Technique of intravitreal injection

Antibody Format and Serum Disposition Govern Ocular Pharmacokinetics of Intravenously Administered Protein Therapeutics

Protein therapeutics have witnessed tremendous use and application in recent years in treatment of various diseases. Predicting efficacy and safety during drug discovery and translational development is a key factor for successful clinical development of these therapies. In general, drug related toxicities are predominantly driven by pharmacokinetic (PK) exposure at off-target sites. This work explores the ocular PK of intravenously administered protein therapeutics to understand impact of antibody format on off-site exposure. Species matched non-binding rabbit antibody proteins (rabFab and rabIgG) were intravenously administered to male New Zealand White rabbits at a single 1 mg bolus dose and exposure was measured up to 3 weeks. As anticipated based on absence of FcRn recycling, rabFab has relatively fast systemic PK (CL–943 mL/day and t_1/2–1.93 days) compared to rabIgG (CL–18.5 mL/day and t_1/2–8.93 days). Similarly, rabFab has lower absolute ocular exposure in ocular compartments (e.g., vitreous and aqueous humor) compared to rabIgG, despite higher relative exposures (measured as percent tissue partition in ocular tissues relative to serum, based on C_max and AUC). In general, percent tissue partition based on AUC (in aqueous and vitreous humor) relative to serum exposure were 10.4 and 8.62 for rabFab respectively and 1.11 and 0.64 for rabIgG respectively. This work emphasizes size and format based ocular exposure of intravenously administered protein therapeutics. Findings from this work enable prediction of format based ocular exposure for systemically administered antibody based therapeutics and aid in selection of molecule format for clinical candidate to minimize ocular exposure.

P-Glycoprotein expression in human retinal pigment epithelium cell lines

P-Glycoprotein (P-gp), an active efflux transporter encoded by the MDR1 gene, has recently been identified in the human and pig retinal pigment epithelium (RPE) in situ. Efflux pumps such as P-gp are major barriers to drug delivery in several tissues. We wished to establish whether human RPE cell lines express P-gp under the culture conditions recommended for each cell line so as to determine their suitability as in vitro models for predicting drug transport across the outer blood-retinal barrier. Three human RPE cell lines, ARPE19, D407 and h1RPE were investigated. Reverse transcriptase-polymerase chain reaction (RT-PCR) was carried out to determine the expression of MDR1 mRNA. Immunocytochemistry using the P-gp-specific antibody C219 was undertaken to investigate the presence of P-gp protein in each cell type. Uptake of rhodamine 123, a P-gp substrate, in the presence or absence of pre-treatment with a P-gp inhibitor, verapamil, was measured in each cell line to determine functional expression of P-gp. For all experiments, MDCK cells stably transfected with the human MDR1 gene (MDCK-MDR1) were used as a positive control. ARPE19 cells were consistently negative for P-gp as assessed by RT-PCR and immunocytochemistry. By contrast, RT-PCR of D407 and h1RPE samples yielded weak bands corresponding to MDR1; P-gp protein expression, as demonstrated by C219 immunoreactivity, was also present. Rhodamine uptake after treatment with verapamil was significantly greater in D407 and MDCK-MDR1, indicating functional expression of P-gp in these two cell lines. No evidence of functional P-gp was found in ARPE19 and h1RPE. In conclusion, D407 and h1RPE cells express P-gp, though functional activity was demonstrable only in D407 cells. ARPE19 cells do not express P-gp. Of these human RPE cells lines D407 could be considered as a suitable model for in vitro drug transport studies, particularly those involving P-gp substrates, without modification of their usual culture conditions.

Etoposide as a virocidal anticytomegalovirus therapy: intravitreal toxicology and pharmacology in rabbits

BACKGROUND

Although Cytomegalovirus (CMV) retinitis is now a common intraocular infection, current therapy is only virostatic so ongoing treatment is required. Etoposide was found to be virocidal for CMV in laboratory experiments and it might prove to be beneficial clinically. We investigated the toxicity and intraocular concentration of etoposide (VP16) and its new analogue etoposide-phosphate (VP16P) following intravitreal injections in rabbit eyes.

METHODS

First a sequential dose-response was assessed with flash electroretinogram for both eyes of light- and dark-adapted rabbits (n = 7; one rabbit for each dose) over a range of light intensities before and after intravitreal injection of VP16 or VP16P to one eye; the other eye was injected with normal saline as a control. A multidose study was then performed on four rabbits. A non-toxic dose of VP16P (50 or 75 g) was injected into the vitreous of one eye on four occasions 1 week apart. A photopic electroretinogram was performed before the first injection and 6 weeks after the last injection. All the eyes from the electroretinogram studies were fixed in formalin, placed in paraffin, then stained with haematoxylin and eosin and examined under a light microscope. To determine the time-course of the intraocular concentrations of VP16P a sequential pharmacokinetic study was performed using a further 12 rabbits. Each rabbit was injected with 50 g VP16P to one eye and 75 g VP16P to the other eye. Three of these rabbits were killed at 1, 3, 6 and 9 h after injection. Samples of vitreous were assayed for both VP16 and VP16P using HPLC. An in vitro dose response assay was performed using third-passage bovine retinal pigment epithelial (RPE) cells cultured in Dulbecco's modified Eagles medium with fetal calf serum. The effect of a log-dose increment of VP16P on the RPE cell proliferation was assessed using tritiated thymidine incorporation.

RESULTS

The electroretinogram studies suggested that VP16 was toxic even with the 10 g dose. For VP16P a toxic effect was noted following injection of a single dose greater than 100 g. Multiple injections of 50 or 75 g VP16P did not produce a toxic response. Histological examination demonstrated significant abnormality only with the 500 g dose of VP16 or VP16P. VP16P was rapidly metabolized to VP16 in the eye, producing concentrations of 2.0 g/mL or more for up to 9 h following a 75-microg dose. This suggests that the electroretinogram findings following VP16 injections were confounded by a toxic effect of the ethanol solvent (which is absent from the VP16P preparation). VP16P was quite potent, the ID50 was about 0.1 g/mL for bovine RPE cells in the in vitro assay.

