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.

EXTH-74. INCREASING CANCER CELL MEMBRANE PERMEABILITY THROUGH APPLICATION OF TUMOR TREATING FIELDS (TTFIELDS)

INTRODUCTION

Tumor Treating Fields (TTFields) are intermediate frequency, alternating electric fields with anti-mitotic effects on cancerous cells. TTFields are delivered non-invasively through arrays placed on the skin at the tumor region. TTFields therapy is approved in several territories for treatment of glioblastoma (GBM) and mesothelioma. Recently, TTFields have been shown to increase GBM cell membrane permeability. The current study aimed to explore this effect in multiple cell lines and examine the potential benefits of combining TTFields with other anticancer agents.

METHODS

TTFields were delivered to GBM (U-87 MG), uterine sarcoma (MES-SA), and breast adenocarcinoma (MCF-7) cell lines for 72hr across a range of frequencies (50-500kHz). Cytotoxicity of TTFields was examined by cell counts, and intracellular accumulation of 7-aminoactinomycin D (7-AAD) was measured by flow cytometry. Exposing the cells to 7-AAD at different time points relative to TTFields application cessation was used to determine the kinetics of cell membrane permeability. The potential of TTFields to facilitate intracellular accumulation of anthracycline chemotherapeutics was tested in chemotherapy-sensitive and chemotherapy-resistant cells.

RESULTS

Elevated intracellular accumulation of 7-AAD was observed in all examined cell lines treated with TTFields, at an optimal frequency that differed from that for maximal TTFields-induced cytotoxicity. No intracellular accumulation of 7-AAD was seen for measurements performed after termination of TTFields application, indicating that increased cell membrane permeability by TTFields was temporary and reversible. Lastly, the accumulation of chemotherapeutic agents in chemotherapy-resistant cancer cells was elevated to the same extent as in matched chemotherapy-sensitive cells when TTFields were delivered concomitant with chemotherapy.

CONCLUSIONS

TTFields increased cancer cell permeability in a transient and reversible manner across multiple cancer cell types. The increased permeability enhanced intracellular accumulation of chemotherapeutics, even within chemotherapy-resistant cells.

726 Tumor Treating Fields (TTFields) induce an altered polarization program in M1/M2 macrophages

Background

Tumor Treating Fields (TTFields) are low intensity (1–3 V/cm), intermediate frequency (100–500 kHz), alternating electric fields, with demonstrated anti-mitotic effects on cancerous cells. TTFields are clinically approved for treatment of patients with glioblastoma and mesothelioma in the US and Europe. The current study aimed to examine the potential of TTFields to polarize unstimulated M0 macrophages and to regulate the phenotypes of M1 and M2 macrophages.

Methods

Bone marrow–derived macrophages (BMDMs) were generated from bone marrow cells flushed from the femurs and tibias of 5–8-week-old Balb\C mice. Unstimulated (M0 phenotype) BMDMs and BMDMs stimulated with LPS+IFN-γ (M1 polarization) or IL-4 (M2 polarization) were treated with TTFields (150 kHz) for 24 or 48 hours. Surface expression of the macrophage biomarker F4/80 and the activation markers CD80, major histocompatibility complex class II (MHC II), and inducible nitric oxide synthase (iNOS) were examined by flow cytometry. The heterogeneity of the stimulated macrophages was examined by a multiplexed secretion assay, capturing 13 different proteins: CXCL1 (KC), IL-18, IL-23, IL-12p70, IL6, TNF-α, IL-12p40, free active TGF-β1, CCL22 (MDC), IL-10, IL-6, G-CSF, CCL17 (TARC) and IL-1β.

Results

Application of TTFields to polarized (M1 or M2) or unpolarized BMDMs significantly increase in the percentage of CD80+/MHC IIhigh cells. M1 polarized BMDMs treated with TTFields also displayed elevation of intracellular iNOS levels. Cell supernatants of M1 and M2 stimulated BMDMs, as well as of unstimulated M0 BMDMs, displayed a pro-inflammatory secretion pattern following delivery of TTFields, with increased levels of CXCL1, IL-18, IL-23, IL-12p70, TNF-α, IL-12p40, CCL22, G-CSF, CCL17 and IL-1β.

