full agonist activity at α1A - and α1L -adrenoceptors, but was less selective than noradrenaline for α1A -adrenoceptors. Like noradrenaline, P-come 102 was highly potent at inducing contractions in all of the LUT tissues tested. However, the potency and intrinsic activity of P-come 102 were significantly lower than those of noradrenaline in human mesenteric artery.

CONCLUSIONS AND IMPLICATIONS

The α1A - and α1L -adrenoceptor phenotypes and LUT α1 -adrenoceptors were demonstrated to have distinct agonist profiles. As adrenergic contractions in LUT are predominantly mediated through α1L -adrenoceptors, the development of α1L -selective agonists may provide clinically useful drugs for SUI therapy.

Effects by silodosin on the partially obstructed rat ureter in vivo and on human and rat isolated ureters

BACKGROUND AND PURPOSE

α1 -adrenoceptor (-AR) antagonists may facilitate ureter stone passage in humans. We aimed to study effects by the α1 A -AR selective antagonist silodosin (compared to tamsulosin and prazosin) on ureter pressures in a rat model of ureter obstruction, and on contractions of human and rat isolated ureters.

EXPERIMENTAL APPROACH

After ethical approval, ureters of male rats were cannulated beneath the kidney pelvis for in vivo ureteral intraluminal recording of autonomous peristaltic pressure waves. A partial ureter obstruction was applied to the distal ureter. Mean arterial blood pressure (MAP) was recorded. Approximate clinical and triple clinical doses of the α1 -AR antagonists were given intravenously. Effects by the α1 -AR antagonists on isolated human and rat ureters were studied in organ baths.

KEY RESULTS

Intravenous silodosin (0.1-0.3 mg kg(-1) ) or prazosin (0.03-0.1 mg kg(-1) ) reduced obstruction-induced increases in intraluminal ureter pressures by 21-37% or 18-40% respectively. Corresponding effects by tamsulosin (0.01 or 0.03 mg kg(-1) ) were 9-20%. Silodosin, prazosin and tamsulosin reduced MAP by 10-12%, 25-26% (P < 0.05), or 18-25% (P < 0.05) respectively. When effects by the α1 A -AR antagonists on obstruction-induced ureter pressures were expressed as a function of MAP, silodosin had six- to eightfold and 2.5- to eightfold better efficacy than tamsulosin or prazosin respectively. Silodosin effectively reduced contractions of both human and rat isolated ureters.

CONCLUSIONS AND IMPLICATIONS

Silodosin inhibits contractions of the rat and human isolated ureters and has excellent functional selectivity in vivo to relieve pressure-load of the rat obstructed ureter. Silodosin as pharmacological ureter stone expulsive therapy should be clinically further explored.

Efficacy and Safety of the Selective α1A-Adrenoceptor Blocker Silodosin for Severe Lower Urinary Tract Symptoms Associated With Benign Prostatic Hyperplasia: A Prospective, Single-Open-Label, Multicenter Study in Korea

Purpose

To evaluate the efficacy and safety of silodosin 8 mg once daily in a 12-week treatment of subjects with severe lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH).

Materials and Methods

A total of 100 subjects from 10 urology centers in Korea were included in this study. The inclusion criteria were as follows: age ≥50 years, International Prostate Symptom Score (IPSS) ≥20, quality of life (QoL) score ≥3, urine volume ≥120 mL and maximal urinary flow rate (Qmax) <15 mL/s, and postvoid residual volume (PVR) <100 mL. We assessed the improvement of LUTS with change in IPSS, QoL score, Qmax, PVR, and adverse events at baseline and 4 and 12 weeks after treatment with silodosin 8 mg once daily.

Results

The IPSS values were 23.27±3.34, 15.89±6.26, and 13.80±6.31 at baseline, 4, and 12 weeks, respectively, with significant improvements (p<0.0001, p=0.0214, respectively). QoL scores were 4.44±0.85, 3.38±1.20, and 3.04±1.20 at baseline, 4, and 12 weeks, respectively, and the differences were statistically significant (p<0.0001). There was a significant difference in Qmax between baseline and 12 weeks (p<0.0001) but not in PVR (p=0.9404) during the clinical trial. The most frequent adverse event in this study was ejaculation failure with 13 cases. However, no subject dropped out because of ejaculation failure, and in 12 of the 13 cases it was fully resolved without further treatment.

Conclusions

Silodosin 8 mg once daily may be effective and safe in Korean patients with severe LUTS associated with BPH.

