Abstract
Intravenous (IV) administration of purified lipopolysaccharide (LPS) from Salmonella abortus equi to cancer patients induces the formation of high amounts of endogenous cytokines such as tumor necrosis factor- alpha (TNF-alpha) and interleukin-6 (IL-6). On repeated administration of LPS at 2-week intervals, a marked downregulation of the cytokine response was observed, especially between the first and the second challenge. This study sought to determine whether it would be possible to prevent this downregulation by pretreating patients with interferon- gamma (IFN-gamma), which is known to enhance cytokine production by monocytes and macrophages in vitro. Ten patients with disseminated cancer received a first injection of 4.0 ng LPS/kg. Thereafter, patients were divided into two groups. One group received two further LPS injections (4.0 ng/kg) at 2-week intervals. The second group was pretreated (-12 hours) with 50 micrograms IFN-gamma subcutaneously (SC) before the second and third LPS challenge. To prevent constitutional side effects such as fever and chills, patients received 1,600 mg ibuprofen orally before LPS injection. The results of the current study demonstrate that apart from TNF-alpha and IL-6, two other cytokines, interleukin-8 (IL-8) and granulocyte colony-stimulating factor (G-CSF) are produced in cancer patients in response to LPS. LPS application at 2-week intervals resulted in a transient attenuation of all cytokines (TNF-alpha, IL-6, IL-8, G-CSF) on the second challenge. In the case of TNF-alpha, IL-6, and G-CSF, pretreatment with IFN-gamma not only prevented the downregulation, but enhanced the production of these cytokines to levels higher than those obtained after the first LPS challenge. In contrast, the downregulation of IL-8 remained unaffected by IFN-gamma pretreatment. Further studies are warranted to determine whether the prevention of cytokine downregulation by IFN-gamma following repeated LPS injections is of clinical relevance in respect to the antitumor activity of LPS.
