Department of Pathology and Experimental Medicine, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata, Okayama 700-8558, Japan.
Mol Cell Biochem. 2011 Dec;358(1-2):297-307. doi: 10.1007/s11010-011-0980-5. Epub 2011 Jul 12.
Accumulation of protoporphyrin IX (PpIX) in cancer cells is a basis of 5-aminolevulinic acid (ALA)-induced photodymanic therapy. We studied factors that affect PpIX accumulation in human urothelial carcinoma cell line T24, with particular emphasis on ATP-binding cassette transporter G2 (ABCG2) and serum in the medium. When the medium had no fetal bovine serum (FBS), ALA induced PpIX accumulation in a time- and ALA concentration-dependent manner. Inhibition of heme-synthesizing enzyme, ferrochelatase, by nitric oxide donor (Noc18) or deferoxamine resulted in a substantial increase in the cellular PpIX accumulation, whereas ABCG2 inhibition by fumitremorgin C or verapamil induced a slight PpIX increase. When the medium was added with FBS, cellular accumulation of PpIX stopped at a lower level with an increase of PpIX in the medium, which suggested PpIX efflux. ABCG2 inhibitors restored the cellular PpIX level to that of FBS(-) samples, whereas ferrochelatase inhibitors had little effects. Bovine serum albumin showed similar effects to FBS. Fluorescence microscopic observation revealed that inhibitors of ABC transporter affected the intracellular distribution of PpIX. These results indicated that ABCG2-mediated PpIX efflux was a major factor that prevented PpIX accumulation in cancer cells in the presence of serum. Inhibition of ABCG2 transporter system could be a new target for the improvement of photodynamic therapy.
原卟啉 IX（PpIX）在癌细胞中的积累是 5-氨基酮戊酸（ALA）诱导光动力疗法的基础。我们研究了影响人膀胱癌细胞系 T24 中 PpIX 积累的因素，特别强调了 ATP 结合盒转运蛋白 G2（ABCG2）和培养基中的血清。当培养基中没有胎牛血清（FBS）时，ALA 以时间和 ALA 浓度依赖的方式诱导 PpIX 积累。一氧化氮供体（Noc18）或去铁胺抑制血红素合成酶亚铁螯合酶会导致细胞内 PpIX 积累大量增加，而 fumitremorgin C 或维拉帕米抑制 ABCG2 会导致 PpIX 略有增加。当培养基中添加 FBS 时，细胞内 PpIX 积累水平停止在较低水平，同时培养基中 PpIX 增加，表明 PpIX 外排。ABCG2 抑制剂将细胞内 PpIX 水平恢复到 FBS（-）样品的水平，而亚铁螯合酶抑制剂的作用很小。牛血清白蛋白显示出与 FBS 相似的效果。荧光显微镜观察显示，ABC 转运蛋白抑制剂影响 PpIX 的细胞内分布。这些结果表明，ABCG2 介导的 PpIX 外排是阻止血清存在时癌细胞中 PpIX 积累的主要因素。抑制 ABCG2 转运蛋白系统可能成为改善光动力疗法的新靶点。
