beta-Catenin signaling: therapeutic strategies in oncology.

Activated Wnt signaling pathways have been found in various human cancers, including those of the colon, liver, endometrium, ovary, prostate, and stomach. As a result, beta-catenin is accumulated and becomes transcriptionally active for proliferative genes and oncogenes. Wnt pathway mutations result in biochemical mechanisms yielding inefficient phosphorylation of beta-catenin by GSK3beta due to APC, beta-catenin and/or axin mutations. Therefore, the needs and the opportunity to develop new cancer therapies exist through reversing oncogenic APC/beta-catenin/Lef/Tcf signals. Exisulind and analogues are inhibitors of cyclic GMP phosphodiesterases (PDE) that have been shown to activate and induce protein kinase G. The data show PKG regulation of beta-catenin in wnt signaling, accounting, at least in part, for apoptosis induction in treated colon cancer cells carrying either APC or beta-catenin mutations. Exisulind and analogs reduce beta-catenin via a novel, GSK3beta independent processing mechanism. Activated PKG directly phosphorylate beta-catenin at its C-terminal domain and causes proteasome dependent degradation of the protein. Since this pathway is independent of APC and GSK3beta, exisulind and analogs provide a superior approach to circumvent the molecular defects of wnt signaling pathway and to treat cancers with such defects.