2016年7月1日 訊 /生物谷BIOON/ --結腸癌（CRC）是世界上第三大常見的癌症類型，同時也是致死率第四高的癌症。常用的針對性療法是結合手術、放療與化療。5-FU是一類常見的治療惡性CRC的化療藥物，結合其藥物，該治療能夠達到40%-50%的反應效果。然而，很多因素影響了患者對5-FU的耐受性，比如胸腺嘧啶合成酶的缺陷以及p53的突變。恢復5-FU在這些患者體內的敏感性是十分重要的挑戰。
儘管5-FU此前被證明能夠誘導癌細胞發生凋亡，不過其它類型的程序性細胞死亡也受到一定的關注，比如壞死性凋亡（necroptosis）。壞死性凋亡是一類有序的細胞壞死現象。與細胞凋亡相似，壞死性凋亡也需要一系列的胞內信號轉導，但是它不依賴caspase激酶的激活。目前研究最清楚的壞死性凋亡依賴RIP1，該激酶是TNFR1受體下遊決定細胞存活或死亡的關鍵分子。Necrostatins是RIP-1特異性的激酶抑制劑，能夠抑制RIP-1介導的細胞壞死。大部分癌細胞對TNFR1介導的細胞凋亡都明顯耐受，因此，找到能夠引發癌細胞發生壞死性凋亡的方法是治療癌症的有效手段。
為了探究化療手段如何引發癌細胞發生壞死性凋亡，來自德國海德堡大學的W Roth課題組進行了深入研究，相關結果發表在最近一期的《oncogene》雜誌上。
首先，作者利用5-FU對結腸癌細胞系進行刺激，同時加入caspase 抑制劑Z-VAD。結果顯示，Z-VAD能夠有效提高癌細胞對5-FU的敏感度，從而引發大量的細胞死亡。
進一步，作者通過生化的手段證明5-FU與Z-VAD的聯合處理使得細胞發生了壞死性凋亡反應，而這一效應依賴於胞內RIP-1以及MLKL的活性。
之後，作者通過RNA沉默的方式證明上述兩種藥物引發的癌細胞壞死性凋亡需要依賴細胞表面的TNFR1的活性，而細胞的壞死性凋亡能夠引發細胞分泌TNFa，而TNFa的分泌依賴胞內NF-kB以及RIP1的活性。上述實驗表明5-FU與Z-VAD引發的壞死性凋亡能夠引發自分泌TNFa的連鎖反應。
最後，作者通過體內試驗證明了上述兩種藥物的聯合處理在殺傷腫瘤中的作用。(生物谷Bioon.com）
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doi:10.1038/onc.2015.398
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Inhibition of caspases primes colon cancer cells for 5-fluorouracil-induced TNF-α-dependent necroptosis driven by RIP1 kinase and NF-κB
M Oliver Metzig, D Fuchs, K E Tagscherer, H-J Gr?ne, P Schirmacher and W Roth
Resistance towards the drug 5-fluorouracil (5-FU) is a key challenge in the adjuvant chemotherapy of colorectal cancer (CRC), and novel targeted approaches are required to improve the therapeutic outcome. Necroptosis is a recently discovered form of programmed cell death, which depends on receptor interacting protein 1 (RIP1) and particularly occurs under caspase-deficient conditions. The targeted induction of necroptosis represents a promising strategy to overcome apoptosis resistance in cancer. The aim of this study was to systematically explore the usage of pan-caspase inhibitors to sensitize resistant CRC cells for 5-FU. We found that pan-caspase inhibitors facilitated 5-FU-induced necroptosis, which was mediated by autocrine secretion of tumor necrosis factor α (TNF-α). TNF-α production was driven by nuclear factor κB (NF-κB) and required RIP1 kinase. In vivo xenograft experiments showed that the novel pan-caspase inhibitor IDN-7314 in combination with 5-FU synergistically blocked tumor growth. Ex vivo experiments with fresh human CRC tissue specimens further indicated that a subgroup of patients could benefit from combinatory treatment. Thereby, elevated levels of secreted TNF-α and expression of components of the necroptotic pathway might help to predict the sensitivity to pro-necroptotic therapies. Together, our results shed new light on the molecular regulation of necroptosis by NF-κB and RIP1. Moreover, we identify necroptotic cell death as an important effector mechanism of 5-FU-mediated anti-tumoral activity. On the basis of this study, we propose pan-caspase inhibitors as a novel approach in the adjuvant chemotherapy of CRC.