Structural dynamics of Na+ and Ca2+ interactions with full-size mammalian NCX

Cytosolic Ca2+ and Na+ allosterically regulate Na+/Ca2+ exchanger (NCX) proteins to vary the NCX-mediated Ca2+ entry/exit rates in diverse cell types. To resolve the structure-based dynamic mechanisms underlying the ion-dependent allosteric regulation in mammalian NCXs, we analyze the apo, Ca2+, and Na+-bound species of the brain NCX1.4 variant using hydrogen-deuterium exchange mass spectrometry (HDX-MS) and molecular dynamics (MD) simulations. Ca2+ binding to the cytosolic regulatory domains (CBD1 and CBD2) rigidifies the intracellular regulatory loop (5L6) and promotes its interaction with the membrane domains. Either Na+ or Ca2+ stabilizes the intracellular portions of transmembrane helices TM3, TM4, TM9, TM10, and their connecting loops (3L4 and 9L10), thereby exposing previously unappreciated regulatory sites. Ca2+ or Na+ also rigidifies the palmitoylation domain (TMH2), and neighboring TM1/TM6 bundle, thereby uncovering a structural entity for modulating the ion transport rates. The present analysis provides new structure-dynamic clues underlying the regulatory diversity among tissue-specific NCX variants.

Complex biophysical changes and reduced neuronal firing in an SCN8A variant associated with developmental delay and epilepsy

Mutations in the SCN8A gene, encoding the voltage-gated sodium channel NaV1.6, are associated with a range of neurodevelopmental syndromes. The p.(Gly1625Arg) (G1625R) mutation was identified in a patient diagnosed with Developmental epileptic encephalopathy (DEE). While most of the characterized DEE-associated SCN8A mutations were shown to cause a gain-of-channel function, we show that the G1625R variant, positioned within the S4 segment of domain IV, results in complex effects. Voltage-clamp analyses of NaV1.6G1625R demonstrated a mixture of gain- and loss-of-function properties, including reduced current amplitudes, increased time constant of fast voltage-dependent inactivation, a depolarizing shift in the voltage dependence of activation and inactivation, and increased channel availability with high-frequency repeated depolarization. Current clamp analyses in transfected cultured neurons revealed that these biophysical properties caused a marked reduction in the number of action potentials when firing was driven by the transfected mutant NaV1.6. Accordingly, computational modeling of mature cortical neurons demonstrated a mild decrease in neuronal firing when mimicking the patients' heterozygous SCN8A expression. Structural modeling of NaV1.6G1625R suggested the formation of a cation-π interaction between R1625 and F1588 within domain IV. Double-mutant cycle analysis revealed that this interaction affects the voltage dependence of inactivation in NaV1.6G1625R. Together, our studies demonstrate that the G1625R variant leads to a complex combination of gain and loss of function biophysical changes that result in an overall mild reduction in neuronal firing, related to the perturbed interaction network within the voltage sensor domain, necessitating personalized multi-tiered analysis for SCN8A mutations for optimal treatment selection.

Chloride intracellular channel (CLIC) proteins function as fusogens

Chloride Intracellular Channel (CLIC) family members uniquely transition between soluble and membrane-associated conformations. Despite decades of extensive functional and structural studies, CLICs' function as ion channels remains debated, rendering our understanding of their physiological role incomplete. Here, we expose the function of CLIC5 as a fusogen. We demonstrate that purified CLIC5 directly interacts with the membrane and induces fusion, as reflected by increased liposomal diameter and lipid and content mixing between liposomes. Moreover, we show that this activity is facilitated by acidic pH, a known trigger for CLICs' transition to a membrane-associated conformation, and that increased exposure of the hydrophobic inter-domain interface is crucial for this process. Finally, mutation of a conserved hydrophobic interfacial residue diminishes the fusogenic activity of CLIC5 in vitro and impairs excretory canal extension in C. elegans in vivo. Together, our results unravel the long-sought physiological role of these enigmatic proteins.

Revealing the tumor suppressive sequence within KL1 domain of the hormone Klotho

Klotho, a 1012 amino acid transmembrane protein, is a potent tumor suppressor in different cancer types. Klotho is composed of two internal repeats KL1 and KL2, and the tumor suppressor activity is primarily attributed to the KL1 domain. Despite its significant role in regulating various cancer-related pathways, the precise mechanism underlying its tumor suppressor activity remains unresolved. In this study, we aimed to identify the sequence responsible for the tumor suppressor function of Klotho and gain insights into its mechanism of action. To accomplish this, we generated expression vectors of truncated KL1 at the C and N-terminal regions and evaluated their ability to inhibit the colony formation of several cancer cell lines. Our findings demonstrated that truncated KL1 1-340 (KL340) effectively inhibited colony formation similar to KL1, while truncated KL1 1-320 (KL320) lost this activity. Furthermore, this correlated with the inhibitory effect of KL1 and KL340 on the Wnt/β-catenin pathway, whereas KL320 had no effect. Transcriptomic analysis of MCF-7 cells expressing the constructs revealed enriched pathways associated with tumor suppressor activity in KL1 and KL340. Interestingly, the α-fold predictor tool highlighted distinct differences in the α and β sheets of the TIM barrel fold of the truncated Klotho constructs, adding to our understanding of their structural variations. In summary, this study identified the 340 N-terminal amino acids as the sequence that possesses Klotho's tumor suppressor activity and reveals a critical role in the 320-340 sequence for this function. It also provides a foundation for the development of Klotho-based therapeutic approaches for cancer treatment.

Compatibility of Topical Products to Manage Skin Irritation Associated with TTFields

PURPOSE/OBJECTIVE(S)

Tumor Treating Fields (TTFields) are electric fields that disrupt cellular processes critical for cancer cell viability and tumor progression. TTFields therapy is approved for the treatment of recurrent glioblastoma (GBM), newly diagnosed GBM, and pleural mesothelioma, and is currently under clinical investigations for the treatment of other types of cancers. TTFields therapy is delivered continuously and non-invasively, using a portable signal generator connected to 4 arrays attached to the skin. Treatment of at least 18 hours per day is recommended for increasing effectiveness. The main treatment-related adverse effect reported in clinical trials and post-marketing surveillance studies has been low-grade skin irritation under the arrays, which may be treated in most cases with the use of topical steroids or intermittent treatment interruptions. However, for maintaining treatment effectiveness, skin care products suitable for use under the TTFields arrays are those that do not affect field currents. The goal of this study was to investigate strategies to alleviate skin irritation without compromising treatment effectiveness.

MATERIALS/METHODS

TTFields (200 kHz) were applied to rats (Sprague Dawley, 10-20 weeks of age, body weight over 250 gr) using ceramic disks and hydrogels identical to those used with human arrays. The rat torso was depilated, and TTFields were applied to the rat torso before and after applying various skin care products to the surface beneath the arrays. After reaching a steady state, average currents were extracted from the device's log files. Percent change in current was calculated from the measurements with and without the product.

RESULTS

Tested products could be divided into groups according to their medical use: antibiotics, antiseptics, cleansers/adhesive removers, skin barriers, moisturizers, topical corticosteroids, and antiperspirants. The products could also be categorized by their type: creams, gels, soaps, sprays, ointments, wipes/pads, foams, and lotions. Skin care products that significantly reduced currents were mainly ointments. Typical ingredients of ointments are mineral oil and petrolatum, which are expected to create a hydrophobic layer, thereby reducing ionic conduction and hence field currents. These ingredients also hinder adherence of the acrylic-based tape to the skin thus compromising mechanical fixation of the arrays, leading to poor connectivity and hence reduced currents.

CONCLUSION

Identification of products for treating skin irritation that are compatible with TTFields therapy is important for improving patient's quality of life and increasing device usage. Skin care products containing petrolatum should not be applied under the arrays to avoid compromising treatment effectiveness.

