KMD-3213, a novel alpha1A-adrenoceptor antagonist, potently inhibits the functional alpha1-adrenoceptor in human prostate

Selective inhibition of neurogenic, but not agonist-induced contractions by phospholipase A2 inhibitors points to presynaptic phospholipase A2 functions in contractile neurotransmission to human prostate smooth muscle

BACKGROUND

Phospholipases A2 (PLA2 ) may be involved in α1 -adrenergic contraction by formation of thromboxane A2 in different smooth muscle types. However, whether this mechanism occurs with α1 -adrenergic contractions of the prostate, is still unknown. While α1 -adrenoceptor antagonists are the first line option for medical treatment of voiding symptoms in benign prostatic hyperplasia (BPH), improvements are limited, probably by nonadrenergic contractions including thromboxane A2 . Here, we examined effects of PLA2 inhibitors on contractions of human prostate tissues.

METHODS

Prostate tissues were obtained from radical prostatectomy. Contractions were induced by electric field stimulation (EFS) and by α1 -adrenergic agonists in an organ bath, after application of the cytosolic PLA2 inhibitors ASB14780 and AACOCF3, the secretory PLA2 inhibitor YM26734, the leukotriene receptor antagonist montelukast, or of solvent to controls.

RESULTS

Frequency-dependent contractions of human prostate tissues induced by EFS were inhibited by 25% at 8 Hz, 38% at 16 Hz and 37% at 32 Hz by ASB14780 (1 µM), and by 32% at 16 Hz and 22% at 32 Hz by AACOCF3 (10 µM). None of both inhibitors affected contractions induced by noradrenaline, phenylephrine or methoxamine. YM26734 (3 µM) and montelukast (0.3 and 1 µM) neither affected EFS-induced contractions, nor contractions by α1 -adrenergic agonists, while all contractions were substantially inhibited by silodosin (100 nM).

CONCLUSIONS

Our findings suggest presynaptic PLA2 functions in prostate smooth muscle contraction, while contractions induced by α1 -adrenergic agonists occur PLA2 -independent. Lacking sensitivity to montelukast excludes an involvement of PLA2 -derived leukotrienes in promotion of contractile neurotransmission.

Silodosin: An Update on Efficacy, Safety and Clinical Indications in Urology

INTRODUCTION

Silodosin determines smooth muscle relaxation in bladder and prostate tissues, increases bladder blood flow in conditions of chronic bladder ischemia and regulates the activity of transcriptional factors responsible for stromal growth and prostate hyperplasia. Phase III trials have already demonstrated the efficacy and safety of silodosin in the treatment of patients bothered by lower urinary tract symptoms (LUTS) secondary to benign prostatic hyperplasia (BPH).

OBJECTIVE

We aimed to describe the rationality for the use of silodosin and to summarize the current literature on the use of Silodosin for the treatment of LUTS.

METHODS

PubMed and Web of Science were queried with the terms: 'silodosin' in combination (AND) with the terms 'lower urinary tract symptoms', 'LUTS', 'pathophysiology', 'symptoms' OR 'therapy'. Studies published in the last 10 years (2007-2017) in adults and core clinical journals in English were included.

RESULTS

Silodosin 8 mg once-daily was superior to placebo in improving IPSS total score, voiding subscore, storage subscore and QoL score, and at least as effective as tamsulosin 0.4 mg once-daily in all the efficacy analyses. In addition, studies assessing the effect on urodynamic parameters showed that silodosin determined a higher improvement in the bladder outlet obstruction index compared to other alpha1 adrenergic receptor antagonists. Concerning the safety profile, long-term data (after 9 months of treatment) confirmed the limited effect of silodosin on the cardiovascular and gastrointestinal systems. Although ejaculatory disorders represented the main complaint of patients taking silodosin, the discontinuation rate due to this condition remained low even in a long-term follow-up study (7.5%). Encouraging findings showed that silodosin may be administered as a medical expulsive therapy for promoting spontaneous stone passage of distal ureteral stones < 10 mm, to relieve LUTS in patients who underwent prostate cancer brachytherapy and to increase the likelihood of successful trials without a catheter in patients experiencing acute urinary retention.

