Faculty of Veterinary Medicine, Okayama University of Science, 1-3 Ikoinooka, Imabari, Ehime 794-8555, Japan.
Faculty of Veterinary Medicine, Okayama University of Science, 1-3 Ikoinooka, Imabari, Ehime 794-8555, Japan; Biomedical Science Examination and Research Center, Okayama University of Science, 1-3 Ikoinooka, Imabari, Ehime 794-8555, Japan.
Res Vet Sci. 2021 Jul;137:159-162. doi: 10.1016/j.rvsc.2021.04.030. Epub 2021 Apr 30.
Indoleamine 2,3-deoxygenase (IDO) produced by cancer cells catabolizes tryptophan (TRP) to kynurenine (KYN) in the environment, resulting induction of cancer immune escape through induction of T cell anergy and enhancement of regulatory T cells. Recently, inhibition of IDO has been recognized as one of therapeutic strategies for human neoplastic diseases. However, there have been few reports about IDO-expressing cancers in dogs. In this study, we attempted to examine whether canine mast cell tumour (MCT) cells express IDO and modulate the concentration of TRP and KYN in the environment. BR, MPT-1.2, and MPT-3 cells were used as canine MCT cells. Expression of IDO was examined with RT-PCR and western blotting. Concentrations of TRP and KYN in the culture medium after incubation with canine MCT cells were detected with liquid chromatography-tandem mass spectrometry. The expression of mRNA and protein of IDO were confirmed in all samples extracted from canine MCT cells. TRP concentration in the culture medium was decreased and that of KYN was increased on incubation with canine MCT cells. The ratio of KYN/TRP, widely considered to represent IDO activity, was also significantly elevated. Moreover, treatment with an IDO inhibitor L-1-methyl-tryptophan (L-1MT) clearly diminished the elevation of KYN/TRP ratio induced by the incubation with canine MCT cells. Our results indicate that canine MCT cells could directly regulate the concentrations of TRP and KYN through expressing IDO, suggesting that canine MCT have an immune escape ability. Therefore, inhibition of IDO might be a novel strategy for the treatment of dogs with MCT.
色氨酸 2,3-双加氧酶（IDO）由癌细胞产生，在环境中分解色氨酸（TRP）为犬尿氨酸（KYN），导致 T 细胞无能和调节性 T 细胞增强，从而诱导癌症免疫逃逸。最近，抑制 IDO 已被认为是人类肿瘤疾病的治疗策略之一。然而，关于犬的 IDO 表达癌症的报道很少。在本研究中，我们试图研究犬肥大细胞瘤（MCT）细胞是否表达 IDO，并调节环境中 TRP 和 KYN 的浓度。BR、MPT-1.2 和 MPT-3 细胞用作犬肥大细胞瘤细胞。使用 RT-PCR 和 Western blot 检查 IDO 的表达。用液相色谱-串联质谱法检测与犬肥大细胞瘤细胞孵育后培养基中 TRP 和 KYN 的浓度。从犬肥大细胞瘤细胞中提取的所有样本均证实 IDO 的 mRNA 和蛋白表达。与犬肥大细胞瘤细胞孵育后，培养基中 TRP 浓度降低，KYN 浓度增加。广泛认为代表 IDO 活性的 KYN/TRP 比值也显著升高。此外，用 IDO 抑制剂 L-1-甲基色氨酸（L-1MT）处理可明显降低犬肥大细胞瘤细胞孵育引起的 KYN/TRP 比值升高。我们的结果表明，犬肥大细胞瘤细胞可通过表达 IDO 直接调节 TRP 和 KYN 的浓度，表明犬肥大细胞瘤具有免疫逃逸能力。因此，抑制 IDO 可能是治疗犬肥大细胞瘤的一种新策略。