Defective cathepsin Z affects EGFR expression and causes autosomal dominant palmoplantar keratoderma

BACKGROUND

The abnormal function of epidermal growth factor receptor (EGFR) has recently been shown to underlie various disorders of cornification.

OBJECTIVES

To delineate the genetic basis of a novel dominant form of palmoplantar keratoderma (PPK).

METHODS

Whole-exome (WES) and direct sequencing, quantitative real-time polymerase chain reaction, protein modelling, confocal immunofluorescence microscopy, immunoblotting, three-dimensional skin equivalents and an enzyme activity assay were used to delineate the genetic basis of a novel dominant form of PPK.

RESULTS

WES revealed heterozygous variants (c.274T > C and c.305C > T) in CTSZ (encoding cathepsin Z) in four individuals (belonging to three unrelated families) with focal PPK. Bioinformatics and protein modelling predicted the variants to be pathogenic. Previous studies have suggested that EGFR expression may be subject to cathepsin regulation. Immunofluorescence revealed reduced cathepsin Z expression in the upper epidermal layers and concomitant increased epidermal EGFR expression in patients harbouring CTSZ variants. Accordingly, human keratinocytes transfected with constructs expressing PPK-causing variants in CTSZ displayed reduced cathepsin Z enzymatic activity, as well as increased EGFR expression. In line with the role played by EGFR in the regulation of keratinocyte proliferation, human keratinocytes transfected with the PPK-causing variants showed significantly increased proliferation that was abolished upon exposure to erlotinib, an EGFR inhibitor. Similarly, downregulation of CTSZ resulted in increased EGFR expression and increased proliferation in human keratinocytes, suggestive of a loss-of-function effect of the pathogenic variants. Finally, three-dimensional organotypic skin equivalents grown from CTSZ-downregulated cells showed increased epidermal thickness and EGFR expression as seen in patient skin; here, too, erlotinib was found to rescue the abnormal phenotype.

CONCLUSIONS

Taken collectively, these observations attribute to cathepsin Z a hitherto unrecognized function in epidermal differentiation.

Tumor Treating Fields (TTFields) increase the effectiveness of temozolomide and lomustine in glioblastoma cell lines

PURPOSE

Tumor Treating Fields (TTFields) are electric fields that disrupt cellular processes critical for cancer cell viability and tumor progression, ultimately leading to cell death. TTFields therapy is approved for treatment of newly-diagnosed glioblastoma (GBM) concurrent with maintenance temozolomide (TMZ). Recently, the benefit of TMZ in combination with lomustine (CCNU) was demonstrated in patients with O⁶-methylguanine DNA methyltransferase (MGMT) promoter methylation. The addition of adjuvant TTFields to TMZ plus CCNU further improved patient outcomes, leading to a CE mark for this regimen. The current in vitro study aimed to elucidate the mechanism underlying the benefit of this treatment protocol.

METHODS

Human GBM cell lines with different MGMT promoter methylation statuses were treated with TTFields, TMZ, and CCNU, and effectiveness was tested by cell count, apoptosis, colony formation, and DNA damage measurements. Expression levels of relevant DNA-repair proteins were examined by western blot analysis.

RESULTS

TTFields concomitant with TMZ displayed an additive effect, irrespective of MGMT expression levels. TTFields concomitant with CCNU or with CCNU plus TMZ was additive in MGMT-expressing cells and synergistic in MGMT-non-expressing cells. TTFields downregulated the FA-BRCA pathway and increased DNA damage induced by the chemotherapy combination.

CONCLUSIONS

The results support the clinical benefit demonstrated for TTFields concomitant with TMZ plus CCNU. Since the FA-BRCA pathway is required for repair of DNA cross-links induced by CCNU in the absence of MGMT, the synergy demonstrated in MGMT promoter methylated cells when TTFields and CCNU were co-applied may be attributed to the BRCAness state induced by TTFields.

Abstract 6182: Tumor treating fields (TTFields) concomitant with PARP inhibitors or carboplatin for treatment of ovarian cancer cell lines

Purpose/Objectives: Ovarian cancer continues to be the leading cause of death among gynecological malignancies. Platinum-based chemotherapy is recommended after surgery for most patients with ovarian cancer; and PARP inhibitors (PARPi) are suggested as maintenance therapy. Both therapies induce DNA damage that require the proper activity of the Fanconi Anemia (FA)- BRCA pathway for its resolution, and hence are most beneficial in cancers with a BRCA mutation. However, 75% of patients with ovarian cancer do not harbor BRCA mutations, and thus may experience limited benefit from these treatments. TTFields are electric fields that disrupt cellular processes critical for cancer cell viability and tumor progression, ultimately leading to cancer cell death. Recently, TTFields have been shown to induce a state of BRCAness in various cancer types, and to be effective in ovarian cancer pre-clinical models. The objective of the current study was to examine the effect of TTFields concomitant with carboplatin or PARPi on ovarian cancer cell lines.

Materials/Methods: A2780 (BRCA wild type) and OVCAR3 (BRCA mutated) ovarian carcinoma cells were treated with TTFields (72 h, 1 V/cm RMS, 200 kHz), alone or with concomitant application of carboplatin or the PARP inhibitors olaparib or niraparib. Efficacy was examined via measurements of cell count, colony formation, and induction of apoptosis. The overall effect was calculated by multiplying cell count with colony formation.

Results: Application of TTFields to A2780 or OVCAR3 cells resulted in reduced cell count, increased overall effect, and elevated apoptosis. Carboplatin, olaparib, and niraparib each displayed dose dependent effects in both cell lines, with higher sensitivity demonstrated in the BRCA mutated cells. Concomitant application of TTFields with any of these drugs displayed a synergistic interaction in the BRCA wild type A2780 cells and an additive effect in the BRCA mutant OVCAR-3 cells.

Conclusions: The data suggest potential benefits for TTFields concomitant with platinum-based chemotherapy and PARPi in ovarian cancer, even in the absence of background BRCA mutations, in accordance with the BRCAness state induced by TTFields. As such, TTFields may enhance the efficacy of treatment for ovarian cancer in both the adjuvant and maintenance settings.

Citation Format: Antonia Martinez-Conde, Hila Ene, Roni Frechtel-Gerzi, Eyal Dor-On, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Tumor treating fields (TTFields) concomitant with PARP inhibitors or carboplatin for treatment of ovarian cancer cell lines. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6182.

Abstract 2666: Preclinical investigations of concomitant tumor treating fields (TTFields) with cisplatin or paclitaxel for treatment of cervical cancer

Introduction: Cervical cancer is a serious health problem despite the fact it is highly preventable. Early-stage cervical cancer treatment often involves surgery; however advanced, recurrent, or metastatic cases require systemic therapy. Chemotherapy, mainly cisplatin, is the most commonly used systemic therapy for this cancer type. Combination regimens may be needed in the recurrent or metastatic settings, with first-line treatments including cisplatin with paclitaxel. TTFields are electric fields that disrupt cellular processes critical for cancer cell viability and tumor progression. Concomitant treatment with TTFields and cisplatin or paclitaxel has shown benefit in other tumor types. In the current in vitro study, we tested the effectiveness of TTFields for the treatment of cervical cancer, and the possible benefit of applying TTFields together with first-line treatments for cervical cancer.

Methods: Human cervical cancer cell lines - squamous cell carcinoma Ca Ski and SiHa cells, and adenocarcinoma HeLa cells - were treated with TTFields (72 h, 1 V/cm RMS) at frequencies of 100 to 400 kHz, and tested for cell count. For examining the efficacy of TTFields concomitant with cisplatin or paclitaxel, various doses of the drugs were applied together with TTFields (200 kHz), followed by measurements of cell count, colony formation, and apoptosis. Overall effect was defined as the product of percent reductions in cell count and colony formation.

Results: TTFields treatment reduced cell count in all tested cervical cancer cell lines. 200 kHz were found to be effective and were used throughout the experiments. Dose response effects were seen with cisplatin or paclitaxel, and were augmented when TTFields were co-applied to the cells.

