Cligosiban, A Novel Brain-Penetrant, Selective Oxytocin Receptor Antagonist, Inhibits Ejaculatory Physiology in Rodents

The oxytocin antagonist cligosiban reduces human prostate contractility: Implications for the treatment of benign prostatic hyperplasia

BACKGROUND AND PURPOSE

With increasing life expectancy, benign prostatic hyperplasia (BPH) consequently affects more ageing men, illustrating the urgent need for advancements in BPH therapy. One emerging possibility may be the use of oxytocin antagonists to relax smooth muscle cells in the prostate, similar to the currently used (although often associated with side effects) α1-adrenoceptor blockers.

EXPERIMENTAL APPROACH

For the first time we used live-imaging, combined with a novel image analysis method, to investigate the multidirectional contractions of the human prostate and determine their changes in response to oxytocin and the oxytocin antagonists atosiban and cligosiban. Human prostate samples were obtained and compared from patients undergoing prostatectomy due to prostate cancer as well as from patients with transurethral resection of prostate tissue due to severe BPH.

KEY RESULTS

The two cohorts of tissue samples showed spontaneous multidirectional contractions, which significantly increased after the addition of oxytocin. Different to atosiban, which showed ambiguous effects of short duration, only long-acting cligosiban reliably prevented, as well as counteracted, any contractile oxytocin effect. Furthermore, cligosiban visibly reduced not only oxytocin-induced contractions, but also showed intrinsic activity to relax prostatic tissue.

CONCLUSION AND IMPLICATIONS

Thus, the oxytocin antagonist cligosiban could be an interesting candidate in the search for novel BPH treatment options.

The Effects of Age on Prostatic Responses to Oxytocin and the Effects of Antagonists

Benign prostatic hyperplasia (BPH) is an age-related enlargement of the prostate with urethral obstruction that predominantly affects the middle-aged and older male population, resulting in disruptive lower urinary tract symptoms (LUTS), thus creating a profound impact on an individual's quality of life. The development of LUTS may be linked to overexpression of oxytocin receptors (OXTR), resulting in increased baseline myogenic tone within the prostate. Thus, it is hypothesised that targeting OXTR using oxytocin receptor antagonists (atosiban, cligosiban, and β-Mercapto-β,β-cyclopentamethylenepropionyl1, O-Me-Tyr2, Orn8]-Oxytocin (ßMßßC)), may attenuate myogenic tone within the prostate. Organ bath and immunohistochemistry techniques were conducted on prostate tissue from young and older rats. Our contractility studies demonstrated that atosiban significantly decreased the frequency of spontaneous contractions within the prostate of young rats (**** p < 0.0001), and cligosiban (* p < 0.05), and ßMßßC (**** p < 0.0001) in older rats. Additionally, immunohistochemistry findings revealed that nuclear-specific OXTR was predominantly expressed within the epithelium of the prostate of both young (*** p < 0.001) and older rats (**** p < 0.0001). In conclusion, our findings indicate that oxytocin is a key modulator of prostate contractility, and targeting OXTR is a promising avenue in the development of novel BPH drugs.

Current and emerging treatment options for premature ejaculation

Premature ejaculation (PE) is a prevalent male sexual dysfunction. Current standard treatment regimens include behavioural therapies, topical anaesthetics, dapoxetine and other selective serotonin reuptake inhibitors (SSRIs). Most of the pharmacotherapeutic options target neurotransmitters (such as serotonin and oxytocin) that have a role in the ejaculation mechanism. However, these treatments are mildly effective and only provide a temporary delay in the ejaculation latency time, and PE recurs when the treatment is stopped. Thus, a treatment for PE is urgently needed and research is ongoing to find the ideal PE therapy. The efficacy and safety of topical anaesthetics and SSRIs in delaying ejaculation have been confirmed in many well-designed controlled trials. Both preclinical and clinical studies on new-generation SSRIs are ongoing. Moreover, promising results came from clinical trials in which the efficacy of on-demand PE therapies targeting neurotransmitters other than serotonin, such as α1-adrenoceptor antagonists and oxytocin antagonists, was assessed. Surgical intervention and neuromodulation have been proposed as potential treatment options for PE; however, current PE guidelines do not recommend these treatments owing to safety concerns.

