Calcimimetics--fooling the calcium receptor

Beneficial effect of cinacalcet in a child with familial hypocalciuric hypercalcemia

We describe a child with familial hypocalciuric hypercalcemia (FHH) in whom the hypercalcemia seemed to interfere with tissue healing after tympanoplasty. Consequently, he was placed on cinacalcet (30 mg/day), changed after 2 weeks to 60 mg/day. The treatment resulted in a decrease in serum parathyroid hormone (PTH) from 148 to 32 pg/mL (normal 7-75) and ionized calcium from 1.48 to 1.23 mmol/L (1.13-1.34), as well as successful healing of the revised surgical scar. Over the 12-month treatment period no complications were noted. We conclude that cinacalcet may be considered a new, and currently the only, tool in treating children with symptomatic FHH.

Calcimimetics in the chronic kidney disease-mineral and bone disorder

Mineral and bone disorders (MBD) are both an early and very common complication of chronic kidney disease (CKD). It is now accepted that they represent a significant risk factor, explaining the high cardiovascular morbidity and mortality in CKD patients. During the last decade, we have been witnessing many advances in the nomenclature, classification, pathophysiology, diagnosis, and treatment of CKD and some of its complications, such as CKD-MBD. The identification of the calcium-sensing receptor (CaSR) involvement in the pathogenesis of primary and secondary hyperparathyroidism (SHPT) and the availability of a new class of drugs called calcimimetics are two outstanding examples. Cinacalcet, the only available calcimimetic, has been shown to be a very effective therapeutic tool in CKD-MBD. Many clinical trials with cinacalcet in hemodialysis patients with SHPT have shown a reduction in parathyroid hormone, calcium (Ca), phosphate (P) and Ca x P product levels, allowing far greater success in reaching therapeutic goals as recommended by international guidelines. Additionally, some studies have shown that the use of cinacalcet may improve other aspects of CKD-MBD, reducing the risk of vascular calcification and parathyroidectomy, among others. Prospective studies on dialysis patients, with hard endpoint data, are currently underway. This review summarizes the most significant aspects of calcimimimetics based on both experimental and clinical results, underlining their possibilities not only for the treatment of isolated SHPT but also for other CKD-MBD related conditions.

Cinacalcet is efficacious in pediatric dialysis patients

Secondary hyperparathyroidism (high-turnover bone disease, or HTBD) is manifested by elevated parathyroid hormone (PTH) levels. Control of HTBD may be achieved by maintaining low serum phosphorous levels and administering vitamin D therapy, although some patients continue to exhibit high PTH levels. We report the results of the efficacy of the calcimimetic cinacalcet in six hemodialysis (HD) and three peritoneal dialysis (PD) pediatric patients with HTBD, age 14.5 +/- 1.0 (range 7.5-17.5) years. Six patients received 30 mg/day, one required 60 mg/day, and two received 120 mg/day. Treatment with cinacalcet resulted in a 61% decline in intact PTH (iPTH) levels (1,070 +/- 171.5 pretreatment to 417.6 +/- 97.8 posttreatment pg/ml, p = 0.005). Serum alkaline phosphatase also declined (561.8 +/- 169.6 U/L pretreatment to 390.3 +/- 110.3 U/L posttreatment pg/ml). During therapy, serum calcium (p = 0.9) and phosphorous (p = 0.9) levels, calcium-phosphorous product (p = 0.8), systolic blood pressure (BP) (p = 1.0), diastolic BP (p = 0.8), and hemoglobin (p = 0.9) remained unchanged. The dose of oral calcitriol for the three patients on PD while receiving cinacalcet trended downward (0.8 +/- 0.2 pretreatment vs. 0.5 +/- 0.0 microg/day posttreatment pg/ml), as did the dose of paracalcitol for those receiving HD (6.6 +/- 2.3 pretreatment vs. 4.3 +/- 1.7 micrograms/day posttreatment pg/ml). We conclude that short-term treatment with the calcimimetic cinacalcet is efficacious in adolescent dialysis patients.

Therapeutic use of calcimimetics

It has long been recognized that the secretion of PTH by chief cells in the parathyroid gland is regulated by extracellular ionized calcium. The molecular mechanism by which extracellular Ca2+ performs this feat was deduced by the cloning of the extracellular calcium-sensing receptor (CaSR) in 1993 in the laboratories of Brown and Hebert. The CaSR is a G protein-coupled cell surface receptor that belongs to family 3 of the GPCR superfamily. The CaSR senses the extracellular ionic activity of the divalent minerals Ca2+ and Mg2+ and translates this information, via a complex array of cellular signaling pathways, to modify cell and tissue function. Genetic studies have demonstrated that the activity of this receptor determines the steady-state plasma calcium concentration in humans by regulating key elements in the calcium homeostatic system. CaSR agonists (calcimimetics) and antagonists (calcilytics) have been identified and have provided both current and potential therapies for a variety of disorders. Calcimimetics can effectively reduce PTH secretion in all forms of hyperparathyroidism. They are likely to become a major therapy for secondary hyperparathyroidism associated with renal failure and for treatment of certain patients with primary hyperparathyroidism. On the therapeutic horizon are calcilytics that can transiently increase PTH and may prove useful in the treatment of osteoporosis.