Ocular topotecan pharmacokinetics following topical administration to rabbits for diffused anterior retinoblastoma.

OBJECTIVES: We characterized and compared the in-vivo absorption of topotecan into the aqueous humor after instillation of aqueous and ointment formulations. METHODS: A lanolin/petrolatum ointment was used. New Zealand rabbits were instilled with topotecan solution (6 µg, group A), a single 10 µg dose of topotecan ointment (group B) or with five 10 µg doses of topotecan ointment (group C). Aqueous humor samples were collected at different times. Corneal samples were collected only for group A. Topotecan was quantified using HPLC, and pharmacokinetic parameters were calculated. Acute corneal epithelial toxicity was assessed after multiple instillations of topotecan ointment. KEY FINDINGS: Total topotecan maximum aqueous humor concentration (Cmax ) was 16.1, 69.9 and 287 ng/ml in group A, B and C, respectively. A single dose of topotecan ointment increased threefold and sevenfold the aqueous humor Cmax , and exposure compared to the aqueous formulation. Aqueous humor concentrations from group C eyes were substantially above the cytotoxic concentration for retinoblastoma cells. No corneal toxicity was evident after ointment instillation. CONCLUSIONS: Topotecan penetrated into the aqueous humor of the rabbit eye after multiple doses of an ointment in concentrations pharmacologically active against retinoblastoma cells without eliciting acute toxicity. Topotecan ointment may translate to the clinical treatment of anterior segment disseminated retinoblastoma.

Sustained-release hydrogels of topotecan for retinoblastoma.

Treatment of retinoblastoma, the most common primary ocular malignancy in children, has greatly improved over the last decade. Still, new devices for chemotherapy are needed to achieve better tumor control. The aim of this project was to develop an ocular drug delivery system for topotecan (TPT) loaded in biocompatible hydrogels of poly(ε-caprolactone)-poly(ethyleneglycol)-poly(ε-caprolactone) block copolymers (PCL-PEG-PCL) for sustained TPT release in the vitreous humor. Hydrogels were prepared from TPT and synthesized PCL-PEG-PCL copolymers. Rheological properties and in vitro and in vivo TPT release were studied. Hydrogel cytotoxicity was evaluated in retinoblastoma cells as a surrogate for efficacy and TPT vitreous pharmacokinetics and systemic as well as ocular toxicity were evaluated in rabbits. The pseudoplastic behavior of the hydrogels makes them suitable for intraocular administration. In vitro release profiles showed a sustained release of TPT from PCL-PEG-PCL up to 7days and drug loading did not affect the release pattern. Blank hydrogels did not affect retinoblastoma cell viability but 0.4% (w/w) TPT-loaded hydrogel was highly cytotoxic for at least 7days. After intravitreal injection, TPT vitreous concentrations were sustained above the pharmacologically active concentration. One month after injection, animals with blank or TPT-loaded hydrogels showed no systemic toxicity or retinal impairment on fundus examination, electroretinographic, and histopathological assessments. These novel TPT-hydrogels can deliver sustained concentrations of active drug into the vitreous with excellent biocompatibility in vivo and pronounced cytotoxic activity in retinoblastoma cells and may become an additional strategy for intraocular retinoblastoma treatment.

Pharmacokinetics of Melphalan After Intravitreal Injection in a Rabbit Model.

PURPOSE: Although widely used for vitreous seed control in retinoblastoma patients, currently there are no data on melphalan pharmacokinetics after intravitreal injections. Therefore, in this study, we characterized the ocular and systemic disposition of melphalan after intravitreal injection in the rabbit eye. METHODS: New Zealand rabbits received a single intravitreal injection of 15 µg of melphalan. Vitreous, aqueous, retina, and blood samples were collected at different times up to 12 h after the injection. Melphalan was quantitated in the biological samples using a validated high-performance liquid-chromatography technique and pharmacokinetic parameters were calculated by means of compartmental models. RESULTS: Model-predicted melphalan maximum vitreous, aqueous, and retina concentrations were 7.8 µg/mL, 0.024 µg/mL, and 9.8 µg/g tissue, respectively, attained immediately and at 0.8 and 0.25 h after intravitreal injection. Melphalan vitreous concentrations were higher than 0.3 µg/mL for 5 h after dosing. The elimination half-life from the vitreous, aqueous humor, and retina was 1.0, 0.2, and 1.2 h, respectively. Aqueous exposure [area under the curve (AUC)] was only 0.7% of that of the vitreous AUC. Melphalan concentrations in the retina were still detectable 12 h after dosing, while plasma exposure was under the limit of quantitation. CONCLUSION: Intravitreal administration of 15 µg melphalan leads to pharmacological vitreous levels with low aqueous exposure. Melphalan concentrations in the retina were measurable up to 12 h after dosing, but we report nondetectable systemic exposure in the rabbit. The results correlate with the clinical features of retinoblastoma patients that show control of vitreous seeds without systemic toxicity using intravitreal melphalan.

