Neil Barua

Aβ-Degrading Enzymes: Potential for Treatment of Alzheimer Disease

There is increasing evidence that deficient clearance of &bgr;-amyloid (A&bgr;) contributes to its accumulation in late-onset Alzheimer disease (AD). Several A&bgr;-degrading enzymes, including neprilysin (NEP), insulin-degrading enzyme, and endothelin-converting enzyme reduce A&bgr; levels and protect against cognitive impairment in mouse models of AD. The activity of several A&bgr;-degrading enzymes rises with age and increases still further in AD, perhaps as a physiological response to minimize the buildup of A&bgr;. The age- and disease-related changes in expression of more recently recognized A&bgr;-degrading enzymes (e.g. NEP-2 and cathepsin B) remain to be investigated, and there is strong evidence that reduced NEP activity contributes to the development of cerebral amyloid angiopathy. Regardless of the role of A&bgr;-degrading enzymes in the development of AD, experimental data indicate that increasing the activity of these enzymes (NEP in particular) has therapeutic potential in AD, although targeting their delivery to the brain remains a major challenge. The most promising current approaches include the peripheral administration of agents that enhance the activity of A&bgr;-degrading enzymes and the direct intracerebral delivery of NEP by convection-enhanced delivery. In the longer term, genetic approaches to increasing the intracerebral expression of NEP or other A&bgr;-degrading enzymes may offer advantages.

Convection-Enhanced Drug Delivery to the Brain: Therapeutic Potential and Neuropathological Considerations

Convection‐enhanced delivery (CED) describes a direct method of drug delivery to the brain through intraparenchymal microcatheters. By establishing a pressure gradient at the tip of the infusion catheter in order to exploit bulk flow through the interstitial spaces of the brain, CED offers a number of advantages over conventional drug delivery methods—bypass of the blood–brain barrier, targeted distribution through large brain volumes and minimization of systemic side effects. Despite showing early promise, CED is yet to fulfill its potential as a mainstream strategy for the treatment of neurological disease. Substantial research effort has been dedicated to optimize the technology for CED and identify the parameters, which govern successful drug distribution. It seems likely that successful clinical translation of CED will depend on suitable catheter technology being used in combination with drugs with optimal physicochemical characteristics, and on neuropathological analysis in appropriate preclinical models. In this review, we consider the factors most likely to influence the success or failure of CED, and review its application to the treatment of high‐grade glioma, Parkinsons disease (PD) and Alzheimers disease (AD).

Convection-enhanced delivery of carboplatin PLGA nanoparticles for the treatment of glioblastoma

We currently use Convection-Enhanced Delivery (CED) of the platinum-based drug, carboplatin as a novel treatment strategy for high grade glioblastoma in adults and children. Although initial results show promise, carboplatin is not specifically toxic to tumour cells and has been associated with neurotoxicity at high infused concentrations in pre-clinical studies. Our treatment strategy requires intermittent infusions due to rapid clearance of carboplatin from the brain. In this study, carboplatin was encapsulated in lactic acid-glycolic acid copolymer (PLGA) to develop a novel drug delivery system. Neuronal and tumour cytotoxicity were assessed in primary neuronal and glioblastoma cell cultures. Distribution, tissue clearance and toxicity of carboplatin nanoparticles following CED was assessed in rat and porcine models. Carboplatin nanoparticles conferred greater tumour cytotoxicity, reduced neuronal toxicity and prolonged tissue half-life. In conclusion, this drug delivery system has the potential to improve the prognosis for patients with glioblastomas.

Convection-Enhanced Delivery of Neprilysin: A Novel Amyloid-β-Degrading Therapeutic Strategy

Enzymatic degradation contributes to the control of intracerebral amyloid-β (Aβ) peptide levels. Previous studies have demonstrated the therapeutic potential of viral vector-mediated neprilysin (NEP) gene therapy in mouse models of Alzheimers disease (AD). However, clinical translation of NEP gene therapy is limited by ethical and practical considerations. In this study we have assessed the potential of convection-enhanced delivery (CED) as a means of elevating intracerebral NEP level and activity and degrading endogenous Aβ. We analyzed the interstitial and perivascular distribution of NEP following CED into rat striatum. We measured NEP protein level, clearance, activity, and toxicity by ELISA for NEP and synaptophysin, NEP-specific activity assay, and immunohistochemistry for NEP, NeuN, glial fibrillary acidic protein and Iba1. We subsequently performed CED of NEP in normal aged rats and measured endogenous Aβ by ELISA. CED resulted in widespread distribution of NEP, and a 20-fold elevation of NEP protein level with preservation of enzyme activity and without evidence of toxicity. CED in normal, aged rats resulted in a significant reduction in endogenous Aβ(40) (p = 0.04), despite rapid NEP clearance from the brain (half-life ~3 h). CED of NEP has therapeutic potential as a dynamically controllable Aβ(40)-degrading therapeutic strategy for AD. Further studies are required to determine the longer term effects on Aβ (including Aβ(42)) and on cognitive function.

