Li B Y, Ramakrishnan S
Department of Pharmacology, University of Minnesota, Minneapolis 55455.
J Biol Chem. 1994 Jan 28;269(4):2652-8.
Bacterial toxins and ribosomal inhibitory proteins isolated from plants are used to prepare tumor-specific cytotoxic conjugates. The ability of these conjugates to kill tumor cells depends on binding, internalization, translocation to cytoplasm, and translation inhibition. Modulation of any one of these processes can improve cytotoxicity. Since bacterial and plant toxins act at a distinct step in translation, a combination of their activities could be more effective. Therefore, a chimeric protein was prepared by genetically fusing the coding region of the ricin A chain (RTA) and the fragment A of diphtheria toxin (DTA). The hybrid protein (RTA-DTA) expressed in bacteria retained the N-glycosidase activity of the RTA and ADP-ribosylation activity of the DTA. The hybrid toxin was more potent than the ricin A chain (11-fold) and the diphtheria toxin (50-fold) in inhibiting cell-free translation. Immunotoxin made with the hybrid toxin was about 100- and 1000-fold more effective than RTA or DTA conjugate, respectively, in inhibiting tumor cell growth in vitro. These results indicate that the hybrid toxin with dual activities could be useful in preparing potent immunotoxins with better anti-tumor cell activity.
从植物中分离出的细菌毒素和核糖体抑制蛋白被用于制备肿瘤特异性细胞毒性缀合物。这些缀合物杀死肿瘤细胞的能力取决于结合、内化、转运至细胞质以及翻译抑制。对这些过程中任何一个进行调节都可以提高细胞毒性。由于细菌毒素和植物毒素在翻译过程中作用于不同步骤，它们活性的组合可能更有效。因此，通过基因融合蓖麻毒素A链（RTA）的编码区和白喉毒素（DTA）的A片段制备了一种嵌合蛋白。在细菌中表达的杂合蛋白（RTA-DTA）保留了RTA的N-糖苷酶活性和DTA的ADP-核糖基化活性。杂合毒素在抑制无细胞翻译方面比蓖麻毒素A链（强11倍）和白喉毒素（强50倍）更有效。用杂合毒素制备的免疫毒素在体外抑制肿瘤细胞生长方面分别比RTA或DTA缀合物有效约100倍和1000倍。这些结果表明，具有双重活性的杂合毒素可用于制备具有更好抗肿瘤细胞活性的强效免疫毒素。
