Tumor Treating Fields Synergistically Enhances Cell Death in Non-Small Cell Lung and Pancreatic Cancer Cells Treated With the Combination of Radiation and Chemo Agents That Interfere With DNA Replication Fork Stability

Abstract

<h3>Purpose/Objective(s)</h3> TTFields is a novel non-invasive physical modality of cancer therapy which was initially thought to interfere with cancer cell mitosis to induce cell death. Genomics and proteomic results suggested the additional mechanisms of action underlying TTFields induced cell death as increased DNA replication stress and DNA damage while decreasing DNA repair through the downregulation of Fanconi's Anemia (FA) pathway genes, chromosome maintenance genes and others. The current study focused on exploiting the conditional vulnerabilities caused by TTFields exposure to test novel combination therapies that target DNA replication fork stability combined with radiation. <h3>Materials/Methods</h3> Human NSCLC cell lines (H157, H4006, H549 and H1299) and pancreatic cancer cell lines (PANC-1 and Panc 04.03) were used in this study. A laboratory research system was used to generate TTFields. TTFields, radiation and drug combination efficacy were tested using clonogenic cell survival assays while the Highest Single Agent approach was used to assess the combinatorial efficacy. <h3>Results</h3> Comparative analysis of genomics and proteomics data revealed dysregulation of pathways including cell cycle, DNA damage repair and replication, and transcriptional and translational regulation under TTFields exposure. Functional characterization studies confirmed the downregulation of FA pathway proteins there by increased replication stress, DNA damage and impaired DNA damage repair. To exploit the conditional vulnerability environment induced by TTFields exposure different chemo agents that target and increase replication stress were tested in novel combination therapy options. It was found that the effect of TTFields exposure concomitant with the PARP1 inhibitor olaparib followed by irradiation (IR) was synergistic compared to IR or olaparib alone or in combination. In addition, TTFields synergistically enhanced the cell killing efficacy of the ATR inhibitor AZD6738 followed by IR. <h3>Conclusion</h3> Expression of FA pathway genes/proteins is modulated by TTFields exposure and likely explains the reduced DNA repair capacity and replication fork maintenance. Hence, targeting DNA damage repair and the DNA replication stress pathway using inhibitors of PARP1 and ATR could be used in combination with TTFields with or without radiation for cancer therapy.