UBC Theses and Dissertations
Towards the development and discovery of inhibitors for Trypanosoma cruzi trans-sialidase Robinson, Kyle Brian
The parasite Trypanosoma cruzi displays a trans-sialidase (TcTS) on its surface that is hypothesized to be a therapeutic target for Chagas disease. TcTS transfers sialic acid from the cells of infected hosts to the surface of the pathogenic parasite, masking it from immune recognition and enhancing cellular invasion. The design of TcTS inhibitors has been largely unsuccessful to date. Accordingly, this work aims to identify new TcTS inhibitors, both by modifying existing inhibitors and by screening natural product and peptide libraries to discover new chemical scaffolds for this purpose. First, analogues of the established mechanism-based inhibitor, difluorosialic acid (DFSA), were investigated in search of increased potency and selectivity for TcTS. The synthesis and kinetic analysis of nine C9 amide-linked DFSAs and seven N-acyl modified DFSAs was explored to this end. One candidate was identified that inhibited TcTS 10-fold better than the unmodified precursor. Further, TcTS showed a tolerance for the C5 functionalized inhibitors, a fact that can be leveraged – together with C9 substitution – for specificity versus human neuraminidases. Next, a library of ~1000 marine organism extracts was screened for TcTS inhibition, from which five hits were selected. Bioassay-guided isolation and structural determination of the active chemicals afforded two new natural product inhibitors of TcTS with IC50 values <25 μM. The most potent species belongs to the ircinialactam family and its structure-activity relationship was assessed by screening a library of synthetic ircinialactam-like compounds. These studies revealed a preference for chemical species bearing furan, tetronic acid or glycinal lactam functional groups separated by unsaturated carbon chains 10-15 atoms in length. The eight best synthetic derivatives had a reversible, non-competitive mode of action with Ki <5 μM. These species were further tested in a parasite growth inhibition assay affording inconclusive results. Finally, random nonstandard peptide integrated discovery (RaPID) screening identified two peptide sequences – bearing 4-5 hydroxylated non-proteinogenic amino acid residues – that were exogenously cyclized with disuccinimidyl glutarate. The best macrocyclic peptide inhibitor had a Ki = 1.4 μM. Together these studies identified a diverse series of new chemical inhibitors that can be further explored to assess the therapeutic relevance of TcTS.
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