Conclusions: These preclinical data suggest that TTFields may be an effective treatment against cervical cancer, and that applying them concomitantly with first-line treatment for this malignancy may provide enhanced effectiveness.

Citation Format: Roni Frechtel-Gerzi, Daria Gerasimova, Einav Zeevi, Inbar Schlachet-Drukerman, Helena Mumblat, Antonia Martinez-Conde, Eyal Dor-On, Itai Tzchori, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti, Greg Palmer, Angeles A. Secord. Preclinical investigations of concomitant tumor treating fields (TTFields) with cisplatin or paclitaxel for treatment of cervical cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2666.

Abstract 1738: Sensitizing cancer cell to doxorubicin by tumor treating fields (TTFields)-induced, elevated membrane permeability

Background: Tumor Treating Fields (TTFields) are electric fields that disrupt cellular processes critical for cancer cell viability and tumor progression, ultimately leading to cell death. In addition, application of TTFields to glioblastoma cells has been shown to increase cell membrane permeability. The aim of the current study was to examine whether this mechanism is relevant in other tumor types, and may be leveraged to facilitate cellular internalization of the anticancer agent doxorubicin (DOX).

Methods: Lung fibroblast (MRC-5), brain endothelial (HBMVEC), and several cancer cell lines - breast mammary carcinoma (4T1), breast adenocarcinoma (MCF-7), and uterine sarcoma (MES-SA) - were treated with TTFields (100-400 kHz, 1.7 V/cm RMS) using the inovitroTM system. Intracellular accumulation of 7-aminoactinomycin D (7-AAD) was measured to determine membrane permeability, and cell counts were examined to evaluate cytotoxicity. To examine the kinetics and reversibility of the phenomenon, 7-AAD was added at different time points following TTFields application initiation or termination. TTFields were also applied together with DOX to DOX-sensitive and matched DOX-resistant 4T1 cells, followed by flow cytometry examination of DOX accumulation and cytotoxicity measurements. Mice orthotopically inoculated with 4T1 cells were treated with TTFields for 72 h and concomitant DOX injected 24 h before treatment cessation. DOX florescence was measured by flow cytometry in single-cell tumor suspension and by whole tumor in vivo imaging system (IVIS).

Results: TTFields increased intracellular accumulation of 7-AAD specifically in the cancer cell lines, with no such effect seen on the non-cancer MRC-5 and HBMVEC cells. In 4T1 cells, maximal TTFields-induced cellular permeability was recorded with 300 kHz TTFields, whereas highest TTFields-induced cytotoxicity was observed at 150 kHz. TTFields application allowed for DOX accumulation to the same extent in both DOX-resistant and DOX-sensitive cells, and sensitized both cell types to DOX cytotoxicity. In vivo, a 2- to 3-fold higher DOX accumulation was seen in tumors isolated from mice treated with TTFields relative to control mice.

Conclusions: TTFields elevated cancer cell permeability, resulting in enhanced cell accumulation of DOX and improved drug efficacy, even in DOX resistant cells. TTFields-induced accumulation of DOX was also demonstrated in vivo.

Citation Format: Bella Koltun, Tali Voloshin, Tal Kan, Cfir David, Lilach Koren, Yaara Porat, Alexandra Volodin, Noa Kaynan, Anat Klein-Goldberg, Rom Paz, Boris Brant, Yiftah Barsheshet, Efrat Zemer-Tov, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Sensitizing cancer cell to doxorubicin by tumor treating fields (TTFields)-induced, elevated membrane permeability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1738.

Abstract 2723: Treatment of gastric cancer cells with tumor treating fields (TTFields) and concomitant FOLFOX

Background: Gastric cancer, one of the most common types of cancers, is mainly treated with the FOLFOX chemotherapy regimen (oxaliplatin, fluorouracil [5-FU], and leucovorin); yet long-term survival remains poor. Tumor Treating Fields (TTFields) are electrical fields that disrupt cellular processes critical for cancer cell viability and tumor progression, ultimately leading to cell death. In several tumor types, the mechanism of action of TTFields included an antimitotic effect and DNA damage induction with impaired DNA damage repair. The current study aimed to examine the efficacy of TTFields for treating gastric cancer cells, and the potential application of TTFields concomitant with FOLFOX.

Methods: Human gastric cancer cell lines, AGS and KATO III, were treated with TTFields (intensity of 1.1 and 1.7 V/cm, respectively; frequency of 150 kHz) using the inovitro system. Cell count and colony formation were examined following treatment, and the overall effect calculated by multiplication of the two. RNA sequencing was also performed on samples from control and TTFields-treated cells. Mitotic spindle defects, chromosome miss-localization, and DNA double strand breaks (DSB) formation were examined by fluorescent staining for α-tubulin, phospho-histone 3 (PH3), and phospho-histone H2AX (γH2AX), respectively. Expression of DNA repair proteins was measured using Western Blot. The impact of TTFields with FOLFOX and its individual therapeutic components, oxaliplatin and 5-FU on cell count and clonogenicity was tested.

Results: TTFields reduced cell count and the colony forming ability of the cells. Cells treated with TTFields displayed abnormal mitotic figures and increased levels of DNA damage. Expression of DNA repair proteins was downregulated following treatment with TTFields, as evident from RNA and protein levels. Furthermore, TTFields augmented the cytotoxic and clonogenic effects of FOLFOX and its individual therapeutic components, oxaliplatin and 5-FU.

Conclusions: TTFields show potential as an effective gastric cancer treatment, with a mechanism of action involving an anti-mitotic effect and DNA damage repair impairment. TTFields may be applied to enhance the efficacy of gastric cancer standard-of-care.

Citation Format: Naama Flint-Brodsly, Einav Zeevi, Kerem Wainer-Katsir, Hila Fishman, Antonia Martinez-Conde, Eyal Dor-On, Mijal Munster, Yaara Porat, Tali Voloshin, Shiri Davidi, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Treatment of gastric cancer cells with tumor treating fields (TTFields) and concomitant FOLFOX [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2723.

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) Concomitant with Immune Checkpoint Inhibitors Are Therapeutically Effective in Non-Small Cell Lung Cancer (NSCLC) In Vivo Model

Tumor Treating Fields (TTFields) are electric fields that exert physical forces to disrupt cellular processes critical for cancer cell viability and tumor progression. TTFields induce anti-mitotic effects through the disruption of the mitotic spindle and abnormal chromosome segregation, which trigger several forms of cell death, including immunogenic cell death (ICD). The efficacy of TTFields concomitant with anti-programmed death-1 (anti-PD-1) treatment was previously shown in vivo and is currently under clinical investigation. Here, the potential of TTFields concomitant with anti- PD-1/anti-cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA-4) or anti-programmed death-ligand 1 (anti-PD-L1) immune checkpoint inhibitors (ICI) to improve therapeutic efficacy was examined in lung tumor-bearing mice. Increased circulating levels of high mobility group box 1 protein (HMGB1) and elevated intratumoral levels of phosphorylated eukaryotic translation initiation factor 2α (p-eIF2α) were found in the TTFields-treated mice, indicative of ICD induction. The concomitant application of TTFields and ICI led to a significant decrease in tumor volume as compared to all other groups. In addition, significant increases in the number of tumor-infiltrating immune cells, specifically cytotoxic T-cells, were observed in the TTFields plus anti-PD-1/anti-CTLA-4 or anti-PD-L1 groups. Correspondingly, cytotoxic T-cells isolated from these tumors showed higher levels of IFN-γ production. Collectively, these results suggest that TTFields have an immunoactivating role that may be leveraged for concomitant treatment with ICI to achieve better tumor control by enhancing antitumor immunity.

