Mitotic disruption and reduced clonogenicity of pancreatic cancer cells in vitro and in vivo by tumor treating fields

Tumor-treating fields in cancer therapy: advances of cellular and molecular mechanisms

Tumor-Treating Fields (TTFields) use intermediate-frequency and low-intensity electric fields to inhibit tumor cells. However, their mechanisms are still not well understood. This article reviews their key antitumor mechanisms at the cellular and molecular levels, including inhibition of proliferation, induction of death, disturbance of migration, and activation of the immune system. The multifaceted biological effects in combination with other cancer treatments are also summarized. The deep insight into their mechanism will help develop more potential antitumor treatments.

Tumor Treating Fields (TTFields) combined with the drug repurposing approach CUSP9v3 induce metabolic reprogramming and synergistic anti-glioblastoma activity in vitro

BACKGROUND

Glioblastoma represents a brain tumor with a notoriously poor prognosis. First-line therapy may include adjunctive Tumor Treating Fields (TTFields) which are electric fields that are continuously delivered to the brain through non-invasive arrays. On a different note, CUSP9v3 represents a drug repurposing strategy that includes 9 repurposed drugs plus metronomic temozolomide. Here, we examined whether TTFields enhance the antineoplastic activity of CUSP9v3 against this disease.

METHODS

We performed preclinical testing of a multimodal approach of TTFields and CUSP9v3 in different glioblastoma models.

RESULTS

TTFields had predominantly synergistic inhibitory effects on the cell viability of glioblastoma cells and non-directed movement was significantly impaired when combined with CUSP9v3. TTFields plus CUSP9v3 significantly enhanced apoptosis, which was associated with a decreased mitochondrial outer membrane potential (MOMP), enhanced cleavage of effector caspase 3 and reduced expression of Bcl-2 and Mcl-1. Moreover, oxidative phosphorylation and expression of respiratory chain complexes I, III and IV was markedly reduced.

CONCLUSION

TTFields strongly enhance the CUSP9v3-mediated anti-glioblastoma activity. TTFields are currently widely used for the treatment of glioblastoma patients and CUSP9v3 was shown to have a favorable safety profile in a phase Ib/IIa trial (NCT02770378) which facilitates transition of this multimodal approach to the clinical setting.

A review of tumor treating fields (TTFields): advancements in clinical applications and mechanistic insights

BACKGROUND

Tumor Treating Fields (TTFields) is a non-invasive modality for cancer treatment that utilizes a specific sinusoidal electric field ranging from 100 kHz to 300 kHz, with an intensity of 1 V/cm to 3 V/cm. Its purpose is to inhibit cancer cell proliferation and induce cell death. Despite promising outcomes from clinical trials, TTFields have received FDA approval for the treatment of glioblastoma multiforme (GBM) and malignant pleural mesothelioma (MPM). Nevertheless, global acceptance of TTFields remains limited. To enhance its clinical application in other types of cancer and gain a better understanding of its mechanisms of action, this review aims to summarize the current research status by examining existing literature on TTFields' clinical trials and mechanism studies.

CONCLUSIONS

Through this comprehensive review, we seek to stimulate novel ideas and provide physicians, patients, and researchers with a better comprehension of the development of TTFields and its potential applications in cancer treatment.

Association of Tumor Treating Fields (TTFields) therapy with survival in newly diagnosed glioblastoma: a systematic review and meta-analysis

PURPOSE

Tumor Treating Fields (TTFields) therapy, an electric field-based cancer treatment, became FDA-approved for patients with newly diagnosed glioblastoma (GBM) in 2015 based on the randomized controlled EF-14 study. Subsequent approvals worldwide and increased adoption over time have raised the question of whether a consistent survival benefit has been observed in the real-world setting, and whether device usage has played a role.

METHODS

We conducted a literature search to identify clinical studies evaluating overall survival (OS) in TTFields-treated patients. Comparative and single-cohort studies were analyzed. Survival curves were pooled using a distribution-free random-effects method.

RESULTS

Among nine studies, seven (N = 1430 patients) compared the addition of TTFields therapy to standard of care (SOC) chemoradiotherapy versus SOC alone and were included in a pooled analysis for OS. Meta-analysis of comparative studies indicated a significant improvement in OS for patients receiving TTFields and SOC versus SOC alone (HR: 0.63; 95% CI 0.53-0.75; p < 0.001). Among real-world post-approval studies, the pooled median OS was 22.6 months (95% CI 17.6-41.2) for TTFields-treated patients, and 17.4 months (95% CI 14.4-21.6) for those not receiving TTFields. Rates of gross total resection were generally higher in the real-world setting, irrespective of TTFields use. Furthermore, for patients included in studies reporting data on device usage (N = 1015), an average usage rate of ≥ 75% was consistently associated with prolonged survival (p < 0.001).

CONCLUSIONS

Meta-analysis of comparative TTFields studies suggests survival may be improved with the addition of TTFields to SOC for patients with newly diagnosed GBM.

Optimization of tumor-treating field therapy for triple-negative breast cancer cells in vitro via frequency modulation

PURPOSE

Currently, tumor-treating field (TTField) therapy utilizes a single "optimal" frequency of electric fields to achieve maximal cell death in a targeted population of cells. However, because of differences in cell size, shape, and ploidy during mitosis, optimal electric field characteristics for universal maximal cell death may not exist. This study investigated the anti-mitotic effects of modulating electric field frequency as opposed to utilizing uniform electric fields.

METHODS

We developed and validated a custom device that delivers a wide variety of electric field and treatment parameters including frequency modulation. We investigated the efficacy of frequency modulating tumor-treating fields on triple-negative breast cancer cells compared to human breast epithelial cells.

RESULTS

We show that frequency-modulated (FM) TTFields are as selective at treating triple-negative breast cancer (TNBC) as uniform TTFields while having a greater efficacy for combating TNBC cell growth. TTField treatment at a mean frequency of 150 kHz with a frequency range of ± 10 kHz induced apoptosis in a greater number of TNBC cells after 24 h as compared to unmodulated treatment which led to further decreased cell viability after 48 h. Furthermore, all TNBC cells died after 72 h of FM treatment while cells that received unmodulated treatment were able to recover to cell number equivalent to the control.

CONCLUSION

TTFields were highly efficacious against TNBC growth, FM TTFields showed minimal effects on epithelial cells similar to unmodulated treatment.

Tumor treating fields as novel combination partner in the multimodal treatment of head and neck cancer

BACKGROUND

We aimed to demonstrate the effects of tumor treating fields (TTFields) in head and neck squamous cell carcinoma (HNSCC) cells when combined with radiotherapy (RT) and chemotherapy.

METHODS

Two human HNSCC cell lines (Cal27, FaDu) received five different treatments: TTFields, RT +/- TTFields and RT + simultaneous cisplatin +/- TTFields. Effects were quantified using clonogenic assays and flow cytometric analyses of DAPI, caspase-3 activation and γH2AX foci.

RESULTS

Treatment with RT + TTFields decreased the clonogenic survival as strong as treatment with RT + simultaneous cisplatin. The triple combination of RT + simultaneous cisplatin + TTFields even further decreased the clonogenic survival. Accordingly, combination of TTFields with RT or RT + simultaneous cisplatin increased cellular apoptosis and DNA double-strand breaks.

CONCLUSION

TTFields therapy seems a promising combination partner in the multimodal treatment of locally advanced HNSCC. It could be used to intensify chemoradiotherapy or as alternative to chemotherapy.

Therapeutic potential of tumor treating fields for malignant brain tumors

BACKGROUND

Malignant brain tumors are among the most threatening diseases of the central nervous system, and despite increasingly updated treatments, the prognosis has not been improved. Tumor treating fields (TTFields) are an emerging approach in cancer treatment using intermediate-frequency and low-intensity electric field and can lead to the development of novel therapeutic options.

