Abstract PS7-86: Molecular determinants of racial disparity guide triple-therapy for triple negative breast cancer
Authors: Siddharth Sumit , Parida Sheetal , Muniraj Nethaji , Hercules Shawn M , Nagalingam Arumugam , Győrffy Balázs , Daniel Juliet , Sharma Dipali 
Published: February 2021

Abstract
Background and Aim: Triple-negative breast cancer (TNBC) is a very aggressive subtype of breast cancer characterized by the absence of estrogen receptor (ER), progesterone receptor (PR) and HER2 receptor expression. Mortality from TNBC is significantly higher in African American (AA) women in comparison to White American (WA) women (5-year relative survival of only 14% for AA in comparison to 36% for WA) even though the incidence rates are lower in AA women. Irrespective of stage at diagnosis, AA-TNBC is more aggressive with higher metastasis and a poorer survival than WA-TNBC; therefore, it is imperative to understand the molecular determinants that drive aggressive progression of AA-TNBC. Overall aim of this study is to decipher the alterations in the molecular circuitry underlying racial disparity in TNBC progression in AA women compared to WA women. Results: AA-TNBC cells (HCC1806 and HCC1569) exhibited increased growth and higher migration potential; higher expression of stemness factors, increased number of mammospheres and higher CD44+/CD49f+ population in comparison to WA-TNBC (Hs578t, BT549, HCC1937 and HCC1187) cells. We analyzed RNA sequencing data of multiple AA and WA TNBC cell lines to query the status self-renewal pathways (Wnt/βCatenin, GLI1/Shh and YAP-TAZ) and observed significantly higher levels of GLI1 in AA-TNBC cell lines while no significant alterations were observed in other pathway components. Further analysis of TCGA dataset revealed a positive correlation between GLI1 and Notch1 in AA-TNBC with a negative correlation in WA-TNBC. Increased expression of components of GLI1 and Notch1 pathway (SHH, Jagged, cleaved-Notch (NICD), Hes1 and FOXM1) were noted in AA-TNBC compared to WA-TNBC cells. AA-TNBC cells showed increased nuclear localization of GLI1 and NICD as compared to WA-TNBC cells. We observed that GLI1 and NICD co-localize and co-immunoprecipitate in AA-TNBC indicating a direct interaction between these two transcription factors. High expression of GLI1 and Notch1 correlated with poor recurrence free survival in TNBC patients. Analyses of clinical samples revealed higher levels of nuclear NICD and GLI1 in AA-TNBC in comparison to WA-TNBC. Concomitant inhibition of GLI1 and Notch1 using respective small molecule inhibitors, GANT61 and DAPT, along with standard chemotherapeutic agents (Doxorubicin and carboplatin) effectively inhibited AA TNBC tumor growth in mice. Also, ex vivo analyses of tumor cells showed reduced migration and invasion potential as well as downregulation of CD44+/CD49f+ and ADLH1A1+ population in a synergistic manner. Combined treatment with GANT61+ DAPT+ Carboplatin effectively reduced stem cell frequency of AA-TNBC tumors in in vivo limiting dilution assay. Conclusions: In conclusion, these results show that AA-TNBC cells are inherently aggressive with increased growth, migration and stemness potential. We found aberrant activation of GLI1 and Notch pathway and a crosstalk between GLI1 and NICD whose inhibition effectively inhibits AA-TNBC and sensitizes AA-TNBC to standard chemotherapy. Our studies propose a ‘triple drug regimen’ for AA-TNBC tumors based on its molecular circuitry.
Citation Format: Sumit Siddharth, Sheetal Parida, Nethaji Muniraj, Shawn M Hercules, Arumugam Nagalingam, Balázs Győrffy, Juliet Daniel, Dipali Sharma. Molecular determinants of racial disparity guide triple-therapy for triple negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS7-86.