Antitumor Synthetic Lipid A Analog DT-5461a Upregulates Cytokine Expression in a Murine Macrophage Cell Line through LPS Pathway

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We previously showed that DT-5461a, a lipid A analog, has antitumor activity and relatively low toxicity in animals. To clarify its immunostimulatory effect we have studied the cytokine inducibility of DT-5461a and the mechanism involved in the cytokine expression in macrophages. While the activity is lower than that of LPS, DT-5461a enhanced production of TNF-α and GM-CSF in the murine macrophage cell line J774.1 in a dose-dependent fashion. Simultaneous addition of IL-4 inhibited DT-5461a and LPS-induced TNF-α production is a similar manner. Expression of cytokine mRNAs including TNF-α IL-1β, IL-6, and GM-CSF was also enhanced by the treatment with DT-5461a. Treatment with cycloheximide indicated that the expression of TNF-α mRNA does not require new protein synthesis. Actinomycin D chase experiments revealed that cytokine mRNAs have rather long half-lives and we could not find significant changes in mRNA stability of cytokines in the J774.1 cells. The binding activity of a nuclear transcription of factor NF-κB was enhanced by treatment with DT-5461a, suggesting enhanced transcription of cytokine genes. Specific binding of [3H]LPS to the cells was significantly inhibited by the addition of DT-5461a. These results indicate that DT-5461a enhances production of a variety of cytokines in macrophages through the LPS receptor sites and that this cytokine induction may occur primarily via transcriptional enhancement. These immunostimulatory effects may provide evidence for the mechanisms of the antitumor effect of this lipid A analog.