RECENT FINDINGS

A series of biological processes induced by TTFields to exert anti-cancer effects have been identified. Recent studies have shown that TTFields can alter the bioelectrical state of macromolecules and organelles involved in cancer biology. Massive alterations in cancer cell proteomics and transcriptomics caused by TTFields were related to cell biological processes as well as multiple organelle structures and activities. This review addresses the mechanisms of TTFields and recent advances in the application of TTFields therapy in malignant brain tumors, especially in glioblastoma (GBM).

CONCLUSIONS

As a novel therapeutic strategy, TTFields have shown promising results in many clinical trials, especially in GBM, and continue to evolve. A growing number of patients with malignant brain tumors are being enrolled in ongoing clinical studies demonstrating that TTFields-based combination therapies can improve treatment outcomes.

Ion channels as molecular targets of glioblastoma electrotherapy

Therapies with weak, non-ionizing electromagnetic fields comprise FDA-approved treatments such as Tumor Treating Fields (TTFields) that are used for adjuvant therapy of glioblastoma. In vitro data and animal models suggest a variety of biological TTFields effects. In particular, effects ranging from direct tumoricidal, radio- or chemotherapy-sensitizing, metastatic spread-inhibiting, up to immunostimulation have been described. Diverse underlying molecular mechanisms, such as dielectrophoresis of cellular compounds during cytokinesis, disturbing the formation of the spindle apparatus during mitosis, and perforating the plasma membrane have been proposed. Little attention, however, has been paid to molecular structures that are predestinated to percept electromagnetic fields-the voltage sensors of voltage-gated ion channels. The present review article briefly summarizes the mode of action of voltage sensing by ion channels. Moreover, it introduces into the perception of ultra-weak electric fields by specific organs of fishes with voltage-gated ion channels as key functional units therein. Finally, this article provides an overview of the published data on modulation of ion channel function by diverse external electromagnetic field protocols. Combined, these data strongly point to a function of voltage-gated ion channels as transducers between electricity and biology and, hence, to voltage-gated ion channels as primary targets of electrotherapy.

Tumor Treating Fields (TTFields) Therapy Concomitant with Taxanes for Cancer Treatment

Non-small cell lung cancer, ovarian cancer, and pancreatic cancer all present with high morbidity and mortality. Systemic chemotherapies have historically been the cornerstone of standard of care (SOC) regimens for many cancers, but are associated with systemic toxicity. Multimodal treatment combinations can help improve patient outcomes; however, implementation is limited by additive toxicities and potential drug-drug interactions. As such, there is a high unmet need to develop additional therapies to enhance the efficacy of SOC treatments without increasing toxicity. Tumor Treating Fields (TTFields) are electric fields that exert physical forces to disrupt cellular processes critical for cancer cell viability and tumor progression. The therapy is locoregional and is delivered noninvasively to the tumor site via a portable medical device that consists of field generator and arrays that are placed on the patient's skin. As a noninvasive treatment modality, TTFields therapy-related adverse events mainly consist of localized skin reactions, which are manageable with effective acute and prophylactic treatments. TTFields selectively target cancer cells through a multi-mechanistic approach without affecting healthy cells and tissues. Therefore, the application of TTFields therapy concomitant with other cancer treatments may lead to enhanced efficacy, with low risk of further systemic toxicity. In this review, we explore TTFields therapy concomitant with taxanes in both preclinical and clinical settings. The summarized data suggest that TTFields therapy concomitant with taxanes may be beneficial in the treatment of certain cancers.

Safety and efficacy of tumour-treating fields (TTFields) therapy for newly diagnosed glioblastoma in Japanese patients using the Novo-TTF System: a prospective post-approval study

BACKGROUND

Tumour-treating fields therapy is a locoregional, anti-cancer treatment. Efficacy and safety of tumour-treating fields therapy in adults with newly diagnosed glioblastoma were demonstrated in the pivotal phase 3 EF-14 study (NCT00916409). Here, we report post-approval data of tumour-treating fields therapy in Japanese patients with newly diagnosed glioblastoma.

METHODS

Unsolicited post-marketing surveillance data from Japanese patients with newly diagnosed glioblastoma treated with tumour-treating fields therapy (December 2016-June 2020) were retrospectively analysed. The primary endpoints were skin, neurological and psychiatric adverse events. The secondary endpoints were 1- and 2-year overall survival rates, and the 6-month progression-free survival. adverse events were analysed using MedDRA v24.0. The overall survival and progression-free survival were assessed using the Kaplan-Meier survival analysis (log-rank testing). The Cox proportional hazard regression analyses were also performed.

RESULTS

Forty patients with newly diagnosed glioblastoma were enrolled (62.5% male; median age 59 years; median baseline Karnofsky Performance Scale score 90). The most common tumour-treating-fields-therapy-related adverse event was beneath-array local skin reaction (60% of patients). The adverse events were mostly mild to moderate in severity. Neurological disorders were observed in 2.5% patients (one patient reported dysesthesia). No psychiatric disorders were reported. The 1- and 2-year overall survival rates were 77.9% (95% CI 60.6-88.3) and 53.6% (35.5-68.7%), respectively. The 6-month progression-free survival was 77.5% (61.2-87.6%). These survival rates compare favourably with those in the EF-14 trial (1- and 2-year overall survival rates: 73% [69-77%] and 43% [39-48%], respectively; 6-month progression-free survival rate: 56% (51-61%).

CONCLUSION

This post-approval, real-world evidence study revealed no new safety signals and suggests the safety and efficacy of tumour-treating fields therapy in Japanese patients with newly diagnosed glioblastoma.

Medical Device Advances in the Treatment of Glioblastoma

Despite decades of research and the growing emergence of new treatment modalities, Glioblastoma (GBM) frustratingly remains an incurable brain cancer with largely stagnant 5-year survival outcomes of around 5%. Historically, a significant challenge has been the effective delivery of anti-cancer treatment. This review aims to summarize key innovations in the field of medical devices, developed either to improve the delivery of existing treatments, for example that of chemo-radiotherapy, or provide novel treatments using devices, such as sonodynamic therapy, thermotherapy and electric field therapy. It will highlight current as well as emerging device technologies, non-invasive versus invasive approaches, and by doing so provide a detailed summary of evidence from clinical studies and trials undertaken to date. Potential limitations and current challenges are discussed whilst also highlighting the exciting potential of this developing field. It is hoped that this review will serve as a useful primer for clinicians, scientists, and engineers in the field, united by a shared goal to translate medical device innovations to help improve treatment outcomes for patients with this devastating disease.

The Mechanisms of Action of Tumor Treating Fields

Tumor treating fields (TTFields), a new modality of cancer treatment, are electric fields transmitted transdermally to tumors. The FDA has approved TTFields for the treatment of glioblastoma multiforme and mesothelioma, and they are currently under study in many other cancer types. While antimitotic effects were the first recognized biological anticancer activity of TTFields, data have shown that tumor treating fields achieve their anticancer effects through multiple mechanisms of action. TTFields therefore have the ability to be useful for many cancer types in combination with many different treatment modalities. Here, we review the current understanding of TTFields and their mechanisms of action.

The schemes, mechanisms and molecular pathway changes of Tumor Treating Fields (TTFields) alone or in combination with radiotherapy and chemotherapy

Tumor Treating Fields (TTFields) is a physical therapy that uses moderate frequency (100-300 kHz) and low-intensity (1-3 V/cm) alternating electric fields to inhibit tumors. Currently, the Food and Drug Administration approves TTFields for treating recurrent or newly diagnosed glioblastoma (GBM) and malignant pleural mesothelioma (MPM). The classical mechanism of TTFields is mitotic inhibition by hindering the formation of tubulin and spindle. In addition, TTFields inhibits cell proliferation, invasion, migration and induces cell death, such as apoptosis, autophagy, pyroptosis, and cell cycle arrest. Meanwhile, it regulates immune function and changes the permeability of the nuclear membrane, cell membrane, and blood-brain barrier. Based on the current researches on TTFields in various tumors, this review comprehensively summarizes the in-vitro effects, changes in pathways and molecules corresponding to relevant parameters of TTFields (frequency, intensity, and duration). In addition, radiotherapy and chemotherapy are common tumor treatments. Thus, we also pay attention to the sequence and dose when TTFields combined with radiotherapy or chemotherapy. TTFields has inhibitory effects in a variety of tumors. The study of TTFields mechanism is conducive to subsequent research. How to combine common tumor therapy such as radiotherapy and chemotherapy to obtain the maximum benefit is also a problem that's worthy of our attention.

