Central nervous system delivery of large molecules: challenges and new frontiers for intrathecally administered therapeutics

MOF-Modified Microrollers for Bioimaging and Sustained Antibiotic Delivery

Central nervous system (CNS) infections caused by neurosurgery or intrathecal injection of contaminated cerebrospinal fluid are a common and difficult complication. Drug-delivery microrobots are among the latest solutions proposed for antibacterial applications. However, there is a lack of research into developing microrobots with the ability to sustain antibody delivery while can move efficiently in the CNS. Here, biocompatible antibacterial metal-organic framework (MOF)-modified microrollers (MMRs) to combat CNS infections are proposed. The MMRs are iron-based metal-organic framework (NH2-MIL-101(Fe)) modified for enhanced adsorption and Fe/Al coated for magnetic actuation and biocompatibility. The MMRs have demonstrated a faster and unhindered magnetically actuated motion on the uneven biological tissue surface in an organ-on-a-chip that mimicked the CNS compared to it on smooth surface. CFD results consistently align with the experimental findings. The MMRs can be loaded with rhodamine 6G for bioimaging, allowing them to be imaged through sections of the main human tissues by fluorescence microscopy, or tetracycline hydrochloride for antibiotic delivery, allowing them to inhibit the growth of Staphylococcus aureus biofilms by sustained release of antibiotics for 9 days. This study provides a strategy to integrate high-capacity adsorption material with magnetically actuated locomotion for long-term targeted antibacterial applications in biological environments.

Gene therapy for CNS disorders: modalities, delivery and translational challenges

Gene therapy is emerging as a powerful tool to modulate abnormal gene expression, a hallmark of most CNS disorders. The transformative potentials of recently approved gene therapies for the treatment of spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS) and active cerebral adrenoleukodystrophy are encouraging further development of this approach. However, most attempts to translate gene therapy to the clinic have failed to make it to market. There is an urgent need not only to tailor the genes that are targeted to the pathology of interest but to also address delivery challenges and thereby maximize the utility of genetic tools. In this Review, we provide an overview of gene therapy modalities for CNS diseases, emphasizing the interconnectedness of different delivery strategies and routes of administration. Important gaps in understanding that could accelerate the clinical translatability of CNS genetic interventions are addressed, and we present lessons learned from failed clinical trials that may guide the future development of gene therapies for the treatment and management of CNS disorders.

A systematic review of cell therapy modalities and outcomes in cerebral palsy

Cerebral palsy is widely recognized as a condition that results in significant physical and cognitive disabilities. Interventions aim to improve the quality of life and reduce disability. Despite numerous treatments and significant advancements, cerebral palsy remains incurable due to its diverse origins. This review evaluated clinical trials, studies, and case reports on various cell therapy approaches for cerebral palsy. It assessed the clinical outcomes of applying different cell types, including mesenchymal stem cells, olfactory ensheathing cells, neural stem/progenitor cells, macrophages, and mononuclear cells derived from peripheral blood, cord blood, and bone marrow. In 60 studies involving 1474 CP patients, six major adverse events (0.41%) and 485 mild adverse events (32.9%) were reported. Favorable therapeutic effects were observed in 54 out of 60 cell therapy trials, indicating a promising potential for cell treatments in cerebral palsy. Intrathecal MSC and BM-MNC applications revealed therapeutic benefits, with MSC studies being generally safer than other cell therapies. However, MSC and BM-MNC trials have shown inconsistent results, with some demonstrating superior efficacy for certain outcomes. Cell dosage, transplantation route, and frequency of administration can affect the efficacy of these therapies. Our findings highlight the promise of cell therapies for improving cerebral palsy treatment and stress the need for ongoing research to refine treatment protocols and enhance safety. To establish conclusive evidence on the comparative effectiveness of various cell types in treating cerebral palsy, randomized, double-blind clinical trials are essential.

