CSIG-12. BXQ-350 INDUCES MITOPHAGY IN GBM CELLS LEADING TO CELL DEATH

Abstract BACKGROUND Mitophagy is an autophagic phenomenon where defective mitochondria are selectively degraded. When mitochondria need recycling, the cell upregulates the production of the lipid C-18 ceramide on the mitochondria and lipoprotein LC3B-II on the lysosome, which transitions to an autophagolysosome. This creates a signal causing the degradation of mitochondria. Here we show that BXQ-350, a novel protein-lipid small molecule consisting of the ceramide creating protein Saposin C and the lipid Dioleoyl Phosphatidylserine (DOPS), induces glioblastoma cells into performing mitophagy. Increased production of mitophagy associated proteins, C-18, and LC3B-II leads to the degradation of healthy mitochondria followed by cell death. METHODS The GBM cell lines, Gli36 and U87 cells, were used to determine if increased mitophagy was occurring in response to BXQ-350 treatment. Protein abundance was measured using SILAC proteomics. Ceramide levels were analyzed using LC/MS-MS. Western Blot analysis was used to measure differences in LC3B-II levels. Mitophagy was measured using Mtphagy Dye from Dojindo and the BioTek Cytation 5 microscope. RESULTS Proteomics showed cells treated with BXQ-350 had an increase in proteins associated with overexpression of C-18 ceramide or autophagolysosome maturation. Western blots analysis showed a marked increase in LC3B-II in BXQ-350 treated cells. Furthermore, cells treated with BXQ-350 had increased levels of C-18 ceramide. The Mtphagy dye showed that as BXQ-350 concentrations increased, the percentage of cells positive for Mitophagy increased. To determine if mitophagy occurs in association with BXQ-350 cytotoxicity, medias with varying BXQ-350 cytotoxicity were used. The Mtphagy dye showed cytotoxic BXQ-350 medias increased levels of mitophagy, while noncytotoxic medias display no increase in mitophagy. CONCLUSION BXQ-350 causes the increase of mitophagy signaling proteins, C-18 ceramide and LC3B-II production, resulting in the formation of autophagolysosomes which track towards the mitochondria initiating mitophagy. This leads to aberrant mitophagy where cells degrade healthy mitochondria leading to mitophagic cell death.