Tumor Treating Fields (TTFields) Reversibly Permeabilize the Blood-Brain Barrier In Vitro and In Vivo

Despite the availability of numerous therapeutic substances that could potentially target CNS disorders, an inability of these agents to cross the restrictive blood-brain barrier (BBB) limits their clinical utility. Novel strategies to overcome the BBB are therefore needed to improve drug delivery. We report, for the first time, how Tumor Treating Fields (TTFields), approved for glioblastoma (GBM), affect the BBB's integrity and permeability. Here, we treated murine microvascular cerebellar endothelial cells (cerebEND) with 100-300 kHz TTFields for up to 72 h and analyzed the expression of barrier proteins by immunofluorescence staining and Western blot. In vivo, compounds normally unable to cross the BBB were traced in healthy rat brain following TTFields administration at 100 kHz. The effects were analyzed via MRI and immunohistochemical staining of tight-junction proteins. Furthermore, GBM tumor-bearing rats were treated with paclitaxel (PTX), a chemotherapeutic normally restricted by the BBB combined with TTFields at 100 kHz. The tumor volume was reduced with TTFields plus PTX, relative to either treatment alone. In vitro, we demonstrate that TTFields transiently disrupted BBB function at 100 kHz through a Rho kinase-mediated tight junction claudin-5 phosphorylation pathway. Altogether, if translated into clinical use, TTFields could represent a novel CNS drug delivery strategy.

Anti-cancer mechanisms of action of therapeutic alternating electric fields (tumor treating fields [TTFields])

Despite improved survival outcomes across many cancer types, the prognosis remains grim for certain solid organ cancers including glioblastoma and pancreatic cancer. Invariably in these cancers, the control achieved by time-limited interventions such as traditional surgical resection, radiation therapy, and chemotherapy is short-lived. A new form of anti-cancer therapy called therapeutic alternating electric fields (AEFs) or tumor treating fields (TTFields) has been shown, either by itself or in combination with chemotherapy, to have anti-cancer effects that translate to improved survival outcomes in patients. Although the pre-clinical and clinical data are promising, the mechanisms of TTFields are not fully elucidated. Many investigations are underway to better understand how and why TTFields is able to selectively kill cancer cells and impede their proliferation. The purpose of this review is to summarize and discuss the reported mechanisms of action of TTFields from pre-clinical studies (both in vitro and in vivo). An improved understanding of how TTFields works will guide strategies focused on the timing and combination of TTFields with other therapies, to further improve survival outcomes in patients with solid organ cancers.

Skull modulated strategies to intensify tumor treating fields on brain tumor: a finite element study

Tumor treating fields (TTFields) are a breakthrough in treating glioblastoma (GBM), whereas the intensity cannot be further enhanced, due to the limitation of scalp lesions. Skull remodeling (SR) surgery can elevate the treatment dose of TTFields in the intracranial foci. This study was aimed at exploring the characteristics of the skull modulated strategies toward TTFields augmentation. The simplified multiple-tissue-layer model (MTL) and realistic head (RH) model were reconstructed through finite element methods (FEM), to simulate the remodeling of the skull, which included skull drilling, thinning, and cranioplasty with PEEK, titanium, cerebrospinal fluid (CSF), connective tissue and autologous bone. Skull thinning could enhance the intensity of TTFields in the brain tumor, with a 10% of increase in average peritumoral intensity (API) by every 1 cm decrease in skull thickness. Cranioplasty with titanium accompanied the most enhancement of TTFields in the MTL model, but CSF was superior in TTFields enhancement when simulated in the RH model. Besides, API increased nonlinearly with the expansion of drilled burr holes. In comparison with the single drill replaced by titanium, nine burr holes could reach 96.98% of enhancement in API, but it could only reach 63.08% of enhancement under craniectomy of nine times skull defect area. Skull thinning and drilling could enhance API, which was correlated with the number and area of skull drilling. Cranioplasty with highly conductive material could also augment API, but might not provide clinical benefits as expected.

Application of the Taguchi method to explore a robust condition of tumor-treating field treatment

Tumor-treating fields have potential as minimally invasive cancer treatment. This study aimed to explore the optimum tumor-treating field conditions that minimize unpredicted variations in therapeutic outcomes resulting from differences in cell size and electrical properties. The electric field concentration that induces a dielectrophoretic force near the division plane of a mitotic cell was calculated by finite element analysis for 144 cases, based on different combinations of six noise factors associated with cells and four controllable factors including frequency, as determined by the Taguchi method. Changing the frequency from 200 to 400 kHz strongly increased robustness in producing a dielectrophoretic force, irrespective of noise factors. However, this frequency change reduced the force magnitude, which can be increased by simply applying a higher voltage. Based on additional simulations that considered this trade-off effect, a frequency of 300 kHz is recommended for a robust TTF treatment with allowable variations. The dielectrophoretic force was almost independent of the angle of applied electric field deviated from the most effective direction by ±20 degrees. Furthermore, increased robustness was observed for extracellular fluid with higher conductivity and permittivity. The Taguchi method was useful for identifying robust tumor-treating field therapy conditions from a considerably small number of replicated simulations.

Tumor treating fields: An emerging treatment modality for thoracic and abdominal cavity cancers

Tumor treating fields (TTFields)-an intermediate-frequency, electric field therapy-has emerged as a promising alternative therapy for the treatment of solid cancers. Since the first publication describing the anticancer effects of TTFields in 2004 there have been numerous follow-up studies by other groups, either to confirm the efficacy of TTFields or to study the primary mechanism of interaction. The overwhelming conclusion from these in vitro studies is that TTFields reduce the viability of aggressively replicating cell lines. However, there is still speculation as to the primary mechanism for this effect; moreover, observations both in vitro and in vivo of inhibited migration and metastases have been made, which may be unrelated to the originally proposed hypothesis of replication stress. Adding to this, the in vivo environment is much more complex spatially, structurally, and involves intricate networks of cell signaling, all of which could change the efficacy of TTFields in the same way pharmaceutical interventions often struggle transitioning in vivo. Despite this, TTFields have shown promise in clinical practice on multiple cancer types, which begs the question: has the primary mechanism carried over from in vitro to in vivo or are there new mechanisms at play? The goal of this review is to highlight the current proposed mechanism of action of TTFields based primarily on in vitro experiments and animal models, provide a summary of the clinical efficacy of TTFields, and finally, propose future directions of research to identify all possible mechanisms in vivo utilizing novel tumor-on-a-chip platforms.

Tumor-Treating Fields: A fourth modality in cancer treatment, new practice updates

Although major innovations in treatment are advancing, cancer persists as one of the leading causes of mortality. With the rising incidence of cancer and as we treat them, patients incur short term and long-term toxicities of current traditional therapies, including chemotherapy. This imposes a significant physical, emotional, and financial burden among patients, which affects their quality of life. Tumor-Treating Fields (TTFields) is a novel innovative new treatment modality that utilizes alternating electric fields at specific intermediate frequencies to diminish tumor growth by inhibiting mitosis and thus proliferation of malignant cells. The distinguishing feature of this new treatment modality is that it is noninvasive and tolerable. In fact, TTFields is currently FDA approved for the treatment of glioblastoma multiforme (GBM) as well as malignant pleural mesothelioma (MPM). Recently, TTFields have also been found to affect immunogenic cell death resulting in stronger anti-neoplastic effects. In this review, we discuss the mechanism of action of TTFields, the plethora of clinical trials being conducted in patients with GBM, pancreatic adenocarcinoma, ovarian cancer, non-small-cell-lung-cancer (NSCLC), brain metastasis from NSCLC, and MPM and toxicity profile.

