The pharmacokinetics of rituximab following an intravitreal injection

Pharmacokinetics of Monoclonal Antibody and Antibody Fragments in The Mouse Eye Following Intravitreal Administration

Mice are rarely used in pharmacokinetic (PK) studies of ocular therapeutics due to the small size of their eyes and challenges in drug administration, tissue collection, and analysis of drug concentrations. Therefore, ocular PK of protein therapeutics in mouse eye following intravitreal (IVT) administration is not known. Here, we have presented the first of its kind investigation, to study the PK of 4 different size non-binding protein therapeutics in mouse plasma, cornea/ICB, vitreous humor, retina, and posterior cup (including choroid) following IVT administration. Administered proteins include trastuzumab (150 kDa) and F(ab)2 (100 kDa), Fab, and scFv (27 kDa) fragments of trastuzumab. An imaging and injection apparatus suitable for performing small (50 nL) IVT injections in mice was developed, and techniques for enucleation of the eye and dissection of ocular tissues were developed. Furthermore, a sensitive enzyme-linked immunosorbent assay (ELISA) for detection of proteins in very small amounts of ocular tissues were developed. It was observed that elimination from the vitreous chamber was the primary driver of PK in the cornea/ICB, retina, posterior cup, and plasma. Trastuzumab displays first-order kinetics in the vitreous humor with a half-life of 18.8 h. F(ab)2, Fab, and ScFv show biphasic PK profiles with distribution phases becoming more rapid as molecular weight decreases, and terminal elimination becoming longer as molecular weight decreases, with terminal half-lives of 16.3, 20.6, and 48.9 h, respectively. The mean residence times of trastuzumab, F(ab)2, Fab, and scFv in the vitreous humor were 26.0, 12.2, 10.7, and 8.16 h, respectively. It was found that the mean residence time in vitreous humor doubles with an increase in molecular weight of ∼69 kDa. Interestingly, the PK of proteins measured in the un-injected eye suggest the presence of a pathway for drug transfer between the eyes, which needs to be further validated. Overall, the findings presented here pave the way for drug discovery and development studies of protein therapeutics for ophthalmic indications in mice.

A comprehensive review of intravitreal immunosuppressants and biologicals used in ophthalmology

Systemic immunosuppressants and biologicals have been a valuable tool in the treatment of inflammatory diseases and malignancies. The safety profile of these drugs has been debatable, especially in localized systems, such as the eye. This has led to the search for fairly local approaches, such as intravitreal, subconjunctival, and topical route of administration. Immunosuppressants have been used as a second-line drug in patients intolerable to corticosteroids or those who develop multiple recurrences on weaning corticosteroids. Similarly, biologicals have also been used as the next line of therapy, when adequate control of inflammation could not be attained or immunosuppressants were contraindicated to patients. Intravitreal immunosuppressants, such as methotrexate and sirolimus, have been extensively studied in noninfectious posterior uveitis, whereas limited studies have established the efficacy of intravitreal biologicals, such as infliximab and adalimumab. Most of these drugs have shown good safety profile and tolerability in animal studies alone and have not been studied further in human subjects. However, most of the studies in literature are single-case reports or case series which limits the level of evidence. In this comprehensive review, we discuss the mechanism of action, pharmacodynamics, pharmacokinetics, indications, efficacy, and side effects of different intravitreal immunosuppressants and biologicals that have been studied in literature.

Primary vitreoretinal lymphoma: A diagnostic and management challenge

Primary vitreoretinal lymphoma (PVRL) is a rare form of primary central nervous system lymphoma (PCNSL) arising in the intraocular compartment without brain involvement. Despite its apparent indolent clinical course, PVRL can cause permanent vision loss and CNS relapse, the major cause of death in PVRL patients. The pathophysiology of PVRL is unknown. As in PCNSL, the transformation of the tumor cells likely originates outside the CNS, before the cells migrate to the eye and proliferate within an immune-permissive microenvironment. PVRL exhibits a biased immunoglobulin repertoire, suggesting underlying antigen selection. The diagnosis remains challenging, requiring close coordination between ophthalmologists and cytologists. Because of their rarity and fragility in the vitreous, lymphoma cells cannot always be identified. Interleukin levels, molecular biology and imaging are used in combination with clinical ophthalmological examination to support the diagnosis of PVRL. Multi-institutional prospective studies are urgently needed to validate the equivocal conclusions regarding treatments drawn from heterogeneous retrospective or small cohort studies. Intravitreal injections of methotrexate or rituximab or local radiotherapy are effective at clearing tumor cells within the eyes but do not prevent CNS relapse. Systemic treatment based on high-dose methotrexate chemotherapy, with or without local treatment, might reduce this risk. At relapse, intensive consolidation chemotherapy followed by stem cell transplantation can be considered. Single-agent ibrutinib, lenalidomide and temozolomide treatments are effective in patients with relapsed PVRL and should be tested as first-line treatments. Therapeutic response assessment based on a clinical examination is improved by measuring cytokine levels but still needs to be refined.

Multimodal imaging characteristics in eyes with vitreoretinal lymphoma treated with intravitreal rituximab

PURPOSE

To characterize the imaging features in eyes with vitreoretinal lymphoma (VRL) using ultra-widefield fundus photography (UWF-FP), swept-source optical coherence tomography (SSOCT) and fundus autofluorescence (FAF) that are correlated to ongoing treatment with intravitreal Rituximab(IVR).

METHODS

Retrospective observational imaging-based study of 15 treatment-naive eyes with VRL treated with IVR. All patients with primary VRL underwent vitreous biopsy using 23/25G microincision vitrectomy system for confirmation of diagnosis. All eyes received monthly IVR (1 mg/0.1 mL) injections till disease remission. Baseline clinical characteristics, treatment details, outcomes, and sequential imaging features on UWF-FP, FAF, and SSOCT were analyzed.