Aneurismas experimentales en conejos por angioplastia con balón / Experimental aneurysms in rabbits by ballon angioplasty

Objetive. To perform a new model of experimental aneurysms in rabbits and to achieve a training in basic endovascular techniques. Material and method. We introduce a new aneurysm model in rabbits. First we performed a balloon angioplasty in the right carotid artery in the neck, then three weeks later we carry out an angiography with a diagnostic catheter from the right femoral artery to check aneurysm patency. Results. We were able to perform 10 aneurysms in ten rabbits; they were patent three weeks after their creation. The aneurysmscreation and the angiography performed to evaluate the aneurysm patency required a similar skill necessary to perform basic endovascular interventions. Conclusion. Aneurysms created from balloon angioplasty in the carotid artery in rabbits are a suitable model at least in the short term. The process of aneurysm formation and its study is an useful training in basic endovascular techniques.

Aneurismas experimentales en conejos por angioplastia con balón / Experimental aneurysms in rabbits by ballon angioplasty

Objetive. To perform a new model of experimental aneurysms in rabbits and to achieve a training in basic endovascular techniques. Material and method. We introduce a new aneurysm model in rabbits. First we performed a balloon angioplasty in the right carotid artery in the neck, then three weeks later we carry out an angiography with a diagnostic catheter from the right femoral artery to check aneurysm patency. Results. We were able to perform 10 aneurysms in ten rabbits; they were patent three weeks after their creation. The aneurysmscreation and the angiography performed to evaluate the aneurysm patency required a similar skill necessary to perform basic endovascular interventions. Conclusion. Aneurysms created from balloon angioplasty in the carotid artery in rabbits are a suitable model at least in the short term. The process of aneurysm formation and its study is an useful training in basic endovascular techniques.(AU)

Aneurismas experimentales en ratas / Experimental aneurysms in rats

Objective. 1. The creation of an aneurysm model in an arterial bifurcation for microsurgical training in rats. 2. To verify angiographically the aneurysms patency performing endovascular maneuvers. Material and method. 10 Wistar rats weighted 400-600g were used. Ten aneurysms were performed, 9 in the final aortic bifurcation and one in the origin of the renal artery. The aneurismal sac derived from the external iliac vein. Angiography in each animal was done to examine aneurysm patency. At the same time we tried to manipulate microcateter and microguidewire in the aortic lumen. After that the aneurysm was microscopically inspected in order to verify the angiographic findings. Results. The aneurysms and the angiographic study could be performed in every animal. Four aortic and the renal artery aneurysms were not visualized in the angiography (totally thrombosed). The other five were partially thrombosed. Under microscopic aneurismal inspection could be found thrombus into the sac. The endovascular navigation was difficult due to the animal size. Conclusion. The bifurcation aneurysm model is a good microsurgical training. In our hands the aneurysms created had a high rate of spontaneous thrombosis. Because of animal size it is not a good model for endovascular training.

Aneurismas experimentales en ratas / Experimental aneurysms in rats

Objective. 1. The creation of an aneurysm model in an arterial bifurcation for microsurgical training in rats. 2. To verify angiographically the aneurysms patency performing endovascular maneuvers. Material and method. 10 Wistar rats weighted 400-600g were used. Ten aneurysms were performed, 9 in the final aortic bifurcation and one in the origin of the renal artery. The aneurismal sac derived from the external iliac vein. Angiography in each animal was done to examine aneurysm patency. At the same time we tried to manipulate microcateter and microguidewire in the aortic lumen. After that the aneurysm was microscopically inspected in order to verify the angiographic findings. Results. The aneurysms and the angiographic study could be performed in every animal. Four aortic and the renal artery aneurysms were not visualized in the angiography (totally thrombosed). The other five were partially thrombosed. Under microscopic aneurismal inspection could be found thrombus into the sac. The endovascular navigation was difficult due to the animal size. Conclusion. The bifurcation aneurysm model is a good microsurgical training. In our hands the aneurysms created had a high rate of spontaneous thrombosis. Because of animal size it is not a good model for endovascular training.(AU)