Naftopidil for the treatment of benign prostate hyperplasia: a systematic review

OBJECTIVES

The aim of the study was to systematically review the effects of the adrenoreceptor A1D antagonist naftopidil in the management of lower urinary tract symptoms (LUTS).

METHODS

A structured and comprehensive MEDLINE search was conducted for original articles, reviews, and metanalyses assessing the clinical pharmacology as well as the safety of naftopidil in the treatment of LUTS secondary to BPH. English-language publications dating from 1950 to 2013 were considered.

RESULTS

In the considered timeframe, 14 randomized clinical trials (RCT) were reported. Overall, the outcome measures assessed in the various reports included in the present review were changes from baseline in: International Prostate Symptom Score (IPSS), quality of life (QoL) score, maximum urinary flow rate (Qmax), residual volume (PVR), and adverse effects. Although additional well designed, worldwide, placebo-controlled and randomized studies are necessary to confirm the long-term outcomes of naftopidil pharmacotherapy, current data suggest that naftopidil administration in BPH patients provides comparable improvements in total IPSS, QoL, and urinary symptoms from baseline relative to 0.2 mg/d tamsulosin and 8 mg/d silodosin. However, improvements in Qmax are generally less with naftopidil than with tamsulosin. Reported adverse effects related to naftopidil administration are negligible and usually mild.

CONCLUSION

It remains unknown whether the data reported on naftopidil in the Japanese population are applicable in symptomatic BPH patients from western countries given that: (1) no English-language clinical trials have compared naftopidil to placebo in Western countries; (2) all clinical trials available were carried out in Japan; (3) in the comparative studies with tamsulosin, the dose of this drug was lower than the recommended dose in Western countries; (4) no data from long-term clinical trials evaluating drug safety beyond 18 weeks.

[Medical therapy of lower urinary tract symptoms [corrected]]

Male lower urinary tract symptoms (LUTS) include storage and voiding disorders and should be carefully evaluated before the start of any treatment. Medical therapy is directed at improving symptoms and reducing the risk of progression in order to improve quality of life and prevent complications, such as acute urinary retention, or the need for surgical intervention. Careful assessment of the individual complaints helps to identify the best drug which should be adapted to each individual patient's risk profile. At present, α(1)-adrenoreceptor inhibitors and 5-alpha reductase inhibitors and their combination form the gold standard for pharmacological treatment. In addition, anticholinergic agents are increasingly being used as monotherapy or in combination with α1-adrenocepetor inhibitors for patients with predominant storage disorders while phosphodiesterase 5 (PDE5) inhibitors may be suitable for patients suffering from LUTS and concomitant erectile dysfunction.

Silodosin inhibits noradrenaline-activated transcription factors Elk1 and SRF in human prostate smooth muscle

Background

The transcription factors Elk1 and serum response factor (SRF) are central regulators of cell cycle and phenotype in various cell types. Elk1 is activated by phosphorylation (serine-383), while activation of SRF requires its co-factor, myocardin. Activation of Elk1 and SRF results in binding to specific DNA sequences in promoter regions, and may be induced by adrenergic receptor activation in different organs.

Objective

To examine the effects of adrenergic stimulation on Elk1 and SRF in the human prostate and the ability of the highly selective α1A-adrenoceptor antagonist, silodosin, on transcription factor activation.

Methods

Prostate tissue was obtained from patients undergoing radical prostatectomy. Expression of Elk1, SRF, and myocardin was estimated by Western blot and immunohistochemistry. Colocalizations were studied by double immunofluorescence staining. Noradrenaline- (NA-) and phenylephrine- (PE-) induced phosphorylation of Elk1 was assessed by Western blot analysis using a phospho-specific antibody. NA-induced activation of Elk1 and SRF was investigated by electrophoretic mobility shift assay (EMSA).

Results

Immunoreactivity for Elk1, SRF, and myocardin was observed in stromal cells of tissues from each patient. In fluorescence stainings, SRF colocalized with myocardin and α-smooth muscle actin (αSMA). Stimulation of prostate tissues with PE (10 µM) or NA (30 µM) increased the phosphorylation of Elk1 at serine-383. NA-induced Elk1 activation was confirmed by EMSA, where a NA-induced binding of Elk1 to the DNA sequence TTTGCAAAATGCAGGAATTGTTTTCACAGT was observed. Similarly, NA caused SRF binding to the SRF-specific DNA sequence CCATATTAGGCCATATTAGG. Application of silodosin (3 µM) to prostate tissues reduced the activity of Elk1 and SRF in NA-stimulated tissues.

