Phage display and experimental brain therapeutics
Smith, Mathew Wayne
Phage display, a powerful polypeptide display technology, affords the rapid identification of peptides and proteins that interact with a target of interest The aims of the project were the phage display identification of peptides that interact with a druggable target in a brain disorder (glioblastoma multiforme) and the identification of peptides that serve as targeting vectors for brain delivery. Validation studies were undertaken to qualify the use of a cyclic 7-mer peptide phage library against targets including streptavidin and paracetamol chosen as examples of a large complex and small simple molecule, respectively. With the aim of identifying peptide phages that bind to the luminal surface of brain micro vasculature, a primary in-vitro porcine model of the blood-brain barrier (BBB) comprising primary brain capillary endothelial cells was established and characterised. An in-vivo phage display was undertaken in the rat with the aim of identifying peptide sequences that mediated translocation across the BBB into brain grey matter. A 7-mer cyclic peptide was identified with sequence AC-SYTSSTM-CGGGS that enhanced the uptake of phages into brain grey matter by 4-fold compared to control wild-type phages. This peptide may serve as a novel targeting vector for the delivery of a therapeutic cargo to the brain. Caveolin-1 was identified as a potential new therapeutic target in in-vitro models of grade IV astrocytomas (glioblastoma multiforme), with siRNA knockdown of caveolin-1 associated with reduced glioma cell proliferation and invasiveness. With the caveolin-1 scaffolding domain (aa 81-101 in the caveolin-1 protein) as a target, an in-vitro peptide phage selection was undertaken and identified a series of peptides that bind the scaffolding domain with high affinity. These peptides will serve as a template for the development of low molecular weight peptidomimetics that inhibit caveolin-1 function. In conclusion, the studies in this thesis have demonstrated the utility of phage display in experimental therapeutics of brain disorders.