Establishment of Tumor Treating Fields Combined With Mild Hyperthermia as Novel Supporting Therapy for Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant tumor with poor prognosis and limited therapeutic options. Alternating electrical fields with low intensity called "Tumor Treating Fields" (TTFields) are a new, non-invasive approach with almost no side effects and phase 3 trials are ongoing in advanced PDAC. We evaluated TTFields in combination with mild hyperthermia. Three established human PDAC cell lines and an immortalized pancreatic duct cell line were treated with TTFields and hyperthermia at 38.5°C, followed by microscopy, assays for MTT, migration, colony and sphere formation, RT-qPCR, FACS, Western blot, microarray and bioinformatics, and in silico analysis using the online databases GSEA, KEGG, Cytoscape-String, and Kaplan-Meier Plotter. Whereas TTFields and hyperthermia alone had weak effects, their combination strongly inhibited the viability of malignant, but not those of nonmalignant cells. Progression features and the cell cycle were impaired, and autophagy was induced. The identified target genes were key players in autophagy, the cell cycle and DNA repair. The expression profiles of part of these target genes were significantly involved in the survival of PDAC patients. In conclusion, the combination of TTFields with mild hyperthermia results in greater efficacy without increased toxicity and could be easily clinically approved as supporting therapy.

An overview on tumor treating fields (TTFields) technology as a new potential subsidiary biophysical treatment for COVID-19

COVID-19 pandemic situation has affected millions of people with tens of thousands of deaths worldwide. Despite all efforts for finding drugs or vaccines, the key role for the survival of patients is still related to the immune system. Therefore, improving the efficacy and the functionality of the immune system of COVID-19 patients is very crucial. The potential new, non-invasive, FDA-approved biophysical technology that could be considered in this regard is tumor treating fields (TTFields) based on an alternating electric field has great biological effects. TTFields have significant effects in improving the functionality of dendritic cell, and cytotoxic T-cells, and these cells have a major role in defense against viral infection. Hence, applying TTFields could help COVID-19 patients against infection. Additionally, TTFields can reduce viral genomic replication, by reducing the expressions of some of the vital members of DNA replication complex genes from the minichromosome maintenance family (MCMs). These genes not only are involved in DNA replication but it has also been proven that they have a crucial role in viral replication. Also, TTFields suppress the formation of the network of tunneling nanotubes (TNTs) which is knows as filamentous (F)-actin-rich tubular structures. TNTs have a critical role in promoting the spread of viruses through improving viral entry and acting as a protective agent for viral components from immune cells and even pharmaceuticals. Moreover, TTFields enhance autophagy which leads to apoptosis of virally infected cells. Thus, it can be speculated that using TTFields may prove to be a promising approach as a subsidiary treatment of COVID-19.

Tumor Treating Fields (TTFields) downregulate the Fanconi Anemia-BRCA pathway and increase the efficacy of chemotherapy in malignant pleural mesothelioma preclinical models

OBJECTIVES

Tumor Treating Fields (TTFields) are low intensity, intermediate frequency, alternating electric fields with antimitotic effects on cancerous cells. TTFields concomitant with pemetrexed and a platinum agent are approved in the US and EU as first line therapy for unresectable, locally advanced or metastatic malignant pleural mesothelioma (MPM). The goal of the current study was to characterize the mechanism of action of TTFields in MPM cell lines and animal models.

METHODS

Human MPM cell lines MSTO-211H and NCI-H2052 were treated with TTFields to determine the frequency that elicits maximal cytotoxicity. The effect of TTFields on DNA damage and repair, and the cytotoxic effect of TTFields in combination with cisplatin and/or pemetrexed were examined. Efficacy of TTFields concomitant with cisplatin and pemetrexed was evaluated in orthotopic IL-45 and subcutaneous RN5 murine models.

RESULTS

TTFields at a frequency of 150 kHz demonstrated the highest cytotoxicity to MPM cells. Application of 150 kHz TTFields resulted in increased formation of DNA double strand breaks, elevated expression of DNA damage induced cell cycle arrest proteins, and reduced expression of Fanconi Anemia (FA)-BRCA DNA repair pathway proteins. Co-treatment of TTFields with cisplatin or pemetrexed significantly increased treatment efficacy versus each modality alone, with additivity and synergy exhibited by the TTFields-pemetrexed and TTFields-cisplatin combinations, respectively. In animal models, tumor volume was significantly lower for the TTFields-cisplatin-pemetrexed combination compared to control, accompanied by increased DNA damage within the tumor.

CONCLUSION

This research demonstrated that the efficacy of TTFields for the treatment of MPM is associated with reduced expression of FA-BRCA pathway proteins and increased DNA damage. This mechanism of action is consistent with the observed synergism for TTFields-cisplatin vs additivity for TTFields-pemetrexed, as cisplatin-induced DNA damage is repaired via the FA-BRCA pathway.

Therapy of pancreatic cancer with alternating electric fields: Limitations of the method

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant tumor with a poor prognosis. More effective treatment options are urgently needed. The use of physical and weak alternating electric fields (TTFields) can inhibit cell division of PDAC carcinoma and is currently being investigated in clinical trials. Here, we analyzed this new physical treatment under non-ideal conditions such as may occur during patient treatment. Three established human PDAC cell lines BxPC-3, gemcitabine-resistant BxPC-3 (BxGem), AsPC-1, and a non-malignant primary pancreatic cell line CRL-4023 were treated with TTFields in vitro. MTT assays, electrical impedance measurement, cell staining with Annexin V/7AAD followed by FACS analysis, digital image analysis and immunohistochemistry were performed. Treatment with TTFields smaller than 0.7 V/cm and field lines in the direction of mitotic spindle orientation significantly inhibited proliferation of all PDAC cells at 150 kHz, but significantly increased viability of AsPC-1 cells at all frequencies between 100 kHz and 300 kHz and that of BxPC-3 and BxGem cells at 250 kHz. Apoptosis or necrosis were not induced. Non-malignant CRL-4023 cells were not affected at 150 kHz. TTFields damaged PDAC cell lines but even favored their viability at very weak field strength and unfavorable frequency or inadequate field direction.

In Vivo Safety of Tumor Treating Fields (TTFields) Applied to the Torso

Background

Tumor Treating Fields (TTFields) therapy is a non-invasive, loco-regional, anti-mitotic treatment modality that targets rapidly dividing cancerous cells, utilizing low intensity, alternating electric fields at cancer-cell-type specific frequencies. TTFields therapy is approved for the treatment of newly diagnosed and recurrent glioblastoma (GBM) in the US, Europe, Israel, Japan, and China. The favorable safety profile of TTFields in patients with GBM is partially attributed to the low rate of mitotic events in normal, quiescent brain cells. However, specific safety evaluations are warranted at locations with known high rates of cellular proliferation, such as the torso, which is a primary site of several of the most aggressive malignant tumors.

Methods

The safety of delivering TTFields to the torso of healthy rats at 150 or 200 kHz, which were previously identified as optimal frequencies for treating multiple torso cancers, was investigated. Throughout 2 weeks of TTFields application, animals underwent daily clinical examinations, and at treatment cessation blood samples and internal organs were examined. Computer simulations were performed to verify that the targeted internal organs of the torso were receiving TTFields at therapeutic intensities (≥ 1 V/cm root mean square, RMS).

Results

No treatment-related mortality was observed. Furthermore, no significant differences were observed between the TTFields-treated and control animals for all examined safety parameters: activity level, food and water intake, stools, motor neurological status, respiration, weight, complete blood count, blood biochemistry, and pathological findings of internal organs. TTFields intensities of 1 to 2.5 V/cm RMS were confirmed for internal organs within the target region.

