Endocrine Abstracts

Autosomal dominant hypocalcaemia (ADH) is a disorder that needs to be distinguished from hypoparathyroidism, as ADH patients are at risk of nephrocalcinosis and renal failure when treated with activated vitamin D preparations. ADH types 1 and 2 are due to gain-of-function mutations of the calcium-sensing receptor (CaSR) and G-protein α 11 (Gα11), respectively. CaSR targeted drugs, known as calcilytics, rectify the gain-of-function associated with ADH1-causing mutations. However, it is unclear whether calcilytics have potential for the treatment of ADH2. The aim of this study was to determine whether a calcilytic agent, known as NPS2143, may ameliorate the gain-of-function associated with ADH2-causing Gα11 mutations. WT and gain-of-function Gα11 mutants (Arg181Gln and Phe341Leu) were expressed by transient transfection in HEK293 cells stably transfected with CaSR and assessed using a quantitative immunoassay (AlphaScreen) to measure levels of phosphorylation of a downstream signaling protein, known as extracellular signal regulated kinase (ERK), in responses to changes in extracellular calcium concentrations ([Ca²⁺]_o) in the presence and absence of NPS2143. These studies demonstrated that both Arg181Gln and Phe341Leu Gα11 mutations led to a leftward shift of the concentration–response curves and significantly (P<0.0001) reduced mean half-maximal (EC₅₀) values (Arg181Gln EC₅₀=2.29 mM, 95% (CI)=2.25–2.34; Phe341Leu EC₅₀=2.30 mM, 95% CI=2.25–2.35) when compared to WT (EC₅₀=2.80 mM, 95% CI=2.74–2.86). The addition of 20 nM of the calcilytic NPS1243 led to significant (P<0.0001) rightward shifts of the concentration–response curves and increase in the EC₅₀ for Arg181Gln (EC₅₀=3.96 mM, 95% CI=3.90–4.02) and Phe341Leu (EC₅₀=3.38 mM, 95% CI=3.33–3.43) when compared to untreated Gα11 mutants. Thus, our findings demonstrate that NPS2143 corrects the gain-of-function associated with ADH2-causing Gα11 mutations, and indicates that calcilytic drugs have potential for the treatment of this hypocalcaemic disorder.