Correction: Davidi et al. Tumor Treating Fields (TTFields) Concomitant with Sorafenib Inhibit Hepatocellular Carcinoma In Vitro and In Vivo. Cancers 2022, 14, 2959

The authors wish to make minor corrections to Figure 1 and Figure 2 of the following paper [...].

Tumor treating fields (TTFields) in combination with sorafenib inhibit hepatocellular carcinoma in vitro and in vivo

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Background: Hepatocellular carcinoma (HCC) is a highly malignant liver cancer and a leading cause of cancer related mortality. Sorafenib was the first approved systemic treatment for HCC, and remains one of few front-line treatments for this malignancy. Tumor treating fields (TTFields) are low intensity (1-3 V/cm), intermediate frequency (100-500 kHz), alternating electric fields that exert antimitotic effects on cancerous cells. Results of the phase 2 HEPANOVA study of TTFields (150 kHz) plus sorafenib for advanced HCC support investigation of TTFields in a randomized controlled phase 3 study. The current research aimed to describe the in vitro and in vivo efficacy of this combination and to elucidate details regarding the underlying mechanism of action. Methods: In vitro examinations were performed in HepG2 and Huh-7D12 human HCC cell lines, to which TTFields at a frequency of 150 kHz were applied using the inovitro system. Autophagy was examined by western blot and fluorescence detection of microtubule-associated protein light chain 3 (LC3) levels, an accepted autophagy marker. The effect of TTFields in combination with sorafenib was evaluated using cytotoxic, clonogenic, and apoptotic assays. In vivo, SD rats were inoculated orthotopically into the left hepatic lobe with N1S1 HCC cells. 7 days later, TTFields or sham (heat) were applied to the abdominal region of the rats, continuously for 6 days. Daily intraperitoneal injections of sorafenib (10 mg/kg/day) or vehicle were performed during this time. To determine tumor volume growth, MRI images were acquired before and after treatment. Levels of autophagy and apoptosis were examined in tumor sections by immunohistochemistry for LC3 and cleaved PARP, respectively. Results: Application of TTFields induced autophagy in HCC cells. TTFields delivery was cytotoxic to the cells, reduced their colony forming ability, and induced apoptosis while combination with sorafenib elevated these effects. In vivo, tumor volume increased 6-fold in control animals vs 1.6-fold in animals treated with TTFields plus sorafenib. This effect was accompanied by significantly elevated levels of cleaved PARP and LC3 within the tumors of treated relative to control rats. Conclusions: The results demonstrate induction of autophagy and apoptosis in HCC following treatment with TTFields. Concomitant application of TTFields with sorafenib enhanced efficacy via a mechanism that may involve overwhelming autophagy, in vitro and in vivo.

EXTH-75. APPLICATION OF TUMOR TREATING FIELDS (TTFIELDS) TO THE HEAD AND TORSO OF MICE WITH THE DEDICATED INOVIVO SYSTEM

INTRODUCTION

Tumor Treating Fields (TTFields) therapy is an approved anti-cancer treatment for glioblastoma and mesothelioma. TTFields are delivered to patients continuously by two sets of arrays placed on opposite sides of the body at the tumor region to generate two perpendicular electric fields. Previously, in vivo studies of TTFields were limited due to the lack of a dedicated system that could maintain continuous and adequate contact of the arrays with the animal’s skin as well as the stress imposed on the animals by individual housing and the motility limitations they experience during treatment.

METHODS

Different electrode layouts were explored to optimize the intensity of the electric fields delivered to the target locations (therapeutic threshold >1 V/cm). The ability of various adhesive materials and wire coiling prevention strategies to increase TTFields device usage was examined. Stress reduction with different housing methods was evaluated via clinical examination of the animals.

RESULTS

Optimal array layouts were identified based on simulation data for TTFields delivery to the torso or the head of the mouse. Compacting conductors into a single printed circuit cable connected to a novel electric swivel machine resulted in fewer wire entanglements, and the improved adhesives resulted in fewer array replacements, overall elevating device usage. Improved cage design permitted pairs of mice to maintain social interactions while individually housed. Less weight loss was seen for animals housed in the dyadic relative to the standard solitary cages, indicating reduced stress.

CONCLUSIONS

The inovivo system provides means for continuous delivery of therapeutic levels of TTFields to the head and torso of mice while minimizing animal stress and increasing device usage. The new head arrays enable application of TTFields to the head of mice for the first time, allowing expansion of glioblastoma treatment research.

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.

Abstract 1063: Effectiveness of Tumor Treating Fields (TTFields) in combination with sorafenib for treatment of hepatocellular carcinoma in vitro and in vivo

Purpose/Objective(s): Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and it is one of the leading causes of related mortality worldwide. Sorafenib is an oral multikinase inhibitor that targets the Raf/MEK/ERK signaling pathway, thus inducing autophagy and blocking angiogenesis. Sorafenib is approved for advanced HCC and is the main first-line chemotherapy, yet its survival benefits are limited. Tumor Treating Fields (TTFields) therapy is an anticancer treatment that is non-invasively and locoregionally delivered to tumor bed via low intensity (1-3 V/cm), intermediate frequency (100-500 kHz), alternating electric fields. Since HCC is a complex, heterogeneous tumor with exhibited aberrant signaling pathways, sorafenib combined with additional chemotherapy agents and other types of treatment modalities, such as TTFields, may be a feasible option for targeting HCC. The purpose of this study was to explore the use of TTFields, alone and in combination with sorafenib, for HCC treatment.

Materials/Methods: HCC cell lines (HepG2 and Huh-7D12) were treated for 72 hours with TTFields at various frequencies. Efficacy of TTFields and sorafenib combination was tested by applying optimal frequency TTFields in the presence of various concentrations of sorafenib. Cytotoxicity, apoptosis, and clonogenicity were determined, and overall effect was calculated as the product of the cytotoxic and clonogenic effects. Changes in autophagy levels were also examined. In vivo, N1S1 HCC cells (50,000) were orthotopically injected into the left hepatic lobe of SD rats. After 1 week, TTFields at the optimal frequency were continuously applied for 6 days to the abdominal region of rat torsos, and sorafenib (10 mg/kg/day) was injected daily. Tumor volume growth was determined by MRI.

Results: The TTFields frequency assessed for optimally treating HCC cell lines was 150 kHz. Cells were sensitive to sorafenib in a dose-dependent manner, and concomitant addition of TTFields augmented this effect. The effect of TTFields, like that of sorafenib, was demonstrated to be related to increases in autophagic flux. In the animal model, tumor growth was significantly reduced in the combination group compared to other treatment groups.

Conclusion: These results demonstrate that TTFields are effective for the treatment of HCC and may further enhance effectiveness in combination with standard of care chemotherapy. The ongoing phase 2 HEPANOVA (NCT03606590) clinical trial will investigate the safety and efficacy of TTFields plus sorafenib combination in patients with unresectable, locally advanced HCC.

Citation Format: Shiri Davidi, Anna Shteingauz, Sara Jacobovitch, Karnit Gotlib, Catherine Tempel-Brami, Mijal Munster, Einav Zeevi, Eyal Dor-On, Rosa S. Schneiderman, Tali Voloshin, Adi Haber, Moshe Giladi, Adrian Kinzel, Uri Weinberg, Yoram Palti. Effectiveness of Tumor Treating Fields (TTFields) in combination with sorafenib for treatment of hepatocellular carcinoma in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1063.