Conclusions

Silodosin blocks the activation of the two transcription factors, Elk1 and SRF, which is induced by noradrenaline in the human prostate. A role of α1-adrenoceptors beyond smooth muscle contraction may be considered, which includes a function in transcriptional regulation.

Benign prostatic hyperplasia: from bench to clinic

Benign prostatic hyperplasia (BPH) is a prevalent disease, especially in old men, and often results in lower urinary tract symptoms (LUTS). This chronic disease has important care implications and financial risks to the health care system. LUTS are caused not only by mechanical prostatic obstruction but also by the dynamic component of obstruction. The exact etiology of BPH and its consequences, benign prostatic enlargement and benign prostatic obstruction, are not identified. Various theories concerning the causes of benign prostate enlargement and LUTS, such as metabolic syndrome, inflammation, growth factors, androgen receptor, epithelial-stromal interaction, and lifestyle, are discussed. Incomplete overlap of prostatic enlargement with symptoms and obstruction encourages focus on symptoms rather than prostate enlargement and the shifting from surgery to medicine as the treatment of BPH. Several alpha antagonists, including alfuzosin, doxazosin, tamsulosin, and terazosin, have shown excellent efficacy without severe adverse effects. In addition, new alpha antagonists, silodosin and naftopidil, and phosphodiesterase 5 inhibitors are emerging as BPH treatments. In surgical treatment, laser surgery such as photoselective vaporization of the prostate and holmium laser prostatectomy have been introduced to reduce complications and are used as alternatives to transurethral resection of the prostate (TURP) and open prostatectomy. The status of TURP as the gold standard treatment of BPH is still evolving. We review several preclinical and clinical studies about the etiology of BPH and treatment options.

Safety and pharmacokinetic studies of silodosin, a new α1A-adrenoceptor selective antagonist, in healthy Chinese male subjects

The objectives of the study were to assess the safety and pharmacokinetics of silodosin capsules in 82 healthy male Chinese subjects. To evaluate the safety after single-dosing escalation, 40 subjects were equally divided into 4 groups (2, 4, 8, 12 mg) by a randomized, double-blind and placebo-controlled design. To assess the pharmacokinetics after single-dosing, 30 subjects were equally divided into 3 groups (4, 8, 12 mg). To assess the safety and pharmacokinetics via multiple-dosing, 12 subjects were included as a group (4 mg once daily at day 1 and day 7; 4 mg twice daily at day 2 through day 6). The safety observations showed that mild adverse events, including postural hypotension, dizziness, and headache, were observed. After single-dosing at doses of 4, 8, and 12 mg, the mean area under the concentration-time curve from 0 to 36 h (AUC(0-36)) values were 136.82±46.38, 270.17±54.66, and 474.63±108.50 µg/l·h and the mean maximal silodosin concentration in plasma (C(max)) values were 26.70±7.48, 48.47±12.35, and 94.07±22.59 µg/l, respectively. After multiple-dosing, the C(max) value at day 7 was 33.84±19.54 µg/l, and the AUC(0-24) value at day 7 was 193.19±68.96 µg/l·h. The accumulation ratio of the AUC value was 1.55 by comparing the multiple-dosing with the single-dosing. It is concluded that silodosin is safe and tolerated in healthy Chinese male subjects at the dosing levels used in this study. The mean C(max) and AUC values of silodosin increased proportionally with dose escalation, showing characteristics of linear pharmacokinetics.

Non-inferiority of silodosin to tamsulosin in treating patients with lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH)

What's known on the subject? and What does the study add? Silodosin administered by 4 mg twice daily is as effective as tamsulosin 0.2 mg daily in treating patients with LUTS associated with BPH. Relative to tamsulosin, silodosin has less cardiovascular side effects as judged by the minimal changes of blood pressure and pulse rats after treatment.

OBJECTIVE

• To test the hypothesis that the efficacy of silodosin would not be inferior to tamsulosin in treating patients with lower urinary tract symptoms associated with benign prostate hyperplasia (BPH).

PATIENTS AND METHODS

• At nine medical centres, 209 patients with an International Prostate Symptom Score (IPSS) of ≥13 were randomized to silodosin (4 mg twice daily) or tamsulosin (0.2 mg once daily) for 12 weeks. • The primary efficacy measure was the mean change from baseline to endpoint in IPSS. • The non-inferiority margin of the IPSS change was set at 1.0. • Secondary efficacy measures included change in maximal urinary flow rate (Q(max)) and health-related quality of life (HRQL) score.

