Cinacalcet: pharmacological and clinical aspects

Vitamin D and Calcium Supplementation and Urolithiasis: A Controversial and Multifaceted Relationship

Patients with urolithiasis, and particularly those with hypercalciuria, frequently have a marked reduction of bone mineral content up to the levels of osteoporosis, with a significant increase in bone fracture risk. For these reasons, the indication to prescribe vitamin D and/or calcium supplementations is very frequent in such patients. On the other hand, both calcium supplementation, and even more vitamin D therapy, can worsen the risk of developing urolithiasis by increasing calcium, phosphate, and oxalate urinary excretion. Despite the clinical and practical relevance of this issue, the evidence on this topic is scarce and contradictory. Therefore, some concerns exist about how and whether to prescribe such supplements to a patient with a history of kidney stones. In this narrative review, we resume some pivotal pathophysiological concepts strictly related to the dealt topic, and we draw some considerations and personal opinions on the pros and cons of such prescriptions. Finally, we share with the reader our pragmatic algorithm for handling the urolithiasis risk in patients who have strong indications to be prescribed vitamin D and calcium supplementations.

Asymmetric activation of class C GPCRs

Class C G-protein-coupled receptors (GPCRs) comprise a unique GPCR subfamily with large ligand-binding extracellular domains and function as obligate dimers. The recently resolved cryo-EM structures of full-length GABA_B, CaSR, and mGlus have revealed that these receptors are activated in an asymmetric manner, leading to G-protein-coupling on one protomer within the receptor dimer. In this review we discuss the mechanisms of asymmetric activation in class C GPCRs and the unique mode of interaction with the inhibitory Gi protein. Upon activation, the two seven-transmembrane domains (7TMs) of class C GPCRs rearrange to form a conserved asymmetric TM6-TM6 interface. In contrast to class A and B GPCRs, G-protein coupling does not involve the cytoplasmic opening of TM6, but is facilitated through the coordination of intracellular loops. Furthermore, positive and negative allosteric modulators (PAMs and NAMs) adopt distinct conformations to regulate the activity of class C GPCRs. Taken together, these recent findings on the mechanism of asymmetric activation of class C GPCRs highlight a novel mechanism of G protein activation and provide new insights into the design of therapeutics targeting these receptors.

Mechanism of calcitriol regulating parathyroid cells in secondary hyperparathyroidism

A common consequence of chronic renal disease is secondary hyperparathyroidism (SHPT) and is closely related to the mortality and morbidity of uremia patients. Secondary hyperparathyroidism (SHPT) is caused by excessive PTH production and release, as well as parathyroid enlargement. At present, the mechanism of cell proliferation in secondary hyperparathyroidism (SHPT) is not completely clear. Decreased expression of the vitamin D receptor (VDR) and calcium-sensing receptor (CaSR), and 1,25(OH)2D3 insufficiency all lead to a decrease in cell proliferation suppression, and activation of multiple pathways is also involved in cell proliferation in renal hyperparathyroidism. The interaction between the parathormone (PTH) and parathyroid hyperplasia and 1,25(OH)2D3 has received considerable attention. 1,25(OH)2D3 is commonly applied in the therapy of renal hyperparathyroidism. It regulates the production of parathormone (PTH) and parathyroid cell proliferation through transcription and post-transcription mechanisms. This article reviews the role of 1,25(OH)2D3 in parathyroid cells in secondary hyperparathyroidism and its current understanding and potential molecular mechanism.

Cinacalcet Targets the Neurokinin-1 Receptor and Inhibits PKCδ/ERK/P65 Signaling to Alleviate Dextran Sulfate Sodium-Induced Colitis