Abstract 1186: Efficacy of Tumor Treating Fields (TTFields) in mesothelioma is associated with reduced capacity for DNA damage repair

Introduction: Malignant pleural mesothelioma (MPM) is an aggressive thoracic cancer with a poor prognosis and limited treatment options. Tumor Treating Fields (TTFields) are a noninvasive, locoregionally, antineoplastic treatment, delivering low intensity (1-3 V/cm), intermediate frequency (100-500 kHz), alternating electric fields, that has demonstrated a promising median overall survival in patients with MPM without increases in systemic toxicity (STELLAR clinical trial). Accordingly, TTFields with pemetrexed and a platinum-based chemotherapy agent received FDA-approval as first line therapy for MPM. While efficacy of TTFields for MPM treatment is well-established, the underlying mechanism of action needs further elucidation.

Methods: Human MPM cell lines (NCI-H2052 and MSTO-211H) were treated using various TTFields frequencies to assess the most effective frequency. The effect of optimal frequency TTFields on levels of DNA double strand breaks (DSB) was examined by fluorescent microscopy detection of γH2AX foci, and the levels of DNA damage repair proteins was evaluated by immunoblotting. The combined cytotoxic effect of TTFields with cisplatin or pemetrexed was tested in vitro, and efficacy of TTFields in combination with both chemotherapeutic agents was examined in C57BL/6 mice injected subcutaneously with RN-5 cells, by measuring tumor volume and through detection for DNA damage within the tumor.

Results: The optimal TTFields frequency in both MPM cell lines was 150 kHz, demonstrating significant cytotoxicity and increases in formation of DNA DSB. These effects were associated with reduced expression of proteins from the Fanconi Anemia (FA) repair pathway for DNA repair - FANCA, FANCD2, FANCJ, and BRCA1. Co-treatment of TTFields with cisplatin or pemetrexed significantly increased treatment efficacy versus each treatment alone, with an additive effect shown by the TTFields-pemetrexed combination, and a tendency towards synergism displayed for TTFields-cisplatin co-administration. In animal models, tumor volume fold increase was significantly decreased for co-treatment with TTFields and chemotherapy (cisplatin + pemetrexed) versus the control, showing also increased DNA damage within the tumor bed in comparison to control or chemotherapy alone.

Conclusions: The results presented here demonstrate that the efficacy of TTFields for treatment of MPM is associated with reduced expression of FA pathway proteins and increased DNA DSB. This effect may account for the synergistic effect seen for TTFields-cisplatin co-treatment, as cisplatin is known to cause DNA damage that requires the FA pathway for repair. This research provides further insights on the mechanism of action of TTFields in MPM, a treatment already approved against this malignancy.

Citation Format: Helena Mumblat, Antonia Martinez, Ori Braten, Mijal Munster, Eyal Dor-On, Rosa S. Schneiderman, Yaara Porat, Tali Voloshin, Shiri Davidi, Roni Blatt, Anna Shteingauz, Catherine Tempel-Brami, Einav Zeevi, Carolina Lajterer, Yuval Shmueli, Shiri Danilov, Adi Haber, Moshe Giladi, Adrian Kinzel, Uri Weinberg, Yoram Palti. Efficacy of Tumor Treating Fields (TTFields) in mesothelioma is associated with reduced capacity for DNA damage repair [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1186.

Abstract 1317: inovivo: a dedicated system for delivery of therapeutic level Tumor Treating Fields (TTFields) to mice

Purpose/objective: Tumor Treating Fields (TTFields) therapy is a noninvasive antineoplastic treatment modality that is FDA approved for treatment of glioblastoma and malignant pleural mesothelioma. TTFields are delivered to the patient continuously by 2 pairs of transducer arrays attached to the skin. In vivo TTFields experiments were so far limited due to the lack of a dedicated animal delivery system. Two main challenges are associated with TTFields application to the animal: 1) there is an absolute requirement for adequate and continuous contact between the electrodes and the animal skin throughout treatment; and 2) the wires connected to the electrodes require individual housing and limit animal movement, thus imposing stress. This work aimed to develop an in vivo system for continuous TTFields delivery to mice bearing cancer tumors in the torso or flank while addressing these challenges. Materials/Methods: To tackle the challenges and develop a viable in vivo system, several solutions were tested: 1) various electrode layouts; 2) a variety of adhesive materials; and 3) devices for preventing wire entanglement. Results: The final design of the transducer array electrodes included 2 adhesive layers, an inner layer for improved adherence, and an outer layer for securing the electrodes to the skin. Conductors were compacted into a single printed circuit cable connected to a novel electric swivel machine, that prevented cable coiling by sensing and rotating according to animal movement. These improvements resulted in fewer electrode entanglements and replacements, and thus in higher compliance (continuity) and less need for animal handling. To further reduce the impact of stress factors on the mice, a new cage was developed, that allows for 2 mice to be housed separately while still maintaining an interaction with one another. Indeed, animals treated with the inovivo system for 1-week displayed lower weight loss than animals treated with the previous non-dedicated system, indicative of reduced stress. Simulation were performed to ensure electric fields were indeed generated at the desired locations, showing above threshold TTFields intensities around the tumor for the flank subcutaneous model. For the torso orthotopic model, TTFields were shown to generate effective electric fields in the lung, liver, and pancreas, suggesting tumors in these organs may be treated effectively using the inovivo system. Conclusion: The new inovivo system provides means for continuous, 2 directions TTFields delivery to tumors in the torso or flank while minimizing stress on the mice. The inovivo system thus provides a tool for conducting TTFields experiments in mice, facilitating further in vivo studies for gaining additional mechanistical insight. The development of mouse head arrays to allow further research of the effect TTFields on glioblastoma, an application of widespread interest, is currently underway.

Citation Format: Shiri Davidi, Roni Blatt, Mijal Munster, Anna Shteingauz, Yaara Porat, Adel Zeidan, Tal Marciano, Zeev Bomzon, Moshe Giladi, Uri Weinberg, Yoram Palti. inovivo: a dedicated system for delivery of therapeutic level Tumor Treating Fields (TTFields) to mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1317.

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.

EXTH-76. THE INOVIVO SYSTEM: A NOVEL PRECLINICAL TOOL FOR IN VIVO DELIVERY OF TUMOR TREATING FIELDS (TTFIELDS)

Tumor Treating Fields (TTFields) are an antineoplastic treatment modality targeting dividing cancer cells, approved by the FDA for treatment of glioblastoma and malignant pleural mesothelioma. TTFields are delivered to the patient continuously, using a portable signal generator and 2 pairs of transducer arrays attached to the skin. While in vitro research tools for TTFields have been available, animal experiments were so far limited due to the lack of a dedicated TTFields in vivo delivery system. The main challenges associated with TTFields application to mice are the absolute requirement for adequate and continuous contact between array electrodes and animal skin throughout treatments; and the need to deliver the electric fields through multiple wired conductors connected to electrodes, which limit animal movement thus imposing stress. This work reports on development of an in vivo system to facilitate continuous delivery of TTFields to mice bearing cancer tumors in the torso or flank that addresses the aforementioned challenges. Three major developments were introduced to the system: 1) transducer array electrodes composed of delicate, flexible inner layer to improve skin adherence and a breathable, durable, outer layer to secure electrodes to the skin; 2) a novel electric swivel to prevent cable coiling; and 3) a cage constructed to house 2 mice separately while still allowing socializing. During a 1-week study, the new inovivo system demonstrated improvement compared to previous systems in the following areas: increased animal treatment compliance, less weight loss, and fewer number of array replacements. In conclusion, the new inovivo system is a comprehensive tool for continuous, 2 directional TTFields delivery to tumors in the torso or flank of mice for conducting TTFields experiments with minimal animal stress, thus allowing further elucidation of the effects of TTFields on the whole animal.