Conclusions

This research demonstrates the safety of therapeutic level TTFields at frequencies of 150 and 200 kHz when applied as monotherapy to the torso of healthy rats.

PTEN mutations predict benefit from tumor treating fields (TTFields) therapy in patients with recurrent glioblastoma

INTRODUCTION

Optimal treatment for recurrent glioblastoma isocitrate dehydrogenase 1 and 2 wild-type (rGBM IDH-WT) is not standardized, resulting in multiple therapeutic approaches. A phase III clinical trial showed that tumor treating fields (TTFields) monotherapy provided comparable survival benefits to physician's chemotherapy choice in rGBM. However, patients did not equally benefit from TTFields, highlighting the importance of identifying predictive biomarkers of TTFields efficacy.

METHODS

A retrospective review of an institutional database with 530 patients with infiltrating gliomas was performed. Patients with IDH-WT rGBM receiving TTFields at first recurrence were included. Tumors were evaluated by next-generation sequencing for mutations in 205 cancer-related genes. Post-progression survival (PPS) was examined using the log-rank test and multivariate Cox-regression analysis.

RESULTS

149 rGBM patients were identified of which 29 (19%) were treated with TTFields. No significant difference in median PPS was observed between rGBM patients who received versus did not receive TTFields (13.9 versus 10.9 months, p = 0.068). However, within the TTFields-treated group (n = 29), PPS was improved in PTEN-mutant (n = 14) versus PTEN-WT (n = 15) rGBM, (22.2 versus 11.6 months, p = 0.017). Within the PTEN-mutant group (n = 70, 47%), patients treated with TTFields (n = 14) had longer median PPS (22.2 versus 9.3 months, p = 0.005). No PPS benefit was observed in PTEN-WT patients receiving TTFields (n = 79, 53%).

CONCLUSIONS

TTFields therapy conferred a significant PPS benefit in PTEN-mutant rGBM. Understanding the molecular mechanisms underpinning the differences in response to TTFields therapy could help elucidate the mechanism of action of TTFields and identify the rGBM patients most likely to benefit from this therapeutic option.

Tumor treating fields (TTFields) impairs aberrant glycolysis in glioblastoma as evaluated by [18F]DASA-23, a non-invasive probe of pyruvate kinase M2 (PKM2) expression

Despite the anti-proliferative and survival benefits from tumor treating fields (TTFields) in human glioblastoma (hGBM), little is known about the effects of this form of alternating electric fields therapy on the aberrant glycolysis of hGBM. [18F]FDG is the most common radiotracer in cancer metabolic imaging, but its utility in hGBM is impaired due to high glucose uptake in normal brain tissue. With TTFields, radiochemistry, Western blot, and immunofluorescence microscopy, we identified pyruvate kinase M2 (PKM2) as a biomarker of hGBM response to therapeutic TTFields. We used [18F]DASA-23, a novel radiotracer that measures PKM2 expression and which has been shown to be safe in humans, to detect a shift away from hGBM aberrant glycolysis in response to TTFields. Compared to unexposed hGBM, [18F]DASA-23 uptake was reduced in hGBM exposed to TTFields (53%, P< 0.05) or temozolomide chemotherapy (33%, P > 0.05) for 3 d. A 6-d TTFields exposure resulted in a 31% reduction (P = 0.043) in 60-min uptake of [18F]DASA-23. [18F]DASA-23 was retained after a 10 but not 30-min wash-out period. Compared to [18F]FDG, [18F]DASA-23 demonstrated a 4- to 9-fold greater uptake, implying an improved tumor-to-background ratio. Furthermore, compared to no-TTFields exposure, a 6-d TTFields exposure caused a 35% reduction in [18F]DASA-23 30-min uptake compared to only an 8% reduction in [18F]FDG 30-min uptake. Quantitative Western blot analysis and qualitative immunofluorescence for PKM2 confirmed the TTFields-induced reduction in PKM2 expression. This is the first study to demonstrate that TTFields impairs hGBM aberrant glycolytic metabolism through reduced PKM2 expression, which can be non-invasively detected by the [18F]DASA-23 radiotracer.

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

Traditional cancer therapy choices for clinicians are surgery, chemotherapy, radiation and immune therapy which are used either standalone therapies or in various combinations. Other physical modalities beyond ionizing radiation include photodynamic therapy and heating and the more recent approach referred to as Tumor Treating Fields (TTFields). TTFields are intermediate frequency, low-intensity, alternating electric fields that are applied to tumor regions and cells using noninvasive arrays. TTFields have revolutionized the treatment of newly diagnosed and recurrent glioblastoma (GBM) and unresectable and locally advanced malignant pleural mesothelioma (MPM). TTFields are thought to kill tumor cells predominantly by disrupting mitosis; however it has been shown that TTFields increase efficacy of different classes of drugs, which directly target mitosis, replication stress and DNA damage pathways. Hence, a detailed understanding of TTFields' mechanisms of action is needed to use this therapy effectively in the clinic. Recent findings implicate TTFields' role in different important pathways such as DNA damage response and replication stress, ER stress, membrane permeability, autophagy, and immune response. This review focuses on potentially novel mechanisms of TTFields anti-tumor action and their implications in completed and ongoing clinical trials and pre-clinical studies. Moreover, the review discusses advantages and strategies using chemotherapy agents and radiation therapy in combination with TTFields for future clinical use.

Physical approaches to treat glioblastoma

PURPOSE OF REVIEW

Glioblastoma (GBM) patients have a poor prognosis despite the use of modern synergistic multimodal treatment strategies, with a progression-free survival estimated at 7-8 months, a median survival of 14-16 months and 5-year overall survival of 9.8%.

RECENT FINDINGS

Physical methods hold the promise to act synergistically with classical treatments to improve the outcome of GBM patients. Fluorescent guided surgery with 5-aminolevulinic acid and tumor-treating fields therapy have already shown positive results in randomized phase III trials and have been incorporated in the standard management. Other techniques such as photodynamic therapy (PDT) and focused ultrasound, often combined whit microbubbles, are reaching clinical development.

SUMMARY

Several clinical trials to evaluate the feasibility and efficacy of ultrasound devices to disrupt the blood-brain barrier are ongoing. PDT enables the creation of a safety margin or treatment of non-resecable tumors. However, randomized trials are urgently required to validate the efficacy of these promising approaches. We aim to critically review physical approaches to treat GBM, focusing on available clinical trial data.

Global post-marketing safety surveillance of Tumor Treating Fields (TTFields) in patients with high-grade glioma in clinical practice

INTRODUCTION

Tumor Treating Fields (TTFields; antimitotic treatment) delivers low-intensity, intermediate-frequency, alternating electric fields through skin-applied transducer arrays. TTFields (200 kHz) was FDA-approved in glioblastoma (GBM), based on the phase 3 EF-11 (recurrent GBM, rGBM) and EF-14 (newly diagnosed GBM, ndGBM) trials. The most common TTFields-related adverse event (AE) in both trials was array-associated skin irritation. We now report on TTFields-related AEs in the real-world, clinical practice setting.

METHODS

Unsolicited, post-marketing surveillance data from TTFields-treated patients (October 2011-February 2019) were retrospectively analyzed using MedDRA v21.1 preferred terms, stratified by region (US, EMEA [Europe, Middle East, Africa], Japan), diagnosis (ndGBM, rGBM, anaplastic astrocytoma/oligodendroglioma, other brain tumors), and age (< 18 [pediatric], 18-64 [adults], ≥ 65 [elderly]; years of age).

