SU9518 inhibits proliferative vitreoretinopathy in fibroblast and genetically modified Müller cell-induced rabbit models

Abstract

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 Müller glia, may be responsible. Platelet-derived growth factor receptor alpha (PDGFRα) 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 PDGFRα specificity, can inhibit the development of PVR in fibroblast and Müller cell rabbit models of PVR.

Methods: SU9518 was injected in rabbit eyes along with fibroblasts, Müller cells (MIO-M1), or Müller cells transfected to increase their expression of PDGFRα (MIO-M1α). Indirect ophthalmoscopy and histopathology were used to assess efficacy and toxicity.

Results: SU9518 was an effective inhibitor of PVR in both fibroblast and Müller 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.

Figure 1.

Western blot of MIO-M1α and MIO-M1 cell lysates shows a 3.65× increase of PDGFRα expression in MIO-M1α cells.

Figure 2.

(a) The SU9518 drug depo (orange arrow) can be observed adjacent to the MIO-M1α cell cluster (white arrow) in the vitreous cavity adjacent to the medullary rays 1 week after cell injection. (b) Four weeks after cell injection, a persistent bolus of drug (orange arrow) and cluster of cells (white arrow) can be observed in an eye with no evidence of PVR. (c) Stage 2 PVR at week 4 in a treated eye. A cluster of MIO-M1α cells can still be observed at the medullary rays. (d) Fundus photos of control rabbit eye injected with MIO-M1α cells shows a total retinal detachment.

Figure 3.

Injection of SU9518 1 week prior to injection of fibroblasts (RCFs) results in effective inhibition of PVR in the rabbit RCF model. Mann-Whitney analysis of mild and severe PVR showed a statistically significant difference (P < 0.05) at all three time points between both groups.

Figure 4.

SU9518 inhibits PVR in rabbits injected with MIO-M1α cells transfected to increase expression of PDGFRα. Mann-Whitney analysis showed a statistically significant difference (P < 0.05) at day 14 and day 28 between both groups.

Figure 5.

SU9518 does not alter the behavior of nontransfected MIO-M1 cells, which are very limited in their capacity to induce PVR. Mann-Whitney analysis showed no statistically significant difference at any of the time points between experimental and control eyes.

Figure 6.

Western blot of vitreous membrane lysates of eyes injected with MIO-M1α cells shows preservation of GFAP expression in both SU9518-treated (D, E) and -untreated (A–C) eyes. As expected, GFAP expression is highest in eyes with more severe PVR (A–C). Relative band densities controlled for β-actin expression are shown.

Figure 7.

Toluidine blue O staining of the rabbit retina 35 days postinjection of 300 μg of SU9518 free-base shows intact nerve fiber layer and photoreceptor outer segments with no disorganization of the retinal layers, and no evidence of autolysis or processing artifacts at ×25 (a) and ×40 (b) magnification.

Figure 8.

Aqueous concentration of SU9518, 300μg, in the rabbit vitreous follows a one-phase decay model. A stable therapeutic concentration is achieved by day 14 and sustained over the course of 3 weeks.