Abstract 572: In vitro and in vivo evidence for the safety and efficacy of Tumor Treating Fields (TTFields) in combination with sorafenib

Objective: Hepatocellular carcinoma (HCC) is the third cause of cancer related mortality. Sorafenib, an oral multikinase inhibitor, is approved for patients with advanced HCC, however its survival benefit is limited. Tumor Treating Fields (TTFields) therapy is an effective, anti-neoplastic treatment modality delivered via noninvasive application of low intensity, intermediate frequency, alternating electric fields. The aim of this work is to explore the potential use of TTFields alone and in combination with sorafenib as a treatment for HCC.

Methods: HepG2 and Huh-7D12 HCC cells were treated with various TTFields frequencies (100-400 kHz) for 72 hours using the inovitroTM system. Efficacy of the combined treatment of TTFields and sorafenib was tested by applying TTFields at the optimal frequency together with various sorafenib concentrations. Cell counts, induction of apoptosis, and clonogenic potential were determined. Moreover, N1S1 HCC cells were injected into the left lobe of the liver of Sprague Dawley rats. After 1 week, TTFields (1.2 V/cm) and sorafenib (10 mg/kg) were applied for 6 days and tumor growth was evaluated, using MRI. Healthy rats were used to study the safety of TTFields (150 kHz) application to the abdomen.

Results: The optimal frequency of TTFields was 150 kHz for both HCC cell lines. TTFields application (1.0 - 1.7 V/cm, 72 hours) at 150 kHz led to a 53-55% reduction in cell counts and to an additional reduction (65-69%) in clonogenic potential. The combination of TTFields and sorafenib led to a significant reduction in cell count (2-way ANOVA, P <0.05) as compared to either treatment alone. HCC tumor growth was significantly reduced in the combined group compared to the control group (student t-test, P <0.01). On average, the HCC tumor volume (fold-increase) in the combination treatment group (1.6-times) was significantly lower than in the control group (5.9-times, P <0.0001), TTFields alone group (3.3-times, P <0.01), and sorafenib alone group (2.3-times, P <0.05). Histological analysis of the KI67 proliferation marker in HCC tumors showed reduced proliferation in all treated groups. Based on preliminary analysis of autophagy marker (LC3) in tumors, we hypothesized the involvement of autophagy as 1 of the mechanisms underlying increased treatment efficacy. Safety studies did not reveal any adverse events associated with TTFields application to the rat abdomen.

Conclusions: These results demonstrate that TTFields can be a safe and effective in the treatment of HCC, and that the combination with sorafenib leads to further enhancements in treatment effectiveness. Based on these results, a Phase 2 clinical trial evaluating the effects of TTFields and sorafenib treatment in patients with HCC is planned (HEPANOVA; NCT03606590).

Citation Format: Shiri Davidi, Catherine Tempel-Brami, Mijal Munster, Anna Shteingauz, Einav Zeevi, Rosa Schneiderman, Tali Voloshin, Moshe Giladi, Adrian Kinzel, Uri Weinberg, Yoram Palti. In vitro and in vivo evidence for the safety and efficacy of Tumor Treating Fields (TTFields) in combination with sorafenib [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 572.

Abstract 2740: The inovivo system: A novel in vivo tool for the application of Tumor Treating Fields (TTFields) to mice

INTRODUCTION

Tumor Treating Fields (TTFields) are an antineoplastic treatment modality that target dividing cancer cells and are delivered continuously to the patient, using a portable signal generator and 2 pairs of transducers arrays attached to the skin. FDA approval was received for glioblastoma (GBM) and malignant pleural mesothelioma (MPM) treatment, following clinical trials demonstrating the safety and efficacy of TTFields. While in vitro research tools for TTFields are now available, in vivo experiments were so far limited due to the lack of a dedicated animal delivery system that allows for continuous TTFields application. The main challenge associated with continuous TTFields delivery to mouse models are an absolute requirement for adequate and continuous contact between array electrodes and skin throughout treatment. Another challenge is the need to deliver the electric fields through multiple wired conductors connected to electrodes, thus limiting movement and imposing stress on the animal. This work aimed to develop an in vivo system that allows for continuous, 2 direction delivery of TTFields to mice bearing cancer tumors in the torso or flank for the duration of 1 week and to address challenges.

METHODS

To overcome limitations and to develop a viable in vivo system, the following approaches were tested: 1) evaluation of various electrode layouts for optimal TTFields delivery to orthotopic torso and subcutaneous flank tumors; 2) examination of different adhesive materials and designs to ensure proper skin adherence; and 3) assessment of various solutions to prevent wire entanglement.

RESULTS

The final design of the transducer array electrodes included 2 different adhesive layers. The adhesives consisted of a more delicate, flexible inner layer to improve skin adherence without harming the mice and a breathable, durable, non-woven outer layer to secure skin electrodes. Multiple conductors were compacted into a single flat, flexible, lightweight printed circuit cable. The system design also included a novel electric swivel machine that prevents the cable from coiling, by sensing animal movement and rotating in accordance. To further reduce the impact of stress factors on the mice during TTFields treatment, a cage that houses 2 mice separately yet providing mice with the opportunity to interact was developed. This in vivo method was modeled to reduce stress on mice and has shown diminished reductions in weight loss throughout the course of treatment.

CONCLUSIONS

The new inovivo system will provide researchers with a comprehensive tool to conduct TTFields experiments in mice; and to further elucidate the effects of TTFields on the whole animal and specifically on the tumor microenvironment and immune system. This devised inovivo tool provides means for continuous, 2 direction TTFields delivery to tumors in the torso or flank for the duration of 1 week with minimal stress on the mice.

Citation Format: Shiri Davidi, Roni Blat, Anna Shteingauz, Sara Gerstein, Yaara Porat, Moshe Giladi, Uri Weinberg, Yoram Palti. The inovivo system: A novel in vivo tool for the application of Tumor Treating Fields (TTFields) to mice [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2740.

Abstract 956: Tumor treating fields (TTFields) elicit an anti-tumor immune response and in combination enhance anti-PD-1 treatment efficacy

Introduction Tumor treating fields (TTFields), a clinically applied anti-neoplastic treatment modality, are low intensity (eg, 1-3 V/cm) alternating electric fields within the intermediate frequency range (100-300 kHz). In this study, we evaluated whether TTFields can elicit an immune response against tumors and the potential of TTFields and anti-programmed cell death protein-1 (PD-1) combination therapy to serve as a viable treatment regimen.

