Commentary on "Pharmacodynamic Activity of the Novel Neurokinin-3 Receptor Antagonist SJX-653 in Healthy Men"

The Emerging Therapeutic Potential of Kisspeptin and Neurokinin B

Kisspeptin (KP) and neurokinin B (NKB) are neuropeptides that govern the reproductive endocrine axis through regulating hypothalamic gonadotropin-releasing hormone (GnRH) neuronal activity and pulsatile GnRH secretion. Their critical role in reproductive health was first identified after inactivating variants in genes encoding for KP or NKB signaling were shown to result in congenital hypogonadotropic hypogonadism and a failure of pubertal development. Over the past 2 decades since their discovery, a wealth of evidence from both basic and translational research has laid the foundation for potential therapeutic applications. Beyond KP's function in the hypothalamus, it is also expressed in the placenta, liver, pancreas, adipose tissue, bone, and limbic regions, giving rise to several avenues of research for use in the diagnosis and treatment of pregnancy, metabolic, liver, bone, and behavioral disorders. The role played by NKB in stimulating the hypothalamic thermoregulatory center to mediate menopausal hot flashes has led to the development of medications that antagonize its action as a novel nonsteroidal therapeutic agent for this indication. Furthermore, the ability of NKB antagonism to partially suppress (but not abolish) the reproductive endocrine axis has supported its potential use for the treatment of various reproductive disorders including polycystic ovary syndrome, uterine fibroids, and endometriosis. This review will provide a comprehensive up-to-date overview of the preclinical and clinical data that have paved the way for the development of diagnostic and therapeutic applications of KP and NKB.

New advances in menopause symptom management

Vasomotor symptoms (VMS) are characteristic of menopause experienced by over 75% of postmenopausal women with significant health and socioeconomic implications. Although the average duration of symptoms is seven years, 10% of women experience symptoms for more than a decade. Although menopausal hormone therapy (MHT) remains an efficacious and cost-effective treatment, its use may not be suitable in all women, such as those at an increased risk of breast cancer or gynaecological malignancy. The neurokinin B (NKB) signaling pathway, together with its intricate connection to the median preoptic nucleus (MnPO), has been postulated to provide integrated reproductive and thermoregulatory responses, with a central role in mediating postmenopausal VMS. This review describes the physiological hypothalamo-pituitary-ovary (HPO) axis, and subsequently the neuroendocrine changes that occur with menopause using evidence derived from animal and human studies. Finally, data from the latest clinical trials using novel therapeutic agents that antagonise NKB signaling are reviewed.

Treatments targeting neuroendocrine dysfunction in polycystic ovary syndrome (PCOS)

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age and is the leading cause of anovulatory subfertility. Increased gonadotrophin releasing hormone (GnRH) pulsatility in the hypothalamus results in preferential luteinizing hormone (LH) secretion from the pituitary gland, leading to ovarian hyperandrogenism and oligo/anovulation. The resultant hyperandrogenism reduces negative feedback from sex steroids such as oestradiol and progesterone to the hypothalamus, and thus perpetuates the increase in GnRH pulsatility. GnRH neurons do not have receptors for oestrogen, progesterone, or androgens, and thus the disrupted feedback is hypothesized to occur via upstream neurons. Likely candidates for these upstream regulators of GnRH neuronal pulsatility are Kisspeptin, Neurokinin B (NKB), and Dynorphin neurons (termed KNDy neurons). Growing insight into the neuroendocrine dysfunction underpinning the heightened GnRH pulsatility seen in PCOS has led to research on the use of pharmaceutical agents that specifically target the activity of these KNDy neurons to attenuate symptoms of PCOS. This review aims to highlight the neuroendocrine abnormalities that lead to increased GnRH pulsatility in PCOS, and outline data on recent therapeutic advancements that could potentially be used to treat PCOS. Emerging evidence has investigated the use of neurokinin 3 receptor (NK3R) antagonists as a method of reducing GnRH pulsatility and alleviating features of PCOS such as hyperandrogenism. We also consider other potential mechanisms by which increased GnRH pulsatility is controlled, which could form the basis of future avenues of research.

Genetic validation of neurokinin 3 receptor antagonists for ischemic heart disease prevention in men – A one-sample Mendelian randomization study

Background

Ischemic heart disease (IHD) is a leading cause of mortality, particularly for men. Few interventions have focused on protecting specifically men. Emerging evidence may implicate testosterone. Neurokinin 3 receptor (NK3R) antagonists, an existing class of drugs being considered as treatments for reproductive conditions in women, affect testosterone; this study addresses genetic validation of their use to prevent IHD in men.

Methods

A one-sample Mendelian randomization (MR) study using the UK Biobank cohort study, based on independent (r² < 0.005) genetic variants predicting testosterone in men (n = 157738) at genome wide significance in the target gene for NK3R antagonists (TACR3), was used to assess associations with IHD (cases=15056, non-cases=151964) and positive control outcomes (relative age voice broke, children fathered, hypertension) in men and a negative control outcome (IHD) in women using summary statistics. A two-sample MR study using the PRACTICAL consortium was used for the positive control outcome of prostate cancer.

Findings

Two relevant TACR3 genetic variants (rs116646027 and rs1351623) were identified in men. Genetically mimicked NK3R antagonists were inversely associated with IHD (odds ratio 0.54 per standard deviation lower testosterone, 95% confidence interval 0.31, 0.94) and with control outcomes (older relative age voice broke, fewer children and lower risk of hypertension and prostate cancer) as expected in men and in women (unrelated to IHD).

Interpretation

Genetic validation of a role of NK3R antagonists in IHD suggests their consideration as a new means of preventing IHD in men. Whether they protect against prostate cancer might bear further consideration.