Upacicalcet Is a Novel Secondary Hyperparathyroidism Drug that Targets the Amino Acid Binding Site of Calcium-Sensing Receptor

Activation profile of the Atlantic salmon (Salmo salar) calcium-sensing receptor (Casr) by selected L-amino acids

In mammals, the calcium-sensing receptor (CaSR) is involved in nutrient sensing and modulated by several amino acids. In teleosts, sequence homologues of the mammalian CaSR have been described but their function in sensing amino acids remains elusive, including in Atlantic salmon (Salmo salar), an important aquaculture species. This study investigated the activation of Atlantic salmon Casr (asCasr)-mediated signaling pathways-Gq, Gi, and ERK1/2-by six selected L-amino acids (histidine, tryptophan, phenylalanine, isoleucine, leucine and valine) and by Ca2+. Using a Flp-In-HEK293 cell line stably expressing asCasr, we confirmed activation of all three pathways. L-histidine, L-phenylalanine, and L-tryptophan triggered Gi signaling independent of Ca²⁺. Notably, no Ca²⁺ concentrations induced Gi activation, but IP1 production increased in a concentration-dependent manner. L-histidine was the only amino acid to activate the Gq pathway without Ca²⁺, and this response was amplified by the presence of Ca²⁺. In the presence of 2.5 mM Ca²⁺, L-phenylalanine and L-tryptophan also activated Gq signaling in a concentration-dependent manner. Additionally, in the presence of 10 mM Ca²⁺, L-histidine, L-phenylalanine, and L-tryptophan triggered ERK phosphorylation. These findings establish asCasr as a functional homologue of mammalian CaSR, activated in a concentration-dependent manner by L-amino acids with an aromatic ring.

Combination Treatment With Intravenous and Oral Calcimimetics for Secondary Hyperparathyroidism in Hemodialysis Patients Who Decline Parathyroidectomy

BACKGROUND AND AIM

Secondary hyperparathyroidism (SHPT) is a common and serious complication in patients on hemodialysis (HD), leading to significant morbidity and mortality. Parathyroidectomy (PTx) is an established treatment for refractory SHPT, but many patients refuse this surgical option. This study evaluates the efficacy of combination treatment using intravenous and oral calcimimetics in managing SHPT in patients who decline PTx. This study aimed to assess the impact of combination calcimimetic treatment on plasma parathyroid hormone (PTH) levels, mineral metabolism, and clinical outcomes in patients on hemodialysis with SHPT who refuse PTx.

METHODS

This retrospective study involved seven patients on HD with refractory SHPT who declined PTX. They were treated with various combinations of intravenous (etelcalcetide or upacicalcet), oral (cinacalcet or evocalcet) calcimimetics, and vitamin D receptor activators (VDRAs), with or without denosumab. Clinical outcomes, including changes in plasma PTH levels, mineral metabolism, and adverse events, were monitored over a period ranging from 10 to 100 months.

RESULTS

Combination treatment significantly reduced plasma PTH levels in all patients (median reduction from 379 pg/mL to 193 pg/mL). No gastrointestinal complications were reported, confirming the tolerability of the regimen. However, two patients developed renal cancer, and one patient died from cardiovascular disease, highlighting the complex comorbidities in this population. These findings underscore the effectiveness of combination calcimimetics in managing SHPT in patients who refuse surgery, although careful monitoring for adverse events is necessary.

CONCLUSION

The combination of intravenous and oral calcimimetics is an effective therapeutic option for managing SHPT in patients on HD who refuse PTX. While promising, the long-term safety and potential risks of this approach, including the occurrence of malignancies, warrant further investigation in larger prospective studies.

[Pharmacological properties and clinical trial results of the novel calcium-sensing receptor agonist upacicalcet sodium hydrate (Upacita® intravenous injection for dialysis)]

Upacicalcet sodium hydrate (upacicalcet) is a novel small-molecule calcium-sensing receptor (CaSR) modulator with an amino acid structure, developed in Japan as a derivative from research into taste enhancement. Upacicalcet specifically targets CaSR and is thought to inhibit parathyroid hormone (PTH) secretion by activating the receptor in the presence of extracellular calcium (Ca). In nonclinical studies, upacicalcet was evaluated for its pharmacological properties, binding characteristics, and effects on ectopic calcification, parathyroid hyperplasia, and bone disorders associated with secondary hyperparathyroidism (SHPT). The results supported its mechanisms of action, binding mode, and efficacy in suppressing disease progression. In clinical trials, upacicalcet demonstrated efficacy and safety in patients with SHPT undergoing hemodialysis, as assessed in domestic Phase I/II trial (AJ1001 trial), Phase II trial (AJ1002 trial), Phase III placebo-controlled trial (AJ1004 trial), and Phase III long-term administration trial (AJ1003 trial). Upacicalcet was approved in June 2021 for the treatment of secondary hyperparathyroidism (SHPT) in patients undergoing hemodialysis and was launched in August of the same year.