Methods For evaluation of immunogenic cell death (ICD), cultured murine cells were treated with TTFields using the inovitroTM system. ICD was characterized by exposure of calreticulin (CRT) on the cell surface, secretion of ATP, and release of HMGB1. For detection of ER stress, phosphorylation of the translation initiation factor eIF2α was assessed. TTFields effect on autophagy was evaluated using electron microscopy and immunoblot and immunofluorescence evaluation of LC3. T-cells migration assays were performed using a modified Matrigel coated Boyden chamber. For in-vivo studies, mice were implanted with either orthotropic lung cancer or subcutaneous colon cancer and treated with TTFields, anti-PD-1, or a combination of the 2 modalities. Tumor volume was monitored and flow cytometry analysis was performed for phenotypic characterization of infiltrating T cells.

Results TTFields treatment promoted release of HMGB1 and ATP, and ER stress leading to CRT cell surface translocation. In T-cell migration assays, no significant difference was observed in the migration rates between untreated and TTFields-treated T cells. In both tumor In vivo models, TTFields plus anti-PD-1 combined treatment of tumor-bearing mice led to a significant decrease in tumor volume compared to anti-PD-1 alone or to the control group. In the lung cancer model, TTFields or anti-PD-1 alone had no effect on CD8+ and CD4+ cellular abundance, while TTFields plus anti-PD-1 combination showed a trend toward increased cell numbers. No significant changes in the levels of CD4+Foxp3+ regulatory T cells were found between the different treatment groups. The combined treatment of TTFields and anti-PD-1 led to a significant increase in IFN- γ production in cytotoxic CD8+ tumor infiltrating lymphocytes. Comparable results were obtained in the colon cancer model, where significant increases in CD8+ and CD4+ were observed following long duration treatment with TTFields plus anti-PD-1.

Conclusions Our results demonstrate the potential of TTFields therapy to induce immunogenic cell death resulting in improved efficacy of anti-PD-1 therapy in mouse cancer models. The combination of TTFields with immune checkpoint inhibitors is currently also being tested in a phase 3 clinical trial (LUNAR - NCT02973789).

Citation Format: Noa Kaynan, Tali Voloshin, Shiri Davidi, Yaara Porat, Anna Shteingauz, Mijal Munster, Rosa Schneiderman, Moshe Giladi, Uri Weinberg, Yoram Palti. Tumor treating fields (TTFields) elicit an anti-tumor immune response and in combination enhance anti-PD-1 treatment efficacy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 956.

Abstract 573: Efficacy of Tumor Treating Fields (TTFields) in combination with cisplatin or pemetrexed for the treatment of mesothelioma in vitro and in vivo

Objective: Malignant pleural mesothelioma (MPM) is an aggressive thoracic cancer, linked to asbestos exposure. The prognosis of patients with MPM is poor, with a median overall survival (OS) of ~12 months reported with historical, standard of care (SOC) cisplatin or carboplatin plus pemetrexed. Tumor Treating Fields (TTFields) is an anti-neoplastic treatment delivered via noninvasive application of low intensity, intermediate frequency, alternating electric fields and was shown to increase OS to 18.2 months in combination with SOC. Based on these data, TTFields were approved for treatment of unresectable MPM. The aim of this study was to further evaluate the effectiveness and safety of TTFields alone and in combination with SOC for MPM treatment, utilizing in vitro and in vivo models.

Methods: NCI-H2052 and MSTO-211H human MPM cells were treated at various TTFields frequencies (100-400 kHz) for 72 hours using the inovitroTM system to determine optimal frequency. The combination of TTFields with cisplatin or pemetrexed was tested by applying TTFields at the optimal frequency in combination with various concentrations of the chemotherapeutic agents. For TTFields alone, cell counts, clonogenic potential, and induction of apoptosis were determined. Also, cytotoxic, apoptotic, and overall (cytotoxic plus clonogenic) effects were evaluated for cisplatin or pemetrexed alone (at various concentration) and in combination with TTFields. TTFields (1.2 V/cm) were applied for 8 days to rats injected with IL-45 MPM cells to the intrapleural cavity and tumor volume was measured.

Results: The optimal frequency of TTFields was 150 kHz in both MPM human cell lines. TTFields application (1.0 V/cm, 72 hours) alone at 150 kHz led to a 45-51% reduction in cell counts and a 64-76% additional reduction in clonogenic potential. The combined treatment of TTFields with cisplatin or pemetrexed led to a significant reduction in cell count, induction of apoptosis, and reduced clonogenic potential as compared to each modality alone. In vivo, TTFields in combination with pemetrexed plus cisplatin significantly decreased the MPM tumor volume in the rat model compared to the control group (P < 0.006). Safety studies did not reveal any adverse events associated with 150 kHz TTFields application to the rat torso.

Conclusions: These preclinical data demonstrate that TTFields are an effective treatment against MPM and the combination with cisplatin or pemetrexed enhanced treatment effectiveness. Results are consistent with the recent phase 2 STELLAR study (EF-23 trial; NCT02397928) that reported improved OS with TTFields in combination with pemetrexed plus platinum-based chemotherapeutic (cisplatin or carboplatin) as compared to historical control for front-line treatment of unresectable MPM, with no increases in systemic toxicity.

Citation Format: Mijal Munster, Helena Mumblat, Shiri Davidi, Rosa Schneiderman, Yaara Porat, Anna Shteingauz, Tali Voloshin, Noa Kaynan, Einav Zeevi, Moshe Giladi, Uri Weinberg, Adrian Kinzel, Yoram Palti. Efficacy of Tumor Treating Fields (TTFields) in combination with cisplatin or pemetrexed for the treatment of mesothelioma in vitro and in vivo [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 573.

Tumor treating fields (TTFields; 150 kHz) and FOLFOX combination treatment effects on gastric cancer in vitro

406

Background: Gastric cancer is the third most common cause of cancer mortality worldwide, yet long-term survival in gastric cancer remains poor despite systemic therapeutic advances. FOLFOX (oxaliplatin, fluorouracil [5-FU], and leucovorin) is an approved chemotherapy regimen for gastric cancer treatment. Tumor Treating Fields (TTFields) are an antimitotic, loco-regional anticancer treatment delivered via non-invasive application of low intensity (1-3V/cm), intermediate frequency (100-500 kHz), alternating electrical fields. TTFields targets rapidly dividing cancer cells by disrupting microtubules leading to mitotic catastrophe, abnormal chromosome segregation, and apoptosis induction. We investigated the potential use of TTFields alone and in combination with FOLFOX for gastric carcinomas. Methods: Gastric cells (AGS and KATO III) were treated for 72 hours with TTFields (1.1 and 1.7 V/cm, respectively) at frequencies of 100-400 kHz using the inovitro system. Efficacy of TTFields and FOLFOX and its individual components was tested by applying TTFields at the optimal frequency in combination with various drug concentrations. Cell counts, apoptosis induction, clonogenic potential, and overall effect were determined. Results: The optimal TTFields frequency that led to the greatest cell count reduction (AGS, 55%; KATO III, 52%) was 150 kHz. The clonogenic potential was reduced by > 70% in both cell lines. TTFields combined with each FOLFOX component (oxaliplatin, 5-FU, or leucovorin) led to a significant reduction in AGS and KATO III cell survival (2-way ANOVA, P < 0.001 for each cell line) versus each treatment alone. In AGS, TTFields plus FOLFOX combination treatment led to a further reduction in the overall effect (cytotoxic and clonogenic; 79%) versus TTFields alone (65%) and FOLFOX alone (34%). Similar results were observed in KATO III cells. Conclusions: These results suggest that TTFields (150 kHz; optimal frequency) are an effective gastric cancer treatment; and combining TTFields with FOLFOX may further enhance efficacy. There is a strong rational to continue exploring the use of TTFields in combination with standard of care for gastric cancer treatment in the clinical settings.