OUTCOME MEASURES

Baseline features and changes in UWF-FP, FAF patterns, and SSOCT features in response to treatment RESULTS: Clinically, patients presented with sub-RPE deposits (n = 15), superficial retinal hemorrhages (n = 2), 'giant' RPE (retinal pigment epithelium) holes (n = 2), and anterior segment reaction (n = 1). Eyes were treated with mean 5.7 IVR injections (median: 5; range 1-13) over a mean 7.2 ± 4.9 months. During the course of treatment, two eyes developed superficial retinal hemorrhages with spontaneous resolution, 2 eyes developed CME, and 4 eyes developed characteristic 'leopard skin' pigmentation. Hyper-autofluorescence corresponding to areas of active lesions decreased with each treatment cycle and was finally replaced by hypo-autofluorescence. Serial OCTs showed regression of sub-RPE/subretinal deposits (n = 15), ellipsoid zone disruption (n = 9), and its resolution with treatment (n = 3), epiretinal membrane (ERM; n = 6), choroidal hyperreflective foci (HRF; n = 4), disorganization of retinal inner layers (DRIL; n = 3), RPE-rip (n = 2), cystoid macular edema (CME; n = 2), and hyperreflective lesions in the choroid (n = 1). Complete resolution was observed in all eyes with extensive hypo-AF. The central foveal thickness decreased from 237 ± 113 μ to 182 ± 114 μ (p = 0.1) and subfoveal choroidal thickness decreased from 258 ± 66 μ to 220 ± 64 μ (p = 0.12) at final follow-up. The mean baseline BCVA was logMAR 0.9 ± 0.9 that deteriorated to mean logMAR 1 ± 1 final visit (p = 0.7). The mean recurrence-free follow-up was 5.9 ± 5.1 months CONCLUSION: Multimodal imaging provides novel insights into features of VRL, a better understanding of regression patterns, and prognostication of outcomes when treated with intravitreal rituximab. Larger, multicentric studies with longer follow-up will help unravel imaging biomarkers to understand these aspects better.

Intravitreal rituximab monotherapy for management of eyes with vitreoretinal lymphoma: initial experience from India

PURPOSE

To evaluate treatment outcomes and complications of intravitreal rituximab (IVR) monotherapy for eyes with vitreoretinal lymphoma (VRL).

METHODS

Patients diagnosed with 'isolated primary VRL' or 'VRL with remission of systemic disease' and treated with IVR (1 mg/0.1 ml) between June 2014 and June 2019 were included in this retrospective, interventional case series. Injections were repeated at monthly intervals until complete resolution. All patients signed a written informed consent form. Institutional review board approval was obtained.

RESULTS

Twelve eyes of 7 patients with VRL were treated with 77 IVR injections at mean 6.42 injections per eye (median = 5; range = 2-13) for complete resolution at mean 8.16 ± 4.62 months (median = 6.97 months; range = 1.97-14.33 months). Mean age at presentation was 53.3 years (median = 54 years; range = 34-74 years). Patients were co-managed with medical oncologist and periodically evaluated. Complications included anterior uveitis (n = 6), raised intraocular pressure (n = 3), posterior synechiae (n = 2), vitreous haemorrhage (n = 1), pre-retinal haemorrhage (n = 1), retinal detachment (n = 1), posterior subcapsular cataract (n = 2) and sectoral iris atrophy (n = 1). Recurrences were seen in 3 eyes (25%), which eventually achieved complete resolution with treatment. None of the patients had systemic involvement or death during follow-up. Mean follow-up was 18.73 ± 8.83 months (median = 21.60 months; range = 7.37-32.67 months).

CONCLUSION

Intravitreal rituximab monotherapy is effective in management of vitreoretinal lymphoma in patients with isolated ocular disease.

TOPICAL DORZOLAMIDE-TIMOLOL WITH INTRAVITREOUS ANTI-VASCULAR ENDOTHELIAL GROWTH FACTOR FOR RETINAL VEIN OCCLUSION: A PILOT STUDY

PURPOSE

To evaluate topical dorzolamide hydrochloride-timolol maleate as an adjunct therapy to intravitreous anti-vascular endothelial growth factor injections in eyes with retinal vein occlusion resistant to treatment.

METHODS

Retinal vein occlusion patients with a history of persistent macular edema, despite fixed-interval intravitreous anti-vascular endothelial growth factor injections, were enrolled between April 4, 2016, and June 4, 2017. On enrollment, patients were instructed to administer one drop of topical dorzolamide-timolol twice daily for the duration of the study. They were maintained on the same anti-vascular endothelial growth factor drug and same interval between injections as preenrollment for the subsequent two visits. Primary outcome measures were change in central foveal thickness, central subfield thickness, and thickest macular cut at the final study visit.

RESULTS

Eight patients (8 eyes) were eligible for enrollment and completed the study. There was a significant decrease in central foveal thickness (P = 0.02), central subfield thickness (P = 0.03), and thickest macular cut (P = 0.01) between the enrollment visit and the final visit. There was a decrease in mean (±SD) logarithm of the minimal angle of resolution from 0.52 (±0.35) (20/66, Snellen equivalent) at the enrollment visit to 0.41 (±0.35) (20/51, Snellen equivalent) at the final visit (P = 0.08).

CONCLUSION

Topical dorzolamide-timolol may have a beneficial anatomical and functional effect in eyes with macular edema secondary to retinal vein occlusion resistant to treatment.

Characterization of Antineovascularization Activity and Ocular Pharmacokinetics of Phosphoinositide 3-Kinase/Mammalian Target of Rapamycin Inhibitor GNE-947

The objectives of the present study were to characterize GNE-947 for its phosphoinositide 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitory activities, in vitro anti-cell migration activity in human umbilical vein endothelial cells (HUVECs), in vivo antineovascularization activity in laser-induced rat choroidal neovascular (CNV) eyes, pharmacokinetics in rabbit plasma and eyes, and ocular distribution using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) and autoradioluminography. Its PI3K and mTOR K _i were 0.0005 and 0.045 µM, respectively, and its HUVEC IC₅₀ was 0.093 µM. GNE-947 prevented neovascularization in the rat CNV model at 50 or 100 µg per eye with repeat dosing. After a single intravenous injection at 2.5 and 500 μg/kg in rabbits, its plasma terminal half-lives (t _1/2) were 9.11 and 9.59 hours, respectively. After a single intravitreal injection of a solution at 2.5 μg per eye in rabbits, its apparent t _1/2 values were 14.4, 16.3, and 23.2 hours in the plasma, vitreous humor, and aqueous humor, respectively. After a single intravitreal injection of a suspension at 33.5, 100, 200 μg per eye in rabbits, the t _1/2 were 29, 74, and 219 days in the plasma and 46, 143, and 191 days in the eyes, respectively. MALDI-IMS and autoradioluminography images show that GNE-947 did not homogenously distribute in the vitreous humor and aggregated at the injection sites after injection of the suspension, which was responsible for the long t _1/2 of the suspension because of the slow dissolution process. This hypothesis was supported by pharmacokinetic modeling analyses. In conclusion, the PI3K/mTOR inhibitor GNE-947 prevented neovascularization in a rat CNV model, with t _1/2 up to approximately 6 months after a single intravitreal injection of the suspension in rabbit eyes. SIGNIFICANCE STATEMENT: GNE-947 is a potent phosphoinositide 3-kinase/mammalian target of rapamycin inhibitor and exhibits anti-choroidal neovascular activity in rat eyes. The duration of GNE-947 in the rabbit eyes after intravitreal injection in a solution is short, with a half-life (t _1/2) of less than a day. However, the duration after intravitreal dose of a suspension is long, with t _1/2 up to 6 months due to low solubility and slow dissolution. These results indicate that intravitreal injection of a suspension for low-solubility drugs can be used to achieve long-term drug exposure.

