E-Poster Presentation 33rd Lorne Cancer Conference 2021

Triple-negative breast cancer (TNBC) is a heterogeneous disease characterized by high risk of relapse and short overall survival. Intratumoural heterogeneity is a major ongoing challenge for effective therapeutic targeting TNBC. Within these tumours, cancer stem cells (CSCs) are primarily responsible for tumour diversity and malignant-associated features promoting chemotherapy resistance and metastasis. CSCs exhibit high plasticity or the ability to dynamically switch between CSC (CD44^high, hybrid epithelial/mesenchymal cells) and non-CSC (CD44^low, epithelial cells) states. In CSCs, high levels of the eukaryotic initiation factor 5A (EIF5A) – a critical promoter of mRNA translation – has been reported. Modulating mRNA translation may therefore provide a rationale for overcoming chemotherapy resistance and abrogating metastasis. Thus, we sought to evaluate the efficacy of inhibiting EIF5A maturation by deoxyhypusine synthase (DHPS) inhibitor N1-guanyl-1,7-diaminoheptane (GC7), alone or in combination with chemotherapy (doxorubicin and docetaxel), using TNBC models. We have extensively explored mRNA translation hallmarks differentiating CD44^high from CD44^low purified populations of TNBC cell lines (HMLER and HCC38) by high throughput RNA sequencing. To investigate the impact of mRNA translation modulation, we treated cells with GC7, alone and in combination with doxorubicin or docetaxel, and monitored the cells by fluorescence-activated cell sorting (FACS). We tested the cells tumourigenicity and migration capabilities by tumoursphere formation and the wound healing assay. High levels of EIF5A, among other initiation factors, were validated in CD44^high cells and correlated with poor survival outcome in TNBC (TCGA and METABRIC). Inhibition of EIF5A maturation effectively decreased CSC (CD44^high) motility. Low concentration of GC7 (10 μΜ) significantly inhibited CSC (CD44^high) proliferation and enhanced chemotherapy cytotoxicity of TNBC cell lines. In combination therapy, GC7 further inhibited the CSC tumour initiation and cell migration capabilities. Our preliminary findings suggest a strong and unexplored link between mRNA translation, CSC phenotype and unfavourable disease outcome. Novel therapeutics targeting dysregulated mRNA translation may therefore constitute an effective strategy for preventing aberrant cell proliferation and dedifferentiation in TNBC.