Secondary hyperparathyroidism in chronic kidney disease: pathophysiology, current treatments and investigational drugs

INTRODUCTION

Secondary hyperparathyroidism (SHPT) is a common complication of chronic kidney disease (CKD). It begins as an adaptive increase in parathyroid hormone levels to prevent calcium and phosphate derangements. Over time, this condition becomes maladaptive and is associated with increased morbidity and mortality. Current therapies encompass phosphate-lowering strategies, vitamin D analogues, calcimimetics and parathyroidectomy. These approaches harbor inherent limitations, stimulating interest in the development of new drugs for SHPT to overcome these limitations and improve survival and quality of life among CKD patients.

AREAS COVERED

This review delves into the main pathophysiological mechanisms involved in SHPT, alongside the treatment options that are currently available and under active investigation. Data presented herein stem from a comprehensive search conducted across PubMed, Web of Science, ClinicalTrials.gov and International Clinical Trials Registry Platform (ICTRP) spanning from 2000 onwards.

EXPERT OPINION

The advancements in investigational drugs for SHPT hold significant promise for enhancing treatment efficacy while minimizing side effects associated with conventional therapies. Although several challenges still hinder their adoption in clinical practice, ongoing research will likely continue to expand the available therapeutic options, refine treatment strategies, and tailor them to individual patient profiles.

Glutathione-Based Photoaffinity Probe Identifies Caffeine as a Positive Allosteric Modulator of the Calcium-Sensing Receptor

The calcium-sensing receptor (CaSR), abundantly expressed in the parathyroid gland and kidney, plays a central role in calcium homeostasis. In addition, CaSR exerts multimodal roles, including inflammation, muscle contraction, and bone remodeling, in other organs and tissues. The diverse functions of CaSR are mediated by many endogenous and exogenous ligands, including calcium, amino acids, glutathione, cinacalcet, and etelcalcetide, that have distinct binding sites in CaSR. However, strategies to evaluate ligand interactions with CaSR remain limited. Here, we developed a glutathione-based photoaffinity probe, DAZ-G, that analyzes ligand binding to CaSR. We showed that DAZ-G binds to the amino acid binding site in CaSR and acts as a positive allosteric modulator of CaSR. Oxidized and reduced glutathione and phenylalanine effectively compete with DAZ-G conjugation to CaSR, while calcium, cinacalcet, and etelcalcetide have cooperative effects. An unexpected finding was that caffeine effectively competes with DAZ-G's conjugation to CaSR and acts as a positive allosteric modulator of CaSR. The effective concentration of caffeine for CaSR activation (<10 μM) is easily attainable in plasma by ordinary caffeine consumption. Our report demonstrates the utility of a new chemical probe for CaSR and discovers a new protein target of caffeine, suggesting that caffeine consumption can modulate the diverse functions of CaSR.

Novel kokumi peptides from yeast extract and their taste mechanism via an in silico study

Yeast extract, a widely utilized natural substance in the food industry and biopharmaceutical field, holds significant potential for flavor enhancement. Kokumi peptides within yeast extracts were isolated through ultrafiltration and gel chromatography, followed by identification using liquid chromatography tandem mass spectrometry (LC-MS/MS). Two peptides, IQGFK and EDFFVR, were identified and synthesized using solid-phase methods based on molecular docking outcomes. Sensory evaluations and electronic tongue analyses conducted with chicken broth solutions revealed taste thresholds of 0.12 mmol L-1 for IQGFK and 0.16 mmol L-1 for EDFFVR, respectively, and both peptides exhibited kokumi properties. Additionally, through molecular dynamics simulations, the binding mechanisms between these peptides and the calcium-sensing receptor (CaSR) were explored. The findings indicated stable binding of both peptides to the receptor. IQGFK primarily interacted through electrostatic interactions, with key binding sites including Asp275, Asn102, Pro274, Trp70, Tyr218, and Ser147. EDFFVR mainly engaged via van der Waals energy and polar solvation free energy, with key binding sites being Asp275, Ile416, Pro274, Arg66, Ala298, and Tyr218. This suggests that both peptides can activate the CaSR, thereby inducing kokumi activity. This study provides a theoretical foundation and reference for the screening and identification of kokumi peptides, successfully uncovering two novel kokumi peptides derived from yeast extract.

Phase 2 study of upacicalcet in Japanese haemodialysis patients with secondary hyperparathyroidism: an intraindividual dose-adjustment study

Background

Upacicalcet is a novel small-molecule calcimimetic agent developed for intravenous injection. Here, we evaluated the long-term efficacy and safety of upacicalcet treatment via intraindividual dose adjustment in haemodialysis patients with secondary hyperparathyroidism (SHPT).