Objective: Inflammatory bowel disease is an immune-mediated chronic inflammatory disease of the gastrointestinal tract for which curative drugs are currently not available. This study was performed to assess the therapeutic effects of cinacalcet on dextran sulfate sodium (DSS)-induced colitis. Methods: Primary macrophages obtained from bone marrow and the macrophage cell line RAW264.7 were used to examine the inhibitory effect of cinacalcet on cytokine production, the PKCδ/ERK/P65 signaling pathway, and NF-κB P65 translocation. Colitis was induced using DSS to assess the treatment effect of cinacalcet. Bioinformatics approaches were adopted to predict potential targets of cinacalcet, and a drug affinity responsive target stability (DARTs) assay was performed to confirm binding between cinacalcet and potential target. Results: In vivo analysis showed that cinacalcet reduced the disease activity score, prevented shortening of the colon, diminished inflammatory cell infiltration, and protected the structural integrity of the intestinal wall. Cinacalcet also reduced production of the inflammatory cytokines TNFα, IL-1β, and IL-6 in the colon and sera of mice with DSS-induced colitis. In vitro studies revealed that cinacalcet suppressed the translocation of P65 and inhibited production of the inflammatory cytokines IL-1β and IL-6. Mechanistic studies revealed that the target of cinacalcet was neurokinin-1 receptor (NK1R) and their binding was confirmed by a DARTs assay. Furthermore, the inhibition of NK-κB P65 activation was found to occur via the suppression of PKCδ/ERK/P65 signaling mediated by cinacalcet. Conclusion: Cinacalcet inhibits the activation of NF-κB and reduces the production of inflammatory cytokines by suppressing the PKCδ/ERK/P65 signaling pathway via targeting NK1R, suggesting that it can be used to treat inflammatory diseases, particularly colitis.

Tertiary and Postrenal Transplantation Hyperparathyroidism

Patients who have undergone kidney transplantation (KTx) (KTxps) are a distinctive population characterized by the persistence of some metabolic anomalies present during end-stage renal disease. Mineral metabolism (MM) parameters are frequently altered after KTx. These alterations involve calcium, phosphorus, vitamin D, and parathormone (PTH) disarrangements. At present, there is little consensus about the correct monitoring and management of PTH disorders in KTxps. This article presents the prevalence and epidemiologic and clinical impact of post-KTx hyper-PTH. The principal biochemical and instrumental investigations and the therapeutic options for these conditions are also reported.

Severe Symptomatic Hypocalcemia, complicating cardiac arrhythmia following Cinacalcet (SensiparTM) administration: A Case Report

Clinicians should closely monitor patients on calcimimetics for hypocalcemic symptoms and arrhythmia, even though asymptomatic hypocalcemia typically resolves without intervention.

Characterization of Ca2+-Sensing Receptor-Mediated Ca2+ Influx in Microvascular bEND.3 Endothelial Cells

Ca²⁺-sensing receptors (CaSR), activated by elevated concentrations of extracellular Ca²⁺, have been known to regulate functions of thyroid cells, neurons, and endothelial cells (EC). In this report, we studied CaSR-mediated Ca²⁺ influx in mouse cerebral microvascular EC (bEND.3 cells). Cytosolic free Ca²⁺ concentration and Mn²⁺ influx were measured by fura-2 microfluorometry. High (3 mM) Ca²⁺ (CaSR agonist), 3 mM spermine (CaSR agonist), and 10 μM cinacalcet (positive allosteric modulator of CaSR) all triggered Ca²⁺ influx; however, spermine, unlike high Ca²⁺ and cinacalcet, did not promote Mn²⁺ influx and its response was poorly sensitive to SKF 96365, a TRP channel blocker. Consistently, 2-aminoethoxydiphenyl borate and ruthenium red (two other general TRP channel blockers) suppressed Ca²⁺ influx triggered by cinacalcet and high Ca²⁺ but not by spermine. Ca²⁺ influx triggered by high Ca²⁺, spermine, and cinacalcet was similarly suppressed by A784168, a potent and selective TRPV1 antagonist. Our results suggest that CaSR activation triggered Ca²⁺ influx via TRPV1 channels; intriguingly, pharmacological, and permeability properties of such Ca²⁺ influx depended on the stimulating ligands.

G protein-coupled receptors: structure- and function-based drug discovery

As one of the most successful therapeutic target families, G protein-coupled receptors (GPCRs) have experienced a transformation from random ligand screening to knowledge-driven drug design. We are eye-witnessing tremendous progresses made recently in the understanding of their structure-function relationships that facilitated drug development at an unprecedented pace. This article intends to provide a comprehensive overview of this important field to a broader readership that shares some common interests in drug discovery.

