Targeted brain delivery of methotrexate by glutathione PEGylated liposomes: How can the formulation make a difference?

The purpose of this study was to quantitatively investigate how conjugation of GSH to different liposomal formulations influence the brain delivery of methotrexate (MTX) in rats. GSH-PEG liposomal MTX based on hydrogenated soy phosphatidylcholine (HSPC) or egg yolk phosphatidylcholine (EYPC) and their corresponding PEG control liposomes were prepared. The brain delivery of MTX after intravenously administering free MTX, four liposomal formulations or free MTX + empty GSH-PEG-HSPC liposomes was evaluated by performing microdialysis in brain interstitial fluid and blood. Compared to free MTX with a steady-state unbound brain-to-plasma concentration ratio (Kp,uu) of 0.10, PEG-HSPC liposomes did not affect the brain uptake of MTX, while PEG-EYPC liposomes improved the uptake (Kp,uu 1.5, p < 0.05). Compared to PEG control formulations, GSH-PEG-HSPC liposomes increased brain delivery of MTX by 4-fold (Kp,uu 0.82, p < 0.05), while GSH-coating on PEG-EYPC liposomes did not result in a further enhancement in uptake. The co-administration of empty GSH-PEG-HSPC liposomes with free MTX did not influence the uptake of MTX into the brain. This work showed that the brain-targeting effect of GSH-PEG liposomal MTX is highly dependent on the liposomal formulation that is combined with GSH, providing insights on formulation optimization of this promising brain delivery platform.

Drug delivery to retinal photoreceptors.

The photoreceptors of the retina are afflicted by diseases that still often lack satisfactory treatment options. Although suitable drugs might be available in some cases, the delivery of these compounds into the eye and across the blood-retinal barrier remains a significant challenge for therapy development. Here, we review the routes of drug administration to the retina and highlight different options for drug delivery to the photoreceptor cells.

In Vivo Quantitative Understanding of PEGylated Liposome's Influence on Brain Delivery of Diphenhydramine.

Despite the promising features of liposomes as brain drug delivery vehicles, it remains uncertain how they influence the brain uptake in vivo. In order to gain a better fundamental understanding of the interaction between liposomes and the blood-brain barrier (BBB), it is indispensable to test if liposomes affect drugs with different BBB transport properties (active influx or efflux) differently. The aim of this study was to quantitatively evaluate how PEGylated (PEG) liposomes influence brain delivery of diphenhydramine (DPH), a drug with active influx at the BBB, in rats. The brain uptake of DPH after 30 min intravenous infusion of free DPH, PEG liposomal DPH, or free DPH + empty PEG liposomes was compared by determining the unbound DPH concentrations in brain interstitial fluid and plasma with microdialysis. Regular blood samples were taken to measure total DPH concentrations in plasma. Free DPH was actively taken up into the brain time-dependently, with higher uptake at early time points followed by an unbound brain-to-plasma exposure ratio ( Kp,uu) of 3.0. The encapsulation in PEG liposomes significantly decreased brain uptake of DPH, with a reduction of Kp,uu to 1.5 ( p < 0.05). When empty PEG liposomes were coadministered with free drug, DPH brain uptake had a tendency to decrease ( Kp,uu 2.3), and DPH was found to bind to the liposomes. This study showed that PEG liposomes decreased the brain delivery of DPH in a complex manner, contributing to the understanding of the intricate interactions between drug, liposomes, and the BBB.

Combination of cGMP analogue and drug delivery system provides functional protection in hereditary retinal degeneration.

Inherited retinal degeneration (RD) is a devastating and currently untreatable neurodegenerative condition that leads to loss of photoreceptor cells and blindness. The vast genetic heterogeneity of RD, the lack of "druggable" targets, and the access-limiting blood-retinal barrier (BRB) present major hurdles toward effective therapy development. Here, we address these challenges (i) by targeting cGMP (cyclic guanosine- 3',5'-monophosphate) signaling, a disease driver common to different types of RD, and (ii) by combining inhibitory cGMP analogs with a nanosized liposomal drug delivery system designed to facilitate transport across the BRB. Based on a screen of several cGMP analogs we identified an inhibitory cGMP analog that interferes with activation of photoreceptor cell death pathways. Moreover, we found liposomal encapsulation of the analog to achieve efficient drug targeting to the neuroretina. This pharmacological treatment markedly preserved in vivo retinal function and counteracted photoreceptor degeneration in three different in vivo RD models. Taken together, we show that a defined class of compounds for RD treatment in combination with an innovative drug delivery method may enable a single type of treatment to address genetically divergent RD-type diseases.