Current status and advances to improving drug delivery in diffuse intrinsic pontine glioma

Diffuse midline glioma (DMG), including tumors diagnosed in the brainstem (diffuse intrinsic pontine glioma - DIPG), is the primary cause of brain tumor-related death in pediatric patients. DIPG is characterized by a median survival of <12 months from diagnosis, harboring the worst 5-year survival rate of any cancer. Corticosteroids and radiation are the mainstay of therapy; however, they only provide transient relief from the devastating neurological symptoms. Numerous therapies have been investigated for DIPG, but the majority have been unsuccessful in demonstrating a survival benefit beyond radiation alone. Although many barriers hinder brain drug delivery in DIPG, one of the most significant challenges is the blood-brain barrier (BBB). Therapeutic compounds must possess specific properties to enable efficient passage across the BBB. In brain cancer, the BBB is referred to as the blood-brain tumor barrier (BBTB), where tumors disrupt the structure and function of the BBB, which may provide opportunities for drug delivery. However, the biological characteristics of the brainstem's BBB/BBTB, both under normal physiological conditions and in response to DIPG, are poorly understood, which further complicates treatment. Better characterization of the changes that occur in the BBB/BBTB of DIPG patients is essential, as this informs future treatment strategies. Many novel drug delivery technologies have been investigated to bypass or disrupt the BBB/BBTB, including convection enhanced delivery, focused ultrasound, nanoparticle-mediated delivery, and intranasal delivery, all of which are yet to be clinically established for the treatment of DIPG. Herein, we review what is known about the BBB/BBTB and discuss the current status, limitations, and advances of conventional and novel treatments to improving brain drug delivery in DIPG.

Blood oxygen regulation via P2Y12R expressed in the carotid body

BACKGROUND

Peripheral blood oxygen monitoring via chemoreceptors in the carotid body (CB) is an integral function of the autonomic cardiorespiratory regulation. The presence of the purinergic P2Y12 receptor (P2Y12R) has been implicated in CB; however, the exact role of the receptor in O2 sensing and signal transduction is unknown.

METHODS

The presence of P2Y12R was established by immunoblotting, RT qPCR and immunohistochemistry. Primary glomus cells were used to assess P2Y12R function during hypoxia and hypercapnia, where monoamines were measured by HPLC; calcium signal was recorded utilizing OGB-1 and N-STORM Super-Resolution System. Ingravescent hypoxia model was tested in anaesthetized mice of mixed gender and cardiorespiratory parameters were recorded in control and receptor-deficient or drug-treated experimental animals.

RESULTS

Initially, the expression of P2Y12R in adult murine CB was confirmed. Hypoxia induced a P2Y12R-dependent release of monoamine transmitters from isolated CB cells. Receptor activation with the endogenous ligand ADP promoted release of neurotransmitters under normoxic conditions, while blockade disrupted the amplitude and duration of the intracellular calcium concentration. In anaesthetised mice, blockade of P2Y12R expressed in the CB abrogated the initiation of compensatory cardiorespiratory changes in hypoxic environment, while centrally inhibited receptors (i.e. microglial receptors) or receptor-deficiency induced by platelet depletion had limited influence on the physiological adjustment to hypoxia.

CONCLUSIONS

Peripheral P2Y12R inhibition interfere with the complex mechanisms of acute oxygen sensing by influencing the calcium signalling and the release of neurotransmitter molecules to evoke compensatory response to hypoxia. Prospectively, the irreversible blockade of glomic receptors by anti-platelet drugs targeting P2Y12Rs, propose a potential, formerly unrecognized side-effect to anti-platelet medications in patients with pulmonary morbidities.

Emerging therapeutics and evolving assessment criteria for intracranial metastases in patients with oncogene-driven non-small-cell lung cancer

The improved survival outcomes of patients with non-small-cell lung cancer (NSCLC), largely owing to the improved control of systemic disease provided by immune-checkpoint inhibitors and novel targeted therapies, have highlighted the challenges posed by central nervous system (CNS) metastases as a devastating yet common complication, with up to 50% of patients developing such lesions during the course of the disease. Early-generation tyrosine-kinase inhibitors (TKIs) often provide robust systemic disease control in patients with oncogene-driven NSCLCs, although these agents are usually unable to accumulate to therapeutically relevant concentrations in the CNS owing to an inability to cross the blood-brain barrier. However, the past few years have seen a paradigm shift with the emergence of several novel or later-generation TKIs with improved CNS penetrance. Such agents have promising levels of activity against brain metastases, as demonstrated by data from preclinical and clinical studies. In this Review, we describe current preclinical and clinical evidence of the intracranial activity of TKIs targeting various oncogenic drivers in patients with NSCLC, with a focus on newer agents with enhanced CNS penetration, leptomeningeal disease and the need for intrathecal treatment options. We also discuss evolving assessment criteria and regulatory considerations for future clinical investigations.

