Le Zhang1, Milana Bochkur Dratver1, Taha Yazal1, Kevin Dong1, Andrea Nguyen1, Garrett Yu1, Amy Dao1, Michael Bochkur Dratver1, Sara Duhachek-Muggy1, Kruttika Bhat1, Claudia Alli1, Frank Pajonk2, Erina Vlashi3. 1. Department of Radiation Oncology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California. 2. Department of Radiation Oncology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California; Jonsson Comprehensive Cancer Center, University of California, Los Angeles, Los Angeles, California. 3. Department of Radiation Oncology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California; Jonsson Comprehensive Cancer Center, University of California, Los Angeles, Los Angeles, California. Electronic address: evlashi@mednet.ucla.edu.
Abstract
PURPOSE: The lack of a molecular target in triple-negative breast cancer (TNBC) makes it one of the most challenging breast cancers to treat. Radiation therapy (RT) is an important treatment modality for managing breast cancer; however, we previously showed that RT can also reprogram a fraction of the surviving breast cancer cells into breast cancer-initiating cells (BCICs), which are thought to contribute to disease recurrence. In this study, we characterize mebendazole (MBZ) as a drug with potential to prevent the occurrence of radiation-induced reprogramming and improve the effect of RT in patients with TNBC. METHODS AND MATERIALS: A high-throughput screen was used to identify drugs that prevented radiation-induced conversion of TNBC cells into cells with a cancer-initiating phenotype and exhibited significant toxicity toward TNBC cells. MBZ was one of the drug hits that fulfilled these criteria. In additional studies, we used BCIC markers and mammosphere-forming assays to investigate the effect of MBZ on the BCIC population. Staining with propidium iodide, annexin-V, and γ-H2AX was used to determine the effect of MBZ on cell cycle, apoptosis, and double-strand breaks. Finally, the potential for MBZ to enhance the effect of RT in TNBC was evaluated in vitro and in vivo. RESULTS: MBZ efficiently depletes the BCIC pool and prevents the ionizing radiation-induced conversion of breast cancer cells into therapy-resistant BCICs. In addition, MBZ arrests cells in the G2/M phase of the cell cycle and causes double-strand breaks and apoptosis. MBZ sensitizes TNBC cells to ionizing radiation in vitro and in vivo, resulting in improved tumor control in a human xenograft model of TNBC. CONCLUSIONS: The data presented in this study support the repurposing of MBZ as a combination treatment with RT in patients with TNBC.
PURPOSE: The lack of a molecular target in triple-negative breast cancer (TNBC) makes it one of the most challenging breast cancers to treat. Radiation therapy (RT) is an important treatment modality for managing breast cancer; however, we previously showed that RT can also reprogram a fraction of the surviving breast cancer cells into breast cancer-initiating cells (BCICs), which are thought to contribute to disease recurrence. In this study, we characterize mebendazole (MBZ) as a drug with potential to prevent the occurrence of radiation-induced reprogramming and improve the effect of RT in patients with TNBC. METHODS AND MATERIALS: A high-throughput screen was used to identify drugs that prevented radiation-induced conversion of TNBC cells into cells with a cancer-initiating phenotype and exhibited significant toxicity toward TNBC cells. MBZ was one of the drug hits that fulfilled these criteria. In additional studies, we used BCIC markers and mammosphere-forming assays to investigate the effect of MBZ on the BCIC population. Staining with propidium iodide, annexin-V, and γ-H2AX was used to determine the effect of MBZ on cell cycle, apoptosis, and double-strand breaks. Finally, the potential for MBZ to enhance the effect of RT in TNBC was evaluated in vitro and in vivo. RESULTS:MBZ efficiently depletes the BCIC pool and prevents the ionizing radiation-induced conversion of breast cancer cells into therapy-resistant BCICs. In addition, MBZ arrests cells in the G2/M phase of the cell cycle and causes double-strand breaks and apoptosis. MBZ sensitizes TNBC cells to ionizing radiation in vitro and in vivo, resulting in improved tumor control in a human xenograft model of TNBC. CONCLUSIONS: The data presented in this study support the repurposing of MBZ as a combination treatment with RT in patients with TNBC.
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