Abstract
Purpose :
Retinoblastoma tumors are known to be highly vascularized and promote angiogenesis through upregulation of vascular endothelial growth factor (VEGF). While the tumor originates in the retina, tumors can disseminate into the vitreous and vitreous seeds have traditionally been difficult to treat and are associated with poorer outcomes. While tumors within the retina benefit from nutrition supplied by the retinal vasculature, the vitreous seeds grow without such support. Thus, the purpose of this study was to assess how vitreous seeds seek vascular support.
Methods :
We studied human retinoblastoma intraretinal tumors and vitreous seeds produced in a rabbit orthotopic xenograft model created by injecting human WERI-RB1 cells either into the retina to grow retinal tumors or into the vitreous to allow these to grow into vitreous seeds. Formalin-fixed, paraffin-embedded sections underwent chromogenic RNA in situ hybridization (RNAscope) using probes specific to rabbit or human vascular endothelial growth factor subtype A (VEGFA) mRNA. VEGFA mRNA present within each cell was assessed visually, comparing the staining patterns of punctate dots. Higher levels of punctate stained areas indicated greater accumulation of VEGFA mRNA.
Results :
VEGFA was highly expressed in the human retinoblastoma vitreous seeds. Interestingly, we observed higher expression of VEGFA closer to the center of the seed as the tumor environment presumably became more hypoxic. VEGFA expression was also higher in seeds than in intraretinal xenograft tumors in the same section. Rabbit VEGFA expression was confined to retinal cells of the inner and outer nuclear layers and photoreceptors.
Conclusions :
VEGF A is a primary signal for endothelial cell mitogenesis and migration, mediated through the cell surface receptors VEGFR1 and VEGFR2. The high expression of human VEGFA in vitreous seeds indicates a signaling push toward endothelial cells to proliferate and ultimately supply the burgeoning tumor with blood supply for accelerated growth. It will be important to see how other proangiogenic factors are expressed by the vitreous seeds to form a better understanding of how these seeds seek vascular support. Targeting these proangiogenic factors may help treat vitreous seeds and potentially save the vision of young retinoblastoma patients.
This is a 2020 ARVO Annual Meeting abstract.