CSIG-41. SENSITIZING CANCER CELLS TO TUMOR TREATING FIELDS (TTFIELDS) BY INHIBITION OF PI3K

Tumor Treating Fields (TTFields) are alternating electric fields, which disrupt cellular process critical for cancer cell survival and tumor progression. TTFields therapy is approved for the treatment of glioblastoma (GBM) and unresectable malignant pleural mesothelioma, and is being tested in clinical studies for the treatment of other solid tumors, including ovarian cancer, non-small cell lung carcinoma (NSCLC), and hepatocellular carcinoma (HCC). The current study aimed to detect potential mechanisms that may reduce cellular sensitivity to TTFields, and target these pathways in order to re-sensitize the cells to TTFields. Cancer cells (Ovarian A2780, GBM U-87 MG, and NSCLC H1299) that display reduced sensitivity to TTFields were generated by continuous long-term TTFields application (7 or 13 days, depending on the cell line). A Luminex multiplex assay revealed activation of the PI3K/AKT/mTOR signaling pathway in these cells, with significant increases in phosphorylation levels of AKT and RPS6. This elevation was also observed by immunohistochemistry in tumor sections from N1S1 HCC tumor-bearing rats treated with TTFields relative to sham. Treatment of cells with PI3K inhibitors re-sensitized them to TTFields and downregulated the phosphorylation of AKT. Concomitant application of TTFields with the PI3K inhibitor alpelisib in mice orthotopically implanted with MOSE-L firefly luciferase (FFL) ovarian cancer cells resulted in enhanced efficacy, as determined by In Vivo Imaging System (IVIS) measurements of tumor volume. Overall, this study demonstrated that the PI3K/AKT/mTOR signaling pathway is involved in reduced cancer cell sensitivity to long-term application of TTFields, and that re-sensitization may be achieved with relevant inhibitors. The results provide a rationale for further examining the potential benefit of TTFields concomitant with PI3K inhibitors.

DNAR-10. THE EFFICACY OF TEMOZOLOMIDE AND LOMUSTINE IN GLIOBLASTOMA CELL LINES MAY BE ENHANCED BY CONCOMITANT TREATMENT WITH TUMOR TREATING FIELDS (TTFIELDS)

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. Temozolomide (TMZ) is part of the standard of care for patients with newly diagnosed GBM (ndGBM). Expression of the enzyme MGMT involved in TMZ-induced DNA damage repair is associated with irresponsiveness of some patients to TMZ. The addition of lomustine (CCNU) to TMZ demonstrated clinical benefit in patients with ndGBM. Tumor Treating Fields (TTFields) are electric fields that display anti-mitotic effects and lower expression levels of proteins from the FA-BRCA DNA repair pathway in cancerous cells. TTFields therapy concomitant with TMZ is approved for the treatment of ndGBM. The aim of the current study was to examine the effect of TTFields in conjunction with TMZ and CCNU in GBM cells. Human GBM cell lines with different MGMT expression levels (U-87 MG, LN229, U118, and LN18) were treated with TTFields (0.83 V/cm RMS, 200 kHz) concomitant with TMZ and/or CCNU. Cell counts, colony formation, and apoptosis were used to measure effectiveness. The effect of TTFields with concomitant TMZ was additive in all cell lines, regardless of MGMT expression levels. TTFields in conjunction with CCNU displayed an additive effect in cell lines with high MGMT expression, and tendency to synergism in cell lines with low or no MGMT expression. TTFields concurrent with both TMZ and CCNU further increased treatment efficacy. Mechanistically, TTFields elevated the levels of DNA double strand breaks and lowered expression of FA-BRCA pathway proteins, as detected by fluorescence microscopy and western blot, respectively. The involvement of the FA-BRCA pathway in repair of DNA damage induced by CCNU and the BRCAness state induced by TTFields rationalize the synergy seen for TTFields with CCNU, especially in cells absent of MGMT. The results suggest a potential benefit of TTFields therapy concomitant with TMZ/CCNU for the treatment of GBM.

Heterozygous variants in the integrin subunit beta 4 gene (ITGB4) cause autosomal dominant nail dystrophy

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

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

Exploring the Li+ transporting mutant of NCX_Mj for assigning ion binding sites of mitochondrial NCLX

The plasma membrane (NCX) and mitochondrial (NCLX) Na⁺/Ca²⁺ exchangers are structurally related proteins, although they operate under strictly different ionic conditions and membrane potentials. In contrast with NCX, NCLX can transport either Li⁺ or Na⁺ in exchange for Ca²⁺. Whereas the crystal structure of the archaeal NCX (NCX_Mj) describes the binding sites for alternative binding of 3Na⁺ or 1Ca²⁺, these features remain elusive for NCLX due to the lack of structural information. To elucidate the ion-binding features of mitochondrial NCLX, we analyzed here the Li⁺-transporting NCLX_Mj mutant, produced by replacing the ion-coordinating residues in the archaeal NCX (NCX_Mj) to match the ion-coordinating residues of human NCLX. The NCLX_Mj-mediated Na⁺/Ca²⁺ or Li⁺/Ca²⁺ exchange rates are insensitive to varying voltage, consistent with an electroneutral ion exchange. Molecular dynamics (MD) simulations revealed that NCLX_Mj contains two novel Li⁺ binding sites with four ion-coordinating residues, derived from the three Na⁺ binding sites of NCX_Mj. The ion-coordination modes, observed in the MD simulations, were further supported by two-dimensional infrared (2D IR) spectroscopy and by testing the mutational effects on the ion fluxes. Collectively, our results revealed a structural basis for Li⁺ binding and electroneutral transport (2Na⁺/Li⁺:1Ca²⁺) by NCLX_Mj, meaning that the NCLX-mediated electroneutral transport may predefine mitochondrial Ca²⁺ and Na⁺ signaling to modulate cellular functions.

Varicocele in adolescence and testicular cancer in young adulthood

BACKGROUND

Elevated intrascrotal temperature has been suggested as a risk factor for testicular cancer, which is the most common neoplasm among young men. Varicocele was linked to increased intrascrotal temperature, but whether it is associated with testicular cancer is unclear.

OBJECTIVE

To explore the possible association between varicocele at adolescence and the incidence of testicular cancer at adulthood.

DESIGN, SETTING AND PARTICIPANTS

This nationwide, population-based, historical cohort study includes 1,521,661 Israeli male adolecents (mean age 17.5 ± 0.4 years), who were screened for varicocele during the years 1967-2012, as part of their medical assessment prior to compulsory military service. The mean follow-up was 18± 4.2 years.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The diagnosis of testicular cancer was ascertained from linkage of records to the the Israeli National Cancer Registry. Survival analysis was applied.

RESULTS

In total, 53,210 adolescents were diagnosed with varicocele stage 2 and 3 prior to military service. Of 1,988 (0.13% of the total cohort) men who were diagnosed with testicular cancer during follow up, 54 (0.1%) had varicocele prior to military service while 1934(99.9%) did not, p = 0.213. The age at cancer diagnosis and the distribution of seminomas vs. non-seminomas did not differ significantly between those with and without varicocele in adolescence. In a multivariable analysis controlling for sociodemographic factors, varicocele was not associated with testicular cancer, odds ratio = 0.816 (CI 0.615-1.083).

CONCLUSIONS

Varicocele in adolecents was not found to be associated with testicular cancer in young adults.

PATIENT SUMMARY

In light of the theoretical association between varicocele and testicular cancer, we conducted this large population study. We found no association between varicocele in young adoulthoot and testicular cancer later in life. This article is protected by copyright. All rights reserved.

