Structure–activity study on the LH- and FSH-releasing and anticancer effects of gonadotropin-releasing hormone (GnRH)-III analogs

Abstract

GnRH-III was reported to have selective FSH-releasing activity in rats and significant anticancer potency on human breast cancer cells. To improve either of these effects, 14 analogs were synthesized and investigated for FSH/LH stimulation and breast cancer inhibition. Analogs with single amino acid changes in positions 5–7 or 10 showed small or no difference in the FSH- or LH-releasing activity compared with GnRH-III but their anticancer potency decreased significantly. Modification of the terminal amino acids, side chain cyclization at the 6–8 regions, or combined amino acid changes at positions 4, 6 and/or 8 resulted in the decrease of both effects. Gonadotropin-releasing activity of Arg 8-GnRH-III was improved 3–11-fold. A copolymer conjugate of GnRH-III showed 2–3-fold anticancer activity while losing endocrine potency. Conclusion The activation of GnRH-receptors on pituitary and breast cancer cells requires a specific structure and/or conformation that makes possible to improve the anticancer selectivity of GnRH analogs.