Brain Metastasis Model Research Articles

CD146 promotes resistance of NSCLC brain metastases to pemetrexed via the NF-κB signaling pathway

IntroductionPemetrexed is a first line drug for brain metastases from lung cancer, either as monotherapy or combined with other drugs. The frequent occurrence of initial and acquired resistance to pemetrexed results in limited treatment effectiveness in brain metastases. CD146 was recently found to play important roles in chemoresistance and tumor progression. However, the underlying mechanisms of CD146’s effects in pemetrexed resistance remain undefined.Method and resultsSensitivity to pemetrexed was assessed with a preclinical brain metastasis (BM) model based on lung adenocarcinoma PC9 cells. The role and mechanism of CD146 in pemetrexed resistance in non-small cell lung cancer (NSCLC) brain metastasis were explored in vitro and in vivo. A subpopulation of brain metastatic cells derived from progenitor PC9 cells (PC9-BrMS) was significantly resistant to pemetrexed. CD146 levels were significantly increased in pemetrexed resistant brain metastases, while CD146 inhibition suppressed pemetrexed resistance in BM cells. Mechanistically, CD146 mediated pemetrexed resistance in brain metastatic cells by promoting DNA damage repair, maintaining normal cell cycle progression, and regulating the NF-KB pathway to counter apoptosis, and these effects was based on increased DNA damage, cell cycle arrest, and occurrence of apoptosis after CD146 inhibition as well as the reemergence of pemetrexed resistance after CD146 restoration.DiscussionIn summary, this study revealed that the resistance of NSCLC brain metastatic cells to PEM was dependent on CD146.Thus CD146 might be targeted in clinic to overcome pemetrexed resistance in brain metastases from NSCLC.

Myeloid Cells Induce Infiltration and Activation of B Cells and CD4+ T Follicular Helper Cells to Sensitize Brain Metastases to Combination Immunotherapy.

Brain metastasis (BM) is a poor prognostic factor in cancer patients. Despite showing efficacy in many extracranial tumors, immunotherapy with anti-PD-1 monoclonal antibody (mAb) or anti-CTLA-4 mAb appears to be less effective against intracranial tumors. Promisingly, recent clinical studies have reported that combination therapy with anti-PD-1 and anti-CTLA-4 mAbs has a potent antitumor effect on BM, highlighting the need to elucidate the detailed mechanisms controlling the intracranial tumor microenvironment (TME) to develop effective immunotherapeutic strategies. Here, we analyzed the tumor-infiltrating lymphocytes in murine models of BM that responded to anti-CTLA-4 mAb to anti-PD-1 mAb. Activated CD4+ T follicular helper (TFH) cells with high CTLA-4 expression characteristically infiltrated the intracranial TME, which were activated by the combination anti-CTLA-4 and anti-PD-1 treatment. Loss of TFH cells suppressed the additive effect of CTLA-4 blockade on anti-PD-1 mAb. B cell-activating factor belonging to the TNF family (BAFF) and a proliferation-inducing ligand (APRIL) produced by abundant myeloid cells, particularly CD80hiCD206lo pro-inflammatory M1-like macrophages, in the intracranial TME, induced B cell and TFH cell infiltration and activation. Furthermore, the intracranial TME of patients with non-small cell lung cancer featured TFH and B cell infiltration as tertiary lymphoid structures. Together, these findings provide insights into the immune cell crosstalk in the intracranial TME that facilitates an additive anti-tumor effect of CTLA-4 blockade with anti-PD-1 treatment, supporting the potential of a combination immunotherapeutic strategy for BM.

ENPP1 induces blood-brain barrier dysfunction and promotes brain metastasis formation in human epidermal growth factor receptor 2-positive breast cancer.

