Abstract

Regulating Wnts at the source

David Virshup, Professor and Director, Duke-NUS Graduate Medical School Singapore

Dysregulation of Wnt signaling is implicated in multiple diseases. 19 different Wnts mediate signaling through diverse downstream pathways. To achieve maximum benefit from inhibition of Wnt signaling, targeting multiple Wnts may be useful. The secretion and biological activity of all human Wnts requires palmitoylation mediated by Porcupine (PORCN), an endoplasmic reticulum-localized membrane bound O-acyltransferase. Several small molecule inhibitors of PORCN have been developed. By a number of criteria, these compounds potently inhibit PORCN catalytic activity and hence suppress downstream Wnt-activated signaling pathways. The compounds effectively reduce autocrine Wnt signaling activity in selected cancer cell lines. Compounds with good oral bioavailability were tested for their in vivo activity and found to be highly efficacious in reversing tumor growth in both MMTV-WNT1 mice and of tumor xenografts. Treated tumors showed marked nuclear exclusion and decreased cytoplasmic staining of beta-catenin compared to vehicle controls. Importantly the treatment modulated downstream markers of Wnt signaling. No signs of toxicity were observed in mice at therapeutically effective doses. Inhibiting the Wnt/beta-catenin pathway by targeting PORCN with small-molecule inhibitors is a feasible and nontoxic strategy. Use of porcupine inhibitors overcomes the problem of redundancy of Wnts, thereby, providing new options for therapy in diseases with high Wnt activity.