Electromagnetic hyperthermia-induced breast cancer cell death in a 3D tumor spheroid model
Introduction
Breast cancer is the most commonly diagnosed malignancy in women worldwide and the leading cause of death. The incidence of breast cancer is constantly increasing, necessitating the search for new therapeutic methods. Among the various therapeutic modalities, electromagnetic hyperthermia (EHT) uses a moderate temperature (41-46°C) to damage tumor cells. It is currently used in the clinic as an adjuvant treatment. Here, we investigate the effect of EHT on induced cell death of breast cancer spheroids. Tumor spheroids have a microenvironment that more closely resembles that of tumors in vivo and thus may be a superior in vitro cancer model than monolayer cultures.
Methods
The response of tumor spheroids formed from the established human cancer cell line MCF7 to EHT was evaluated in the shielded chamber of the National University of Colombia, Bogotá headquarters, the temperature increase in the cell line was obtained using a horn antenna excited at 2.45 GHz and at 900 W. The spheroids were placed in a 3D-printed multi-well culture box with 4 Bragg grating sensors embedded in fiber optics, where data was acquired by an SM125 interrogator system; additionally, images were captured by a thermal camera. Data were extracted to determine the correlation between wavelength and temperature. Cellular response was analyzed in terms of spheroid growth, cell viability, and live/dead cell distribution. Microscopic imaging was used to evaluate mechanisms of cell death and cell detachment.
Results
Spheroids were found to be significantly less sensitive to heat than monolayer cultures. Spheroids showed different patterns of shrinkage and regrowth when exposed to heat; however, cells showed faster growth after exposure than untreated samples. Heated spheroids exhibited a granular structure, indicating a loosening of cell packaging that resulted in equivalent levels of clonogenic cell survival and increased ROS generation and release. We suggest that hyperthermia-induced cell death affects cells independently of their proliferative status. This induces microenvironmental changes that promote spheroid growth, reducing viability in approximately 50-90% with respect to the control group which has 95% viability.
Conclusion
This work demonstrates that EHT causes damage in MCF7 cell spheroids. The mechanism involves ROS production and activation of mitochondria-dependent cell death. 3D tumor spheroid growth studies reveal differences in response to heating temperature that were not apparent in 2D clonogenic assays, but which may significantly influence treatment efficacy.