Methods

A phase 2, multicentre, open-label, single-arm study was conducted. Upacicalcet was administered for 52 weeks; the starting dose was 50 μg thrice a week, and then adjusted to 25, 50, 100, 150, 200, 250, or 300 μg, according to the dose-adjustment method set in the protocol. The primary endpoint was the percentage of patients with serum intact parathyroid hormone (iPTH) level achieving a target range of 60-240 pg/mL (target achievement rate) at week 18.

Results

A total of 58 patients were administered upacicalcet. The target achievement rate of serum iPTH level at week 18 was 57.9%, which increased to 80.8% at week 52. The serum-corrected calcium (cCa) level decreased immediately after upacicalcet administration, but no further decrease was observed. Adverse events were observed in 94.8% of patients, and adverse drug reactions (ADRs) occurred in 20.7% of patients. The most common ADR was decreased adjusted calcium in eight patients; dizziness occurred as a serious ADR in one patient. The serum cCa level of patients who interrupted upacicalcet treatment at a serum cCa level of <7.5 mg/dL recovered to ≥7.5 mg/dL immediately after the interruption.

Conclusions

In haemodialysis patients with SHPT, upacicalcet doses of 25-300 μg for 52 weeks were found to be highly effective and well-tolerated, with minor safety concerns.

Efficacy and Safety of Upacicalcet in Hemodialysis Patients with Secondary Hyperparathyroidism: A Randomized Placebo-Controlled Trial

BACKGROUND

Secondary hyperparathyroidism is a major complication of patients undergoing hemodialysis (HD). Upacicalcet, a new injectable calcimimetic, acts on calcium-sensing receptors to suppress parathyroid hormone (PTH) secretion. We examined the efficacy and safety of upacicalcet in patients with secondary hyperparathyroidism receiving HD.

METHODS

In this phase 3, double-blind, placebo-controlled study, we randomized Japanese patients undergoing HD with serum intact PTH (iPTH) concentrations >240 pg/ml and corrected calcium concentrations ≥8.4 mg/dl. Either upacicalcet or placebo was administered after each HD session for 24 weeks. The primary outcome was the percentage of participants achieving the target mean serum iPTH concentration (60-240 pg/ml) at weeks 22-24.

RESULTS

A total of 103 participants received upacicalcet, and 50 participants received the placebo. The percentage of participants achieving mean serum iPTH concentrations of 60-240 pg/ml during the evaluation period was 67% (69/103) in the upacicalcet group and 8% (4/50) in the placebo group. The difference between the two groups was 59% (95% confidence interval, 48% to 71%). Upacicalcet also decreased serum fibroblast growth factor-23, bone-specific alkaline phosphatase, total type 1 procollagen-N-propeptide, and tartrate-resistant acid phosphatase-5b concentrations. Adverse events were reported in 85% (88/103) and 72% (36/50) participants in the upacicalcet and placebo groups, respectively. The incidence of upper gastrointestinal adverse events, such as nausea and vomiting, was similar between the two groups. Serum corrected calcium concentrations <7.5 mg/dl were observed in 2% of participants in the upacicalcet group and no participants in the placebo group.

CONCLUSIONS

Upacicalcet, a novel injectable calcimimetic, is effective and safe for secondary hyperparathyroidism patients receiving HD.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Phase 3 Study of SK-1403, NCT03801980 .

Effects of evocalcet on parathyroid calcium-sensing receptor and vitamin D receptor expression in uremic rats

Little is known about the effect of the recently developed calcimimetic evocalcet (Evo) on parathyroid calcium-sensing receptor (CaSR) and vitamin D receptor (VDR) expression. We examined the effects of Evo and cinacalcet (Cina) on CaSR and VDR expression in 5/6 nephrectomized Sprague-Dawley rats fed a high-phosphorus diet for 4 weeks to develop secondary hyperparathyroidism (SHPT). These uremic rats were divided into 4 groups-baseline control (Nx4W) and groups with additional treatment with either the Vehicle, Evo, or Cina for 2 weeks; normal rats were used as normal controls (NC). Blood parameters and parathyroid tissue were analyzed. CaSR and VDR expression levels were determined using immunohistochemistry. The degree of kidney injury and hyperphosphatemia was similar in the uremic groups (Nx4W, Vehicle, Cina, and Evo). Serum parathyroid hormone levels were significantly higher in the Nx4W and Vehicle groups than in the NC group. This increase was significantly suppressed in the Cina and Evo groups compared with that in the Vehicle group. Serum calcium levels were significantly and equally lower in the Cina and Evo groups relative to those in the Vehicle group. CaSR expression was significantly lower in the Nx4W and Vehicle groups than in the NC group. This downregulation was of an equally lesser magnitude in the Cina and Evo groups. A similar trend was observed for VDR expression. These results indicate that Evo and Cina treatment can increase parathyroid CaSR and VDR expression in uremic rats with SHPT, which could provide better control of mineral and bone disorder markers.