Objective: The prognosis of glioblastoma (GBM) correlates with residual tumor volume after surgery. In fluorescence-guided surgery, 5-aminolevulinic acid (ALA) has been used to maximize resection while avoiding neurological morbidity. However, not all tumor cells, particularly glioma stem cells (GSCs), display 5-ALA-mediated protoporphyrin IX (PpIX) fluorescence (5-ALA fluorescence). The authors searched for repositioned drugs that affect mitochondrial functions and energy metabolism, identifying berberine (BBR) as a potential enhancer of 5-ALA fluorescence. In this study, they investigated whether BBR can enhance 5-ALA fluorescence in GSCs and whether BBR can be applied to clinical practice as a 5-ALA fluorescence enhancer.
Methods: The effects of BBR on 5-ALA fluorescence in glioma and GSCs were evaluated by flow cytometry (fluorescence-activated cell sorting [FACS]) analysis. As 5-ALA is metabolized for heme synthesis, the effects of BBR on mRNA expressions of 7 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 showed that BBR greatly enhanced 5-ALA fluorescence compared with 5-ALA alone, and enhancement was much higher for GSCs than for glioma cells. Among the 7 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. An 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 surrounding the tumor mass.
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 significantly augment fluorescence-guided surgery and photodynamic therapy.
Keywords: 5-aminolevulinic acid; berberine; fluorescence-guided surgery; glioblastoma; heme synthesis; tumor.