The immunomodulatory effect of levamisole is influenced by postoperative changes and type of lymphocyte stimulant.

The results of both laboratory and clinical research into the immunomodulatory activity of levamisole have shown a considerable degree of inconsistency and sometimes contradiction. This is probably a reflection of the lack of understanding of the mechanism(s) of action of levamisole and it is therefore necessary to base conclusions about its immunomodulatory efficacy in the treatment of disease on experimental assays that take into consideration the in vivo conditions. This investigation was designed to compare the immunomodulatory activity of levamisole under clinically achievable and non-achievable conditions as judged by changes in the perioperative proliferative response of lymphocytes from 30 patients with colorectal cancer. The results obtained showed that proliferation in antigen (purified protein derivative, PPD)-stimulated, but not phytohaemagglutinin(PHA)- or staphylococcal-enterotoxin-B(SEB)-stimulated, lymphocyte cultures was consistently and significantly augmented by levamisole in concentrations of 25 ng-25 micrograms/ml. High concentrations of levamisole (25 micrograms/ml and 100 micrograms/ml) were inhibitory to PHA- and SEB-stimulated, but not PPD-stimulated, lymphocyte cultures, especially in the postoperative period. Of particular interest was the observation that, although levamisole temporarily lost its stimulatory activity in the postoperative period (third postoperative day), it did enhance antigen-stimulated lymphocytes at the time of the nadir of the postoperative suppression of lymphocyte proliferation (first postoperative day). Clinically achievable concentrations of levamisole are therefore effective both before and after operation in enhancing the response of lymphocytes to antigens.

Mechanism of synergy of levamisole and fluorouracil: induction of human leukocyte antigen class I in a colorectal cancer cell line.

BACKGROUND: 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. PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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. IMPLICATIONS: 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.