Ocular Half-Life of Intravitreal Biologics in Humans and Other Species: Meta-Analysis and Model-Based Prediction

Therapeutic antibodies administered intravitreally are the current standard of care to treat retinal diseases. The ocular half-life (t_1/2) is a key determinant of the duration of target suppression. To support the development of novel, longer-acting drugs, a reliable determination of t_1/2 is needed together with an improved understanding of the factors that influence it. A model-based meta-analysis was conducted in humans and nonclinical species (rat, rabbit, monkey, and pig) to determine consensus values for the ocular t_1/2 of IgG antibodies and Fab fragments. Results from multiple literature and in-house pharmacokinetic studies are presented within a mechanistic framework that assumes diffusion-controlled drug elimination from the vitreous. Our analysis shows, both theoretically and experimentally, that the ocular t_1/2 increases in direct proportion to the product of the hydrodynamic radius of the macromolecule (3.0 nm for Fab and 5.0 nm for IgG) and the square of the radius of the vitreous globe, which varies approximately 24-fold from the rat to the human. Interspecies differences in the proportionality factors are observed and discussed in mechanistic terms. In addition, mathematical formulae are presented that allow prediction of the ocular t_1/2 for molecules of interest. The utility of these formulae is successfully demonstrated in case studies of aflibercept, brolucizumab, and PEGylated Fabs, where the predicted ocular t_1/2 values are found to be in reasonable agreement with the experimental data available for these molecules.

Pharmacokinetic Simulations of Intravitreal Biologicals: Aspects of Drug Delivery to the Posterior and Anterior Segments

Biologicals are important ocular drugs that are be delivered using monthly and bimonthly intravitreal injections to treat retinal diseases, such as age-related macular degeneration. Long acting delivery systems are needed for prolongation of their dosing interval. Intravitreal biologicals are eliminated from the eye via the aqueous humor outflow. Thus, the anterior and posterior segments are exposed to the drug. We utilized a kinetic simulation model to estimate protein drug concentrations in the vitreous and aqueous humor after bolus injection and controlled release administration to the vitreous. The simulations predicted accurately the experimental levels of 5 biologicals in the vitreous and aqueous humor. The good match between the simulations and experimental data demonstrated almost complete anterior segment bioavailability, and major dose sparing with ocular controlled release systems. Overall, the model is a useful tool in the design of intraocular delivery of biologicals.

Intraocular lymphoma

Intraocular lymphoma (IOL) is a rare lymphocytic malignancy which contains two main distinct forms. Primary intraocular lymphoma (PIOL) is mainly a sub-type of primary central nervous system lymphoma (PCNSL). Alternatively, IOL can originate from outside the central nervous system (CNS) by metastasizing to the eye. These tumors are known as secondary intraocular lymphoma (SIOL). The IOL can arise in the retina, uvea, vitreous, Bruch's membrane and optic nerve. There are predominantly of B-cell origin; however there are also rare T-cell variants. Diagnosis remains challenging for ophthalmologists and pathologists, due to its ability to masquerade as noninfectious or infectious uveitis, white dot syndromes, or occasionally as other metastatic cancers. Laboratory tests include flow cytometry, immunocytochemistry, interleukin detection (IL-10: IL-6, ratio >1), and polymerase chain reaction (PCR) amplification. Methotrexate-based systemic chemotherapy with external beam radiotherapy and intravitreal chemotherapy with methotrexate are useful for controlling the disease, but the prognosis remains poor. Therefore, it is important to make an early diagnose and treatment. This review is focused on the clinical manifestations, diagnosis, treatment and prognosis of the IOL.

Ocular Pharmacokinetics

Although the fundamental concepts of pharmacokinetics remain the same, ocular pharmacokinetics has its own challenges due to the uniqueness of barrier properties posed by various ocular tissues and its growing complexity with different routes of ocular administration. A thorough understanding of the barrier nature will aid in tailoring a drug or its carrier's physicochemical properties to its advantage. In order to deliver the right payload of a drug at the target site, various approaches can be taken to leverage the pharmacokinetics that includes molecular design based on desirable physicochemical properties, formulation approaches, and alternative routes of administration. In this chapter, a brief overview of the barrier properties with respect to various routes of administration is presented along with the physicochemical properties that influence the pharmacokinetics of ocular drugs. Recent advances in ocular pharmacokinetics are discussed in addition to new perspectives in interpreting existing data.

Primary Vitreoretinal Lymphoma: Management of Isolated Ocular Disease

BACKGROUND

The prognosis for patients with primary vitreoretinal is dismal. The close association of primary vitreoretinal lymphoma with primary central nervous system lymphoma is responsible for high rates of mortality. Traditional treatments consist of systemic chemotherapy and whole-brain radiotherapy. The optimal approach for the treatment of isolated primary vitreoretinal lymphoma is unclear.

METHODS

A review of the relevant medical and scientific literature was performed, focusing on the clinical features of primary vitreoretinal lymphoma and the progress made in the management of isolated ocular disease.

RESULTS

Ocular treatment options for primary vitreoretinal lymphoma have recently expanded with the addition of intravitreal chemotherapeutic agents and localized radiation. Based on several retrospective reports, a general shift has been made toward local therapy (eg, orbital radiotherapy, intravitreal chemotherapy) for ocular disease. No prospective, randomized clinical trials yet exist to guide therapy.

CONCLUSIONS

Optimal treatment regimens for isolated primary vitreoretinal lymphoma continue to evolve. Further investigations into novel therapies and protocols are needed to decrease recurrence rates, reduce or prevent central nervous system involvement, and improve rates of overall survival.

The PK-Eye: A Novel In Vitro Ocular Flow Model for Use in Preclinical Drug Development

A 2-compartment in vitro eye flow model has been developed to estimate ocular drug clearance by the anterior aqueous outflow pathway. The model is designed to accelerate the development of longer-acting ophthalmic therapeutics. Dye studies show aqueous flow is necessary for a molecule injected into the vitreous cavity to clear from the model. The clearance times of proteins can be estimated by collecting the aqueous outflow, which was first conducted with bevacizumab using phosphate-buffered saline in the vitreous cavity. A simulated vitreous solution was then used and ranibizumab (0.5 mg) displayed a clearance time of 8.1 ± 3.1 days, which is comparable to that observed in humans. The model can estimate drug release from implants or the dissolution of suspensions as a first step in their clearance mechanism, which will be the rate-limiting step for the overall resident time of a candidate dosage form in the vitreous. A suspension of triamcinolone acetonide (Kenalog®) (4.0 mg) displayed clearance times spanning 26-28 days. These results indicate that the model can be used to determine in vitro-in vivo correlations in preclinical studies to develop long-lasting therapeutics to treat blinding diseases at the back of the eye.