Correction to: Current research into brain barriers and the delivery of therapeutics for neurological diseases: a report on CNS barrier congress London, UK, 2017.

After publication of the article [1], it has been brought to our attention that there are some errors in the formatting of names in the final version of the article.

Current research into brain barriers and the delivery of therapeutics for neurological diseases: a report on CNS barrier congress London, UK, 2017.

This is a report on the CNS barrier congress held in London, UK, March 22-23rd 2017 and sponsored by Kisaco Research Ltd. The two 1-day sessions were chaired by John Greenwood and Margareta Hammarlund-Udenaes, respectively, and each session ended with a discussion led by the chair. Speakers consisted of invited academic researchers studying the brain barriers in relation to neurological diseases and industry researchers studying new methods to deliver therapeutics to treat neurological diseases. We include here brief reports from the speakers.

Treatment with penicillin G and hydrocortisone reduces ALS-associated symptoms: a case series of three patients.

Three male Caucasian patients with ALS were admitted to the hospital due to progressive dysphagia and dysarthria. During two 21-day courses of penicillin G and hydrocortisone, these patients' dysphagia and dysarthria resolved. The patient's other ALS-associated symptoms also improved, including respiratory function, coordination, walking, and muscle strength. This is the first report of a treatment with a protocol for treating dysphagia, dysarthria, respiratory depression and other ALS-related symptoms. Furthermore, the observations are consistent with the recent hypothesis that the successful treatment of ALS symptoms with this treatment course in six patients with syphilitic ALS was not directly due to the treatment of syphilis; but that the administered penicillin G and/or hydrocortisone treated these patients' ALS symptoms due the off-target pharmacological activity of penicillin G and/or hydrocortisone. This report therefore underscores the need to evaluate the efficacy of this treatment course in a clinical trial.

Preclinical evaluation of convection-enhanced delivery of liposomal doxorubicin to treat pediatric diffuse intrinsic pontine glioma and thalamic high-grade glioma.

OBJECTIVE Pediatric high-grade gliomas (pHGGs) including diffuse intrinsic pontine gliomas (DIPGs) are primary brain tumors with high mortality and morbidity. Because of their poor brain penetrance, systemic chemotherapy regimens have failed to deliver satisfactory results; however, convection-enhanced delivery (CED) may be an alternative mode of drug delivery. Anthracyclines are potent chemotherapeutics that have been successfully delivered via CED in preclinical supratentorial glioma models. This study aims to assess the potency of anthracyclines against DIPG and pHGG cell lines in vitro and to evaluate the efficacy of CED with anthracyclines in orthotopic pontine and thalamic tumor models. METHODS The sensitivity of primary pHGG cell lines to a range of anthracyclines was tested in vitro. Preclinical CED of free doxorubicin and pegylated liposomal doxorubicin (PLD) to the brainstem and thalamus of naïve nude mice was performed. The maximum tolerated dose (MTD) was determined based on the observation of clinical symptoms, and brains were analyzed after H & E staining. Efficacy of the MTD was tested in adult glioma E98-FM-DIPG and E98-FM-thalamus models and in the HSJD-DIPG-007-Fluc primary DIPG model. RESULTS Both pHGG and DIPG cells were sensitive to anthracyclines in vitro. Doxorubicin was selected for further preclinical evaluation. Convection-enhanced delivery of the MTD of free doxorubicin and PLD in the pons was 0.02 mg/ml, and the dose tolerated in the thalamus was 10 times higher (0.2 mg/ml). Free doxorubicin or PLD via CED was ineffective against E98-FM-DIPG or HSJD-DIPG-007-Fluc in the brainstem; however, when applied in the thalamus, 0.2 mg/ml of PLD slowed down tumor growth and increased survival in a subset of animals with small tumors. CONCLUSIONS Local delivery of doxorubicin to the brainstem causes severe toxicity, even at doxorubicin concentrations that are safe in the thalamus. As a consequence, the authors could not establish a therapeutic window for treating orthotopic brainstem tumors in mice. For tumors in the thalamus, therapeutic concentrations to slow down tumor growth could be reached. These data suggest that anatomical location determines the severity of toxicity after local delivery of therapeutic agents and that caution should be used when translating data from supratentorial CED studies to treat infratentorial tumors.

The Impact of Liposomal Formulations on the Release and Brain Delivery of Methotrexate: An In Vivo Microdialysis Study.

