Development of radioimmunoassay for a potent luteinizing hormone-releasing hormone antagonist. Evaluation of serum levels after injection of [Ac-3-(2-naphthyl)-D-Ala1,D-Phe(pCl)2,3-(3-pyridyl)-D-Ala3, D-Cit6,D-Ala10] LHRH

V. J. Csernus, B. Szende, K. Groot, T. W. Redding, A. V. Schally

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Highly potent antagonistic analogs of luteinizing hormone-releasing hormone (LHRH), free of edematogenic effects have been developed. These analogs proved to be potent inhibitors of LH, follicle stimulating hormone (FSH) and sex steroid levels in animals and human beings. The clinical utility of these compounds would be greatly enhanced by a sustained delivery system, capable of maintaining therapeutic peptide levels in blood over an extended period of time. Consequently, long acting formulations of microcapsules were prepared from one of the most potent antagonists, [Ac-3-(2-naphthyl)-D-Ala1,D-Phe(pCl)2,3-(3-pyridyl)-D-Ala3, D-Cit6,D-Ala10] LHRH (SB-75). The microcapsules consisted of 2% w/w SB-75 in poly-DL-lactide-co-glycolide (PLGA), a biocompatible, biodegradable polymer. To facilitate pharmacokinetic studies necessary for experimental and clinical investigation of the microencapsulated analog, a highly sensitive and specific radioimmunoassay was developed. The antibody against SB-75 was generated in rabbits. No significant cross-reaction could be detected with several natural peptides and analogs tested. The sensitivity of the assay is 0.6 pg/tube. The RIA is suitable for direct determination of SB-75 level in 20 μl serum. The two lots of SB-75 microcapsules exhibited different pharmacokinetic release patterns. Single intramuscular injection of 20 mg SB-75 microcapsules, PLGA batch No. 001, into female rats maintained elevated serum SB-75 levels for three weeks. The suppression of LH secretion during this period was indicated by histological findings. The ovaries in the treated group were polyfollicular and no corpora lutea were present, indicating a prolonged ovarian inactivity due to LH deprivation. There was also a significant reduction in the size and weight of the ovaries (40.4 mg vs 66.7 mg for controls). The administration of SB-75 microcapsules, PLGA batch Nr. 002, to male rats produced high serum SB-75 levels for about 10 days, but a significant elevation in SB-75 values was maintained at least until day 29. Serum testosterone (T), LH and prolactin levels were significantly decreased. A greater depression in serum T occurred on days 2-7, than on days 14-24, indicating that this batch exerted maximal effects during the first 7 days. Histological examinations of the testicles revealed signs of impaired spermatogenesis. The histological picture of the prostate gland in these rats also indicated reduced activity. Our results suggest that improved sustained delivery formulations should be capable of maintaining therapeutic levels of the antagonist for several weeks. The RIA developed should be of value for monitoring SB-75 levels during long-term therapy.

Original languageEnglish (US)
Pages (from-to)111-118
Number of pages8
JournalArzneimittel-Forschung/Drug Research
Issue number2
StatePublished - 1990
Externally publishedYes


  • [Ac-3-(2-naphthyl)-D-Ala,D-Phe(pCl),3-(3-pyridyl)-D-Ala, D-Cit,D-Ala] LHRH, serum levels
  • Luteinizing hormone-releasing hormone, antagonistic analogs, long acting delivery systems, radioimmunoassay
  • SB-75

ASJC Scopus subject areas

  • Drug Discovery
  • Organic Chemistry
  • Chemistry(all)
  • Pharmacology


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