Abstract 863: LKB1 inhibits NFkB to suppress cancer stem cells in triple negative breast cancer
Authors: Nguyen Khoa , Alzoubi Madlin , Cheng Thomas , Hebert Katherine , Elliott Steven , Yousefi Hassan , Alahari Suresh , Burow Matthew , Collins-Burow Bridgette 
Published: June 2022

Abstract
Breast cancer is the most common malignancy diagnosed in US women and is the second leading global cause of death for women. Triple Negative Breast Cancer (TNBC) is a more aggressive subtype of breast cancer that is categorized by negative expression of estrogen receptors, progesterone receptors, and amplification of HER2/neu. Because of its receptor phenotype, traditional hormone therapy fails to produce significant short- or long-term benefits for patients. Additionally, chemotherapeutic and surgical interventions often result in relapse and development of a more aggressive disease with higher rates of growth, metastasis, and drug resistance. TNBC also tends to affect women younger than 40 as well as black women, making it a disease of disparities. The Liver Kinase B1 (LKB1/STK11) signaling pathway has been well characterized to have a role in defining cellular responses to energy homeostasis, metabolism, as well as tumor suppressive capabilities. It functions as a master regulator through a set of 14 known kinase targets to maintain its role in cell-type specific regulation. Peutz Jeghers Syndrome, a genetic disorder with a predisposition to developing malignancies, and many other solid tumor cancers are associated with a loss of expression, somatic mutation, or functional deficiencies of LKB1 activity. While studies have been done to understand the role of LKB1 signaling, its role and mechanism in the regulation of TNBC remains unknown. We previously demonstrated LKB1 expression to be associated with increased survival rates for patients diagnosed with TNBC. Therefore, we hypothesize that LKB1 activity in TNBC cell lines will inhibit cancer function. To test this, TNBC cell lines were transfected to overexpress LKB1 with vector transfections generated for controls. Initial molecular results demonstrate a reversal of EMT gene expression by qPCR in cells that overexpressed LKB1. Flow cytometry analysis of LKB1 overexpressing cells show a decrease in the GD2+ cancer stem cells (CSCs). Additionally, functional assays show a reduction growth and proliferation in 3D culture systems. Interestingly, there was no effect on proliferation in standard 2D culture conditions. GD2 was previously identified to be regulated by NFkB signaling. Because LKB1 overexpression resulted in the suppression of CSCs, we hypothesized that LKB1 expression suppresses NFkB signaling. To test this, we ran a western blot panel for NFkB antibodies. Interestingly, LKB1 OE cells had lower levels of IKKα, IKKß, and p65 compared to pcDNA controls. This suggests that LKB1 functions to inhibit NFkB signaling, resulting in the suppression of the CSC phenotype in TNBC. To summarize, LKB1 expression inhibits NFkB signaling, which leads to decreased CSCs. This results in reversal of EMT genes and diminished capabilities to form spheres. Future studies will be dedicated to identifying which of the 14 downstream kinases LKB1 activates to exert its functions.
Citation Format: Khoa Nguyen, Madlin Alzoubi, Thomas Cheng, Katherine Hebert, Steven Elliott, Hassan Yousefi, Suresh Alahari, Matthew Burow, Bridgette Collins-Burow. LKB1 inhibits NFkB to suppress cancer stem cells in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 863.