Unresectable Malignant Pleural Mesothelioma Research Articles

True Benefits of Immune Checkpoint Inhibitors in the Treatment of Malignant Pleural Mesothelioma in Japan.

In February 2004, the Food and Drug Administration (FDA) was the first to approve the combination of cisplatin (CDDP) and pemetrexed (PEM) as standard first-line chemotherapy for untreated, unresectable malignant pleural mesothelioma (MPM). However, after that approval, no progress was made in the standard first-line treatment of MPM for almost 15 years. Positive results from a phase 3 study (Mesothelioma Avastin Cisplatin Pemetrexed Study: MAPS) verifying the effect of bevacizumab, an anti-angiogenesis agent added to CDDP/PEM for unresectable MPM, were published in The Lancet in December 2015; however, this did not lead to approval by national drug regulatory agencies. Furthermore, no second-line treatment was established for cases refractory to CDDP/PEM. In August 2018, the Pharmaceuticals and Medical Devices Agency of Japan was the first in the world to approve monotherapy with nivolumab, an immune checkpoint inhibitor (ICI), for previously unresectable, advanced, or recurrent MPM. Following Japan, in October 2020, the FDA approved the combination of nivolumab and ipilimumab for the treatment of previously untreated, unresectable MPM. In this article, we review the transition of drug treatment for MPM, in light of the historical background, focusing on the benefits of ICIs.

Real-world safety of nivolumab in patients with malignant pleural mesothelioma in Japan: post-marketing surveillance study.

This post-marketing surveillance (PMS) was conducted to evaluate the incidence of adverse events with nivolumab in patients with unresectable, advanced or recurrent malignant pleural mesothelioma (MPM) that had progressed after first-line chemotherapy and to identify factors that potentially affected its safety in real-world clinical practice. Patients who had not received nivolumab previously were registered between November 2018 and February 2021. Nivolumab was given intravenously 240mg every 2weeks or 480mg every 4weeks. Patients were followed up for 6months after treatment initiation. Information on patient characteristics, treatment status, and adverse events was collected. This PMS enrolled 124 patients, involving 48 sites across Japan. At 6months, nivolumab therapy was ongoing in 35.5% of patients (44/124) and had been discontinued in 64.5% (80/124). The overall incidence of treatment-related adverse events (TRAEs) was 40.3%; the incidence of Grade 3 or higher TRAEs was 12.9%. The pattern of TRAEs based on System Organ Class categories was generally consistent with those seen in the Japanese phase II MERIT study. The most common Grade 3 or higher TRAEs were interstitial lung disease (2.4%), lung disorder, and diarrhea (each 1.6%). The incidence of TRAEs was significantly higher in inpatients or patients who had good PS, high bodyweight, high body mass index, or autoimmune diseases than in those without these characteristics. The post-marketing incidence of TRAEs with nivolumab in patients with MPM has been evaluated, and no new safety signals were identified compared to the phase II clinical trial in Japan.

Comparison of FDG-PET/CT and CT for evaluation of tumor response to nivolumab plus ipilimumab combination therapy and prognosis prediction in patients with unresectable malignant pleural mesothelioma.

