Abstract Leptomeningeal metastasis (LM), a spread of cancer to the cerebrospinal fluid and meninges, is universally and rapidly fatal due to poor detection and no effective treatment. Breast cancers account for a majority of LMs from solid tumors, with triple-negative breast cancers (TNBCs) having the highest propensity to metastasize to LM. The treatment of LM is challenged by poor drug penetration into CNS and high neurotoxicity. Therefore, there is an urgent need for new modalities and targeted therapies able to overcome the limitations of current treatment options. Quadriga has discovered a novel, brain-permeant chemotherapeutic agent that is currently in development as a potential treatment for glioblastoma (GBM). Recently, we have demonstrated dose-dependent in vitro and in vivo anti-tumor activity with various breast cancer cell lines including the human TNBC cell line MDA-MB-231. To evaluate the in vivo antitumor activity of the compound on LM, we used the mouse model of LM based on the internal carotid injection of luciferase-expressing MDA-MB-231-BR3 cells. Once the bioluminescence signal intensity from the metastatic spread reached (0.2 - 0.5) x 106photons/sec, mice were dosed i.v. (8 mg/kg once a week for nine weeks) or i.p. (4 or 8 mg/kg twice a week for nine weeks). Tumor growth was monitored by bioluminescence. The compound was well tolerated and caused a significant delay in metastatic growth resulting in significant extension of survival. Tumors regressed completely in ~ 28 % of treated animals in the i.p. group. Given that current treatments for LM are palliative with only few studies reporting a survival benefit, Quadriga’s new agent could be effective as a therapeutic for both primary and metastatic brain tumors such as LM. REF: https://onlinelibrary.wiley.com/doi/full/10.1002/pro6.43