Sung C, Wilson D, Youle R J
Chemical Engineering Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 1991 Aug 5;266(22):14159-62.
Immunotoxins comprised of a monoclonal antibody covalently coupled to recombinant ricin A chain or to a binding-defective form of diphtheria toxin were compared with respect to their rates of protein synthesis inhibition and efficiencies of killing target cells. Protein synthesis inhibition rates were established by measuring the incorporation of L-[14C]leucine in toxin-treated cells relative to untreated cells at several times after exposure of cells to an immunotoxin. Cell killing was assessed by a limiting dilution assay which measures the number of cells surviving toxin treatment relative to untreated cells. At equivalent protein concentrations, the diphtheria toxin immunotoxin inhibited protein synthesis significantly more rapidly than the ricin A immunotoxin but, contrary to previous predictions, achieved a significantly lower cell kill. Thus, the kinetics of protein synthesis inactivation do not necessarily correlate with killing efficiencies. Possible explanations for these results are that the effect of the diphtheria toxin immunotoxin on protein synthesis is partially reversible or that the diphtheria toxin immunotoxin enters the cytosol at a faster rate than the ricin A immunotoxin but also is degraded at a faster rate.
将由单克隆抗体与重组蓖麻毒素A链或与结合缺陷型白喉毒素共价偶联而成的免疫毒素，就其蛋白质合成抑制率和杀伤靶细胞的效率进行了比较。通过在细胞暴露于免疫毒素后的几个时间点，测量毒素处理细胞中L-[14C]亮氨酸的掺入量相对于未处理细胞的情况，来确定蛋白质合成抑制率。通过有限稀释试验评估细胞杀伤情况，该试验测量毒素处理后存活细胞的数量相对于未处理细胞的数量。在等效蛋白质浓度下，白喉毒素免疫毒素抑制蛋白质合成的速度明显比蓖麻毒素A免疫毒素快，但与先前的预测相反，其细胞杀伤率明显较低。因此，蛋白质合成失活的动力学不一定与杀伤效率相关。这些结果的可能解释是，白喉毒素免疫毒素对蛋白质合成的作用部分是可逆的，或者白喉毒素免疫毒素进入细胞质的速度比蓖麻毒素A免疫毒素快，但降解速度也更快。