Results for malignant pleural mesothelioma (MPM) patients following first-line treatment with nivolumab plus ipilimumab obtained with immunotherapy-modified PERCIST (imPERCIST), shown by [18F]fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT), and modified RECIST (mRECIST), shown by CT, were compared for response evaluation and prognosis prediction. imPERCIST indicated nine progressive metabolic disease (PMD), eight stable metabolic disease (SMD), four partial metabolic response (PMR), and five complete metabolic response (CMR) cases. mRECIST showed nine with progressive disease (PD), nine stable disease (SD), seven partial response (PR), and one complete response (CR). Although high concordance was noted (κ = 0.827), imPERCIST correctly judged a greater percentage with CMR (15.4%). Following a median 10.0 months, 15 patients showed progression and eight died from MPM. With both, progression-free survival (PFS) and overall survival (OS) were significantly longer in patients without progression (CMR/PMR/SMD, CR/PR/SD, respectively) as compared to PMD/PD patients (imPERCIST p < 0.0001 and p = 0.015, respectively; mRECIST p < 0.0001 and p = 0.015, respectively). Twenty-six patients (23 males, 3 females; median 73.5 years) with histologically proven MPM and no curative surgery received nivolumab plus ipilimumab combination therapy. FDG-PET/CT and diagnostic CT scanning at the baseline, and after 2-4 cycles (2 in three, 3 in 17, 4 in six patients) were performed. Therapeutic response findings evaluated using imPERCIST and mRECIST were compared. PFS and OS analyses were done using log-rank and Cox methods. For unresectable MPM patient examinations, FDG-PET and CT provide accurate findings for evaluating tumor response and also prognosis prediction following first-line nivolumab plus ipilimumab immunotherapy (approximately three cycles).

60 First-line Nivolumab/Ipilimumab in patients with unresectable malignant pleural Mesothelioma (MPM): West of Scotland experience

60 First-line Nivolumab/Ipilimumab in patients with unresectable malignant pleural Mesothelioma (MPM): West of Scotland experience

P2.18-04 Real-world Study on Efficacy of First-Line Nivolumab + Ipilimumab in Unresectable Malignant Pleural Mesothelioma (ImmunoMeso)

P2.18-04 Real-world Study on Efficacy of First-Line Nivolumab + Ipilimumab in Unresectable Malignant Pleural Mesothelioma (ImmunoMeso)

First-line nivolumab plus ipilimumab for unresectable MPM in China: a cost-effectiveness analysis

BackgroundThe regimen of nivolumab plus ipilimumab (NI) has been recommended by the National Comprehensive Cancer Network Clinical Practice Guidelines in Oncology-Malignant Pleural Mesothelioma (Version 1.2022) and Chinese Guidelines for the Clinical Diagnosis and Treatment of Malignant Pleural Mesothelioma (2021 edition) as the first-line treatment for Malignant Pleural Mesothelioma (MPM). But whether immunotherapy has a financial advantage over conventional chemotherapy (pemetrexed plus cisplatin/carboplatin, C) is uncertain.MethodsBased on survival and safety data from the CheckMate 743 clinical trial (NCT02899299), a partitioned survival model was constructed using TreeAge Pro2022 software. The model cycle was set to 1 month and the study period was 10 years. The output indicators included total cost, quality-adjusted life year (QALY) and incremental cost-effectiveness ratio (ICER). One-way and probabilistic sensitivity analyses were used to assess the robustness of the results, considering only direct medical costs.Results and discussionThe ICER for group NI versus Group C was $375,656/QALY in all randomized patients, $327,943/QALY in patients with epithelioid histology, and $115,495/QALY in patients with non-epithelioid histology. The ICERs of all three different populations all exceeded the willingness-to-pay threshold (three times the per capita gross domestic product of China in 2021). The results of univariate sensitivity analysis showed that the price of pemetrexed and nivolumab had great influence on the analysis results. The results of the probabilistic sensitivity analysis show that the probability of the NI scheme being more economical in all three different populations was 0.What is new and conclusionFrom the perspective of the Chinese healthcare system, in patients with unresectable MPM, NI has no economic advantage over C.

2187P Efficacy and safety of gemcitabine as maintenance treatment in unresectable malignant pleural mesothelioma: A phase II randomized study

2187P Efficacy and safety of gemcitabine as maintenance treatment in unresectable malignant pleural mesothelioma: A phase II randomized study

ONCOS-102 plus pemetrexed and platinum chemotherapy in malignant pleural mesothelioma: a randomized phase 2 study investigating clinical outcomes and the tumor microenvironment

BackgroundONCOS-102, an oncolytic adenovirus expressing granulocyte-macrophage colony-stimulating factor, can alter the tumor microenvironment to an immunostimulatory state. Combining ONCOS-102 with standard-of-care chemotherapy for malignant pleural mesothelioma (MPM) may improve treatment...

