P18.02.B COMBINED TREATMENT WITH PHOTODYNAMIC THERAPY AND BCL-XL INHIBITION HAS A PREDOMINANTLY SYNERGISTIC ANTINEOPLASTIC ACTIVITY IN MEDULLOBLASTOMA IN VITRO

Abstract BACKGROUND Medulloblastoma represents one of the most common brain tumors in children. Photodynamic therapy has gained substantial interest as a therapeutic measure for brain tumors. In this study, we performed a preclinical testing of a combined treatment with 5-ALA-based photodynamic therapy (PDT) and the Bcl-xL inhibitor A-1331852 in vitro. MATERIAL AND METHODS The combination therapy was tested on established, primary cultured and stem-like medulloblastoma cells using MTT assays. BLISS analysis was performed for thorough evaluation of the nature of the interaction of both treatment modalities. Spheroids were used to examine the effects of the combination therapy in a 3-dimensional setting. Annexin V/PI staining followed by flowcytometric analysis was used to detect pro-apoptotic effects. Western blot analyses were performed to examine mechanistic effects on the molecular level. Extracellular flux analyses served at examining effects on the tumor cell metabolism. AI-based analysis was performed to examine antimigratory effects. RESULTS Treatment with PDT in combination with Bcl-xL inhibition led to a predominantly synergistic anti-proliferative effect on established, primary cultured and stem-like medulloblastoma cells. The nature of the response towards this combinatorial approach was independent of baseline c-myc expression. In the 3-dimensional setting, this multi-modal therapy resulted in a significantly enhanced inhibitory effect on medulloblastoma spheroids. On the molecular level, PDT and Bcl-xL inhibition combined led to enhanced cleavage of caspases 9 and 3. On the metabolic level, the combination therapy led to a reduction in both, oxidative phosphorylation and the glycolytic rate. In line with this finding, a reduced expression of respiratory chain proteins was found. Moreover, the velocity and the total distance of migrating cells was significantly impaired by the combination treatment. CONCLUSION PDT in combination with Bcl-xL inhibition had a predominantly synergistic inhibitory effect on the cell viability of a broad panel of medulloblastoma cells. This effect was associated with enhanced cleavage of caspases and energy depletion. Further studies are warranted.