Abstract 1024: Targeting PAK1 activity in breast cancer: Inhibition of cell growth, survival, motility, and signaling (2015)

Abstract Breast cancer (BrCa) is one of the most common cancers diagnosed and is the second leading cause of cancer-related deaths of women in the United States. BrCa is divided into four major molecular subtypes; these categories are based upon the expression of hormone receptors (i.e., estrogen receptor (ER) and progesterone receptor (PR)), HER2/neu receptor, and proliferation rate. Of these subtypes triple negative (ER-, PR-, HER2-) BrCa are among the most lethal, are highly aggressive, have poor prognosis, limited treatment options, and lack effective targeted therapies. Our lab has shown p-21 activated kinase 1 (PAK1) protein expression increases with BrCa progression in human tumor samples. PAK1 is highly expressed in invasive tumor tissues in comparison to normal tissues. The role of PAK1 in BrCa development and progression is through its activity as a serine/threonine kinase involved in the regulation of several key oncogenic pathways (i.e., WNT/β-catenin and MAPK/ERK/JNK). Although PAK1 expression is increased in invasive tumor tissues, our studies have found that in human BrCa cell cultures PAK1 expression is independent of hormonal receptor status. Our hypothesis for this study is that triple negative BrCa cell lines are more reliant upon PAK1's activity for cell growth, survival, and motility. To test our hypothesis two triple negative BrCa cell lines, MDA-MB-231 and MDA-MB-468, and two ER+ BrCa cell lines, T47D and ZR75-1, were used. Our results demonstrate there are significantly higher levels of PAK1 protein in T47D and MDA-MB-468, compared to ZR75-1 and MDA-MB-231. To determine if the cells were reliant on the activity of PAK1 for cell viability, a trypan blue exclusion assay was performed. The PAK1 inhibitor 1,1′-Dithiodi-2-napthol (IPA-3) significantly inhibited all four BrCa cell lines, cell growth and viability in a dose-dependent manner. IPA-3 further inhibited cell proliferation of MDA-MB-468 (IC50 = 11.5μM), MDA-MB-231 (IC50 = 14.5μM), ZR75-1 (IC50 = 13.3μM), and T47D (IC50 = 17.1μM). IPA-3 also inhibited the phosphorylation and nuclear translocation of PAK1 in a dose-dependent manner in MDA-MB-231 cells. The inhibition of PAK1 by IPA-3 also significantly inhibited the migration of MDA-MB-231 cells in a time- and dose-dependent manner. The regulation of PAK1 activation by the WNT/β-catenin pathway was further explored in ER+ and triple negative BrCa cell lines. Additional studies are currently underway investigating the role of PAK1 activation on the MAPK/ERK/JNK pathway and its effects on cell migration and invasion. These studies explore the role of PAK-1 in triple negative BrCa cell growth, survival, motility, and oncogenic signaling. Further investigation of PAK1's targets within these signaling pathways will provide opportunities for the development of novel prevention and/or therapeutic strategies. Citation Format: Alexandra M. Fajardo, Tristan Browne, Hannah Graff, Kelly Kleier, Kyle Neltner, Courtney McCall, Brad Meyer, Larry Douglass, Julia Carter. Targeting PAK1 activity in breast cancer: Inhibition of cell growth, survival, motility, and signaling. [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 1024. doi:10.1158/1538-7445.AM2015-1024