1. New antagonists of LHRH. II. Inhibition and potentiation of LHRH by closely related analogues
S Bajusz, V J Csernus, T Janaky, L Bokser, M Fekete, A V Schally Int J Pept Protein Res. 1988 Dec;32(6):425-35. doi: 10.1111/j.1399-3011.1988.tb01373.x.
Modifications of the previously described LHRH antagonists, [Ac-D-Nal(2)1, D-Phe(4Cl)2, D-Trp3, D-Cit6, D-Ala10]LHRH and the corresponding D-Hci6 analogue, have been made to alter the hydrophobicity of the N-terminal acetyl-tripeptide portion. Substitution of D-Trp3 with the less hydrophobic D-Pal(3) had only marginal effects on the antagonistic activities and receptor binding potencies of the D-Cit/D-Hci6 analogues, but it appeared to further improve the toxicity lowering effect of D-Cit/D-Hci6 substitution. Antagonists containing D-Pal(3)3 and D-Cit/D-Hci6 residues, i.e. [Ac-D-Nal(2)1, D-Phe(4Cl)2, D-Pal(3)3, D-Cit6, D-Ala10]LHRH (SB-75) and [Ac-D-Nal(2)1, D-Phe(4Cl)2, D-Pal(3)3, D-Hci6, D-Ala10]LHRH (SB-88), were completely free of the toxic effects, such as cyanosis and respiratory depression leading to death, which have been observed in rats with the D-Trp3, D-Arg6 antagonist and related antagonists. Replacement of the N-acetyl group with the hydrophilic carbamoyl group caused a slight decrease in antagonistic activities, particularly in vitro. Introduction of urethane type acyl group such as methoxycarbonyl (Moc) or t-butoxycarbonyl (Boc) led to analogues that showed LHRH-potentiating effect. The increase in potency induced by these analogues, e.g. [Moc-D-Nal(2)1, D-Phe(4Cl)2, D-Trp3, D-Cit6, D-Ala10]LHRH and [Boc-D-Phe1, D-Phe(4Cl)2, D-Pal(3)3, D-Cit6, D-Ala10]LHRH, was 170-260% and persisted for more than 2 h when studied in a superfused rat pituitary system.
2. Inhibition of growth of human mammary tumor cells by potent antagonists of luteinizing hormone-releasing hormone
Y Sharoni, E Bosin, A Miinster, J Levy, A V Schally Proc Natl Acad Sci U S A. 1989 Mar;86(5):1648-51. doi: 10.1073/pnas.86.5.1648.
Various studies support the view that analogs of luteinizing hormone-releasing hormone (LH-RH) exert some direct effects on mammary tumor cells. Recently, new LH-RH antagonists [Ac-D-Nal(2)1,D-Phe(pCl)2,D-Trp3,D-Hci6,D-Ala10]-LH-RH (SB-29) and [Ac-D-Nal(2)1,D-Phe(pCl)2,D-Trp3,D-Cit6,D-Ala10]LH-RH (SB-30), which are devoid of edematogenic effects, were synthesized. In this study, we examined whether these LH-RH antagonists inhibit the proliferation of MDA-MB-231 human mammary tumor cells in culture. [3H]Thymidine incorporation into DNA and cell number were measured. The antagonists induced up to 40% inhibition of [3H]thymidine incorporation in MDA-MB-231 cells. This inhibition was dose-dependent in the 0.3-30 microM range and could be demonstrated after 2 days of incubation in the presence of the peptides. An older antagonist, [Ac-D-Phe(pCl)1,2,D-Trp3,D-Arg6,D-Ala10]-LH-RH (ORG 30276), had a lesser effect, and the agonist des-Gly10-[D-Ser(tBu)6]LH-RH ethylamide (buserelin) had no effect. The antagonists SB-29 and SB-30 also inhibited the rate of cell growth, as measured by cell number, while the LH-RH agonist buserelin had no significant effect. These results support the concept that these new LH-RH antagonists can directly inhibit the growth of human mammary tumors and thus might be suitable for the treatment of breast cancer.
3. Evaluation of the in vitro and in vivo activity of the L-, D,L- and D-Cit6 forms of the LH-RH antagonist Cetrorelix (SB-75)
J Pinski, A V Schally, T Yano, K Groot, G Srkalovic, P Serfozo, T Reissmann, M Bernd, W Deger, B Kutscher Int J Pept Protein Res. 1995 May;45(5):410-7. doi: 10.1111/j.1399-3011.1995.tb01056.x.
The objective of this study was to examine the in vivo and in vitro gonadotropin-inhibiting potencies, edematogenic activities and the receptor binding affinities of the D-Cit6, D,L-Cit6 and L-Cit6 forms of the LH-RH antagonist Cetrorelix (SB-75) [Ac-D-Nal(2)1,D-Phe(4Cl)2,D-Pal(3)3,D-Cit6,D-Ala10]LH- RH. In order to demonstrate the suppressive effects of two different diastereomers of SB-75 and their racemic mixture on LH and FSH release, [D-Cit6] SB-75 was injected subcutaneously in doses of 2.5 and 10 micrograms/rat, [D,L-Cit6]-SB-75 in doses of 5 and 20 micrograms/rat and [L-Cit6] SB-75 in doses of 12.5 and 50 micrograms/rat to castrated male rats. Two hours after administration, there was no difference in LH levels between rats injected with the L-form and control animals, indicating a low activity and/or a rapid enzymatic degradation of this peptide. The (1:1) diastereomeric mixture was only about half as potent in suppression of LH release compared to [D-Cit6] SB-75. Serum FSH levels were suppressed significantly (p < 0.01) for more than 48 h after the administration of 10 micrograms [D-Cit6] SB-75 and 20 micrograms of [D,L-Cit6] SB-75, respectively. [D-Cit6] SB-75 administered at a dose of 2 micrograms/rat induced 100% inhibition of ovulation, while 4 micrograms/rat of the D,L-Cit6 peptide were necessary to produce the same effect.(ABSTRACT TRUNCATED AT 250 WORDS)