Quality by Design Enabled Development of Oral Self-Nanoemulsifying Drug Delivery System of a Novel Calcimimetic Cinacalcet HCl Using a Porous Carrier: In Vitro and In Vivo Characterisation

In this present research, work quality by design-enabled development of cinacalcet HCl (CH)-loaded solid self-nanoemulsifying drug delivery system (S-SNEDDS) was conducted using a porous carrier in order to achieve immediate drug release and better oral bioavailability. Capmul MCM (CAP), Tween 20 (TW 20) and Transcutol P (TRP) were selected as excipients. Cumulative % drug release at 30 min (Q30), emulsification times (ET), mean globule size (GS) and polydispersity index (PDI) were identified as critical quality attributes (CQAs). Factor mode effect analysis (FMEA) and Taguchi screening design were applied for screening of factors. The optimised single dose of S-SNEDDS obtained using Box-Behnken design (BBD) consisted of 30 mg of CH, 50 mg of CAP, 149.75 mg of TW 20, 55 mg of TRP and 260.75 mg of Neusilin US2. It showed an average Q30 of 97.6%, ET of 23.3 min, GS of 89.5 nm and PDI of 0.211. DSC, XRD and SEM predict the amorphous form of S-SNEDDS. In vivo pharmacokinetic study revealed better pharmacokinetic parameters of S-SNEDDS. The above study concluded that the optimised S-SNEDDS is effective to achieve the desired objective. Graphical Abstract.

The Calcium-Sensing Receptor and the Parathyroid: Past, Present, Future

Parathyroid hormone (PTH) defends the extracellular fluid from hypocalcemia and has powerful and well-documented actions on the skeleton and renal tubular system. To achieve a satisfactory stable plasma calcium level, the secretion of PTH, and the resulting serum PTH level, is titrated carefully to the prevailing plasma ionized Ca²⁺ concentration via a Ca²⁺ sensing mechanism that mediates feedback inhibition of PTH secretion. Herein, I consider the properties of the parathyroid Ca²⁺ sensing mechanism, the identity of the Ca²⁺ sensor, the intracellular biochemical mechanisms that it controls, the manner of its integration with other components of the PTH secretion control mechanism, and its modulation by other nutrients. Together the well-established, recently elucidated, and yet-to-be discovered elements of the story constitute the past, present, and future of the parathyroid and its calcium-sensing receptor (CaSR).

Cinacalcet attenuates the renal endothelial-to-mesenchymal transition in rats with adenine-induced renal failure

Elevated serum parathyroid hormone (PTH) is an important complicated phenomenon in patients with chronic kidney disease (CKD). Emerging evidence indicates the involvement of PTH in organ fibrosis, and suppression of PTH by cinacalcet (CINA) ameliorates the progression of fibrotic disorders. However, the underlying mechanisms are largely unknown. The endothelial-to-mesenchymal transition (EndMT) has been shown to be an important mechanism involved in renal fibrosis. The present study aimed to investigate whether CINA treatment attenuated renal EndMT in rats with adenine-induced chronic renal failure (CRF). Compared with the control group, serum PTH was significantly higher in the CRF group and was suppressed after CINA treatment. Serum calcium, phosphorus, and calcium × phosphorus product levels were similar in the CRF group and CINA-treated CRF group. Renal collagen accumulation was significantly increased in the CRF group, which was markedly ameliorated by CINA treatment. Expression of the endothelial marker CD31 was significantly downregulated in rats with CRF, whereas expression of the mesenchymal markers fibroblast specific-protein 1 and α-smooth muscle actin was markedly upregulated. These changes were inhibited by CINA treatment. The protein levels of these EndMT-related markers were strongly correlated with serum PTH concentrations. Furthermore, the in vitro study showed that PTH could significantly increase the expression of fibroblast specific-protein 1 and α-smooth muscle actin and decrease CD31 in mRNA and protein levels in a concentration- and time-dependent manner. In conclusion, our study suggests that reducing serum PTH by CINA treatment could attenuate renal fibrosis via suppression of EndMT in the adenine-induced CRF rat model.

Cinacalcet effects on the perioperative course of patients with secondary hyperparathyroidism

PURPOSE

Since its registration in 2004, the calcimimetic agent cinacalcet has been established as an alternative treatment for secondary hyperparathyroidism (SHPT). Working by allosteric activation of the calcium-sensing receptor, cinacalcet can lower parathyroid hormone (PTH) and calcium (Ca) in patients with SHPT. The influence of calcimimetics on the perioperative course has been unclear so far.

METHODS

We retrospectively analyzed the data of patients with primary operation for SHPT between 2004 and 2011, comparing the perioperative course of patients with and without preoperative cinacalcet treatment.

