| Summary: | <p>Peptides have attracted increasing attention as therapeutics in recent years, at least partially as a consequence of the widespread acceptance of protein therapeutics; but also as possible solutions to problems such as short half-life and delivery of molecules, and as therapeutics in their own right. The current work presents three projects that involve applications of peptides in a therapeutic environment.</p><p>The first project studies the use of ER retaining peptides and CPPs (Cell penetrating peptides) in enhancing the effective concentration of DNJ (1-deoxynojirimycin), an α-glucosidase inhibitor, in cells. DNJ constructs with ER retaining peptides (6-[N-(1-deoxynojirimycino)]-hexanoyl-KDEL and 6-[N-(1-deoxynojirimycino)]-hexanoyl-KKAA) and CPPs (6-[N-(1-deoxynojirimycino)]-hexanoyl-TAT and 6-[N-(1-deoxynojirimycino)]-hexanoyl-MAP) were synthesised and analysed for their inhibitory activity against α-glucosidase I and II <em>in vitro</em>. The constructs were then analysed in a cell-based assay to determine their inhibitory activity on α¬-glucosidase-mediated hydrolysis of N-linked oligosaccharides. FITC-labelled ER retaining peptides were also synthesised to determine the internalisation and trafficking of the constructs by FACS and IF-microscopy. While none of the DNJ-constructs showed higher cellular inhibition than NB-DNJ (N-butyl DNJ; Miglustat), the CPP construct 6-[N-(1-deoxynojirimycino)]-hexanoyl-TAT showed comparable activity and the ER retaining construct 6-[N-(1-deoxynojirimycino)]-hexanoyl-KDEL showed a small but significant increase in activity following long-term administration.</p><p>The second project focuses on beauveriolides, a cyclic depsipeptide family shown to have activity as ACAT inhibitors and thus a possible treatment for Alzheimer’s disease by the decrease in the production of Amyloid β (Aβ). A published total synthetic method was improved by the use of a cross-metathesis to reduce the total synthesis by 5 steps and increase its flexibility to allow the production of analogues. The synthesised beauveriolide III was used in attempts to develop an IF-FACS-based assay to measure the intracellular concentrations of Aβ. However, the location of γ-secretase in the used cell-line meant that levels of intracellular Aβ were not sufficient to track any decrease caused by ACAT inhibition.</p><p>The third project involves the design of a cyclic peptide that could block the binding site for the influenza virus in the host cell. The cyclic peptide (cGSGRGYGRGWGVGA) was developed from a comparative study of four different sialic acid-binding proteins and synthesised by solution cyclisation of the linear peptide synthesised by traditional solid phase peptide synthesis (SPPS). An <em>in silico</em> study showed that the cyclic peptide allowed overlap with the binding site of Hemagglutinin. A 1H NMR titration determined the dissociation constant of the cyclic peptide to sialic acid. The KD corresponded to a low binding affinity, however the observed binding seemed to be specific and caused by a single bound conformation.</p>
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