Intrahepatic Gallbladder Rupture and Biloma Mimicking Pulmonary Embolism Following Orthopedic Surgery

In this case report, a 75-year-old male with a history of coronary artery disease, type 2 diabetes, hypertension, and benign prostate hypertrophy developed postoperative fever and chest pain following left knee arthroplasty. Upon admission to the emergency department, pulmonary embolism was considered highly probable, and the patient was treated with anticoagulation and antibiotics due to diagnostic uncertainty. However, further investigations revealed a complex condition involving an intraparenchymal gallbladder rupture resulting in a biloma secondary to choledocholithiasis. The patient's history of receiving spinal anesthesia with intrathecal morphine was identified as a potential causative factor to the sphincter of Oddi constriction, leading to increased biliary pressure and gallbladder rupture. This case highlights the importance of having a broad differential diagnosis in postoperative patients, especially when the clinical presentation is atypical. With the diagnosis being confirmed, the patient underwent successful treatment, including biliary stenting, drainage of the biloma, and ultimately cholecystectomy. This case underlines the need for vigilance and a multidisciplinary approach in managing complex postoperative complications, emphasizing that clinical presentations may sometimes deviate significantly from the expected, requiring further investigation and individualized treatment.

Intrathecal delivery of Macromolecules: Clinical status and emerging technologies

The proximity and association of cerebrospinal fluid (CSF) and the intrathecal (IT) space with deep targets in the central nervous system (CNS) parenchyma makes IT injection an attractive route of administration for brain drug delivery. However, the extent to which intrathecally administered macromolecules are effective in treating neurological diseases is a question of both clinical debate and technological interest. We present the biological, chemical, and physical properties of the intrathecal space that are relevant to drug absorption, distribution, metabolism, and elimination from CSF. We then analyze the evolution of IT drug delivery in clinical trials over the last 20 years. Our analysis revealed that the percentage of clinical trials assessing IT delivery for the delivery of biologics (i.e., macromolecules, cells) for treatment of chronic conditions (e.g., neurodegeneration, cancer, and metabolic diseases) has steadily increased. Clinical trials exploring cell or macromolecular delivery within the IT space have not evaluated engineering technologies, such as depots, particles, or other delivery systems. Recent pre-clinical studies have evaluated IT macromolecule delivery in small animals, postulating that delivery efficacy can be assisted by external medical devices, micro- or nanoparticles, bulk biomaterials, and viral vectors. Further studies are necessary to evaluate the extent to which engineering technologies and IT administration improve CNS targeting and therapeutic outcome.

Nucleic acid therapies for CNS diseases: Pathophysiology, targets, barriers, and delivery strategies

Nucleic acid therapeutics have emerged as one of the very advanced and efficacious treatment approaches for debilitating health conditions, including those diseases affecting the central nervous system (CNS). Precise targeting with an optimal control over gene regulation confers long-lasting benefits through the administration of nucleic acid payloads via viral, non-viral, and engineered vectors. The current review majorly focuses on the development and clinical translational potential of non-viral vectors for treating CNS diseases with a focus on their specific design and targeting approaches. These carriers must be able to surmount the various intracellular and extracellular barriers, to ensure successful neuronal transfection and ultimately attain higher therapeutic efficacies. Additionally, the specific challenges associated with CNS administration also include the presence of blood-brain barrier (BBB), the complex pathophysiological and biochemical changes associated with different disease conditions and the existence of non-dividing cells. The advantages offered by lipid-based or polymeric systems, engineered proteins, particle-based systems coupled with various approaches of neuronal targeting have been discussed in the context of a variety of CNS diseases. The possibilities of rapid yet highly efficient gene modifications rendered by the breakthrough methodologies for gene editing and gene manipulation have also opened vast avenues of research in neuroscience and CNS disease therapy. The current review also underscores the extensive scientific efforts to optimize specialized, efficacious yet non-invasive and safer administration approaches to overcome the therapeutic delivery challenges specifically posed by the CNS transport barriers and the overall obstacles to clinical translation.

