Measurement of the Compressibility of Cell and Nucleus Based on Acoustofluidic Microdevice

Cell mechanics play an important role in tumor metastasis, malignant transformation of cells, and radiosensitivity. During these processes, studying the ...

Sun Yat-sen University

Cancer stem-like cells (CSCs) are the principal causes of tumor radio-resistance, dormancy and recurrence after radiotherapy. Clinical trials show hyperthermia (HT) might be a potent radiation sensitizer. In this study, CSCs were found to be more susceptible to radiation when combined with HT treatment. Treated cells showed significantly reduced self-renewal, cell survival and proliferation , as well as significant reduced tumor formation . Further study demonstrated that the radiosensitization effect was associated with increased intracellular reactive oxygen species (ROS) level in CSCs, confirmed by modifying redox status in CSCs bidirectionally. Pharmacologic depletion of glutathione by buthionine sulphoximine mimicked HT induced radiosensitivity in CSCs. Antioxidant N-acetylcysteine could efficiently rescue HT induced radiosensitivity in CSCs. To our knowledge, this may be the first report suggesting the association between elevated intracellular ROS level and HT induced radiosensitization in human breast CSCs and pancreatic CSCs, which might provide new strategy for improving CSCs radiosensitivity.

Association of elevated reactive oxygen species and hyperthermia induced radiosensitivity in cancer stem-like cells.

Hyperthermia (HT) acts as a cancer treatment by direct cell killing, radiosensitization, and promotion of tumor reoxygenation. The sensor proteins of the DNA damage response (DDR) are the direct targets of HT. However, the spatiotemporal properties of sensor proteins under HT are still unclear. Therefore, investigating the impact of HT on sensor proteins is of great importance. In the present study, the human fibrosarcoma cell line HT1080 stably transfected with 53BP1-GFP [the DDR protein 53BP1 fused to green fluorescent protein (GFP)] was used to investigate the real-time cellular response to DNA double-strand breaks (DSBs) induced by γ-rays. Using live-cell imaging combined with HT treatment, the spatiotemporal properties of the 53BP1 protein were directly monitored and quantitatively studied. We found that HT could delay and decrease the formation of 53BP1 ionizing radiation-induced foci (IRIF). Moreover, through the in situ tracking of individual IRIF, it was found that HT resulted in more unrepaired IRIF over the period of observation compared with IR alone. Additionally, the unrepaired IRIF had a larger area, higher intensity, and slower repair rate. Indeed, almost every cell treated with HT had unrepaired IRIF, and the majority of these IRIF increased in area individually, while the rest increased in area by the merging of adjacent IRIF. In summary, our study demonstrated that HT could perturb the primary event in the DDR induced by IR, and this may have important implications for cancer treatment and heat radiosensitization.

The effect of hyperthermia on the DNA damage response induced by γ-rays, as determined through in situ cell tracking.

Radiotherapy works by generating large amounts of DNA double-strand breaks (DSBs). Cancer stem-like cells (CSCs) are the principal cause of tumor radioresistance. Therefore, investigating the dynamics and mechanisms of DNA damage response (DDR) in CSCs is of great importance.

Characterizing the DNA damage response in fibrosarcoma stem cells by in-situ cell tracking.

Epithelial-mesenchymal transition (EMT) confers migratory and invasiveness abilities on cancer cells, as well as leading to changes in biomechanical properties and cytoskeletal structure. Cell mechanical properties are considered to be promising label-free markers for diagnosis of cancer metastasis. In this work, cell compressibility, a novel and important parameter of cell mechanical properties, was measured directly and quickly using a specially designed acoustofluidic microdevice. The compressibilities of cells with different metastatic potentials were investigated. Based on a comparison of the measurement results, non-metastatic cells exhibited lower compressibility than metastatic cells. The correlation between cell compressibility and EMT status was further studied; the results showed that the acquisition of mesenchymal status was accompanied by an increase in cell compressibility. These findings imply strong correlations among cell compressibility, EMT status, and invasiveness. Therefore, cell compressibility represents a novel biomechanical marker for evaluating malignant transformation and metastasis of cancer.

Measurement of cell compressibility changes during epithelial-mesenchymal transition based on acoustofluidic microdevice.

Radiotherapy is an important treatment modality for cancer patients. Ionizing radiation kills cancer cells by inducing DNA damage. However, it remains unclear how this process affects the biomechanical properties of cells and how cellular mechanics affect DNA damage and repair. In this study, the effects of ionizing radiation on cell mechanics were investigated by precisely measuring the compressibility of cells in suspension using an in-house developed microfluidic device. We found that cell compressibility significantly increased after irradiation, depending on cell type and radiation dose. Radiation-induced DNA damage response (DDR) is an important process that alters cell mechanics, and this association was confirmed experimentally by inhibiting the DDR process. Furthermore, the mechanisms involved in changes in cell compressibility were investigated from the perspective of the nucleus and cytoplasm. Experiments showed that radiation reduced H3K9me3 staining intensity but had no effect on F-actin. This suggested that chromatin decondensation caused by radiation-induced DDR is the primary cause of changes in cell compressibility after radiation. The effects of cell mechanics on radiation-induced DNA damage were also investigated. The addition of blebbistatin reduced cytoskeletal forces on the nucleus, which resulted in a reduction in radiation-induced DNA damage. Collectively, this study elucidated reciprocal mechanisms of radiation-induced DNA damage and cell mechanics.

Qibin Fu

Sino-French Institute of Nuclear Engineering and Technology

Sun Yat-sen University

Measurement of the Compressibility of Cell and Nucleus Based on Acoustofluidic Microdevice

Qibin Fu

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Sun Yat-sen University

Measurement of the Compressibility of Cell and Nucleus Based on Acoustofluidic Microdevice

Sino-French Institute of Nuclear Engineering and Technology