Intravitreal clearance and volume of distribution of compounds in rabbits: In silico prediction and pharmacokinetic simulations for drug development

The aims of this research were to (1) create a curated universal database of intravitreal volumes of distribution (Vss, ivt) and clearances (CL ivt) of small molecular weight compounds and macromolecules and (2) to develop quantitative structure property relationship (QSPR) and pharmacokinetic models for the estimation of vitreal drug concentrations based on the compound structure. Vss, ivt and CL ivt values were determined from the available literature on intravitreal drug administration using compartmental models and curve fitting. A simple QSPR model for CL ivt of small molecular weight compounds was obtained with two descriptors: Log D7.4 and hydrogen bond donor capacity. The model predicted the internal and external test sets reliably with a mean fold error of 1.50 and 1.33, respectively (Q(2)Y=0.62). For 80% of the compounds the Vss, ivt was 1.18-2.28 ml; too narrow range for QSPR model building. Integration of the estimated Vss, ivt and predicted CL ivt parameters into pharmacokinetic simulation models allows prediction of vitreous drug concentrations after intravitreal administration. The present work presents for the first time a database of CL ivt and Vss, ivt values and the dependence of the CL ivt values on the molecular structure. The study provides also useful in silico tools to investigate a priori the intravitreal pharmacokinetic profiles for intravitreally injected candidate compounds and drug delivery systems.

Intraocular pharmacokinetics of intravitreal vascular endothelial growth factor-Trap in a rabbit model

PURPOSE

To determine intraocular pharmacokinetic properties of intravitreally injected vascular endothelial growth factor (VEGF)-Trap in a rabbit model.

METHODS

VEGF-Trap was intravitreally injected in 18 rabbit eyes. Eyes were enucleated 1 h and 1, 2, 5, 14, and 30 days after injections and immediately frozen at -80 °C. Concentration of VEGF-Trap in vitreous, aqueous humor, and retina/choroid was determined using an indirect enzyme-linked immunosorbent assay and analyzed to obtain pharmacokinetic properties.

RESULTS

Maximum concentration of VEGF-Trap was achieved at 1 h in all three tissues. A one-compartment model of distribution was selected as the final model for all tissues studied. Estimated half-life of VEGF-Trap in vitreous, aqueous humor, and retinal/choroid was 87.1, 36.8, and 35.0 h, respectively, and estimated mean residence time was 125.7, 53.1, and 50.5 h, respectively. Area under the curve from time 0 to the end point was 10009.8, 3945.1, and 1189.3, respectively. Total exposure of the aqueous humor and retina/choroid to VEGF-Trap was 39.4% and 11.9% of vitreous exposure, respectively.

CONCLUSION

The vitreous half-life of VEGF-Trap is 3.63 days. This is shorter than that of bevacizumab (6.99 days) and longer than that of ranibizumab (2.51 days), as shown in studies using the same experimental settings. The concentration of VEGF-Trap peaked at 1 h after injections in all eye tissues studied.

High-throughput in vitro drug release and pharmacokinetic simulation as a tool for drug delivery system development: application to intravitreal ocular administration

In vitro estimation of release kinetics from drug delivery systems is needed in formulation development. Cost-effective methods of assessment for delivery systems are needed particularly in the case of biologicals and drug administration routes that are difficult to screen in vivo (e.g. intraocular drug delivery). As a proof-of-concept, we demonstrate here a practical high-throughput methodology to investigate in vitro drug release and predict resulting drug concentrations in the eye after intravitreal administration. 96-well plate based assay aided with robotic sampling was used to study release of eight model drugs of varying physicochemical properties (dexamethasone, vancomycin, alpha-lactalbumin, lysozyme, myoglobin, albumin, lactoferrin, human IgG) from twelve alginate microsphere formulations. The amount of drug released over a period of time was assessed by photometric and fluorescence methods. In vitro drug release rates obtained were used in pharmacokinetic simulations using one-compartment model of the vitreal cavity with anatomical volume of distribution and clearance estimates based on the literature precedence. An integrated approach of drug release screening and pharmacokinetic simulations can prove to be a useful methodology in guiding formulation development for ocular delivery in animal models. In general, the methodology has the potential to be a cost-effective tool for early stage drug delivery system discovery and development.

Primary central nervous system lymphoma: current state of anti-CD20 therapy and appraisal of reported response criteria

Primary central nervous system lymphoma (PCNSL) is an aggressive non-Hodgkin's lymphoma which is confined to the central nervous system and may also affect intraocular structures. Despite high initial rates of response to methotrexate-based chemotherapy, more than 50% of patients will experience relapse and about 10% have disease that is refractory to chemotherapy. Outcome in patients who fail treatment is very poor, and therefore new therapeutic approaches that may increase the rate of complete response and the proportion of durable remission are sought. Based on the pivotal role that anti-CD20 therapy now plays in the treatment outcome of aggressive systemic B-cell lymphomas, a similar approach is commonly being adapted for PCNSL despite the lack of evidence for its effectiveness. This review examines the current status and level of evidence for the use of monoclonal antibodies against the CD20 surface antigen, which is present on normal and malignant B-cells in PCNSL. The review covers both systemic and local (intracerebrospinal fluid or intravitreal) administration of CD20 monoclonal antibodies in PCNSL. In addition, it scrutinizes the response criteria commonly reported for evaluation of treatment outcome. The importance of differentiating unconfirmed complete response from partial response is outlined and the lack of consensus on response criteria for atypical imaging presentations of PCNSL is delineated.

