Abstract
BackgroundThe indoleamine 2, 3-dioxygenase (IDO) inhibitor 1-methyl-tryptophan (1-MT) is currently being used in clinical trials in patients with relapsed or refractory solid tumors by inhibiting tumor immune escape. A greater understanding of IDO activity is required to begin to understand the molecular mechanism by which drugs work. This study was conducted to investigate of the clinical significance of 1-methyl-tryptophan (1-MT) in treating carboplatin-resistant (CBP-resistant) ovarian cancer and its mechanism of action.MethodsUsing a medium dose, intermittent treatment method, a clinically relevant CBP-resistant human ovarian cancer cell line (SKOV3/CBP) was established. SKOV3/CBP cells were treated with normal serum (control) or 1-MT (0.25 ng/mL) for 4 h (SKOV3/CBP + 1-MT). Cell proliferation, invasion and IDO expression in SKOV3, SKOV3/CBP and SKOV3/CBP + 1-MT cells were determined by MTT assays, Matrigel invasion chambers assays and ELISAs, respectively. The half-maximal inhibitory concentration (IC50) and resistance index (RI) were also calculated. The killing ability of the NK cells and CD8+ T cells co-cultured with SKOV3, SKOV3/CBP and SKOV3/CBP + 1-MT cells were determined by LDH activity assays and the INF-γcounting method.ResultsThe SKOV3/CBP cell line displayed an increased IC50 compared to the SKOV3 cell line (P < 0.05) under CBP treatment. Treatment with 1-MT significantly decreased the IC50 and RI of SKOV3/CBP cells. Furthermore, 1-MT treatment not only reduced the invasion ability, but also suppressed IDO expression in the drug-resistant SKOV3/CBP + 1-MT cell line as compared to the SKOV3/CBP cell line. Furthermore, 1-MT enhanced the killing ability of NK cells and the amount of INF-γsecreted from CD8+ T cells which were co-cultured with the SKOV3/CBP cell line.ConclusionOur data suggested that 1-MT inhibits the invasion of CBP-resistant ovarian cancer cells via down-regulation of IDO expression which leads to re-activation of immune cell function. We provide a conceptual foundation for the clinical development of 1-MT as an anti-tumor immunomodulator for chemotherapy resistant ovarian cancer patients.
Highlights
The indoleamine 2, 3-dioxygenase (IDO) inhibitor 1-methyl-tryptophan (1-MT) is currently being used in clinical trials in patients with relapsed or refractory solid tumors by inhibiting tumor immune escape
The results showed that IDO was expressed in the SKOV3, SKOV3/CBP and SKOV3/CBP + 1-MT cell lines
IDO expression in the drug-resistant SKOV3/CBP cell line was significantly higher than SKOV3 cells and IDO expression was significantly decreased in CBPresistant SKOV3 cell after 1-MT treatment (Fig. 2)
Summary
The indoleamine 2, 3-dioxygenase (IDO) inhibitor 1-methyl-tryptophan (1-MT) is currently being used in clinical trials in patients with relapsed or refractory solid tumors by inhibiting tumor immune escape. Clinical trials combining chemotherapy and IDO inhibitors, such as 1-methy-D-tryptophan (1-MT) and NLG919, for treatment of human tumors have commenced [9,10,11,12]. Such approaches have not been attempted in ovarian tumors and the mechanism by which IDO regulates tumor progression in this setting is unknown
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