A Wnt-ow of opportunity: targeting the Wnt/beta-catenin pathway in breast cancer.

Aberrant activation of the Wnt/beta-catenin signaling pathway is a hallmark of many tumors, including breast cancer. In the normal breast, tightly regulated expression of Wnt/beta-catenin pathway components, including Wnts and the APC tumor suppressor, dictates its role in balancing stem cell self-renewal, maintenance and differentiation during embryonic and postnatal development. Therefore, not surprisingly, dysregulation of Wnt/beta-catenin signaling through overexpression of pathway activators, such as Wnts or stabilized beta-catenin, or targeted disruption of inhibitors, such as APC, leads to mammary tumorigenesis in several genetically engineered mouse (GEM) models. These models are powerful tools to dissect the importance of Wnt/beta-catenin signaling in human breast cancer because they recapitulate some of the histological features of human breast cancers that demonstrate pathway dysregulation. Over the last decade, numerous approaches have been developed to target the Wnt/beta-catenin pathway in tumor cells, from antagonizing Wnt ligand secretion or binding to promoting beta-catenin degradation to specifically blocking beta-catenin-mediated transcriptional activity. Despite sizeable hurdles because of gaps in our knowledge of most efficacious ways to inhibit the pathway, the breast cancer subtypes to target and how pathway antagonists might be used in combination therapy, crippling Wnt/beta-catenin signaling offers a tremendous opportunity to impact breast cancer pathogenesis. This review will provide an overview of the current understanding of Wnt/beta-catenin pathway involvement in regulating normal breast development and morphogenesis, the generation of Wnt/beta-catenin-dependent GEM models of human breast cancer, upregulation of signaling in human breast cancers and the compelling therapeutic strategies aimed at targeting the Wnt/beta-catenin pathway that show promising anti-tumor activity.