Ali Seyed Mohamed, Chee Soo Khee, Yuen Gan Yik, Olivo Malini
Department of Medical Sciences, National Cancer Centre, Singapore.
Int J Mol Med. 2002 Mar;9(3):257-70.
Photodynamic therapy (PDT) is a clinical approach that utilizes light-activated drugs for the treatment of a variety of pathologic conditions. Human poorly (CNE2) and moderately differentiated (TW0-1) human nasopharyngeal carcinoma (NPC) cells undergo rapid apoptosis when treated with PDT sensitized with Hypocrellin A (HA) and Hypocrellin B (HB). It has been shown that these compounds have a strong photodynamic effect on tumors and viruses. The initiating events of PDT sensitized HA and HB-induced apoptosis are poorly defined. In the current study, we sought to determine whether Fas/FasL upregulation and involvement of mitochondrial events are an early event in HA and HB-treated PDT induced apoptosis. Loss of mitochondrial transmembrane potential, release of cytochrome c, involvement of caspases-8 and -3 and the status caspase-3 specific substrate PARP, were evaluated in PDT treated tumor cells. Photoactivation of HA and HB enhanced both CD95/CD95L expression and induced CD95-signaling dependent cell death in all tumor cell lines studied. CD95/ CD95L expression appeared within 2 h following light activation and appeared to be a primary event in PDT induced apoptosis. Furthermore, these results indicate that release of mitochondrial cytochrome c into the cytoplasm is a secondary event following the activation of initiator caspase-8 preceding caspase-3 activation, cleavage of PARP and DNA fragmentation. Cytochrome c appeared in the cytosol within 2-3 h post PDT. Cleavage of PARP was observed at 3-4 h following PDT and caspase-3 specific inhibitor DEVD-CHO and broad-spectrum caspases inhibitor z-VAD-fmk blocked caspase-3 activation and PARP cleavage suggesting that caspase-3 plays an important role in HA and HB-induced apoptosis.
光动力疗法（PDT）是一种临床治疗方法，它利用光激活药物来治疗多种病理状况。当用竹红菌甲素（HA）和竹红菌乙素（HB）致敏的光动力疗法处理时，人低分化（CNE2）和中分化（TW0-1）人鼻咽癌（NPC）细胞会迅速发生凋亡。已表明这些化合物对肿瘤和病毒具有强烈的光动力效应。HA和HB致敏的光动力疗法诱导凋亡的起始事件尚不清楚。在当前研究中，我们试图确定Fas/FasL上调和线粒体事件的参与是否是HA和HB处理的光动力疗法诱导凋亡的早期事件。在光动力疗法处理的肿瘤细胞中评估线粒体跨膜电位的丧失、细胞色素c的释放、半胱天冬酶-8和-3的参与以及半胱天冬酶-3特异性底物PARP的状态。HA和HB的光激活增强了所有研究的肿瘤细胞系中CD95/CD95L的表达，并诱导了CD95信号依赖性细胞死亡。CD95/CD95L表达在光激活后2小时内出现，似乎是光动力疗法诱导凋亡的主要事件。此外，这些结果表明，线粒体细胞色素c释放到细胞质中是在起始半胱天冬酶-8激活、半胱天冬酶-3激活、PARP裂解和DNA片段化之前的次级事件。细胞色素c在光动力疗法后2-3小时出现在细胞质中。在光动力疗法后3-4小时观察到PARP的裂解，半胱天冬酶-3特异性抑制剂DEVD-CHO和广谱半胱天冬酶抑制剂z-VAD-fmk阻断了半胱天冬酶-3的激活和PARP的裂解，表明半胱天冬酶-3在HA和HB诱导的凋亡中起重要作用。
