title: Localization of CaSR antagonists in CaSR-expressing medullary thyroid cancer.
abstract: OBJECTIVE
  Image-based localization of medullary thyroid cancer (MTC) and parathyroid glands would improve the surgical outcomes of these diseases. MTC and parathyroid glands express high levels of calcium-sensing receptor (CaSR). The aim of this study was to prove the concept that CaSR antagonists specifically localize to CaSR-expressing tumors in vivo.
  
  
  METHODS
  We synthesized two isomers of a known CaSR calcilytic, Calhex 231, and four new analogs, which have a favorable structure for labeling. Their antagonistic activity was determined using immunoblots demonstrating decreased ERK1/2 phosphorylation after calcium stimulation in human embryonic kidney cells overexpressing CaSR. Compound 9 was further radiolabeled with (125)I and evaluated in nude mice with and without heterotransplanted xenografts of MTC cell lines, TT and MZ-CRC-1, that do and do not express CaSR, respectively.
  
  
  RESULTS
  Two newly synthesized compounds, 9 and 11, exhibited better antagonistic activity than Calhex 231. The half-life of (125)I-compound 9 in nude mice without xenografts was 9.9 hours. A biodistribution study in nude mice bearing both tumors demonstrated that the uptake of radioactivity in TT tumors was higher than in MZ-CRC-1 tumors at 24 hours: 0.39 ± 0.24 vs 0.18 ± 0.12 percentage of injected dose per gram of tissue (%ID/g) (P = .002), with a ratio of 2.25 ± 0.62. Tumor-to-background ratios for TT tumors, but not MZ-CRC-1 tumors, increased with time. Tumor-to-blood values increased from 2.02 ± 0.52 at 1 hour to 3.29 ± 0.98 at 24 hour (P = .015) for TT tumors, and 1.7 ± 0.56 at 1 hour to 1.48 ± 0.33 at 24 hour (P = .36) for MZ-CRC-1 tumors.
  
  
  CONCLUSIONS
  Our new CaSR antagonists specifically inhibit CaSR function in vitro, preferentially localize to CaSR-expressing tumors in vivo, and therefore have the potential to serve as scaffolds for further development as imaging pharmaceuticals.
authors.affiliation: MD, Department of Surgery, 410 West 10th Avenue, N907 Doan Hall, Columbus, OH 43210. john.phay@osumc.edu.
authors.forename: Haiming
authors.initials: H
authors.lastname: Ding
authors.forename: Adlina Mohd
authors.initials: AM
authors.lastname: Yusof
authors.forename: Shankaran
authors.initials: S
authors.lastname: Kothandaraman
authors.forename: Motoyasu
authors.initials: M
authors.lastname: Saji
authors.forename: Chaojie
authors.initials: C
authors.lastname: Wang
authors.forename: Krishan
authors.initials: K
authors.lastname: Kumar
authors.forename: Keisha
authors.initials: K
authors.lastname: Milum
authors.forename: Michelle
authors.initials: M
authors.lastname: Carleton
authors.forename: Xueliang
authors.initials: X
authors.lastname: Pan
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Ringel
authors.forename: Michael F
authors.initials: MF
authors.lastname: Tweedle
authors.forename: John E
authors.initials: JE
authors.lastname: Phay
mesh_terms: D000818:Animals; D001549:Benzamides / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D018278:Carcinoma, Neuroendocrine; D045744:Cell Line, Tumor; D003514:Cyclohexylamines / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D008819:Mice, Nude; D010280:Parathyroid Glands / Q000378:metabolism / Q000601:surgery; D044169:Receptors, Calcium-Sensing / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000378:metabolism* / Q000473:pathology* / Q000601:surgery; D023041:Xenograft Model Antitumor Assays
chemical_list: D001549:Benzamides; C095550:CASR protein, human; D003514:Cyclohexylamines; D007457:Iodine Radioisotopes; C482333:N(1)-(4-chlorobenzoyl)-N(2)-(1-(1-naphthyl)ethyl)-1,2-diaminocyclohexane; D044169:Receptors, Calcium-Sensing
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