Frizzled (Fzd) proteins are a family of seven transmembrane helices (7-TM) receptors for secreted Wnt glycolipoproteins. The Fzd receptors can respond to Wnt proteins in the presence of the Wnt co-receptor low density lipoprotein receptor-related protein 5 (LRP5) or LRP6 to activate the canonical -catenin pathway. Disruption of Wnt/-catenin signal represents an opportunity for rational cancer chemoprevention and therapy. Of the 10 members of the Fzd family, Fzd7 is the most important member governing cancer development and progression, and is a promising therapeutic target in cancer. The Fzd family is listed by the International Union of Pharmacology (IUPHAR) as a novel and separated family of G-protein-coupled receptors (GPCRs). Accumulated evidences, especially the very recent studies that demonstrate Fzd proteins act as GPCRs on the heterotrimeric Go/i proteins, further provide solid proof for the genuine GPCR nature of Fzd proteins. As major targets for drug development, GPCRs have been studied for many years and it is now well accepted that GPCR molecule exists in a conformational equilibrium between active and inactive biophysical states, ligands that shift the equilibrium toward the active/inactie receptor states can be used as GPCR modulators for different therapeutic purposes. This unique GPCR property makes Fzd7 transmembrane domain as an ideal drug target for suppressing Wnt/-catenin signaling in cancer. Nevertheless, our understanding of Wnt/Fzd signaling has only been greatly enhanced in recently years and there is no reported small molecule that directly targets Fzds, especially their transmembrane domain where the classical GPCR ligands bind. Recent advances in structural biology, especially the high resolution crystal structures of both agonist-bound and antagonist-bound GPCRs, have significantly increased the understanding of the mechanisms of GPCR activation and provided excellent structural templates for applying structure-based approaches to study Fzd receptors. In our preliminary study, we have identified one novel small molecule Wnt inhibitor, which fits very well into the binding pocket of Fzd7 model. We herein proposed a collaborative drug discovery effort, involving virtual screening and biological evaluations, to identify small molecule inhibitors of Fzd7 as anti-cancer drug candidates. The proposed specific aims include: 1) Identify potential Fzd7 inhibitors through ligand-based and structure-based virtual screening; and 2) Evaluate the selected hit compounds in various biological assays to verify their inhibitory effects on Wnt/Fzd7-induced activation of G proteins and Wnt/-catenin signaling in cancer cells. The identified Fzd7 inhibitory compounds will be promising drug leads for novel chemopreventive and chemotherapeutic strategies for Wnt-dependent cancers. Proof of the concept that Wnt signaling can be regulated by small-molecule modulators at the transmembrane domain of Fzd receptors will lead to the establishment of a new drug discovery strategy with broad therapeutic potentials.
Inhibitors of the Wnt/?-catenin signaling pathway have great therapeutic potential for cancer. Frizzled 7 (Fzd7) is the most commonly upregulated Wnt receptor in a variety of cancers, and is an attractive target for cancer therapy. In the current proposed studies, we proposed a collaborative drug discovery effort, involving molecular modeling, ligand-based and structure-based virtual screening and biological evaluations, to identify small molecule inhibitors of Fzd7 as anti-cancer drug candidates.
