Degradation Product Of Thymidine Research Articles

Thymidine phosphorylase enhances reactive oxygen species generation and interleukin-8 expression in human cancer cells

Thymidine phosphorylase (TP) is an angiogenic factor that plays a pivotal role in tumor angiogenesis. Various kinds of solid tumors express TP and high TP activity is correlated with microvessel density. We have previously reported that TP enhances interleukin-8 (IL-8) expression in KB human epidermoid carcinoma cells. In this study, TP was shown to be involved in enhanced expression of IL-8 in EJ human bladder cancer cells and Yumoto human cervical cancer cells as well as KB human epidermoid carcinoma cells. The enzymatic activity of TP was required for the enhanced expression of IL-8. A degradation product of thymidine was implicated in the enhanced expression of IL-8. TP augmented reactive oxygen species (ROS) generation in KB and Yumoto cells, and the enzymatic activity of TP was again required for the generation of ROS. An antioxidant, N-acetylcysteine (NAC), attenuated the generation of ROS and IL-8mRNA expression in KB and Yumoto cells, and H2O2 increased IL-8mRNA expression in Yumoto cells, suggesting that ROS generated by TP caused the increased expression of IL-8mRNA. Since TP also reduced cellular glutathione levels and transcription of γ-GCS in KB cells, the TP-induced augmentation of ROS may be partially attributed to the decreased glutathione. Our findings suggest that thymidine-derived sugars enhanced ROS generation and consequently increased IL-8 expression.

Abstract 3487: Molecular basis for induction of IL-8 expression by thymidine phosphorylase

Abstract Thymidine phosphorylase (TP) is identical to platelet-derived endothelial cell growth factor (PD-ECGF) and has an angiogenic activity. 2-Deoxy-D-ribose, one of the degradation products of thymidine, is a down stream mediator of the TP function. We investigated the molecular basis for the induction of an angiogenic factor, interleukin-8 (IL-8) by TP. First we confirmed that the enzymatic activity of TP is needed for the induction of IL-8 by TP in KB cells, and 2-deoxy-D-ribose increased the expression level of IL-8. ROS generated by TP augmented the expression of heme oxygenase-1 (HO-1) and increased the expression of IL-8. Two inhibitors of NADPH oxidase, apocynin and diphenyleneiodonium, suppressed the expression of HO-1 and IL-8 in TP-overexpressing KB/TP cells. Knock down of the component of NADPH oxidase, Nox2 or p22phox, also suppressed the enhanced expression of IL-8 in KB/TP cells. ROS generated by TP activated NFκB, which subsequently enhanced the promoter activity of IL-8. Our findings suggest that NADPH oxidase is involved in the ROS generation by TP, and the ROS caused the activation of NF-κB, which subsequently enhanced the expression of IL-8. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3487. doi:10.1158/1538-7445.AM2011-3487

Inhibition of metastasis of tumor cells overexpressing thymidine phosphorylase by 2-deoxy-L-ribose.

Thymidine phosphorylase (TP) catalyzes the reversible conversion of thymidine to thymine, thereby generating 2-deoxy-D-ribose-1-phosphate, which upon dephosphorylation forms 2-deoxy-D-ribose (D-dRib), a degradation product of thymidine. We have previously shown that D-dRib promotes angiogenesis and chemotaxis of endothelial cells and also confers resistance to hypoxia-induced apoptosis in some cancer cell lines. 2-Deoxy-L-ribose (L-dRib), a stereoisomer of D-dRib, can inhibit D-dRib anti-apoptotic effects and suppressed the growth of KB cells overexpressing TP (KB/TP cells) transplanted into nude mice. In this study, we examined the ability of L-dRib to suppress metastasis of KB/TP cells using two different models of metastasis. The antimetastatic effect of L-dRib was first investigated in a liver-metastasis model in nude mice inoculated with KB/TP cells. Oral administration of L-dRib for 28 days at a dose of 20 mg/kg/day significantly reduced the number of metastatic nodules in the liver and suppressed angiogenesis and enhanced apoptosis in KB/TP metastatic nodules. Next, we compared the ability of L-dRib and tegafur alone or in combination to decrease the number of metastatic nodules in organs in the abdominal cavity in nude mice receiving s.c. of KB/TP cells into their backs. L-dRib (20 mg/kg/day) was significantly (P < 0.05) more efficient than tegafur (100 mg/kg/day) in decreasing the number of metastatic nodules in organs in the abdominal cavity. By in vitro invasion assay, L-dRib also reduced the number of invading KB/TP cells. L-dRib anti-invasive activity may be mediated by its ability to suppress the enhancing effect of TP and D-dRib on both mRNA and protein expression of vascular endothelial growth factor and interleukin-8 in cultured KB cells. These findings suggest that L-dRib may be useful in a clinical setting for the suppression of metastasis of tumor cells expressing TP.

Thymidine degradation products in plant tissues labeled with tritiated thymidine.

A study of the metabolic pathways of H(3)-thymidine utilization in buds of Lilium longiflorum and root tips of Vicia faba was undertaken in order to obtain information that might explain the binding of H(3) from H(3)-thymidine in the cytoplasm of these plants. H(3)-thymidine was administered for various periods of time, the tissues were fixed and processed in the manner routinely used in preparation for sectioning and autoradiography, and the radioactivity removed in this way from the tissues was determined. It was found that the ethanol/acetic acid fixative contained the major portion of the radioactivity. Analysis of this extract by paper chromatography showed that the radioactivity was distributed among various degradation products of thymidine, principally beta-ureidoisobutyric acid and beta-aminoisobutyric acid. Time course experiments with Vicia showed that these degradation products rapidly appeared in the tissue during incubation with H(3)-thymidine, while H(3)-thymine appeared in the incubation medium. Preliminary studies indicated that Vicia root tips incubated with H(3)-dihydrothymine for 24 hours would bind a small amount of H(3) non-specifically in the cells. It seems unlikely that utilization of degradation products of H(3)-thymidine is sufficient to explain labeling which is concentrated in the cytoplasm.