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NMeSer 4 and their counterparts. Besides that, inhibition of cell proliferation, on hormonesensitiveLNCaP cells was in general higher than that on PC3 cells under the sameexperimental conditions.Concerning treatment of the three analogues with NMeSer in position 4 (II, IV andVII) with α-chymotrypsin (Figure 1), peptide VII with DGlu in position 6 remained intactin the reaction mixture for the longest period (33% after 12 h) followed by analogue II withDLys 6 (Sar) (9% after 12 h), while analogue IV with DLys 6 [Gly(tBu)] was completelydigested in 6 h. Analogous results were obtained by incubation of peptides with subtilisin.However, degradation rate was much slower and 56% of peptide [NMeSer 4 , DGlu 6 ,Fig. 1. Peptide degradation rates upon incubation with (left) α-chymotrypsin and (right)Subtilisin.desGly 10 ]-GnRH-NHEt (analogue VII) remained in the reaction mixture even after 24 h.In general, all four peptide solution structures exhibit a common fold to a U-typeconformation (Figure 2). This conformation brings the N-terminal close to C-terminalresidues and the type of N-to-C interaction depends on the different NOE interactionsobserved in each peptide. Long range proton-proton interactions have been observed in theNOESY spectra between Ser 4 and Arg 8 in the analogues V and VI suggesting that L/Damino acids have the same effect on theturn formation of the GnRH backbone.Despite the fact that such a long range NOEis totally absent in the [NMeSer 4 ,Fig. 2. Superimposition of the backboneof the four analogues in pairs.(A)leuprolide (grey) and [NMeSer 4 ,DGlu 6 ,desGly 10 ]-GnRH-NHEt (black)(B)[Glu 6 , desGly 10 ]-GnRH-NHEt (grey) and[DGlu 6 , desGly 10 ]-GnRH-NHEt (black).DGlu 6 ,desGly 10 ]-GnRH-NHEt analogue,the β-turn structure of Ser 4 -Arg 8 fragmentremained intact in all conformers of theensemble, demonstrating that thecalculation of the β-turn structure spanningresidues Ser 4 -Arg 8 is based exclusively onNOE constraints of the above residues. Theconformational characteristics and theincreased stability against proteolysis ofNMeSer 4 - containing analogs are promisingand might provide new options in GnRHdrug development but further in vivocharacterization of pharmacokinetic properties and activity studies are necessary.References1. Dondi, D., Festuccia, C., Piccolella, M., Bologna, M., Motta, M. Oncol. Rep. 15, 393 (2006).2. Kraus, S., Naor, Z., Seger, R. Cancer Lett. 234, 109 (2006).3. Naor, Z. Front. Neuroendocrinol. 30, 10 (2009).4. Zompra, A.A., Magafa, V., Lamari, F.N., Nikolopoulou, A., Nock, B., Maina, Th., Spyroulias,G.A., Karamanos, N.K., Cordopatis, P. J. Pept. Res. 66, 57 (2005).5. Pappa, E.V, Zompra, A.A., Spyranti, Z., Diamantopoulou, Z., Pairas, G., Lamari, F.N., Katsoris, P.,Spyroulias, G.A., Cordopatis, P. Biopolymers, in press (2010).437