CONCLUSION

Silodosin is one of the drugs approved for the treatment of BPH, being highly effective in improving not only LUTS but also urodynamic parameter impairments secondary to BPH. Moreover, it has shown efficacy as medical expulsive therapy for distal ureteral stones in previous prospective randomized trials.

FUNDING

Sponsorship for this study and article processing charges were funded by Recordati.

Silodosin for the treatment of clinical benign prostatic hyperplasia: safety, efficacy, and patient acceptability

α1-Adrenergic receptor antagonists are commonly used to treat male lower urinary tract symptoms and benign prostatic hyperplasia (BPH). We performed a literature search using PubMed, Medline via Ovid, Embase, and the Cochrane Library databases to identify studies on the treatment of BPH by silodosin. Silodosin is a novel α1-adrenergic receptor antagonist whose affinity for the α1A-adrenergic receptor is greater than that for the α1B-adrenergic receptor. Therefore, silodosin does not increase the incidence of blood pressure-related side effects, which may result from the inhibition of the α1B-adrenergic receptor. Patients receiving silodosin at a daily dose of 8 mg showed a significant improvement in the International Prostate Symptom Score and maximum urinary flow rate compared with those receiving a placebo. Silodosin also improved both storage and voiding symptoms, indicating that silodosin is effective, even during early phases of BPH treatment. Follow-up extension studies performed in the United States, Europe, and Asia demonstrated its long-term safety and efficacy. In the European study, silodosin significantly reduced nocturia compared to the placebo. Although retrograde or abnormal ejaculation was the most commonly reported symptom in these studies, only a few patients discontinued treatment. The incidence of adverse cardiovascular events was also very low. Evidence showing solid efficacy and cardiovascular safety profiles of silodosin will provide a good solution for the treatment of lower urinary tract symptoms associated with BPH in an increasingly aging society.

Prediction of alpha1-adrenoceptor occupancy in the human prostate from plasma concentrations of silodosin, tamsulosin and terazosin to treat urinary obstruction in benign prostatic hyperplasia

Alpha1-adrenoceptor antagonists are clinically useful for the improvement of urinary obstruction due to benign prostatic hyperplasia (BPH), and their therapeutic effects are mediated through the blockade of prostatic alpha(1)-adrenoceptors. The present study was undertaken to predict the magnitude and duration of alpha(1)-adrenoceptor occupancy in the human prostate after oral alpha(1)-adrenoceptor antagonists. Prostatic alpha(1)-adrenoceptor-binding parameters of silodosin were estimated by measuring specific [(3)H]prazosin binding in rat prostate after oral administration of this drug. The plasma concentration of silodosin after oral administration in rats and healthy volunteers was measured using a high-performance liquid chromatographic method. The alpha(1)-adrenoceptor-binding affinities (K(i)) of silodosin, tamsulosin, and terazosin in the human prostate and plasma concentrations of tamsulosin and terazosin were obtained from the literature. Using the alpha(1)-adrenoceptor binding parameters of silodosin in rat prostate, alpha(1)-adrenoceptor occupancy in the human prostate was estimated to be around 60-70% at 1-6 h after oral administration of silodosin at doses of 3.0, 8.1, and 16.1 micromol. Thereafter, the receptor occupancy was periodically decreased, to 24% (8.1 micromol) and 54% (16.1 micromol) 24 h later. A similar magnitude and time course of alpha(1)-adrenoceptor occupancy by silodosin in the human prostate were estimated using alpha(1)-adrenoceptor-binding affinities (K(i)) in the human prostate. Despite about two orders of differences in the plasma unbound concentrations after clinically effective oral dosages of silodosin, tamsulosin, and terazosin, there was a comparable magnitude of prostatic alpha(1)-adrenoceptor occupancy by these drugs. In conclusion, the prediction of alpha(1)-adrenoceptor occupancy in the human prostate by alpha(1)-adrenoceptor antagonists may provide the rationale for the optimum dosage regimen of these drugs in the therapy of BPH.