Conclusions

This research showed that TTFields polarized unstimulated BMDMs to the M1 phenotype, elevated the pro-inflammatory phenotype of M1 polarized BMDMs, and induced phenotype skewing of M2 polarized BMDMs to the M1 phenotype. These results elucidate a novel immunoregulatory role of TTFields on macrophage polarization. Future studies will aim to focus on the mechanism governing this phenotypic skewing.

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.

Abstract 1382: Targeting Akt signaling pathway potentiates the antitumor effect of Tumor Treating Fields (TTFields) in vitro

Introduction Tumor Treating Fields (TTFields) therapy is a clinically applied anti-neoplastic treatment modality, approved for the treatment of glioblastoma and malignant pleural mesothelioma. TTFields are low intensity (1-3 V/cm) alternating electric fields within the intermediate frequency range (100-300 kHz), that are applied loco-regionally and non-invasively to the tumor site. Although TTFields therapy has demonstrated improved progression free survival and overall survival, tumor recurrence still occurs in some patients. To evaluate the cellular mechanisms of treatment resistance to TTFields, we analyzed changes in signaling pathway mediators in treated human glioma (U-87 MG) and ovarian (A2780) cancer cell lines. Also, we examined the in vitro efficacy of TTFields in combination with therapies that target molecular candidates that may confer resistance to TTFields.

Methods To establish TTFields resistant glioma and ovarian cancer cell lines in vitro, 2 approaches were tested: 1) cyclic repetitions, where TTFields treatment was repeatedly applied for 72 hours with 24 hours breaks between treatment cycles; and 2) continuous, long-duration application of TTFields (1 or 2 weeks, depending on the cancer cell line type) without treatment breaks. Luminex assay followed by Western blot analysis were used to study changes in signaling pathways following TTFields treatment. Finally, we examined the in vitro efficacy of continuous, long-duration application of TTFields in combination with BGT226 (a phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dual inhibitor).

Results Application of TTFields using cyclic repetition significantly decreased proliferation of human glioma and ovarian cancer cells, whereas cells treated using continuous, long-duration application of TTFields showed reduced sensitivity to TTFields. Luminex analysis clearly showed activation of the PI3K/mTOR/AKT signaling pathway in response to TTFields treatment. To clarify the importance of this signaling pathway on regulating treatment resistance to TTFields, we examined the effect of TTFields, alone and in combination, with a PI3K/mTOR inhibitor (BGT226) on cancer cell proliferation, apoptosis, and activation of AKT. While long-duration application of TTFields led to Akt activation, TTFields in combination with BGT226 resulted in reduction of p-AKT S473, with a corresponding blockade of proliferation, induction of apoptosis, and decrease in the clonogenic potential.

Conclusions We propose here a new mechanism of resistance to prolonged TTFields treatment mediated by the PI3K/mTOR/AKT signaling pathway in glioma and ovarian cancer cells. We demonstrate that combination therapy of TTFields and a targeted PI3K/mTOR dual inhibitor (BGT226) inhibited AKT S473 phosphorylation and sensitized cancer cells to “long-duration” TTFields application.

Citation Format: Anat Klein-Goldberg, Tali Voloshin, Efrat Zemer-Tov, Rom Paz, Lilach Koren, Alexandra Volodin, Boris Brant, Moshe Giladi, Uri Weinberg, Yoram Palti. Targeting Akt signaling pathway potentiates the antitumor effect of Tumor Treating Fields (TTFields) in vitro [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 1382.

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.

TAMI-04. TUMOR TREATING FIELDS (TTFIELDS) HINDER GLIOMA CELL MOTILITY THROUGH REGULATION OF MICROTUBULE AND ACTIN DYNAMICS

