Lead Optimization Yields High Affinity Frizzled 7‑Targeting Peptides That Modulate Clostridium difficile Toxin B Pathogenicity in Epithelial Cells

Frizzled 7 (FZD7) receptors have
been shown to play a central role
in intestinal stem cell regeneration and, more recently, in Clostridium difficile pathogenesis. Yet, targeting
FZD7 receptors with small ligands has not been explored as an approach
to block C. difficile pathogenesis.
Here, we report the discovery of high affinity peptides that selectively
bind to FZD7 receptors. We describe an integrated approach for lead
optimization, utilizing structure-based rational design and directed
evolution, to enhance the peptide binding affinity while still maintaining
FZD7 receptor selectivity. This work yielded new peptide leads with
picomolar binding constants to FZD7 as measured by biophysical methods.
The new peptides block the interaction between C. difficile toxin B (TcdB) and FZD receptors and perturb C. difficile pathogenesis in epithelial cells. As such, our findings provide
a proof of concept that targeting FZD receptors could be a viable
pharmacological approach to protect epithelial cells from TcdB pathogenicity.