Effects of KMD-3213, a uroselective alpha 1A-adrenoceptor antagonist, on the tilt-induced blood pressure response in normotensive rats

KMD-3213 ((-)-1-(3-hydroxypropyl)-5-((2R)-2-[[2-([2-[(2,2,2-trifluoroethyl)oxy]phenyl]oxy)ethyl]amino]propyl)-2,3-dihydro-1H-indole-7-carboxamide), an alpha(1A)-adrenoceptor antagonist with potency similar to that of tamsulosin, is under development for the treatment of bladder outlet obstruction in patients with benign prostatic hypertrophy. In the present study, we investigated the effects of KMD-3213 on the tilt-induced blood pressure response in anesthetized normotensive rats. Male normotensive Sprague-Dawley rats were placed in the supine position on a board under cocktail anesthetization (alpha-chloralose, urethane and sodium pentobarbital). The arterial blood pressure was measured from the carotid artery. The animals were given consistent 45 degrees head-up tilt from the horizontal position, following the transient decrease in the blood pressure, and then recovery of the blood pressure to the normal level. Significant orthostatic hypotension was seen with intravenous administration of both prazosin and tamsulosin at doses over 3 micro g/kg, and these drugs completely blocked the tilt-induced blood pressure responses at 30 micro g/kg. On the other hand, these responses were still retained when KMD-3213 was administered intravenously at a dose up to 75 micro g/kg of KMD-3213. Moreover, KMD-3213 showed the highest uroselectivity of the test drugs. These results indicate that KMD-3213 is not likely to induce orthostatic hypotension and would be a useful compound for the treatment of urinary outlet obstruction in patients with benign prostatic hyperplasia.

Selective and sustained occupancy of prostatic alpha1-adrenoceptors by oral administration of KMD-3213 and its plasma concentration in rats

This study examined the ex-vivo occupancy by KMD-3213 of alpha1-adrenoceptors in the prostate and other tissues of rats in terms of tissue selectivity and duration of occupancy in relation to plasma concentration. Oral administration of KMD-3213 (0.2-20.2 micromol kg(-1), 0.5 h) dose-dependently decreased [3H]prazosin binding sites (Bmax) in the prostate (42-74%) and submaxillary gland (54-88%) compared with the control value. In contrast, there was only a slight change in the Bmax values in the spleen and cerebral cortex of KMD-3213-treated rats. The alpha1-adrenoceptor occupancy in the prostate and submaxillary gland was increased, with plasma free concentration of KMD-3213 at 0.5 h after oral administration of KMD-3213 (0.6-20.2 micromol kg(-1)). The receptor occupancy in these tissues was much greater than that in the spleen, heart or cerebral cortex. After oral administration of KMD-3213 (6.1 micromol kg(-1)), the alpha1-adrenoceptor occupancy in the prostate and submaxillary gland occurred rapidly, in parallel with the rise in the plasma concentration of the drug, and it lasted for at least 24 h, despite a remarkable decrease in the plasma concentration. It is concluded that KMD-3213 may produce fairly selective and sustained occupancy of alpha1-adrenoceptors in the prostate, a target organ for treatment of bladder outlet obstruction in patients with benign prostatic hyperplasia.

Effect of KMD-3213, an alpha1A-adrenoceptor antagonist, on the prostatic urethral pressure and blood pressure in male decerebrate dogs

BACKGROUND

KMD-3213 is an alpha1A-adrenoceptor-selective antagonist currently being developed for the treatment of urinary outlet obstruction in patients with benign prostatic hyperplasia. In the present study, the uroselectivity of KMD-3213 was evaluated and compared with that of prazosin and tamsulosin in a decerebrate dog model.

METHODS

Intercollicular decerebration was carried out in male mongrel dogs under anesthesia. The inhibitory effects of intravenously and intraduodenally administered compounds on the increase in intraurethral pressure (IUP) induced by electrical stimulation of the hypogastric nerve were estimated. Systemic blood pressure was measured simultaneously.

