Abstract 1492: Unveiling the re-programming of choroid plexus and leptomeningeal metastasis

Abstract Leptomeningeal metastasis (LM) is an increasingly common, fatal complication of breast and lung cancer. Despite aggressive treatment, neurologic deficits accumulate rapidly, and patients generally succumb to LM within months. We must expand our limited mechanistic knowledge of this disease. Under homeostatic conditions, choroid plexus (ChP), highly vascularized structures within the brain ventricles, restrict the entry of macromolecules and cells into the leptomeninges; however, select cancer cells can cross this barrier and grow within the leptomeningeal space. We hypothesize that interactions between cancer and ChP niche cells alter both the niche and the cancer cells, ultimately supporting LM.During neurogenesis, the ChP display substantial extracellular matrix (ECM) remodeling, which is elegantly modulated by dynamic spatiotemporal regulation of MMPs, Wnt signaling, among other effector proteins. Similarly, 2-photon imaging of ChP collected from mice harboring LM revealed a profound ECM remodeling of the ChP when compared with naïve mice. This remodeling was accompanied by increased levels of MMP2 and MMP9 in LM mice. Upon pharmacological inhibition of MMP2 and MMP9 in vivo, we observed a decrease in LM burden and increase in overall survival, which correlates with a decrease in ChP permeability. Interestingly, human CSF from patients with leptomeningeal metastases is also enriched in collagen 1 fragments, MMP2, MMP9 and TIMP1. TIMP1, a MMP9 natural inhibitor, is not present in complex with MMP9, suggesting a role of TIMP1 as a cytokine in LM progression. TIMP1 neutralization and knockout from the cancer cells leads to a decrease in LM burden and increase in overall survival. Together, these data suggest a provocative link between proteolysis and inflammation in LM progression. The use of clinically-annotated human samples and mouse models of LM, and the integration of transcriptomics and proteomics enabled us to identify key signaling pathways, and capture the re-programming of ChP niche and cancer cells that unlock the leptomeningeal space to cancer cells. The timeframe for this evolution will be further revealed by analysis of mouse and human samples at different stages of cancer progression. Citation Format: Ana Rita Nobre, Helen Wang, Rachel Estrera, Isaiah Osei-Gyening, Adrienne Boire. Unveiling the re-programming of choroid plexus and leptomeningeal metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1492.