RESULTS

• Of the 170 (81.3%) patients who completed the study, 86.2% in the silodosin group vs 81.9% in the tamsulosin group achieved a ≥25% decrease in IPSS (P= 0.53). • The mean difference (silodosin minus tamsulosin) in IPSS change from baseline was -0.60 (95% confidence interval -2.15, 0.95), inferring the non-inferiority of silodosin to tamsulosin. • The mean changes in the Q(max) and HRQL score from baseline were comparable between the groups (both, P > 0.05). Although patients receiving silodosin had a significantly higher incidence of abnormal ejaculation (9.7% vs tamsulosin 1.0%, P= 0.009), only 1.9% discontinued treatment. • Tamsulosin treatment resulted in a significant reduction in mean systolic blood pressure (-4.2 mmHg, within-group P= 0.004) relative to the negligible change of silodosin (-0.1 mmHg, within-group P= 0.96)

CONCLUSION

• The trial shows the non-inferiority of silodosin 4 mg twice daily to tamsulosin 0.2 mg once daily in patients with symptoms of BPH.

Silodosin: a selective alpha1A-adrenergic receptor antagonist for the treatment of benign prostatic hyperplasia

BACKGROUND

Silodosin is a new alpha(1)-adrenergic receptor antagonist that is selective for the alpha(1A)-adrenergic receptor. It was approved by the US Food and Drug Administration (FDA) in 2008 for the treatment of lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH).

OBJECTIVE

This article reviews the pharmacology, pharmacokinetics, clinical efficacy, adverse effects, drug interactions, and dosage and administration of silodosin in adult male patients with BPH.

METHODS

A search of MEDLINE (1950-October 8, 2009), International Pharmaceutical Abstracts (1970-October 8, 2009), and the Iowa Drug Information Service database (1966-October 8, 2009) was conducted using the terms silodosin, KMD-3213, benign prostatic hyperplasia, and alpha(1)-adrenergic receptor antagonist. Reports of research and review articles published in English were identified and evaluated, and the bibliographies of these articles were reviewed for additional relevant publications. A search of the FDA Web site was performed, and abstracts and posters presented at scientific meetings of the American Urological Association were reviewed.

RESULTS

By antagonizing alpha(1A)-adrenergic receptors in the prostate and urethra, silodosin causes smooth muscle relaxation in the LUT. Silodosin has greater affinity for the alpha(1A)-adrenergic receptor than for the alpha(1B)-adrenergic receptor (by a factor of 583), minimizing the propensity for blood pressure-related adverse effects mediated by alpha(1B) blockade. In 3 controlled clinical studies in patients with BPH-related LUTS (1 published; 2 presented in the prescribing information and published in a pooled analysis), patients receiving silodosin at a total daily dose of 8 mg had significant improvements in the International Prostate Symptom Score (IPSS) and maximum urinary flow rate (Q(max)) compared with those receiving placebo (both, P < 0.05). The most commonly reported adverse effect was abnormal or retrograde ejaculation (>22%), and the incidence of orthostatic hypotension was low (<3%).

CONCLUSIONS

In the small number of clinical trials reviewed, silodosin was associated with significant reductions in IPSS and Q(max) compared with placebo. To determine whether silodosin's selectivity for the alpha(1A)-adrenergic receptor translates into a clinical advantage relative to other available agents, long-term studies evaluating the comparative efficacy and tolerability of silodosin and other alpha(1)-blockers (specifically tamsulosin) are necessary.

Conversion to Silodosin in Men on Conventional α1 -Blockers for Symptomatic Benign Prostatic Hyperplasia

OBJECTIVES

α1 -blockers have commonly been used as first-line medical therapy for symptomatic benign prostatic hyperplasia (BPH). Recently, a highly selective α1A -adrenoceptor antagonist, silodosin, was developed in Japan. We examined the efficacy and safety of conversion from conventional α1 -blockers to silodosin in men with BPH.

METHODS

Conversion to silodosin was proposed to consecutive patients on conventional α1 -blockers for symptomatic BPH for at least 6 months. The effects of conversion were examined by the International Prostate Symptom Score, quality of life index, overactive bladder symptom score, peak flow rate, residual urine volume, and adverse events at 12 weeks. The efficacy of silodosin was also evaluated by patients' impression.