Physiological and pharmacological impact of oxytocin on epididymal propulsion during the ejaculatory process in rodents and men

During the emission phase of ejaculation, the sperm is driven from the cauda epididymidis, where it is stored, through the vas deferens by strong contractions. These contractions are thought of as being mainly induced by the sympathetic nervous system and the neurotransmitter noradrenaline. In the present study, we investigated the effect of oxytocin (suggested to exert effects during ejaculation as well) on defined segments of the rat and human epididymis using live imaging. Our results indicate that it is the very last part of the epididymis, segment 19 (S19) in rat and likewise segment 9 in human, which responds in a uniquely strong and rapid manner to oxytocin (similar to noradrenaline). Because of the complex nature of this contractile response, we developed an imaging analysis method, which allowed us to quantify multidirectional contractions and to display them using heat maps. The reaction of S19 to oxytocin was concentration-dependent and could be inhibited by pretreatment with oxytocin antagonists (atosiban and cligosiban), but not with an arginine vasopressin 1_A antagonist (SR49059). In both rat and human tissue, pretreatment with the alpha-1 adrenoreceptor antagonist tamsulosin inhibited the response to noradrenaline, whereas the effect of oxytocin was unimpaired. Our data (from men and rodents) strongly suggest that the hormone oxytocin is involved in the ejaculatory process. Thus, oxytocin-based medications might be a promising non-adrenergic treatment option for ejaculatory disorders. Additionally, we propose that S19 could be an advantageous model (detecting very low concentrations of oxytocin) to test the bioactivity of new oxytocin agonists and oxytocin antagonists.

Oxytocin in the Male Reproductive Tract; The Therapeutic Potential of Oxytocin-Agonists and-Antagonists

In this review, the role of oxytocin and oxytocin-like agents (acting via the oxytocin receptor and belonging to the oxytocin-family) in the male reproductive tract is considered. Previous research (dating back over 60 years) is revised and connected with recently found aspects of the role oxytocin plays in male reproductive health. The local expression of oxytocin and its receptor in the male reproductive tract of different species is summarized. Colocalization and possible crosstalk to other agents and receptors and their resulting effects are discussed. The role of the newly reported oxytocin focused signaling pathways in the male reproductive tract, other than mediating contractility, is critically examined. The structure and effect of the most promising oxytocin-agonists and -antagonists are reviewed for their potential in treating male disorders with origins in the male reproductive tract such as prostate diseases and ejaculatory disorders.

Pharmacokinetics, Safety, and Tolerability of Multiple Doses of the Novel Oxytocin Receptor Antagonist Cligosiban in Development for Premature Ejaculation: Two Randomized Clinical Trials in Healthy Subjects

BACKGROUND

Cligosiban (formerly IX-01) is a selective oxytocin receptor antagonist being developed for the treatment of premature ejaculation (PE).

AIM

To investigate the plasma pharmacokinetics, safety, and tolerability of multiple oral doses of cligosiban in healthy male subjects; measure the amount of cligosiban in semen; and evaluate the potential of cligosiban to modulate CYP3A4.

METHODS

Both studies were double-blind, placebo-controlled, parallel group designs involving sequential cohorts of 12 subjects each. Cligosiban dosage regimens were 100 mg, 400 mg, 800 mg, 1200 mg, 1,600 mg and 2,400 mg once daily for 10 days, administered as an aqueous dispersion.

OUTCOMES

Blood samplings for cligosiban assays and safety assessments were performed throughout both studies. Semen was collected on day 9 at 2-4 hours postdose in study 1 only. Safety assessments included monitoring of adverse events, 12-lead electrocardiography, vital signs, and laboratory safety assessments. Urine samples for assessment of the 6β-hydroxycortisol/cortisol ratio were collected before dosing on days 1 and 10.

RESULTS

Cligosiban was rapidly absorbed after both single and multiple dosing, with maximum plasma concentrations typically measured at 1-3 hours postdose. The terminal half-life was approximately 12 hours, and steady state was achieved by day 3. Exposure increased approximately proportionally to dose after single dosing but less than proportionally after multiple dosing. Accumulation ratios were higher at the lower doses compared with higher doses (2.3 at 100 mg vs 1.1 at 2,400 mg). The mean amount of cligosiban in semen ranged from 0.22 to 2.01 μg over the 100-1,200 mg dose range (<0.0003% of the administered dose). There were no meaningful differences in the urinary 6β-hydroxycortisol/cortisol ratio after multiple dosing with cligosiban. Cligosiban appeared to be well tolerated at all dose levels.

CLINICAL IMPLICATIONS

Cligosiban is well tolerated following once-daily dosing over a wide dose range and does not appear to modulate CYP3A4 activity, suggesting limited potential for perpetrating drug-drug interactions via this mechanism.

STRENGTHS & LIMITATIONS

The 2 controlled trials show good toleration and pharmacokinetic data, including negligible amounts of cligosiban in semen at doses expected to be therapeutic. Toleration of cligosiban will need to be confirmed in studies in patients with PE.

CONCLUSION

Cligosiban showed a good safety profile at doses predicted to be therapeutic or supratherapeutic along with a pharmacokinetic profile appropriate for as-required or once-daily dosing. There was no evidence that cligosiban inhibited or induced CYP3A4 at doses up to 2,400 mg. Muirhead GJ, Osterloh IH, Whaley S, et al. Pharmacokinetics, Safety, and Tolerability of Multiple Doses of the Novel Oxytocin Receptor Antagonist Cligosiban in Development for Premature Ejaculation: Two Randomized Clinical Trials in Healthy Subjects. J Sex Med 2019;16:213-222.