Encapsulated cells for long-term secretion of soluble VEGF receptor 1: Material optimization and simulation of ocular drug response

Anti-angiogenic therapies with vascular endothelial growth factor (VEGF) inhibiting factors are effective treatment options for neovascular diseases of the retina, but these proteins can only be delivered as intravitreal (IVT) injections. To sustain a therapeutic drug level in the retina, VEGF inhibitors have to be delivered frequently, every 4-8weeks, causing inconvenience for the patients and expenses for the healthcare system. The aim of this study was to investigate cell encapsulation as a delivery system for prolonged anti-angiogenic treatment of retinal neovascularization. Genetically engineered ARPE-19 cells secreting soluble vascular endothelial growth factor receptor 1 (sVEGFR1) were encapsulated in a hydrogel of cross-linked collagen and interpenetrating hyaluronic acid (HA). The system was optimized in terms of matrix composition and cell density, and long-term cell viability and protein secretion measurements were performed. sVEGFR1 ARPE-19 cells in the optimized hydrogel remained viable and secreted sVEGFR1 at a constant rate for at least 50days. Based on pharmacokinetic/pharmacodynamic (PK/PD) modeling, delivery of sVEGFR1 from this cell encapsulation system is expected to lead only to modest VEGF inhibition, but improvements of the protein structure and/or secretion rate should result in strong and prolonged therapeutic effect. In conclusion, the hydrogel matrix herein supported the survival and protein secretion from the encapsulated cells. The PK/PD simulation is a convenient approach to predict the efficiency of the cell encapsulation system before in vivo experiments.

Topical drug delivery to retinal pigment epithelium with microfluidizer produced small liposomes

Drug delivery from topically instilled eye drops to the posterior segment of the eye has long been one of the greatest challenges of ocular drug development. We developed methods of liposome preparation utilizing a microfluidizer to achieve adjustable nanoparticle size (even less than 80 nm) and high loading capacity of plasmid DNA. The microfluidizing process parameters were shown to affect the size of the liposomes. Higher operating pressures and passage for at least 10 times through the microfluidizer produced small liposomes with narrow size distribution. The liposomes were physically stable for several months at +4°C. In vivo distribution of the optimized liposome formulations in the rat eyes was investigated with confocal microscopy of the histological specimens. Transferrin was used as a targeting ligand directed to retinal pigment epithelium. Size dependent distribution of liposomes to different posterior segment tissues was seen. Liposomes with the diameter less than 80 nm permeated to the retinal pigment epithelium whereas liposomes with the diameter of 100 nm or more were distributed to the choroidal endothelium. Active targeting was shown to be necessary for liposome retention to the target tissue. In conclusion, these microfluidizer produced small liposomes in eye drops are an attractive option for drug delivery to the posterior segment tissues of the eye.

Novel endogenous glycan therapy for retinal diseases: safety, in vitro stability, ocular pharmacokinetic modeling, and biodistribution

Asialo, tri-antennary oligosaccharide (NA3 glycan) is an endogenous compound, which supports proper folding of outer segment membranes, promotes normal ultrastructure, and maintains protein expression patterns of photoreceptors and Müller cells in the absence of retinal pigment epithelium support. It is a potential new therapeutic for atrophic age-related macular degeneration (AMD) and other retinal degenerative disorders. Herein, we evaluate the safety, in vitro stability, ocular pharmacokinetics and biodistribution of NA3. NA3 was injected into the vitreous of New Zealand white rabbits at two concentrations viz. 1 nM (minimum effective concentration (MEC)) and 100 nM (100XMEC) at three time points. Safety was evaluated using routine clinical and laboratory tests. Ocular pharmacokinetics and biodistribution of [(3)H]NA3 were estimated using scintillation counting in various parts of the eye, multiple peripheral organs, and plasma. Pharmacokinetic parameters were estimated by non-compartmental modeling. A 2-aminobenzamide labeling and hydrophilic interaction liquid interaction chromatography were used to assess plasma and vitreous stability. NA3 was well tolerated by the eye. The concentration of NA3 in eye tissues was in the order: vitreous > retina > sclera/choroid > aqueous humor > cornea > lens. Area under the curve (0 to infinity) (AUC∞) was the highest in the vitreous thereby providing a positive concentration gradient for NA3 to reach the retina. Half-lives in critical eye tissues ranged between 40 and 60 h. NA3 concentrations were negligible in peripheral organs. Radioactivity from [(3)H]NA3 was excreted via urine and feces. NA3 was stable at 37°C in vitreous over a minimum of 6 days, while it degraded rapidly in plasma. Collectively, these results document that NA3 shows a good safety profile and favorable ocular pharmacokinetics.

Primary intraocular lymphoma

Primary intraocular lymphoma (PIOL) is an ocular malignancy that is a subset of primary central system lymphoma (PCNSL). Approximately one-third of PIOL patients will have concurrent PCNSL at presentation, and 42-92% will develop PCNSL within a mean of 8-29 months. Although rare, the incidence has been rising in both immunocompromised and immunocompetent populations. The majority of PIOL is diffuse large B-cell lymphoma, though rare T-cell variants are described. Recently, PIOL has been classified by main site of involvement in the eye, with vitreoretinal lymphoma as the most common type of ocular lymphoma related to PCNSL. Diagnosis remains challenging for ophthalmologists and pathologists. PIOL can masquerade as noninfectious or infectious uveitis, white dot syndromes, or occasionally as other neoplasms such as metastatic cancers. Laboratory diagnosis by cytology has been much aided by the use of immunocytochemistry, flow cytometry, biochemical finding of interleukin changes (IL10:IL6 ratio > 1), and cellular microdissection with polymerase chain reaction amplification for clonality. Use of several tests improves the diagnostic yield. Approaches to treatment have centered on systemic methotrexate-based chemotherapy, often with cytarabine (Ara-C) and radiotherapy. Use of intravitreal chemotherapy with methotrexate (0.4 mg/0.1 mL) is promising in controlling ocular disease, and intravitreal rituximab (anti-CD20 monoclonal antibody) has also been tried. Despite these advances, prognosis remains poor.

How I treat CNS lymphomas

The pathogenesis of primary and secondary central nervous system (CNS) lymphoma poses a unique set of diagnostic, prognostic, and therapeutic challenges. During the past 10 years, there has been significant progress in the elucidation of the molecular properties of CNS lymphomas and their microenvironment, as well as evolution in the development of novel treatment strategies. Although a CNS lymphoma diagnosis was once assumed to be uniformly associated with a dismal prognosis, it is now reasonable to anticipate long-term survival, and possibly a cure, for a significant fraction of CNS lymphoma patients. The pathogenesis of CNS lymphomas affects multiple compartments within the neuroaxis, and proper treatment of the CNS lymphoma patient requires a multidisciplinary team with expertise not only in hematology/oncology but also in neurology, neuroradiology, neurosurgery, clinical neuropsychology, ophthalmology, pathology, and radiation oncology. Given the evolving principles of management and the evidence for improvements in survival, our goal is to provide an overview of current knowledge regarding the pathogenesis of CNS lymphomas and to highlight promising strategies that we believe to be most effective in establishing diagnosis, staging, and therapeutic management.