RESULTS

Eighty-one men underwent conversion, for the most part because of dissatisfaction with the efficacy of their current treatment in improving nocturia or weak stream. The International Prostate Symptom Score total score significantly improved from 12.7 ± 5.9 at baseline to 10.6 ± 5.4 at 4 weeks (P < 0.001) and 10.9 ± 5.8 at 12 weeks (P < 0.01). The progress was mostly due to improvement in voiding symptoms, although reduction of storage symptoms was also significant. The quality of life index also significantly decreased with conversion to silodosin. Efficacy as judged by patients' impression was 76% (37/49) at 12 weeks of treatment. None of the overactive bladder symptom score, peak flow rate, and residual urine volume exhibited significant change. No serious adverse events were observed during the study period.

CONCLUSION

Conversion to silodosin may be beneficial in men who are dissatisfied with conventional α1 -blockers for BPH, and be particularly useful in improving voiding symptoms.

Subtypes of functional alpha1-adrenoceptor

In this review, subtypes of functional alpha1-adrenoceptor are discussed. These are cell membrane receptors, belonging to the seven-transmembrane-spanning G-protein-linked family of receptors, which respond to the physiological agonist noradrenaline. alpha1-Adrenoceptors can be divided into alpha1A-, alpha1B- and alpha1D-adrenoceptors, all of which mediate contractile responses involving Gq/11 and inositol phosphate turnover. A fourth alpha1-adrenoceptor, the alpha1L-, represents a functional phenotype of the alpha1A-adrenoceptor. alpha1-Adrenoceptor subtype knock-out mice have refined our knowledge of the functions of alpha-adrenoceptor subtypes, particuarly as subtype-selective agonists and antagonists are not available for all subtypes. alpha1-Adrenoceptors function as stimulatory receptors involved particularly in smooth muscle contraction, especially contraction of vascular smooth muscle, both in local vasoconstriction and in the control of blood pressure and temperature, and contraction of the prostate and bladder neck. Central actions are now being elucidated.

Silodosin for benign prostatic hyperplasia

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical trials, and safety of silodosin, a recently approved alpha(1A)-adrenergic receptor (AR) antagonist for benign prostatic hyperplasia (BPH).

DATA SOURCES

English-only articles obtained from MEDLINE (1966-October 2009) using the search terms silodosin and KMD-3213 were reviewed. In addition, a search of International Pharmaceutical Abstracts (1970-October 2009) was conducted.

STUDY SELECTION AND DATA EXTRACTION

Available English-language articles were reviewed, as well as abstracts from available non-English articles.

DATA SYNTHESIS

Silodosin reduces urinary symptoms associated with BPH in as little as 1 day after initiation. The largest clinical trial conducted to date demonstrated a decrease in International Prostate Symptom Score of -6.4 +/- 6.63 points compared to -3.5 +/- 5.84 in patients receiving placebo (p < 0.0001). Silodosin also improved urinary flow rates by approximately 2.8 +/- 3.44 mL/sec, which is comparable to other alpha(1)-AR antagonists. The usual dose of silodosin is 8 mg once daily and should be reduced to 4 mg for patients with moderate renal dysfunction. Use is contraindicated in patients with severe renal and hepatic impairment or taking strong CYP3A4 inhibitors. In clinical trials, the most prevalent adverse effects were ejaculatory disturbances, occurring in approximately 28% of patients, although only 2.8% of patients discontinued treatment due to this adverse effect. Preliminary data suggest that, similar to other third-generation alpha(1A)-AR antagonists, silodosin has little potential to cause significant cardiovascular adverse effects such as orthostatic hypotension or syncope. To confirm these findings, long-term studies are still needed, especially in patients taking antihypertensive agents and in those with a history of intolerance to other alpha(1)-AR antagonists.

CONCLUSIONS

Silodosin was approved by the Food and Drug Administration in 2008. Long-term studies demonstrating improvement in clinically important outcomes of BPH have yet to be published. In addition, pharmacoeconomic analyses would assist in defining its current place in therapy. Until this information is available, silodosin may be best reserved as an alternative to other second- and third-generation alpha(1)-AR antagonists.

Visualization and tissue distribution of alpha1L-adrenoceptor in human prostate by the fluorescently labeled ligand Alexa-488-silodosin

PURPOSE

Although alpha(1L)-adrenoceptor is recognized as a target of alpha(1) antagonist therapy for benign prostatic hyperplasia, the most common techniques, such as immunohistochemistry and in situ hybridization, are not applicable to examine alpha(1L)-AR vs alpha(1A)-AR tissue distribution because alpha(1L)-AR is now considered another phenotype sharing the alpha(1A)-AR gene and protein molecule. We labeled the alpha(1A) and alpha(1L)-adrenoceptor selective antagonist silodosin (Kissei Pharmaceutical, Matsumoto, Japan) with the fluorophore Alexa Fluor(R) 488 (Alexa-488-silodosin) to visualize alpha(1L)-AR expression.

