Abstract 2659: Inhibition of PI3K sensitized cancer cells to Tumor Treating Fields (TTFields)
Authors: Klein-Goldberg Anat , Voloshin Tali , Zemer-Tov Efrat , Paz Rom , Koren Lilach , Wainer-Katsir Kerem , Volodin Alexandra , Koltun Bella , Brant Boris , Barsheshet Yiftah , Kan Tal , Haber Adi , Giladi Moshe , Weinberg Uri , Palti Yoram 
Published: June 2022

Abstract
Introduction: Tumor Treating Fields (TTFields) are alternating electric fields, delivered noninvasively to the tumor site. TTFields therapy is currently approved for treatment of patients with newly diagnosed glioblastoma (GBM), recurrent GBM, or unresectable malignant pleural mesothelioma. Investigations are ongoing in additional tumor types, including non-small cell lung carcinoma (NSCLC), ovarian cancer, and hepatocellular carcinoma (HCC). Although TTFields have been demonstrated to extend life, most patients will eventually progress. The current research aimed to identify molecular mechanisms involved in reduced cancer cellular sensitivity to TTFields, and the potential of targeting these pathways to re-sensitize the cells to TTFields.
Methods: Continuous long-term application of TTFields (7 or 13 days, depending on the cell line) generated cancer cells with reduced sensitivity to TTFields. Luminex multiplex assay was used to detect changes in signaling pathways in ovarian A2780 and GBM U-87 MG cells, and relevant pathway markers were validated by Western blot. Further validation was performed by immunohistochemistry of tumor sections from N1S1 HCC tumor-bearing rats treated with sham or TTFields. The significance of the identified pathways in reducing cancer cell sensitivity to TTFields was evaluated through in vitro combination treatment with PI3K inhibitors, followed by cell count measurements. Finally, the concomitant application of TTFields and the PI3K inhibitor Alpelisib was evaluated in mice orthotopically implanted with MOSE-L firefly luciferase (FFL) ovarian cancer cells. Tumor volume was measured using the In Vivo Imaging System (IVIS) to detect the luciferin signal, before and after treatment.
Results: Cancer cell sensitivity to TTFields was reduced following continuous long-term application of TTFields. This was accompanied by activation of the PI3K/AKT/mTOR signaling pathway, with significant increases in the levels of phosphorylated AKT and RPS6 observed in cell cultures and in rat tumor sections following application of TTFields. Application of PI3K inhibitors re-sensitized the cells to TTFields in vitro. In vivo, concomitant application of TTFields with Alpelisib resulted in enhanced efficacy.
Conclusions: The current study demonstrated that reduced cancer cell sensitivity to long-term application of TTFields is mediated by activation of the PI3K/AKT/mTOR signaling pathway. Furthermore, PI3K inhibitors were shown to re-sensitize the cells to TTFields, providing a rationale for further examining the potential benefit of TTFields concomitant with PI3K inhibitors.
Citation Format: Anat Klein-Goldberg, Tali Voloshin, Efrat Zemer-Tov, Rom Paz, Lilach Koren, Kerem Wainer-Katsir, Alexandra Volodin, Bella Koltun, Boris Brant, Yiftah Barsheshet, Tal Kan, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Inhibition of PI3K sensitized cancer cells to Tumor Treating Fields (TTFields) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2659.