Tumor treating fields increases membrane permeability in glioblastoma cells

Abstract

Glioblastoma is the most common yet most lethal of primary brain cancers with a one-year post-diagnosis survival rate of 65% and a five-year survival rate of barely 5%. Recently the U.S. Food and Drug Administration approved a novel fourth approach (in addition to surgery, radiation therapy, and chemotherapy) to treating glioblastoma; namely, tumor treating fields (TTFields). TTFields involves the delivery of alternating electric fields to the tumor but its mechanisms of action are not fully understood. Current theories involve TTFields disrupting mitosis due to interference with proper mitotic spindle assembly. We show that TTFields also alters cellular membrane structure thus rendering it more permeant to chemotherapeutics. Increased membrane permeability through the imposition of TTFields was shown by several approaches. For example, increased permeability was indicated through increased bioluminescence with TTFields exposure or with the increased binding and ingress of membrane-associating reagents such as Dextran-FITC or ethidium D or with the demonstration by scanning electron microscopy of augmented number and sizes of holes on the cellular membrane. Further investigations showed that increases in bioluminescence and membrane hole production with TTFields exposure disappeared by 24 h after cessation of alternating electric fields thus demonstrating that this phenomenom is reversible. Preliminary investigations showed that TTFields did not induce membrane holes in normal human fibroblasts thus suggesting that the phenomenom was specific to cancer cells. With TTFields, we present evidence showing augmented membrane accessibility by compounds such as 5-aminolevulinic acid, a reagent used intraoperatively to delineate tumor from normal tissue in glioblastoma patients. In addition, this mechanism helps to explain previous reports of additive and synergistic effects between TTFields and other chemotherapies. These findings have implications for the design of combination therapies in glioblastoma and other cancers and may significantly alter standard of care strategies for these diseases.

Tumor Treating Fields in the Management of Patients with Malignant Gliomas

“…These perforations were large enough to allow for the uptake of fluorescently labeled dextran particles of up to 20 kDa in size. In rodent brains, TTFields induce temporary BBB disruption, lasting up to 96 h [47,48]. These findings provide a potential new application for TTFields to enhance CNS delivery of small molecule BBB-impermeant pharmacological agents.…”

“…This is achieved through dysregulation of cytoskeletal structures and proteins related to the epithelial-mesenchymal transition (e.g., actins, vimentin, and cadherin), potentially reducing the likelihood of recurrence or metastases [43][44][45][46]. TTFields also increase permeability of the plasma membrane in human GBM cells in vitro by triggering mislocalization of the tight junction proteins Claudin-5 and ZO-1 from the plasma membrane to the cytoplasm [47,48]. Election microscopic images of the human GBM cell line U87-MG and murine astrocytoma cell line KR158B treated with TTFields for 1 h revealed a large number of perforations scattered throughout the plasma membrane [47,48].…”

“…TTFields also increase permeability of the plasma membrane in human GBM cells in vitro by triggering mislocalization of the tight junction proteins Claudin-5 and ZO-1 from the plasma membrane to the cytoplasm [47,48]. Election microscopic images of the human GBM cell line U87-MG and murine astrocytoma cell line KR158B treated with TTFields for 1 h revealed a large number of perforations scattered throughout the plasma membrane [47,48]. These perforations were large enough to allow for the uptake of fluorescently labeled dextran particles of up to 20 kDa in size.…”

“…The first are patients using TTFields combined with adjuvant maintenance TMZ or salvage therapies such as cytotoxic chemotherapy, compassionate-use immunotherapy, anti-angiogenic therapy, or targeted small molecule therapy. Combinatorial approaches are based on the premise that TTFields offer possible synergistic effects, for example, enhancing BBB and tumor cell permeability [45,47,48]. The second category is TTFields used as monotherapy due to patient factors that may limit systemic therapy tolerance such as myelosuppression, decline in functional status, or patient preference.…”

Barium Titanate Nanoparticles Sensitise Treatment-Resistant Breast Cancer Cells to the Antitumor Action of Tumour-Treating Fields

“…S2), suggesting that BTNP accumulation in cytoplasm is not mediated by clathrin-dependent pathway or macro-pinocytosis pathway. Instead, a recent study showed that TTFields have a capacity to induce membrane pores in glioblastoma cells, which may allow cancer cells to be susceptible to drug delivery 34 . Therefore, it seems that increased membrane permeability by TTFields may induce BTNP accumulation in cytoplasm of cancer cells.…”