Brain metastasis (BrM) is a devastating end-stage neurological complication that occurs in up to 50% of human epidermal growth factor receptor 2-positive (HER2+) breast cancer (BC) patients. Understanding how disseminating tumor cells manage to cross the blood-brain barrier (BBB) is essential for developing effective preventive strategies. We identified the ecto-nucleotidase ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase 1) as specifically enriched in the secretome of HER2+ brain metastatic cells, prompting us to explore its impact on BBB dysfunction and BrM formation. We used in vitro BBB and in vivo premetastatic mouse models to evaluate the effect of tumor-secreted ENPP1 on brain vascular permeability. BBB integrity was analyzed by real-time fluorescence imaging of 20 kDa Cy7.5-dextran extravasation and immunofluorescence staining of adherens and tight junction proteins. Pro-metastatic effects of ENPP1 were evaluated in an experimental brain metastatic model. Systemically secreted ENPP1 from primary breast tumors impaired the integrity of BBB with loss of tight and adherens junction proteins early before the onset of BrM. Mechanistically, ENPP1 induced endothelial cell dysfunction by impairing insulin signaling and its downstream AKT/GSK3β/β-catenin pathway. Genetic ablation of ENPP1 from HER2+ brain metastatic cells prevented endothelial cell dysfunction and reduced metastatic burden while prolonging the overall and metastasis-free survival of mice. Furthermore, plasmatic ENPP1 levels correlate with brain metastatic burden and inversely with overall survival. We demonstrated that metastatic BC cells exploit the ENPP1 signaling for cell transmigration across the BBB and brain colonization. Our data implicate ENPP1 as a potential biomarker for poor prognosis and early detection of BrM in HER2+ BC.

Metastatic brain tumors: from development to cutting-edge treatment.

Metastatic brain tumors, also called brain metastasis (BM), represent a challenging complication of advanced tumors. Tumors that commonly metastasize to the brain include lung cancer and breast cancer. In recent years, the prognosis for BM patients has improved, and significant advancements have been made in both clinical and preclinical research. This review focuses on BM originating from lung cancer and breast cancer. We briefly overview the history and epidemiology of BM, as well as the current diagnostic and treatment paradigms. Additionally, we summarize multiomics evidence on the mechanisms of tumor occurrence and development in the era of artificial intelligence and discuss the role of the tumor microenvironment. Preclinically, we introduce the establishment of BM models, detailed molecular mechanisms, and cutting-edge treatment methods. BM is primarily treated with a comprehensive approach, including local treatments such as surgery and radiotherapy. For lung cancer, targeted therapy and immunotherapy have shown efficacy, while in breast cancer, monoclonal antibodies, tyrosine kinase inhibitors, and antibody-drug conjugates are effective in BM. Multiomics approaches assist in clinical diagnosis and treatment, revealing the complex mechanisms of BM. Moreover, preclinical agents often need to cross the blood-brain barrier to achieve high intracranial concentrations, including small-molecule inhibitors, nanoparticles, and peptide drugs. Addressing BM is imperative.

Current preclinical models of brain metastasis.

Brain metastases (BMs) represent the most prevalent intracranial malignancy within the adult. They are identified in up to 20% of patients with solid tumors and this percentage varies between tumor types and age. Due to the selective permeability of the blood-brain barrier, most anticancer drugs can't reach significant concentrations in the brain, representing a major obstacle to the patients' survival. Furthermore, intra- and inter-patient heterogeneity and the unique brain microenvironment add a layer of complexity to the clinical management of BMs. In the perspective of finding new therapeutic approaches and better understanding the molecular mechanisms involved in brain metastasis, the use of appropriate preclinical models is essential. Here, we review current in vivo, in vitro and ex vivo models for the study of brain metastasis while outlining their advantages and limitations.

Abstract PR004: Brain penetrant allosteric EGFR inhibitors for NSCLC

Abstract Approximately 30-50% of Non-Small Cell Lung Cancer (NSCLC) patients already have CNS disease at time of diagnosis or else develop it during treatment, and there remains a need for better outcomes in these patients. The 3rd-generation covalent EGFR inhibitor osimertinib is an effective therapy for NSCLC patients, improving upon 1st-generation inhibitors gefitinib and erlotinib, and achieving enhanced brain penetration relative to those agents. However, the survival benefit relative to the 1st-generation inhibitors is observed primarily in patients with exon19 deletions rather than the L858R mutation. We developed a series of mutant-selective allosteric EGFR inhibitors that specifically target the L858R mutation (and subsequent resistance mutations), with high selectivity over wt EGFR and across the kinome. Early compounds including the isoindolinone JBJ-09-063 demonstrated good in vivo efficacy in mouse tumor models, despite limited bioavailability. Diversification and optimization of the chemistry, involving a scaffold hopping approach and the replacement of the thiazole amide with benzimidazole, delivered a set of compounds with promising potency and rodent PK. A subset of these achieved good brain exposure in mice and efficacy in an intracranial H1975 brain metastasis model. The mutant-selectivity and ability to co-bind with osimertinib makes an allosteric EGFR inhibitor an ideal partner for combination therapy, with the potential to deliver enhanced outcomes in L858R-driven NSCLC, especially for patients with CNS disease. Citation Format: David Scott, Courtney Cullis, Tyler Beyett, Frederic Feru, Thomas Gero, Krista Gipson, Praful Gokhalle, Nathanael Gray, David Heppner, Sampson Huang, Pasi Jänne, Sandeepraj Pusalkar, Michael Eck. Brain penetrant allosteric EGFR inhibitors for NSCLC [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Optimizing Therapeutic Efficacy and Tolerability through Cancer Chemistry; 2024 Dec 9-11; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(12_Suppl):Abstract nr PR004