The ability of glioma cells to invade adjacent brain tissue remains a major obstacle to therapeutic disease management. Therefore, the development of novel treatment modalities that disrupt glioma cell motility could facilitate greater disease control. Tumor Treating Fields (TTFields), encompassing alternating electric fields within the intermediate frequency range, is an anticancer treatment delivered to the tumor region through transducer arrays placed non-invasively on the skin. This novel loco-regional treatment has demonstrated efficacy and safety and is FDA-approved in patients with glioblastoma and malignant pleural mesothelioma. TTFields are currently being investigated in other solid tumors in ongoing trials, including the phase 3 METIS trial (brain metastases from NSCLC; NCT02831959). Although established as an anti-mitotic treatment, the anti-metastatic potential of TTFields and its effects on cytoskeleton rapid dynamics during cellular motility warrant further investigation. Previous studies have demonstrated that TTFields inhibits metastatic properties of cancer cells. Identification of a unifying mechanism connecting the versatile TTFields-induced molecular responses is required to optimize the therapeutic potential of TTFields. In this study, confocal microscopy, computational tools, and biochemical analyses were utilized to show that TTFields disrupt glioma cellular polarity by interfering with microtubule assembly and directionality. Under TTFields application, changes in microtubule organization resulted in activation of GEF-H1, which led to an increase in active RhoA levels and consequent focal adhesion formation with actin cytoskeleton architectural changes. Furthermore, the optimal TTFields frequency for inhibition of invasion in glioma cells was 300 kHz, which differed from the optimal anti-mitotic frequency leading to glioma cell death of 200 kHz. The inhibitory effect of TTFields on migration was observed at fields intensities of 0.6 V/cm RMS (below the threshold of 1 V/cm RMS previously reported for cytotoxic effects). Together, these data identify discrete TTFields effects that disrupt processes crucial for glioma cell motility.

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.

EXTH-69. INCREASED CANCER CELL PERMEABILITY FOLLOWING TUMOR TREATING FIELDS (TTFIELDS) APPLICATION IN VITRO

INTRODUCTION

Tumor Treating Fields (TTFields), encompassing alternating electric fields within the intermediate frequency range, is an anticancer treatment delivered to the tumor region through transducer arrays placed non-invasively on the skin. This novel loco-regional treatment has demonstrated efficacy and safety and is FDA-approved in patients with glioblastoma (GBM) and malignant pleural mesothelioma. TTFields are currently being investigated in other solid tumors in ongoing trials. Recently, TTFields were reported to alter the cellular membrane structure of GBM cells, rendering them more permeable. The objective of this study was to characterize TTFields-induced cellular permeability in cancerous cell lines.

METHODS

TTFields were applied to uterine sarcoma, glioblastoma, and breast adenocarcinoma cell lines across a range of frequencies (50–500 kHz). Cellular permeability was assessed by quantifying the percentages of cells with accumulated 7-aminoactinomycin D (7-AAD) using flow cytometry and cytotoxicity was assessed based on cell counts. Kinetics were determined using different 7-AAD exposure times relative to TTFields treatment end. Changes in intracellular accumulation of anthracycline chemotherapeutics were evaluated in chemotherapy-sensitive and chemotherapy-resistant cells.

RESULTS

TTFields induced cellular permeability to 7-AAD in all 4 cancer cell lines tested. The optimal frequency for TTFields-induced cellular permeability was different from the optimal cytotoxic frequency. Kinetics measurements demonstrated that TTFields-induced permeability is transient and is effective only during application of TTFields. In combination experiments, TTFields improved intracellular accumulation of chemotherapeutic agents. Furthermore, combining chemotherapy with TTFields treatment facilitated accumulation of chemotherapeutics in chemotherapy-resistant cells to levels comparable with accumulation in chemotherapy-sensitive cancer cells.

CONCLUSIONS

This study demonstrates that TTFields can transiently increase cancer cell permeability in vitro with an optimal frequency that is variable from the frequency that is used to induce cancer cell cytotoxicity. Moreover, this effect is reversible and cellular permeability is restored to a normal state upon TTFields treatment cessation.

Abstract 5848: Tumor treating fields (TTFields) induce cancer cell permeability in vitro

Introduction Tumor Treating Fields (TTFields) are a clinically applied anti-neoplastic treatment modality delivered via noninvasive application of low-intensity, intermediate-frequency (100-500 kHz), alternating electric fields. TTFields had been shown to inhibit the growth of different cancerous cells, both in vitro and in vivo, by interrupting cancer cell mitosis. TTFields were recently reported to alter cellular membrane structure of glioblastoma cells, thus rendering them more permeable. In the current study, we characterized TTFields-induced cellular permeability in several cancerous cell lines including breast adenocarcinoma, uterine sarcoma and glioma.

Methods Flow cytometry analysis of intracellular 7-aminoactinomycin D (7-AAD; fluorescent DNA marker of cell viability) accumulation was used to quantify the percentages of cells showing increased cellular permeability following TTFields application. The optimal TTFields frequency for membrane permeability was evaluated using a frequency scan of TTFields in the range of 100-500 kHz. Kinetics were determined using different 7-AAD exposure times. Changes in intracellular accumulation of anthracycline chemotherapeutics (doxorubicin and mitoxantron) were evaluated in chemotherapy-sensitive and chemotherapy-resistant cells.

