Abstract 4444: Small molecule drug Verteporfin inhibits TAZ/YAP-driven signaling and tumorigenicity of breast cancer cells

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA More than 1.6 million people worldwide are diagnosed with breast cancer (BC) each year, making it the second most common form of cancer. An essential step toward a safe and effective BC therapy is to develop clinically translatable strategies to target major oncogenic drivers in BC cells. Transcription co-activators TAZ and YAP, both of which are nuclear effectors of the Hippo pathway, have recently been identified as major oncogenic drivers in BC that promote tumor propagation, metastasis and resistance to current therapies. To date, pharmacological strategies for TAZ/YAP inhibition are still lacking. Here, we successfully inhibited TAZ/YAP-driven signaling in BC models by repurposing Verteporfin, an FDA-approved drug currently used to treat neovascular macular degeneration but not human cancers. We found that Verteporfin treatment inhibited the nuclear translocation and protein expression of TAZ/YAP as well as TAZ/YAP-driven signaling (e.g. EMT signaling) in MDA-MB-231 and BT-549 breast cancer cells. Verteporfin potently inhibited cell proliferation and induced apoptotic cell death up to 90% in BC cells. Systemic Verteporfin treatment was well tolerated in mice and inhibited the growth of orthotopic tumor xenografts derived from MDA-MB-231 cells by more than 100% (p<0.01). We further characterized the molecular response of BC cells to Verteporfin using RNA-seq followed by qPCR and western blot validation. We found that Verteporfin inhibited multiple EMT marker genes (e.g. Fibronectin 1, Vimentin, Snail and Slug). In addition, Verteporfin suppressed the expression of genes that mediate BC metastasis (e.g. ANGPTL4, COX2, EREG and MMP1), and also downregulated major components of signaling pathways (e.g. Notch and Integrin) that are essential for tumorigenicity of BC cells. Some of these genes had been identified as TAZ/YAP-activated gene targets, supporting the inhibition of TAZ/YAP-driving signaling by Verteporfin. A number of novel targets were also discovered. Furthermore, we found that transcription factor SOX4, a downstream target of TGFβ signaling, was activated in BC cells surviving from Verteporfin treatment. Manipulating SOX4 expression in BC cells changed Verteporfin sensitivity. Cells with enhanced SOX4 expression were more resistant to Verteporfin. These results elucidate a novel mechanism underlying Verteporfin resistance and suggest that Verteporfin and TGFβ inhibitors could work in combination to inhibit BC. In conclusion, we identified Verteporfin as a potential inhibitor of TAZ/YAP-driven signaling in BC, and established a global map of Verteporfin-response genes in BC cells. We systematically characterized the inhibitory effects of Verteporfin on BC cells at the molecular and cellular levels, and further identified SOX4-driven mechanism that mediates Verteporfin resistance. These results will facilitate the development of Verteporfin-based therapy for BC. Citation Format: Han Sun, Mingyao Ying. Small molecule drug Verteporfin inhibits TAZ/YAP-driven signaling and tumorigenicity of breast cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4444. doi:10.1158/1538-7445.AM2015-4444