SSTR1- and SSTR3-selective somatostatin analogues

Area of Science:

• Medicinal Chemistry
• Peptide Chemistry
• Pharmacology

Background:

• Somatostatin 14 (SRIF-14) is a peptide hormone with diverse physiological roles.
• Selective modulation of somatostatin receptors (SSTRs) is a therapeutic goal.
• Understanding structure-activity relationships is crucial for designing novel SRIF-14 analogues.

Purpose of the Study:

• To synthesize and characterize novel SRIF-14 analogues by replacing tryptophan (Trp8) with enantiomers of 3-(3"-quinolyl)-alanine (Qla8).
• To evaluate the receptor binding selectivity of these new analogues for SSTR1-5.
• To investigate the impact of Qla8 substitution on peptide conformation and receptor interaction.

Main Methods:

• Asymmetric hydrogenation for multigram-scale preparation of Qla enantiomers.
• Solid-phase synthesis of Fmoc-protected Qla-containing SRIF-14 analogues.
• Radio-ligand binding assays to determine receptor selectivity and affinity for SSTR1-5.

Main Results:

• Peptide 8a (L-Qla8) exhibited high selectivity for SSTR1 and SSTR3, with SRIF-14-like affinity.
• Peptide 8b (D-Qla8) showed high affinity for SSTR3 and significant affinity for SSTR1, SSTR2, and SSTR5.
• Bulky, electron-poor aromatic amino acids at position 8 are compatible with potent SSTR1 and SSTR3 activity.
• Increased conformational mobility in Qla8 analogues correlated with high affinity, suggesting rigidity may not be essential.

Conclusions:

• Novel SRIF-14 analogues with Qla8 demonstrate potent and selective SSTR1/SSTR3 binding.
• The Qla8 substitution introduces conformational flexibility, challenging the notion of required rigidity for receptor interaction.
• These findings offer insights into designing SRIF-14 analogues with tailored receptor selectivity and potentially improved therapeutic profiles.