RESULTS

Fifty-six patients had cinacalcet therapy, and 54 patients had no calcimimetic medication prior to surgery. Gender, age, hemodialysis, and medical treatment were similar in both groups. Also, PTH levels were similar preoperatively and postoperatively (preoperative, 1,249 ± 676 vs. 1,196 ± 601 pg/ml; postoperative, 86 ± 220 vs. 62 ± 91 pg/ml). Patients with cinacalcet preoperatively had significant lower Ca levels preoperatively (2.49 ± 0.25 vs. 2.61 ± 0.24 mmol/l) and postoperatively (1.75 ± 0.37 vs. 1.86 ± 0.35 mmol/l) and had a higher rate of oral Ca substitution postoperatively (93 vs. 74 %). The risk for postoperative persistent disease was slightly higher in these patients compared to those without preoperative cinacalcet therapy (5 vs. 0 %, not significant).

CONCLUSIONS

In our experience, cinacalcet did not alter the perioperative course in SHPT patients.

Outcomes after the long interdialytic break: implications for the dialytic prescription

A thrice-weekly schedule dominates hemodialysis practice today. Inherent in such a schedule is a 72-hour interweek break over the weekend. A growing body of evidence suggests that this break may be associated with increased cardiovascular morbidity and mortality. Five recent studies have linked dialysis session timing to higher cardiovascular event rates, and have shed light on possible underlying physiologic mechanisms. We reviewed outcome data linking the "long break" to cardiovascular outcomes, and suggest physiologic rationale for this relationship while identifying knowledge gaps that require further study to inform discussions regarding the application and composition of individualized dialysis prescriptions. Further work is needed to determine the relative importance of electrolyte perturbations and hemodynamic shifts in the relationship between the long break and cardiovascular mortality. The evidence suggests that at least in some at-risk patients, an individualized approach to the dialytic schedule and prescription is warranted.

Pharmacodynamic responses to combined treatment regimens with the calcium sensing receptor antagonist JTT-305/MK-5442 and alendronate in osteopenic ovariectomized rats

Parathyroid hormone (PTH) is the anabolic standard of care for patients with severe osteoporosis. The CaSR allosteric antagonist JTT-305/MK-5442, a PTH secretagogue, could offer an oral osteoanabolic treatment alternative for postmenopausal women with osteoporosis. Here we disclose the pharmacokinetic profile of JTT-305/MK-5442 and its activity on bone remodeling in ovariectomized (OVX) osteopenic rats. Daily treatments (0.3 to 2.4 mg/kg/d) for 12 weeks resulted in plateaued BMD increases (3.8 to 5.3%) at axial and appendicular skeletal sites. However, treatment effects were not statistically significant, in agreement with effects seen in animals treated with low dose PTH (1-84) (5 μg/kg/d). In a consecutive study we tested JTT-305/MK-5442 effects on bone formation in OVX-rats challenged with combined alendronate (ALN) treatment paradigms. At 7 month, JTT-305/MK-5442 treatment significantly increased BMD in lumbar vertebrae (LV), while no change in BMD was observed in femora or tibiae. ALN add-on co-treatment produced incremental increases in LV, distal femur (DF) and proximal tibia (PT) BMD over the respective ALN control. Histological analyses confirmed modest increases in mineralized surface (MS/BS) and bone formation rate (30.5±1.9%) on trabecular surfaces by JTT-305/MK-5442. As expected, ALN administration profoundly reduced bone formation, however, JTT-305/MK-5442 significantly stimulated MS/BS and BFR in ALN treated groups. In summary, JTT-305/MK-5442 acts as a PTH secretagogue in the osteopenic OVX-rat, eliciting consistent, though modest effects on remediation of BMD due to estrogen depletion. Induction of bone formation by JTT-305/MK-5442 at trabecular bone surfaces appears to be resilient to ALN-mediated suppression of bone formation. This study provides for the first time, a mechanistic evaluation of combination treatment of a PTH secretagogue with ALN.

Efficacy and safety of cinacalcet for the treatment of secondary hyperparathyroidism in patients with advanced chronic kidney disease before initiation of regular dialysis

AIM

To evaluate the compassionate use of cinacalcet for the management of secondary hyperparathyroidism in patients who are not on dialysis.

METHODS

Patients with stage 4-5 chronic kidney disease (CKD) who were not on dialysis, had an intact parathyroid hormone (iPTH) level greater than 300 pg/mL, and had not responded satisfactorily to treatment with phosphate binders and vitamin D were prospectively studied. Patients received 6 months of compassionate treatment with cinacalcet, which was initiated at a dose of 30 mg/day orally and flexibly dosed thereafter based on iPTH levels.