The glymphatic system: implications for drugs for central nervous system diseases

In the past decade, evidence for a fluid clearance pathway in the central nervous system known as the glymphatic system has grown. According to the glymphatic system concept, cerebrospinal fluid flows directionally through the brain and non-selectively clears the interstitium of metabolic waste. Importantly, the glymphatic system may be modulated by particular drugs such as anaesthetics, as well as by non-pharmacological factors such as sleep, and its dysfunction has been implicated in central nervous system disorders such as Alzheimer disease. Although the glymphatic system is best described in rodents, reports using multiple neuroimaging modalities indicate that a similar transport system exists in the human brain. Here, we overview the evidence for the glymphatic system and its role in disease and discuss opportunities to harness the glymphatic system therapeutically; for example, by improving the effectiveness of intrathecally delivered drugs.

Investigation of Human Intrathecal Solute Transport Dynamics Using a Novel in vitro Cerebrospinal Fluid System Analog

BACKGROUND

Understanding the relationship between cerebrospinal fluid (CSF) dynamics and intrathecal drug delivery (ITDD) injection parameters is essential to improve treatment of central nervous system (CNS) disorders.

METHODS

An anatomically detailed in vitro model of the complete CSF system was constructed. Patient-specific cardiac- and respiratory-induced CSF oscillations were input to the model in the subarachnoid space and within the ventricles. CSF production was input at the lateral ventricles and CSF absorption at the superior sagittal sinus. A model small molecule simulated drug product containing fluorescein was imaged within the system over a period of 3-h post-lumbar ITDD injections and used to quantify the impact of (a) bolus injection volume and rate, (b) post-injection flush volume, rate, and timing, (c) injection location, and (d) type of injection device. For each experiment, neuraxial distribution of fluorescein in terms of spatial temporal concentration, area-under-the-curve (AUC), and percent of injected dose (%ID) to the brain was quantified at a time point 3-h post-injection.

RESULTS

For all experiments conducted with ITDD administration in the lumbar spine, %ID to the brain did not exceed 11.6% at a time point 3-h post-injection. Addition of a 12 mL flush slightly increased solute transport to the brain up to +3.9%ID compared to without a flush (p < 0.01). Implantation of a lumbar catheter with the tip at an equivalent location to the lumbar placed needle, but with rostral tip orientation, resulted in a small improvement of 1.5%ID to the brain (p < 0.05). An increase of bolus volume from 5 to 20 mL improved solute transport to the brain from 5.0 to 6.3%ID, but this improvement was not statistically significant. Increasing bolus injection rate from 5 to 13.3 mL/min lacked improvement of solute transport to the brain, with a value of 6.3 compared to 5.7%ID.

CONCLUSION

The in vitro modeling approach allowed precisely controlled and repeatable parametric investigation of ITDD injection protocols and devices. In combination, the results predict that parametric changes in lumbar spine ITDD-injection related parameters and devices can alter %ID to the brain and be tuned to optimize therapeutic benefit to CNS targets.

Human in silico trials for parametric computational fluid dynamics investigation of cerebrospinal fluid drug delivery: impact of injection location, injection protocol, and physiology

Background

Intrathecal drug delivery has a significant role in pain management and central nervous system (CNS) disease therapeutics. A fluid-physics based tool to assist clinicians in choosing specific drug doses to the spine or brain may help improve treatment schedules.

Methods

This study applied computational fluid dynamics (CFD) and in vitro model verification to assess intrathecal drug delivery in an anatomically idealized model of the human CSF system with key anatomic features of the CNS. Key parameters analyzed included the role of (a) injection location including lumbar puncture (LP), cisterna magna (CM) and intracerebroventricular (ICV), (b) LP injection rate, injection volume, and flush volume, (c) physiologic factors including cardiac-induced and deep respiration-induced CSF stroke volume increase. Simulations were conducted for 3-h post-injection and used to quantify spatial–temporal tracer concentration, regional area under the curve (AUC), time to maximum concentration (T_max), and maximum concentration (C_max), for each case.

Results

CM and ICV increased AUC to brain regions by ~ 2 logs compared to all other simulations. A 3X increase in bolus volume and addition of a 5 mL flush both increased intracranial AUC to the brain up to 2X compared to a baseline 5 mL LP injection. In contrast, a 5X increase in bolus rate (25 mL/min) did not improve tracer exposure to the brain. An increase in cardiac and respiratory CSF movement improved tracer spread to the brain, basal cistern, and cerebellum up to ~ 2 logs compared to the baseline LP injection.

