Abstract 4454: Cancer cell permeability induced by tumor treating fields (TTFields) improves chemotherapy uptake and requires cells to transverse through the G2/M phase under TTFields application
Authors: Bella Koltun, Tali Voloshin, Cfir David, Tal Kan, Yiftah Barsheshet, Alexandra Volodin, Shay Cahal, Catherine Tempel-Brami, Mai Shai, Sara Jacobovitch, David Lancry Abittan, Boris Brant, Noa Kaynan, Lilach Koren, Anat Klein-Goldberg, Efrat Zemer Tov, Rom Paz, Naama Flint-Brodsly, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti
Journal: Cancer Research (2025)

Abstract Background: Multidrug resistance (MDR) poses a significant challenge in cancer treatment, and efforts to overcome it have not yet resulted in meaningful improvements in survival rates. Tumor Treating Fields (TTFields), a cancer treatment based on the application of electric fields, have recently been shown to increase the membrane permeability of glioblastoma cells. The current study aimed to characterize this phenomenon and examine whether it can be leveraged to facilitate uptake of anticancer agents and overcome MDR. Methods: 4T1 breast mammary carcinoma cells were treated with TTFields (300 kHz; 1.7 V/cm). Intracellular 7-aminoactinomycin D (7-AAD) accumulation was measured by flow cytometry, adding the agent before or after treatment cessation. Cell cycle analysis using the Hoechst reagent was performed with or without G1/S blockage using thymidine. 4T1-MDR (doxorubicin (DOX)-resistant) cells were generated by repeated DOX exposure of the parental 4T1 (DOX-sensitive) cells. TTFields together with DOX were applied to the 4T1 and 4T1-MDR cells, followed by analysis of DOX accumulation and cell count. For testing drug accumulation in vivo, mice were orthotopically inoculated with 4T1 cells or with lung carcinoma LL/2 cells, followed by TTFields treatment and injection of DOX or paclitaxel (PTX), respectively. Drug accumulation was measured in single-cell tumor suspension and whole tumors, using flow cytometry or an in vivo imaging system (IVIS) for DOX, and LC-MS/MS for PTX. For the latter, accumulation was also measured in the healthy lung. For the efficacy studies, mice were orthotopically inoculated with 4T1 or 4T1-MDR cells. The mice were treated with TTFields or sham-heat continuously for 8 days, with DOX (1 mg/kg for 4T1 cells; 5 mg/kg for 4T1-MDR cells) or vehicle injections on days 2 and 6 of treatment. Tumor volumes were measured using caliper. Results: 7-AAD accumulation tests demonstrated that TTFields-induced cancer cell permeability is reversible and requires that cells transverse through the G2/M phase under TTFields application. The application of TTFields allowed DOX accumulation to the same extent in both DOX-resistant and DOX-sensitive cells and sensitized both cell types to DOX cytotoxicity. Enhanced drug accumulation was observed in vivo, with DOX in breast tumors and PTX specifically in lung tumors. The application of TTFields concomitantly with DOX significantly decreased tumor growth in both 4T1 and 4T1-MDR tumor-bearing mice. Conclusions: TTFields reversibly and in a G2/M dependent manner increased cancer cell permeability, allowing enhanced intracellular accumulation of chemotherapy, in vitro and in vivo. TTFields treatment concomitant with DOX improved treatment efficacy, in DOX-resistant and DOX-sensitive cells, in vitro and in vivo. Citation Format: Bella Koltun, Tali Voloshin, Cfir David, Tal Kan, Yiftah Barsheshet, Alexandra Volodin, Shay Cahal, Catherine Tempel-Brami, Mai Shai, Sara Jacobovitch, David Lancry Abittan, Boris Brant, Noa Kaynan, Lilach Koren, Anat Klein-Goldberg, Efrat Zemer Tov, Rom Paz, Naama Flint-Brodsly, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Cancer cell permeability induced by tumor treating fields (TTFields) improves chemotherapy uptake and requires cells to transverse through the G2/M phase under TTFields application [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4454.