The impact of liposomal formulations on the in vivo release and brain delivery of methotrexate (MTX) was quantitatively assessed in rats. Two PEGylated liposomal MTX formulations based on hydrogenated soy phosphatidylcholine (HSPC) or egg-yolk phosphatidylcholine (EYPC) were prepared. The drug release and uptake into the brain after intravenous administration of both formulations were compared with unformulated MTX by determining the released, unbound MTX in brain and plasma using microdialysis. Total MTX concentrations in plasma were determined using regular blood sampling. The administration of both high- and low-dose EYPC liposomes resulted in 10 times higher extent of MTX release in plasma compared to that obtained from HSPC liposomes (p < 0.05). MTX itself possessed limited brain uptake with steady-state unbound brain-to-plasma concentration ratio (Kp,uu) of 0.10 ± 0.06. Encapsulation in HSPC liposomes did not affect MTX brain uptake (Kp,uu 0.11 ± 0.05). In contrast, EYPC liposomes significantly improved MTX brain delivery with a 3-fold increase of Kp,uu (0.28 ± 0.14 and 0.32 ± 0.13 for high- and low-dose EYPC liposomal MTX, respectively, p < 0.05). These results provide unique quantitative evidence that liposomal formulations based on different phospholipids can result in very different brain delivery of MTX.

Glutathione conjugation dose-dependently increases brain-specific liposomal drug delivery in vitro and in vivo.

The blood-brain barrier (BBB) represents a major obstacle for the delivery and development of drugs curing brain pathologies. However, this biological barrier presents numerous endogenous specialized transport systems that can be exploited by engineered nanoparticles to enable drug delivery to the brain. In particular, conjugation of glutathione (GSH) onto PEGylated liposomes (G-Technology®) showed to safely enhance delivery of encapsulated drugs to the brain. Yet, understanding of the mechanism of action remains limited and full mechanistic understanding will aid in the further optimization of the technology. In order to elucidate the mechanism of brain targeting by GSH-PEG liposomes, we here demonstrate that the in vivo delivery of liposomal ribavirin is increased in brain extracellular fluid according to the extent of GSH conjugation onto the liposomes. In vitro, using the hCMEC/D3 human cerebral microvascular endothelial (CMEC) cell line, as well as primary bovine and porcine CMEC (and in contrast to non-brain derived endothelial and epithelial cells), we show that liposomal uptake occurs through the process of endocytosis and that the brain-specific uptake is also glutathione conjugation-dependent. Interestingly, the uptake mechanism is an active process that is temperature-, time- and dose-dependent. Finally, early endocytosis events rely on cytoskeleton remodeling, as well as dynamin- and clathrin-dependent endocytosis pathways. Overall, our data demonstrate that the glutathione-dependent uptake mechanism of the G-Technology involves a specific endocytosis pathway indicative of a receptor-mediated mechanism, and supports the benefit of this drug delivery technology for the treatment of devastating brain diseases.

Patient-reported adverse effects of high-dose intravenous methylprednisolone treatment: a prospective web-based multi-center study in multiple sclerosis patients with a relapse.

In a prospective multi-center observational study, we evaluated the frequency, severity, and impact on activities of daily living (ADL) of adverse effects (AEs) of high-dose intravenous methylprednisolone (IVMP) in relapsing remitting multiple sclerosis (MS) patients with a relapse. Online self-report questionnaires stating IVMP's most common AEs were completed at baseline, the 2nd day of treatment, and 1 day and 1 week after treatment. Eighty-five patients were included, 66 completed the baseline questionnaire, and 59 completed at least one post-baseline questionnaire. Patients reported on average 4 (median) AEs; two (3.4 %) reported no AE. Most frequent was change in taste (61 %), facial flushing (61 %), sick/stomach pain (53 %), sleep disturbance (44 %), appetite change (37 %), agitation (36 %), and behavioral changes (36 %). Of all AEs, 34.3 % were severe and 37.9 % impacted on ADL. A 3-day course resulted in 4 (median) AEs and a 5-day course in 7. All patients with high disease impact had two or more AEs, compared with 79 % of those with low impact (p < 0.01). Of patients with high disability, 45 % had severe AEs, compared with 16 % of those with low disability. Severe central nervous system (CNS)-related AEs occurred two times more frequently in patients with high disease impact, and two-and-a-half times more frequently in patients with high disability. Therefore, in virtually all patients, high-dose IVMP leads to AEs, with about one of three AEs being severe with impact on ADL. Patients with high disease impact or high disability may experience more (severe) AEs, due to a higher occurrence of severe CNS-related AEs.