P10.10.A Tumor Treating Fields (TTFields), temozolomide and lomustine co-application is efficacious in glioblastoma cancer cell lines

Background

Temozolomide (TMZ) is the standard of care chemotherapy for newly diagnosed glioblastoma (ndGBM), the most common primary malignant brain tumor in adults. However, 50% of patients do not respond to TMZ due to expression of O6-methylguanine-DNA methyltransferase (MGMT), the enzyme involved in repair of TMZ-induced damage. Tumor Treating Fields (TTFields) are alternating electric fields that display anti-mitotic effects on cancerous cells, and have been shown to induce a state of BRCAness in various cancer types. Concurrent treatment with TMZ and TTFields demonstrated a major advance in treatment of patients with ndGBM, and was approved by the FDA in 2014. Recently, the addition of lomustine (CCNU) to TMZ demonstrated clinical benefit in ndGBM patients, with improved overall and progression free survival. The aim of the current study was to examine in GBM cells the effect of TTFields in conjunction with TMZ and CCNU.

Materials and Methods

U-87 MG, LN229, U118 and LN18 human GBM cell lines were tested for their MGMT expression levels, and treated with TTFields (200 kHz, of 0.83 V/cm RMS) for 72 h using the inovitro system. Efficacy of concomitant application of TTFields with TMZ and/or CCNU was tested by measuring cell count, colony formation, and apoptosis levels.

Results

U-87 MG and LN229 displayed no expression of MGMT, while U118 and LN18 expressed low and high levels of MGMT, respectively. Application of TMZ and TTFields resulted in increased cytotoxicity compared with each treatment alone, with an additive interaction seen in all examined cell lines. The cytotoxic effect resulting from co-application of CCNU with TTFields suggested a synergistic interaction between the two modalities for U-87 MG, LN229, and U118, an additivity for LN18. Concurrent TTFields/TMZ/CCNU was more efficacious than TTFields or TMZ/CCNU separately in all cell lines.

Conclusions

Application of TTFields with TMZ was additive, irrespective of MGMT expression levels, while TTFields with CCNU was additive when MGMT was plentiful, but displayed tendency to synergism when MGMT was absent or limited. These outcomes are in line with the BRCAness state induced by TTFields, as in the absence of MGMT, DNA damage induced by CCNU requires the BRCA pathway for repair. Application of TTFields together with TMZ and CCNU demonstrated increased efficacy, suggesting potential benefit of such therapy for ndGBM treatment.

P10.11.B Re-sensitizing cancer cells to Tumor Treating Fields (TTFields) through PI3K/AKT/mTOR pathway inhibition

Background

Tumor Treating Fields (TTFields) are alternating electric fields disrupting cellular processes critical for cancer cell replication and tumor progression. TTFields therapy is approved for treatment of newly diagnosed glioblastoma (GBM), recurrent GBM, and unresectable malignant pleural mesothelioma, and is currently under clinical investigation for treating other solid tumors, such as ovarian cancer, non-small cell lung carcinoma (NSCLC), and hepatocellular carcinoma (HCC). The research herein aimed to identify potential treatment escape mechanisms and explore the possibility of targeted inhibition of these pathways for re-sensitizing the cells to TTFields.

Material and Methods

GBM U-87 MG, ovarian A2780, and NSCLC H1299 cells were treated with TTFields (1.7 V/cm RMS, 200 or 150 kHz) for continuous long-term application (7 or 13 days, specific conditions depending on the cell line). Changes in signaling pathways in these cells relative to cells exposed to short term TTFields application (3 or 7 days, depending on cell line) were examined by Luminex multiplex assay. Specific pathway markers were examined by immunohistochemistry of tumor sections from sham or TTFields-treated rats bearing N1S1 HCC tumors. TTFields were then co-applied with relevant pathway inhibitors, followed by cell count measurements and western blot examinations for specific pathway markers. The concomitant application of TTFields with a selected inhibitor was tested in mice inoculated orthotopically with MOSE-L firefly luciferase (FFL) ovarian cancer cells. Tumor volume was measured at study end by luciferin signal detection using the In Vivo Imaging System (IVIS).

Results

Cancer cells exposed to long-term application of TTFields displayed decreased sensitivity to TTFields. The PI3K/AKT/mTOR pathway was activated in these cells, with significant increases in AKT and RPS6 phosphorylation levels also observed in HCC tumors from rats treated with TTFields. PI3K inhibitors re-sensitized the cells to TTFields cytotoxicity, with associated down regulation of AKT phosphorylation. Application of TTFields concomitant with the PI3K inhibitor alpelisib resulted in enhanced efficacy in the ovarian cancer mouse model.

Conclusions

The current research demonstrated that PI3K/AKT/mTOR signaling pathway activation was involved in the response to long-term application of TTFields, with increased phosphorylation of key proteins observed both in vitro and in vivo. Concomitant treatment with PI3K inhibitors and TTFields re-sensitized the cells to TTFields, as it alleviated TTFields-induced AKT activation.

P10.01.A Reversible blood-brain barrier (BBB) disruption by Tumor Treating Fields (TTFields) in a human 3Din vitro model

Background

Drug delivery to the central nervous system (CNS) is often impeded by the restrictive nature of the blood brain barrier (BBB). Since many therapeutic molecules are not able to traverse this barrier, the development of new methods to disrupt the BBB is of paramount importance. Tumor Treating Fields (TTFields) are alternating electric fields of low intensity (1-3 V/cm) and intermediate frequency (100-300 kHz), which are approved and effective for the treatment of glioblastoma at a frequency of 200 kHz. We recently demonstrated that TTFields at lower frequencies are able to transiently induce BBB permeability in in vitro and in vivo murine models. Here, we explored whether the transient opening of the BBB by TTFields in our murine systems also translates to a human cell-based 3D model.

Material and Methods

A three-dimensional BBB model was established by co-culturing primary human brain microvascular endothelial cells (HBMVEC) on a transwell insert together with human pericytes on the bottom of a well-plate. The model was treated with TTFields at 100-300 kHz for 2496 h using the inovitro™ TTFields Lab Bench System (Novocure®). Afterwards, the cells recovered for 24-96 h. In order to analyze the effects of TTFields on barrier integrity and compromise, transendothelial electrical resistance (TEER) of the HBMVEC monolayer was measured before the start of TTFields treatment, immediately after TTFields cessation, as well as 24-96 h after TTFields treatment. Permeability of the barrier was assessed by visualizing the movement of FITC-dextran through the HBMVEC monolayer. In addition, changes in expression and localization of the tight junction protein (TJP) claudin-5 (Cl-5) after application of TTFields were analyzed by fractionated Western-blotting and immunofluorescence (IF) staining, respectively.

Results

Application of TTFields at all investigated frequencies significantly decreased TEER across the HBMVEC monolayer after as early as 24 h, with the strongest effects seen after 72 h at a TTFields frequency of 100 kHz. TTFields treatment delocalized TJP Cl5 from the cell boundaries to the cytoplasm as evidenced by Western-blots and IF stainings. Restoration of the cell barrier was already measurable as early as 24 h after TTFields cessation and a complete recovery was evident after 48 h.

Conclusion

These results in a human 3D in vitro model confirm our previous observations from mouse models that TTFields could transiently open the BBB. These fundamental pre-clinical data demonstrate the feasibility of facilitating drug delivery to the CNS via concomitant application of TTFields. This method opens up the prospect of improved drug-based treatment of devastating CNS diseases such as GBM if these results could be translated to the clinical setting in the future.

Abstract 2601: Concomitant treatment of ovarian cell lines with Tumor Treating Fields (TTFields) and PARP inhibitors

Background: PARP inhibitors (PARPi) are an effective treatment option for ovarian cancer patients harboring deleterious BRCA mutations. While such mutations prevail in one third of ovarian cancer patients, most of the other patients gain little survival benefit by the use of PARPi. Tumor Treating Fields (TTFields) are alternating electric fields with antimitotic effects on cancerous cells, also shown to induce a state of BRCAness in several types of cancer cell lines. The current study aimed to explore the potential of combining TTFields with PARP inhibition for the treatment of ovarian cancer in vitro.

