Abstract B37: Dural and parenchymal brain metastases in breast cancer are characterized by distinct inflammatory tumour microenvironments
Authors: Rippaus Nora , Williams Jennifer , Taggart David , Andreou Tereza , Wronski Krzysztof , Lorger Mihaela 
Published: May 2019

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.