Development of Substance P 1–7 Related Peptides and Peptidomimetics Targeting Neuropathic Pain

Skogh, A. 2018. Development of Substance P 1–7 Related Peptides and Peptidomimetics. Targeting Neuropathic Pain. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy 249. 68 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-513-0254-6. The neuropeptide substance P 1–7 (SP1–7, H-Arg-Pro-Lys-Pro-Gln-Gln-Phe-OH) and its amidated analogue SP1–7 amide, have displayed intriguing effects in experimental models for neuropathic pain acting on a specific, yet unknown SP1–7 target. The aim of this thesis was to design and synthesise SP1–7 related peptides and peptidomimetics, to be used as research tools to study the SP1–7 system, and to serve as drug leads in the neuropathic pain area. The in vivo structure activity relationship (SAR) of the SP1–7 amide was elucidated using Ala-substituted, N-terminally truncated and N-methylated variants. By evaluation of the antiallodynic effect in spared nerve injury (SNI) mice and the pharmacokinetic properties it is suggested that Phe acts as a message residue and Arg as an address residue, both important for the overall anti-allodynic activity. In contrast, Lys could be substituted by alanine, and the Pro-Lys and Pro-Gln bond could be N-methylated with retained anti-allodynic effect. The Pro-Lys bond was found most sensitive towards proteolysis and indeed, N-methylation of this bond delivered peptides completely inert in plasma. Conversely, prolonged plasma stability did not improve the overall in vivo activity for these peptides. Instead, the SP1–7 amide remained the most potent peptide in vivo, despite fast degradation in plasma. Besides peptide synthesis, the synthetic work included development of a Pd-catalysed aminocarbonylation protocol using an amino acid nucleophile, which was used for the synthesis of an imidazole-based peptidomimetic. This peptidomimetic was equipotent to the SP1–7 amide, and more potent than the drug gabapentin, in regard to its anti-allodynic effect in SNI mice, and it is a promising drug lead for further development. The Pd-catalysed aminocarbonylation protocol was refined further, in regards to reaction scope and requirements for solid-phase peptide synthesis and has proven useful for N-capping, isotopic labelling, and intramolecular cyclisation of peptides. In summary, the work presented herein resulted in an in vivo SAR for SP1–7 related peptides, a novel small molecule SP1–7 peptidomimetic, and methods expanding the toolbox for synthesising modified peptides and peptidomimetics – a field in drug discovery that presently gaining increasing attention.