Tumor microvasculature with endothelial fenestrations as a potent predictive marker and target of anti-VEGF therapy in clear cell renal cell carcinoma

背景血管内皮生长因子靶向治疗对晚期肾癌有显著的抗肿瘤作用。现在，对成功预测肿瘤反应的各种替代标志物的需求越来越高。此前，利用血管内皮生长因子中和小鼠肿瘤模型的实验研究表明，在电子显微镜下的研究表明，在肿瘤血管中存在血管内皮细胞开窗的特征。在这些结果的基础上，我们检查血管内皮细胞窗是否与肾细胞癌的VHL状态和肿瘤对抗血管内皮生长因子治疗的反应有关。结果在大多数有VHL突变的散发性CC-RCC中发现了大量的内皮细胞窗，而那些没有突变的CC则没有。这一发现在小鼠异种移植模型中也得到了证实，因为与VHL野生型WT8甚至WT8/HIF2αP531A细胞相比，由VHL缺失的pRC3细胞建立的毛细血管具有更丰富的内皮窗口。Bevacizumab治疗后，pRC3细胞的平均肿瘤体积明显减小，但后两种细胞的平均肿瘤体积没有明显减小。在Bevacizumab敏感的pRC3异种移植瘤中，治疗后内皮细胞窗数目和微血管密度显著减少。结论VHL突变的散发性肾细胞癌含有依赖于血管内皮生长因子的肿瘤血管，这些微血管可能是抗血管内皮生长因子治疗的靶点。因此，内皮开窗可作为预测RCC对该疗法易感性的一个有用的替代标记物。我们的结果还表明，VHL-/-肾癌中依赖血管内皮生长因子的毛细血管的增加不仅仅是由于随后的血管内皮生长因子过度生产和HIF2α积聚所致。

BackgroundVEGF-targeted therapy show substantial anti-tumor effects for advanced renal cell carcinomas. Now, kinds of surrogate markers which successfully predict the tumor response are highly required. Previously, experimental studies using VEGF neutralization in mice tumor model showed that VEGF-dependent capillaries in tumor vessels were characterized by the existence of fenestrations in endothelium on electron microscopy study. Based on those results, we examined if endothelial fenestrations were associated with VHL status and tumor responses to anti-VEGF therapy in RCC.ResultsAbundant endothelial fenestrations were found in a majority of sporadic CC-RCCs with VHL mutation but not those without. This finding was also confirmed in mice xenograft models in that capillaries established from VHL null pRC3 cells harbored more abundant endothelial fenestrations compared to those from VHL wild WT8 or even WT8/HIF2α P531A cells. Treatment with Bevacizumab resulted in the significant decrease in the mean tumor size of pRC3 but not the latter two cells. In Bevacizumab sensitive pRC3 xenografts, a significant reduction of the number of endothelial fenestrations and microvessel density was observed after the treatment.ConclusionsOur results suggest that sporadic RCCs with VHL mutation harbor VEGF-dependent tumor vessels and those capillaries are possible target for anti-VEGF therapy. Therefore, endothelial fenestration could be a useful surrogate marker in predicting susceptibilities of RCCs to that therapy. Our results also indicated that an increase of VEGF dependent capillaries in VHL-/-RCC is not merely caused by the subsequent VEGF overproduction followed by HIF2α accumulation.