Over 257 mutations in the human calcium sensing receptor (hCaSR) gene have been reported. Heterozygous inactivating mutations can result in familial hypocalciuric hypercalcemia (FHH) while homozygous inactivating mutations can cause life-threatening neonatal severe hyperparathyroidism (NSHPT). Activating mutations in the hCaSR can result in hypercalciuria and hypocalcemia. A recent publication on the successful treatment of a patient suffering from FHH with the hCaSR positive allosteric modulator, cinacalcet, prompted our interest in exploring the molecular pharmacology of calcimimetics to correct signaling defects associated with inactivating hCaSR mutations. We prepared 11 mutant hCaSRs, previously identified in patients suffering from NSHPT or FHH, and tested their ability to couple to inositol phosphate accumulation and intracellular calcium mobilization in transiently transfected HEK293 and CHO cells using the calcimimetic R-568. We found that extracellular Ca(2+) was significantly less potent on the mutated receptors as compared to wild-type hCaSR. However, R-568 was able to enhance the potency of extracellular Ca(2+) toward the mutant hCaSRs. Furthermore, R-568 increased the maximum agonist response on several of the mutant CaSRs. We applied a novel operational model of allosteric modulation/agonism that provided a common mechanism to account for the behavior of the wild-type and mutant hCaSRs. The data provide evidence for the potential use of calcimimetics to treat diseases such as FHH and NSHPT where severe hypercalcemia can be life-threatening.
|Pages (from-to)||775 - 786|
|Number of pages||12|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|Publication status||Published - 2009|