MATERIALS AND METHODS

Radioligand binding and functional bioassay experiments were done to assess alpha(1)-AR expression in Chinese hamster ovary cells and human prostate tissues. Confocal imaging was subsequently performed.

RESULTS

Although Alexa-488-silodosin had about 10 times lower affinity for all alpha(1)-AR subtypes than silodosin in binding and functional studies, it had high selectivity to alpha(1A) and alpha(1L)-ARs. Confocal imaging revealed clear localization of fluorescence on the membrane of Chinese hamster ovary cells expressing alpha(1A)-AR but not alpha(1B)-and alpha(1D)-ARs, and in the muscle layer of the human prostate. The fluorescent signal in Chinese hamster ovary cells disappeared in the presence of 3 nM prazosin but fluorescence was observed in the human prostate even in the presence of 100 nM prazosin.

CONCLUSIONS

Alexa-488-silodosin is a powerful fluorescent probe with high selectivity to alpha(1A) and alpha(1L)-ARs. Thus, Alexa-488-silodosin successfully visualizes the site of alpha(1L)-ARs in the muscle layer of the human prostate without losing its distinct pharmacological profile.

Silodosin: an orally active selective α1-adrenoceptor antagonist for benign prostatic hyperplasia

α1-adrenoceptor antagonists play a central role in the treatment of uncomplicated symptomatic benign prostatic hyperplasia, frequently in combination with the 5-α-reductase inhibitors such as finasteride and dutasteride. Clinically useful examples include alfuzosin, doxazosin, tamsulosin and terazosin. These can be subdivided into nonselective (doxazosin and terazosin) and uroselective (alfuzosin and tamsulosin) agents. In general, these agents appear to be equieffective. However, they can be distinguished on the basis of their adverse event profiles. Such adverse events include those due to their vasodilatory effects (dizziness, orthostatic hypotension and rhinitis), genitourinary effects (ejaculatory dysfunction) and nonspecific effects (e.g., asthenia, malaise and gastrointestinal upset). A new α1A-adrenoceptor antagonist, silodosin, has recently been approved. In most ways, it is similar to tamsulosin in its pharmacodynamic effects in vitro and in vivo (in both animals and humans). Limited clinical trial data have shown silodosin to significantly improve lower urinary tract symptoms associated with benign prostatic hyperplasia and quality of life, with effects sustainable for at least 1 year. Its adverse-event profile reflects that seen with other uroselective α-adrenoceptor antagonists with the exception of a relatively high-incidence rate of ejaculatory dysfunction (22 vs 2% with tamsulosin and 28 vs 1% with placebo). This article reviews the preclinical and clinical data concerning silodosin and introduces the reader to this new drug for the treatment of benign prostatic hyperplasia.

Ejaculatory dysfunction caused by the new alpha1-blocker silodosin: A preliminary study to analyze human ejaculation using color Doppler ultrasonography

OBJECTIVES

In order to clinically investigate the mechanism of ejaculatory dysfunction attributable to the alpha1-blocker silodosin, a real-time observation of ejaculation by healthy males was performed.

METHODS

Following intake of silodosin, a newly developed selective alpha1-blocker for benign prostatic hypertrophy, ejaculation was dynamically observed using color Doppler ultrasound in three healthy males. Normal ejaculation was also investigated in the same manner.

RESULTS

With silodosin intake, no antegrade ejaculation was observed in cases 1 or 2. In case 1, seminal fluid slowly but continuously flowed out from the seminal vesicles into the bladder. In case 2, only a small amount of seminal fluid flowed into the bladder during the ejaculatory sensation. In case 3, ejection of a small amount of semen from the external urethral orifice was observed and inflow of a small amount of seminal fluid into the bladder was also captured. Without silodosin intake, all three subjects exhibited antegrade ejaculation.

CONCLUSIONS

The mechanism of ejaculatory dysfunction is intricately related to retrograde ejaculation (retrograde inflow of seminal fluid), insufficient contraction of the seminal vesicles, and insufficient rhythmic contraction of the muscles of the pelvic floor.

