Department of Stem Cell Regulation, Medical Research Institute, Tokyo Medical and Dental University (TMDU), Bunkyo-ku, Tokyo, 1138510, Japan.
Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259-B102, Nagatsuta-cho, Midori-ku, Yokohama, 2268501, Japan.
Sci Rep. 2017 Feb 7;7:42070. doi: 10.1038/srep42070.
Cancer stem cells (CSCs) are dominantly responsible for tumor progression and chemo/radio-resistance, resulting in tumor recurrence. 5-aminolevulinic acid (ALA) is metabolized to fluorescent protoporphyrin IX (PpIX) specifically in tumor cells, and therefore clinically used as a reagent for photodynamic diagnosis (PDD) and therapy (PDT) of cancers including gliomas. However, it remains to be clarified whether this method could be effective for CSC detection. Here, using flow cytometry-based analysis, we show that side population (SP)-defined C6 glioma CSCs (GSCs) displayed much less 5-ALA-derived PpIX fluorescence than non-GSCs. Among the C6 GSCs, cells with ultralow PpIX fluorescence exhibited dramatically higher tumorigenicity when transplanted into the immune-deficient mouse brain. We further demonstrated that the low PpIX accumulation in the C6 GSCs was enhanced by deferoxamine (DFO)-mediated iron chelation, not by reserpine-mediated inhibition of PpIX-effluxing ABCG2. Finally, we found that the expression level of the gene for heme oxygenase-1 (HO-1), a heme degradation enzyme, was high in C6 GSCs, which was further up-regulated when treated with 5-ALA. Our results provide important new insights into 5-ALA-based PDD of gliomas, particularly photodetection of SP-defined GSCs by iron chelation based on their ALA-PpIX-Heme metabolism.
癌症干细胞（CSCs）主要负责肿瘤的进展和化疗/放疗耐药性，导致肿瘤复发。5-氨基酮戊酸（ALA）在肿瘤细胞中特异性代谢为荧光原卟啉 IX（PpIX），因此临床上用作光动力诊断（PDD）和治疗（PDT）包括神经胶质瘤在内的癌症的试剂。然而，仍不清楚这种方法是否能有效用于 CSC 的检测。在这里，我们使用基于流式细胞术的分析方法，表明侧群（SP）定义的 C6 神经胶质瘤 CSCs（GSCs）比非 GSCs 显示出更少的 5-ALA 衍生的 PpIX 荧光。在 C6 GSCs 中，当移植到免疫缺陷小鼠脑中时，具有超低 PpIX 荧光的细胞表现出更高的致瘤性。我们进一步证明，DFO 介导的铁螯合可增强 C6 GSCs 中 PpIX 的低积累，而不是通过利血平介导的 PpIX 外排 ABCG2 抑制。最后，我们发现血红素加氧酶-1（HO-1）基因的表达水平在 C6 GSCs 中较高，用 5-ALA 处理后进一步上调。我们的结果为基于血红素的胶质瘤 5-ALA 基 PDD 提供了重要的新见解，特别是基于 ALA-PpIX-血红素代谢的铁螯合对 SP 定义的 GSCs 的光探测。
