Radiosynthesis of high affinity fluorine-18 labeled GnRH peptide analogues: In vitro studies and in vivo assessment of brain uptake in rats

Dag Erlend Olberg, Sven H. Hausner, Nadine Bauer, Jo Klaveness, Bård Indrevoll, Kjetil Wessel Andressen, Marie Dahl, Finn Olav Levy, Julie Sutcliffe, Ira Haraldsen

Research output: Contribution to journalArticle

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Abstract

Gonadotropin releasing hormone (GnRH) is recognized as an important neuromodulator affecting behavior and has been associated with the progression of Alzheimer's disease. The peptide has been shown to have a bidirectional transport through the blood-brain-barrier (BBB), which may account for the cognitive effects of systemically administered GnRH. In this study, four novel <sup>18</sup>F-GnRH peptide analogues were synthesized and their in vitro and in vivo characteristics studied in male rats. GnRH peptides were assembled by solid-phase peptide synthesis, either as the full length d-Lys<sup>6</sup>-GnRH (pyroGlu<sup>1</sup>-His<sup>2</sup>-Trp<sup>3</sup>-Ser<sup>4</sup>-Tyr<sup>5</sup>-d-Lys<sup>6</sup>-Leu<sup>7</sup>-Arg<sup>8</sup>-Pro<sup>9</sup>-Gly<sup>10</sup>-NH<inf>2</inf>) or as d-Lys<sup>6</sup>-desGly<sup>10</sup>-GnRH-NHEt. In all, four GnRH peptide analogues were synthesized and reacted with N-succinimidyl-4-fluorobenzoate (SFB) to yield the fluorinated versions. Binding affinities of the analogues were determined in a competitive binding assay for both human and rat GnRH receptors. K<inf>i</inf>-values for the GnRH peptides were found to be subnanomolar, with d-Lys<sup>6</sup>(FBA)-desGly<sup>10</sup>-GnRH-NHEt (7) being most potent with a K<inf>i</inf>-value of around 50 pM for GnRH receptor species. Radiolabeling was performed using N-succinimidyl-4-[<sup>18</sup>F]fluorobenzoate ([<sup>18</sup>F]SFB) in 33.3 ± 12.8% isolated decay corrected (d.c.) yield within 1.5-2 h. Rat serum stability over 2 h revealed minor degradation (≤5%). For in vivo studies, <sup>18</sup>F-peptides (4-30 MBq) were injected intravenously via the tail vein into rats and brain uptake was evaluated by means of dynamic PET (2 h) followed by biodistribution studies. PET showed limited or no uptake in brain for the <sup>18</sup>F-peptides which predominantly cleared rapidly by renal excretion. Specific binding in the pituitary gland was confirmed for the <sup>18</sup>F-peptide, 7, by blocking with the GnRH agonist buserelin. This journal is

Original languageEnglish (US)
Pages (from-to)708-714
Number of pages7
JournalMedChemComm
Volume6
Issue number4
DOIs
StatePublished - Apr 1 2015

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Fluorine
Gonadotropin-Releasing Hormone
Rats
Brain
Peptides
LHRH Receptors
In Vitro Techniques
Buserelin
Solid-Phase Synthesis Techniques
Competitive Binding
Pituitary Gland
Blood-Brain Barrier
Neurotransmitter Agents
Tail
Veins
Assays
Alzheimer Disease
Degradation

ASJC Scopus subject areas

  • Biochemistry
  • Pharmaceutical Science

Cite this

Olberg, D. E., Hausner, S. H., Bauer, N., Klaveness, J., Indrevoll, B., Andressen, K. W., ... Haraldsen, I. (2015). Radiosynthesis of high affinity fluorine-18 labeled GnRH peptide analogues: In vitro studies and in vivo assessment of brain uptake in rats. MedChemComm, 6(4), 708-714. https://doi.org/10.1039/c4md00486h

Radiosynthesis of high affinity fluorine-18 labeled GnRH peptide analogues : In vitro studies and in vivo assessment of brain uptake in rats. / Olberg, Dag Erlend; Hausner, Sven H.; Bauer, Nadine; Klaveness, Jo; Indrevoll, Bård; Andressen, Kjetil Wessel; Dahl, Marie; Levy, Finn Olav; Sutcliffe, Julie; Haraldsen, Ira.

In: MedChemComm, Vol. 6, No. 4, 01.04.2015, p. 708-714.

Research output: Contribution to journalArticle

Olberg, DE, Hausner, SH, Bauer, N, Klaveness, J, Indrevoll, B, Andressen, KW, Dahl, M, Levy, FO, Sutcliffe, J & Haraldsen, I 2015, 'Radiosynthesis of high affinity fluorine-18 labeled GnRH peptide analogues: In vitro studies and in vivo assessment of brain uptake in rats', MedChemComm, vol. 6, no. 4, pp. 708-714. https://doi.org/10.1039/c4md00486h
Olberg, Dag Erlend ; Hausner, Sven H. ; Bauer, Nadine ; Klaveness, Jo ; Indrevoll, Bård ; Andressen, Kjetil Wessel ; Dahl, Marie ; Levy, Finn Olav ; Sutcliffe, Julie ; Haraldsen, Ira. / Radiosynthesis of high affinity fluorine-18 labeled GnRH peptide analogues : In vitro studies and in vivo assessment of brain uptake in rats. In: MedChemComm. 2015 ; Vol. 6, No. 4. pp. 708-714.
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