P10.16.A Repurposing thioridazine as a novel treatment of melanoma brain metastasis

Abstract

Abstract Background Melanoma shows increasing incidence and has the highest propensity to metastasize to the brain of all primary malignant tumors. Untreated, the median survival time is 2-3 months after diagnosis, while aggressive treatment extends survival to only 4-12 months. Even though targeted therapies and immunotherapy has changed the therapeutic landscape, many of these patient relapse. In this respect, drug repurposing, using old drugs for new purposes, has had several successes for other diseases. The anti-psychotic drug thioridazine (THD) is a dopamine receptor 2 antagonist, with properties to cross an intact blood brain barrier, has shown promising effect on melanoma cells that has escaped prior treatment and on cancer stem cells. However, the therapeutic effects on melanoma brain metastasis (MBM) have not been previously investigated. Material and Methods All experiments were done on MBM cell lines (H1, H2, H3 and H10), which were developed in our lab from patient biopsies obtained after surgery. A monolayer viability assay (WST-1) was used to determine IC50 doses. Migration and proliferation after treatment was studied by IncuCyte live cell imaging. Colony forming properties and the ability of cells to grow in an anchorage free environment after THD treatment was investigated using a 2D clonogenic assay and a 3D soft agar model. Potential drug effects were also studied on normal human astrocytes (NHA) and on fetal rat brain organoids (FRBO), using a Live/Dead viability kit and confocal imaging. Apoptosis and necrosis was studied by Annexin V/propidium iodide (PI) double staining followed by flow cytometric analysis after 72 hours of treatment. Results THD shows a strong cytotoxic effect on MBM cell lines. Cell viability studies showed that THD exerted a dose-dependent inhibition of tumor cell viability (IC50 doses 9-12 µM), while NHA tolerated similar drug concentrations. Tumor cell migration and proliferation were almost completely inhibited with concentrations below the IC50 doses. An inhibition of clonogenic formation and 3D growth was also observed. Bright field microscopy showed changes in MBM morphology in monolayers, but FRBOs were intact after drug treatment. Further, apoptosis in MBM cells was induced after treatment with THD. Conclusion Our preliminary data shows that THD has a strong selective cytotoxicity in MBM cells with minimal effects on NHA and FBRO.