P10.03.a antipsychotics to treat brain tumors: drug repurposing to bypass the blood brain barrier

Abstract BACKGROUND Approximately half of late-stage melanoma patients develop brain metastases (BM), once metastasized to the brain, survival is generally measured in months. Current treatments, although increasingly effective, are not sufficient for this patient group, necessitating development of new therapeutic options. Drugs targeting BM specifically are a scarcity. To broaden therapeutic options, drug repurposing, i.e. novel uses of drugs already approved for other medical conditions, may prove to be a valuable asset. By design, antipsychotics effectively cross an intact blood-brain barrier. Interestingly, although carrying an increased burden of comorbidity, the schizophrenic population has a similar incidence of cancer when compared to the normal population. Hypotheses regarding the antitumor effect of antipsychotics have therefore been postulated along with several other theories that seek to explain these seemingly contradictory incidence rates. We currently present preliminary data showing that clozapine, a second-generation antipsychotic, effectively inhibits growth of human melanoma brain metastasis (MBM) cell lines in vitro. Objective: To explore the potential of antipsychotics in treating MBM. METHODS Cell cultures including H1, H2, H3 MBM cell lines, as well as normal human astrocytes (NHA) were selected for our experiments. Monolayer, 3D, and IncuCyte viability experiments were performed to determine IC50 doses. FBRO, fetal rat brain organoids were used to study clozapine’s effect on the normal brain environment. Cell migration was measured by scratch wound assays. Apoptosis was studied by flow cytometry. Colony formation assays were performed using 2D clonogenic assays. A protein array was used to find signaling proteins potentially affected by clozapine, which where verified by western blots. RESULTS A viability screening using 6 different neuroleptics showed that clozapine was most effective in inhibiting MBM cell viability, with a favorable therapeutic window to astrocytes. Doses significantly above MBM IC50 doses did not affect viability of brain organoids. MBM cells exhibited a dose-dependent inhibition of cell proliferation, migration, and clonogenic formation. Flow cytometry demonstrated that apoptosis was a major mechanism of cytotoxicity. The protein array showed that CCL3, IL8 and VEGF were downstream targets of clozapine. These results were confirmed by western blots. A partnership with the Dept. of Chemistry (UiB) has resulted in the development and testing of several novel clozapine derivates to reduce therapeutic doses and hopefully minimize potential side effects. CONCLUSION Clozapine shows proof of concept in treating BM with antipsychotics and should be explored further as an adjuvant treatment for melanoma patients at risk of developing brain metastasis.