Phenotypic characterisation of the Mucopolysaccharidosis Type I (MPSI) Idua-W392X mouse model reveals increased anxiety-related traits in female mice

Mucopolysaccharidosis Type I (MPSI) is a rare inherited lysosomal storage disease that arises due to mutations in the IDUA gene. Defective alpha-L-iduronidase (IDUA) enzyme is unable to break down glucosaminoglycans (GAGs) within the lysosomes and, as a result, there is systemic accumulation of undegraded products in lysosomes throughout the body leading to multi-system disease. Here, we characterised the skeletal/craniofacial, neuromuscular and behavioural outcomes of the MPSI Idua-W392X mouse model. We demonstrate that Idua-W392X mice have gross craniofacial abnormalities, showed signs of kyphosis, and show signs of hypoactivity compared to wild-type mice. X-ray imaging analysis revealed significantly shorter and wider tibias and femurs, significantly wider snouts, increased skull width and significantly thicker zygomatic arch bones in Idua-W392X female mice compared to wild-type mice at 9 and 10.5 months of age. Idua-W392X mice display decreased muscle strength, especially in the forelimbs, which is already apparent from 3 months of age. Female Idua-W392X mice display hypoactivity in the open-field test from 9 months of age and anxiety-like behaviour at 10 months of age. As these behaviours have been identified in Hurler children, the MPSI Idua-W392X mouse model may be important for the investigation of new therapeutic approaches for MPSI-Hurler.

Biglycan and reduced glycolysis are associated with breast cancer cell dormancy in the brain

Exit of quiescent disseminated cancer cells from dormancy is thought to be responsible for metastatic relapse and a better understanding of dormancy could pave the way for novel therapeutic approaches. We used an in vivo model of triple negative breast cancer brain metastasis to identify differences in transcriptional profiles between dormant and proliferating cancer cells in the brain. BGN gene, encoding a small proteoglycan biglycan, was strongly upregulated in dormant cancer cells in vivo. BGN expression was significantly downregulated in patient brain metastases as compared to the matched primary breast tumors and BGN overexpression in cancer cells inhibited their growth in vitro and in vivo. Dormant cancer cells were further characterized by a reduced expression of glycolysis genes in vivo, and inhibition of glycolysis in vitro resulted in a reversible growth arrest reminiscent of dormancy. Our study identified mechanisms that could be targeted to induce/maintain cancer dormancy and thereby prevent metastatic relapse.

P08.02 Harnessing T cells to target brain metastasis

BACKGROUND

Up to 60% of melanoma patients develop brain metastases (BrM). These patients have a poor prognosis and limited treatment options. Immune checkpoint inhibitors (ICI) targeting Cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) and Programmed cell death protein-1 (PD-1) have revolutionized the treatment of melanoma and their efficacy has been also demonstrated in melanoma BrM. Our group previously demonstrated that ICI (combined α-PD-1 and α-CTLA-4) enhances chemokine-dependent infiltration of cytotoxic T lymphocytes (CTLs) into melanoma BrMs in preclinical models, accompanied by upregulated expression of T cell attracting chemokines in tumours. Notably, CTLs infiltrating BrM expressed only some of the chemokine receptors (CRs) interacting with ICI-induced chemokines in BrM, providing a rationale to over-express the “missing” CRs in T cells to enhance their homing to tumours in the context of adoptive T cell therapy (ACT).

MATERIALS AND METHODS

OT-I cells were isolated from OT-I mice and differentiated ex vivo into effector (TEF) and memory (TCM) CD8+ T cells. Tumour infiltrating lymphocytes (TILs) from B16 tumour-bearing mice treated with ICI were isolated using magnetic beads, activated and expanded ex vivo. Expression of CRs and activation markers in ex vivo cultured T cells were quantified by qPCR and/or flow cytometry. The migration of human blood CD8+ T cells towards chemokines of interest were measured in ex vivo migration assays.