RESULTS

Twenty-six patients with a mean age±standard deviation (SD) of 58.8±16.1 years were enrolled in the study and included in the statistical analysis. The mean percentage change in iPTH levels from baseline after 6 months of treatment was -67.9±17.0%, with 92.3% (95% confidence interval (CI), 75.9-97.9) of patients showing an iPTH level within the limits recommended by Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines. The mean serum calcium concentrations had decreased significantly at the end of the study (-8.0±6.9%), while the mean serum phosphorus concentration had significantly increased (+8.3±17.0%).

CONCLUSION

Our results suggest that cinacalcet may be a useful alternative for the treatment of secondary hyperparathyroidism in pre-dialysis patients who are unresponsive to other treatments. The hypocalcemia and hyperphosphatemia reported in previous studies may not occur if a moderate dose of calcimimetics is used in patients with marginal glomerular filtration rates, especially if combined with vitamin D analogues and calcium-based phosphate binders.

[Effect of cinacalcet on parathyroid hormone level in hypercalcemic hyperparathyroidism of patients with renal transplantation]

BACKGROUND AND OBJECTIVES

Cinacalcet reduces parathyroid hormone (PTH) levels in uremic hyperparathyroidism (HPT), and in renal transplantation it is useful in the management of HPT with hypercalcemia. Our main aim is to evaluate if cinacalcet administered once daily, reduces and maintains reduced PTH levels for 24 hours in renal transplant recipients with HPT and hypercalcemia.

PATIENTS AND METHOD

We studied PTH levels and other bone biomarkers in two groups of renal transplant recipients: one with HPT and hypercalcemia (Group 1), another without alteration of mineral metabolism (Group 2), and a third group of healthy volunteers (Group 3): 35 subjets. Group 1 received a single dose of 60 mg of cinacalcet at 9 am. In all the groups we withdrew blood samples at 8, 10, 11, 12, 13, 19 hours (day 1) and 9 am the following day (day 2), determining levels of PTH and bone biomarkers.

RESULTS

In Group 1, basal PTH levels decreased shortly after dispensing cinacalcet (basal PTH level 237 [86.7] versus 10 hour level 113 [54.7] p<0.05), objectifying a progressive increase to a similar level to baseline after 24 hours of the administration (day 2 9h PTH level 241 [117.4] ns). In Group 2, comparisons among PTH mean levels were not different at any time. In Group 3, the mean baseline PTH level was higher than that observed at 10h (47 [22.7] versus 28 [11.2] p<0.05) and other comparisons were not significant. Beta-ctx was higher at baseline in the three groups in comparison with levels at 11, 12, 13 and 19 hour, and similar to that at 10 am on day 1 and 9 am on day 2. With respect to other bone biomarkers, no differences were observed.

CONCLUSION

Cinacalcet administered once daily reduces PTH in renal transplant recipients with HPT and hypercalcemia, without holding it for 24 hours.

Regulation of stability and trafficking of calcium-sensing receptors by pharmacologic chaperones

Gain- or loss-of-function mutations and polymorphisms of the calcium-sensing receptor (CaSR) cause Ca(2+) handling diseases. Altered expression and/or signaling of wild-type CaSR can also contribute to pathology. Recent studies have demonstrated that a significant proportion of mutations cause altered targeting and/or trafficking of CaSR to the plasma membrane. Pharmacological approaches to rescue of CaSR function include treatment with allosteric modulators, which potentiate the effects of the orthosteric agonist Ca(2+). Dissection of the mechanism(s) contributing to allosteric agonist-mediated rescue of loss-of-function CaSR mutants has demonstrated pharmacologic chaperone actions coincident with CaSR biosynthesis. The distinctive responses to the allosteric agonist (NPS R-568), which promotes CaSR stability, and the allosteric antagonist (NPS 2143), which promotes CaSR degradation, have led to a model for a conformational checkpoint during CaSR biosynthesis. The conformational checkpoint would "tune" CaSR biosynthesis to cellular signaling state. Navigation of a distinct checkpoint for endoplasmic release can also be augmented by pharmacologic chaperones. The diverse, post-endoplasmic reticulum quality control site(s) for pharmacologic chaperone modulation of CaSR stability and trafficking redefines the role(s) of allosteric modulators in regulation of overall GPCR function.

