Synthesis and biological evaluation of antagonists of growth hormone-releasing hormone with high and protracted in vivo activities

József L. Varga, Andrew V. Schally, Valér J. Csernus, Márta Zarándi, Gábor Halmos, Kate Groot, Zoltán Rékási

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Abstract

Some antagonists of human growth hormone-releasing hormone (hGH-RH) synthesized previously were shown to inhibit in vivo proliferation of various human cancers in nude mice. However, the activity of these analogs requires an increase to assure clinical efficacy. In an attempt to prepare hGH-RH antagonists with a high and protracted activity, we synthesized and biologically tested 22 antagonistic analogs of hGH-RH(1-29)NH2. The ability of the antagonists to inhibit hGH-RH-induced GH release was evaluated in vitro in a superfused rat pituitary system, as well as in vivo after i.v. injection into rats. The binding affinity of the peptides to GH-RH receptors also was determined. All antagonistic analogs had the common core sequence [PhAc-Tyr1,D-Arg2, Phe(4-Cl)6 (para-chlorophenylalanine), Abu15 (α-aminobutyric acid),Nle27]hGH-RH(1-29)NH2 and contained Arg, D-Arg, homoarginine (Har), norleucine (Nle), and other substitutions. The following analogs were determined to have a high and/or protracted antagonistic activity: [PhAc-Tyr1,D-Arg2,Phe(4-Cl)6,Arg 9,Abu15,Nle27,D-Arg 29]hGH-RH(1-29)NH2 (JV-1-10), [PhAc-Tyr1,D-Arg2,Phe(4-Cl)6,Abu 15,Nle27, D-Arg28,Har29]hGH-RH(1-29)NH2 (MZ-6-55), [PhAc-Tyr1,D-Arg2,Phe(4-Cl)6,Arg 9,Abu15,Nle27,D-Arg28,Har 29]hGH-RH(1-29)NH2 (JV-1-36), and [PhAc-Tyr1,D-Arg2,Phe(4-Cl)6, Har9,Tyr(Me)10,Abu15,Nle 27,D-Arg28,Har29]hGH-RH(1-29)NH2 (JV-1-38). Among the peptides tested, analog JV-1-36 showed the highest GH-RH antagonistic activity in vitro and also induced a strong and prolonged inhibition of GH release in vivo for at least 30 min. The antagonist JV-1-38 was slightly less potent than JV-1-36 both in vitro and in vivo but proved to be very long-acting in vivo, suppressing the GH-RH-induced GH release even after 60 min. High and protracted in vivo activities of these antagonists indicate an improvement over earlier GH-RH analogs. Some of these hGH-RH antagonists could find clinical applications in the treatment of cancers dependent on insulin-like growth factors I and II.

Original languageEnglish
Pages (from-to)692-697
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume96
Issue number2
DOIs
Publication statusPublished - Jan 19 1999

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Keywords

  • Cancer therapy
  • Inhibitors of GH release
  • Structure-activity relationships

ASJC Scopus subject areas

  • General

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