Mechanical function and gene expression of alpha(1)-adrenoceptor subtypes in dog intravesical ureter

OBJECTIVES

To characterize the contractile functions and gene expression of the alpha(1)-adrenoceptor (AR) subtypes present in the dog intravesical ureter.

METHODS

In a functional study, alpha(1)-AR antagonists were evaluated against phenylephrine (alpha(1)-AR agonist)-induced contractions in dog isolated intravesical ureteral preparations. The quantitative expression of alpha(1)-AR subtype mRNA in this tissue was determined using real-time quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

In the isolated intravesical ureter, prazosin (nonselective alpha(1)-AR antagonist), silodosin (selective alpha(1A)-AR antagonist), naftopidil (selective alpha(1D)-AR antagonist), and BMY-7378 (selective alpha(1D)-AR antagonist) all shifted the concentration-contractile response curve for phenylephrine to the right. The rank order of potencies (pK(B) value) was silodosin (9.45 +/- 0.14), prazosin (8.16 +/- 0.08), naftopidil (7.39 +/- 0.19), and BMY-7378 (6.78 +/- 0.20). The alpha(1A)-AR antagonist silodosin was much more potent than the 2 alpha(1D)-AR antagonists. The rank order of mRNA expression levels among the alpha(1)-AR subtypes was alpha(1d) (72.68%), alpha(1a) (24.14%), and alpha(1b) (3.18%).

CONCLUSIONS

In the dog intravesical ureter, alpha(1A)-AR plays a major role in contraction, despite the prevalence of alpha(1D)-AR.

Different affinities of native alpha1B-adrenoceptors for ketanserin between intact tissue segments and membrane preparations

The pharmacological profiles of alpha1-adrenoceptors for ketanserin, prazosin, silodosin, and BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]decane-7,9-dione dihydrochloride) were examined under different assay conditions. Among the tested antagonists and alpha1-adrenoceptors subtypes, ketanserin showed significantly lower affinity for the alpha1B-adrenoceptor subtype in intact tissue sampled from the rat tail artery, thoracic aorta, and cerebral cortex (functional pKB and binding pKi were approximately 6), than in cerebral cortex membrane preparations or whole cell and membrane preparations of alpha1B-adrenoceptor transfected human embryonic kidney 293T (HEK 293T) cells (pKi was approximately 8). In these tissues and cells, however, ketanserin showed a similar affinity (pKi = approximately 8) for alpha1A- and alpha1D-adrenoceptors even though the assays were conducted under different conditions. In contrast, the affinities of alpha1A-, alpha1B-, and alpha1D-adrenoceptors for prazosin, silodosin, and BMY 7378 did not significantly change under different assay conditions and in different tissues. The present study reveals that the pharmacological profiles of native alpha 1B-adrenoceptors for ketanserin is strongly influenced by the assay conditions and suggest that antagonist affinity is not necessarily constant.

Identification of the alpha1L-adrenoceptor in rat cerebral cortex and possible relationship between alpha1L- and alpha1A-adrenoceptors

BACKGROUND AND PURPOSE

In addition to alpha1A, alpha1B and alpha1D-adrenoceptors (ARs), putative alpha1L-ARs with a low affinity for prazosin have been proposed. The purpose of the present study was to identify the alpha1A-AR and clarify its pharmacological profile using a radioligand binding assay.

EXPERIMENTAL APPROACH

Binding experiments with [3H]-silodosin and [3H]-prazosin were performed in intact tissue segments and crude membrane preparations of rat cerebral cortex. Intact tissue binding assays were also conducted in rat tail artery.

KEY RESULTS

[3H]-silodosin at subnanomolar concentrations specifically bound to intact tissue segments and membrane preparations of rat cerebral cortex at the same density (approximately 150 fmol mg(-1) total tissue protein). The binding sites in intact segments consisted of alpha1A and alpha1L-ARs that had different affinities for prazosin, while the binding sites in membranes showed an alpha1A-AR-like profile having single high affinity for prazosin. [3H]-prazosin also bound at subnanomolar concentrations to alpha1A and alpha1B-ARs but not alpha1L-ARs in cerebral cortex; the binding densities being approximately 200 and 290 fmol mg(-1) protein in the segments and the membranes, respectively. In the segments of tail artery, [3H]-silodosin only recognized alpha1A-ARs, whereas [3H]-prazosin bound to alpha1A and alpha1B-ARs.

