Abstract LB-222: Aberrant activation of GLI1 and Notch1 contributes to racial disparity in triple-negative breast cancer progression
Authors: Siddharth Sumit , Saxena Anirudh , Muniraj Nethaji , Parida Sheetal , Nagalingam Arumugam , Sharma Dipali 
Published: September 2020

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 European American (EA) women (5-year relative survival of only 14% for AA in comparison to 36% for EA) 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 EA-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 EA 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 EA-TNBC (Hs578t, BT549, HCC1937 and HCC1187) cells. We analyzed RNA sequencing data of multiple AA and EA TNBC cell lines for 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 EA-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 EA-TNBC cells. AA-TNBC cells showed increased nuclear localization of GLI1 and NICD as compared to EA-TNBC cells. We observed that GLI and NICD co-localize in AA-TNBC. High expression of GLI1 and Notch1 correlated with poor overall survival in TNBC patients. AA TNBC Tumor samples show higher expression of GLI1 and NICD in comparison to TNBC tumors from EA patients. 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 growth and progression in mice; growth, proliferation, migration and invasion of ex vivo tumor cells and downregulated 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 GLI and Notch pathway and a crosstalk between GLI1 and NICD whose inhibition effectively inhibits AA-TNBC and sensitizes AA-TNBC to standard chemotherapy.
Citation Format: Sumit Siddharth, Anirudh Saxena, Nethaji Muniraj, Sheetal Parida, Arumugam Nagalingam, Dipali Sharma. Aberrant activation of GLI1 and Notch1 contributes to racial disparity in triple-negative breast cancer progression [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-222.