Abstract B49: Profiling of GLI antagonists in phenotypic models for effects on inflammatory breast cancer cell growth

Our objective was to assess GLI pathway antagonists for activity in inflammatory breast cancer (IBC) phenotypic models. Introduction: IBC is one of the most lethal forms of breast cancer and accounts for ~15% of all breast cancer deaths. IBC affects younger patients and is diagnosed in minorities at higher rates than in other racial and ethnic groups1. African-American women with IBC appear to have worse survival regardless of inflammatory status, stage, socioeconomic position, tumor, or treatment characteristics2,3. IBC is characterized by rapid progression, is highly invasive and is not usually detected by mammograms or ultrasounds. The presence of tumor emboli (TE) is a hallmark of the disease in which distinctive clusters of tumor cells migrate collectively and drive lymphatic invasion and metastasis. Activation of GLI1, the terminal effector of hedgehog (Hh) signaling, via gene amplification, has been linked to tumorigenesis, and invasiveness in many cancers including our studies on IBC4. Targeting at the level of GLI1 with small molecules has been effective with some demonstrating activity in vivo. Experimental procedures: In our studies we have used a tiered approach of phenotypic and functional assays to evaluate a panel of GLI antagonists for effects on IBC cell growth, in particular assessing their effects in models that more closely model or predict tumor growth in vivo including; migration, anchorage independent growth (AIG), mammosphere formation and TE assays. Results: Using our previously described quantitative cell proliferation assay5 we first identified a subset of GLI antagonists that effected IBC proliferation and down-regulated GLI1 transcriptional activity. We have now used high content imaging to simultaneously measure nuclear count, morphology, cell integrity, and mitochondrial health in live cells. We have identified GLI antagonists that show an anti-proliferative response but have no effect on nuclear size suggesting a lack of general cytotoxicity. In contrast, other antagonists had dramatic effects on nuclear area and nuclear texture indicative of cytotoxicity. We further examined their effects on colony formation using the AIG assay. SUM149 cells were treated with GLI inhibitors and effects on colony size and number noted. All three GLI antagonists tested reduced the size of the colonies with one also giving a significant reduction in number of colonies formed. Recently we have optimized an in vitro TE assay and are using this to screen GLI antagonists for effects on TE formation. Conclusion: we have identified a subset of GLI antagonists by phenotypic profiling for those with effects in cancer-specific functional assays that will be prioritized for testing in vivo. Funded in part by DOD/CDMRP IDEA (BC121850) (KPW). 1 Anderson, W. F., Schairer, C., Chen, B. E., Hance, K. W. & Levine, P. H. Epidemiology of inflammatory breast cancer (IBC). Breast disease 22, 9-23 (2006). 2 Schlichting, J. A., Soliman, A. S., Schairer, C., Schottenfeld, D. & Merajver, S. D. Inflammatory and non-inflammatory breast cancer survival by socioeconomic position in the Surveillance, Epidemiology, and End Results database, 1990-2008. Breast Cancer Research and Treatment 134, 1257-1268 (2012). 3 Yang, R. et al. A comprehensive evaluation of outcomes for inflammatory breast cancer. Breast cancer research and treatment 117, 631-641 (2009). 4 Thomas, Z. et al. Targeting GLI1 expression in human inflammatory breast cancer cells enhances apoptosis and attenuates migration. British Journal of Cancer 104, 1575-1586, doi:10.1038/bjc.2011.133 (2011). 5 Williams, K. P. et al. Quantitative high-throughput efficacy profiling of approved oncology drugs in inflammatory breast cancer models of acquired drug resistance and re-sensitization. Cancer Letters 337, 77-89 (2013). Citation Format: Helen Oladapo, Scott Sauer, Michael Tarpley, Gayathri Devi, Kevin P. Williams. Profiling of GLI antagonists in phenotypic models for effects on inflammatory breast cancer cell growth. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr B49.