Intraperitoneal Fluid Neopterin, Nitrate, and Tryptophan After Regional Administration of Interleukin-12

Activated monocytes-macrophages may be associated with antitumor activity, and activation of these cells by certain cytokines, primarily interferon gamma (IFN-γ), can be indicated by alterations in the concentrations of neopterin, nitrate, or tryptophan. Specimens of peritoneal fluid were obtained from patients with intra-abdominal neoplasia who were undergoing treatment in a phase I trial of weekly intraperitoneal recombinant interleukin-12 (rhIL-12), an inducer of IFN-γ. Concentrations of neopterin, nitrate, tryptophan, IFN-γ, and tumor necrosis factor alpha (TNF-α) were determined at various times during the first 48 hours in 11 patients who received intraperitoneal rhIL-12 in doses ranging from 100 to 1,500 ng/kg. An increase in peritoneal fluid nitrate concentrations was observed in nine of these patients. Increased concentrations of TNF-α and IFN-γ were detected in 3 of 9 and 8 of 11 patients, respectively. Increased peritoneal fluid neopterin concentrations were detected by 24 hours after the injection in all patients studied. A significant increase in the ascitic fluid neopterin level could still be detected after 1 or 2 weeks of treatment (mean ± standard error, 7.8 ± 1.5 nM vs. 4.6 ± 0.3 nM; Wilcoxon test, p = 0.0019), which is consistent with monocyte-macrophage activation. In contrast, the tryptophan concentration was lower (4.7 ± 1.1 μM vs. 6.1 ± 1.2 μM; p = 0.0428) after 1 or 2 weeks of treatment. There was a significant correlation between the dose of rhIL-12 and posttreatment neopterin concentrations (r^s = 0.559, p = 0.0102). The intraperitoneal delivery of rhIL-12 appears to be associated with an immediate, sustained, and dose-dependent increase in peritoneal fluid neopterin, associated in most patients by an increase in IFN-γ and in certain patients by an increase in nitrate and a decrease in tryptophan concentrations.