Abstract 2312: Identifying novel cancer stem cell target for triple-negative breast cancer

Triple negative breast cancer is characterized by its aggressive clinical behavior with high incidence of metastasis to the lungs and brain. These patients do not respond to hormonal therapy and show intrinsic resistance to conventional chemotherapy. Robust evidence indicates that treatment-resistance and metastases may arise from a subpopulation of cells with tumor-initiating capacity called breast cancer stem cells (BCSC). We are one of the first groups to demonstrate that residual tumors after exposure to chemotherapy are enriched for BCSC. We have previously described a treatment-resistant gene signature of 493 genes derived from patient biopsies.This finding narrowed down the possible cancer stem cell growth related genes from genome wide to only 493 genes and provided candidate genes for screening potential targets that affect BCSC self-renewal. Re-evaluation of the candidate genes determined a previously unidentified cancer gene, Hematological and Neurological Expressed 1-Like (HN1L) as the target of cancer stem cell self-renewal. The objective of this study was to investigate the role of HN1L in regulating BCSC and metastasis in TNBC, and to determine the mechanism of action of HN1L in BCSC. Knocking down HN1L by shRNA in SUM159 and MDAMB231 cell lines significantly decreased mammosphere forming efficiency (MSFE) and CD44+/CD24low/- population. To assess the contribution of HN1L to BCSC and tumor growth, a patient derived human-cancer-in-mouse xenograft model and two cancer cell line xenograft models were employed. To ensure targeted delivery, siRNA was packaged into DOPC liposomes and delivered into mice via intraperitoneal injection. Results showed that silencing HN1L alone or in combination with chemotherapy in xenografts reduced tumor volume and BCSC population as measured by MSFE, CD44+/CD24low/- markers, ALDF+ cell population and limiting dilution assay. Liposomal HN1L siRNA treated mice also showed lower level of lung metastasis. A gene signature obtained from microarray analysis on HN1L siRNA treated tumor tissues highly correlated with better prognosis in TNBC patients. Overexpression of HN1L in TNBC cell lines activated STAT3 signaling, induced CD44+/CD24low/- population and cancer cell migration. Moreover, chemoresistance were also observed with HN1L overexpression. HN1L colocalized with CNTFR and STAT3 in cytoplasm and nucleus by immunofluorescence staining. Changes in HN1L expression level resulted in corresponding changes in phospho-STAT3. Furthermore, CNTFR knockdown compromised the effect of HN1L overexpression in activating STAT3.These results suggest that the HN1L gene plays an important role in BCSC through regulating CNTFR-STAT3 signaling pathway, and is associated with poor prognosis. Taken together, the results from our study demonstrate for the first time that HN1L is a novel target for TNBC. Targeting HN1L and/or CNTFR-STAT3 pathway might provide an alternative therapeutic strategy for TNBC. Citation Format: Yi Liu, Dong Soon Choi, Sergio Grandos-Principal, Wei Qian, Lacey Burey, Helen Wong, Crisitian Rodriguez-Aguayo, Anil Sood, Zheng Li, Stephen Wong, Heidi Weiss, Bhuvanesh Dave, Melissa Landis, Jenny C. Chang. Identifying novel cancer stem cell target for triple-negative breast cancer. [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 2312. doi:10.1158/1538-7445.AM2015-2312