Machine learning-based prediction model for brain metastasis in patients with extensive-stage small cell lung cancer

Brain metastases (BMs) in extensive-stage small cell lung cancer (ES-SCLC) are often associated with poor survival rates and quality of life, making the timely identification of high-risk patients for BMs in ES-SCLC crucial. Patients diagnosed with ES-SCLC between 2010 and 2018 were screened from the Surveillance, Epidemiology, and End Results (SEER) database. Four different machine learning (ML) algorithms were used to create prediction models for BMs in ES-SCLC patients. The accuracy, sensitivity, specificity, AUROC, and AUPRC were compared among these models and traditional logistic regression (LR). The random forest (RF) model demonstrated the best performance and was chosen for further analysis. The AUROC and AUPRC were calculated and compared. The findings from the RF model were utilized to identify the risk factors linked to BMs in patients diagnosed with ES-SCLC. Examining 4,716 instances of ES-SCLC, the research conducted an analysis, with brain metastases arising in 1,900 cases. Through evaluation of the ROC curve and PRC concerning the RF Model, results depicted an AUROC of 0.896 (95% CI: 0.889–0.899) and AUPRC of 0.900 (95% CI: 0.895–0.904). Test accuracy measured at 0.810 (95% CI: 0.784–0.833), sensitivity at 0.797 (95% CI: 0.756–0.841), and specificity at 0.819 (95% CI: 0.754–0.879). Based on the SHAP analysis of the RF predictive model, the top 10 most relevant features were identified and ranked in order of relative importance: bone metastasis, liver metastasis, radiation, age, tumor size, primary tumor location, N-stage, race, T-stage, and chemotherapy. The research developed and validated a predictive RF model using clinical and pathological data to predict the risk of BMs in patients with ES-SCLC. This model may assist physicians in making clinical decisions that could delay the onset of BMs and improve patient survival rates.

Abstract A002: Dissecting the brain metastatic microenvironment to uncover immune and molecular correlates of response to immunotherapy

Abstract Despite promising results with immune checkpoint blockade (ICB) therapy, brain metastases (BrM) remain a deadly complication for cancer patients. Understanding the highly specialized brain metastatic tumor microenvironment (BrTME) is crucial for identifying determinants of response, however, progress has been hindered by limited access to patient samples and scarcity of relevant preclinical models. Here, we developed two mouse melanoma BrM models by intracardiac injection of cells derived from our previously established M4-B2905 melanoma mouse cell line. We characterized their mutational landscape and performed single-cell phenotypic and transcriptomic analysis, demonstrating that these models recapitulate the cellular and molecular features of human melanoma BrMs. Comparative and interactome analysis of our models revealed key factors contributing to ICB response and resistance. We found that the responsive model (BR1) was characterized by tumor cells that polarize microglia toward reactive states via inflammatory programs and response to IFN signaling. These microglia express high levels of antigen presentation and immunostimulatory molecules, triggering T cell recruitment and activation and promoting ICB therapy response. In contrast, in the resistant model (BR3), the tumor cells express neurological molecular signatures and ligands that sustain microglia homeostasis. This results in poor T cell infiltration predominantly composed of naïve cells, evading immune reaction and promoting ICB resistance. While we showed that systemic ICB therapy induced BrTME changes in both models, differences between responder and resistant models were maintained, emphasizing the importance of tumor cell-intrinsic programs in dictating the BrTME. We validated the translational relevance of our findings and demonstrated that BR1 signatures positively correlate with T cell infiltration and are associated with improved patient outcomes, whereas BR3 signatures negatively correlate with T cells and are found in patients with worse prognosis. Here we address an important challenge in the field by providing clinically relevant BrM models that recapitulate both the cellular and molecular features of human disease and the variability of ICB response seen in patients. We further reveal mechanistic insights into BrM ICB response and identify potential therapeutic targets to modulate the BrTME. Citation Format: Amelie Daugherty-Lopes, Eva Perez-Guijarro, Vishaka Gopalan, Jessica Rappaport, Quanyi Chen, April Huang, Khiem C. Lam, Sung Chin, Jessica Ebersole, Emily Wu, Gabriel Needle, Isabella Church, George Kyriakopoulos, Shaojun Xie, Yongmei Zaho, Charli Gruen, Antonella Sassano, Romina E Araya, Andres Thorkelsson, Cari Smith, Maxwell P. Lee, Sridhar Hannenhalli, Chi-Ping Day, Glenn Merlino, Romina S. Goldszmid, Shaojun Xie. Dissecting the brain metastatic microenvironment to uncover immune and molecular correlates of response to immunotherapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr A002.

