Pre-existing neurovascular inflammation increases the occurrence of brain metastases

Abstract BACKGROUND: Brain metastases (BM) are the most prevalent intracranial neoplasm. Inflammation is central to the development of cancer. While an intra-tumoral inflammatory microenvironment contributes to the acquisition of malignant phenotypes and leads to the release of circulating tumor cells (CTCs), pre-existing inflammation at distant sites facilitates the adhesion of CTCs to the activated vascular endothelium and the consequent formation of metastases. Cell adhesion molecules expressed by activated endothelial cells contribute to metastatic spread outside of the brain and the vascular cell adhesion molecule-1 (VCAM-1) is a key mediator of inflammation. Herein we assessed if cancer cells entry into the brain is aided by VCAM-1 upregulation with inflammation. METHODS: Stereotaxic lipopolysaccharide (LPS, 1 µg) injection into the right hemisphere was used to induce neurovascular inflammation in Balb/c mice. The distribution of VCAM-1 was semi-quantified 24 h post LPS injection using molecular magnetic resonance imaging (MRI) with microparticles of iron oxide (MPIOs) functionalized with VCAM-1 antibody (MPIO-VCAM-1). Mice injected with saline served as control. VCAM-1 is also expressed on vessels associated with metastases, MPIO-VCAM-1 were therefore used to detect metastases. Basal level of metastases in animal brains was measured in a group of mice intracardially injected with cancer cells without LPS intra-cortical injection. To study the impact of pre-existing inflammation on tumor cell entry into the brain, mice were injected with LPS (or saline as above) 24 h prior to intracardiac injection of 4T1 breast cancer cells (105 cells in 100 µL PBS). Metastases imaging was performed 18 days post cancer cells injection. To assess if blocking VCAM-1 would affect metastases implantation, an extra LPS-injected group of mice was injected intravenously with MPIO-VCAM-1 4 hours before 4T1 cells injection. In this group, MRI was performed 3 hours after MPIO-VCAM-1 injection (VCAM-1 imaging), and on day 18 post tumor cell injection (metastases imaging). All MRI experiments were conducted on a small animal 7T scanner (Varian Inc.) with a dedicated mouse head-coil (RAPID MR International) using a T2*-weighted sequence. Following the final imaging session brains were extracted for histological analysis. RESULTS: Both MR and histological data reveal that the metastatic burden significantly increases in the LPS-injected group compared to control conditions. In inflamed animals, blocking VCAM-1 with MPIO-VCAM-1 reduces the metastatic burden back to control values. This suggests that (1) a pre-existing inflammation increases the occurrence of brain metastases and (2) blocking VCAM-1 reduces this effect. CONCLUSION: We demonstrate that inflammation-induced VCAM-1 contributes to tumor cells adhesion in the brain. Therefore, VCAM-1 may represent an attractive therapeutic target to reduce risks of metastasis. Citation Format: Dina Sikpa, Lisa Whittingstall, Jérémie P. Fouquet, Luc Tremblay, Réjean Lebel, Martin Lepage. Pre-existing neurovascular inflammation increases the occurrence of brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 86.