Alternating Electric Fields (TTFields) Activate Cav1.2 Channels in Human Glioblastoma Cells

Abstract

Tumor treating fields (TTFields) represent a novel FDA-approved treatment modality for patients with newly diagnosed or recurrent glioblastoma multiforme. This therapy applies intermediate frequency alternating electric fields with low intensity to the tumor volume by the use of non-invasive transducer electrode arrays. Mechanistically, TTFields have been proposed to impair formation of the mitotic spindle apparatus and cytokinesis. In order to identify further potential molecular targets, here the effects of TTFields on Ca2+-signaling, ion channel activity in the plasma membrane, cell cycle, cell death, and clonogenic survival were tested in two human glioblastoma cell lines in vitro by fura-2 Ca2+ imaging, patch-clamp cell-attached recordings, flow cytometry and pre-plated colony formation assay. In addition, the expression of voltage-gated Ca2+ (Cav) channels was determined by real-time RT-PCR and their significance for the cellular TTFields response defined by knock-down and pharmacological blockade. As a result, TTFields stimulated in a cell line-dependent manner a Cav1.2-mediated Ca2+ entry, G1 or S phase cell cycle arrest, breakdown of the inner mitochondrial membrane potential and DNA degradation, and/or decline of clonogenic survival suggesting a tumoricidal action of TTFields. Moreover, inhibition of Cav1.2 by benidipine aggravated in one glioblastoma line the TTFields effects suggesting that Cav1.2-triggered signaling contributes to cellular TTFields stress response. In conclusion, the present study identified Cav1.2 channels as TTFields target in the plasma membrane and provides the rationale to combine TTFields therapy with Ca2+ antagonists that are already in clinical use.

Tumor treating fields cause replication stress and interfere with DNA replication fork maintenance: Implications for cancer therapy

“…49 This suggests that stalled replication fork stabilization confers resistance to replication stress-inducing chemotherapeutics but because of the general suppression of a host of genes and proteins involved in replication fork maintenance and stability, checkpoint control and DNA repair pathways, TTFields exposure may overcome such resistance. Indeed the results herein provide a rationale for the additive to synergistic effects of TTFields seen in earlier preclinical reports 10,[12][13][14][15] with chemotherapeutic drugs such as paclitaxel, cisplatin, gemcitabine, doxorubicin, 5-FU, cyclophosphamide, DTIC, and Irinotecan which are known to primarily increase replication stress but not directly affect mitosis. [7][8][9][10][11] DNA replication is a mandatory and prerequisite step for mitosis.…”

“…[7][8][9][10][11][12] TTFields also target the calcium channel Cav1.2, and combinations of calcium antagonists, such as benidipine enhance glioma cell killing. 13 Furthermore, AMPK-dependent autophagy, which occurred after cells had undergone mitosis in response to aneuploidy and ER (Endoplasmic reticulum) stress, was identified as a survival mechanism upon TTFields exposure and serves as a druggable resistance mechanism to TTFields. 14 These preclinical results cannot be explained by the interruption of mitosis, which suggests that there are other mechanisms by which TTFields used in combination with different chemotherapeutic agents elicit additive or synergistic cell killing.…”

An overview of potential novel mechanisms of action underlying Tumor Treating Fields-induced cancer cell death and their clinical implications

“…TTFields exposure was also shown to induce calcium signals in a dose-dependent manner by activating L-type calcium channels (CACNA1C) in GBM cells (Neuhaus et al 2019). Those results suggest that the pharmacological blockade of calcium channels with agents like benidipine and nifedipine may augment the effects of TTFields exposure.…”

Evaluation of a tumor electric field treatment system in a rat model of glioma

“…Indeed, a study using two different human glioblastoma lines revealed cell line-specific responses to TTFields. 8 In addition, the application of TTFields may delay DNA damage repair following radiation treatment, leading to the emergence of therapeutic resistance. 8,13 All these conditions suggest that the therapeutic efficacy of TEFTS may vary between patients and in different stages of tumor, which necessitates the need to adjust the intensity and frequency of TTFields during the course of treatment.…”

“…4,6,7 Finally, the electric fields therapy is recently reported to work through a cell line-specific mechanism to stimulate Ca 2+ entry via Cav1.2, which culminates in cell cycle arrest, DNA degradation, and cell death. 8 Intriguingly, the TTfields preferentially target tumor cells but leave the normal cells intact, rendering it a promising therapy for cancers.…”