RESULTS

Of 11,029 patients, 53% were diagnosed with ndGBM and 39% were diagnosed with rGBM at any line of disease recurrence. Most were adults (73%), 26% were elderly, and the male-to-female ratio was ~ 2:1 (close to published ratios of typical GBM populations). The most commonly reported TTFields-related AE was array-associated skin reaction, occurring in patients with ndGBM (38%), rGBM (29%), anaplastic astrocytoma/oligodendroglioma (38%), and other brain tumors (31%); as well as 37% of pediatric, 34% of adult, and 36% of elderly patients. Most skin AEs were mild/moderate and manageable. Other TTFields-related AEs in patients with ndGBM/rGBM included under-array heat sensation (warmth; 11%, 10%, respectively) and electric sensation (tingling; 11%, 9%, respectively), and headache (7%, 6%, respectively).

CONCLUSIONS

This TTFields safety surveillance analysis in > 11,000 patients revealed no new safety concerns, with a favorable safety profile comparable with published TTFields/GBM trials. The safety profile remained consistent among subgroups, suggesting feasibility in multiple populations, including elderly patients.

Thermoplastic microfluidic bioreactors with integrated electrodes to study tumor treating fields on yeast cells

Tumor-treating fields (TTFields) are alternating electrical fields of intermediate frequency and low intensity that can slow or inhibit tumor growth by disrupting mitosis division of cancerous cells through cell cycle proteins. In this work, for the first time, an in-house fabricated cyclo-olefin polymer made microfluidic bioreactors are integrated with Cr/Au interdigitated electrodes to test TTFields on yeast cells with fluorescent protein:Nop56 gene. A small gap between electrodes (50 μm) allows small voltages (<150 mV) to be applied on the cells; hence, uninsulated gold electrodes are used in the non-faradaic region without causing any electrochemical reaction at the electrode-medium interface. Electrochemical modeling as well as impedance characterization and analysis of the electrodes are done using four different cell nutrient media. The experiments with yeast cells are done with 150 mV, 150 kHz and 30 mV, 200 kHz sinusoidal signals to generate electrical field magnitudes of 6.58 V/cm and 1.33 V/cm, respectively. In the high electrical field experiment, the cells go through electroporation. In the experiment with the low electrical field magnitude for TTFields, the cells have prolonged mitosis from typical 80-90 min to 200-300 min. Our results confirm the validity of the electrochemical model and the importance of applying a correct magnitude of the electrical field. Compared to the so far reported alternatives with insulated electrodes, the here developed thermoplastic microfluidic bioreactors with uninsulated electrodes provide a new, versatile, and durable platform for in vitro cell studies toward the improvement of anti-cancer therapies including personalized treatment.

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

Tumor treating fields (TTFields) is a noninvasive physical modality of cancer therapy that applies low-intensity, intermediate frequency, and alternating electric fields to a tumor. Interference with mitosis was the first mechanism describing the effects of TTFields on cancer cells; however, TTFields was shown to not only reduce the rejoining of radiation-induced DNA double-strand breaks (DSBs), but to also induce DNA DSBs. The mechanism(s) by which TTFields generates DNA DSBs is related to the generation of replication stress including reduced expression of the DNA replication complex genes MCM6 and MCM10 and the Fanconi's Anemia pathway genes. When markers of DNA replication stress as a result of TTFields exposure were examined, newly replicated DNA length was reduced with TTFields exposure time and there was increased R-loop formation. Furthermore, as cells were exposed to TTFields a conditional vulnerability environment developed which rendered cells more susceptible to DNA damaging agents or agents that interfere with DNA repair or replication fork maintenance. The effect of TTFields exposure with concomitant exposure to cisplatin or PARP inhibition, the combination of TTFields plus concomitant PARP inhibition followed by radiation, or radiation alone at the end of a TTFields exposure were all synergistic. Finally, gene expression analysis of 47 key mitosis regulator genes suggested that TTFields-induced mitotic aberrations and DNA damage/replication stress events, although intimately linked to one another, are likely initiated independently of one another. This suggests that enhanced replication stress and reduced DNA repair capacity are also major mechanisms of TTFields effects, effects for which there are therapeutic implications.

Tumor-Treating Fields Induce RAW264.7 Macrophage Activation Via NK-κB/MAPK Signaling Pathways

Objective:

Tumor-treating fields are currently used to successfully treat various cancers; however, the specific pathways associated with its efficacy remain unknown in the immune responses. Here, we evaluated tumor-treating fields–mediated initiation of the macrophage-specific immune response.

Materials and Methods:

We subjected RAW 264.7 mouse macrophages to clinically relevant levels of tumor-treating fields (0.9 V/cm, 150 kHz) and evaluated alterations in cytokine expression and release, as well as cell viability. Additionally, we investigated the status of immunomodulatory pathways to determine their roles in tumor-treating fields–mediated immune activation.

Results and Discussion:

Our results indicated that tumor-treating fields treatment at 0.9 V/cm decreased cell viability and increased cytokine messenger RNA/protein levels, as well as levels of nitric oxide and reactive oxygen species, relative to controls. The levels of tumor necrosis factor α, interleukin 1β, and interleukin 6 were markedly increased in tumor-treating fields–treated RAW 264.7 cells cocultured with 4T1 murine mammary carcinoma cells compared with those in 4T1 or RAW 264.7 cells with or without tumor-treating fields treatment. Moreover, the viability of 4T1 cells treated with the conditioned medium of tumor-treating fields–stimulated RAW 264.7 cells decreased, indicating that macrophage activation by tumor-treating fields effectively killed the tumor cells. Moreover, tumor-treating fields treatment activated the nuclear factor κB and mitogen-activated protein kinase pathways involved in immunomodulatory signaling.

Conclusion:

These results provide critical insights into the mechanisms through which tumor-treating fields affect macrophage-specific immune responses and the efficacy of this method for cancer treatment.

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

Although tumour-treating fields (TTFields) is a promising physical treatment modality based on disruption of dipole alignments and generation of dielectrophoretic forces during cytokinesis, not much is known about TTFields-responsive sensitisers. Here, we report a novel TTFields-responsive sensitiser, barium titanate nanoparticles (BTNPs), which exhibit cytocompatibility, with non-cytotoxic effects on breast cancer cells. BTNPs are characterised by high dielectric constant values and ferroelectric properties. Notably, we found that BTNPs sensitised TTFields-resistant breast cancer cells in response to TTFields. In addition, BTNPs accumulated in the cytoplasm of cancer cells in response to TTFields. Further, we showed that TTFields combined with BTNPs exhibited antitumor activity by modulating several cancer-related pathways in general, and the cell cycle-related apoptosis pathway in particular. Therefore, our data suggest that BTNPs increase the antitumor action of TTFields by an electric field-responsive cytosolic accumulation, establishing BTNP as a TTFields-responsive sensitiser.

5-Fluorouracil as a Tumor-Treating Field-Sensitizer in Colon Cancer Therapy

Colorectal cancer (CRC) is a major cause of mortality that can be treated effectively with chemotherapy and radiotherapy, although resistance to these therapeutic modalities often occurs. Tumor-treating fields (TTFields) can block tumor growth by selectively impairing tumor cell division. In this study, we investigated the mechanism by which 5-fluorouracil (5-FU) sensitizes tumor cells to TTFields. Human HCT116 and SW480 CRC cells were treated with 5-FU and/or TTFields, and characterized in vitro in terms of cell viability, apoptosis through reactive oxygen species production, autophagy, and metastatic potentials. The biological effects of 5-FU and/or TTFields were studied via positron emission tomography and computed tomography on xenograft tumor growth and were confirmed with organoid models of patients. Our results revealed that combination treatment with 5-FU and TTFields increased the efficiency of TTFields therapy in colon cancer cells by downregulating signaling pathways associated with cell proliferation, survival, cell invasion, and migration while upregulating pathways mediating apoptosis and autophagic cell death. The novel mechanistic insights gleaned in this study suggest that combination therapy with TTFields and 5-FU may be effective in treating CRC, although safety and efficacy testing in patients with CRC will need to be performed before this strategy can be implemented clinically for TTF-sensitization.