Cost Effectiveness and Budget Impact of Nivolumab Plus Ipilimumab Versus Platinum Plus Pemetrexed (with and Without Bevacizumab) in Patients with Unresectable Malignant Pleural Mesothelioma in Switzerland.

Malignant pleural mesotheliomas (MPMs) are aggressive and often unresectable. In the past, chemotherapy was the standard for palliative treatment. However, immunotherapy with nivolumab+ipilimumab has recently received marketing approval. This study evaluated the cost effectiveness of nivolumab+ipilimumab versus pemetrexed+platinum (with/without bevacizumab) for Swiss patients with unresectable MPM, overall and by histological subtype. We developed a three-state Markov cohort model with a cycle length of 1month, a 30-year time horizon, and a discount rate of 3% per year for costs and benefits. The model included the updated survival and treatment-dependent utility results from the Checkmate-743 and MAPS registration trials. A Swiss statutory health insurance perspective was considered with unit costs for 2022 from publicly available and real-world sources. We assumed a willingness-to-pay (WTP) threshold of CHF100,000/QALY. Model robustness was explored in sensitivity and scenario analyses. Compared with chemotherapy, nivolumab+ipilimumab incurred additional costs of CHF109,115 and 0.57 additional quality-adjusted life-years (QALYs), yielding an incremental cost-effectiveness ratio (ICER) of CHF192,585/QALY (i.e. USD201,829/QALY) gained. Relative to their 2022 list price, nivolumab+ipilimumab may be cost effective if priced at 48% across all histologies. Assuming cisplatin-based instead of carboplatin-based chemotherapy reduced the ICER to CHF158,911/QALY (i.e. USD166,539/QALY). For the non-epithelioid subtype, nivolumab+ipilimumab was cost effective compared with chemotherapy (ICER of CHF97,894/QALY, i.e. USD102,593/QALY). Chemotherapy+bevacizumab was often a dominated strategy or would require a bevacizumab cost reduction to 28%. Our model projected nivolumab+ipilimumab to be cost effective for the non-epithelioid subtype but not for all histologies. Substantial discounts for nivolumab+ipilimumab would be necessary to achieve cost effectiveness for all histologies.

Granular analysis of individual immune-related gene expression in a randomized phase I/II study of the oncolytic adenovirus, ONCOS-102, in combination with pemetrexed/cisplatin (P/C) in patients (pts) with unresectable malignant pleural mesothelioma (MPM).

