Vitreous Seed and Soil: Elevated Levels of Platelet-Derived Growth Factor (PDGF) in the Vitreous of Patients with Retinoblastoma

Abstract

Purpose : Vitreous seeding remains the greatest challenge in treating retinoblastoma (Rb). Due to their unique location and resistance, current therapies fail to target and clear these vitreous seeds. Recent work from our lab has illustrated how PDGF-PDGFRβ from Rb and the tumor microenvironment regulate Rb cell survival and invasion. In this study, we investigated members of the PDGF-PDGFRβ signaling pathway within the vitreous microenvironment.

Methods : Using RNA isolated from collected vitreous of enucleated Rb patients with recalcitrant vitreous seeding (SJRET6), we did a qualitative assessment of both vascular endothelial growth factor A and its receptor (VEGFA and FLT1) as well as those from members of the platelet-derived growth factor family (PDGFA, PDGFB, PDGFRA, and PDGFRB) by qPCR, and compared them to 5 healthy controls. As seeds are known to be resistant, we also probed for the presence of cancer stem cells markers (CD44, CD133, CD24). With the same vitreous samples, we measured protein levels of VEGF as well as PDGF-AB and PDGF-BB using commercially available, human-specific Enzyme-Linked Immunosorbent Assays (ELISAs).

Results : Genetic analyses revealed upregulation of VEGFA, PDGFA, and PDGFB mRNA in the Rb patients’ samples compared to healthy controls. These results were confirmed in our protein analyses as we measured a significant difference in the levels of VEGF and PDGFs in the vitreous of enucleated Rb patients with vitreous seeding compared to controls. Moreover, we found mRNA expression of the markers associated with cancer stem cells.

Conclusions : Furthering our previous work showing how PDGF-PDGFRβ signaling was capable of sustaining Rb cell survival, we used ex vivo samples to evaluate the abundance of these growth factors in the vitreous of Rb patients. We also detected the presence of cancer stem cells within in the vitreous that may be contribute to the resistance of these seeds to conventional therapies and thus, warrant further investigation.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.