Integration of Tumor-Treating Fields into the Multidisciplinary Management of Patients with Solid Malignancies

Tumor treating fields, a noninvasive cancer treatment using low intensity alternating electric fields, offers clinical opportunities with unique challenges. This review focuses on the mechanism of action of this treatment, the known pre‐clinical and clinical experience, and the practical issues surrounding its use in the multidisciplinary management of patients with solid malignancies.

Tumor‐treating fields (TTFields) are a noninvasive antimitotic cancer treatment consisting of low‐intensity alternating electric fields delivered to the tumor or tumor bed via externally applied transducer arrays. In multiple in vitro and in vivo cancer cell lines, TTFields therapy inhibits cell proliferation, disrupts cell division, interferes with cell migration and invasion, and reduces DNA repair. Human trials in patients with primary glioblastoma showed an improvement in overall survival, and trials in patients with unresectable malignant pleural mesothelioma showed favorable outcomes compared with historical control. This led to U.S. Food and Drug Administration approval in both clinical situations, paving the way for development of trials investigating TTFields in other malignancies. Although these trials are ongoing, the existing evidence suggests that TTFields have activity outside of neuro‐oncology, and further study into the mechanism of action and clinical activity is required. In addition, because TTFields are a previously unrecognized antimitotic therapy with a unique mode of delivery, the oncological community must address obstacles to widespread patient and provider acceptance. TTFields will likely join surgery, systemic therapy, and radiation therapy as a component of multimodality management of patients with solid malignancies.

Implications for Practice.

Tumor‐treating fields (TTFields) exhibit a broad range of antitumor activities. Clinically, they improve overall survival for patients with newly diagnosed glioblastoma. The emergence of TTFields has changed the treatment regimen for glioblastoma. Clinicians need to understand the practical issues surrounding its use in the multidisciplinary management of patients with glioblastoma. With ongoing clinical trials, TTFields likely will become another treatment modality for solid malignancies.

Tumour-treating fields (TTFields): Investigations on the mechanism of action by electromagnetic exposure of cells in telophase/cytokinesis

Tumour-treating fields (TTFields) use alternating electric fields which interfere with dividing cells, thereby reducing tumour growth. Previous reports suggest that electrical forces on cell structure proteins interfered with the chromosome separation during mitosis and induced apoptosis. In the present report we evaluate electromagnetic exposure of cells in telophase/cytokinesis in order to further analyse the mechanism of action on cells. We performed numerical electromagnetic simulations to analyse the field distribution in a cell during different mitotic phases. Based thereon, we developed an electric lumped element model of the mitotic cell. Both the electromagnetic simulation and the lumped element model predict a local increase of the specific absorption rate (SAR) as a measure of the electromagnetically induced power absorption density at the mitotic furrow which may help to explain the anti-proliferative effect. In accordance with other reports, cell culture experiments confirmed that TTFields reduce the proliferation of different glioma cell lines in a field strength- and frequency-dependent manner. Furthermore, we found an additional dependence on the commutation time of the electrical fields. The report gives new insights into TTFields’ anti-proliferative effect on tumours, which could help to improve future TTFields application systems.

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

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⁺ (Ca_v) 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 Ca_v1.2-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 Ca_v1.2 by benidipine aggravated in one glioblastoma line the TTFields effects suggesting that Ca_v1.2-triggered signaling contributes to cellular TTFields stress response. In conclusion, the present study identified Ca_v1.2 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 in combination with gemcitabine or gemcitabine plus nab-paclitaxel in pancreatic cancer: Results of the PANOVA phase 2 study

BACKGROUND

Tumor Treating Fields (TTFields), low intensity alternating electric fields with antimitotic activity, have demonstrated survival benefit in patients with glioblastoma. This phase 2 PANOVA study was conducted to examine the combination of TTFields plus chemotherapy in patients with pancreatic ductal adenocarcinoma (PDAC).

METHODS

Forty patients with newly-diagnosed, locally advanced or metastatic PDAC received continuous TTFields (150 KHz for ≥18 h/day) plus gemcitabine (1000 mg/m2), or gemcitabine plus nab-paclitaxel (125 mg/m2). The primary endpoint was safety and secondary endpoints included compliance to TTFields, progression-free survival (PFS), and overall survival (OS).

RESULTS

Seventeen patients (85%) in each cohort reported Grade ≥3 adverse events (AEs). No increase in serious AEs (SAEs) was observed compared to that anticipated with systemic chemotherapy alone. Twenty-one patients reported TTFields-related skin toxicity, of which 7 were Grade 3; all resolved following temporary reduction of daily TTFields usage. No TTFields-related SAEs were reported. Compliance to TTFields was 68-78% of the recommended average daily use in both cohorts. Median PFS was 8.3 months (95% CI 4.3, 10.3) and median OS was 14.9 months (95% CI 6.2, NA) in the TTFields + gemcitabine cohort. In the TTFields + gemcitabine + nab-paclitaxel cohort, the median PFS was 12.7 months (95% CI 5.4, NA); median OS has not been reached.

CONCLUSION

The PANOVA trial demonstrated that the combination of TTFields and systemic chemotherapy is safe and tolerable in patients with advanced PDAC. Based on the safety and preliminary efficacy results of this phase 2 study, a randomized phase 3 study (PANOVA-3) is underway.

AMPK-dependent autophagy upregulation serves as a survival mechanism in response to Tumor Treating Fields (TTFields)

Tumor Treating Fields (TTFields), an approved treatment modality for glioblastoma, are delivered via non-invasive application of low-intensity, intermediate-frequency, alternating electric fields. TTFields application leads to abnormal mitosis, aneuploidy, and increased cell granularity, which are often associated with enhancement of autophagy. In this work, we evaluated whether TTFields effected the regulation of autophagy in glioma cells. We found that autophagy is upregulated in glioma cells treated with TTFields as demonstrated by immunoblot analysis of the lipidated microtubule-associated protein light chain 3 (LC3-II). Fluorescence and transmission electron microscopy demonstrated the presence of LC3 puncta and typical autophagosome-like structures in TTFields-treated cells. Utilizing time-lapse microscopy, we found that the significant increase in the formation of LC3 puncta was specific to cells that divided during TTFields application. Evaluation of selected cell stress parameters revealed an increase in the expression of the endoplasmic reticulum (ER) stress marker GRP78 and decreased intracellular ATP levels, both of which are indicative of increased proteotoxic stress. Pathway analysis demonstrated that TTFields-induced upregulation of autophagy is dependent on AMP-activated protein kinase (AMPK) activation. Depletion of AMPK or autophagy-related protein 7 (ATG7) inhibited the upregulation of autophagy in response to TTFields, as well as sensitized cells to the treatment, suggesting that cancer cells utilize autophagy as a resistance mechanism to TTFields. Combining TTFields with the autophagy inhibitor chloroquine (CQ) resulted in a significant dose-dependent reduction in cell growth compared with either TTFields or CQ alone. These results suggest that dividing cells upregulate autophagy in response to aneuploidy and ER stress induced by TTFields, and that AMPK serves as a key regulator of this process.