e20536 Background: ONCOS-102 is an oncolytic adenovirus expressing granulocyte-macrophage colony stimulating factor (GM-CSF; Ad5/3-D24-GMCSF) that stimulates immune responses and modulates the tumor microenvironment, both as a monotherapy and in combination with programmed cell death protein 1 (PD-1) blockade. We present granular analyses of individual immune-related gene expression in response to ONCOS-102 in a randomized phase I/II study in MPM. Methods: Following a safety run-in (n = 6), 25 pts were randomized to receive ONCOS-102 (3 x 1011 virus particles in 2.5 mL) intratumorally under CT or US guidance on Days 1, 4, 8, 36, 78 and 120, plus six cycles of P/C starting on Day 22 (ONCOS+P/C), or six cycles of P/C only (control). Both treatment-naïve (1L) and previously treated patients were enrolled. Survival was followed up to 30 months. Tumor biopsies were collected at baseline and Day 36, and immunofluorescence for immune cell subsets, RNASeq and qPCR were performed. Results: In the pooled population (n = 31), median overall survival (OS) was 16.6 vs 18.3 months for ONCOS-102 + P/C vs control arms ( P&gt; 0.05). In 1L patients (n = 17) median OS was 20.3 vs 13.5 months ( P&gt; 0.05), and 30-month OS rate was 34.1% vs 0. A significant increase in tumour-infiltrating immune cells was observed (baseline to Day 36) with ONCOS-102 + P/C (n = 20) but not control (n = 11) using immunofluorescence and transcriptome analysis. CD8+, GranzymeB+ CD8+ cells, and CD8+:regulatory T-cell and M1:M2 macrophage ratios increased in ONCOS-102-treated pts (P≤0.016). A difference in tumor immune-infiltration was observed in ONCOS-102 + P/C pts stratified by survival at Month 18: while deregulation of complement pathways and inflammatory response was seen at baseline, at Day 36 adaptive immune response and T-cell activation were observed in pts who were alive but not in those deceased. Additionally, GM-CSF protein, likely derived from ONCOS-102, was transiently present in higher concentration at Days 4 and 8 in 18-month survivors vs deceased pts. Based on a previously described predictive inflammatory gene signature for treatment with checkpoint inhibitors in mesothelioma, a binomial model assessing baseline transcriptome levels demonstrated 89% accuracy in predicting 18-month survival. Conclusions: ONCOS-102 caused increased T-cell infiltration and upregulated immune response-related gene expression in tumor lesions. A trend for prolonged OS was observed in the 1L setting, only. Consistent with observations in PD-1 resistant melanoma, ONCOS-102-induced immune response in the tumor is hallmarked by a high prevalence of cytotoxic T-cells and depolarization of macrophages, which may support addition of checkpoint inhibitors to the combination of ONCOS-102 plus P/C in MPM. Clinical trial information: NCT02879669 .

Real-life efficacy of nivolumab plus ipilimumab combination in untreated, unresectable malignant pleural mesotheliomas: Result of French early access program—MESOIMMUNE – GFPC 04-2021.

8536 Background: The SOC for unresectable malignant pleural mesothelioma (MPM) has changed in 2020 with the combination nivolumab plus ipilimumab (NIVO+IPI) results of CheckMate 743 study. As CheckMate 743 was therapeutic trial in selected MPM patients (pts), additional data would be of interest to confirm the results in real-life setting. Methods: The present multicenter, retrospective study assessed the outcomes of NIVO+IPI, via an early access program (EAP) in France, in pts with treatment naïve unresectable MPM. The primary objective was investigator-assessed real world progression-free survival (rwPFS) from initiation of NIVO+IPI, defined as time from first dose of NIVO+IPI to first documentation of objective disease progression or death from any cause. The secondary objectives were real world OS (rwOS), objective response rate (ORR), and safety of NIVO+IPI combination. Results: From April 1, 2021 to Feb 15, 2022 (last day of EAP) there were 143 pts included out of 350 pts treated by EAP for unresectable MPM in 44 centers. Population characteristics are described in the table. With a median follow-up of 14.1 months, median rwPFS was 7.8 months (95%CI 6.2-9.5). rwPFS rates no differ according to histological subtypes: rwPFS for epithelioid MPM was 8.1 months (95%CI 6.0-12.6) and 7.4 months (95% CI 5.3-11.2) for other histological subtypes. The median rwOS was not reached (NR), 1-year survival rate was 65% (95% CI 57-75%). Median rwOS was NR and 13.1 (95% CI 7.8- NA) in epithelioid and non-epithelioid MPM, respectively. At 1 year, 71.2% of pts with epithelioid MPM are still alive versus 51.2% in pts with other histological subtypes. ORR was 23.9% (95% CI 16.9-32.0%) with median time to response of 3.68 months (2.33-5.09) after introduction of NIVO+IPI. Disease control rate was 80.4%. Grade 3-4 adverse events (AE) occurred in 37.8%. Severe immune-related AE occurred in 13.9% of patients. Five deaths were associated with treatment-related AEs according to investigators judgment. Conclusions: While pt’s characteristics differed from the pivotal trial, notably with older and unselected patients, efficacy outcomes that we observed here compares favorably with CheckMate 743 results. Tolerance looks acceptable in real-life setting despite 5 toxic deaths reported. Extended follow-up of our cohort will allow consolidation of the results. Clinical trial information: NCT05308966 . [Table: see text]

