AbdAlla E E, Blair G E, Jones R A, Sue-Ling H M, Johnston D
Department of Biochemistry and Molecular Biology, University of Leeds, England.
J Natl Cancer Inst. 1995 Apr 5;87(7):489-96. doi: 10.1093/jnci/87.7.489.
The use of the combination of fluorouracil (5-FU) and levamisole has been shown to improve the survival of patients with resected Dukes' stage C colon carcinoma. 5-FU is incorporated into RNA, which results in aberrant processing and turnover of RNA. Neither the mechanism of synergy between the two drugs nor the precise molecular mechanism of action of levamisole is known. Each drug has previously been shown to alter the expression of class I human leukocyte antigens (HLA class I) in colorectal cancer cell lines.
The purpose of this study was to explore the mechanism of interaction between 5-FU and levamisole by investigating the effect of this combination on HLA class I gene expression in the colorectal cancer cell line WiDr.
WiDr cells were treated either with 5-FU alone or with 5-FU and levamisole. Expression of HLA class I antigens was analyzed by flow cytometry using the monoclonal antibody W6/32. Specific DNA probes for HLA class I, beta 2-microglobulin, beta-actin, HLA class II, and p53 (also known as TP53) were used in Northern blot analysis of the steady-state level of messenger RNAs (mRNAs) and for "run-on" transcription analysis.
5-FU alone produced more than 50% increases in the expression of the HLA class I antigens, and levamisole caused a further 8%-18% increase. 5-FU caused the steady-state level of HLA class I mRNAs to increase by about 80%, and levamisole enhanced this effect of 5-FU by a further 70%. 5-FU did not increase the other mRNAs. In vitro run-on transcription revealed that 5-FU caused a 20%-57% reduction in RNA synthesis, while levamisole caused a 30%-190% increase in RNA synthesis. Levamisole therefore reversed the inhibition of RNA synthesis caused by 5-FU. Both drugs had a general effect on RNA synthesis that was not restricted to HLA class I transcription.
The apparent synergy between levamisole and 5-FU is a result of the incorporation of 5-FU, which may stabilize HLA class I mRNAs, leading to their accumulation, while levamisole augments the accumulation of these stable mRNAs by increasing the rate of transcription.
Levamisole reduces the toxicity of 5-FU caused by generalized inhibition of RNA synthesis, and at the same time augments the effects of 5-FU, which may be due to selective stabilization of certain mRNAs.
已证明氟尿嘧啶（5-FU）与左旋咪唑联合使用可提高 Dukes' C 期结肠癌切除患者的生存率。5-FU 掺入 RNA 中，导致 RNA 异常加工和周转。两种药物之间的协同作用机制以及左旋咪唑的确切分子作用机制均不清楚。此前已证明每种药物都会改变结肠癌细胞系中 I 类人类白细胞抗原（HLA I 类）的表达。
本研究的目的是通过研究该组合对结肠癌细胞系 WiDr 中 HLA I 类基因表达的影响，探讨 5-FU 与左旋咪唑之间的相互作用机制。
WiDr 细胞分别用单独的 5-FU 或 5-FU 与左旋咪唑处理。使用单克隆抗体 W6/32 通过流式细胞术分析 HLA I 类抗原的表达。用于 HLA I 类、β2-微球蛋白、β-肌动蛋白、HLA II 类和 p53（也称为 TP53）的特异性 DNA 探针用于信使 RNA（mRNA）稳态水平的 Northern 印迹分析和“连续”转录分析。
单独使用 5-FU 使 HLA I 类抗原的表达增加超过 50%，左旋咪唑使表达进一步增加 8%-18%。5-FU 使 HLA I 类 mRNA 的稳态水平增加约 80%，左旋咪唑使 5-FU 的这种作用进一步增强 70%。5-FU 未增加其他 mRNA。体外连续转录显示，5-FU 使 RNA 合成减少 20%-57%，而左旋咪唑使 RNA 合成增加 30%-190%。因此，左旋咪唑逆转了 5-FU 对 RNA 合成的抑制作用。两种药物对 RNA 合成均有普遍影响，不限于 HLA I 类转录。
左旋咪唑与 5-FU 之间明显的协同作用是 5-FU 掺入的结果，5-FU 可能使 HLA I 类 mRNA 稳定，导致其积累，而左旋咪唑通过增加转录速率增强这些稳定 mRNA 的积累。
左旋咪唑降低了因 RNA 合成普遍抑制引起的 5-FU 的毒性，同时增强了 5-FU 的作用，这可能是由于某些 mRNA 的选择性稳定。
