Personalised medicines for familial hypercalcemia and hyperparathyroidism

Abstract

Loss-of-function calcium-sensing receptor (CaSR) mutations cause the mineral metabolism disorders familial hypocalciuric hypercalcemia or neonatal severe hyperparathyroidism,and increase the risk of femoral fracture, chronic kidney disease, coronary heart disease, and other diseases. In severe cases, CaSR mutations are lethal. Off-label use of the CaSR positive allosteric modulator (PAM), cinacalcet, corrects hypercalcemia in some patients with CaSR mutations. However, other patients remain unresponsive to cinacalcet, attesting to the need for novel treatments. Here we compared the effects of cinacalcet to two other clinically approved synthetic CaSR activators, evocalcet and etelcalcetide, as well as a novel PAM, 1-(2,4-dimethylphenyl)-1-(4,5-dimethylthiazol-2-yl)ethan-1-ol (MIPS-VD-836-108) on clinically relevant CaSR mutations. We assessed the compounds in CaSR-expressing HEK293 cells for correction of mutation-induced impairments in intracellular calcium (Ca2+i) mobilization and cell surface expression. While cinacalcet, MIPS-VD-836-108 and evocalcet rescued the signaling of cell surface-expressed mutants, albeit to varying degrees, etelcalcetide was ineffective. Cinacalcet and evocalcet, but not MIPS-VD-836-108 or etelcalcetide, restored expression of a R680H mutant. However, no compound rescued expression of I81K and C582R mutants or a receptor missing 77 amino acids in the extracellular domain mimicking deletion of CASR exon 5, which impairs CaSR function. These data suggest specific compounds may be clinically effective in some patients with CaSR mutations, but other patients will remain refractory to treatment with currently available CaSR-targeting activators, highlighting the need for new generation drugs to rescue both the signaling and expression of mutant CaSRs.

Identification and characterization of a novel CASR mutation causing familial hypocalciuric hypercalcemia

“…Furthermore, CASR mutations have been found to cluster in three regions: the second peptide loop of the ECD, the VFT cleft region (eCa 2+ o -binding site), and the region encompassing transmembrane domains (TMD) 6 and 7 ( 5 , 12 ). Intriguingly, FHH1 patients with CASR mutations in different domains exhibit distinct and variable phenotypic severities ( 1 , 11 ). Although one in vitro study showed that calcimimetics can correct the expression in some CASR mutations ( 11 ), research on personalized treatment using calcimimetics for different CASR variants is limited ( 28 – 30 ).…”

“…Intriguingly, FHH1 patients with CASR mutations in different domains exhibit distinct and variable phenotypic severities (1,11). Although one in vitro study showed that calcimimetics can correct the expression in some CASR mutations (11), research on personalized treatment using calcimimetics for different CASR variants is limited (28)(29)(30). In addition, cinacalcet-unresponsive patients might harbor the missense mutations or in-frame deletions of CASR exon 5 encoding amino acids 460-536 in the extracellular domain (ECD) (31,32), indicating that the different CASR mutations are likely responsible for the biodiversity in calcimimetics treatment.…”

“…Based on the causative genetic mutations, FHH type 1 (FHH1; OMIM #145980) caused by a heterozygous loss-of-function mutation in the Ca 2+ -sensing receptor (CASR) gene is the most common and estimated to represent approximately 85-90% of all FHH cases, followed by the AP2S1 gene (FHH3), at approximately 5-10%, and the GNA11 gene (FHH2), at less than 5% (3)(4)(5)(6)(7). Although most FHH patients are usually asymptomatic or mildly symptomatic, e.g., fatigue, weakness, or thought disturbances (8), the increased risk of chronic kidney disease (CKD), coronary heart disease, pancreatitis, femoral fracture, and chondrocalcinosis with advancing age has been reported (9)(10)(11). Additionally, patients with FHH may be misdiagnosed as primary hyperparathyroidism, receiving an unnecessary parathyroidectomy, which typically does not successfully normalize hypercalcemia (12).…”

Molecular regulation of calcium‐sensing receptor (CaSR)‐mediated signaling

“…This new structural evidence in biochemical and structural determination of the framework of CaSR and its interaction sites with natural ligands, as well as exogenous PAMs and NAMs, further support a coactivation model involving calcium and amino acids for functional cooperativity and provide molecular insights into disease‐related mutations. These key structural determinants in ligand interaction and regulation have the potential to promote rapid development of novel drugs against various calciotropic and noncalciotropic diseases 55,111,273,274 …”

“…These key structural determinants in ligand interaction and regulation have the potential to promote rapid development of novel drugs against various calciotropic and noncalciotropic diseases. 55,111,273,274 Newly developed Ca 2+ sensors, such as R-CatchER and G-CatchER + , are capable of capturing rapid Ca 2+ dynamics in the ER. These new tools will improve our understanding of CaSR-mediated Ca 2+ signaling, the molecular basis of diseases, and functional cooperativity of ligands, as well as facilitate drug discovery.…”