Methods: Ovarian carcinoma cells A2780 (BRCA1/2 wild type) and OVCAR3 (BRCA1 wild type, BRCA2 deep deletion) were treated with TTFields using the inovitro system. Treatment was applied for 72 h at an intensity of 1.2 V/cm RMS and frequency of 200 kHz. The efficacy of concomitant application of TTFields with the PARP inhibitors niraparib and olaparib was examined via measurements of cell survival, colony forming ability, overall effect (multiplicity product of cytotoxicity and clonogenicity), and apoptosis induction.

Results: A2780 or OVCAR3 cells treated with TTFields displayed about 50% reduction in cell counts. Co-application of TTFields with PARPi enhanced the cytotoxic effect compared to that demonstrated by TTFields or PARPi alone. Concomitant application also resulted in reduced clonogenicity, enhanced overall effect, and increased apoptosis.

Conclusions: The results suggest potential benefits for TTFields concomitant with PARP inhibiting agents for treatment of ovarian cancer.

Citation Format: Antonia Martinez-Conde, Eyal Dor-On, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Concomitant treatment of ovarian cell lines with Tumor Treating Fields (TTFields) and PARP inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2601.

Abstract 1801: Application of Tumor Treating Fields (TTFields) to cancer cells enhances their membrane permeability

INTRODUCTION: Tumor Treating Fields (TTFields) are alternating electric fields at intermediate frequencies that exert anti-mitotic effects on cancerous cells. TTFields therapy is approved in several territories for treatment of glioblastoma (GBM) and unresectable malignant pleural mesothelioma. Recently, membrane permeability of GBM cells has been found to be increased in response to TTFields application. The current study aimed to further explore this effect, testing the potential of TTFields to facilitate cellular accumulation of the anticancer agent doxorubicin (DOX) in breast carcinoma cells.

METHODS: 4T1 breast mammary carcinoma cells were treated with TTFields (1.7 V/cm RMS) for 72 h across a frequency range (50-500 kHz). Cytotoxicity was examined by cell counts, and permeability determined by 7-aminoactinomycin D (7-AAD) intracellular accumulation, both measured by flow cytometry. Next, TTFields at the frequency inducing highest permeability was applied to chemotherapy-sensitive and matched chemotherapy-resistant cells. Intracellular accumulation of DOX and drug-induced cytotoxicity were measured by flow cytometry. In vivo validation was performed by 72 h delivery of TTFields at the frequency of maximal permeability to mice orthotopically inoculated with 4T1 cells and injected with DOX 24 h before treatment cessation. DOX florescence was measured using in vivo imaging system (IVIS) for whole tumor assessment and flow cytometry for detection at the single-cell level.

RESULTS: While highest TTFields-induced cytotoxicity was observed at 150 kHz, 7-AAD intracellular accumulation was maximal at 300 kHz. When TTFields were delivered concomitant with DOX, the drug accumulated to the same extent in chemotherapy-resistant cells as in chemotherapy-sensitive cells. Application of TTFields also sensitized both cell types to DOX, with cytotoxicity observed at low drug concentrations. Furthermore, 2- to 3-fold higher DOX accumulation was seen in tumors isolated from mice treated with TTFields relative to control.

CONCLUSIONS: Permeability of 4T1 breast cancer cells was elevated by TTFields, allowing enhanced intracellular accumulation of DOX and improving drug efficacy, even in chemotherapy-resistant cells. Increased cellular accumulation of DOX was also demonstrated in vivo.

Citation Format: Bella Koltun, Tali Voloshin, Tal Kan, Lilach Koren, Yaara Porat, Alexandra Volodin, Noa Kaynan, Anat Klein-Goldberg, Rom Paz, Boris Brant, Yiftah Barsheshet, Efrat Zemer-Tov, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Application of Tumor Treating Fields (TTFields) to cancer cells enhances their membrane permeability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1801.

Abstract 387: Blood brain barrier (BBB) disruption by tumor treating fields (TTFields) in a human 3D in vitro model

The clinical translatability of novel drug delivery systems begins with basic scientific breakthroughs. Our recent discovery of the ability of Tumor Treating Fields (TTFields) to potentially and transiently disrupt the blood brain barrier (BBB) using our murine in vitro and in vivo models, led us to validate our findings in a human 3D in vitro model established in our lab. The model consists of primary brain microvascular endothelial cells co-cultured with immortalized perciytes in a transwell system. TTFields are alternating electric fields of low intensity (1-3V/cm) and intermediate frequency (100-300kHz), which are effective and approved for the treatment of glioblastoma (GBM) using 200kHz frequency. Our murine data point out that TTFields could disrupt the BBB optimally at 100kHz. To investigate if TTFields exhibit similar effects in the human cell-based in vitro model, it was subjected to TTFields at various frequencies for 24-96h. Cells were afterwards made to recover for 24-96h. To assess BBB integrity and compromise, transendothelial electrical resistance (TEER) was measured before start of TTFields, immediately after end of TTFields, as well as 24-96h after TTFields. In addition, a permeability assay was performed. Finally, immunofluorescence (IF) staining visualized the effects of TTFields on tight junction protein claudin-5 localization. TTFields application of all investigated frequencies significantly decreased TEER. However, the strongest effects were observed with 100kHz after 72h. IF staining revealed delocalization of claudin-5 from the cell boundaries to the cytoplasm. Restoration of cell integrity was already evident as early as 24h, with complete recovery after 48h. Results using our human 3D in vitro model validated our previous observations from murine in vitro and in vivo models that TTFields could transiently disrupt the BBB. These findings provide fundamental pre-clinical data for translation from bench to bedside. Accordingly, TTFields demonstrate to be a promising novel approach in opening the BBB to facilitate drug delivery for improved treatment of central nervous system diseases including devastating brain tumors such as GBM.

Citation Format: Ellaine Salvador, Almuth F. Kessler, Theresa Köppl, Sebastian Schönhärl, Malgorzata Burek, Catherine Tempel Brami, Tali Voloshin, Moshe Giladi, Ralf-Ingo Ernestus, Mario Löhr, Carola Y. Förster, Carsten Hagemann. Blood brain barrier (BBB) disruption by tumor treating fields (TTFields) in a human 3D in vitro model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 387.

Abstract 3465: Efficacy of concomitant application of Tumor Treating Fields (TTFields), temozolomide and lomustine in glioblastoma cancer cells in vitro

Background: Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. Newly diagnosed GBM (ndGBM) is treated with adjuvant temozolomide (TMZ), however, more than 50% of patients do not respond to therapy. Tumor Treating Fields (TTFields) therapy concomitant with maintenance TMZ was approved by the FDA in 2015 and represents a major advance in treatment of patients with ndGBM. Recently, lomustine (CCNU) together with TMZ demonstrated improved overall and progression-free survival following resection and radiochemotherapy in patients with ndGBM. Accordingly, the current study aimed to examine the effect of concomitant application of TTFields with TMZ and CCNU in GBM cells.

Methods: GBM cells (U-87 MG and LN229) were treated for 72 h with TTFields at a frequency of 200 kHz and an intensity of 1 V/cm RMS using the inovitro system. Efficacy of combining TTFields with TMZ and/or CCNU was tested by measuring cell survival, clonogenic potential, overall effect (multiplicity product of cytotoxicity and clonogenicity), and apoptosis induction.

Results: Combination of TMZ and TTFields resulted in increased cytotoxicity compared with each treatment alone. The cytotoxic effect resulting from co-application of CCNU with TTFields suggested a synergistic interaction between the two modalities. The clonogenic, overall, and apoptotic effects of TMZ and CCNU were also enhanced following co-treatment with TTFields. The triple combination of TTFields with both TMZ and CCNU was more efficacious than TMZ/CCNU or TTFields separately.

Conclusions: The current research suggests potential benefits for the treatment of GBM using concomitant application of TTFields with TMZ/CCNU.

Citation Format: Hila Fishman, Roni Monin, Eyal Dor-On, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Efficacy of concomitant application of Tumor Treating Fields (TTFields), temozolomide and lomustine in glioblastoma cancer cells in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3465.