138P Cost-effectiveness of nivolumab and ipilimumab versus chemotherapy (with and without bevacizumab) in patients with unresectable malignant pleural mesothelioma in Switzerland

138P Cost-effectiveness of nivolumab and ipilimumab versus chemotherapy (with and without bevacizumab) in patients with unresectable malignant pleural mesothelioma in Switzerland

Three distinct mechanisms underlying human γδ T cell-mediated cytotoxicity against malignant pleural mesothelioma.

Malignant pleural mesothelioma (MPM) is a rare and highly aggressive thoracic tumor with poor prognosis and limited therapeutic options. Although immune checkpoint inhibitors exhibit a promising effect in some patients with unresectable MPM in clinical trials, the majority of MPM patients show only modest response rates to the currently available treatments. It is thus imperative to develop novel and innovative therapeutic modalities for MPM, including immune effector cell-based therapies. γδ T cells were expanded using tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino) ethylidene-1,1-bisphosphonate (PTA) and interleukin-2, and the therapeutic potential of γδ T cells was examined through analyzing cell surface markers and cellular cytotoxicity against MPM in vitro using a europium chelate-based time-resolved fluorescence assay system and a luciferase-based luminescence assay system. We successfully expanded γδ T cells from peripheral blood mononuclear cells of healthy donors and MPM patients. γδ T cells expressed natural killer receptors such as NKG2D and DNAM-1 and exhibited a moderate level of cytotoxicity to MPM cells in the absence of antigens. The inclusion of PTA, (E)-4-hydroxy-3- methylbut-2-enyl diphosphate (HMBPP) or zoledronic acid (ZOL) induced a TCR-dependent cytotoxicity in γδ T cells and secreted interferon-γ (IFN-γ). In addition, γδ T cells expressing CD16 exhibited a significant level of cytotoxicity against MPM cells in the presence of an anti-epidermal growth factor receptor (EGFR) mAb, at lower concentrations than in clinical settings, whereas a detectable level of IFN-γ was not produced. Taken together, γδ T cells showed cytotoxic activity against MPM in three distinct mechanisms through NK receptors, TCRs and CD16. Since major histocompatibility complex (MHC) molecules are not involved in the recognition, both autologous and allogeneic γδ T cells could be used for the development of γδ T cell-based adoptive immunotherapy for MPM.

Selected Articles from This Issue

Highlights| February 01 2023 Selected Articles from This Issue Author & Article Information Online ISSN: 1557-3265 Print ISSN: 1078-0432 ©2023 American Association for Cancer Research2023American Association for Cancer Research Clin Cancer Res (2023) 29 (3): 503. https://doi.org/10.1158/1078-0432.CCR-29-3-HI Related Content A commentary has been published: Clinical Features Associated with Outcomes and Biomarker Analysis of Dabrafenib plus Trametinib Treatment in Patients with BRAF-Mutant Melanoma Brain Metastases A commentary has been published: Safety and Efficacy of MEDI0457 plus Durvalumab in Patients with Human Papillomavirus–Associated Recurrent/Metastatic Head and Neck Squamous Cell Carcinoma A commentary has been published: A Phase II Window of Opportunity Study of Neoadjuvant PD-L1 versus PD-L1 plus CTLA-4 Blockade for Patients with Malignant Pleural Mesothelioma View more A commentary has been published: HER2 Copy Number and Resistance Mechanisms in Patients with HER2-positive Advanced Gastric Cancer Receiving Initial Trastuzumab-based Therapy in JACOB Trial View less Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Article Versions Icon Versions Version of Record February 1 2023 Citation Selected Articles from This Issue. Clin Cancer Res 1 February 2023; 29 (3): 503. https://doi.org/10.1158/1078-0432.CCR-29-3-HI Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest Search Advanced Search The study from Wilmott and colleagues aimed to identify baseline clinical features associated with the outcomes of patients enrolled in the COMBI-MB phase II study of dabrafenib and trametinib treatment in patients with V600 BRAF-mutant metastatic melanoma with melanoma brain metastases (MBM). Exploratory biomarker analysis also was conducted as part of the synergistic COMBI-BRV trial (BRV116521) to identify molecular and immunological changes associated with dabrafenib in MBM and extracranial (ECM) metastases. Corticosteroid treatment was associated with reduced ICRR and PFS in COMBI-MB, similar to results with immunotherapy for MBM. Baseline corticosteroid treatment is a key factor to consider in MBM patient management and clinical trial design/interpretation. Immune checkpoint blockade (ICB) with nivolumab and ipilimumab has become standard treatment for patients with unresectable malignant pleural mesothelioma (MPM). However, the impact of neoadjuvant ICB in MPM has not yet been evaluated. Lee and colleagues report the results of a randomized, phase II,... You do not currently have access to this content.

