Sustained intraocular rapamycin delivery effectively prevents high-risk corneal allograft rejection and neovascularization in rabbits

PURPOSE: To evaluate the immunosuppressive and antiangiogenic activities of an intraocular rapamycin (RAPA) drug delivery system (DDS) in a rabbit model of high-risk penetrating keratoplasty. METHODS: Forty New Zealand White rabbits with corneal neovascularization underwent allograft cornea transplantation and were randomly divided into four groups: a control group, a glycolide-co-lactide-co-caprolactone copolymer (PGLC)-implanted group, a RAPA eye drop group, and a RAPA-PGLC DDS-implanted group. Graft survival, corneal neovascularization, and RAPA concentration in the aqueous humor were monitored for 90 days. Corneal grafts were also examined by in situ hybridization and immunohistochemistry for proinflammatory gene expression. RESULTS: In the control and PGLC groups, graft rejection occurred within 3 weeks of keratoplasty. In the RAPA eye drop and RAPA-PGLC groups, corneal rejection was significantly delayed, and neovascularization was markedly inhibited. Median graft survival times were 36 and >90 days in the eye drop and RAPA-PGLC groups, respectively. Mean RAPA concentrations in the aqueous humor were 10.7 ng/mL, 12.0 ng/mL, 9.2 ng/mL, and 7.0 ng/mL in the RAPA-PGLC group 2, 4, 8, and 12 weeks after surgery, respectively. By contrast, RAPA was undetectable in the aqueous humor in the eye drop group. High levels of IL-2R, MCP-1, TNF-alpha, and VEGF were detected in the corneal grafts of the control and PGLC groups but not in those of the RAPA-treated groups. CONCLUSIONS: RAPA-PGLC DDS and RAPA eye drops can significantly prolong the survival of allografts at high risk and inhibit corneal neovascularization. However, RAPA-PGLC DDS is far more effective than RAPA eye drops in preventing corneal graft rejection.