Immunomodulatory effects of tumor treating fields (TTFields) on colon cancer models

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Background: Tumor Treating Fields (TTFields) are clinically approved in glioblastoma and malignant pleural mesothelioma as an anti-mitotic treatment modality delivered via noninvasive application of low intensity (1-3 V/cm), intermediate frequency (100-500 kHz), alternating electric fields. We evaluated whether TTFields (150 kHz) induced colon cancer cell death can be perceived as immunogenic and suitable for combination with anti-programmed cell death protein 1 (anti-PD-1; immune checkpoint inhibitor) therapy. Methods: Murine colorectal carcinoma cells (CT-26) were treated with TTFields using the inovitro system. Immunogenic cell death was evaluated by assessing changes in the levels of calreticulin (CRT) on the surface of treated cells, phosphorylation of eukaryotic translation initiation factor alpha (eIF2α), and secretion of ATP and high-mobility group box 1 (HMGB1). For in-vivo studies, CT-26 cells were subcutaneously implanted in BALB/c mice. The mice were treated with TTFields (150 kHz), anti-PD-1 (200 μg/mouse), or a combination of the 2 modalities. Tumor volume was monitored and flow cytometry analyses performed for phenotypic characterization of infiltrating immune cells. Results: We demonstrate that cancer cell death under TTFields application exhibited release of HMGB1, ATP secretion from cells, and ER stress leading to CRT translocation to the cell surface, all of which are signs of immunogenic cell death. The combined treatment of colon tumor-bearing mice with TTFields plus anti-PD-1 led to a significant decrease in tumor volume compared to anti-PD-1 alone or to the control group. Significant increases in CD45+ tumor infiltrating cells were observed in the TTFields plus anti-PD-1 group. We demonstrate significant increases in both CD8 and CD4 T-cells in tumors treated with combination therapy, and in CD8 in tumors treated with anti-PD-1 alone. Conclusions: Our results establish the potential of TTFields therapy to induce immunogenic cell death. We also demonstrate efficacy of concurrent application of TTFields and anti PD-1 therapy in mouse cancer models. These data suggest that TTFields plus anti-PD-1 combination treatment may achieve tumor control by further enhancing anti-tumor immunity.

Abstract 3961: Alternating electric fields (TTFields) induce immunogenic cell death resulting in enhanced antitumor efficacy when combined with anti-PD-1 therapy

Tumor Treating Fields (TTFields) are a clinically applied anti-neoplastic treatment modality delivered via noninvasive application of low intensity, intermediate frequency, alternating electric fields. In this study we evaluated whether TTFields-induced cell death is immunogenic. For evaluation of immunogenic cell death (ICD), cultured murine cells were treated with TTFields using the inovitro system. ICD was characterized by the pre-apoptotic exposure of calreticulin (CRT) on the cell surface, secretion of adenosine triphosphate (ATP), and release of the chromatin-binding protein high mobility group B1 (HMGB1). For detection of ER stress, phosphorylation of the translation initiation factor eIF2α was assessed. TTFields effect on autophagy was evaluated using electron microscopy and immunoblot and immunofluorescence evaluation of LC3. For evaluation of the effect of TTFields on dendritic cells (DCs), bone marrow derived dendritic cells were co-incubated with TTFields treated LLC-1 cells and phagocytosis by DCs and DCs maturation were evaluated using flow cytometry. For in-vivo studies, mice orthotopically implanted with LLC cells were treated with TTFields, the immune checkpoint inhibitor anti-PD-1 or a combination of the two modalities. Tumor volume was monitored and flow cytometry analysis was performed for phenotypic characterization of infiltrating immune cells. We demonstrate that cancer cells that die under TTFields application exhibit release of HMGB1, ATP depletion from cells, and ER stress leading to CRT translocation to the cell surface. Moreover, we show that TTFields treated cells promote phagocytosis by DCs, DC maturation in vitro, and initiate inflammation in vivo. We also show that the combined treatment of lung tumor-bearing mice with TTFields plus the immune checkpoint inhibitor anti-PD-1 led to a significant decrease in tumor volume compared to anti-PD-1 alone or to the control group. Significant increases in CD45+ tumor infiltrating cells were observed in the TTFields plus anti-PD-1 group. These infiltrating cells, specifically macrophages and DCs, demonstrated upregulation of surface PD-L1 expression. Correspondingly, cytotoxic T-cells isolated from these tumors have shown higher levels of IFN-γ production relative to untreated mice. Our results demonstrate the potential of TTFields therapy to induce ICD. We also demonstrate robust efficacy of concurrent application of TTFields and anti PD-1 therapy in a mouse model of lung cancer. These data suggest that combining TTFields with anti-PD-1 might achieve tumor control by further enhancing antitumor immunity.

Citation Format: Tali Voloshin, Noa Kaynan, Shiri Davidi, Yaara Porat, Anna Shteingauz, Mijal Munster, Rosa S. Schneiderman, Catherine Tempel Brami, Einav Zeevi, Karnit Gotlib, Shay Cahal, Aviran Itzhaki, Moshe Giladi, Eilon D. Kirson, Uri Weinberg, Adrian Kinzel, Yoram Palti. Alternating electric fields (TTFields) induce immunogenic cell death resulting in enhanced antitumor efficacy when combined with anti-PD-1 therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3961.

Abstract 307: The combined treatment of 150 kHz Tumor Treating Fields (TTFields) and Cisplatin or Pemetrexed inhibit mesothelioma cells in vitro

Malignant pleural mesothelioma (MPM) is a rare thoracic solid tumor cancer that has been strongly linked to asbestos exposure. The standard of care treatment for unresectable mesothelioma is cisplatin plus pemetrexed chemotherapy which offer short and insufficient efficacy. Furthermore, no validated treatment beyond first-line therapy is available. Thus, there is an urgent need to identify more effective treatments for mesothelioma patients. Tumor Treating Fields (TTFields) therapy is an effective anti-neoplastic treatment modality delivered via noninvasive application of low intensity, intermediate frequency, alternating electric fields. TTFields are employed as a local treatment with the intent to target dividing cells by disrupting microtubules leading to mitotic catastrophe, abnormal chromosome segregation and the induction of different forms of cancer cell death. The aim of this work is to explore the potential of the use of TTFields alone and in combination with cisplatin or pemetrexed as a treatment for Mesothelioma. MSTO-211H and NCI-H2052 cells were treated with various TTFields frequencies for 72 hours using the inovitro system. Efficacy of the combined treatment of TTFields and Cisplatin or Pemetrexed was tested by applying TTFields at the optimal frequency together with various drug concentrations. Cell counts, induction of apoptosis, and clonogenic potential were determined at the end of treatment. The optimal TTFields frequency leading to the highest reduction in cell counts was found to be 150 kHz for both MSTO-211H and NCI-H2052 cells. TTFields application (1.1 V/cm, 72 hours) at 150 kHz led to 51%, 65% reduction in cell counts, 40%, 55% reduction in the clonogenic potential in NCI-H2052 and MSTO-211H cells, respectively. The combined treatment of TTFields and Cisplatin or Pemetrexed led to a significant reduction in cell count, induction of apoptosis and reduced clonogenic potential as compared to each modality alone. (2-way ANOVA, p&lt0.0001). Safety studies did not reveal any adverse event associated with 150 kHz TTFields application to the rat torso. The results presented in this work demonstrate that TTFields can be an effective treatment against Mesothelioma cells and that the combination with cisplatin or pemetrexed may further enhance treatment efficacy. In accordance with these results, it was recently reported that patients treated by the combined treatment of TTFields with pemetrexed and cisplatin experienced improved overall survival as compared to historical control with no increase in systemic toxicity.