Can rituximab induce long-term disease remission in patients with intra-ocular non-infectious inflammation?

Treatment of non-infectious uveitis is based primarily on the use of systemic corticosteroids and second-line immunosuppressive drugs. However, their extensive side effect profile, particularly for steroids, has led to the increased use of other immunosuppressive drugs, as sparing capacity agents. Rituximab is an anti-CD20 chimeric antibody, often given as a single course of 2 infusions, resulting in complete depletion of peripheral mature B cells. While it is licensed to treat refractory systemic lymphoma patients, it has also shown promising results in systemic auto-immune diseases, where a single course of treatment is able to achieve long-term clinical remission. Treatment with rituximab has been reported for various ocular conditions, suggesting it may be effective in inducing long-term disease control and other systemic immunosuppressive agents can be reduced or discontinued. When disease relapse occurs, a further course or courses can be given with good results. This review summarizes the current evidence regarding the role of rituximab in treating non-infectious uveitis.

Pharmacokinetics of intravitreally injected bevacizumab in vitrectomized eyes

PURPOSE

To compare the pharmacokinetics (PKs) of intravitreally injected bevacizumab in vitrectomized versus nonvitrectomized control rabbit eyes.

METHODS

Twenty-five-gauge pars plana vitrectomy without lensectomy was performed in 17 right rabbit eyes (V) and 18 nonvitrectomized right rabbit eyes served as controls (C). After 1.25 mg/0.05 mL intravitreal bevacizumab (IVB) injections, eyes were enucleated at 1 h, 1, 2, 5, 14, and 30 days after the injection and immediately frozen at -80°C. Bevacizumab concentrations were determined after separation of frozen vitreous and aqueous humor (AH) compartments using indirect enzyme-linked immunosorbent assay. Bevacizumab concentration-time data were analyzed to obtain PK data.

RESULTS

Vitreous clearance of IVB consisted of 2 phases, the first fast distribution and second slow elimination phase. Clearance of IVB was accelerated in V eyes only during the first phase and not in the second phase. The vitreous concentration percent ratios between V and C eyes were 94.7% (1 h), 70.5% (1 day), 89.2% (2 days), 94.2% (5 days), 99.2% (14 days), and 79.1% (30 days). Overall vitreous half-lives were 6.99 and 7.06 days for V and C eyes, respectively (1.6-h difference).

CONCLUSION

Overall IVB PKs in rabbit eyes after vitrectomy without lensectomy are not substantially different from nonvitrectomized control eyes.

Rituximab biosimilars

INTRODUCTION

Rituximab is a monoclonal antibody targeting CD20, used to treat B cell malignancies and B cell-mediated autoimmune diseases. Rituximab has the largest market of any monoclonal antibody therapeutic. Its patent will expire within the next few years and several manufacturers have already produced or are developing rituximab biosimilars that aim to match the innovator rituximab as closely as possible.

AREAS COVERED

In this review, we discuss key factors that determine the efficacy of rituximab therapy, potential technical challenges in the manufacture and evaluation of biosimilars, regulatory considerations regarding the review and approval of biosimilars, and the current status of biosimilar rituximab development by various manufacturers. Due to the nature of the topic, literature searches included conference abstracts, regulatory and industry websites as well as peer reviewed literature.

EXPERT OPINION

Cost is a key limitation of current biologics usage and there is a political impetus to the licensing of biosimilars. Concerns regarding potential dissimilarities of biosimilars are legitimate, but surmountable with techniques for in vitro, in vivo and clinical testing and more clearly defined regulatory requirements. These should provide reassurance to prescribers. However, the cost of manufacturing and licensing a biosimilar remains high and the reduction in cost may be more limited than for a non-biologic small molecule drug and its generic version. This cost reduction will be critical to the impact and use of rituximab biosimilars.

Efficacy and Complications of Intravitreal Rituximab Injection for Treating Primary Vitreoretinal Lymphoma

PURPOSE

To assess the long-term clinical outcomes of intravitreal injections of rituximab (IVR), an anti-CD20 monoclonal antibody, to treat CD20-positive primary vitreoretinal lymphoma (PVRL).

METHODS

Twenty eyes of 13 women (mean age, 66.2 ± 9.9 years) with CD20-positive PVRL were included in this prospective, interventional case series. All patients had discontinued previous intravitreal methotrexate (IVM) treatment because of severe corneal epitheliopathy. Weekly IVR injections (1 mg/0.1 ml) for 4 weeks were administered as a one-course protocol. Additional injections were administered when the PVRL recurred. The effects and the adverse events associated with IVR injections were evaluated.

RESULTS

All patients completed a 1-year follow-up (mean observation after IVR injections, 24.7 ± 6.3 months). Before treatment, diffuse keratic precipitates (KPs), anterior vitreous cells, or both were observed in 18 (90%) eyes of 11 patients, and typical subretinal infiltrates were seen in eight (40%) eyes of six patients; all improved with one treatment course. The anterior segment lesions recurred in 11 (55%) eyes of nine patients and resolved with another course of injections. Transient IOP elevations occurred in 12 (60%) eyes of 10 patients within 3.8 ± 1.9 weeks after the first treatment course; iridocyclitis with mutton-fat KPs developed in seven (35%) eyes of six patients with elevated IOP and resolved with topical treatment. No other significant ocular complications or systemic side effects developed.

CONCLUSIONS

Injections of IVR were shown to be an efficacious alternative treatment for PVRL, although the disease recurred in approximately half of the eyes. Complications included transient IOP elevations and iridocyclitis with mutton-fat KPs that were managed topically.

TRANSLATIONAL RELEVANCE

The results of this trial support IVR as one element of combined modality therapy for treating PVRL patients without CNS involvement, particularly for those who respond poorly and have side effects with IVM. (http://www.umin.ac.jp/ctr/ number, UMIN000005604).

Retina-choroid-sclera permeability for ophthalmic drugs in the vitreous to blood direction: quantitative assessment

PURPOSE

To determine the outward permeability of retina-choroid-sclera (RCS) layer for different ophthalmic drugs and to develop correlations between drug physicochemical properties and RCS permeability.

METHODS

A finite volume model was developed to simulate pharmacokinetics in the eye following drug administration by intravitreal injection. The RCS permeability was determined for 32 compounds by best fitting the drug concentration-time profile obtained by simulation with previously reported experimental data. Multiple linear regression was then used to develop correlations between best fit RCS permeability and drugs physicochemical properties.

