Tumor treating fields affect mesothelioma cell proliferation by exerting histotype-dependent cell cycle checkpoint activations and transcriptional modulations

Abstract

Although clinical antitumor activity of Tumor Treating Fields (TTFields) has been reported in malignant pleural mesothelioma (MPM) patients, the mechanisms behind the different selectivity displayed by the various MPM histotypes to this physical therapy has not been elucidated yet. Taking advantage of the development of well characterized human MPM cell lines derived from pleural effusion and/or lavages of patients’ thoracic cavity, we investigated the biological effects of TTFields against these cells, representative of epithelioid, biphasic, and sarcomatoid histotypes. Growth inhibition and cell cycle perturbations caused by TTFields were investigated side by side with RNA-Seq analyses at different exposure times to identify pathways involved in cell response to treatment. We observed significant differences of response to TTFields among the cell lines. Cell cycle analysis revealed that the most sensitive cells (epithelioid CD473) were blocked in G2M phase followed by formation of polyploid cells. The least sensitive cells (sarcomatoid CD60) were only slightly affected by TTFields with a general delay in all cell cycle phases. Apoptosis was present in all samples, but while epithelioid cell death was already observed during the first 24 h of treatment, sarcomatoid cells needed longer times before they engaged apoptotic pathways. RNA-Seq experiments demonstrated that TTFields induced a transcriptional response already detectable at early time points (8 h). The number of differentially expressed genes was higher in CD473 than in CD60 cells, involving several pathways, such as those pertinent to cell cycle checkpoints, DNA repair, and histone modifications. Our data provide further support to the notion that the antitumor effects of TTFields are not simply related to a non-specific reaction to a physical stimulus, but are dependent on the biological background of the cells and the particular sensitivity to TTFields observed in epithelioid MPM cells is associated with a higher transcriptional activity than that observed in sarcomatoid models.

Pulsed Electric Fields in Oncology: A Snapshot of Current Clinical Practices and Research Directions from the 4th World Congress of Electroporation

“…Understanding the underlying causes of this behaviour may allow the design of a more efficacious treatment schedule. In a preclinical model, Mannarino et al provided convincing evidence that TTFs induce specific effects on cell proliferation in different subsets of mesothelioma cells and provided a mechanistic rationale for future combination therapies [ 246 ].…”

Important functional role of the protein osteopontin in the progression of malignant pleural mesothelioma

“…(A, C) Effect of anti-CD44 mAbs on AB1 shOPN tumor growth. Mice were treated intra-peritoneally with anti-CD44 (10 mg/kg) or with irrelevant mAbs at day (4,7,12,16,19)…”

“…Another treatment modality that gained credit is the use of alternating electric fields, a noninvasive therapeutic approach that can complement chemotherapy in mesothelioma patients. A combination of cisplatin-based therapies with Tumor-Treating Fields (TTF) has shown in vitro anti-tumor activity (19) and clinical activity in a phase 2 study (20). Despite these encouraging successes, it is clear that more effective treatments are urgently needed to assist these patients, and for this we need to increase our knowledge on the biology of MPM, especially on the molecular pathways that govern its continuous proliferation and resistance to treatments.…”