Abstract C051: Epigenetic reprogramming of brain-infiltrating myeloid cells deters brain metastasis outgrowth

Abstract The unique brain immune microenvironment (BrIME) co-evolves with brain metastasis (BrM) and is marked by immune suppression, posing a significant therapeutic challenge. BrIME is dominated by myeloid cells, with monocyte-derived macrophages (MDMs) comprising nearly half of the tumor-infiltrating leukocytes. Targeting MDMs remains challenging due to their inherent heterogeneity and high plasticity, which are regulated by epigenetic modifiers, including histone deacetylases (HDACs). Yet, the impact of HDAC inhibition in BrIME and its implications for BrM immunotherapy remains unclear. Here, we establish BrM syngenetic model by intracarotid artery (ICA) injection. Immune profiling by mass cytometry (CyTOF) analysis shows that selective class I HDAC inhibitor (HDACi) Entinostat (ENT) significantly enriches inflammatory MDMs in E0771 murine mammary tumor BrM model. Additionally, functional assay with bone marrow-derived macrophages (BMDMs) shows that ENT significantly enhances tumor cell phagocytosis and antigen presentation, increasing the proliferation of antigen-specific T cells in vitro. To test whether HDAC inhibition enhances antitumoral response in the BrIME, we designed a novel sequential treatment: with (1) ENT pre-conditioning the BrIME, (2) low- dose whole brain radiotherapy (LD-WBRT) to release tumor antigen followed by (3) anti-PD1 immune checkpoint therapy (ICT) to reinvigorate tumor-infiltrating. Our result shows that sequential triple treatment demonstrates significant BrM deterrence and induce a specific interferon-responsive MDM subset with robust type I interferon response in single-cell RNA sequencing, correlating with improved ICT clinical outcomes. Our data show that selective HDACi treatment reprograms the suppressive BrIME by steering the BrM-infiltrating MDMs toward immuno-stimulatory status. Sequential triple combinatorial therapy impedes BrM by activating innate and adaptive immunity simultaneously and is well tolerated in the animal model. Our findings highlight the potential of HDACi-mediated epigenetic reprogramming of the BrIME to enhance therapeutic efficacy in treating BrM. Citation Format: Shao-Ping Yang, Yimin Duan, Xiangliang Yuan, Lin Zhang, Wendao Liu, Jun Yao, Patrick Zhang, Jason T Huse, Zhongming Zhao, Dihua Yu. Epigenetic reprogramming of brain-infiltrating myeloid cells deters brain metastasis outgrowth [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr C051.