Citation Format: Mijal Munster, Rosa Schneiderman, Yaara Porat, Tali Voloshin, Shiri Davidi, Anna Shteingauz, Noa Kaynan, Einav Zeevi, Karnit Gotlib, Moshe Giladi, Eilon Kirson, Uri Weinberg, Adrian Kinzel, Yoram Palti. The combined treatment of 150 kHz Tumor Treating Fields (TTFields) and Cisplatin or Pemetrexed inhibit mesothelioma cells in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 307.

Abstract 303: The efficacy of the combined treatment of 150 kHz Tumor Treating Fields (TTFields) and FOLFOX in gastric cancer in vitro

Background: Gastric cancer is the fourth most common cancer and the second most common cause of cancer death worldwide. Despite systemic therapies improvement in recent era, long-term survival rates for patients with advanced gastric cancer remains poor. FOLFOX (Oxaliplatin, 5-FU and Leucovorin) is an approved chemotherapy regimen for treatment of gastric cancer. Tumor Treating Fields (TTFields) therapy is an effective anti-neoplastic treatment modality delivered via noninvasive application of low intensity, intermediate frequency, alternating electric fields. The aim of this work is to explore the potential of the use of TTFields alone and in combination with FOLFOX as a treatment for gastric carcinomas.

Methods: AGS and KATO III cells were treated for 72 hours with TTFields (1.1 and 1.7 V/cm, respectively) at various frequencies, using the inovitro system. Efficacy of the combined treatment of TTFields and FOLFOX was tested by applying TTFields at the optimal frequency together with various drug concentrations. Cell counts, induction of apoptosis, clonogenic potential and overall effect were determined at the end of treatment.

Results: The optimal TTFields frequency leading to the highest reduction in cell counts was found to be 150 kHz for both cell lines resulting in 55% and 52% reduction in cell counts for AGS and KATO III, respectively. In addition, clonogenic potential of both cell lines was reduced by more than 70%. The combined treatment of TTFields with each chemotherapy (Oxaliplatin, 5-FU or Leucovorin), led to a significant reduction in the survival of AGS and KATO III cells (2-way ANOVA, p&lt;0.001 for both cell lines) as compared to each treatment alone. The combined treatment of TTFields with FOLFOX led to further reduction in the overall effect (cytotoxic and clonogenic) of AGS (79%) compared to TTFields alone (65%) and FOLFOX alone (34%). Similar results were observed for the combined treatment of TTFields and FOLFOX in KATO III cells.

Conclusions: The results presented in this work demonstrate that TTFields can be an effective treatment against gastric carcinoma and that the combination with FOLFOX may further enhance treatment efficacy. Based on the above, there is a strong rational to continue exploring the potential of the use of TTFields together with standard of care for the treatment of gastric cancer in the clinical settings.

Citation Format: Tali Voloshin, Einav Zeevi, Karnit Gotlib, Rosa S. Schneiderman, Mijal Munster, Yaara Porat, Shiri Davidi, Anna Shteingauz, Noa Kaynan, Moshe Giladi, Eilon D. Kirson, Uri Weinberg, Adrian Kinzel, Yoram Palti. The efficacy of the combined treatment of 150 kHz Tumor Treating Fields (TTFields) and FOLFOX in gastric cancer in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 303.

The combined treatment of 150 kHz tumor treating fields (TTFields) and cisplatin or pemetrexed inhibits mesothelioma cells in vitro and in vivo

e20069

Background: Malignant pleural mesothelioma (MPM) is an aggressive thoracic cancer mostly linked to asbestos exposure. The standard of care (SOC) therapy for unresectable MPM is cisplatin plus pemetrexed. Treating Fields (TTFields) therapy is an effective anti-neoplastic treatment modality delivered via noninvasive application of low intensity, intermediate frequency, alternating electric fields. We explored the potential use of TTFields alone and in combination with SOC as a treatment for MPM. Methods: NCI-H2052 and MSTO-211H cells were treated at various TTFields frequencies for 72 hours using the inovitro system. The combined treatment of TTFields and cisplatin or pemetrexed was tested by applying TTFields at the optimal frequency together with various drug concentrations. Cell counts, clonogenic potential and induction of apoptosis were determined. TTFields (1.2 V/cm) were applied for 8 days to rats injected to the intrapleural cavity with IL-45 cells, and overall survival was tested. Results: TTFields optimal frequency was 150 kHz for both human cell lines. TTFields application (1.1 V/cm, 72 hours) at 150 kHz led to 45%-51% reduction in cell counts and 46-64%% additional reduction in clonogenic potential. The combined treatment of TTFields and cisplatin or pemetrexed led to a significant reduction in cell count, induction of apoptosis and reduced clonogenic potential as compared to each modality alone (p < 0.0001(. TTFields significantly prolonged the survival of rats compared to control group. Safety studies did not reveal any adverse events associated with 150 kHz TTFields application to the rat torso. Conclusions: These results demonstrate that TTFields can be an effective treatment against mesothelioma and the combination with cisplatin or pemetrexed may further enhance treatment efficacy. These results are in consistency with the recent phase 2 study (EF-23 trial) that showed improved overall survival for combined treatment as compared to historical control with no increase in systemic toxicity.

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.

Abstract 1343: Induction of autophagy following TTFields application serves as a survival mechanism mediated by AMPK activation

Tumor treating fields (TTFields) are an approved treatment modality for patients with glioblastoma. TTFields are delivered via noninvasive application of low-intensity, intermediate-frequency, alternating electric fields. Previous studies have shown that TTFields lead to increased granularity which is often associated with autophagy. In this study we evaluated the effect of TTFields on the induction of autophagy in glioma and NSCLC cells. Cells were treated with TTFields using the inovitro system. Cellular granularity was evaluated using flow cytometry. Autophagy was monitored by quantifying levels of lipidated Microtubule Associated Protein Light Chain 3 (LC3-II), in the presence and absence of the lysomotropic agent and autophagy inhibitor chloroquine (CQ), using immunoblotting and immunofluorescence microscopy. Transmission Electron Microscopy (TEM) was used to visualize autophagosome-like structures. Western blot analysis was utilized to evaluate autophagy regulatory activity of the mammalian target of rapamycin (mTOR) through p70 S6 kinase1 (S6K1) and AMP activated protein kinase (AMPK) and its downstream target ULK-1. To determine if AMPK is responsible for TTFields stimulated autophagy pool of siRNAs was used to deplete siAMPK from U87-MG cells. To evaluate involvement of autophagy in cell fate after TTFields treatment we produced glioma cell lines depleted from ATG7 by shATG7 infection. Flow cytometry analysis demonstrated that TTFields application leads to a significant increase in cellular granularity in all tested cell lines. Significant elevation in LC3-II levels was observed in treated cells using fluorescence microscopy, where punctate distribution of LC3-II was observed. TEM micrographs demonstrated the presence of autophagy typical, autophagosome-like structures, in TTFields treated cells. . Evidence of increased autophagic flux following TTFields application was also detected using immunoblotting analysis in the presence of CQ. Western blot analysis of cells after TTFields treatment revealed stimulation of AMPK signaling as well as activation of p70. Depletion of AMPK from U87-MG cells resulted in reduction of autophagy as reflected by LC3-II levels and enhancement of TTFields cytotoxicity. ER stress in treated cells has been evident by immunoblotting, showing increased levels of ER stress marker GRP78. Combination of TTFields with CQ resulted in a significant dose dependent reduction of cell growth compared with TTFields treatment alone. Cells with ATG7 depletion showed similar results. Combined, these results suggest that cells upregulate autophagy in response to ER stress induced by TTFields application and that AMPK may serve as a key regulator of this process.

