Elucidation of Altered Pathways in Tumor-Initiating Cells of Triple-Negative Breast Cancer: A Useful Cell Model System for Drug Screening

作者：Christensen Anne G; Ehmsen Sidse; Terp Mikkel G; Batra Richa; Alcaraz Nicolas; Baumbach Jan; Noer Julie B; Moreira Jose; Leth Larsen Rikke; Larsen Martin R; Ditzel Henrik J^*

来源：Stem Cells, 2017, 35(8): 1898-1912.

DOI：10.1002/stem.2654

• Cancer stem cells
• Triple-negative breast cancer
• Apoptosis
• NF-kappa B
• Mammospheres
• Targeted treatment

A limited number of cancer cells within a tumor are thought to have self-renewing and tumor-initiating capabilities that produce the remaining cancer cells in a heterogeneous tumor mass. Elucidation of central pathways preferentially used by tumor-initiating cells/cancer stem cells (CSCs) may allow their exploitation as potential cancer therapy targets. We used single cell cloning to isolate and characterize four isogenic cell clones from a triple-negative breast cancer cell line; two exhibited mesenchymal-like and two epithelial-like characteristics. Within these pairs, one, but not the other, resulted in tumors in immunodeficient NOD/Shi-scid/IL-2 R gamma null mice and efficiently formed mammospheres. Quantitative proteomics and phosphoproteomics were used to map signaling pathways associated with the tumor-initiating ability. Signaling associated with apoptosis was suppressed in tumor-initiating versus nontumorigenic counterparts with pro-apoptotic proteins, such as Bcl2-associated agonist of cell death (BAD), FAS-associated death domain protein (FADD), and myeloid differentiation primary response protein (MYD88), downregulated in tumor-initiating epithelial-like cells. Functional studies confirmed significantly lower apoptosis in tumor-initiating versus nontumorigenic cells. Moreover, central pathways, including beta-catenin and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappa B)-related signaling, exhibited increased activation in the tumor-initiating cells. To evaluate the CSC model as a tool for drug screening, we assessed the effect of separately blocking NF-kappa B and Wnt/beta-catenin signaling and found markedly reduced mammosphere formation, particularly for tumor-initiating cells. Similar reduction was also observed using patient-derived primary cancer cells. Furthermore, blocking NF-kappa B signaling in mice transplanted with tumor-initiating cells significantly reduced tumor outgrowth. Our study demonstrates that suppressed apoptosis, activation of pathways associated with cell viability, and CSCs are the major differences between tumor-initiating and nontumorigenic cells independent of their epithelial-like/mesenchymal-like phenotype. These altered pathways may provide targets for future drug development to eliminate CSCs, and the cell model may be a useful tool in such drug screenings.

• 出版日期2017-8