Conclusion

The computational modeling approach provides ability to conduct in silico trials representative of CSF injection protocols. Taken together, the findings indicate a strong potential for delivery protocols to be optimized to reach a target region(s) of the spine and/or brain with a needed therapeutic dose. Parametric modification of bolus rate/volume and flush volume was found to have impact on tracer distribution; albeit to a smaller degree than injection location, with CM and ICV injections resulting in greater therapeutic dose to brain regions compared to LP. CSF stroke volume and frequency both played an important role and may potentially have a greater impact than the modest changes in LP injection protocols analyzed such as bolus rate, volume, and flush.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00304-4.

A Robust Intrinsically Green Fluorescent Poly(Amidoamine) Dendrimer for Imaging and Traceable Central Nervous System Delivery in Zebrafish

Intrinsically fluorescent poly(amidoamine) dendrimers (IF-PAMAM) are an emerging class of versatile nanoplatforms for in vitro tracking and bio-imaging. However, limited tissue penetration of their fluorescence and interference due to auto-fluorescence arising from biological tissues limit its application in vivo. Herein, a green IF-PAMAM (FGP) dendrimer is reported and its biocompatibility, circulation, biodistribution and potential role for traceable central nervous system (CNS)-targeted delivery in zebrafish is evaluated, exploring various routes of administration. Key features of FGP include visible light excitation (488 nm), high fluorescence signal intensity, superior photostability and low interference from tissue auto-fluorescence. After intravenous injection, FGP shows excellent imaging and tracking performance in zebrafish. Further conjugating FGP with transferrin (FGP-Tf) significantly increases its penetration through the blood-brain barrier (BBB) and prolongs its circulation in the blood stream. When administering through local intratissue microinjection, including intracranial and intrathecal injection in zebrafish, both FGP and FGP-Tf exhibit excellent tissue diffusion and effective cellular uptake in the brain and spinal cord, respectively. This makes FGP/FGP-Tf attractive for in vivo tracing when transporting to the CNS is desired. The work addresses some of the major shortcomings in IF-PAMAM and provides a promising application of these probes in the development of drug delivery in the CNS.

Nanoparticle formulations that allow for sustained delivery and brain targeting of the neuropeptide oxytocin

Oxytocin is a promising candidate for the treatment of social-deficit disorders such as Autism Spectrum Disorder, but oxytocin cannot readily pass the blood-brain barrier. Moreover, oxytocin requires frequent dosing as it is rapidly metabolized in blood. We fabricated four polymeric nanoparticle formulations using poly(lactic-co-glycolic acid) (PLGA) or bovine serum albumin (BSA) as the base material. In order to target them to the brain, we then conjugated the materials to either transferrin or rabies virus glycoprotein (RVG) as targeting ligands. The formulations were characterized in vitro for size, zeta potential, encapsulation efficiency, and release profiles. All formulations showed slightly negative charges and sizes ranging from 100 to 278 nm in diameter, with RVG-conjugated BSA nanoparticles exhibiting the smallest sizes. No formulation was found to be immunogenic or cytotoxic. The encapsulation efficiency was ≥75% for all nanoparticle formulations. Release studies demonstrated that BSA nanoparticle formulation exhibited a faster initial burst of release compared to PLGA particles, in addition to later sustained release. This initial burst release would be favorable for clinical dosing as therapeutic effects could be quickly established, especially in combination with additional sustained release to maintain the therapeutic effects. Our size and release profile data indicate that RVG-conjugated BSA nanoparticles are the most favorable formulation for brain delivery of oxytocin.

A numerical investigation of intrathecal isobaric drug dispersion within the cervical subarachnoid space

Intrathecal drug and gene vector delivery is a procedure to release a solute within the cerebrospinal fluid. This procedure is currently used in clinical practice and shows promise for treatment of several central nervous system pathologies. However, intrathecal delivery protocols and systems are not yet optimized. The aim of this study was to investigate the effects of injection parameters on solute distribution within the cervical subarachnoid space using a numerical platform. We developed a numerical model based on a patient-specific three dimensional geometry of the cervical subarachnoid space with idealized dorsal and ventral nerve roots and denticulate ligament anatomy. We considered the drug as massless particles within the flow field and with similar properties as the CSF, and we analyzed the effects of anatomy, catheter position, angle and injection flow rate on solute distribution within the cerebrospinal fluid by performing a series of numerical simulations. Results were compared quantitatively in terms of drug peak concentration, spread, accumulation rate and appearance instant over 15 seconds following the injection. Results indicated that solute distribution within the cervical spine was altered by all parameters investigated within the time range analyzed following the injection. The presence of spinal cord nerve roots and denticulate ligaments increased drug spread by 60% compared to simulations without these anatomical features. Catheter position and angle were both found to alter spread rate up to 86%, and catheter flow rate altered drug peak concentration up to 78%. The presented numerical platform fills a first gap towards the realization of a tool to parametrically assess and optimize intrathecal drug and gene vector delivery protocols and systems. Further investigation is needed to analyze drug spread over a longer clinically relevant time frame.

