Genetic alterations in components that make up the Wnt signaling pathway, which includes APC (adenomatous polyposis coli) and β-catenin, are prevalent in a number of cancer types, occurring in upwards of 80% of colorectal cancers. Additionally, germline mutations of APC lead to the hereditary cancer syndrome Familial Adenomatous Polyposis (FAP). Wnt signaling controls the level of intracellular activated β-catenin, a key effector of oncogenic signal transduction, and oncogenic alterations in Wnt, APC, or β-catenin all result in elevated and uncontrolled levels of β-catenin. Wnt signaling is initiated upon binding of secreted Wnt ligands to Frizzled receptors and low-density lipoprotein receptor-related protein (LRP) co-receptors, which induces phosphorylation of Dishevelled (Dvl). Phosphorylated Dvl then associates with Axin, leading to dissociation of the β-catenin destruction complex (which includes APC and GSK3β). Free β-catenin then accumulates in the cytoplasm and translocates to the nucleus.
Recent studies have shown that the cyclic nucleotide phosphodiesterase 10A (PDE10) is overexpressed during early stages of tumorigenesis and is essential for tumor cell growth. PDE10 inhibition increases cyclic GMP levels in tumor cells to activate protein kinase G (PKG) signaling leading to the degradation of the oncogenic pool of β-catenin to suppress critical proteins essential for tumor cell proliferation and survival. Thus, targeting PDE10 provides a novel approach to selectively suppress β-catenin mediated transcriptional activity.
Our program has identified small molecules that selectively and potently inhibit PDE10 and suppress Wnt/β-catenin signaling in preclinical models. PDE10 inhibition has been shown to down regulate β-catenin expression and inhibits polyp and tumor growth. It has potential for application in the treatment of cancer as well as spontaneous and familial polyposis syndromes.