RESULTS

The alpha1-antagonists tested produced a dose-dependent inhibition of the induced IUP response and decreased mean blood pressure (MBP). The ID50 of KMD-3213, tamsulosin and prazosin for IUP (dose required to inhibit the increase in IUP by 50%) was 3.15, 1.73 and 11.8 microg/kg i.v., respectively, and the ED20 for the hypotensive effect (dose required to reduce MBP by 20%) was 8.03, 0.59 and 2.46 microg/kg i.v., respectively. The data indicate that uroselectivity (ED20/ID50) of KMD-3213 is 12- and 7.5-fold higher than that of prazosin and tamsulosin, respectively. When the drugs were administered intraduodenally, KMD-3213 was sufficiently absorbed from the digestive tract and continued to demonstrate at least 3.8-fold higher uroselectivity than tamsulosin.

CONCLUSION

Based on these findings, KMD-3213 appears to be an effective orally active compound for decreasing urethral resistance during micturition that does not induce any negative cardiovascular effects in patients with benign prostatic hyperplasia.

In vitro studies on L-771,688 (SNAP 6383), a new potent and selective alpha1A-adrenoceptor antagonist

L-771,688 (SNAP 6383, methyl(4S)-4-(3, 4-difluorophenyl)-6-[(methyloxy)methyl]-2-oxo-3-[(¿3-[4-(2-pyridin yl)-1-piperidinyl]propyl¿amino)carbonyl]-1,2,3, 4-tetrahydro-5-pyrimidine carboxylate) had high affinity (Ki less than or = 1 nM) for [3H]prazosin binding to cloned human, rat and dog alpha1A-adrenoceptors and high selectivity (>500-fold) over alpha1B and alpha1D-adrenoceptors. [3H]Prazosin / (+/-)-beta-[125I]-4-hydroxy-phenyl)-ethyl-aminomethylteralone ([125I]HEAT) binding studies in human and animal tissues known to contain alpha1A and non-alpha1A-adrenoceptors further demonstrated the potency and alpha1A-subtype selectivity of L-771,688. [3H]L-771,688 binding studies at the cloned human alpha1A-adrenoceptors and in rat tissues indicated that specific [3H]L-771,688 binding was saturable and of high affinity (Kd=43-90 pM) and represented binding to the pharmacologically relevant alpha1A-adrenoceptors. L-771,688 antagonized norepinephrine-induced inositol-phosphate responses in cloned human alpha1A-adrenoceptors, as well as phenylephrine or A-61603 (N-[5-4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7, 8-terahydro-naphthlen-1-yl] methanesulfonamide hydrobromide) induced contraction in isolated rat, dog and human prostate, human and monkey bladder neck and rat caudal artery with apparent Kb values of 0.02-0.28 nM. In contrast, the contraction of rat aorta induced by norepinephrine was resistant to L-771,688. These data indicate that L-771,688 is a highly selective alpha1A-adrenoceptor antagonist.

Distribution of alpha1-adrenoceptor subtype mRNA and identification of subtype responsible for renovascular contraction in human renal artery

This study was intended to quantify the amounts of the alpha1-adrenoceptor subtype mRNAs in human renal artery and to demonstrate the distribution of receptor subtypes responsible for the contraction of the renal artery. RNase protection assay showed that the mean amount of alpha1a mRNA was much greater than that of alpha1b or alpha1d mRNAs in both the main and branch renal arteries. However, the abundance of alpha1a mRNA in human renal artery was much less than in our previous data in the prostate. In situ hybridization showed that all alpha1 subtype mRNAs were localized in the smooth muscle cells of the tunica media of the artery, and the distribution pattern of these three mRNAs in the main artery was the same as in the branch artery. However, the intensity of signals for alpha1d and alpha1b antisense RNAs probes was lower than that for the alpha1a antisense RNA probe. In the functional study, concentration-response curves to noradrenaline pretreated with KMD-3213, an alpha1A/L-adrenoceptor selective antagonist, seemed to be biphasic in nature. Chloroethyclonidine (CEC) failed to inactivate the noradrenaline-induced contraction, and prazosin showed relatively low affinity with a pA2 value of 8.8. These data suggest that the alpha1A/L-adrenoceptor mediates primarily those responses to noradrenaline in this artery. The other alpha1-adrenoceptor subtypes could also mediate the secondary contractile response to noradrenaline in this artery.