Abstract 2037: Spatial omic changes of malignant pleural mesothelioma following treatment using tumor-treating fields

Background: Application of alternating-electric fields as cancer-directed therapy known as Tumor-Treating Fields (TTFields) has been shown to be effective by exerting dipole alignment forces on polar microtubule subunits and dielectrophoretic forces in the cytokinetic furrow. This effect results in disruption of mitosis at the cellular level, and at the clinical level with significantly prolonged overall survival of patients with glioblastoma and malignant pleural mesothelioma (MPM). The molecular alterations that occur at the genomic and transcriptomic levels following TTFields treatment are unknown. We applied a spatial omics approach to elucidate spatial intratumoral effects of TTFields at the molecular level in regions of interest (ROI) in a mouse model of MPM.

Methods: Eight Balb/C mice were injected with AB1 MPM cells until sizable tumors were observed (2-3 weeks). TTFields were applied, with heat sham used as a negative control. After 14 days (6 days of treatment, 2 days of rest, then 6 more days of treatment) tumors were resected, fixed and paraffin embedded. Following the Nanostring GeoMx protocol, thin sections of all eight tumors were placed on a slide, and incubated with both Ki-67 antibodies, and a GeoMx Mouse Cancer Transcriptome Atlas RNA probe set. Using Ki-67 staining as a guide, 12 ROIs were selected across each tumor to capture intratumoral heterogeneity, including the core and periphery of each tumor The DSP barcoded RNA probes were cleaved, sequenced and analyzed. We compared differential expression of subset gene classes of TTFields vs heat sham treated tumors; results were further stratified into Ki-67 high and low subsets for each sample. Results were assessed by Gene Set Enrichment.

Results: Sham-treated tumors grew to over 300 mm3; TTFields-treated tumors averaged 100 mm3, confirming anti-tumor effect. Gene Set Enrichment Analysis uncovered upregulation of genes associated with interferon-alpha and -gamma responses in TTFields-treated tumors, which also displayed downregulation of pathway components associated with glycolysis, mTOR signaling, oxidative phosphorylation, cell invasion, hypoxia, and TNF-alpha signaling. Spatial analysis detected a heterogeneous response and differential expression between different portions of tumors.

Conclusions: TTFields application induces clear patterns of differential expression in the transcriptome of treated tumors, including an increasingly immune-stimulated tumor microenvironment that also affects molecular pathways critical to cellular proliferation and invasion. These findings point the way toward improved understanding of timing and sequences of TTFields in relation to systemic cytotoxic, targeted, and immune modulation forms of therapeutic strategies. Our finding of upregulated immune response implicates TTFields as a potential synergistic tactic when coupled with immunotherapeutic approaches.

Citation Format: Emil Lou, Katherine Ladner, Kerem Wainer-Katsir, Karina Deniz, Yaara Porat, Boris Brant, Shiri Davidi, Yuki Padmanabhan, Phillip Wong, Amrinder Nain, Clifford J. Steer, Moshe Giladi. Spatial omic changes of malignant pleural mesothelioma following treatment using tumor-treating fields [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2037.

Abstract 1866: Transcriptomics analysis for identification of pathways involved in the response to Tumor Treating Fields (TTFields)

Introduction: Tumor Treating Fields (TTFields) are alternating electric fields that disrupt the function of polarized molecules within cancer cells. Initial data showed an anti-mitotic effect on cancerous cells whilst more recent findings confirmed additional effects such as downregulation of DNA double strand break repair, replication stress, upregulation of autophagy, and immunogenic cell death. Identification of TTFields-driven alterations in pan-cancer and tumor specific pathway is needed to aid selection of therapeutic modalities to be applied concomitant with TTFields for improved treatment outcomes. The aim of this study was to identify common pathways involved in the response to TTFields by comparing transcriptomics of various tumor type.

Methods: Control and TTFields-treated non-small cell lung carcinoma cell lines and animal model, glioblastoma (GBM) cell lines and patient-derived cell lines, and a hepatocellular carcinoma animal model were examined. Samples from GBM patients treated with concomitant TTFields and temozolomide (TMZ) were compared to samples from patients treated with TMZ alone. A list of differentially expressed genes (DEGs) was generated from transcriptomics analysis. Enrichment analysis was conducted according to the Gene Set Enrichment Analysis (GSEA) of MSigDB, Reactome, and Kegg pathway databases. Significantly overlapping pathways were identified using ActivePathways package according to the Reactome and Kegg gene sets, and an enrichment map was created according to the number of datasets supporting each pathway.

Results: DEGs in response to TTFields application included genes of the cytoskeleton, immune system, and some secretion proteins. Common pathways downregulated by TTFields (negative GSEA) included DNA repair, DNA and RNA synthesis, and cell cycle regulation, specifically the G2M checkpoint, E2F targets, and Myc targets. Common pathways upregulated by TTFields (positive GSEA) included the immune response, specifically complement cascades, coagulation, and lysosome activity. ActivePathways enrichment map results agreed with the gene set enrichment results, and revealed additional pathways involved in the response to TTFields, such as SUMOylation, metabolism of carbohydrates, unfolded protein response, and signaling by interleukins.

Conclusions: Transcriptomic analysis revealed common pathways involved in the responses to TTFields, regardless of the origin of the sample. Some identified pathways were in line with previously demonstrated effect of TTFields, such as mitotic interference, inhibition of DNA damage repair and upregulation of the innate immune response. New pathways revealed in this work support the examination of novel combination strategies with TTFields to increase the therapeutic effect in patients bearing various solid tumor types.

Citation Format: Kerem Wainer-Katsir, Gitit Lavy-Shahaf, Shiri Davidi, Sara Jacobovitch, Tali Voloshin, Itai Tzchori, Yaara Porat, Lianghao Ding, Michael Story, Niv Pencovich, Ilan Volovitz, Joshua Branter, Stuart J. Smith, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Transcriptomics analysis for identification of pathways involved in the response to Tumor Treating Fields (TTFields) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1866.

Abstract 2659: Inhibition of PI3K sensitized cancer cells to Tumor Treating Fields (TTFields)

Introduction: Tumor Treating Fields (TTFields) are alternating electric fields, delivered noninvasively to the tumor site. TTFields therapy is currently approved for treatment of patients with newly diagnosed glioblastoma (GBM), recurrent GBM, or unresectable malignant pleural mesothelioma. Investigations are ongoing in additional tumor types, including non-small cell lung carcinoma (NSCLC), ovarian cancer, and hepatocellular carcinoma (HCC). Although TTFields have been demonstrated to extend life, most patients will eventually progress. The current research aimed to identify molecular mechanisms involved in reduced cancer cellular sensitivity to TTFields, and the potential of targeting these pathways to re-sensitize the cells to TTFields.

Methods: Continuous long-term application of TTFields (7 or 13 days, depending on the cell line) generated cancer cells with reduced sensitivity to TTFields. Luminex multiplex assay was used to detect changes in signaling pathways in ovarian A2780 and GBM U-87 MG cells, and relevant pathway markers were validated by Western blot. Further validation was performed by immunohistochemistry of tumor sections from N1S1 HCC tumor-bearing rats treated with sham or TTFields. The significance of the identified pathways in reducing cancer cell sensitivity to TTFields was evaluated through in vitro combination treatment with PI3K inhibitors, followed by cell count measurements. Finally, the concomitant application of TTFields and the PI3K inhibitor Alpelisib was evaluated in mice orthotopically implanted with MOSE-L firefly luciferase (FFL) ovarian cancer cells. Tumor volume was measured using the In Vivo Imaging System (IVIS) to detect the luciferin signal, before and after treatment.

Results: Cancer cell sensitivity to TTFields was reduced following continuous long-term application of TTFields. This was accompanied by activation of the PI3K/AKT/mTOR signaling pathway, with significant increases in the levels of phosphorylated AKT and RPS6 observed in cell cultures and in rat tumor sections following application of TTFields. Application of PI3K inhibitors re-sensitized the cells to TTFields in vitro. In vivo, concomitant application of TTFields with Alpelisib resulted in enhanced efficacy.