Calcilytics: antagonists of the calcium-sensing receptor for the treatment of osteoporosis

The only bone anabolic agents currently available on the market are based on the parathyroid hormone (PTH). Secretion of endogenous PTH is controlled by a calcium-sensing receptor at the surface of the parathyroid glands. Antagonists of this receptor (calcilytics) induce the release of the hormone. Provided the effect of the calcilytic is of short duration, a bone anabolic effect should also result. Although the first calcilytic series became known approximately 10 years ago, the number of different structural types is still small today. This article outlines the quest from hits to potent development candidates of all relevant calcilytic series currently known. Even after the front-runners unexpectedly failed in the clinic, the approach for an oral alternative to parenteral PTH remains highly attractive.

Vascular actions of calcimimetics: role of Ca²(+) -sensing receptors versus Ca²(+) influx through L-type Ca²(+) channels

BACKGROUND AND PURPOSE

The calcimimetic, (R)-N-(3-(3-(trifluoromethyl)phenyl)propyl)-1-(1-napthyl)ethylamine hydrochloride (cinacalcet), which activates Ca²(+) -sensing receptors (CaR) in parathyroid glands, is used to treat hyperparathyroidism. Interestingly, CaR in perivascular nerves or endothelial cells is also thought to modulate vascular tone. This study aims to characterize the vascular actions of calcimimetics.

EXPERIMENTAL APPROACH

In rat isolated small mesenteric arteries, the relaxant responses to the calcimimetics, cinacalcet and (R)-2-[[[1-(1-naphthyl)ethyl]amino]methyl]-1H-indole hydrochloride (calindol) were characterized, with particular emphasis on the role of CaR, endothelium, perivascular nerves, K(+) channels and Ca²(+) channels. Effects of L-ornithine, which activates a Ca(2+) -sensitive receptor related to CaR (GPRC6A), were also tested.

KEY RESULTS

Cinacalcet induced endothelium-independent relaxation (pEC₅₀ 5.58 ± 0.07, E(max) 97 ± 6%) that was insensitive to sensory nerve desensitization by capsaicin or blockade of large-conductance Ca²(+) -activated K(+) channels by iberiotoxin. Calindol, another calcimimetic, caused more potent relaxation (pEC₅₀ 6.10 ± 0.10, E(max) 101 ± 6%), which was attenuated by endothelial removal or capsaicin, but not iberiotoxin. The negative modulator of CaR, calhex 231 or changes in [Ca²(+) ](o) had negligible effect on relaxation to both calcimimetics. The calcimimetics relaxed vessels precontracted with high [K(+) ](o) and inhibited Ca²(+) influx in endothelium-denuded vessels stimulated by methoxamine, but not ionomycin. They also inhibited contractions to the L-type Ca²(+) channel activator, BayK8644. L-ornithine induced small relaxation alone and had no effect on the responses to calcimimetics.

CONCLUSION AND IMPLICATIONS

Cinacalcet and calindol are potent arterial relaxants. Under the experimental conditions used, they predominantly act by inhibiting Ca²(+) influx through L-type Ca²(+) channels into vascular smooth muscle, whereas Ca²(+) -sensitive receptors (CaR or GPRC6A) play a minor role.

Calcium input potentiates the transforming growth factor (TGF)-beta1-dependent signaling to promote the export of inorganic pyrophosphate by articular chondrocyte

Transforming growth factor (TGF)-β1 stimulates extracellular PP(i) (ePP(i)) generation and promotes chondrocalcinosis, which also occurs secondary to hyperparathyroidism-induced hypercalcemia. We previously demonstrated that ANK was up-regulated by TGF-β1 activation of ERK1/2 and Ca(2+)-dependent protein kinase C (PKCα). Thus, we investigated mechanisms by which calcium could affect ePP(i) metabolism, especially its main regulating proteins ANK and PC-1 (plasma cell membrane glycoprotein-1). We stimulated articular chondrocytes with TGF-β1 under extracellular (eCa(2+)) or cytosolic Ca(2+) (cCa(2+)) modulations. We studied ANK, PC-1 expression (quantitative RT-PCR, Western blotting), ePP(i) levels (radiometric assay), and cCa(2+) input (fluorescent probe). Voltage-operated Ca(2+)-channels (VOC) and signaling pathways involved were investigated with selective inhibitors. Finally, Ank promoter activity was evaluated (gene reporter). TGF-β1 elevated cCa(2+) and ePP(i) levels (by up-regulating Ank and PC-1 mRNA/proteins) in an eCa(2+) dose-dependent manner. TGF-β1 effects were suppressed by cCa(2+) chelation or L- and T-VOC blockade while being mostly reproduced by ionomycin. In the same experimental conditions, the activation of Ras, the phosphorylation of ERK1/2 and PKCα, and the stimulation of Ank promoter activity were affected similarly. Activation of SP1 (specific protein 1) and ELK-1 (Ets-like protein-1) transcription factors supported the regulatory role of Ca(2+). SP1 or ELK-1 overexpression or blockade experiments demonstrated a major contribution of ELK-1, which acted synergistically with SP1 to activate Ank promoter in response to TGF-β1. TGF-β1 promotes input of eCa(2+) through opening of L- and T-VOCs, to potentiate ERK1/2 and PKCα signaling cascades, resulting in an enhanced activation of Ank promoter and ePP(i) production in chondrocyte.

