Integrated Cancer Research Program, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, India.
Cell Death Dis. 2011 Sep 8;2(9):e207. doi: 10.1038/cddis.2011.90.
Mitochondrial cytochrome c (cyt. c) release and caspase activation are often impaired in tumors with Bcl-2 overexpression or Bax and Bak-defective status. Direct triggering of cell death downstream of Bax and Bak is an attractive strategy to kill such cancers. Small molecule compounds capable of direct caspase activation appear to be the best mode for killing such tumors. However, there is no precise model to screen such compounds. The currently employed cell-free systems possess the inherent drawback of lacking cellular contents and organelles that operate in integrating cell death signaling. We have developed highly refined cell-based approaches to validate direct caspase activation in cancer cells. Using this approach, we show that PAC-1 (first procaspase-activating compound), the first direct activator of procaspases identified in a cell-free system, in fact requires mitochondrial cyt. c release for triggering caspase activation similar to other antitumor agents. It can induce significant caspase activation and cell death in the absence of Bax and Bak, and in cells overexpressing Bcl-2 and Bcl-xL. This study for the first time defines precise criteria for the validation of direct caspase-activating compounds using specialized cellular models that is expected to accelerate the discovery of potential direct caspase activators.
线粒体细胞色素 c（cyt. c）释放和半胱天冬酶激活在 Bcl-2 过表达或 Bax 和 Bak 缺陷的肿瘤中经常受损。直接触发 Bax 和 Bak 下游的细胞死亡是杀死此类癌症的一种有吸引力的策略。能够直接激活半胱天冬酶的小分子化合物似乎是杀死此类肿瘤的最佳方式。然而，目前还没有精确的模型来筛选此类化合物。目前使用的无细胞系统存在固有缺陷，即缺乏参与整合细胞死亡信号的细胞内容物和细胞器。我们已经开发了高度精细的基于细胞的方法来验证癌细胞中直接半胱天冬酶的激活。使用这种方法，我们表明 PAC-1（第一个细胞因子激活化合物），第一个在无细胞系统中鉴定的直接前半胱天冬酶激活剂，实际上需要线粒体 cyt. c 释放来触发半胱天冬酶激活，类似于其他抗肿瘤药物。它可以在没有 Bax 和 Bak 的情况下诱导显著的半胱天冬酶激活和细胞死亡，并且在过度表达 Bcl-2 和 Bcl-xL 的细胞中也是如此。这项研究首次使用专门的细胞模型定义了验证直接半胱天冬酶激活化合物的精确标准，预计将加速潜在直接半胱天冬酶激活剂的发现。