CSIG-12. YAP1-TEAD SIGNALING CONTRIBUTES TO LUNG CANCER COLONIZATION OF THE BRAIN

Abstract BACKGROUND Lung cancer is the most common primary tumor to metastasize to the brain. Poor understanding of the brain metastasis process limits therapeutic options. Despite emerging data on the role of YAP signaling pathway in the development of brain tumors, a gap in knowledge remains regarding its role in brain colonization. We hypothesize that YAP1 and the associated TEAD transcriptional factors are responsible for lung cancer progression and that intervention with YAP/TEAD-targeted therapy will prevent brain dissemination. METHODS Lung cancer cells at different stages of cancer progression (VMRC-LCD and NCI-H1975, lung cancer cell lines; NCI-H1915 and LN001, brain metastatic cancer cells) were genetically engineered to overexpress or silence/knockout YAP1 using lentiviral transduction of constructs expressing shRNA/sgRNA or YAP1. We tested several tumor cell capabilities using well-established in vitro assays, including invasion and migration assays, and an in vivo brain metastasis (BM) model to determine the biological effects of YAP1/TEAD suppression at different stages of lung cancer progression. Dose-response assays were performed to determine IC50 of the TEAD inhibitor, verteporfin. RESULTS YAP overexpression enhances the proliferative phenotype in metastatic and BM cell lines but not in non-metastatic cells. However, YAP overexpression only increases the migration ability of BM cell lines such as LN001 and NCI-H1915 compared to the metastatic NCI-H1975 and non-metastatic lung cancer cells. Moreover, we showed the efficacy of the YAP1/TEAD inhibitor in patient-derived lung BM cells. Finally, our in vivo preliminary data showed YAP1 involvement in lung cancer cell colonization of the brain but not in sustaining brain metastasis growth. CONCLUSIONS Our findings showed YAP1 involvement in lung cancer cell colonization of the brain, suggesting YAP1 inhibition is a clinically actionable target for preventing lung cancer dissemination and providing a strong rationale to further evaluate the benefit of a YAP1/TEAD-targeted therapy in in vivo models of BM.

STEM-17. THE UROKINASE RECEPTOR AS A NOVEL IMMUNOTHERAPEUTIC TARGET IN BRAIN CANCERS

Abstract Glioblastoma (GBM) is the common malignant brain tumor in adults, accounting for approximately 15% of all CNS tumors, and 48.6% of malignant brain tumors, with a median survival of approximately 15 months. GBM is characterized by extensive inter- and intra-tumoral heterogeneity and an extremely immunosuppressive tumor microenvironment. Following Standard-of-Care surgical resection and chemoradiotherapy, patients inevitably relapse, at which point few therapeutic avenues exist, owing in part due to a lack of clinically relevant targets. Data from our target identification pipeline shows the urokinase plasminogen activator receptor (uPAR) is significantly upregulated at recurrence on putative GBM brain tumor initiating cells (BTICs), which are believed to drive de novo tumor formation, recurrence, and therapeutic resistance. uPAR plays an important role in the plasminogen activation system, and in the context of cancer, has been implicated in numerous pro-tumorigenic processes such as invasion, proliferation, and therapy resistance. We used CRISPR-Cas9 to genetically delete uPAR from our in-house patient-derived GBM cell lines, and found that knockout of uPAR in recurrent GBM cells significantly reduces various functional characteristics of BTICs in vitro. In our patient-derived mouse model of GBM, we found that knockout of uPAR significantly increases survival, and decreases tumor burden. Further, we generated novel anti-uPAR single domain antibodies (sdAbs) which specifically and efficiently bind uPAR at low nanomolar concentrations in vitro. We developed anti-uPAR CAR Ts using the binder sequence of the sdAbs, which showed potent cytotoxicity in vitro, and drastically reduced tumor burden and extended survival in vivo. Further, we identified uPAR as being highly expressed on brain metastases from multiple origins (lung-to-brain, melanoma-to-brain, etc.), and demonstrate that anti-uPAR CAR Ts effectively kill brain metastases in vitro, and significantly extend survival using in vivo brain metastasis models. From this work we believe uPAR to be a clinically relevant target in both recurrent GBM and brain metastases, and investigation into therapeutic strategies targeting uPAR-positive brain cancers should be explored further.