Prostate selectivity of JTH-601-G1, an active metabolite of JTH-601, in dogs

OBJECTIVE

To evaluate the effect of JTH-601-G1, an active metabolite and glucuronide conjugate of JTH-601 (an alpha1-adrenoceptor antagonist), on smooth muscle contraction in canine prostate and artery, and to examine the effect of JTH-601-G1 on prostatic urethral pressure and blood pressure in anaesthetized dogs. Materials and methods Male beagle dogs were used in both an in vitro and an in vivo study. In the former, the prostate and right common carotid artery were isolated, and smooth muscle strips from the prostate and open-ring strips from the carotid artery prepared. The effects of JTH-601-G1 on phenylephrine- and noradrenaline-induced contraction were assessed in these tissues. In the in vivo study, four dogs were anaesthetized and the change in urethral pressure, blood pressure and heart rate measured continuously. Vehicle (saline) and JTH-601-G1 were then infused intravenously in increasing doses (0.33-3.3 microg/kg/min for 30 min). In three other dogs, the effect of JTH-601-G1 infusion at a higher rate (25 microg/kg/min for 3 h) on blood pressure was evaluated, and the plasma concentration of JTH-601-G1 measured using high-performance liquid chromatography-mass spectrometry.

RESULTS

Of the distinct metabolites of JTH-601, JTH-601-G1 had the most potent alpha1-adrenoceptor antagonistic effect in isolated canine prostate. JTH-601-G1 also antagonized alpha1-adrenoceptor agonist-induced contraction in common carotid artery, but the pA2 value in the artery was approximately 25 times higher than that in the prostate. In anaesthetized dogs, JTH-601-G1 decreased urethral pressure in a dose-dependent manner; at the highest dose, urethral pressure decreased by 24.5% and blood pressure by 7.0%. However, there was no significant change in heart rate at any dose. The plasma concentration of JTH-601-G1 increased with the dose of JTH-601-G1, but the concentration of both JTH-601 and other metabolites was below the detection limit. The higher JTH-601-G1 infusion rate caused blood pressure to decrease by only 6-10% even at JTH-601-G1 plasma concentrations of approximately 1500 ng/mL during the infusion. Although there was a negative correlation between mean blood pressure and plasma JTH-601-G1 concentration, the decrease in blood pressure was small compared with the reduction in urethral pressure.

CONCLUSION

JTH-601-G1 appears to be a major active metabolite of JTH-601 but with a higher selectivity for canine prostate than artery. The results also indicate that in addition to the alpha1A-adrenoceptor, the alpha1L-adrenoceptor plays an important prostatic selective role in smooth muscle contraction via the alpha1-adrenoceptor.

Design and synthesis of novel alpha(1)(a) adrenoceptor-selective antagonists. 1. Structure-activity relationship in dihydropyrimidinones

Dihydropyrimidinones such as compound 12 exhibited high binding affinity and subtype selectivity for the cloned human alpha(1a) receptor. Systematic modifications of 12 led to identification of highly potent and subtype-selective compounds such as (+)-30 and (+)-103, with high binding affinity (K(i) = 0.2 nM) for alpha(1a) receptor and greater than 1500-fold selectivity over alpha(1b) and alpha(1d) adrenoceptors. The compounds were found to be functional antagonists in human, rat, and dog prostate tissues. Compound (+)-103 exhibited excellent selectively to inhibit intraurethral pressure (IUP) as compared to lowering diastolic blood pressure (DBP) in mongrel dogs (K(b)(DBP)/K(b)(IUP) = 40) suggesting uroselectivity for alpha(1a)-selective compounds.

