Disulfiram and copper combination therapy targets NPL4, cancer stem cells and extends survival in a medulloblastoma model

BACKGROUND: Medulloblastoma (MB) is the most common brain malignancy in children, and is still responsible for significant mortality and morbidity. The aim of this study was to assess the safety and efficacy of Disulfiram (DSF), an FDA-approved inhibitor of Aldehyde-Dehydrogenase (ALDH), and Copper (Cu(++)) in human SSH-driven and Group 3 MB. The molecular mechanisms, effect on cancer-stem-cells (CSC) and DNA damage were investigated in xenograft models. METHODS: The cytotoxic and anti-CSC effects of DSF/Cu(++) were evaluated with clonogenic assays, flow-cytometry, immunofluorescence, western-blotting. ONS76, UW228 (SHH-driven with Tp53m), D425med, D283 and D341 (Group 3) cell-lines were used. In vivo survival and nuclear protein localization protein-4 (NPL4), Ki67, Cleaved-Caspase-3, GFAP and NeuN expression were assessed in two Group 3 MB xenografts with immunohistochemistry and western-blotting. RESULTS: Significant in vitro cytotoxicity was demonstrated at nanomolar concentrations. DSF/Cu(++) induced cell-death through NPL4 accumulation in cell-nucleus and buildup of poly-ubiquitylated proteins. Flow-cytometry demonstrated a significant decrease in ALDH(+), Nestin(+) and CD133(+) following treatment, anti-CSC effect was confirmed in vitro and in vivo. DSF/Cu(++) prolonged survival, and increased nuclear NPL4 expression in vivo. CONCLUSIONS: Our data suggest that this combination may serve as a novel treatment, as monotherapy or in combination with existing therapies, for aggressive subtypes of pediatric MB.