Tislelizumab combined with anlotinib in the second-line treatment of malignant pleural mesothelioma.

Malignant pleural mesothelioma (MPM) is a malevolent tumor originated from pleura and often leads to poor prognosis. Chemotherapy of pemetrexed and cisplatin combined with antiangiogenic therapy of bevacizumab is recommended as the first-line regimen by guidelines. However, there are few sustainable second-line anti-tumor theraies that bring distinct survival benefit after the occurrence of drug resistance as the reported mPFS (median progression-free survival) scarcely exceeds 6 months. Immune checkpoint inhibitors are extensively investigated in pan-cancer, and dual immunotherapy has been listed in the first-line recommendation of MPM in several guidelines, while MPM patients benefit modestly from immune checkpoint inhibitors combination or monotherapy in second-line practice. We report a 59-year-old male patient who was diagnosed with unresectable MPM in April 2021. He received firstly pemetrexed combined with platinum and bevacizumab, which barely curbed disease progression; When the first line treatment failed, he was switched to tislelizumab combined with anlotinib. Tislelizumab combined with anlotinib significantly relieved his clinical symptoms, and imaging examination further validated the improvement. Until present, the second-line treatment PFS is more than 10 months. The case firstly demonstrated the efficacy of tislelizumab combined with anlotinib in the second-line management of MPM. Thus, immunotherapy combined with small-molecule multi-target anti-angiogenic medication may be alternative for the second-line schemes of MPM.

EE302 Cost-Effectiveness of Nivolumab + Ipilimumab in First-Line Treatment of Unresectable Malignant Pleural Mesothelioma (uMPM) in the Netherlands

uMPM is associated with poor prognosis and high burden of disease with a high need for new therapeutic options. CheckMate-743 (NCT02899299) has demonstrated survival and quality of life benefits for nivolumab plus ipilimumab vs. pemetrexed plus cisplatin/carboplatin (chemotherapy) as first-line (1L) treatment in uMPM. Nivolumab+ipilimumab is the new standard of care for 1L treatment in the recent ESMO and Dutch guidelines. To assess the long-term survival and economic benefits, we conducted a cost-effectiveness analysis of nivolumab+ipilimumab vs. chemotherapy for 1L uMPM in the Netherlands for the overall population.

CDK4/6 Inhibition Enhances the Efficacy of Standard Chemotherapy Treatment in Malignant Pleural Mesothelioma Cells