Systems-level thinking for nanoparticle-mediated therapeutic delivery to neurological diseases

Neurological diseases account for 13% of the global burden of disease. As a result, treating these diseases costs $750 billion a year. Nanotechnology, which consists of small (~1-100 nm) but highly tailorable platforms, can provide significant opportunities for improving therapeutic delivery to the brain. Nanoparticles can increase drug solubility, overcome the blood-brain and brain penetration barriers, and provide timed release of a drug at a site of interest. Many researchers have successfully used nanotechnology to overcome individual barriers to therapeutic delivery to the brain, yet no platform has translated into a standard of care for any neurological disease. The challenge in translating nanotechnology platforms into clinical use for patients with neurological disease necessitates a new approach to: (1) collect information from the fields associated with understanding and treating brain diseases and (2) apply that information using scalable technologies in a clinically-relevant way. This approach requires systems-level thinking to integrate an understanding of biological barriers to therapeutic intervention in the brain with the engineering of nanoparticle material properties to overcome those barriers. To demonstrate how a systems perspective can tackle the challenge of treating neurological diseases using nanotechnology, this review will first present physiological barriers to drug delivery in the brain and common neurological disease hallmarks that influence these barriers. We will then analyze the design of nanotechnology platforms in preclinical in vivo efficacy studies for treatment of neurological disease, and map concepts for the interaction of nanoparticle physicochemical properties and pathophysiological hallmarks in the brain. WIREs Nanomed Nanobiotechnol 2017, 9:e1422. doi: 10.1002/wnan.1422 For further resources related to this article, please visit the WIREs website.

An analytical model for nanoparticles concentration resulting from infusion into poroelastic brain tissue

We consider the infusion of a diluted suspension of nanoparticles (NPs) into poroelastic brain tissue, in view of relevant biomedical applications such as intratumoral thermotherapy. Indeed, the high impact of the related pathologies motivates the development of advanced therapeutic approaches, whose design also benefits from theoretical models. This study provides an analytical expression for the time-dependent NPs concentration during the infusion into poroelastic brain tissue, which also accounts for particle binding onto cells (by recalling relevant results from the colloid filtration theory). Our model is computationally inexpensive and, compared to fully numerical approaches, permits to explicitly elucidate the role of the involved physical aspects (tissue poroelasticity, infusion parameters, NPs physico-chemical properties, NP-tissue interactions underlying binding). We also present illustrative results based on parameters taken from the literature, by considering clinically relevant ranges for the infusion parameters. Moreover, we thoroughly assess the model working assumptions besides discussing its limitations. While not laying any claims of generality, our model can be used to support the development of more ambitious numerical approaches, towards the preliminary design of novel therapies based on NPs infusion into brain tissue.

Neuronopathic lysosomal storage disorders: Approaches to treat the central nervous system

Pharmacological research has always focused on developing new therapeutic strategies capable of modifying a disease's natural history and improving patients' quality of life. Despite recent advances within the fields of medicine and biology, some diseases still represent a major challenge for successful therapy. Neuronopathic lysosomal storage disorders, in particular, have high rates of morbidity and mortality and a devastating socio-economic effect. Many of the available therapies, such as enzyme replacement therapy, can reverse the natural history of the disease in peripheral organs but, unfortunately, are still unable to reach the central nervous system effectively because they cannot cross the blood-brain barrier that surrounds and protects the brain. Moreover, many lysosomal storage disorders are characterized by a number of blood-brain barrier dysfunctions, which may further contribute to disease neuropathology and accelerate neuronal cell death. These issues, and their context in the development of new therapeutic strategies, will be discussed in detail in this chapter.

