Novel sst₄-Selective Somatostatin (SRIF) Agonists. 3. Analogues Amenable to Radiolabeling

Abstract

After our discovery that H-c[Cys-Phe-Phe-DNal-Lys-Thr-Phe-Cys]-OH (ODN-8) had high affinity and marginal selectivity for human sst(3) (part 2 of this series: Erchegyi et al. J. Med. Chem., preceding paper in this issue)(11) and that H-c[Cys-Phe-Phe-DTrp-Lys-Thr-Phe-Cys]-OH (ODT-8, 3) had high affinity and marginal selectivity for human sst(4), that H-c[Cys-Phe-Tyr-D-threo-beta-Me2Nal-Lys-Thr-Phe-Cys]-OH had high affinity for all sst's except for sst(1), and that H-c[Cys-Phe-Tyr-L-threo-beta-Me2Nal-Lys-Thr-Phe-Cys]-OH had high affinity for sst(4) (IC(50) = 2.1 nM), with more than 50-fold selectivity toward the other receptors (parts 1 and 2 of this series: Rivier et al. and Erchegyi et al. J. Med. Chem., preceding papers in this issue), we found H-c[Cys-Phe-Phe-Trp-Lys-Thr-Phe-Cys]-OH (OLT-8, 2), H-c[Cys-Phe-Phe-L-threo-beta-MeTrp-Lys-Thr-Phe-Cys]-OH (4) and H-c[Cys-Phe-Phe-D-threo-beta-MeTrp-Lys-Thr-Phe-Cys]-OH (5) to have very high affinity for sst(4) (IC(50) = 0.7, 1.8, and 4.0 nM, respectively) and 5- to 10-fold selectivity versus the other sst's. From earlier work, we concluded that an l-amino acid at position 8 and a tyrosine or 4-aminophenylalanine substitution at position 7 may lead to high sst(4) selectivity. In fact, [Tyr(7)]-2 (6) and [Tyr(7)]-3 (7) show ca. 5-fold selectivity for sst(4), and [Aph(7)]-2 (8) and [Aph(7)]-3 (9) have high sst(4) affinity (IC(50) = 1.2 and 0.88 nM, respectively) and selectivity, suggesting that indeed an l-residue at position 8 will direct selectivity toward sst(4). Unexpectedly, [Ala(7)]-2 (10) and [Ala(7)]-3 (11) have very high sst(4) affinity (IC(50) = 0.84 and 0.98 nM, respectively) and selectivity (>600- and 200-fold, respectively). The combination of Tyr(2) and dTrp(8) in analogues 14 and 22 did not affect the affinity of the analogues for sst(4) (IC(50) = 1.2 and 1.1 nM, respectively) but resulted in loss of selectivity, whereas the combination of Tyr(2) and LTrp(8) in H-Tyr-c[Cys-Phe-Aph-Trp-Lys-Thr-Phe-Cys]-OH (13) and H-Tyr-c[Cys-Phe-Ala-Trp-Lys-Thr-Phe-Cys]-OH(19) retained high affinity (IC(50) = 1.9 and 1.98 nM, respectively) and sst(4) selectivity (>50 and >250, respectively). Interestingly, the same substitutions at positions 2 and 7, with l-threo-beta-MeTrp at position 8, yielded a much less selective analogue (20). Carbamoylation of the N-terminus of most of these analogues resulted in slightly improved affinity, selectivity, or both. Other amino acid substitutions in this series, such as those with Amp (25, 26), Orn (27), or IAmp (29) at position 7, were also tolerated but with a 2- to 3-fold loss of affinity and concomitant loss of selectivity. Analogous peptides with a tyrosine at position 11 (31-36) were less selective than the corresponding peptides with a tyrosine at position 2. Several analogues in this series compared favorably with the non-peptide L-803,087 (37) in terms of affinity and selectivity. Analogues 8, 10, and 21 potently inhibited the forskolin-stimulated cAMP production in sst(4)-transfected cells, therefore acting as full agonists. Cold...

Central Injection of the Stable Somatostatin Analog ODT8-SST Induces a Somatostatin2 Receptor-Mediated Orexigenic Effect: Role of Neuropeptide Y and Opioid Signaling Pathways in Rats

“…15 in (26) (Clayton Foundation Laboratories, Salk Institute, La Jolla, CA) were synthesized and purity assessed as previously described (21,(25)(26)(27). Peptides and the NPY-Y 1 receptor antagonist, BIBP-3226 (Sigma-Aldrich, St. Louis, MO) were kept in powder form at Ϫ80 C and dissolved in pyrogen-free distilled water immediately before the experiments.…”

“…Because all studies related to SST or octreotide influence on food intake have been performed in rats (6,7) and recently in chicks (8), we also investigated whether mice are similarly responsive. We characterized the receptor subtype involved in ODT8-SST-induced stimulation of food intake using selective peptide sst 1 or sst 4 receptor agonists and a recently developed selective peptide sst 2 antagonist (25)(26)(27). We thereafter examined whether the underlying mechanisms of ODT8-SST action involve established orexigenic pathways.…”

Novel sst2-Selective Somatostatin Agonists. Three-Dimensional Consensus Structure by NMR

“…The products were also characterized by mass spectroscopy; the observed (M+H) + values coincided with the calculated (M+H) + values. NMR samples were prepared by dissolving 2 mg of the analogue in 0.5 mL of DMSO-d 6 . The 1 H NMR spectra were recorded on a Bruker 700 MHz spectrometer operating at proton frequency of 700 MHz.…”

“…20,21 These models of the pharmacophores are different from that of the reported sst 2/3/5 selective pharmacophore in the following manner. The sst 4 pharmacophore has one aromatic side chain, either Phe 6 or Phe 11 involved in binding in addition to the DTrp 8 and Lys 9 pair. The distance between DTrp 8 and Lys 9 is 4.5−6.5 Å, between DTrp 8 and Phe 6/11 is 5.5−9.5 Å and between Lys 9 and Phe 6/11 is 4.5−6.5 Å.…”

A practical synthesis of enantiopure β-methyltryptophan ethyl ester for a preparation of diabetes drug

“…[1][2][3] In this context, b-methyltryptophan (b-MeTrp) has received considerable attention in the field of peptide-based drug design, [4][5][6][7] and it has been used as a bioisostere of amino acid residue of peptide mimetic compounds ( Fig. 1), such as the diabetes drug candidates N-[(1R,2S)-1-({5-[(dimethylamino)methyl]-2-ethoxyphenyl}aminocarbonyl)-2-(1H-indol-3-yl)propyl]-4-phenyl-1-piperidinecarboxamide (1), 8 L-054,522, 9 and L-779,976.…”