In vivo Functional Evaluation of Increased Brain Delivery of the Opioid Peptide DAMGO by Glutathione-PEGylated Liposomes.

PURPOSE: The purpose of this study was to evaluate formulation factors causing improvement in brain delivery of a small peptide after encapsulation into a targeted nanocarrier in vivo. METHODS: The evaluation was performed in rats using microdialysis, which enabled continuous sampling of the released drug in both the brain (striatum) and blood. Uptake in brain could thereby be studied in terms of therapeutically active, released drug. RESULTS: We found that encapsulation of the peptide DAMGO in fast-releasing polyethylene glycol (PEG)ylated liposomes, either with or without the specific brain targeting ligand glutathione (GSH), doubled the uptake of DAMGO into the rat brain. The increased brain delivery was observed only when the drug was encapsulated into the liposomes, thus excluding any effects of the liposomes themselves on the blood-brain barrier integrity as a possible mechanism. The addition of a GSH coating on the liposomes did not result in an additional increase in DAMGO concentrations in the brain, in contrast to earlier studies on GSH coating. This may be caused by differences in the characteristics of the encapsulated compounds and the composition of the liposome formulations. CONCLUSIONS: We were able to show that encapsulation into PEGylated liposomes of a peptide with limited brain delivery could double the drug uptake into the brain without using a specific brain targeting ligand.

Enhanced glutathione PEGylated liposomal brain delivery of an anti-amyloid single domain antibody fragment in a mouse model for Alzheimer's disease.

Treatment of neurodegenerative disorders such as Alzheimer's disease is hampered by the blood-brain barrier (BBB). This tight cerebral vascular endothelium regulates selective diffusion and active transport of endogenous molecules and xenobiotics into and out of the brain parenchyma. In this study, glutathione targeted PEGylated (GSH-PEG) liposomes were designed to deliver amyloid-targeting antibody fragments across the BBB into the brain. Two different formulations of GSH-PEG liposomes based on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and egg-yolk phosphatidylcholine (EYPC) were produced. Both formulations encapsulate 15kDa amyloid beta binding llama single domain antibody fragments (VHH-pa2H). To follow the biodistribution of VHH-pa2H rather than the liposome, the antibody fragment was labeled with the radioisotope indium-111. To prolong the shelf life of the construct beyond the limit of radioactive decay, an active-loading method was developed to efficiently radiolabel the antibody fragments after encapsulation into the liposomes, with radiolabeling efficiencies of up to 68% after purification. The radiolabeled liposomes were administered via a single intravenous bolus injection to APPswe/PS1dE9 double transgenic mice, a mouse model of Alzheimer's disease, and their wildtype littermates. Both GSH-PEG DMPC and GSH-PEG EYPC liposomes significantly increased the standard uptake values (SUV) of VHH-pa2H in the blood of the animals compared to free VHH-pa2H. Encapsulation in GSH-PEG EYPC liposomes resulted in the highest increase in SUV in the brains of transgenic animals. Overall, these data provide evidence that GSH-PEG liposomes may be suitable for specific delivery of single domain antibody fragments over the BBB into the brain.

Glutathione PEGylated liposomal methylprednisolone (2B3-201) attenuates CNS inflammation and degeneration in murine myelin oligodendrocyte glycoprotein induced experimental autoimmune encephalomyelitis.

Methylprednisolone (MP) pulses are the mainstay for relapse therapy in multiple sclerosis (MS). To improve the efficacy of treatment and reduce the side effects of MP, a long circulating brain-targeted formulation was developed; glutathione polyethylene glycol (PEG)ylated liposomal MP (2B3-201). Here we investigate the efficacy of 2B3-201 in murine myelin oligodendrocyte induced experimental autoimmune encephalomyelitis (MOG-EAE), an animal model mimicking inflammatory features and neurodegenerative aspects of MS. After disease onset, mice were randomized to receive either saline, three injections of free MP (high dose MP, 100mg/kg i.v.), two injections of free MP (low dose MP, 10mg/kg; i.v.), or two injections of 2B3-201 (10mg/kg i.v.). Treatment with a low dose of 2B3-201 significantly reduced the severity of EAE as compared to saline control, similar to treatment with high dose free MP, while a low dose of free MP was not effective. In a histological analysis of the spinal cord, treatment with 2B3-201 significantly decreased T cell as well as macrophage/microglia infiltration in the CNS by about 50%. Moreover, application of a low dose of 2B3-201 or a high dose of free MP reduced the amount of astrocyte activation as well as the extent of axonal loss and also demyelination in spinal cord lesions as compared to low dose MP or sham treatment. In summary, in the murine MOG-EAE model of MS, a glutathione PEGylated liposomal formulation of MP (2B3-201) is clinically and histologically as effective as free MP at one tenth of the dosage as well as at a lower application frequency and clearly more effective than the same dosage of free MP. These positive proof-of-concept efficacy studies warrant further development of 2B3-201 for the treatment of neuroinflammatory conditions such as MS.