Conclusions: The current study demonstrated that reduced cancer cell sensitivity to long-term application of TTFields is mediated by activation of the PI3K/AKT/mTOR signaling pathway. Furthermore, PI3K inhibitors were shown to re-sensitize the cells to TTFields, providing a rationale for further examining the potential benefit of TTFields concomitant with PI3K inhibitors.

Citation Format: Anat Klein-Goldberg, Tali Voloshin, Efrat Zemer-Tov, Rom Paz, Lilach Koren, Kerem Wainer-Katsir, Alexandra Volodin, Bella Koltun, Boris Brant, Yiftah Barsheshet, Tal Kan, Adi Haber, Moshe Giladi, Uri Weinberg, Yoram Palti. Inhibition of PI3K sensitized cancer cells to Tumor Treating Fields (TTFields) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2659.

Structural basis for long-chain isoprenoid synthesis by cis-prenyltransferases

Isoprenoids are synthesized by the prenyltransferase superfamily, which is subdivided according to the product stereoisomerism and length. In short- and medium-chain isoprenoids, product length correlates with active site volume. However, enzymes synthesizing long-chain products and rubber synthases fail to conform to this paradigm, because of an unexpectedly small active site. Here, we focused on the human cis-prenyltransferase complex (hcis-PT), residing at the endoplasmic reticulum membrane and playing a crucial role in protein glycosylation. Crystallographic investigation of hcis-PT along the reaction cycle revealed an outlet for the elongating product. Hydrogen-deuterium exchange mass spectrometry analysis showed that the hydrophobic active site core is flanked by dynamic regions consistent with separate inlet and outlet orifices. Last, using a fluorescence substrate analog, we show that product elongation and membrane association are closely correlated. Together, our results support direct membrane insertion of the elongating isoprenoid during catalysis, uncoupling active site volume from product length.

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

464

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.

DDRE-46. REDUCED CANCER CELL SENSITIVITY TO TUMOR TREATING FIELDS (TTFields) THROUGH ACTIVATION OF THE PI3K/AKT/mTOR SIGNALING PATHWAY CAN BE MITIGATED USING PI3K INHIBITORS OR PI3K/mTOR DUAL INHIBITORS

INTRODUCTION

Tumor Treating Fields (TTFields) therapy is an approved anti-cancer treatment modality applied non-invasively and loco-regionally to the tumor region. TTFields have been demonstrated to extend life, however, most patients do eventually progress. The current study aimed to identify potential molecular mechanisms involved in reduced cellular sensitivity to TTFields.

METHODS

Cancer cells that exhibit reduced sensitivity to TTFields were generated by continuous long duration application of TTFields (7 or 13 days, depending on the cell line). Changes in cellular signaling pathways were evaluated in ovarian A2780 and glioblastoma U-87 MG cancer cells exposed to long-term relative to short-term (3 or 7 days, depending on the cell line) treatment with TTFields using Luminex multiplex assay followed by Western blot validation. The relevance of the affected pathways was confirmed through evaluation of the response to long-term application of TTFields in combination with pharmacological pathway inhibitors by measuring cell counts, apoptosis, and clonogenicity. Relevant pathway markers in tumor sections from tumor-bearing rats treated with TTFields were examined using immunohistochemistry.

RESULTS

Continuous long-term application of TTFields reduced cellular sensitivity to TTFields and was accompanied by increased levels of phosphorylated AKT, mTOR and additional proteins from the PI3K/AKT/mTOR signaling pathway. Increased phosphorylation of AKT was also evident in tumor sections from rats treated with TTFields. Concomitant use of TTFields with PI3K inhibitors or PI3K/mTOR dual inhibitors sensitized A2780 cells to long-term TTFields application.

CONCLUSION

Our study demonstrates that decreased cancer cell sensitivity to long-term TTFields application is mediated by activation of the PI3K/AKT/mTOR signaling pathway and provides a rationale for further examining the potential benefit of combining TTFields with PI3K or PI3K/mTOR dual inhibitors.

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.

Two de novo GluN2B mutations affect multiple NMDAR-functions and instigate severe pediatric encephalopathy

The N-methyl-D-aspartate receptors (NMDARs; GluNRS) are glutamate receptors, commonly located at excitatory synapses. Mutations affecting receptor function often lead to devastating neurodevelopmental disorders. We have identified two toddlers with different heterozygous missense mutations of the same, and highly conserved, glycine residue located in the ligand-binding-domain of GRIN2B: G689C and G689S. Structure simulations suggest severely impaired glutamate binding, which we confirm by functional analysis. Both variants show three orders of magnitude reductions in glutamate EC₅₀, with G689S exhibiting the largest reductions observed for GRIN2B (~2000-fold). Moreover, variants multimerize with, and upregulate, GluN2Bwt-subunits, thus engendering a strong dominant-negative effect on mixed channels. In neurons, overexpression of the variants instigates suppression of synaptic GluNRs. Lastly, while exploring spermine potentiation as a potential treatment, we discovered that the variants fail to respond due to G689’s novel role in proton-sensing. Together, we describe two unique variants with extreme effects on channel function. We employ protein-stability measures to explain why current (and future) LBD mutations in GluN2B primarily instigate Loss-of-Function.

Abstract 2011: Tumor treating fields induce cellular and morphologic changes including disruption of intercellular communication networks in malignant pleural mesothelioma

Tumor Treating Fields (TTFields) is a novel therapeutic strategy that uses alternating electric fields to disrupt mitosis in actively dividing cells through exertion of dielectrophoretic force and dipole alignment on microtubule subunits. However, the additional effects of TTFields on cellular morphology and communication remain unclear. Tunneling nanotubes (TNTs) are ultrafine F-actin-based protrusions that facilitate intercellular communication through cell-cell contact, including efficient transport of molecular cargo that accelerate invasive potential and chemoresistance. We hypothesized that by creating dielectrophoretic force on polar actin subunits, treatment with TTFields would lead to sustained disruption or prevention of formation of MPM TNTs.

TTFields (200 kHz) were applied at 0.5 or 1.0 V/cm to VAMT and MSTO MPM cell lines using the Inovitro system (Novocure). TNT index (average # of TNTs/cell) was determined at 0, 24, 48, and 72 hours of TTFields application. At the 72 hour period, TTFields were discontinued and assessment for recovery of TNT formation was performed after an additional 24 hours. Cell viability was determined by staining with NucGreen 488 dye. We also used time-lapse microscopy with concurrent application of TTFields and the chemotherapeutic agents cisplatin and pemetrexed to analyze effects on TNTs and functional cargo transfer.

Application of continuous TTFields at 1.0 V/cm, but not at 0.5 V/cm, suppressed TNT formation by 48.9% in MSTO (p=0.005). This suppression was achieved at the 48-hour time point and was independent of cell proliferation. No significant differences in TNT index were noted for VAMT. Cell viability was consistently above 95% at all time points for both cell lines at the stated frequency and intensities. Cargo transfer rates were lower in experimental groups treated with TTFields and either cisplatin, pemetrexed, or both.

Here, we show that treatment with TTFields suppresses formation of TNTs between MSTO cells, but not VAMT, suggesting additional factors that may determine susceptibility to TTFields treatment. Additionally, TTFields treatment of MSTO decreased the function of TNTs in these cells, as demonstrated by lower cargo transfer rates. In sum, these data identify effects of TTFields on TNTs as a novel mechanism for this therapeutic modality.

Citation Format: Akshat Sarkari, Sophie Korenfeld, Katherine Ladner, Phillip Wong, Antonia Martinez, Eyal Dor-On, Moshe Giladi, Amrinder Nain, Emil Lou. Tumor treating fields induce cellular and morphologic changes including disruption of intercellular communication networks in malignant pleural mesothelioma [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 2011.

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.