PURPOSE: Proliferative vitreoretinopathy (PVR) is a complication of retinal detachment that can lead to surgical failure and vision loss. Previous studies suggest that a variety of retinal cells, including RPE and Muller glia, may be responsible. Platelet-derived growth factor receptor alpha (PDGFRalpha) has been strongly implicated in the pathogenesis, and found to be intrinsic to the development of PVR in rabbit models. We examine whether SU9518, a tyrosine kinase inhibitor with PDGFRalpha specificity, can inhibit the development of PVR in fibroblast and Muller cell rabbit models of PVR. METHODS: SU9518 was injected in rabbit eyes along with fibroblasts, Muller cells (MIO-M1), or Muller cells transfected to increase their expression of PDGFRalpha (MIO-M1alpha). Indirect ophthalmoscopy and histopathology were used to assess efficacy and toxicity. RESULTS: SU9518 was an effective inhibitor of PVR in both fibroblast and Muller cell models of PVR. No toxic effects were identified by indirect ophthalmoscopy or histopathology. CONCLUSIONS: SU9518 is an effective and safe inhibitor of PVR in rabbit models, and could potentially be used in humans for the treatment of this and other proliferative diseases of the retina involving fibrosis and gliosis. Further animal studies need to be performed to examine retinal toxicity and sustained delivery mechanisms.

We have previously reported that platelet-derived growth factor (PDGF) receptor mutants that lack high affinity binding sites for phosphatidylinositol 3-kinase (PI 3-kinase) fail to concentrate in juxtanuclear vesicular structures after activation with PDGF. We have now identified the point in the endocytic pathway at which PI 3-kinase binding sites are required. Receptor internalization from the plasma membrane, measured as the acquisition of acid resistance of prebound 125I-PDGF, was only slightly decreased in cells expressing a PDGF receptor mutant (F5) lacking PI 3-kinase, GTPase-activating protein (GAP), phospholipase C gamma, and Syp binding sites but not expressing mutants where any of these individual sites were restored nor expressing a mutant lacking exclusively PI 3-kinase binding sites. In contrast, the extent of down-regulation of PDGF binding sites from the cell surface after prolonged incubation with PDGF as well as the degradation of [35S]methionine-labeled receptor were markedly reduced in cells expressing the F5 mutant, mutants restored in GAP, phospholipase C gamma, or Syp binding sites or expressing the mutant exclusively lacking PI 3-kinase binding sites but not in cells expressing the mutant where PI 3-kinase binding sites were restored. Inhibition of PI 3-kinase activity with wortmannin caused a dramatic decrease in the rates of down-regulation and degradation of wild-type receptors. These results suggest that PI 3-kinase binding sites are not required for internalization of PDGF receptor but are required to divert the PDGF receptor to a degradative pathway. Furthermore, the requirement for PI 3-kinase binding sites on the receptor appears to be due to a requirement for PI 3-kinase catalytic activity.