All ETDs from UAB

Advisory Committee Chair

Donald J Buchsbaum

Advisory Committee Members

Andra R Frost

Yancey Gillespie

Alber F Lobuglio

Rosa A Serra

Document Type

Dissertation

Date of Award

2013

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Basal-like breast cancers (BLBC) display aggressive clinical behavior attributed to the presence of cancer stem cells (CSCs). TRA-8, a monoclonal antibody that binds specifically to TRAIL death receptor 5, preferentially induces apoptosis in BLBC subtype cells; however it is unknown if TRA-8 is also cytotoxic to the CSC population. Moreover, some BLBC cell lines are resistant to TRA-8, and overcoming resistance is critical for clinical translation of this therapy. One potential approach to overcome TRA- 8 resistance is to target the Wnt/ß-catenin pathway. LRP6 is a cell surface receptor that is an indispensable element of the Wnt/ß-catenin signaling pathway that regulates BLBC tumor progression. Niclosamide is a potent Wnt/ß-catenin inhibitor that degrades the LRP6 receptor. This study examined two questions: 1) whether TRA-8 or niclosamide as single agents are cytotoxic to CSCs and non-CSC populations of BLBCs; 2) and whether niclosamide enhances TRA-8 sensitivity of these cell population both in vitro and in vivo. CSCs from BLBC cell lines expressed cell surface DR5 and were sensitive to TRA-8 mediated cytotoxicity. TRA-8 inhibited secondary tumorsphere formation and produced a decrease in the percentage of CSCs. Ex vivo treatment of the BLBC CSCs produced significant inhibition of tumorigenicity in NOD/SCID mice. BLBC cells and CSCs showed a dose-dependent cytotoxic response to treatment with niclosamide, and reduced Wnt/ß-catenin activity. Similar results were observed in primary BLBC cells isolated from patient pleural effusions obtained from patients with TNBC. The combination of niclosamide and TRA-8 further reduced Wnt/ß-catenin activity and resulted in synergistic inhibition of secondary tumorsphere formation in the BLBC cell lines. In vivo studies showed that intraperitoneal administration of niclosamide in combination with TRA-8 significantly suppressed growth of established 2LMP orthotopic tumor xenografts. The results described in this study indicate that combining TRA-8 with niclosamide might be an effective way to overcome TRA-8 resistance in differentiated cancer cells and CSCs by inhibition of the Wnt/ß-catenin pathway. This study provides valuable pre-clinical results that give insight into the potential use of these novel agents in future clinical trials in patients with BLBC.

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