Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut, United States of America.
PLoS One. 2010 Jul 15;5(7):e11607. doi: 10.1371/journal.pone.0011607.
DCB-3503, a tylophorine analog, inhibits the growth of PANC-1 (human pancreatic ductal cancer cell line) and HepG2 (human hepatocellular cancer cell line) tumor xenografts in nude mice. The inhibition of growth leads to cancer cell differentiation instead of cell death. However, the mechanisms of action of tylophorine analogs is unknown.
METHODOLOGY/PRINCIPAL FINDINGS: In this study, we show that DCB-3503 suppresses the expression of pro-oncogenic or pro-survival proteins with short half-lives, including cyclin D1, survivin, beta-catenin, p53, and p21, without decreasing their mRNA levels. Proteasome inhibitor reversed the inhibitory effect of DCB-3503 on expression of these proteins. DCB-3503 inhibited the incorporation of radiolabeled amino acid and thymidine, and to a much lesser degree of uridine, in a panel of cell lines. The mechanism of inhibition of protein synthesis is different from that of cycloheximide (CHX) as assayed in cell culture and HeLa in vitro translation system. Furthermore, in contrast to rapamycin, DCB-3503 does not affect protein synthesis through the mTOR pathway. DCB-3503 treatment shifts the sedimentation profiles of ribosomes and mRNAs towards the polysomal fractions while diminishing monosome abundance, indicative of the inhibition of the elongation step of protein synthesis. Preferential down regulation of several studied proteins under these conditions is likely due to the relative short half-lives of these proteins.
CONCLUSION/SIGNIFICANCE: The inhibitory effect of DCB-3503 on translation is apparently distinct from any of the current anticancer compounds targeting protein synthesis. Translation inhibitors with novel mechanism could complement current chemotherapeutic agents for the treatment of human cancers and suppress the occurrence of drug resistance.
DCB-3503 是一种土波依定类似物，可抑制裸鼠体内 PANC-1（人胰腺导管癌细胞系）和 HepG2（人肝癌细胞系）肿瘤异种移植物的生长。生长抑制导致癌细胞分化而不是细胞死亡。然而，土波依定类似物的作用机制尚不清楚。
方法/主要发现：在这项研究中，我们表明 DCB-3503 抑制具有短半衰期的原癌基因或生存蛋白的表达，包括细胞周期蛋白 D1、存活素、β-连环蛋白、p53 和 p21，而不降低其 mRNA 水平。蛋白酶体抑制剂逆转了 DCB-3503 对这些蛋白表达的抑制作用。DCB-3503 抑制了一系列细胞系中放射性标记氨基酸和胸苷的掺入，而对尿苷的抑制作用要小得多。在细胞培养和 HeLa 体外翻译系统中，蛋白质合成的抑制机制与环己酰亚胺（CHX）不同。此外，与雷帕霉素不同，DCB-3503 不会通过 mTOR 途径影响蛋白质合成。DCB-3503 处理将核糖体和 mRNA 的沉降谱向多核糖体部分转移，同时减少单核糖体的丰度，表明蛋白质合成的延伸步骤受到抑制。在这些条件下，几种研究蛋白的优先下调可能是由于这些蛋白的半衰期相对较短。
结论/意义：DCB-3503 对翻译的抑制作用显然与任何一种针对蛋白质合成的当前抗癌化合物都不同。具有新机制的翻译抑制剂可以补充当前的化疗药物，用于治疗人类癌症，并抑制耐药性的发生。
