Cooperative stimulation of vascular endothelial growth factor expression by hypoxia and reactive oxygen species: the effect of targeting vascular endothelial growth factor and oxidative stress in an orthotopic xenograft model of bladder carcinoma

Abstract

Elevated thymidine phosphorylase has been shown to correlate with increased angiogenesis and poor prognosis in many cancers including transitional cell carcinoma of the bladder. In vitro studies have demonstrated that thymidine phosphorylase activity causes cellular oxidative stress and increases secretion of vascular endothelial growth factor. In this study, we show that thymidine phosphorylase activity also augments levels of the hypoxia-inducible factor-1a during in vitro hypoxia, and that thymidine phosphorylase activity and hypoxia act in concert to increase vascular endothelial growth factor (VEGF) secretion. We also demonstrate that thymidine phosphorylase overexpression confers tumorigenicity on an orthotopically implanted transitional cell carcinoma cell line. Administration of the antioxidant N-acetylcysteine together with a blocking anti-VEGF antibody abrogates the increase in tumorigenicity. Our results support the increased efficacy of combination approaches to antiangiogenic therapy.

Accumulation of thymidine-derived sugars in thymidine phosphorylase overexpressing cells

“…However, whether protein glycation of AGEs are formed in the cells used in our study, remains to be identified. Brown et al previously reported a possible Schiff base reaction in RT112 cells, and demonstrated the presence of reactive oxygen species by expression levels of the oxidative stress marker heme oxygenase-1 (HO-1) [31].…”

No relationship between thymidine phosphorylase (TP, PD-ECGF) expression and hypoxia in carcinoma of the cervix

“…It might be, therefore, that TP is preferentially induced by HIF-2a. Of interest is the observation that TP increased the hypoxic expression of HIF-1a in an orthoptic xenograft model of bladder cancer (Brown et al, 2005). This finding suggests that TP can be added to the long list of factors that promote HIF activation.…”

“…A relationship between TP expression and microvessel density, a histological measure of angiogenesis, has been reported in several solid tumours such as breast (Toi et al, 1995a), ovarian (Reynolds et al, 1994) renal (Imazano et al, 1997), and gastric (Takebayashi et al, 1996). In experimental models, TP overexpression increased tumour cell invasion (Ueda et al, 2001) and tumorigenicity (Griffiths and Stratford 1998;Brown et al, 2005). In man, high tumour expression of TP generally correlates with a poor prognosis in various solid malignancies (Takebayashi et al, 1996;Ikeda et al, 1999) including cervix cancer (Fujimoto et al, 1999;Hata et al, 1999;Ueda et al, 1999).…”

“…There is evidence that VEGF may act downstream of TP (Brown et al, 2000), and that hypoxia augments the effect of TP on VEGF (Brown et al, 2005). The two proteins coexpress in breast carcinomas (Toi et al, 1995b) and this coexpression was the most potent angiogenic phenotype in endometrial carcinoma (Sivridis et al, 2002a).…”

“…Indeed, Sivridis et al (2002b) showed that HIF-2a overexpression was linked to TP expression in human endometrial adenocarcinomas. Interestingly, in the TP-overexpressing cell line RT112-TP, TP augmented the hypoxic induction of HIF-1a (Brown et al, 2005).…”