Pharmacokinetics, biocompatibility and bioavailability of a controlled release monoclonal antibody formulation

The sustained and localized delivery of monoclonal antibodies has become highly relevant, because of the increasing number of investigated local delivery applications in recent years. As the local delivery of antibodies is associated with high technological hurdles, very few successful approaches have been reported in the literature so far. Alginate-based delivery systems were previously described as promising sustained release formulations for monoclonal antibodies (mAbs). In order to further investigate their applicability, a single-dose animal study was conducted to compare the biocompatibility, the pharmacokinetics and the bioavailability of a human monoclonal antibody liquid formulation with two alginate-based sustained delivery systems after subcutaneous administration in rats. 28 days after injection, the depot systems were still found in the subcutis of the animals. A calcium cross-linked alginate formulation, which was injected as a hydrogel, was present as multiple compartments separated by subcutaneous tissue. An in situ forming alginate formulation was recovered as a single compact and cohesive structure. It can be assumed that the multiple compartments of the hydrogel formulation led to almost identical pharmacokinetic profiles for all tested animals, whereas the compact nature of the in situ forming system resulted in large interindividual variations in pharmacokinetics. As compared to the liquid formulation the hydrogel formulations led to lower mAb serum levels, and the in situ forming system to a shift in the time to reach the maximum mAb serum concentration (Tmax) from 2 to 4 days. Importantly, it was shown that after 28 days only marginal amounts of residual mAb were present in the alginate matrix and in the tissue at the injection site indicating nearly complete release. In line with this finding, systemic drug bioavailability was not affected by using the controlled release systems. This study successfully demonstrates the suitability and underlines the potential of polyanionic systems for local and controlled mAb delivery.

Non-viral nanosystems for gene and small interfering RNA delivery to the central nervous system: formulating the solution

The application of gene and RNAi-based therapies to the central nervous system (CNS), for neurological and neurodegenerative disease, offers immense potential. The issue of delivery to the target site remains the single greatest barrier to achieving this. There are challenges to gene and siRNA (small interfering RNA) delivery which are specific to the CNS, including the post-mitotic nature of neurons, their resistance to transfection and the blood-brain barrier. Viral vectors are highly efficient and have been used extensively in pre-clinical studies for CNS diseases. However, non-viral delivery offers an exciting alternative. In this review, we will discuss the extracellular and intracellular barriers to gene and siRNA delivery in the CNS. Our focus will be directed towards various non-viral strategies used to overcome these barriers. In this regard, we describe selected non-viral vectors and categorise them according to the barriers that they overcome by their formulation and targeting strategies. Some of the difficulties associated with non-viral vectors such as toxicity, large-scale manufacture and route of administration are discussed. We provide examples of optimised formulation approaches and discuss regulatory hurdles to clinical validation. Finally, we outline the components of an "ideal" formulation, based on a critical analysis of the approaches highlighted throughout the review.

Physiology of the intrathecal bolus: the leptomeningeal route for macromolecule and particle delivery to CNS

Presently, there are no effective treatments for several diseases involving the CNS, which is protected by the blood-brain, blood-CSF, and blood-arachnoid barriers. Traversing any of these barriers is difficult, especially for macromolecular drugs and particulates. However, there is significant experimental evidence that large molecules can be delivered to the CNS through the cerebrospinal fluid (CSF). The flux of the interstitial fluid in the CNS parenchyma, as well as the macro flux of CSF in the leptomeningeal space, are believed to be generally opposite to the desirable direction of CNS-targeted drug delivery. On the other hand, the available data suggest that the layer of pia mater lining the CNS surface is not continuous, and the continuity of the leptomeningeal space (LMS) with the perivascular spaces penetrating into the parenchyma provides an unexplored avenue for drug transport deep into the brain via CSF. The published data generally do not support the view that macromolecule transport from the LMS to CNS is hindered by the interstitial and CSF fluxes. The data strongly suggest that leptomeningeal transport depends on the location and volume of the administered bolus and consists of four processes: (i) pulsation-assisted convectional transport of the solutes with CSF, (ii) active "pumping" of CSF into the periarterial spaces, (iii) solute transport from the latter to and within the parenchyma, and (iv) neuronal uptake and axonal transport. The final outcome will depend on the drug molecule behavior in each of these processes, which have not been studied systematically. The data available to date suggest that many macromolecules and nanoparticles can be delivered to CNS in biologically significant amounts (>1% of the administered dose); mechanistic investigation of macromolecule and particle behavior in CSF may result in a significantly more efficient leptomeningeal drug delivery than previously thought.

