TMET-11. BERBERINE AS A POTENTIAL ENHANCER FOR 5-ALA-MEDIATED FLUORESCENCE IN GLIOBLASTOMA: INCREASING DETECTABILITY OF INFILTRATING GLIOMA STEM CELLS TO OPTIMIZE 5-ALA-GUIDED SURGERY

Abstract

Abstract OBJECTIVE The prognosis of glioblastoma multiforme correlates with residual tumor volume. In fluorescence-guided surgery, 5-aminolevulinic acid (5-ALA) has been used to maximize safe resection. We searched for repositioning drugs that affect mitochondrial functions and energy metabolism, identifying berberine (BBR) as a potential enhancer of 5-ALA-mediated protoporphyrin IX (PpIX) fluorescence (5-ALA-fluorescence). Here, we investigated whether BBR can be applied to clinical practice as a 5-ALA-fluorescence enhancer. METHODS Effects of BBR on 5-ALA-fluorescence in glioma cells and GSCs were evaluated by flow cytometry (fluorescence-activated cell sorting; FACS) analysis. As 5-ALA is metabolized for heme synthesis, effects of BBR on mRNA expressions of seven enzymes in the heme-synthesis pathway were analyzed. Enzymes showing significantly higher expression than control in all cells were identified and protein analysis was performed. To examine clinical availability, the detectability and cytotoxicity of BBR in tumor-transplanted mice were analyzed. RESULTS Fluorescence microscopy revealed much more intense 5-ALA-fluorescence in both GSCs and non-stem cells with 5-ALA and BBR than with 5-ALA alone. FACS disclosed that BBR greatly enhanced 5-ALA-fluorescence compared to 5-ALA alone and enhancement was much higher for GSCs than for glioma cells. Among the seven enzymes examined, BBR upregulated mRNA expressions of ALA synthetase 1 (ALAS1) more highly in all cells, and activated ALAS1 through deregulating ALAS1 activity inhibited by the negative feedback of heme. In vivo study showed that 5-ALA-fluorescence with 5-ALA and BBR was significantly stronger than with 5-ALA alone, and the sensitivity and specificity of BBR-enhanced fluorescence were both 100%. In addition, BBR did not show any cytotoxicity for normal brain tissue. CONCLUSIONS BBR enhanced 5-ALA-mediated PpIX fluorescence by upregulating and activating ALAS1 through deregulation of negative feedback inhibition by heme. BBR is a clinically used drug with no side effects. BBR is expected to augment fluorescence-guided surgery and photodynamic therapy.