DISCUSSION

These results indicate that multiple 75-gVP16P intravitreal injections were not toxic to the rabbit eye and provide a therapeutic intraocular concentration for up to 9 h after the injection.

High-dose (2000-microgram) intravitreous ganciclovir in the treatment of cytomegalovirus retinitis

OBJECTIVE

The authors prospectively studied visual outcome, relapse, complications, and survival of patients with acquired immune deficiency syndrome (AIDS)-related cytomegalovirus (CMV) treated with high-dose intravitreous ganciclovir (2 mg/0.1 ml) injections. The outcomes were compared with those of patients treated with standard doses of intravenous ganciclovir in the same institution. The histopathologic and electrophysiologic effects of high-dose intravitreous ganciclovir injections in rabbits also were studied.

DESIGN

A nonrandomized case series.

PARTICIPANTS

A total of 42 patients (74 eyes) were treated with intravitreous injections and 18 patients (27 eyes) were treated with intravenous ganciclovir. Five eyes of three New Zealand white rabbits were injected with ganciclovir, and the sixth eye was a control specimen.

INTERVENTION

Patients treated with intravitreous injections received twice-weekly doses of 2 mg/0.1 ml ganciclovir for 3 weeks, then weekly injections. Patients treated with intravenous ganciclovir received standard doses. Patients were monitored with regular examinations. Rabbit eyes were given intravitreous injections of 1 mg/0.1 ml of ganciclovir weekly for 4 weeks.

MAIN OUTCOME MEASURES

Assessments of vision, retinal inflammation, and survival were made. Electroretinograms were performed on the rabbit eyes, and they were processed for light and electron microscopy.

RESULTS

In the intravitreous group, visual acuity (VA) was stable in 64 of 74 eyes, 5 improved, and 5 deteriorated. Sixty-three (85%) of 74 eyes had final VA of 20/20 to 20/40. Relapse occurred in five eyes (7%; median time, 42 weeks). There were three cases of endophthalmitis. Median survival after diagnosis of CMV retinitis was 36 weeks. In the intravenous group, VA was stable in 18 eyes, 0 improved, and 9 deteriorated. Sixteen (59%) of 27 eyes had final VA of 20/20 to 20/40. Relapse occurred in 15 eyes (56%) at a median time of 21 weeks. Median survival was 21 weeks. The rabbit studies showed no evidence of toxicity.

CONCLUSION

High-dose intravitreous ganciclovir effectively suppressed CMV retinitis, preserved vision, and prevented relapse without deterioration in survival.

High dose intravitreal ganciclovir injection provides a prolonged therapeutic intraocular concentration

BACKGROUND

Although intravitreal high dose ganciclovir has previously been found to provide excellent control of cytomegalovirus (CMV) retinitis, little was known about the vitreous concentrations of ganciclovir after a 2 mg intravitreal injection.

METHODS

Eleven vitreous samples were taken from seven patients with CMV retinitis at 24 and 72 hours after a 2 mg intravitreal injection of ganciclovir and the concentration of ganciclovir was measured by high performance liquid chromatography.

RESULTS

The mean concentration of ganciclovir at 24 hours was 143.8 mg/l (95% confidence interval 97.8-190) and at 72 hours was 23.4 mg/l (95% CI 0-49.7). The half life ranged from 11.9 to 26.3 (mean 18.8) hours in the four patients who had two samples taken. The mean half life calculated from the mean concentrations at 24 and 72 hours was 18.3 hours, so the calculated mean concentration at 7 days was 0.6 mg/l.

CONCLUSIONS

This suggests that it takes about 7 days to eliminate the intravitreal ganciclovir, and that it is not likely to accumulate with weekly injections. The intravitreal concentrations achieved with high dose therapy remained above the ID50 for CMV (0.25-1.22 mg/l) for up to 7 days.

High dose intravitreal ganciclovir for CMV retinitis: a shelf life and cost comparison study

BACKGROUND

It was previously found that high dose intravitreal ganciclovir provided superior treatment of cytomegalovirus retinitis compared with intravenous treatment. This study examined the stability and solubility of the ganciclovir solution to determine the shelf life of prepared solution, and compared the cost of intravitreal with intravenous therapy.

METHODS

For the solubility studies high performance liquid chromatography was used to determine the ganciclovir concentration in various solutions. Measurements were taken of freshly made 20 mg/ml solution, the same solution stored at room temperature or frozen for 10, 17, and 24 days, after the solution was filtered, and after it was heated at 56 degrees C. For the cost comparison analysis the cost of 22 patients treated exclusively with intravitreal high dose ganciclovir was compared with cost estimates for the same patients treated with a standard intravenous therapy regimen over the same time.

RESULTS

There was little variation in the concentration of ganciclovir regardless of the storage conditions, suggesting that the 20 mg/ml solution was very stable. The heating and filtering experiments suggest that maximum solubility was achieved both in the freshly prepared and thawed frozen stored solution. The total cost of the intravitreal treatment was Aus $172,435 and the estimate of intravenous treatment was Aus $490,521. This represents a total saving of $318,086 (65%), or $14,458 per patient. The average number of weeks of treatment for each patient was 27.9 (613 weeks/22 patients), so the saving per patient per year was $29,946.

CONCLUSION

High dose intravitreal ganciclovir therapy may be administered in a very cost effective way, which along with its acceptability, safety, and clinical efficacy make it an attractive method of treatment of CMV retinitis.