RESULTS

The RCS drug permeabilities had values that ranged over 3 × 10(-6) m/s. Regression analysis for hydrophilic compounds showed that more than 92% of the variation in permeability values can be explained by correlative models of drug properties that include logarithm of the octanol-water partition coefficient (LogP), protein binding (PB), number of hydrogen bond acceptors (HBA), hydrogen bond donors (HBD), polar surface area (PSA) and dissociation constant (pKa) as independent variables. Regression analysis for lipophilic compounds showed that no significant correlation can be found between just physicochemical properties and RCS permeability.

CONCLUSION

Using the RCS permeability obtained from this study for different drugs, one can predict pharmacokinetics of intravitreal drug delivery systems such as solid implants or colloidal systems. Furthermore, the developed correlations between RCS permeability and physicochemical properties of drugs are useful in early drug development by predicting RCS permeability and drug concentration in the vitreous without experimental data.

Retinal toxicity of intravitreal rituximab in albino rabbits

PURPOSE

To evaluate retinal toxicity of intravitreal rituximab.

METHODS

Twelve albino rabbits were included in the study. 1 mg/0.1 mL of rituximab was injected to the right (experimental) eye of each rabbit, and 0.1 mL of saline was injected into the left (control) eye. Electroretinogram was recorded before injection and 3 hours, 4 days, 1 week, 2 weeks and 4 weeks after injection (12 rabbits), and visual evoked potential was recorded before injection and 4 weeks after injection (10 rabbits). Histology and glial fibrillary acidic protein immunocytochemistry (12 rabbits) were performed at 4 weeks after injection. Clinical examination was conducted at all time points in all rabbits.

RESULTS

The average dark-adapted electroretinogram b-wave Vmax ratios, and the average light-adapted b-wave amplitude ratios were approximately 1, and the average log σ difference was around zero throughout the follow-up period. The average visual evoked potential amplitude ratio and the average visual evoked potential implicit time difference were approximately 1 and 0, respectively. No histologic damage was seen, but glial fibrillary acidic protein was mildly expressed in 6 of 12 experimental eyes. Results of clinical examination were normal in all the eyes.

CONCLUSION

Intravitreal injection of 1 mg rituximab does not cause functional or histologic signs of retinal toxicity in albino rabbits. Mild glial fibrillary acidic protein expression in Müller cells probably indicates a mild degree of retinal stress.

Uveitis, the Comparison of Age-Related Macular Degeneration Treatments Trials (CATT), and intravitreal biologics for ocular inflammation

PURPOSE

To provide perspective on the implications of the Comparison of Age-Related Macular Degeneration Treatments Trials (CATT) on intravitreal biologic agents in uveitis and retinal diseases in which ocular inflammatory pathways are central to their pathogenesis.

DESIGN

Interpretative essay.

METHODS

Literature review and interpretation.

RESULTS

Besides the clear importance of CATT from a patient treatment perspective in age-related macular degeneration (AMD), these data highlight the critical relevance of highly specific protein immunotherapies offered with biologic agents. The CATT trial also provides a reminder regarding the importance of rigorous efficacy and safety monitoring required when administering intravitreal biologic therapy. Within the field of uveitis, systemic and local biologics have been used to effectively treat uveitis, targeting pathways implicated in both angiogenesis and inflammation (eg, tumor necrosis factor-α [TNF-α] and interleukin-2 pathways), and research on intravitreal biologic therapy for uveitis and AMD will continue to expand. With over 25 ongoing clinical trials on intravitreal biologic therapy for AMD, enthusiasm for vanguard biologic therapies should be tempered by judicious monitoring for adverse events.

CONCLUSION

The importance of the CATT trial encompasses day-to-day treatment decisions for AMD, as well as lessons on how biologics for ocular disease should be implemented into clinical practice. Specifically, the introduction of intravitreal biologic therapies into clinical practice for uveitis, AMD, and other ocular diseases in which inflammation is involved should be guided by a clear understanding of the immunotherapeutic agent and its molecular target and with rigorous monitoring for both patient benefit and patient safety.

Vitreous pharmacokinetics and electroretinographic findings after intravitreal injection of acyclovir in rabbits

OBJECTIVES

Acute retinal necrosis is a rapidly progressive and devastating viral retinitis caused by the herpesvirus family. Systemic acyclovir is the treatment of choice; however, the progression of retinal lesions ceases approximately 2 days after treatment initiation. An intravitreal injection of acyclovir may be used an adjuvant therapy during the first 2 days of treatment when systemically administered acyclovir has not reached therapeutic levels in the retina. The aims of this study were to determine the pharmacokinetic profile of acyclovir in the rabbit vitreous after intravitreal injection and the functional effects of acyclovir in the rabbit retina.

METHODS

Acyclovir (Acyclovir; Bedford Laboratories, Bedford, OH, USA) 1 mg in 0.1 mL was injected into the right eye vitreous of 32 New Zealand white rabbits, and 0.1 mL sterile saline solution was injected into the left eye as a control. The animals were sacrificed after 2, 9, 14, or 28 days. The eyes were enucleated, and the vitreous was removed. The half-life of acyclovir was determined using high-performance liquid chromatography. Electroretinograms were recorded on days 2, 9, 14, and 28 in the eight animals that were sacrificed 28 days after injection according to a modified protocol of the International Society for Clinical Electrophysiology of Vision.

RESULTS

Acyclovir rapidly decayed in the vitreous within the first two days after treatment and remained at low levels from day 9 onward. The eyes that were injected with acyclovir did not present any electroretinographic changes compared with the control eyes.

CONCLUSIONS

The vitreous half-life of acyclovir is short, and the electrophysiological findings suggest that the intravitreal delivery of 1 mg acyclovir is safe and well tolerated by the rabbit retina.

Ocular pharmacokinetic study using T₁ mapping and Gd-chelate- labeled polymers

PURPOSE

Recent advances in drug discovery have led to the development of a number of therapeutic macromolecules for treatment of posterior eye diseases. We aimed to investigate the clearance of macromolecular contrast probes (polymers conjugated with Gd-chelate) in the vitreous after intravitreal injections with the recently developed ms-DSEPI-T12 MRI and to examine the degradation of disulfide-containing biodegradable polymers in the vitreous humor in vivo.

METHODS

Intravitreal injections of model contrast agents poly[N-(2-hydroxypropyl)methacrylamide]-GG-1,6-hexanediamine-(Gd-DO3A), biodegradable (Gd-DTPA)-cystine copolymers, and MultiHance were performed in rabbits; their distribution and elimination from the vitreous after injections were determined by MRI.

RESULTS

Times for macromolecular contrast agents to decrease to half their initial concentrations in the vitreous ranged from 0.4-1.3 days post-injection. Non-biodegradable polymers demonstrated slower vitreal clearance than those of disulfide-biodegradable polymers. Biodegradable polymers had similar clearance as MultiHance.