RESULTS

The same CRs that were missing on BrM-infiltrating CTLs in vivo models were also absent from OT-I TEF (CCR7low/CD44high/CD62Llow) and TCM (CCR7high/CD44low/CD62Lhigh) cells, as well as from TILs expanded ex vivo for use in ACT. Furthermore, we observed no increase in migration of human T cells towards chemokines interacting with the “missing” CRs in comparison to the baseline migration, suggesting that these CRs are also absent from human T cells.

CONCLUSION

Ex vivo expanded T cells that are used in ACT are missing several CRs that are interacting with chemokines upregulated in BrM. We hypothesise that the use of genetically engineered T cells expressing the “missing” CRs in ACT has the potential to enhance ACT efficacy in combination with ICI.

Hematopoietic stem cell gene therapy targeting TGFβ enhances the efficacy of irradiation therapy in a preclinical glioblastoma model

Patients with glioblastoma (GBM) have a poor prognosis, and inefficient delivery of drugs to tumors represents a major therapeutic hurdle. Hematopoietic stem cell (HSC)-derived myeloid cells efficiently home to GBM and constitute up to 50% of intratumoral cells, making them highly appropriate therapeutic delivery vehicles. Because myeloid cells are ubiquitously present in the body, we recently established a lentiviral vector containing matrix metalloproteinase 14 (MMP14) promoter, which is active specifically in tumor-infiltrating myeloid cells as opposed to myeloid cells in other tissues, and resulted in a specific delivery of transgenes to brain metastases in HSC gene therapy. Here, we used this novel approach to target transforming growth factor beta (TGFβ) as a key tumor-promoting factor in GBM. Transplantation of HSCs transduced with lentiviral vector expressing green fluorescent protein (GFP) into lethally irradiated recipient mice was followed by intracranial implantation of GBM cells. Tumor-infiltrating HSC progeny was characterized by flow cytometry. In therapy studies, mice were transplanted with HSCs transduced with lentiviral vector expressing soluble TGFβ receptor II-Fc fusion protein under MMP14 promoter. This TGFβ-blocking therapy was compared with the targeted tumor irradiation, the combination of the two therapies, and control. Tumor growth and survival were quantified (statistical significance determined by t-test and log-rank test). T cell memory response was probed through a repeated tumor challenge. Myeloid cells were the most abundant HSC-derived population infiltrating GBM. TGFβ-blocking HSC gene therapy in combination with irradiation significantly reduced tumor burden as compared with monotherapies and the control, and significantly prolonged survival as compared with the control and TGFβ-blocking monotherapy. Long-term protection from GBM was achieved only with the combination treatment (25% of the mice) and was accompanied by a significant increase in CD8+ T cells at the tumor implantation site following tumor rechallenge. We demonstrated a preclinical proof-of-principle for tumor myeloid cell-specific HSC gene therapy in GBM. In the clinic, HSC gene therapy is being successfully used in non-cancerous brain disorders and the feasibility of HSC gene therapy in patients with glioma has been demonstrated in the context of bone marrow protection. This indicates an opportunity for clinical translation of our therapeutic approach.

Hematopoietic Stem Cell Gene Therapy for Brain Metastases Using Myeloid Cell-Specific Gene Promoters

BACKGROUND

Brain metastases (BrM) develop in 20-40% of cancer patients and represent an unmet clinical need. Limited access of drugs into the brain because of the blood-brain barrier is at least partially responsible for therapeutic failure, necessitating improved drug delivery systems.

METHODS

Green fluorescent protein (GFP)-transduced murine and nontransduced human hematopoietic stem cells (HSCs) were administered into mice (n = 10 and 3). The HSC progeny in mouse BrM and in patient-derived BrM tissue (n = 6) was characterized by flow cytometry and immunofluorescence. Promoters driving gene expression, specifically within the BrM-infiltrating HSC progeny, were identified through differential gene-expression analysis and subsequent validation of a series of promoter-green fluorescent protein-reporter constructs in mice (n = 5). One of the promoters was used to deliver tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to BrM in mice (n = 17/21 for TRAIL vs control group).

