Based on the recent observation of others that IL-10 has little toxicity when administered systemically to human volunteers and also on the findings of this study that it has antitumor and antimetastitic properties in mice, possible use of IL-10 in the treatment of human metastatic cancers deserves consideration.

Recent studies suggest that endogenously generated nitric oxide (NO) may mediate the effects of cytokines in a variety of tissues. In an effort to determine whether NO generation mediates any of the intraovarian actions of interleukin-1 beta (IL-1 beta), we have looked for and characterized the accumulation of nitrite by IL-1 beta-treated, cultured whole ovarian dispersates. Application of IL-1 beta significantly enhanced basal nitrite release in a dose-, cell density- and time-dependent manner, the latter characterized by a lag time of about 20 h, suggestive of induction of NO synthase (NOS). Cellular NOS activity was also elevated by IL-1 beta. Sustained nitrite accumulation required continuous application of IL-1 beta. The maximally stimulating dose of IL-1 beta (50 ng/ml) produced a 10-fold increase in nitrite accumulation by 96 h of culture, an effect reduced 23% when cells were cultured in substrate (i.e., arginine)-free media. IL-1 beta-stimulated nitrite accumulation was reduced to control levels by the simultaneous application of an IL-1 beta receptor antagonist, thereby suggesting a specific receptor-mediated effect. Both the control and IL-1 beta-stimulated levels of nitrite accumulation were attenuated in a dose-dependent manner by inhibitors that favor the inducible form of NOS. In contrast, selective inhibitors of the constitutive form of NOS were significantly less potent. No inhibition was noted after application of an inactive stereoisomeric analogue. IL-1 beta-induced nitrite accumulation was shown to require cell-cell interaction between granulosa and theca-interstitial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

Transfection of cDNA for IL‐10 into line 66.1 murine mammary tumor cells results in marked suppression of tumor growth and metastasis. Others have reported that nitric oxide has potent antitumor activity and IL‐10 is known to regulate the inducible isoform of nitric oxide synthase (iNOS) expressed in macrophages. We identified nitric oxide production in mammary tumors as indicated by electron paramagnetic resonance detection of nitric oxide‐hemoglobin (NO‐Hb). IL‐10 expression resulted in elevated levels of NO‐Hb in mammary tumors. Immunohistochemical examination of mammary tumors for iNOS protein revealed few positively staining cells in parental or control neo‐transfected tumors but strong iNOS staining in all IL‐10 transfected tumors, consistent with the NO‐Hb data. To determine if mammary epithelial tumor cells themselves, express nitric oxide synthase activity, cultured tumor cells were treated with pro‐inflammatory cytokines and nitrite accumulation was assessed in the conditioned medium. All IL‐10 producing cell lines accumulated uM concentrations of nitrite in response to short term (24 hr) cytokine stimulation. Cells not expressing IL‐10 (parental and neo‐transfectants) accumulated no nitrite under similar culture conditions. After longer stimulation (48 hr), parental and 66‐neo cells accumulated lower amounts of nitrite. IL‐10 gene transfer is associated with increased iNOS protein expression and enzymatic activity detected both in vitro<0R> and in vivo<0R>. Our findings suggest that the antimetastatic and antitumor activity of IL‐10 is related to enhanced production of nitric oxide. Int. J. Cancer 76:713–719, 1998.© 1998 Wiley‐Liss, Inc.