Chimploy Korakod, Díaz G Dario, Li Qingjie, Carter Orianna, Dashwood Wan-Mohaiza, Mathews Christopher K, Williams David E, Bailey George S, Dashwood Roderick H
Linus Pauling Institute, Oregon State University, Corvallis, OR 97331-6512, USA.
Int J Cancer. 2009 Nov 1;125(9):2086-94. doi: 10.1002/ijc.24559.
Chlorophyllin (CHL) is a water-soluble derivative of chlorophyll that exhibits cancer chemopreventive properties, but which also has been studied for its possible cancer therapeutic effects. We report here that human colon cancer cells treated with CHL accumulate in S-phase of the cell cycle, and this is associated with reduced expression levels of p53, p21, and other G(1)/S checkpoint controls. At the same time, E2F1 and E2F4 transcription factors become elevated and exhibit increased DNA binding activity. In CHL-treated colon cancer cells, bromodeoxyuridine pulse-chase experiments provided evidence for the inhibition of DNA synthesis. Ribonucleotide reductase (RR), a pivotal enzyme for DNA synthesis and repair, was reduced at the mRNA and protein level after CHL treatment, and the enzymatic activity was inhibited in a concentration-dependent manner both in vitro and in vivo. Immunoblotting revealed that expression levels of RR subunits R1, R2, and p53R2 were reduced by CHL treatment in HCT116 (p53(+/+)) and HCT116 (p53(-/-)) cells, supporting a p53-independent mechanism. Prior studies have shown that reduced levels of RR small subunits can increase the sensitivity of colon cancer cells to clinically used DNA-damaging agents and RR inhibitors. We conclude that by inhibiting R1, R2, and p53R2, CHL has the potential to be effective in the clinical setting, when used alone or in combination with currently available cancer therapeutic agents.
叶绿酸（CHL）是叶绿素的一种水溶性衍生物，具有癌症化学预防特性，但也因其可能的癌症治疗作用而受到研究。我们在此报告，用CHL处理的人结肠癌细胞积聚在细胞周期的S期，这与p53、p21和其他G(1)/S检查点控制的表达水平降低有关。同时，E2F1和E2F4转录因子升高并表现出增加的DNA结合活性。在CHL处理的结肠癌细胞中，溴脱氧尿苷脉冲追踪实验为DNA合成的抑制提供了证据。核糖核苷酸还原酶（RR）是DNA合成和修复的关键酶，CHL处理后其mRNA和蛋白质水平降低，并且酶活性在体外和体内均以浓度依赖性方式受到抑制。免疫印迹显示，在HCT116（p53(+/+)）和HCT116（p53(-/-)）细胞中，CHL处理降低了RR亚基R1、R2和p53R2的表达水平，支持了一种不依赖p53的机制。先前的研究表明，RR小亚基水平降低可增加结肠癌细胞对临床使用的DNA损伤剂和RR抑制剂的敏感性。我们得出结论，通过抑制R1、R2和p53R2，CHL单独使用或与目前可用的癌症治疗药物联合使用时，在临床环境中可能有效。