Protein-polyanion interactions for the controlled release of monoclonal antibodies

The objective of the present study was to investigate ionic interactions between alginate and a monoclonal antibody (mAb1) and to utilize those interactions for the sustained release of mAb1. The existence of ionic interactions between alginate and mAb1 was strongly reflected by their rheological behavior. A 3-4 times increase in storage modulus (G') was observed by addition of 30 mg/mL mAb1 to a 20 mg/mL alginate solution. This increase was strongly dependent on pH and ionic strength. In vitro release studies revealed a marked pH-dependence of release rates and the reversibility of alginate-mAb1 complexation under physiological conditions. Two alginate-mAb1 sustained release formulations were developed by an internal gelation technique using CaCO(3) and CaHPO(4) as calcium sources for physical cross-linking. The CaCO(3) formulation provided a stable pH-environment, optimally suited for pH-sensitive proteins. CaHPO(4) led to a lower pH and stronger alginate-mAb1 interactions. The CaHPO(4) cross-linked alginate released mAb1 over a period of 10-15 days. The long release period and changes in viscoelastic properties of alginate, when being mixed with mAb1, indicate the incorporation of mAb1 molecules into a mixed network with alginate. The results of this study demonstrate that ionic interactions between polyanions and mAb1 are present and that they can be exploited for sustained release delivery of mAb1.

CNS penetration of intrathecal-lumbar idursulfase in the monkey, dog and mouse: implications for neurological outcomes of lysosomal storage disorder

A major challenge for the treatment of many central nervous system (CNS) disorders is the lack of convenient and effective methods for delivering biological agents to the brain. Mucopolysaccharidosis II (Hunter syndrome) is a rare inherited lysosomal storage disorder resulting from a deficiency of iduronate-2-sulfatase (I2S). I2S is a large, highly glycosylated enzyme. Intravenous administration is not likely to be an effective therapy for disease-related neurological outcomes that require enzyme access to the brain cells, in particular neurons and oligodendrocytes. We demonstrate that intracerebroventricular and lumbar intrathecal administration of recombinant I2S in dogs and nonhuman primates resulted in widespread enzyme distribution in the brain parenchyma, including remarkable deposition in the lysosomes of both neurons and oligodendrocytes. Lumbar intrathecal administration also resulted in enzyme delivery to the spinal cord, whereas little enzyme was detected there after intraventricular administration. Mucopolysaccharidosis II model is available in mice. Lumbar administration of recombinant I2S to enzyme deficient animals reduced the storage of glycosaminoglycans in both superficial and deep brain tissues, with concurrent morphological improvements. The observed patterns of enzyme transport from cerebrospinal fluid to the CNS tissues and the resultant biological activity (a) warrant further investigation of intrathecal delivery of I2S via lumbar catheter as an experimental treatment for the neurological symptoms of Hunter syndrome and (b) may have broader implications for CNS treatment with biopharmaceuticals.

Epidermal growth factor targeting of bacteriophage to the choroid plexus for gene delivery to the central nervous system via cerebrospinal fluid

Because the choroid plexus normally controls the production and composition of cerebrospinal fluid and, as such, its many functions of the central nervous system, we investigated whether ligand-mediated targeting could deliver genes to its secretory epithelium. We show here that when bacteriophages are targeted with epidermal growth factor, they acquire the ability to enter choroid epithelial cells grown in vitro as cell cultures, ex vivo as tissue explants or in vivo by intracerebroventricular injection. The binding and internalization of these particles activate EGF receptors on targeted cells, and the dose- and time-dependent internalization of particles is inhibited by the presence of excess ligand. When the phage genome is further reengineered to contain like green fluorescent protein or firefly luciferase under control of the cytomegalovirus promoter, gene expression is detectable in the choroid plexus and ependymal epithelium by immunohistochemistry or by noninvasive imaging, respectively. Taken together, these data support the hypothesis that reengineered ligand-mediated gene delivery should be considered a viable strategy to increase the specificity of gene delivery to the central nervous system and bypass the blood-brain barrier so as to exploit the biological effectiveness of the choroid plexus as a portal of entry into the brain.