Citation Format: Anna Shteingauz, Yaara Porat, Moshe Giladi, Roza Schneiderman, Tali Voloshin, Mijal Munster, Eilon Kirson, Uri Weinberg, Yoram Palti. Induction of autophagy following TTFields application serves as a survival mechanism mediated by AMPK activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1343.

Abstract 4194: Tumor Treating Fields (TTFields) affect invasion properties and cell morphology of various cancer cells in vitro

Tumor Treating Fields (TTFields) therapy is an approved modality for the treatment of glioblastoma. TTFields are delivered via continuous, noninvasive application of low intensity, intermediate frequency alternating electric fields. The antimitotic effects of TTFields have been extensively investigated. We explored other processes that may be affected by TTFields such as cellular invasion. Human glioma, human and mouse melanoma, human breast cancer and human colon cancer cell lines were treated with TTFields using the inovitro system. Invasion assays were performed using a modified Matrigel coated Boyden chamber. TTFields effect on cells size, focal adhesions and stress fibers morphology was studied using immuno-fluorescent confocal microscopy.

Invasion was significantly reduced compared to untreated cells in all tested cell lines.

Furthermore, the optimal frequency for inhibition of invasion in tested cells was 300 kHz while the optimal anti mitotic frequency leading to glioma cell death is 200 kHz. The inhibitory effect on migration was observed at electric fields intensities of 0.6 V/cm RMS which is below the 1 V/cm RMS threshold previously reported for induction of cell death. Combining TTFields with Bumetanide, an agent that inhibits cellular motility, resulted in further inhibition of glioma cell invasion.

TTFields application resulted in an increase in cell size, as well as in focal adhesion size, number and peripheral distribution of the adhesion sites. Also, treated cells adopted a more flattened and spread shape in comparison with control cells.

TTFields treated cells exhibit reduction in appearance of stress fibers and a dense meshwork of actin filaments around the entire cell periphery.

Our results suggest that cancer cell motility is impaired by exposure to TTFields. The TTFields parameters (intensity and frequency) which led to the maximal inhibition of cellular motility are different from those required for exerting anti-mitotic effects. The alterations in cells morphology during exposure to TTFields may contribute to reduction in cell motility. Further studies are needed to elucidate the mechanism by which TTFields disrupts cellular motility in glioma cancer cells.

Citation Format: Rosa S. Schneiderman, Moshe Giladi, Einav Zeevi, Anna Shteingauz, Tali Voloshin, Yaara Porat, Mijal Munster, Eilon D. Kirson, Yoram Palti. Tumor Treating Fields (TTFields) affect invasion properties and cell morphology of various cancer cells in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4194.

Abstract 3315: Cancer cells upregulate autophagy as a survival mechanism in response to tumor treating fields (TTFields)

Tumor treating fields (TTFields) are an established anti-neoplastic treatment modality in patients with glioblastoma. TTFields are delivered via noninvasive application of low-intensity, intermediate-frequency, alternating electric fields to the region of the tumor. Previous studies have shown that TTFields treatment lead to increased cellular granularity, which is often associated with autophagy. Autophagy has been shown to regulate cell survival and proliferation under stress conditions and to influence cellular response to cytotoxic drugs. This study evaluated the role of autophagy in cancer cells treated with TTFields.

Immunoblot analysis showed significant elevations in levels of lipidated Microtubule Associated Protein Light Chain (LC3-II) in TTFields-treated glioma and lung cancer cells. Increased autophagy following TTFields application in these cell lines was also detected using fluorescence microscopy, where punctate distribution of LC3-II was observed. TEM micrographs demonstrated the presence of autophagy typical, autophagosome-like structures in TTFields-treated U-87 MG cells. Combination of TTFields with autophagy inhibitors, chloroquine and melfoquine, resulted in a significant dose-dependent reduction in cell growth compared with TTFields treatment alone. Inhibition of autophagy with chloroquine triggered apoptosis as indicated by elevated levels of AnnexinV/7AAD double staining. Increased levels of autophagic flux in TTFields-treated cells were not associated with reduced mTOR activity, which was monitored by p70S6K phosphorylation immunoblot analysis.

TTFields are known to exert anti-mitotic effects by disrupting highly dipolar structures that play critical roles in mitosis. Our results demonstrate that TTFields additionally induce cellular autophagy by an mTOR-independent mechanism. TTFields- treated cell lines appear to utilize autophagy as a survival mechanism. Thus, inhibition of autophagy sensitizes tumor cells to TTFields treatment, resulting in elevated apoptotic cell death.

Future studies are warranted to examine the extent to which TTFields-elicited autophagy may affect treatment outcomes and to investigate the therapeutic implications of combining TTFields with autophagy inhibitors in vivo.

Citation Format: Yaara Porat, Anna Shteingauz, Moshe Giladi, Rosa S. Schneiderman, Tali Voloshin, Mijal Munster, Roni Blat, Eilon D. Kirson, Uri Weinberg, Yoram Palti. Cancer cells upregulate autophagy as a survival mechanism in response to tumor treating fields (TTFields) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3315. doi:10.1158/1538-7445.AM2017-3315

Abstract 3665: Tumor Treating Fields (TTFields) plus anti-PD-1 therapy induce immunogenic cell death resulting in enhanced antitumor efficacy

Tumor Treating Fields (TTFields) are an effective anti-neoplastic treatment modality delivered via noninvasive application of low intensity, intermediate frequency, alternating electric fields. TTFields is approved for the treatment of both newly diagnosed and recurrent glioblastoma. TTFields interrupt cancer cell mitosis by disrupting microtubules and septin filaments, which play key roles in mitosis. The mitotic effects of TTFields include abnormal chromosome segregation and ER stress, which trigger different forms of cell death.

We evaluated the in vitro and in vivo effects of TTFields combined with an immune checkpoint inhibitor (anti-PD1) on immunogenic cell death.

Murine Lewis lung carcinoma (LLC) and ovarian surface epithelial (MOSE) cells were treated with TTFields using the inovitroTM system. Levels of calreticulin (CRT) on the surface of treated cells and intracellular ATP levels were evaluated using flow cytometry. High mobility group box 1 (HMGB1) secretion was measured using an ELISA assay. Mice were implanted with LLC cells were treated with TTFields, anti-PD-1, or a combination of the two modalities. Tumor volume was monitored; flow cytometry analysis was performed for phenotypic characterization of infiltrating immune cells.

