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[N α(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[N α(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 IC 50 of 50nM, compared to IC 50 = 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.
Published Version
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