CNS-targeted glucocorticoid reduces pathology in mouse model of amyotrophic lateral sclerosis.

BACKGROUND: Hallmarks of CNS inflammation, including microglial and astrocyte activation, are prominent features in post-mortem tissue from amyotrophic lateral sclerosis (ALS) patients and in mice overexpressing mutant superoxide dismutase-1 (SOD1G93A). Administration of non-targeted glucocorticoids does not significantly alter disease progression, but this may reflect poor CNS delivery. Here, we sought to discover whether CNS-targeted, liposomal encapsulated glucocorticoid would inhibit the CNS inflammatory response and reduce motor neuron loss. SOD1G93A mice were treated with saline, free methylprednisolone (MP, 10 mg/kg/week) or glutathione PEGylated liposomal MP (2B3-201, 10 mg/kg/week) and compared to saline treated wild-type animals. Animals were treated weekly with intravenous injections for 9 weeks from 60 days of age. Weights and motor performance were monitored during this period. At the end of the experimental period (116 days) mice were imaged using T2-weighted MRI for brainstem pathology; brain and spinal cord tissue were then collected for histological analysis. RESULTS: All SOD1G93A groups showed a significant decrease in motor performance, compared to baseline, from ~100 days. SOD1G93A animals showed a significant increase in signal intensity on T2 weighted MR images, which may reflect the combination of neuronal vacuolation and glial activation in these motor nuclei. Treatment with 2B3-201, but not free MP, significantly reduced T2 hyperintensity observed in SOD1G93A mice. Compared to saline-treated and free-MP-treated SOD1G93A mice, those animals given 2B3-201 displayed significantly improved histopathological outcomes in brainstem motor nuclei, which included reduced gliosis and neuronal loss. CONCLUSIONS: In contrast to previous reports that employed free steroid preparations, CNS-targeted anti-inflammatory agent 2B3-201 (liposomal methylprednisolone) has therapeutic potential, reducing brainstem pathology in the SOD1G93A mouse model of ALS. 2B3-201 reduced neuronal loss and vacuolation in brainstem nuclei, and reduced activation preferentially in astrocytes compared with microglia. These data also suggest that other previously ineffective therapies could be of therapeutic value if delivered specifically to the CNS.

Enhanced doxorubicin delivery to the brain administered through glutathione PEGylated liposomal doxorubicin (2B3-101) as compared with generic Caelyx,(®)/Doxil(®)--a cerebral open flow microperfusion pilot study.

The neuroprotective blood-brain barrier (BBB) keeps many drug candidates below therapeutic levels in the central nervous system. Glutathione PEGylated liposomal doxorubicin (2B3-101) has been developed to safely enhance the delivery of doxorubicin to brain tumors. However, doxorubicin concentration in extracellular brain fluid cannot yet be reliably measured using conventional techniques. Cerebral open flow microperfusion (cOFM), a recently developed sampling technique, allows monitoring of drug concentrations in the brain independent of molecular weight and lipophilicity. In combination with cOFM sampling, sodium fluorescein (NaF) is used as a marker for BBB integrity. Rats received one intravenous dose of 7 mg/kg of either 2B3-101 or PEGylated liposomal doxorubicin (generic Caelyx(®)). Blood and cOFM sampling was performed for 5 h after dose injection. NaF concentration in the brain was monitored and remained low indicating an intact BBB. The brain-to-blood ratio of doxorubicin was 4.8-fold higher after administration of 2B3-101 as compared with generic Caelyx(®) (p = 0.0016). In conclusion, by using cOFM it was possible to show that 2B3-101 leads to enhanced doxorubicin concentration in the brain without affecting the BBB integrity.

Systemic treatment with glutathione PEGylated liposomal methylprednisolone (2B3-201) improves therapeutic efficacy in a model of ocular inflammation.