TMIC-12. LITT RESULTS IN ROBUST T CELL INFILTRATION WITHIN THE TUMOR MICROENVIRONMENT IN A BRAIN METASTASIS MURINE MODEL

Abstract INTRODUCTION Laser interstitial thermal therapy (LITT) is a novel minimally invasive neurosurgical technique used to ablate intra-axial brain tumors with real-time thermometry. The impact of LITT on the brain metastatic tumor microenvironment (TME) is unknown in patients due to limitations of tumor tissue collection post-LITT. The primary objective of this study was to describe the kinetics of immunologic infiltration within the TME in a melanoma brain metastasis model. METHOD: C57BL6 mice underwent intra-cranial implantation of B16F10-OVA tumor cells and treated with LITT using a custom-made murine LITT system developed in our laboratory. The tumors were treated to 42°C (near infra-red 1064 nm DPSS laser system) 7 days post-surgery. Tumors were collected 2 days and 10 days post-LITT for immune-phenotyping using flow cytometry. Blood was collected 6 h and 48 h post-LITT to perform the ELISA for IFN-g and TNF-a. RESULTS LITT treatment triggered a cascade of local infiltration of immune cells at different time points. 2-days post-LITT resulted in increased CD8 T cells (p<0.05), macrophage (p<0.05) and microglia infiltration (p<0.01) within the TME compared to control and sham surgery animals. By 10 days after LITT, significant infiltration by CD8 T cells (p<0.0001) and M1 macrophages (p<0.0001) was observed. The CD8 T cells were T central memory (TCM) and T effector memory (TEM). Moreover, comparison between 2 days and 10 days after LITT revealed significant increase of TEM (p<0.0001) and TCM (p<0.001) 10 days post-LITT. In an ELISA assay, non-significant differences were observed in IFN-g and TNF-a level at 48 h. CONCLUSIONS LITT enhances the recruitment of cytotoxic CD8 T cells within TME in a time-dependent manner. The ability of LITT to recruit TCM and TEM to the TME strongly support its potential therapeutic benefit, especially in the context of immunotherapy.

IMMUNE AND MOLECULAR CORRELATES OF RESPONSE TO IMMUNOTHERAPY REVEALED BY BRAIN-METASTATIC MELANOMA MODELS.

Despite the promising results of immune checkpoint blockade (ICB) therapy, outcomes for patients with brain metastasis (BrM) remain poor. Identifying resistance mechanisms has been hindered by limited access to patient samples and relevant preclinical models. Here, we developed two mouse melanoma BrM models that recapitulate the disparate responses to ICB seen in patients. We demonstrate that these models capture the cellular and molecular complexity of human disease and reveal key factors shaping the tumor microenvironment and influencing ICB response. BR1-responsive tumor cells express inflammatory programs that polarize microglia into reactive states, eliciting robust T cell recruitment. In contrast, BR3-resistant melanoma cells are enriched in neurological programs and exploit tolerance mechanisms to maintain microglia homeostasis and limit T cell infiltration. In humans, BR1 and BR3 expression signatures correlate positively or negatively with T cell infiltration and BrM patient outcomes, respectively. Our study provides clinically relevant models and uncovers mechanistic insights into BrM ICB responses, offering potential biomarkers and therapeutic targets to improve therapy efficacy.

TIMP1 Mediates Astrocyte-Dependent Local Immunosuppression in Brain Metastasis Acting on Infiltrating CD8+ T Cells.

Immunotherapies against brain metastases have shown clinical benefits when applied to asymptomatic patients, but they are largely ineffective in symptomatic cases for unknown reasons. Here, we dissect the heterogeneity in metastasis-associated astrocytes using single-cell RNA sequencing and report a population that blocks the antitumoral activity of infiltrating T cells. This protumoral activity is mediated by the secretion of tissue inhibitor of metalloproteinase-1 (TIMP1) from a cluster of pSTAT3+ astrocytes that acts on CD63+ CD8+ T cells to modulate their function. Using genetic and pharmacologic approaches in mouse and human brain metastasis models, we demonstrate that combining immune checkpoint blockade antibodies with the inhibition of astrocyte-mediated local immunosuppression may benefit patients with symptomatic brain metastases. We further reveal that the presence of tissue inhibitor of metalloproteinase-1 in liquid biopsies provides a biomarker to select patients for this combined immunotherapy. Overall, our findings demonstrate an unexpected immunomodulatory role for astrocytes in brain metastases with clinical implications. Significance: This study presents a significant advancement in understanding immune modulation in brain tumors and offers new insights into the potential therapeutic interventions for brain metastases. See related commentary by Lorger and James, p. 11.

