Astroglia Induce Cytotoxic Effects on Brain Tumors via a Nitric Oxide-dependent Pathway Both in Vitro and in Vivo

OBJECTIVE: In the central nervous system, astroglia produce nitric oxide (NO) in response to cytokines. We investigated whether cytokine stimulation of astroglia could inhibit brain tumor cell growth in vitro and prolong survival in vivo via an NO-dependent pathway. METHODS: Astroglia cultures were stimulated with the cytokines lipopolysaccharide and interferon-γ and subsequently seeded with tumor cell lines. Wild-type mice and inducible NO synthase-knockout mice received in vivo cytokine stimulation followed by B16F10 murine melanoma challenge. RESULTS: Our in vitro studies demonstrate that astroglia stimulated to produce NO by the addition of cytokines dose-dependently inhibit the growth of one primary rat brain tumor cell line (9L) and three primary human brain tumor cell lines (H80, U87, and U373). This inhibition of tumor cell growth is also observed in metastatic cell lines (B16F10 melanoma, Lewis lung carcinoma, and CT26 colon). Cultured astrocytes from inducible NO synthase-knockout mice, which are incapable of induction of NO, are without the enhanced tumoricidal effect. Furthermore, when C57BL/6 mice are primed to produce NO through stereotactic intracranial administration of lipopolysaccharide plus interferon-γ and subsequently challenged with B16F10 murine melanoma, survival is significantly prolonged, with a median survival of 26 days versus 16 days in the control group (P < 0.001). The addition of an NO synthase inhibitor (N^G-nitro-L-arginine methyl ester) decreases this beneficial effect (median survival, 21 d). CONCLUSION: These findings suggest that NO may have an important role as a defense mechanism molecule against brain tumors; stimulation or modification of this mechanism may represent a new approach to the treatment of primary and metastatic brain tumors.