Khazanov Elena, Simberg Dmitri, Barenholz Yechezkel
Laboratory of Membrane and Liposome Research, Department of Biochemistry, The Hebrew University-Hadassah Medical School Jerusalem, Israel.
J Gene Med. 2006 Aug;8(8):998-1007. doi: 10.1002/jgm.933.
Recent studies demonstrated the cytotoxic activity of bacterial DNA (pDNA) complexed with cationic lipids. This cytotoxicity is related to the ability of pDNA to induce potently the immune system, which is associated with release of inflammatory cytokines. Both activities seem to be related to the nonmethylated CpG sequences present in the pDNA. Here we study the cytotoxic activity of nonbacterial DNA complexed with cationic lipids against various tumor cell lines.
Various nucleic acids complexed with cationic liposomes were prepared and their cytotoxic activity was studied in cell cultures and in tumor-bearing mice. Cell uptake of lipoplexes was evaluated, and mechanism of DNA cytotoxic activity was studied.
We found that nonbacterial (vertebrate) genomic DNA when complexed with cationic lipids is highly cytotoxic against C-26 and M-109 tumor cells. Cationic lipids alone were not toxic to these cells. The cytotoxic activity does not result from nonspecific acidification of the intracellular milieu, as substitution of DNA by poly-L-glutamate did not result in cytotoxicity, although the level of uptake of anionic charges per cell was similar to that of the nucleic acids, suggesting that this cytotoxic effect is specific to nucleic acids. By studying the nucleic acid fate using confocal microscopy, we found that cytotoxicity correlated with the release of DNA into the cytoplasm following uptake of lipoplexes. Injection of calf thymus DNA-based lipoplexes to mice with peritoneal C-26 metastases resulted in doubling of median survival time and long-term survival in 20% of the tumor-bearing mice. Judging by low levels of IFN-gamma, TNF-alpha and IL-6 in the treated mice, this effect cannot be ascribed to Th-1 inflammation, but rather to a direct cytotoxic effect on the tumor cells.
The above data provide a new insight into the mechanisms of lipoplex-mediated antitumor effects in vitro and in vivo and new perspectives in cancer therapy.
最近的研究表明，与阳离子脂质复合的细菌DNA（pDNA）具有细胞毒性活性。这种细胞毒性与pDNA有效诱导免疫系统的能力有关，而这又与炎性细胞因子的释放相关。这两种活性似乎都与pDNA中存在的非甲基化CpG序列有关。在此，我们研究与阳离子脂质复合的非细菌DNA对各种肿瘤细胞系的细胞毒性活性。
制备了与阳离子脂质体复合的各种核酸，并在细胞培养物和荷瘤小鼠中研究了它们的细胞毒性活性。评估了脂质体复合物的细胞摄取情况，并研究了DNA细胞毒性活性的机制。
我们发现，与阳离子脂质复合的非细菌（脊椎动物）基因组DNA对C-26和M-109肿瘤细胞具有高度细胞毒性。单独的阳离子脂质对这些细胞无毒。细胞毒性活性并非由细胞内环境的非特异性酸化导致，因为用聚-L-谷氨酸替代DNA不会产生细胞毒性，尽管每个细胞摄取的阴离子电荷水平与核酸相似，这表明这种细胞毒性作用是核酸特有的。通过共聚焦显微镜研究核酸的命运，我们发现细胞毒性与脂质体复合物摄取后DNA释放到细胞质中相关。向患有腹膜C-26转移瘤的小鼠注射基于小牛胸腺DNA的脂质体复合物，使中位生存时间加倍，并且20%的荷瘤小鼠实现了长期存活。从治疗小鼠中低水平的干扰素-γ、肿瘤坏死因子-α和白细胞介素-6判断，这种作用不能归因于Th-1炎症，而应归因于对肿瘤细胞的直接细胞毒性作用。
上述数据为脂质体复合物在体外和体内介导的抗肿瘤作用机制提供了新的见解，并为癌症治疗提供了新的视角。