CONCLUSIONS

Usefulness of T(1) mapping and ms-DSEPI-T12 MRI to study ocular pharmacokinetics was demonstrated. Results suggest an enzymatic degradation mechanism for the disulfide linkage in polymers in the vitreous leading to breakup of polymers in vitreous humor over time.

Barrier analysis of periocular drug delivery to the posterior segment

Periocular administration is a potential way of delivering drugs to their targets in posterior eye segment (vitreous, neural retina, retinal pigment epithelium (RPE), choroid). Purpose of this study was to evaluate the role of the barriers in periocular drug delivery. Permeation of FITC-dextrans and oligonucleotides in the bovine sclera was assessed with and without Pluronic gel in the donor compartment. Computational model for subconjunctival drug delivery to the choroid and neural retina/vitreous was built based on clearance concept. Kinetic parameters for small hydrophilic and lipophilic drug molecules, and a macromolecule were obtained from published ex vivo and in vivo animal experiments. High negative charge field of oligonucleotides slows down their permeation in the sclera. Pluronic does not provide adequate rate control to modify posterior segment drug delivery. Theoretical calculations for subconjunctival drug administration indicated that local clearance by the blood flow and lymphatics removes most of the drug dose which is in accordance with experimental results. Calculations suggested that choroidal blood flow removes most of the drug that has reached the choroid, but this requires experimental verification. Calculations at steady state using the same subconconjunctival input rate showed that the choroidal and vitreal concentrations of the macromolecule is 2-3 orders of magnitude higher than that of small molecules. The evaluation of the roles of the barriers augments to design new drug delivery strategies for posterior segment of the eye.

Emerging biologics in the treatment of uveitis

The pathogenic mechanisms underlying uveitis syndromes continue to be evaluated using animal models and in the clinical setting. As the complex interactions between ocular immune cells, proinflammatory cytokines, chemokines and cellular adhesion molecules are uncovered, targeted therapies directed against these immune mediators will continue to be developed. Traditional immunosuppressive medications, such as corticosteroids and steroid-sparing immunomodulatory agents, have demonstrated efficacy in the treatment of uveitic syndromes, but side effects and drug toxicities often limit the use of these medications. The biologic agents, a newer class of medications, target specific immune pathways and have demonstrated efficacy in rheumatologic, dermatologic and neurologic conditions. Biologic therapies (e.g., TNF-alpha inhibitors and IL-2 receptor inhibitor) targeting ocular immune cell surface receptors, cytokines and chemokines continue to be developed and have shown promise in the treatment of uveitis and ocular inflammatory diseases. Clinical and basic aspects of monoclonal antibody therapy for uveitis are presented in this review. Additional studies are needed to further evaluate the role of monoclonal antibodies in the therapeutic armamentarium for uveitis.

Clinical review: treatment of vitreoretinal lymphoma

Vitreoretinal lymphoma is the most common type of intraocular lymphoma. It is mostly a high-grade B-cell malignancy with a poor prognosis, and is often associated with primary central nervous system lymphoma. Since intraocular lymphoma was first recognized almost 60 years ago, its treatment has gradually evolved. In the early years enucleation was often performed. Since that time, radiation therapy alone, systemic chemotherapy alone, or a combination of the two have been used extensively Because of the limited intraocular penetration of drugs administered systemically, the systemic and local toxicity of chemotherapy and radiation therapy and the high rate of recurrence, intravitreous chemotherapy, mainly using methotrexate, has become popular in the last decade, with encouraging results. More recently, biological treatment with intravitreal injections of rituximab has been investigated, with good results and minimal side effects. This review summarizes the present knowledge on vitreoretinal lymphoma therapy, with an eye to future molecular approaches.

Intravitreal injection of therapeutic agents

BACKGROUND

Intravitreal injection (IVI) with administration of various pharmacological agents is a mainstay of treatment in ophthalmology for endopthalmitis, viral retinitis, age-related macular degeneration, cystoid macular edema, diabetic retinopathy, uveitis, vascular occlusions, and retinal detachment. The indications and therapeutic agents are reviewed in this study.

METHODS

A search of the English, German, and Spanish language MEDLINE database was conducted. A total of 654 references spanning the period through early 2008 were individually evaluated.

RESULTS

The advantage of the IVI technique is the ability to maximize intraocular levels of medications and to avoid the toxicities associated with systemic treatment. Intravitreal injection has been used to deliver several types of pharmacological agents into the vitreous cavity: antiinfective and antiinflammatory medications, immunomodulators, anticancer agents, gas, antivascular endothelial growth factor, and several others. The goal of this review is to provide a detailed description of the properties of numerous therapeutic agents that can be delivered through IVI, potential complications of the technique, and recommendations to avoid side effects.

CONCLUSION

The IVI technique is a valuable tool that can be tailored to the disease process of interest based on the pharmacological agent selected. This review provides the reader with a comprehensive summary of the IVI technique and its multitude of uses.

Biology and treatment of primary central nervous system lymphoma

Primary central nervous system lymphoma (PCNSL) is a rare variant of extranodal non-Hodgkin lymphoma that is restricted in distribution to the brain, leptomeninges, spinal cord, and intraocular compartments. Although PCNSL shares overlapping features with systemic lymphoma, recent studies also reveal a unique pattern of gene and protein expression in PCNSL. These findings have yielded new insights into the pathophysiology of the disease, as well as the identification of novel prognostic biomarkers. Immune system compromise, such as is seen in acquired immune deficiency syndrome (AIDS), is the best established known risk factor for PCNSL. Like other lesions of the brain, meninges, and eye, the presenting symptoms associated with PCNSL typically include focal neurological deficits related to the site of disease or more global consequences of increased intracranial pressure. Diagnosis of PCNSL typically includes gadolinium-enhanced MRI and pathologic tissue analysis, as well as additional studies aimed at excluding concurrent systemic disease. PCNSL typically has a worse overall prognosis than systemic lymphoma. High-dose chemotherapy, particularly with methotrexate-based regimens, is the backbone of therapy for most patients, and chemotherapy is associated with much lower rates of treatment-related morbidity and mortality than whole-brain irradiation. Autologous stem cell transplantation is an emerging treatment modality, particularly in younger patients with relapsed disease, but high rates of treatment-related mortality are observed in older patients. Immunotherapy, including treatment with intrathecal rituximab, is another area of active research that may have promise in refractory or relapsed disease. Treatment options for intraocular lymphoma parallel those for PCNSL elsewhere in the brain: systemic chemotherapy, radiation, and local delivery of cytotoxic and immunologically active agents such as anti-CD20 antibody.