1Department of Internal Medicine, Chonbuk National University, Korea. 2Department of Nuclear Medicine, Chonbuk National University, Korea. 3Department of Veterinary Medicine, Chonbuk National University, Korea. 4Institute for Medical Sciences, Chonbuk National University, Korea.
ABSTRACT
PURPOSE: Nitric oxide (NO) synthesis has been known to be induced during interleukin-2 (IL-2) therapy. The present study was designed to elucidate mechanisms and roles of IL-2-induced NO synthesis in tumor cells.
MATERIALS AND METHODS: Mechanisms of IL-2-induced NO synthesis were evaluated using in vitro culture systems of BALB/c mouse splenic lymphocytes and Meth-A tumor cells.
Effects of IL-2-induced NO synthesis by Meth-A tumor cells on the tumor cell proliferation were also evaluated using an NO synthase inhibitor, N -monomethyl- L-arginine (MLA).
RESULTS: Cultures of both lymphocytes alone and Meth-A tumor cells alone did not produce any significant amounts of nitrite, a stable metabolite of NO during IL-2 stimulation.
In contrast, cocultures of lymphocytes and Meth-A tumor cells produced a large amount of nitrite during IL-2 stimulation. Addition of culture supernatants of lymphocytes incubated with IL-2 induced nitrite production in Meth-A tumor cell cultures. However, addition of culture supernatants of Meth-A tumor cells incubated with IL-2 did not induce nitrite production in lymphocyte cultures.
Nitrite accumulation was markedly inhibited by addition of anti-interferon-y antibody, confirming the role of the cytokine in mediating tumor cell NO synthesis. MLA inhibited nitrite production by Meth-A tumor cells in a dose-dependent manner in the presence of culture supernatants of lymphocytes incubated with IL-2. Meth-A tumor cell nitrite production in the presence of increasing concentrations of MLA correlated inversely with tumor cell proliferation.
CONCLUSION: NO synthesis can be induced by tumor cells by the secondarily released cytokines from lymphocytes during IL-2 stimulation. Autologous NO synthesized by tumor cells during IL-2 stimulation inhibits proliferation of tumor cells themselves.
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