430P A novel survival predicting model for breast cancer brain metastasis based on multimodal data

430P A novel survival predicting model for breast cancer brain metastasis based on multimodal data

MicroRNA-522-3p promotes brain metastasis in non-small cell lung cancer by targeting Tensin 1 and modulating blood-brain barrier permeability

Brain metastases account for more than 50 % of intracranial central nervous system tumors. The blood-brain barrier (BBB) is mainly composed of endothelial cells, which exhibit low endocytosis and high efflux pumps. Although they are connected by continuous tight junctions and serve as a protective insulation, the BBB does not prevent the development of brain metastases from non-small cell lung cancer (NSCLC). Improving understanding on the mechanisms underlying the development of brain metastasis and the differential molecular characteristics relative to the primary tumor are therefore key in the treatment of brain metastases. This study evaluated the differential expression of miR-522-3p in NSCLC and brain metastases using the Gene Expression Omnibus database. NSCLC brain metastasis model was constructed to screen for cell lines that demonstrated high potential for brain metastasis; We also observed differential expression of miRNA-522-3p in the paraffin-embedded specimens of non-small cell lung cancer and brain metastases from our hospital. The molecular biological functions of miRNA-522-3p were verified using 5-ethynyl-2′-deoxyuridine (EdU) proliferation assay and Transwell invasion assays. RNA-seq was employed to identify downstream target proteins, and the dual-luciferase reporter assay confirmed Tensin 1 (TNS1), a protein that links the actin cytoskeleton to the extracellular matrix, as the downstream regulatory target protein. In vitro blood-brain barrier models and co-culture models were constructed to further identify the role of miRNA-522-3p and TNS1; the expression of BBB-related proteins (ZO-1 and OLCN) was also identified. In vivo experiments were performed to verify the effects of miRNA-522-3p on the time and incidence of NSCLC brain metastasis. The results showed significantly high expression in GSE51666; consistent results were obtained in brain metastasis cells and paraffin samples. RNA-seq combined with miRNA target protein prediction demonstrated TNS1 to be directly downstream of miR-522-3p and to be associated with cell proliferation and invasion. By regulating ZO-1 and OCLN expression, mi-522-3p/TNS1 may increase tumor cell penetration through the BBB while decreasing its permeability. In vivo, miR-522-3p was further demonstrated to significantly promote the formation of brain metastases. miR-522-3p/TNS1 can affect BBB permeability and encourage the growth of brain metastases by modifying the BBB TJ proteins. This axis offers new therapeutic targets for the prevention of brain metastasis.

Irradiated tumor cell-released microparticles enhance the therapeutic efficacy of PD-1 inhibitors by promoting M1-TAMs polarization in NSCLC brain metastases

Brain metastases (BMs) are the most common sites of metastasis in patients with non-small cell lung cancer (NSCLC). However, BMs are not responsive to immunotherapy because of the blood-brain barrier. This is because intracranial immune cells such as M2 tumor-associated macrophages (TAMs) accumulate, creating an immunosuppressive tumor microenvironment. In this study, we focused on irradiated tumor cell-released microparticles (RT-MPs) that can cross the blood-brain barrier and influence the intracranial immune microenvironment. Using animal models of BMs, we observed that RT-MPs could penetrate the blood-brain barrier and be swallowed by TAMs. Then the microenvironment of TAMs is shifted from the M2 phenotype to the M1 phenotype, thereby modulating the interactions between TAMs and tumor cells. Single-cell sequencing analysis demonstrated that TAMs, after internalizing RT-MPs, active chemokine signaling pathways and secrete more chemokines, such as CCL5, CXCL2, CXCL1, CCL3, CCL4, and CCL22, attracting more CD4+ T cells and CD8+ T cells, improving immune-mediated killing, and enhancing subsequent combination anti-PD-1 therapy. These findings provide a preclinical foundation for exploring alternative treatments for patients with immunoresistant NSCLC BMs.

Aqueous extract of Chuan Xiong Rhizoma enhances inhibitory effect of temozolomide against brain metastasis of melanoma in mice

