Mebendazole Potentiates Radiation Therapy in Triple-Negative Breast Cancer

PurposeThe 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 materialsA 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.ResultsMBZ 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.ConclusionsThe data presented in this study support the repurposing of MBZ as a combination treatment with RT in patients with TNBC

PK-M2-mediated metabolic changes in breast cancer cells induced by ionizing radiation

PurposeRadiotherapy (RT) constitutes an important part of breast cancer treatment. However, triple negative breast cancers (TNBC) exhibit remarkable resistance to most therapies, including RT. Developing new ways to radiosensitize TNBC cells could result in improved patient outcomes. The M2 isoform of pyruvate kinase (PK-M2) is believed to be responsible for the re-wiring of cancer cell metabolism after oxidative stress. The aim of the study was to determine the effect of ionizing radiation (IR) on PK-M2-mediated metabolic changes in TNBC cells, and their survival. In addition, we determine the effect of PK-M2 activators on breast cancer stem cells, a radioresistant subpopulation of breast cancer stem cells.MethodsGlucose uptake, lactate production, and glutamine consumption were assessed. The cellular localization of PK-M2 was evaluated by western blot and confocal microscopy. The small molecule activator of PK-M2, TEPP46, was used to promote its pyruvate kinase function. Finally, effects on cancer stem cell were evaluated via sphere forming capacity.ResultsExposure of TNBC cells to IR increased their glucose uptake and lactate production. As expected, PK-M2 expression levels also increased, especially in the nucleus, although overall pyruvate kinase activity was decreased. PK-M2 nuclear localization was shown to be associated with breast cancer stem cells, and activation of PK-M2 by TEPP46 depleted this population.ConclusionsRadiotherapy can induce metabolic changes in TNBC cells, and these changes seem to be mediated, at least in part by PK-M2. Importantly, our results show that activators of PK-M2 can deplete breast cancer stem cells in vitro. This study supports the idea of combining PK-M2 activators with radiation to enhance the effect of radiotherapy in resistant cancers, such as TNBC