Clinical utilization of cinacalcet in hypercalcemic conditions

INTRODUCTION

Cinacalcet has recently been introduced as a treatment for secondary hyperparathyroidism in dialysis patients and for parathyroid carcinoma. However, there has been an increasing interest in finding out whether cinacalcet can be used as a treatment for other parathyroid hormone (PTH)-dependent hypercalcemic conditions also.

AREAS COVERED

The article reports the most relevant recent contributions dealing with calcium sensing receptor (CaSR) physiology as well as cinacalcet pharmacokinetics and pharmacodynamics. It also looks at the different hypercalcemic conditions where the use of cinacalcet has been proposed. This article was researched using clinical trials, case reports and outstanding basic research published in the last 3 years (MEDLINE database up to 31 November 2010). It provides the reader with an insight into the many unaddressed issues regarding cinacalcet that need to be resolved before it can be used in newly proposed fields.

EXPERT OPINION

Since cinacalcet may not only have an effect on parathyroid CaSR but also on CaSR expressed at bone and renal levels, it can currently only be considered a good alternative to parathyroidectomy in PTH-dependent hypercalcemic conditions when surgical intervention is burdened by a high failure rate or when it can be considered a risky procedure. At present, cinacalcet cannot be considered the first choice treatment in asymptomatic primary hyperparathyroidism or in mild-to-moderate forms of familial hypocalciuric hypocalcemia.

1-Alkyl-4-phenyl-6-alkoxy-1H-quinazolin-2-ones: a novel series of potent calcium-sensing receptor antagonists

Parathyroid hormone (PTH) is an effective bone anabolic agent. However, only when administered by daily sc injections exposure of short duration is achieved, a prerequisite for an anabolic response. Instead of applying exogenous PTH, mobilization of endogenous stores of the hormone can be envisaged. The secretion of PTH stored in the parathyroid glands is mediated by a calcium sensing receptor (CaSR) a GPCR localized at the cell surface. Antagonists of CaSR (calcilytics) mimic a state of hypocalcaemia and stimulate PTH release to the bloodstream. Screening of the internal compound collection for inhibition of CaSR signaling function afforded 2a. In vitro potency could be improved >1000 fold by optimization of its chemical structure. The binding mode of our compounds was predicted based on molecular modeling and confirmed by testing with mutated receptors. While the compounds readily induced PTH release after iv application a special formulation was needed for oral activity. The required profile was achieved by using microemulsions. Excellent PK/PD correlation was found in rats and dogs. High levels of PTH were reached in plasma within minutes which reverted to baseline in about 1-2 h in both species.

[Medical treatment of primary hyperparathyroidism: role of calcimimetics]

Primary hyperparathyroidism (PHPT) is a common endocrinological process, characterized by chronic elevation of serum concentrations of calcium and parathyroid hormone (PTH). The only intervention able to cure the disease is parathyroidectomy. However, there are few valid medical alternatives for patients whose PHPT is unresolved by surgery, or in those with contraindications for surgery or who refuse the procedure. The discovery of calcium-sensing receptors (CaSRs), which regulate PTH secretion according to extracellular calcium concentrations, has allowed specific anti-parathyroid drugs called calcimimetics to be designed. Cinacalcet is an allosteric modulator of CaSR that has demonstrated safety and efficacy in controlling serum calcium values and in reducing PTH levels in patients with PHPT. The exact role of calcimimetics in the overall management of PHPT is promising and should be considered in future clinical practice guidelines.