To investigate the effect of the aqueous extract of Chuan Xiong Rhizoma (CR) on brain metastasis of melanoma B16F10 cells in mice. C57BL/6J mouse models of brain metastasis of melanoma were established by ultrasound-guided intraventricular injection of Luc-labeled B16F10 cells, and brain tumor growth was monitored by in vivo imaging. The mouse models were then randomized for daily gavage of saline or aqueous extract of CR (equivalent crude drug concentration of 1 mg/g). Behavioral tests were used to evaluate the neuroprotective effects of CR in the tumor-bearing mice, and the changes in proteins associated with blood-brain barrier integrity, neuronal cell proliferation and apoptosis, and microglial cell apoptosis and activation were observed using immunofluorescence assay. The efficacy of CR combined with temozolomide (25 mg/kg) against brain metastases of B16F10 cells was observed by in vivo imaging. CR-treated mouse models did not show obvious progression of brain metastases and had a reduced rate of body weight loss and lowered protein expressions of ZO-1, claudin-5, occludin, P-gp, TNF-α, AQP4 and PDGFRβ. In the behavioral tests, the CR-treated mice showed prolonged stay on the wooden stick with a shortened time of sticky stick removal. Immunofluorescence assay showed increased proliferation and decreased apoptosis of neuronal cells and microglia in CR-treated mice. CR treatment significantly increased the levels of CD86, CD206, IL-4 and IL-10 and decreased the levels of CD163 and IL-1β in the microenvironment of brain metastases. The mice receiving combined treatments with CR and temozolomide showed significantly lower intensity of fluorescent signals in the brain than those treated with temozolomide alone. CR does not promote brain metastasis of melanoma while inducing opening of the blood-brain barrier, and its combined use with TMZ results in enhanced inhibition against brain metastasis of melanoma B16F10 cells in mice.

DUSP6 inhibition overcomes neuregulin/HER3-driven therapy tolerance in HER2+ breast cancer

Despite clinical benefits of tyrosine kinase inhibitors (TKIs) in cancer, most tumors can reactivate proliferation under TKI therapy. Here we present transcriptional profiling of HER2+ breast cancer cells transitioning from dormant drug tolerant cells to re-proliferating cells under continuous HER2 inhibitor (HER2i) therapy. Focusing on phosphatases, expression of dual-specificity phosphatase DUSP6 was found inhibited in dormant cells, but strongly induced upon regrowth. DUSP6 expression also selectively associated with poor patient survival in HER2+ breast cancers. DUSP6 overexpression conferred apoptosis resistance, whereas its pharmacological blockade prevented therapy tolerance development under HER2i therapy. DUSP6 targeting also synergized with clinically used HER2i combination therapies. Mechanistically DUSP6 is a positive regulator of HER3 expression, and its impact on HER2i tolerance was mediated by neuregulin-HER3 axis. In vivo, genetic targeting of DUSP6 reduced tumor growth in brain metastasis model, whereas its pharmacological targeting induced synthetic lethal therapeutic effect in combination with HER2i. Collectively this work demonstrates that DUSP6 drives escape from HER2i-induced dormancy, and that DUSP6 is a druggable target to overcome HER3-driven TKI resistance.

Abstract A007: Assessment of metabolic vulnerabilities of breast cancer brain metastasis

Abstract The metastasis of cancer to the brain is a major contributor to patient morbidity and mortality. Prior work suggests that there is therapeutic potential in targeting metabolic processes within brain metastatic cancer, however how best to identify novel targets and select patient populations remains unclear. In this study, we determine what nutrients are available to breast cancer cells in the brain and how those nutrients are used. We also engineer breast cancer cells that are auxotrophic for specific nutrients and assess how this impacts tumor growth in the brain using various approaches. These methodologies include direct implantation into the brain and introduction into the circulation to evaluate tumor formation as brain metastases. Unexpectedly, we find that no single approach, including assessment of brain nutrient availability, tumor biosynthetic activity, and evaluation of genetic dependencies using in vivo CRISPR screens reliably predicts metabolic dependencies that broadly extend across models of breast cancer brain metastasis. Our findings underscore the necessity of a holistic approach in considering how best to identify and prioritize new targets for treating metastatic cancer. Citation Format: Keene L. Abbott, Sonu Subudhi, Raphael Ferreira, Yetiş Gültekin, Sophie C. Steinbuch, Sophie E. Honeder, Ashwin S Kumar, Michelle Wu, Diya Ramesh, Jacob Hansen, Lisa M. Riedmayr, Mark Duquette, Ahmed Ali, Nicole Henning, Sharanya Sivanand, Tenzin Kunchok, Millenia Waite, Brian T. Do, Virginia Spanoudaki, Francisco J. Sánchez-Rivera, George M. Church, Rakesh K Jain, Matthew G. Vander Heiden. Assessment of metabolic vulnerabilities of breast cancer brain metastasis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Expanding and Translating Cancer Synthetic Vulnerabilities; 2024 Jun 10-13; Montreal, Quebec, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(6 Suppl):Abstract nr A007.