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

Radiotherapy (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.

Methods

Glucose 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.

Results

Exposure 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.

Conclusions

Radiotherapy 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.

Background

Resistance to existing therapies is a significant challenge in improving outcomes for glioblastoma (GBM) patients. Metabolic plasticity has emerged as an important contributor to therapy resistance, including radiation therapy (RT). Here, we investigated how GBM cells reprogram their glucose metabolism in response to RT to promote radiation resistance.

Methods

Effects of radiation on glucose metabolism of human GBM specimens were examined in vitro and in vivo with the use of metabolic and enzymatic assays, targeted metabolomics, and FDG-PET. Radiosensitization potential of interfering with M2 isoform of pyruvate kinase (PKM2) activity was tested via gliomasphere formation assays and in vivo human GBM models.

Results

Here, we show that RT induces increased glucose utilization by GBM cells, and this is accompanied with translocation of GLUT3 transporters to the cell membrane. Irradiated GBM cells route glucose carbons through the pentose phosphate pathway (PPP) to harness the antioxidant power of the PPP and support survival after radiation. This response is regulated in part by the PKM2. Activators of PKM2 can antagonize the radiation-induced rewiring of glucose metabolism and radiosensitize GBM cells in vitro and in vivo.

Conclusions

These findings open the possibility that interventions designed to target cancer-specific regulators of metabolic plasticity, such as PKM2, rather than specific metabolic pathways, have the potential to improve the radiotherapeutic outcomes in GBM patients.