P10.08.B PI3K INHIBITION FOR SENSITIZING CANCER CELLS TO TUMOR TREATING FIELDS (TTFIELDS)

Abstract

Abstract BACKGROUND Tumor Treating Fields (TTFields) are electric fields that disrupt cellular processes critical for cancer cell viability and tumor progression, ultimately leading to cell death. TTFields therapy is approved for treatment of adult patients with glioblastoma (GBM) or unresectable pleural mesothelioma. Clinical trials are underway in other solid tumors, including ovarian cancer and non-small cell lung carcinoma (NSCLC). The objective of this study is to identify possible mechanisms involved in reduced sensitivity of cancer cell to TTFields, and explore strategies to circumvent them. MATERIAL AND METHODS GBM U-87 MG, ovarian cancer A2780, and NSCLC H1299 cells were treated with continuous long-term application of TTFields (1.7 V/cm RMS, 200 or 150 kHz, 6 or 13 days, specific conditions depending on cell line). Changes in signaling pathways were examined for cells following 3 days of treatment with Luminex multiplex assay, followed by Western blot validation for specific pathway markers. In vivo validation was performed in ovarian cancer (MOSE-L), hepatocellular carcinoma (N1-S1), and NSCLC (LL/2) tumor sections from animals treated with TTFields utilizing immunohistochemistry. Next, efficacy of TTFields concomitant with relevant inhibitors was evaluated in vitro and in mice inoculated orthotopically with ovarian cancer cells (MOSE-L). Tumor volume was measured at study end by luciferin signal detection using the In Vivo Imaging System (IVIS). RESULTS TTFields inflicted a cytotoxic effect on the cancer cells that increased over time, though with moderately reduced sensitivity following prolonged treatment application. PI3K/AKT signaling pathway was shown to be activated in treated cells, with the amplitude of AKT phosphorylation increasing over time. AKT phosphorylation was also demonstrated in tumor sections of animals treated with TTFields. Experiments performed with concomitant PI3K/AKT pathway inhibitors sensitized the cells to TTFields, enhancing cytotoxicity in vitro and treatment efficacy in vivo. CONCLUSION PI3K/AKT signaling pathway is involved in cancer cell reduced sensitivity to TTFields, and inhibition of this pathway sensitizes cancer cells to TTFields.