Results TTFields induced cellular permeability to 7-AAD, which is typically excluded by intact cells and was detected in all cancer cell lines tested with the highest permeability frequency of up to 80% of treated cells. The optimal frequency for TTFields induced cellular permeability was found to be different from the optimal cytotoxic frequency. Moreover, measurements of kinetics revealed that TTFields-induced permeability is transient and is effective only during application of TTFields. In combination experiments, TTFields improved intracellular accumulation of chemotherapeutic agents, which may explain the enhanced efficacy of combination treatment of TTFields with different chemotherapies. Furthermore, the combined treatment also facilitated the accumulation of chemotherapeutics in chemotherapy-resistant cells, and restored it to the level observed in the chemotherapy-sensitive cancer cells.

Conclusions This study demonstrates that TTFields can transiently increase cancer cell permeability in vitro with an optimal frequency that is variable from the frequency that is used to induce cancer cell cytotoxicity. Moreover, this effect is reversible and cellular permeability is restored to normal state function upon TTFields treatment cessation. Future studies will include in vivo experiments to validate TTFields-induced permeability and to evaluate the efficacy of TTFields and chemotherapy combinations in tumor models that are both sensitive and resistant to chemotherapy.

Citation Format: Tali Voloshin, Yaara Porat, Noa Kaynan, Anat Klein-Goldberg, Rom Paz, Alexandra Volodin, Moshe Giladi, Uri Weinberg, Yoram Palti. Tumor treating fields (TTFields) induce cancer cell permeability in vitro [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 5848.

Abstract 6662: Effects of tumor treating fields (TTFields) on dendritic cells functionality

Introduction Tumor Treating Fields (TTFields) are a clinically applied anti-neoplastic treatment modality delivered via noninvasive application of low intensity (1-3 V/cm), intermediate frequency (100-500 kHz), alternating electric fields. In this study we evaluated the effects of in vitro TTFields application on dendritic cell (DC) properties that include maturation, phagocytosis, and migration.

Methods Bone marrow cells were flushed from the femurs and tibias of 5-7 week old C57BL/6 mice to generate bone marrow-derived DCs. For the DC maturation assay, TTFields treated cancer cells were added at a ratio of 1:1 for 24 h. DC maturation was analyzed using flow cytometry to assess surface expression of major histocompatibility complex class II (MHC II), CD40, and CD80 activation markers. For the phagocytosis assay, CellTrackerTM Deep Red Dye, pre-stained TTFields treated cancer cells were added at a ratio of 1:1 for 2h and phagocytosis by DCs was evaluated using flow cytometry. DC migration assays were performed using a modified Matrigel coated Boyden chamber either with or without C-C Motif Chemokine Ligand 19 (CCL19), utilized as a chemoattractant.

Results TTFields treated cancer cells were effectively phagocytosed by DCs, while untreated control cells did not show similar outcomes. In addition, activation markers were found to be upregulated in DCs that were co-cultured with TTFields treated cells. This up-regulation was observed for all the costimulatory molecules analyzed. DC migration assays, showed no significant difference in migration rates between untreated and TTFields treated DCs, with or without the chemoattractant CCL19.

Conclusions These in vitro results indicate that TTFields treated cancer cells promote DC elicited phagocytosis and DC maturation. Moreover, in contrast to previous studies reporting that TTFields show an inhibitory effect on cancer cell migration, we demonstrate that TTFields do not impair the migratory properties of DCs.

Citation Format: Tali Voloshin, Shiri Davidi, Noa Kaynan, Rosa Schneiderman, Alexandra Volodin, Moshe Giladi, Uri Weinberg, Yoram Palti. Effects of tumor treating fields (TTFields) on dendritic cells functionality [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 6662.

Abstract 2411: Cancer cell lines meta-analysis according to both short-term and long-term responses to Tumor Treating Fields (TTFields)

Tumor Treating Fields (TTFields) therapy is an approved modality for the treatment of glioblastoma. These alternating electric fields were shown to exert an inhibitory effect in numerous cancer cell lines with some variability in the response of different cell lines. The goal of the present study is to compare characteristics of cell lines based on their response pattern to TTFields.