RESULTS

HSC progeny (consisting mostly of macrophages) efficiently homed to macrometastases (mean [SD] = 37.6% [7.2%] of all infiltrating cells for murine HSC progeny; 27.9% mean [SD] = 27.9% [4.9%] of infiltrating CD45+ hematopoietic cells for human HSC progeny) and micrometastases in mice (19.3-53.3% of all macrophages for murine HSCs). Macrophages were also abundant in patient-derived BrM tissue (mean [SD] = 8.8% [7.8%]). Collectively, this provided a rationale to optimize the delivery of gene therapy to BrM within myeloid cells. MMP14 promoter emerged as the strongest promoter construct capable of limiting gene expression to BrM-infiltrating myeloid cells in mice. TRAIL delivered under MMP14 promoter statistically significantly prolonged survival in mice (mean [SD] = 19.0 [3.4] vs mean [SD] = 15.0 [2.0] days for TRAIL vs control group; two-sided P = .006), demonstrating therapeutic and translational potential of our approach.

CONCLUSIONS

Our study establishes HSC gene therapy using a myeloid cell-specific promoter as a new strategy to target BrM. This approach, with strong translational value, has potential to overcome the blood-brain barrier, target micrometastases, and control multifocal lesions.

Immune Checkpoint Blockade - How Does It Work in Brain Metastases?

Immune checkpoints restrain the immune system following its activation and their inhibition unleashes anti-tumor immune responses. Immune checkpoint inhibitors revolutionized the treatment of several cancer types, including melanoma, and immune checkpoint blockade with anti-PD-1 and anti-CTLA-4 antibodies is becoming a frontline therapy in metastatic melanoma. Notably, up to 60% of metastatic melanoma patients develop metastases in the brain. Brain metastases (BrM) are also very common in patients with lung and breast cancer, and occur in ∼20-40% of patients across different cancer types. Metastases in the brain are associated with poor prognosis due to the lack of efficient therapies. In the past, patients with BrM used to be excluded from immune-based clinical trials due to the assumption that such therapies may not work in the context of "immune-specialized" environment in the brain, or may cause harm. However, recent trials in patients with BrM demonstrated safety and intracranial activity of anti-PD-1 and anti-CTLA-4 therapy. We here discuss how immune checkpoint therapy works in BrM, with focus on T cells and the cross-talk between BrM, the immune system, and tumors growing outside the brain. We discuss major open questions in our understanding of what is required for an effective immune checkpoint inhibitor therapy in BrM.

Anti-PD-1/anti-CTLA-4 efficacy in melanoma brain metastases depends on extracranial disease and augmentation of CD8+ T cell trafficking

Inhibition of immune checkpoints programmed death 1 (PD-1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) on T cells results in durable antitumor activity in melanoma patients. Despite high frequency of melanoma brain metastases (BrM) and associated poor prognosis, the activity and mechanisms of immune checkpoint inhibitors (ICI) in metastatic tumors that develop within the "immune specialized" brain microenvironment, remain elusive. We established a melanoma tumor transplantation model with intracranial plus extracranial (subcutaneous) tumor, mimicking the clinically observed coexistence of metastases inside and outside the brain. Strikingly, intracranial ICI efficacy was observed only when extracranial tumor was present. Extracranial tumor was also required for ICI-induced increase in CD8+ T cells, macrophages, and microglia in brain tumors, and for up-regulation of immune-regulatory genes. Combined PD-1/CTLA-4 blockade had a superior intracranial efficacy over the two monotherapies. Cell depletion studies revealed that NK cells and CD8+ T cells were required for intracranial anti-PD-1/anti-CTLA-4 efficacy. Rather than enhancing CD8+ T cell activation and expansion within intracranial tumors, PD-1/CTLA-4 blockade dramatically (∼14-fold) increased the trafficking of CD8+ T cells to the brain. This was mainly through the peripheral expansion of homing-competent effector CD8+ T cells and potentially further enhanced through up-regulation of T cell entry receptors intercellular adhesion molecule 1 and vascular adhesion molecule 1 on tumor vasculature. Our study indicates that extracranial activation/release of CD8+ T cells from PD-1/CTLA-4 inhibition and potentiation of their recruitment to the brain are paramount to the intracranial anti-PD-1/anti-CTLA-4 activity, suggesting augmentation of these processes as an immune therapy-enhancing strategy in metastatic brain cancer.

