Cell-cycle dependence on the biological effects of boron neutron capture therapy and its modification by polyvinyl alcohol.

Boron neutron capture therapy (BNCT) is a unique radiotherapy of selectively eradicating tumor cells using boron compounds (e.g., 4-borono-L-phenylalanine [BPA]) that are heterogeneously taken up at the cellular level. Such heterogenicity potentially reduces the curative efficiency. However, the effects of temporospatial heterogenicity on cell killing remain unclear. With the technical combination of radiation track detector and biophysical simulations, this study revealed the cell cycle-dependent heterogenicity of BPA uptake and subsequent biological effects of BNCT on HeLa cells expressing fluorescent ubiquitination-based cell cycle indicators, as well as the modification effects of polyvinyl alcohol (PVA). The results showed that the BPA concentration in the S/G2/M phase was higher than that in the G1/S phase and that PVA enhances the biological effects both by improving the uptake and by canceling the heterogenicity. These findings might contribute to a maximization of therapeutic efficacy when BNCT is combined with PVA and/or cell cycle-specific anticancer agents.

Evaluation of Cell Cycle-Dependent Migration Activity after X-ray Exposure: A Radiobiological Approach for Optimization of Radiotherapy with Cell Cycle-Targeting Agents.

Radiotherapy with cell cycle-specific anticancer agents has become an important option in the control of both primary tumors and metastases. Here, we used image analysis algorithms that enable quick segmentation and tracking to describe a radiobiological approach for the optimized selection of cell cycle-targeting anticancer drugs for radiotherapy. We confirmed cell cycle-synchronization using human cervical cancer HeLa cells expressing a fluorescent ubiquitination-based cell cycle indicator (FUCCI) as a cell cycle-monitoring probe. Cells synchronized in the G1 and G2 phases were irradiated with X rays at 0.5-2 Gy. Each cell was identified using Cellpose, a deep learning-based algorithm for cellular segmentation, and the velocity and direction of migration were analyzed using the TrackMate plugin in Fiji ImageJ. G1 phase synchronized cells showed a dose-dependent decrease in velocity after irradiation, while G2 cells tended to increase their velocity. The migration pattern of all cells appeared to be a random walk model, regardless of the exposure dose. In addition, we used cisplatin to arrest the cell cycle. HeLa-FUCCI cells arrested at the G2 phase via cisplatin treatment showed enhanced cell migration after X-ray exposure. These results indicated that anticancer agents that arrest the cell cycle of cancer cells in a specific phase may enhance cell migration after radiotherapy. Our approach, using cellular segmentation and tracking algorithms, could enhance the radiobiological assessment of cell cycle-specific migration after irradiation to aid in optimizing radiotherapy using cell cycle-targeting agents.

Cell cycle dependence of cell survival following exposure to X-rays in synchronous HeLa cells expressing fluorescent ubiquitination-based cell cycle indicators.

The cell cycle dependence of radiosensitivity has yet to be fully determined, as it is technically difficult to achieve a high degree of cell cycle synchronization in cultured cell systems and accurately detect the cell cycle phase of individual cells simultaneously. We used human cervical carcinoma HeLa cells expressing fluorescent ubiquitination-based cell cycle indicators (FUCCI), and employed the mitotic harvesting method that is one of the cell cycle synchronization methods. The imaging analysis confirmed that the cell cycle is highly synchronized after mitotic cell harvesting until 18-20 h of the doubling time has elapsed. Also, flow cytometry analysis revealed that the S and G2 phases peak at approximately 12 and 14-16 h, respectively, after mitotic harvesting. In addition, the clonogenic assay showed the changes in surviving fractions following exposure to X-rays according to the progress through the cell cycle. These results indicate that HeLa-FUCCI cells become radioresistant in the G1 phase, become radiosensitive in the early S phase, rapidly become radioresistant in the late S phase, and become radiosensitive again in the G2 phase. Our findings may contribute to the further development of combinations of radiation and cell cycle-specific anticancer agents.

Validation of mitotic harvesting method with human cervical carcinoma HeLa cells expressing fluorescent ubiquitination-based cell cycle indicators for radiation research.

The cell cycle is a series of events in the process of one cell giving rise to two daughter cells. The mitotic harvesting method, established by Terasima and Tolmach in the 1960s, causes minimal physiological stress on the cells and achieves a high degree of cell cycle synchrony by collecting only mitotic cells from a cultured cell system. The purpose of the present study is to validate the versatility of the mitotic harvesting method using human cervical cell line HeLa cells expressing Fluorescent Ubiquitination-based Cell Cycle Indicators (FUCCI) and to estimate the cell cycle-dependent changes in radiosensitivity in HeLa-FUCCI cells. The image analysis showed that cell cycle synchrony was maintained for at least 24 hours after mitotic cell collection. Also, the clonogenic assay demonstrated changes in radiosensitivity that were cell cycle dependent. These results indicate that the mitotic harvesting method using FUCCI-expressing cells has high versatility in the field of radiation cell biology.