CONCLUSIONS AND IMPLICATIONS

The present study clearly reveals the presence of alpha1L-ARs as a pharmacologically distinct entity from alpha1A and alpha1B-ARs in intact tissue segments of rat cerebral cortex but not tail artery. However, the alpha1L-ARs disappeared after tissue homogenization, suggesting their decomposition and/or their pharmacological profile changes to that of alpha1A-ARs.

Expressions and mechanical functions of α1-adrenoceptor subtypes in hamster ureter

We characterized the alpha(1)-adrenoceptor subtypes in hamster ureters according to gene and protein expressions and contractile function. Real-time quantitative reverse-transcription polymerase chain reaction and immunohistochemical analysis were performed to determine mRNA levels and receptor protein expressions respectively, for alpha(1A)-, alpha(1B)- and alpha(1D)-adrenoceptors in hamster ureteral smooth muscle. alpha(1)-Adrenoceptor antagonists were tested against the phenylephrine (alpha(1)-adrenoceptor agonist)-induced contraction in isolated hamster ureteral preparations using a functional experimental approach. In the smooth muscle, relative mRNA expression levels for alpha(1a)-, alpha(1b)- and alpha(1d)-adrenoceptors were 10.7%, 1.2% and 88.1%, respectively, and protein expressions were identified for alpha(1A)- and alpha(1D)-adrenoceptors immunohistochemically. Noradrenaline and phenylephrine (alpha(1)-adrenoceptor agonist) each produced a concentration-dependent tonic contraction, their pD(2) values being 6.87+/-0.08 and 6.10+/-0.05, respectively. Prazosin (nonselective alpha(1)-adrenoceptor antagonist), silodosin (selective alpha(1A)-adrenoceptor antagonist) and BMY-7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione dihydrochloride) (selective alpha(1D)-adrenoceptor antagonist) competitively antagonized the phenylephrine-induced contraction (pA(2) values, 8.60+/-0.07, 9.44+/-0.06 and 5.75+/-0.07, respectively). Chloroethylclonidine (3x10(-6) mol/L or more) produced a rightward shift in the concentration-response curve for phenylephrine. Thus, in hamster ureters, alpha(1A)- and alpha(1D)-adrenoceptors were more prevalent than the alpha(1B)-adrenoceptor, with contraction being mediated mainly via alpha(1A)-adrenoceptors. If these findings hold true for humans, alpha(1A)-adrenoceptor antagonists could become useful medication for stone passage in urolithiasis patients.

Identification of alpha-1L and alpha-1A adrenoceptors in human prostate by tissue segment binding

PURPOSE

Silodosin (KMD-3213 or [(-)-1-(3-hydroxypropyl)-5-[(2R)-2-({2-[2-(2,2,2trifluoroethoxy)phenoxy]ethyl}amino)propyl]-2,3-dihydro-1H-indole-7-carboxamide]) (Kissei Pharmaceutical Co., Ltd., Matsumoto, Japan) is a selective antagonist for alpha-1A and alpha-1L adrenoceptors. Using this tritiated ligand the 2 alpha-1 adrenoceptors were examined in binding studies with intact tissue segments and membrane preparations of human prostate, and compared with functionally identified alpha-1 adrenoceptor.

MATERIALS AND METHODS

Binding assays with tissue segments and membrane preparations of human prostate samples were performed using [3H]-silodosin and binding affinities for various drugs were estimated. In functional experiments antagonist affinities were evaluated from the inhibitory potency against the contractile response to noradrenaline.

RESULTS

[3H]-silodosin bound to intact segments and membrane preparations of human prostate with subnanomolar affinity. [3H]-silodosin binding sites in intact segments were divided into 2 distinct components with different affinities for prazosin and RS-17053 (N-[2(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha, alpha-dimethyl1H-indole-3-ethanamine hydrochloride) (Research Biochemicals International, Natick, Massachusetts), while binding in membrane preparations showed single high affinity for these drugs. [3H]-silodosin binding sites also showed high affinity for silodosin and tamsulosin but low sensitivity to BMY 7378 (8-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-8-azaspiro(4.5)decane-7,9-dione) (Research Biochemicals International) in intact segments and in membrane preparations. In functional experiments silodosin and tamsulosin potently inhibited the contractile response to noradrenaline but prazosin, RS-17053 and BMY 7378 showed low antagonistic affinity.

CONCLUSIONS

The current binding studies in human prostate samples clearly show that alpha-1L and alpha-1A adrenoceptors coexist as pharmacologically distinct entities in intact tissues but not in crude membrane preparations. Also, alpha-1 adrenoceptors involved in the contractile response to noradrenaline are the alpha-1L subtype.