rIFN-γ-mediated growth suppression of platinum-sensitive and -resistant ovarian tumor cell lines not dependent upon arginase inhibition

Background. Arginine metabolism in tumor cell lines can be influenced by various cytokines, including recombinant human interferon-γ (rIFN-γ), a cytokine that shows promising clinical activity in epithelial ovarian cancer (EOC). Methods. We examined EOC cell lines for the expression of arginase in an enzymatic assay and for transcripts of arginase I and II, inducible nitric oxide synthase (iNOS), and indoleamine 2,3-dioxygenase (IDO) by reverse transcription-polymerase chain reaction. The effects of rIFN-γ on arginase activity and on tumor cell growth inhibition were determined by measuring [³H]thymidine uptake. Results. Elevated arginase activity was detected in 5 of 8 tumor cell lines, and analysis at the transcriptional level showed that arginase II was involved but arginase I was not. rIFN-γ reduced arginase activity in 3 EOC cell lines but increased activity in the 2008 cell line and its platinum-resistant subline, 2008.C13. iNOS transcripts were not detected in rIFN-γ-treated or untreated cell lines. In contrast, IDO activity was induced or increased by rIFN-γ. Suppression of arginase activity by rIFN-γ in certain cell lines suggested that such inhibition might contribute to its antiproliferative effects. However, supplementation of the medium with polyamine pathway products did not interfere with the growth-inhibitory effects of rIFN-γ EOC cells. Conclusions. Increased arginase activity, specifically identified with arginase II, is present in most of the tested EOC cell lines. rIFN-γ inhibits or stimulates arginase activity in certain EOC cell lines, though the decrease in arginase activity does not appear to be associated with the in vitro antiproliferative activity of rIFN-γ. Since cells within the stroma of EOC tissues could also contribute to arginine metabolism following treatment with rIFN-γ or rIFN-γ-inducers, it would be helpful to examine these effects in vivo.