title: Amino alcohol- (NPS-2143) and quinazolinone-derived calcilytics (ATF936 and AXT914) differentially mitigate excessive signalling of calcium-sensing receptor mutants causing Bartter syndrome Type 5 and autosomal dominant hypocalcemia.
abstract: BACKGROUND
  Activating calcium sensing receptor (CaSR) mutations cause autosomal dominant hypocalcemia (ADH) characterized by low serum calcium, inappropriately low PTH and relative hypercalciuria. Four activating CaSR mutations cause additional renal wasting of sodium, chloride and other salts, a condition called Bartter syndrome (BS) type 5. Until today there is no specific medical treatment for BS type 5 and ADH. We investigated the effects of different allosteric CaSR antagonists (calcilytics) on activating CaSR mutants.
  
  
  METHODS
  All 4 known mutations causing BS type 5 and five ADH mutations were expressed in HEK 293T cells and receptor signalling was studied by measurement of intracellular free calcium in response to extracellular calcium ([Ca2+]o). To investigate the effect of calcilytics, cells were stimulated with 3 mM [Ca2+]o in the presence or absence of NPS-2143, ATF936 or AXT914.
  
  
  RESULTS
  All BS type 5 and ADH mutants showed enhanced signalling activity to [Ca2+]o with left shifted dose response curves. In contrast to the amino alcohol NPS-2143, which was only partially effective, the quinazolinone calcilytics ATF936 and AXT914 significantly mitigated excessive cytosolic calcium signalling of all BS type 5 and ADH mutants studied. When these mutants were co-expressed with wild-type CaSR to approximate heterozygosity in patients, ATF936 and AXT914 were also effective on all mutants.
  
  
  CONCLUSIONS
  The calcilytics ATF936 and AXT914 are capable of attenuating enhanced cytosolic calcium signalling activity of CaSR mutations causing BS type 5 and ADH. Quinazolinone calcilytics might therefore offer a novel treatment option for patients with activating CaSR mutations.
authors.affiliation: Division of Endocrinology and Diabetes, Department of Medicine I, Universitätsklinikum Erlangen, Erlangen, Germany.
authors.forename: Saskia
authors.initials: S
authors.lastname: Letz
authors.affiliation: Endocrine Practice, Heidelberg, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Haag
authors.affiliation: Endocrine Practice, Heidelberg, Germany.
authors.forename: Egbert
authors.initials: E
authors.lastname: Schulze
authors.affiliation: Endocrine Practice, Heidelberg, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Frank-Raue
authors.affiliation: Endocrine Practice, Heidelberg, Germany.
authors.forename: Friedhelm
authors.initials: F
authors.lastname: Raue
authors.affiliation: Department of Medical Informatics, Biometry and Epidemiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Hofner
authors.affiliation: Division of Endocrinology and Diabetes, Department of Medicine I, Universitätsklinikum Erlangen, Erlangen, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Mayr
authors.affiliation: Division of Endocrinology and Diabetes, Department of Medicine I, Universitätsklinikum Erlangen, Erlangen, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Schöfl
mesh_terms: D001477:Bartter Syndrome / Q000235:genetics*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects* / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D053565:Hypercalciuria / Q000235:genetics*; D006996:Hypocalcemia / Q000235:genetics*; D007011:Hypoparathyroidism / Q000151:congenital* / Q000235:genetics; D009154:Mutation; D009281:Naphthalenes / Q000494:pharmacology*; D052999:Quinazolinones / Q000494:pharmacology*; D044169:Receptors, Calcium-Sensing / Q000187:drug effects* / Q000235:genetics
chemical_list: C000604141:ATF936; C000595249:AXT914; C436740:N-(2-hydroxy-3-(2-cyano-3-chlorophenoxy)propyl)-1,1-dimethyl-2-(2-nephthyl)ethylamine; D009281:Naphthalenes; D052999:Quinazolinones; D044169:Receptors, Calcium-Sensing; D002118:Calcium