Forty one different human cancerous cell lines were treated for 72 hours with TTFields at their optimal frequency with the same nominal intensity (1.7 V/cm). Two response values were quantified. The first cytotoxic response, is considered a short-term quantification of the response. The second clonogenic response, is considered a long-term response to TTFields.

Genomic analysis of 26 cell lines was performed based on the Cancer Cell Line Encyclopedia (CCLE) database. Association of mutated genes, mutations and copy number variations with cell lines response to TTFields was investigated.

TTFields application demonstrated varying degree of cytotoxic effect in all cell lines tested. The inhibitory response to TTFields was found to be distributed around an average of 50% with a cytotoxic effects ranging between 14% and 86% reductions in cell counts, and a clonogenic effect ranging between no effect and 88% reduction in the number of colonies. The “Overall response” was considered as the multiplication of the two values and represents the response both in short-term and long-term effects of TTFields. Lower values of all response quantifications indicate a better

response to TTFields. Cell lines were partitioned to responding and non-responding cell lines according to their “Overall response”.

Response to treatment doesn't seem to be affected by the number of mutations in each of the cell lines, and not by the type of the cancer the cell lines originated from. Mutations in genes that associate with the response to TTFields are enriched in GO terms that include muscle function and the intracellular organelle compartment. Mutation association with response to TTFields revealed mutations in genes related to the cytoskeleton, mitotic spindle, receptors and membrane transporters.

This multi parameter, large scale comparison of cancerous cell line response to TTFields demonstrate the broad effectiveness of TTFields in various cell lines and define the optimal frequency to be applied for each cell line. The data presented in this work, suggest that beside their anti-mitotic properties, TTFields may have effects on other cellular pathways.

Citation Format: Kerem Wainer Katsir, Gitit Lavy Shahaf, Moshe Giladi, Rosa S. Schneiderman, Noa Urman, Karnit Gotlieb, Einav Zeevi, Yaara Porat, Mijal Munster, Adrian Kinzel, Uri Weinberg, Eilon D. Kirson, Yoram Palti. Cancer cell lines meta-analysis according to both short-term and long-term responses to Tumor Treating Fields (TTFields) [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 2411.

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.

Compatibility of topical agents with tumor treating fields (TTFields) for treatment of associated skin events in glioblastoma (GBM)

e24126

Background: TTFields are low intensity, intermediate frequency, alternating electric fields applied continuously using 2 pairs of skin-affixed transducer arrays. TTFields are FDA-approved in GBM and mesothelioma. The most common TTFields-related adverse event (AE) is mild-to-moderate dermatitis (beneath arrays), via long-term irritant exposure and local hyperhidrosis and occlusion exacerbation. Skin reaction mitigation strategies may improve quality-of-life (QoL) and ensure usage, as maximal survival benefits have been correlated with duration of use. Not all skin care products are TTFields compatible and may increase electrical impedance and lead to beneath array temperature increases. The aim of this in vivo study was to investigate the effects of 62 commercially available skin care products on electrical impedance during TTFields treatment. Methods: TTFields (200 kHz; optimal GBM frequency) were applied to rats using transducer arrays made of the same ceramic disks and hydrogels used in patients with GBM. To test electrical impedance effects, skin care products were applied to the skin immediately before array placement. The change in impedance relative to naïve skin was measured using the Optune device. Sixty-two commercially available products from 8 groups (adhesive removers, antibiotics, antiperspirants, antiseptics, cleansers, moisturizers, skin barriers, and topical corticosteroids) were evaluated. Results: Most lotions, soaps, foams, and solutions had minimal effect on electrical impedance, while petrolatum-based ointments significantly increased electrical impedance. Conclusions: TTFields compatible skin care products that did not affect electrical impedance were identified from each of the 8 groups and could be considered for further evaluation. All petrolatum-based ointments that were tested led to an increase in electrical impedance and are thus not recommended. Local application of TTFields compatible skin care products should be prospectively investigated in the clinical setting for their potential role in minimizing TTFields–related skin AEs. The randomized, double-blind PROTECT (PROphylactic skin Toxicity thErapy with Clindamycin and triamcinolone in GBM patients Treated with TTFields) study, should help establish which products best reduce skin AEs in patients with GBM and assess impact on QoL.