Long-term Sustained Intraocular Delivery of CNTF by Encapsulated Cell Technology Implants in Patients with Retinitis Pigmentosa

Abstract

Purpose: : To investigate the pharmacokinetics of the intraocular CNTF secreting encapsulated cell technology (ECT) implant, NT-501, in human subjects for periods up to 2 years.

Methods: : NT-501 implants were manufactured using standard protocols and held at 37°C in closed packages containing Endo-SFM. Prior to release to clinical sites, the implants were pulsed for CNTF release in 1 ml of Endo-SFM for 24 hours at 2 weeks post manufacture. Cell containing implants were subsequently analyzed for metabolic activity and then subjected to either total DNA or histological analysis. Devices were shipped to qualified clinical sites and implanted. The duration of the implantation period ranged from 6 months to 2 years. Explanted devices were pulsed for CNTF release and subjected to histological analysis. During the implantation period, the serum CNTF levels and the circulating antibodies against the encapsulated cells and CNTF were quantified by ELISA. During explant, vitreal samples were collected and analyzed for CNTF levels. The CNTF released from devices was quantified using a commercial ELISA kit (R&D Systems). Cell metabolism was determined using the CCK-8 assay (Dojindo). Total DNA was determined using the Hoefer DyNA Quant 200 fluorometer. Histological examination of the devices was performed using standard hematoxylin and eosin staining techniques.

Results: : The NT-501 devices released consistent levels of CNTF during the two to eight week shelf life and CCK-8 results showed devices maintained viable cells. Total DNA analysis of devices showed a consistent number of cells was maintained during the two to eight week period and histological analysis of device sections showed a high density of healthy cells distributed evenly throughout the device. In vivo performance: The devices appeared to be well tolerated during the implantation period. Explanted devices contained healthy cells and released consistent levels of CNTF upon explant at 6, 12, 18, and 24 months. Vitreal samples showed that the level of CNTF was maintained throughout the implantation period. No CNTF was detected in serum. No circulating antibodies against the encapsulated cells nor CNTF were detected.

Conclusions: : The data suggests that the ECT platform is able to achieve sustained, long term intraocular delivery of CNTF for periods up to 2 years in human subjects. Both the surgical implantation procedure and the NT-501 device were well tolerated. This technology could be used to deliver other factors for a broad range of indications where long-term treatment is required.

Keywords: retina