TTFields induced elevated cell surface expression of CRT, decreased intracellular ATP levels, and promoted HMGB1 secretion. In vivo, the combined treatment of lung tumor-bearing mice with TTFields plus anti-PD-1 led to a significant decrease in tumor volume compared to anti-PD-1 alone or to the control group. Significant increases in CD45+ tumor infiltrating cells were observed in the TTFields plus anti-PD-1 group. Infiltrating cells demonstrated a significant upregulation of surface PD-L1 expression. Both F4/80+CD11b+ cells and CS11c+ cells exhibited higher tumor infiltration and elevated PD-L1 expression as compared to infiltrating immune cell in the control group.

Our results demonstrate that TTFields treatment potentiates immunogenic cell death in cancer cells. Combining TTFields with specific immunotherapies such as anti-PD-1 may enhance antitumor immunity and result in increased tumor control.

Citation Format: Tali Voloshin, Orna Tal-Yitzhaki, Noa Kaynan, Moshe Giladi, Anna Shteingauz, Mijal Munster, Roni Blat, Yaara Porat, Rosa S. Schneiderman, Shay Cahal, Aviran Itzhaki, Eilon D. Kirson, Uri Weinberg, Yoram Palti. Tumor Treating Fields (TTFields) plus anti-PD-1 therapy induce immunogenic cell death resulting in enhanced antitumor efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3665. doi:10.1158/1538-7445.AM2017-3665

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.

Alternating electric fields (TTFields) in combination with paclitaxel are therapeutically effective against ovarian cancer cells in vitro and in vivo

Long-term survival rates for advanced ovarian cancer patients have not changed appreciably over the past four decades; therefore, development of new, effective treatment modalities remains a high priority. Tumor Treating Fields (TTFields), a clinically active anticancer modality utilize low-intensity, intermediate frequency, alternating electric fields. The goal of this study was to evaluate the efficacy of combining TTFields with paclitaxel against ovarian cancer cells in vitro and in vivo. In vitro application of TTFields on human ovarian cancer cell lines led to a significant reduction in cell counts as compared to untreated cells. The effect was found to be frequency and intensity dependent. Further reduction in the number of viable cells was achieved when TTFields treatment was combined with paclitaxel. The in vivo effect of the combined treatment was tested in mice orthotopically implanted with MOSE-L_TICv cells. In this model, combined treatment led to a significant reduction in tumor luminescence and in tumor weight as compared to untreated mice. The feasibility of effective local delivery of TTFields to the human abdomen was examined using finite element mesh simulations performed using the Sim4life software. These simulations demonstrated that electric fields intensities inside and in the vicinity of the ovaries of a realistic human computational phantom are about 1 and 2 V/cm pk-pk, respectively, which is within the range of intensities required for TTFields effect. These results suggest that prospective clinical investigation of the combination of TTFields and paclitaxel is warranted.

Abstract 3543: Alternating electric fields (TTFields) induce autophagy in human cancer cell lines

Tumor treating fields (TTFields) are an established anti-neoplastic treatment modality in patients with glioblastoma. TTFields are delivered via noninvasive application of low-intensity, intermediate-frequency, alternating electric fields to the region of the tumor. Previous studies have shown that TTFields lead to increased granularity in treated cells. Granular or vesicular structures can indicate the formation of autophagosomes which are key structures in autophagy. Autophagy has been shown to regulate cell survival and proliferation under stress conditions and, in certain cases, influence cellular response to cytotoxic drugs. The goal of this study was to evaluate the possible effect of TTFields on the induction of autophapgy in treated cells.

Different cancerous cell lines were treated with TTFields using the inovitro system. Cellular granularity was evaluated using flow cytometry. Autophagy was monitored by quantifying Lipidated Microtubule Associated Protein Light Chain 3 (LC3-II, a consensus marker for autophagosomes) levels using immunoblotting and immunofluorescence microscopy. Transmission Electron Microscopy (TEM) was used to visualize autophagosome-like structures.

Flow cytometry analysis demonstrated that TTFields application leads to a significant increase in cellular granularity in all tested cell lines (up to 40%, P&lt;0.05). Significant elevation in LC3-II levels was observed in treated U-87 MG cells using immunoblotting analysis (37%, P = 0.01). Evidence of increased autophagy following TTFields application was also detected using fluorescence microscopy, where punctate distribution of LC3-II was observed. TEM micrographs demonstrated the presence of autophagy typical, autophagosome-like structures in TTFields treated cells.

TTFields are known to exert anti-mitotic effects by disrupting highly dipolar structures which play critical roles in mitosis. Our results suggest that in addition, TTFields can also induce cellular autophagy. Future studies are warranted to examine to what extent TTFields-elicited- autophagy may affect treatment outcomes, and to investigate the therapeutic implications of combining TTFields with autophagy inhibitors.

Citation Format: Yaara Porat, Anna Shteingauz, Moshe Giladi, Rosa S. Schneiderman, Tali Voloshin, Mijal Munster, Roni Blat, Eilon D. Kirson, Uri Weinberg, Yoram Palti. Alternating electric fields (TTFields) induce autophagy in human cancer cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3543.

Abstract 5078: Tumor treating fields (TTFields) reduce migration and invasion properties of human glioma cancer cells in vitro

The ability of glioblastoma cells to invade adjacent brain tissue remains one of the major obstacles in obtaining therapeutic success. The development of novel treatment modalities that hinder glioma cancer cell motility could therefore facilitate disease control. TTFields are an effective treatment modality delivered via continuous, noninvasive application of low intensity, intermediate frequency, alternating electric fields. This therapy is approved for the treatment of patients with glioblastoma. Previous investigations have shown that TTFields disrupt microtubules and septin filaments, both of which govern key roles in mitosis. The goal of this study was to evaluate the possible effect of TTFields on human glioma cell migration and invasion properties. Four human glioma cell lines: U-87 MG, A-172, LN-229, and LN-18 (ATCC, USA) were treated with TTFields (1.75 V/cm RMS, 200 kHz) for 24 hours using the inovitro system. Cell migration was measured using in vitro wound healing assays. These were analyzed with Image Pro Premier (Media Cybernetics, USA) to determine migration rates. Invasion assays were performed using modified Matrigel coated Boyden chamber. Cells were stained, photographed and counted using image J (NIH, USA).

Application of TTFields in-vitro led to a significant reduction in both migratory and invasive phenotype in all tested cell lines. Specifically, cell migration velocity, as assessed by the wound healing assay, was significantly reduced in U-87 MG (60%, P&lt;0.001), and in A-172 (33%, P&lt;0.001) compared with untreated control cells. The number of invading cells, as assessed by the modified Boyden chamber assay, was reduced in U-87 MG (54%, P&lt;0.01), A-172 (51%, P&lt;0.001), LN-229 (52%, P&lt;0.001) and in LN-18 (30%, P&lt;0.001) compared with untreated control cells.

Our results suggest that human glioma cell motility is impaired by exposure to TTFields. Further studies are needed to elucidate the mechanism by which TTFields disrupts cellular motility in glioma cancer cells.

Citation Format: Rosa S. Schneiderman, Anna Shteingauz, Moshe Giladi, Tali Voloshin, Yaara Porat, Mijal Munster, Roni Blat, Eilon D. Kirson, Uri Weinberg, Yoram Palti. Tumor treating fields (TTFields) reduce migration and invasion properties of human glioma cancer cells in vitro. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5078.