Backbone metal cyclization: Novel 99mTc labeled GnRH analog as potential SPECT molecular imaging agent in cancer

Yaniv Barda, Nasi Cohen, Vered Lev, Nurit Ben-Aroya, Yitzhak Koch, Eyal Mishani, Mati Fridkin, Chaim Gilon*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Scopus citations

Abstract

Gonadotropin-releasing hormone (GnRH) is a decapeptide secreted to the pituitary where it binds to specific receptors on the gonadotropes to regulate gonadotropic hormones (luteinizing hormone (LH) and follicle-stimulating hormone (FSH)) synthesis and secretion. Specific GnRH receptors are overexpressed in breast, prostatic, ovarian, and other tumors. The aim of this study was to synthesize a cyclic GnRH analog with high affinity to GnRH receptors that can be radiolabeled with 99mTc. A precyclic GnRH analog, [Cys-Gly] 1[D-Ala]6[Nα(η-Cys-amino hexyl)] 10GnRH (Gn-2), containing two hemi-chelator groups was synthesized. It was cyclized applying the recently reported backbone metal cyclization (BMC) approach, to obtain cyclo(Re(O)1-10)[Cys-Gly]1[D-Ala] 6[Nα(η-Cys-amino hexyl)]10GnRH (cyclo[Re(O)-Gn-2]). For comparative evaluations, Gn-2 was oxidized on-resin to yield cyclo(S-S,1-10)[Cys-Gly]1[D-Ala]6[N α(η-Cys-amino hexyl)]10GnRH, (cyclo[S-S-Gn-2]). The binding affinity of cyclo[Re(O)-Gn-2] to rat pituitary membranes showed IC50 of 50nM, compared to IC50 = 10 nM in the native GnRH. Cyclo(99mTc(O)1-10)[Cys-Gly]1[D-Ala]6[N α(η-Cys-amino hexyl)]10GnRH (cyclo[ 99mTc(O)-Gn-2]) was synthesized from Gn-2 and showed similar chromatographic behavior to its rhenium surrogate.

Original languageEnglish
Pages (from-to)921-933
Number of pages13
JournalNuclear Medicine and Biology
Volume31
Issue number7
DOIs
StatePublished - Oct 2004

Keywords

  • Backbone metal cyclization
  • Prostate cancer
  • Radiolabeled GnRH analogs
  • Technetium-99m

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