Abstract 2436: CIRBP is a functional mediator of leptomeningeal metastasis

Background: Cold-Inducible RNA Binding Protein (CIRBP) has been implicated in cancer initiation. Moreover, we have previously identified an association of CIRBP with the invasive growth of parenchymal brain metastases. Using a patient-derived xenograft (PDX) model, in which cells implanted in the mouse mammary fat pad spontaneously metastasize to the leptomeninges, we identified CIRBP as being elevated in leptomeningeal metastases (LM) compared to matched primary mammary tumors. LM grow in the subarachnoid space that harbors the cerebral spinal fluid (CSF). The leptomeninges represent an inhospitable environment for disseminated cancer cells since the CSF is mitogen and nutrient poor. To investigate the importance of CIRBP for metastatic breast cancer cells in the leptomeninges, we stably reduced CIRBP expression in MDA-MB-231 cells and performed mammary fat pad and cranial injections. CIRBP knockdown had no influence on primary tumor growth, but diminished growth within the brain. Hypothesis: We hypothesize that CIRBP functions as a stress response protein enabling cancer cells to grow in the harsh environment of the CSF. Results: In response to various cellular stressors, such as hypothermia, hypoxia or UV irradiation, CIRBP can translocate from the nucleus to the cytoplasm. We show that culturing MDA-MB-231 cells in artificial CSF (aCSF) also causes CIRBP relocation from nucleus to cytoplasm. Using RNA-IP approaches, we have identified mRNAs bound by CIRBP in breast cancer cells treated with aCSF. Ultimately, we will determine whether any of the identified CIRBP-regulated targets contribute to the formation of LM. Finally, we have generated CIRBP variants that are confined either to the nucleus or the cytoplasm. We are currently assessing the ability of these compartment-restricted CIRBP proteins to promote the formation of central nervous system metastases. Conclusions: We have identified CIRBP as a promoter of leptomeningeal metastasis. Our results have begun to reveal the mechanisms through which CIRBP mediates this process. Citation Format: Rima Ezzeddine, Matthew Dankner, Paul Savage, Steven Hebert, William Brothers, Matthew G. Annis, Sarah M. Maritan, Marc R. Fabian, Claudia Kleinman, Morag Park, Peter M. Siegel. CIRBP is a functional mediator of leptomeningeal metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr