Table 1.
Structure and receptor binding affinity of somatostatin and somatostatin receptor agonists.
| Peptide | Structure | Receptor binding affinity (IC50, nM)a | ||||
|---|---|---|---|---|---|---|
| sst1 | sst2 | sst3 | sst4 | sst5 | ||
| Somatostatin-14 (Viollet et al., 1995) | Ala-Gly-c[Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys]-OH | 0.1–1.5 | 1.7 | 1.7 | 1.0–1.6 | 0.2–2.2 |
| Somatostatin-28 (Viollet et al., 1995) | Ser-Ala-Asn-Ser-Asn-Pro-Ala-Met-Ala-Pro-Arg-Glu-Arg-Lys-Ala-Gly-c[Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys]-OH | 0.1–4.7 | 0.4–5.2 | 0.2 | 0.3–1.1 | 0.05–0.19 |
| Octreotide (Grace et al., 2008) | H-(D)-Phe2-c[Cys3-Phe7-DTrp8-Lys9-Thr10-Cys14]-Thr15(ol) | >1K | 1.9 ± 0.3 | 39 ± 14 | >1K | 5.1 ± 1.1 |
| ODT8-SST (Erchegyi et al., 2008) | des-AA1,2,4,5,12,13-(DTrp8)-SST | 27.0 ± 3.4 | 41.0 ± 8.7 | 13.0 ± 3.2 | 1.8 ± 0.7 | 46.0 ± 27.0 |
| Cortistatin-17 (Fukusumi et al., 1997) | Asp-Arg-Met-Pro-cyclo-[Cys-Arg-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Ser-Ser-Cys]Lys | 0.3–7.0 | 0.6–0.9 | 0.4–0.6 | 0.5–0.6 | 0.3–0.4 |
| sst1 agonist (Erchegyi et al., 2009) | des-AA1,4-6,10,12,13-[DTyr2,D-Agl(NMe,2naphtoyl)8,IAmp9]-SST-Thr-NH2 | 0.19 ± 0.04 | >1K | 158.0 ± 14.0 | 27.0 ± 7.5 | >1K |
| sst2 agonist (Grace et al., 2006) | des-AA1,4-6,11-13-[DPhe2,Aph7(Cbm),DTrp8]-Cbm-SST-Thr-NH2 | >1K | 7.5–20 | 942–1094 | 872–957 | 109–260 |
| sst2 antagonist (Cescato et al., 2008) | des-AA1,4-6,11-13-[pNO2-Phe2,DCys3,Tyr7,DAph(Cbm)8]-SST-2Nal-NH2 | >1K | 2.6 ± 0.7 | 384.0 ± 97.0 | >1K | >1K |
Receptor affinities were derived from competitive radioligand displacement assays in cells stably expressing the cloned human receptor using 125I-[Leu8DTrp22Tyr25]SST-28 (Grace et al., 2006, 2008; Cescato et al., 2008; Erchegyi et al., 2008, 2009) except for somatostatin-14 (Viollet et al., 1995), somatostatin-28 (Viollet et al., 1995), and cortistatin (Fukusumi et al., 1997).