Metastatic site-specific polarization of macrophages in intracranial breast cancer metastases

In contrast to primary tumors, the understanding of macrophages within metastases is very limited. In order to compare macrophage phenotypes between different metastatic sites, we established a pre-clinical mouse model of intracranial breast cancer metastasis in which cancer lesions develop simultaneously within the brain parenchyma and the dura. This mimics a situation that is commonly occurring in the clinic. Flow cytometry analysis revealed significant differences in the activation state of metastasis-associated macrophages (MAMs) at the two locations. Concurrently, gene expression analysis identified significant differences in molecular profiles of cancer cells that have metastasized to the brain parenchyma as compared to the dura. This included differences in inflammation-related pathways, NF-kB1 activity and cytokine profiles. The most significantly upregulated cytokine in brain parenchyma- versus dura-derived cancer cells was Lymphotoxin β and a gain-of-function approach demonstrated a direct involvement of this factor in the M2 polarization of parenchymal MAMs. This established a link between metastatic site-specific properties of cancer cells and the MAM activation state.

Abstract B37: Dural and parenchymal brain metastases in breast cancer are characterized by distinct inflammatory tumour microenvironments

Central nervous system metastases develop in ~15% of metastatic breast cancer patients and are associated with a very poor prognosis due to the lack of effective therapies. Intracranial metastases are mainly located within the brain parenchyma, in the skull, at the leptomeninges or at the dura. Although simultaneous involvement of multiple intracranial locations is very common in breast cancer, the experimental studies have been focusing mainly on parenchymal brain metastases. To address the knowledge gap in understanding of metastases at other CNS locations, we developed preclinical mouse models of intracranial breast cancer metastases with simultaneous involvement of brain parenchyma and the dura. This enabled us to subsequently study and compare cancer cell phenotype and inflammatory tumour microenvironment at the two intracranial locations.

Simultaneous colonization of brain parenchyma and the dura was achieved by administration of cancer cells into the internal carotid artery of mice. This resulted in a significantly higher dural as compared to the parenchymal tumour burden across 3 different breast cancer models. The inflammatory tumour microenvironment in dural and parenchymal brain metastases was subsequently analysed by flow cytometry. Although model-specific differences in metastases-infiltrating immune cell populations were detected, microglia/macrophages were the most abundant cell population across all 3 models. Further analysis of this cell population revealed that microglia were the predominant population within parenchymal metastases, while they were almost absent from the dural metastases. Macrophages were present at both locations and were significantly more abundant at the dura. In comparison to parenchymal macrophages, dural macrophages expressed significantly higher levels of MHCII and CD11c, which was suggestive of a higher antigen presenting capacity.

We next investigated site-specific cancer cell phenotypes. To this end, dura- and brain parenchyma-tropic cancer cell variants were generated through 3 rounds of in vivo selection and investigated by gene expression profiling. Among others, this revealed significant differences in inflammation-related pathways, expression of inflammatory cytokines and differences in activity of transcription factors NFKB1 and TCF4. This was in line with distinct expression of antigen presenting cell markers in dural versus parenchymal macrophages. Further investigation into polarization of macrophages revealed site-specific polarization patterns, with dural macrophages being skewed towards M1 phenotype as compared to the parenchymal macrophages.

In the above study we established pre-clinical models of intracranial breast cancer metastases with simultaneous involvement of brain parenchyma and the dura. Our study demonstrated that cancer cells at those two clinically relevant intracranial locations acquire different site-specific phenotypes, which was reflected in distinct polarization phenotypes of macrophages. Due to distinct phenotypes of cancer cells as well as macrophages, parenchymal brain metastases and dural metastases may respond differently to certain therapies (e.g. immune therapies). Therefore, these site-specific differences may need to be considered in the treatment of “multi-site” central nervous system metastases.

Citation Format: Nora Rippaus, Jennifer Williams, David Taggart, Tereza Andreou, Krzysztof Wronski, Mihaela Lorger. Dural and parenchymal brain metastases in breast cancer are characterized by distinct inflammatory tumour microenvironments. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr B37.