Topotecan vitreous and plasma levels and retinal toxicity after transcorneal intravitreal delivery in healthy albino rabbits: Alternative retinoblastoma treatment

Hydrogel implants for transscleral diffusion delivery of topotecan: In vivo proof of concept in a rabbit eye model

Treatment of retinoblastoma (Rb) has greatly improved in recent years in terms of survival and eye salvage rates, using mainly intra-arterial or intravitreal chemotherapy. However, the treatment of vitreous tumor seeding still represents a challenge and it is of great interest to develop new strategies to deliver pharmacologically sufficient drug amounts to the vitreous humor. In the present work, we present a lens-shaped bi-layered hydrogel implant for delivery of topotecan (TPT) via transscleral diffusion. The implant consists of an inner TPT-loaded poly(2-hydroxyethyl methacrylate) (pHEMA) layer adjacent to the sclera and an outer covering poly(2-ethoxyethyl methacrylate) (pEOEMA) layer impermeable to TPT. TPT-loaded pHEMA samples exhibit long-lasting in vitro cytotoxicity against the Rb cell line Y79. In an in vivo experiment, pHEMA/pEOEMA implants are successfully surgically administered to the posterior segment of rabbit eyes. The determination of TPT pharmacokinetics demonstrates the attainment of promising levels of TPT (10 ng/ml) in vitreous humor 8 h after implant placement. The results from the pilot experiment constitute the proof of principle for the use of the proposed implants as a drug delivery system for the local treatment of intraocular diseases.

Is intravitreal topotecan toxic to retinal function?

Background

Intravitreal injections of topotecan are used in the management of retinoblastoma with vitreous seeds. This study evaluated whether intravitreal topotecan was associated with retinal toxicity.

Methods

Retrospective cohort study of patients with retinoblastoma who were treated with intravitreal topotecan at Memorial Sloan Kettering Cancer Center between December 2014 and May 2019. Electroretinogram (ERG) responses under anaesthesia were measured immediately before treatment with intravitreal topotecan and at the next visitor approximately one-month. Ocular toxicity was defined by a decrease in the ERG response at 30 Hz at follow-up.

Results

Ocular toxicity was evaluated by ERG on 50 evaluable injections administered to 28 eyes. 22 (44.0%) injections were performed with concurrent intravitreal melphalan. The median time to ERG measurement following an injection was 27 days. By using a paired t-test, intravitreal topotecan combined with melphalan (n=22) at a dose of 25 μg or 30 μg was associated with a significant decrease in ERG amplitude at follow-up (p=0.046, 95% CI −20.4 μV to −0.2 μV). Among eyes that only received topotecan (n=28) at doses of 20 μg or 30 μg, there was not a significant difference in ERG amplitude measured (p=0.85, 95% CI −7.0 μV to 5.8 μV).

Conclusion

Intravitreal topotecan combined with intravitreal melphalan was associated with a decrease in ERG amplitude; there was not a significant decrease in ERG amplitude observed in patients who received topotecan alone. These findings suggest that intravitreal topotecan injections at doses of 20 μg or 30 μg are not associated with retinal toxicity in patients with retinoblastoma.