Abstract

Novel and highly selective molecular tools to monitor and modulate activity of oncogenic b-catenin in Wnt-associated cancers

Ramanuj Gupta, Senior Investigator, Genome Institute of Singapore, A*STAR, NYU Cancer Institute

The Wnt pathway is one of a core set of evolutionarily conserved signaling pathways that regulate many aspects of metazoan development. Inappropriate activation of the Wnt pathway has been associated with tumorigenesis of the liver, colon, breast and skin. A key effector of the Wnt pathway is encoded by ?-catenin (?-cat). Since ?-cat Responsive Transcription (CRT) has been implicated in the genesis of many cancers, it makes an ideal target for developing therapeutics that could be utilized to modulate its nuclear activity. We conducted a high-throughput RNAi-based chemical genetic screen where we screened for small molecule “modifiers” of RNAi-induced loss-of-function phenotypes of tumor suppressor genes, such as Axin and APC, that are commonly mutated in Wnt/?-cat associated cancers. We identified a specific structural class of potent inhibitors of CRT, called iCRTs that specifically and potently inhibit Wnt/?-cat-induced phenotypes in several Wnt-responsive cell lines. Mechanistic studies suggest that the iCRTs directly bind to ?-cat and disrupt its interaction with its transcriptional partner TCF4. Importantly, the iCRTs inhibit cell growth/proliferation of pathologically relevant and ?-cat-addicted colon cancer cells (HCT116, HT29) both in vitro and in xenograft models in vivo. Notably, iCRTs display potent cytotoxic effect on patient-derived primary tumor microspheroids from a variety of cancers at concentrations that are comparable to known FDA-approved chemotherapeutics. Using these inhibitors, we are currently investigating molecular mechanisms by which dysregulated Wnt signaling may influence tumor progression and relapse in other cancers, including castrate-resistant prostate cancer, where the role for oncogenic ?-cat activity remains largely underexplored.