Synergistic inhibition of glioma cell proliferation by Withaferin A and tumor treating fields

Glioblastoma (GBM) is the most aggressive and lethal form of brain cancer. Standard therapies are non-specific and often of limited effectiveness; thus, efforts are underway to uncover novel, unorthodox therapies against GBM. In previous studies, we investigated Withaferin A, a steroidal lactone from Ayurvedic medicine that inhibits proliferation in cancers including GBM. Another novel approach, tumor treating fields (TTFields), is thought to disrupt mitotic spindle formation and stymie proliferation of actively dividing cells. We hypothesized that combining TTFields with Withaferin A would synergistically inhibit proliferation in glioblastoma. Human glioblastoma cells (GBM2, GBM39, U87-MG) and human breast adenocarcinoma cells (MDA-MB-231) were isolated from primary tumors. The glioma cell lines were genetically engineered to express firefly luciferase. Proliferative potential was assessed either by bioluminescence imaging or cell counting via hemocytometer. TTFields (4 V/cm) significantly inhibited growth of the four cancer cell lines tested (n = 3 experiments per time point, four measurements per sample, p < 0.02 at least; 2-way ANOVA, control vs. treatment). The combination of Withaferin A (10-100 nM) with TTFields significantly inhibited the growth of the glioma cells to a degree beyond that of Withaferin A or TTFields alone. The interaction of the Withaferin A and TTFields on glioma cells was found to be synergistic in nature (p < 0.01, n = 3 experiments). These findings were validated by both bioluminescence and hemocytometric measurements. The combination of Withaferin A with TTFields represents a novel approach to treat GBM in a manner that is likely better than either treatment alone and that is synergistic.

Tumor treating fields: a novel treatment modality and its use in brain tumors

Tumor treating fields (TTFields) are low-intensity electric fields alternating at an intermediate frequency (200kHz), which have been demonstrated to block cell division and interfere with organelle assembly. This novel treatment modality has shown promise in a variety of tumor types. It has been evaluated in randomized phase 3 trials in glioblastoma (GBM) and demonstrated to prolong progression-free survival (PFS) and overall survival (OS) when administered together with standard maintenance temozolomide (TMZ) chemotherapy in patients with newly diagnosed GBM. TTFields are continuously delivered by 4 transducer arrays consisting each of 9 insulated electrodes that are placed on the patient's shaved scalp and connected to a portable device. Here we summarize the preclinical data and mechanism of action, the available clinical data, and further outlook of this treatment modality in brain tumors and other cancer indications.

Tumor-Treating Fields: A Fourth Modality in Cancer Treatment

Despite major advances in therapy, cancer continues to be a leading cause of mortality. In addition, toxicities of traditional therapies pose a significant challenge to tolerability and adherence. TTFields, a noninvasive anticancer treatment modality, utilizes alternating electric fields at specific frequencies and intensities to selectively disrupt mitosis in cancerous cells. TTFields target proteins crucial to the cell cycle, leading to mitotic arrest and apoptosis. TTFields also facilitate an antitumor immune response. Clinical trials of TTFields have proven safe and efficacious in patients with glioblastoma multiforme (GBM), and are FDA approved for use in newly diagnosed and recurrent GBM. Trials in other localized solid tumors are ongoing. Clin Cancer Res; 24(2); 266-75. ©2017 AACR.

Determining the Optimal Inhibitory Frequency for Cancerous Cells Using Tumor Treating Fields (TTFields)

Tumor Treating Fields (TTFields) are an effective treatment modality delivered via the continuous, noninvasive application of low-intensity (1-3 V/cm), alternating electric fields in the frequency range of several hundred kHz. The study of TTFields in tissue culture is carried out using the TTFields in vitro application system, which allows for the application of electric fields of varying frequencies and intensities to ceramic Petri dishes with a high dielectric constant (Ɛ > 5,000). Cancerous cell lines plated on coverslips at the bottom of the ceramic Petri dishes are subjected to TTFields delivered in two orthogonal directions at various frequencies to facilitate treatment outcome tests, such as cell counts and clonogenic assays. The results presented in this report demonstrate that the optimal frequency of the TTFields with respect to both cell counts and clonogenic assays is 200 kHz for both ovarian and glioma cells.

Biological activity of tumor-treating fields in preclinical glioma models

Glioblastoma is the most common and aggressive form of intrinsic brain tumor with a very poor prognosis. Thus, novel therapeutic approaches are urgently needed. Tumor-treating fields (TTFields) may represent such a novel treatment option. The aim of this study was to investigate the effects of TTFields on glioma cells, as well as the functional characterization of the underlying mechanisms. Here, we assessed the anti-glioma activity of TTFields in several preclinical models. Applying TTFields resulted in the induction of cell death in a frequency- and intensity-dependent manner in long-term glioma cell lines, as well as glioma-initiating cells. Cell death occurred in the absence of caspase activation, but involved autophagy and necroptosis. Severe alterations in cell cycle progression and aberrant mitotic features, such as poly- and micronucleation, preceded the induction of cell death. Furthermore, exposure to TTFields led to reduced migration and invasion, which are both biological hallmarks of glioma cells. The combination of TTFields with irradiation or the alkylating agent, temozolomide (TMZ), resulted in additive or synergistic effects, and the O⁶-methyl-guanine DNA methyltransferase status did not influence the efficacy of TTFields. Importantly, TMZ-resistant glioma cells were responsive to TTFields application, highlighting the clinical potential of this therapeutic approach. In summary, our results indicate that TTFields induce autophagy, as well as necroptosis and hamper the migration and invasiveness of glioma cells. These findings may allow for a more detailed clinical evaluation of TTFields beyond the clinical data available so far.

Tumor-treating fields elicit a conditional vulnerability to ionizing radiation via the downregulation of BRCA1 signaling and reduced DNA double-strand break repair capacity in non-small cell lung cancer cell lines

The use of tumor-treating fields (TTFields) has revolutionized the treatment of recurrent and newly diagnosed glioblastoma (GBM). TTFields are low-intensity, intermediate frequency, alternating electric fields that are applied to tumor regions and cells using non-invasive arrays. The predominant mechanism by which TTFields are thought to kill tumor cells is the disruption of mitosis. Using five non-small cell lung cancer (NSCLC) cell lines we found that there is a variable response in cell proliferation and cell killing between these NSCLC cell lines that was independent of p53 status. TTFields treatment increased the G2/M population, with a concomitant reduction in S-phase cells followed by the appearance of a sub-G1 population indicative of apoptosis. Temporal changes in gene expression during TTFields exposure was evaluated to identify molecular signaling changes underlying the differential TTFields response. The most differentially expressed genes were associated with the cell cycle and cell proliferation pathways. However, the expression of genes found within the BRCA1 DNA-damage response were significantly downregulated (P<0.05) during TTFields treatment. DNA double-strand break (DSB) repair foci increased when cells were exposed to TTFields as did the appearance of chromatid-type aberrations, suggesting an interphase mechanism responsible for cell death involving DNA repair. Exposing cells to TTFields immediately following ionizing radiation resulted in increased chromatid aberrations and a reduced capacity to repair DNA DSBs, which were likely responsible for at least a portion of the enhanced cell killing seen with the combination. These findings suggest that TTFields induce a state of ‘BRCAness' leading to a conditional susceptibility resulting in enhanced sensitivity to ionizing radiation and provides a strong rationale for the use of TTFields as a combined modality therapy with radiation or other DNA-damaging agents.

An Overview of Sub-Cellular Mechanisms Involved in the Action of TTFields

Long-standing research on electric and electromagnetic field interactions with biological cells and their subcellular structures has mainly focused on the low- and high-frequency regimes. Biological effects at intermediate frequencies between 100 and 300 kHz have been recently discovered and applied to cancer cells as a therapeutic modality called Tumor Treating Fields (TTFields). TTFields are clinically applied to disrupt cell division, primarily for the treatment of glioblastoma multiforme (GBM). In this review, we provide an assessment of possible physical interactions between 100 kHz range alternating electric fields and biological cells in general and their nano-scale subcellular structures in particular. This is intended to mechanistically elucidate the observed strong disruptive effects in cancer cells. Computational models of isolated cells subject to TTFields predict that for intermediate frequencies the intracellular electric field strength significantly increases and that peak dielectrophoretic forces develop in dividing cells. These findings are in agreement with in vitro observations of TTFields' disruptive effects on cellular function. We conclude that the most likely candidates to provide a quantitative explanation of these effects are ionic condensation waves around microtubules as well as dielectrophoretic effects on the dipole moments of microtubules. A less likely possibility is the involvement of actin filaments or ion channels.