PURPOSE: Ocular inflammation is associated with the loss of visual acuity and subsequent blindness. Since their development, glucocorticoids have been the mainstay of therapy for ocular inflammatory diseases. However, the clinical benefit is limited by side effects due to the chronic use and generally high dosage that is required for effective treatment. We have developed the G-Technology to provide a means for sustained drug delivery, increased drug half-life, and reduced bodily drug exposure. Glutathione PEGylated liposomal methylprednisolone (2B3-201) has been developed as treatment for neuroinflammatory conditions and was evaluated in ocular inflammation. METHODS: The efficacy of 2B3-201 was investigated in rats with experimental autoimmune uveitis (EAU). Rats received 10 mg/kg of 2B3-201 intravenously at disease onset and at peak of the disease. The same dose of free methylprednisolone served as control treatment. Clinical signs of ocular inflammation were assessed by slit-lamp and immunohistochemistry. RESULTS: Whereas free methylprednisolone was ineffective, two doses of 2B3-201 almost completely abolished clinical signs of EAU. This was corroborated further by immunohistochemical analyses of isolated eyes. Treatment with 2B3-201 significantly reduced the infiltration of inflammatory cells and subsequent destruction of the retina cell layers. CONCLUSIONS: In this study, we show that systemic treatment with 2B3-201, a glutathione PEGylated liposomal methylprednisolone formulation, resulted in a superior efficacy in rats with EAU. Altogether, our findings hold promise for the development of a safe and more convenient systemic treatment for uveitis.

Glutathione pegylated liposomal methylprednisolone administration after the early phase of status epilepticus did not modify epileptogenesis in the rat.

It has been reported that glucocorticoids (GCs) can effectively control seizures in pediatric epilepsy syndromes, possibly by inhibition of inflammation. Since inflammation is supposed to be involved in epileptogenesis, we hypothesized that treatment with GCs would reduce brain inflammation and thereby modify epileptogenesis in a rat model for temporal lobe epilepsy, in which epilepsy gradually develops after electrically induced status epilepticus (SE). To prevent the severe adverse effects that are inevitable with long-term GC treatment, we used liposome nanotechnology (G-Technology(®)) to enhance the sustained delivery to the brain. Starting 4h after onset of SE, rats were treated with glutathione pegylated liposomal methylprednisolone (GSH-PEG liposomal MP) according to a treatment protocol (1× per week; 10mg/kg) that is effective in other models of neuroinflammation. Continuous electro-encephalogram (EEG) recordings revealed that SE duration and onset of spontaneous seizures were not affected by GSH-PEG liposomal MP treatment. The number and duration of spontaneous seizures were also not different between vehicle and GSH-PEG liposomal MP-treated animals. Six weeks after SE, brain inflammation, as assessed by quantification of microglia activation, was not reduced by GSH-PEG liposomal MP-treatment. Also, neuronal cell loss and mossy fiber sprouting were not affected. Our study shows that the selected GSH-PEG liposomal MP treatment regimen that was administered beyond the acute SE phase does not reduce brain inflammation and development of temporal lobe epilepsy.

Glutathione PEGylated liposomes: pharmacokinetics and delivery of cargo across the blood-brain barrier in rats.

Partly due to poor blood-brain barrier drug penetration the treatment options for many brain diseases are limited. To safely enhance drug delivery to the brain, glutathione PEGylated liposomes (G-Technology®) were developed. In this study, in rats, we compared the pharmacokinetics and organ distribution of GSH-PEG liposomes using an autoquenched fluorescent tracer after intraperitoneal administration and intravenous administration. Although the appearance of liposomes in the circulation was much slower after intraperitoneal administration, comparable maximum levels of long circulating liposomes were found between 4 and 24 h after injection. Furthermore, 24 h after injection a similar tissue distribution was found. To investigate the effect of GSH coating on brain delivery in vitro uptake studies in rat brain endothelial cells (RBE4) and an in vivo brain microdialysis study in rats were used. Significantly more fluorescent tracer was found in RBE4 cell homogenates incubated with GSH-PEG liposomes compared to non-targeted PEG liposomes (1.8-fold, p < 0.001). In the microdialysis study 4-fold higher (p < 0.001) brain levels of fluorescent tracer were found after intravenous injection of GSH-PEG liposomes compared with PEG control liposomes. The results support further investigation into the versatility of GSH-PEG liposomes for enhanced drug delivery to the brain within a tolerable therapeutic window.