Pharmacological analysis of the novel, selective alpha1-adrenoceptor antagonist, KMD-3213, and its suitability as a tritiated radioligand

Pharmacological profiles of tritiated KMD-3213, a new antagonist of alpha1-adrenoceptor (AR), were examined in recombinant and native alpha1-AR, and compared with those of prazosin (PZ) and tamsulosin (YM-617). In saturation experiments, [3H]-KMD (10-2000 pM) showed high affinity for alpha1a-AR (pK(D) = 10.5). However, no significant binding to alpha1b-AR and insufficient/unsaturated binding to alpha1d-AR were observed at concentrations up to 2000 pM. In contrast, [3H]-PZ and [3H]-YM bound to all subtypes with high affinity (pK(D)>9). In competition experiments, KMD-3213 also had higher affinity for alpha1a-AR than for other two subtypes; pKi = 10.4, 8.1 and 8.6 for alpha1a-, alpha1b- and alpha1d-AR, respectively. [3H]-KMD also bound to the native alpha1A-AR (rat submaxillary gland) with high affinity, but not to alpha1B-AR (rat liver). In rat kidney which expresses alpha1A- and alpha1B-AR, [3H]-KMD and [3H]-PZ bound to a single high-affinity site (pK(D) = 10.8 and 10.1, respectively) with distinct amount of binding sites (Bmax = 159 and 267 fmol mg(-1) protein, respectively). [3H]-PZ binding sites consisted of low- and high-affinity sites for KMD-3213 (pKi = 7.6 and 10.7, respectively), for WB4101 (pK = 8.1 and 10.0) and for YM-617 (pKi = 8.7 and 10.8). The proportion of the high affinity site was approximately 60% in these drugs which was compatible to the ratio between Bmax of [3H]-KMD and [3H]-PZ. [3H]-KMD binding sites consisted of a single site for these drugs with affinities which were similar to those of the high affinity sites in [3H]-PZ binding. In functional experiments, KMD-3213 antagonized the contractile responses to NS-49 or noradrenaline (NA) with higher affinity in functional alpha1A- (rat caudal artery, pA2= 10.0 against NS-49) and alpha1L-AR (dog mesenteric artery, pA2 = 9.9 against NA) than in alpha1B- (dog carotid artery, pA2 = 7.7 against NA) and alpha1D-AR (rat thoracic aorta, pA2 = 8.3 against NA). These results confirm the alpha1A-AR selectivity and high affinity of KMD-3213, and indicate that [3H]-KMD can label selectively alpha1A-AR.

Design and synthesis of novel alpha1a adrenoceptor-selective dihydropyridine antagonists for the treatment of benign prostatic hyperplasia

We report the synthesis and evaluation of novel alpha1a adrenoceptor subtype-selective antagonists. Systematic modification of the lipophilic 4,4-diphenylpiperidinyl moiety of the dihydropyridine derivatives 1 and 2 provided several highly selective and potent alpha1a antagonists. From this series, we identified the 4-(methoxycarbonyl)-4-phenylpiperidine analogue SNAP 5540 (-) [(-)-63] for further characterization. When examined in an isolated human prostate tissue assay, this compound was found to have a Ki of 2.8 nM, in agreement with the cloned human receptor binding data (Ki = 2.42 nM). Further evaluation of the compound in isolated dog prostate tissue showed a Ki of 3.6 nM and confirmed it to be a potent antagonist (Kb = 1.6 nM). In vivo, this compound effectively blocked the phenylephrine-stimulated increase in intraurethral pressure (IUP) in mongrel dogs, at doses which did not significantly affect the arterial pressure (diastolic blood pressure, DBP), with a DBP Kb/IUP Kb ratio of 16. In addition, (-)-63 also showed greater than 40 000-fold selectivity over the rat L-type calcium channel and 200-fold selectivity over several G protein-coupled receptors, including histamine and serotonin subtypes. These findings prove that alpha1a adrenoceptor-subtype selective antagonists such as (-)-63 may be developed as uroselective agents for an improved treatment of BPH over nonselective alpha1 antagonists such as prazosin and terazosin, with fewer side effects.