The loss of the CDKN2A/ARF (cyclin-dependent kinase inhibitor 2A/alternative reading frame) gene is the most common alteration in malignant pleural mesothelioma (MPM), with an incidence of about 70%, thus representing a novel target for mesothelioma treatment. In the present study, we evaluated the antitumor potential of combining the standard chemotherapy regimen used for unresectable MPM with the CDK4/6 (cyclin-dependent kinase 4 or 6) inhibitor abemaciclib. Cell viability, cell death, senescence, and autophagy induction were evaluated in two MPM cell lines and in a primary MPM cell culture. The simultaneous treatment of abemaciclib with cisplatin and pemetrexed showed a greater antiproliferative effect than chemotherapy alone, both in MPM cell lines and in primary cells. This combined treatment induced cellular senescence or autophagic cell death, depending on the cell type. More in detail, the induction of cellular senescence was related to the increased expression of p21, whereas autophagy induction was due to the impairment of the AKT/mTOR signaling. Notably, the effect of the combination was irreversible and no resumption in tumor cell proliferation was observed after drug withdrawal. Our results demonstrated the therapeutic potential of CDK4/6 inhibitors in combination with chemotherapy for the treatment of MPM and are consistent with the recent positive results in the MiST2 arm in abemaciclib-treated patients.

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

Abstract 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.

336P Spatial characterisation of immune microenvironment in malignant pleural mesothelioma

Following the result of Checkmate 743, dual checkpoint inhibition is a standard of care for unresectable malignant pleural mesothelioma (MPM). There is an ongoing need for potential predictive biomarkers for both efficacy and toxicity. To determine how the tumour microenvironment impacts ICI treatment outcomes and irAEs, we have designed a pilot study to determine the role of tumour-infiltrating immune cells on Ipilimumab (IPI) + Nivolumab (NIVO) treatment.

Enhancing Cancer Cell Membrane Permeability by Application of Tumor Treating Fields (TTFields)

<h3>Purpose/Objective(s)</h3> Tumor Treating Fields (TTFields) are alternating electric fields that display anti-mitotic effects on cancer cells. TTFields therapy is approved for treatment of glioblastoma (GBM) and unresectable malignant pleural mesothelioma. It has recently been shown that treatment of GBM cells with TTFields increases cell membrane permeability. The current study aimed to further explore this effect, testing the potential of TTFields to facilitate cellular accumulation of the anticancer agent doxorubicin (DOX) <i>in vitro</i> and <i>in vivo</i>. <h3>Materials/Methods</h3> Breast mammary carcinoma (4T1), breast adenocarcinoma (MCF-7), uterine sarcoma (MES-SA), and lung fibroblast (MRC-5) cell lines were treated with TTFields for 72 h at an intensity of 1.7 V/cm RMS across a range of frequencies (100-400 kHz). Membrane permeability was determined by 7-aminoactinomycin D (7-AAD) intracellular accumulation, and cytotoxicity was examined by cell counts, both measured by flow cytometry. TTFields at the frequency inducing highest permeability were applied together with DOX to DOX-sensitive and matched DOX-resistant 4T1 cells, followed by flow cytometry measurements of intracellular DOX accumulation and cytotoxicity. Mice orthotopically inoculated with 4T1 cells were treated with TTFields for 72 h, with DOX injected 24 h before end of treatment. DOX florescence was measured using flow cytometry for detection at the single-cell level and <i>in vivo</i> imaging system (IVIS) for whole tumor assessment. <h3>Results</h3> While TTFields increased 7-AAD intracellular accumulation in 4T1, MCF-7, and MES-SA cancer cells, there was no such effect when TTFields were applied to the non-cancer MRC-5 cells. Maximal permeability was induced in 4T1 cells with 300 kHz TTFields, whereas highest TTFields-induced cytotoxicity was observed at 150 kHz. TTFields application allowed for DOX accumulation in DOX-resistant cells to the same extent as in DOX-sensitive cells. TTFields delivery also sensitized both cell types to DOX, with cytotoxicity observed at low drug concentrations. <i>In vivo</i>, DOX accumulation was elevated by 2- to 3-fold in tumors isolated from mice treated with TTFields relative to control mice. <h3>Conclusion</h3> TTFields elevated the permeability of 4T1 breast cancer cells, allowing for enhanced intracellular accumulation of DOX and improved drug efficacy, even in cells resistant to DOX. TTFields-induced accumulation of DOX was also demonstrated <i>in vivo</i>.