BSLD-05 Homoharringtonine Is Effective Against Leptomeningeal Disease From Melanoma in Preclinical Models Using Patient-Derived Circulating Tumor Cells

Abstract BACKGROUND Leptomeningeal disease in melanoma (M-LMD) is a rare but fatal metastasis with limited treatment options and a poor prognosis. A major challenge in developing effective therapies is the lack of patient-derived models, such as cerebrospinal fluid-circulating tumor cells (PD-CSF-CTCs). Additionally, collecting and analyzing M-LMD specimens is difficult. To overcome these barriers, we established CSF and tissue collection methods, successfully propagated ex vivo CSF-CTCs, and generated patient-derived xenograft models. These resources enabled proteomic and transcriptomic analyses, revealing unique LMD-specific biological pathways. This study explores PD-CSF-CTCs to identify clinical compounds targeting these pathways with in vitro and in vivo efficacy. METHODS PD-CSF-CTCs were derived and propagated from M-LMD patients. A 384-well high-throughput assay screened over 1,400 FDA-approved small-molecule compounds to identify those inhibiting cell proliferation. The most sensitive compound was validated in vivo using intrathecal (IT) delivery in M-LMD xenografts. RESULTS Of 1,436 FDA-approved compounds, 20 (~1.4%) exhibited complete cytotoxicity in PD-CSF-CTCs and murine melanoma cell lines. The most potent included ponatinib (EC50: 1.85–4.06e-06), sorafenib (EC50: 9.57–9.77e-06), ceritinib (EC50: 1.84–2.05e-06), and homoharringtonine (HHT) (3.63–4.11e-08). In a randomized murine M-LMD study, we selected HHT, a plant-derived, semisynthetic cephalotaxine ester compound that can penetrate the blood-brain and blood-CSF barriers and has cytotoxic effects against multiple cancers, including melanoma. Our results showed that IT HHT (24.0 μg daily) was well-tolerated, significantly prolonged survival (P 0.001; Mantel-Cox test), and induced a complete response in 27% of mice, maintaining body weight and motor function. CONCLUSION This study presents a novel approach for rational therapeutic development in M-LMD. Our data suggest the potential of FDA-approved HHT for M-LMD treatment. Future studies will explore HHT's molecular mechanisms and its efficacy in other LMD types, including breast and lung cancers.