# Diabetic Retinopathy and Ocular Melanoma: How Far We Are?
## 4 Uveal Melanoma, Angiogenesis and Anti-Angiogenic Therapy
In this tumour, angiogenesis is driven by  
Figure 2: Oxidative stress and its effect in angiogenesis: release of reactive oxygen species and generation of endogenous antioxidant pathway in mitochondria. SOD, superoxide dismutase; MPO, myeloperoxidase; ROS, reactive oxygen species; HIF, hypoxia-inducible factor; VEGF, vascular endothelial growth factor; VEGF2, vascular endothelial growth factor/receptor; TLR, toll-like receptor; Rac1, cytosolic oxidase component; NF-\(\kappa\)B, factor nuclear kappa B.  
soluble proangiogenic cytokines, especially basic fibroblast growth factor (bFGF) and VEGF-A. VEGF is known to be present in uveal melanomas and bFGF is the autocrine growth factor in cutaneous melanoma, and therefore, through immunohistochemistry and reverse transcriptase polymerase chain reaction, [PERSON] et al. studied the expression of these cytokines in this type of melanoma. In the immunohistochemicalty, an elevated number of tumour cells expressed bFGF at protein level, whereas way less expressed VEGF. The authors concluded that, in this tumour, the development of blood vessels resulted from the relationship between endothelial and tumour cells, with bFGF and VEGF playing a crucial role in this function [189]. The first investigation of VEGF gene expression in uveal melanoma was done in 7 different cell lines using RT-PCR [190]. [PERSON] et al. have shown that enucleated eye sampling has VEGF immunostaining; the relationship between the onset of metastases and VEGF levels in uveal melanoma could not be fully disclosed [191]. [PERSON] et al. previously showed only moderate VEGF staining in similar samples. However, all tested uveal melanomas expressed VEGF mRNA [189]. In another study, and always using healthy eye samples as a control, high levels of VEGF were also found in vitreous and anterior chamber fluids of affected eyes [192]. In several studies, including the study by [PERSON] et al., higher VEGF concentrations have also been reported in the aqueous humour of the affected eyes, possibly justifying the larger basal diameter and the height of the uveal melanoma. They also found that VEGF is expressed in tumour and retinal cells [193]. [PERSON] et al. studied the role in VEGF in uveal melanoma in vitro, demonstrating that in tumour cell cultures, hypoxia drives the expression of hypoxia-inducible factor (HIF-1\(\alpha\)) and VEGF. On the other hand, under these conditions the antiangiogenic factor thrombospondin TSP-1 was downregulated. To respond to this situation, uvea melanoma cell lines positively regulate VEGF but do not increase cell proliferation [40; 160]. By modulating VEGF expression, it is possible to initiate tumour vascularization. It is well known that this growth factor is crucial for tumour angiogenesis; thus, in vivo studies should be done on identical models of the tumour environment, considering paracrine signalling of endothelial cells. Several studies have shown that VEGF levels are indicative of the disease phase and also possible metastasis [40]. On the other hand, some studies have reported the relationship between VEGF expression and the onset of experimental metastases [194; 195]. Patients with metastatic uveal melanoma have higher VEGF levels compared to patients without metastatic uveal melanoma [40; 196]. In addition, in vivo studies have shown increased VEGF levels in the presence of liver metastases at liver hypoxia sites [197]. [PERSON] et al. also showed that there is an increase in VEGF levels after the metastatic development [159]. A preclinical study conducted by [PERSON] et al. evaluated in vitro and in vivo the relationship of radiotherapy and monoclonal anti-VEGF antibody (bevacizumab) [198]. Through the viability of OCM-1 cells, an extra antitumor action of the combined treatment (bevacizumab + radiotherapy) occurs in vivo. The same effect was observed in mice inoculated with OCM-1 cells. In separately cultured cells, bevacizumab prevented a radiation-induced increase in VEGF, which may alter the radiosensitivity of tumour cells [199].