A novel implantable catheter system with transcutaneous port for intermittent convection-enhanced delivery of carboplatin for recurrent glioblastoma

Abstract Context: Inadequate penetration of the blood–brain barrier (BBB) by systemically administered chemotherapies including carboplatin is implicated in their failure to improve prognosis for patients with glioblastoma. Convection-enhanced delivery (CED) of carboplatin has the potential to improve outcomes by facilitating bypass of the BBB.Objective: We report the first use of an implantable CED system incorporating a novel transcutaneous bone-anchored port (TBAP) for intermittent CED of carboplatin in a patient with recurrent glioblastoma.Materials and methods: The CED catheter system was implanted using a robot-assisted surgical method. Catheter targeting accuracy was verified by performing intra-operative O-arm imaging. The TBAP was implanted using a skin-flap dermatome technique modeled on bone-anchored hearing aid surgery. Repeated infusions were performed by attaching a needle administration set to the TBAP. Drug distribution was monitored with serial real-time T2-weighted magnetic resonance imaging (MRI).Results: All catheters were implanted to within 1.5 mm of their planned target. Intermittent infusions of carboplatin were performed on three consecutive days and repeated after one month without the need for further surgical intervention. Infused volumes of 27.9 ml per day were well tolerated, with the exception of a single seizure episode. Follow-up MRI at eight weeks demonstrated a significant reduction in the volume of tumor enhancement from 42.6 ml to 24.6 ml, and was associated with stability of the patient’s clinical condition.Conclusion: Reduction in the volume of tumor enhancement indicates that intermittent CED of carboplatin has the potential to improve outcomes in glioblastoma. The novel technology described in this report make intermittent CED infusion regimes an achievable treatment strategy.

Chronic, intermittent convection-enhanced delivery devices

BACKGROUND Intraparenchymal convection-enhanced delivery (CED) of therapeutics directly into the brain has long been endorsed as a medium through which meaningful concentrations of drug can be administered to patients, bypassing the blood brain barrier. The translation of the technology to clinic has been hindered by poor distribution not previously observed in smaller pre-clinical models. In part this was due to the larger volumes of target structures found in humans but principally the poor outcome was linked to reflux (backflow) of infusate proximally along the catheter track. Over the past 10 years, improvements have been made to the technology in the field which has led to a small number of commercially available devices containing reflux inhibiting features. NEW METHOD While these devices are currently suitable for acute or short term use, several indications would benefit from longer term repeated, intermittent administration of therapeutics (Parkinsons, Alzheimers, Amyotrophic lateral sclerosis, Brain tumours such as Glioblastoma Multiforme (GBM) and Diffuse intrinsic Pontine Glioma (DIPG), etc.). RESULTS Despite the need for a chronically accessible platform for such indications, limited experience exists in this part of the field. COMPARISON WITH EXISTING METHOD(S) At the time of writing no commercially available clinical platform, indicated for chronic, intermittent or continuous delivery to the brain exists. CONCLUSIONS Here we review the improvements that have been made to CED devices over recent years and current state of the art for chronic infusion systems.

Clearance and Toxicity of Recombinant Methionyl Human Glial Cell Line-Derived Neurotrophic Factor (r-metHu GDNF) Following Acute Convection-Enhanced Delivery into the Striatum

Background Despite promising early results, clinical trials involving the continuous delivery of recombinant methionyl human glial cell line-derived neurotrophic factor (r-metHuGDNF) into the putamen for the treatment of Parkinsons disease have shown evidence of poor distribution and toxicity due to point-source accumulation. Convection-enhanced delivery (CED) has the potential to facilitate more widespread and clinically effective drug distribution. Aims We investigated acute CED of r-metHuGDNF into the striatum of normal rats in order to assess tissue clearance, toxicity (neuron loss, gliosis, microglial activation, and decreases in synaptophysin), synaptogenesis and neurite-outgrowth. We investigated a range of clinically relevant infused concentrations (0.1, 0.2, 0.6 and 1.0 µg/µL) and time points (2 and 4 weeks) in order to rationalise a dosing regimen suitable for clinical translation. Results Two weeks after single dose CED, r-metHuGDNF was below the limit of detection by ELISA but detectable by immunohistochemistry when infused at low concentrations (0.1 and 0.2 µg/µL). At these concentrations, there was no associated neuronal loss (neuronal nuclei, NeuN, immunohistochemistry) or synaptic toxicity (synaptophysin ELISA). CED at an infused concentration of 0.2 µg/µL was associated with a significant increase in synaptogenesis (p<0.01). In contrast, high concentrations of r-metHuGDNF (above 0.6 µg/µL) were associated with neuronal and synaptic toxicity (p<0.01). Markers for gliosis (glial fibrillary acidic protein, GFAP) and microglia (ionized calcium-binding adapter molecule 1, Iba1) were restricted to the needle track and the presence of microglia had diminished by 4 weeks post-infusion. No change in neurite outgrowth (Growth associated protein 43, GAP43, mRNA) compared to artificial cerebral spinal fluid (aCSF) control was observed with any infused concentration. Conclusion The results of this study suggest that acute CED of low concentrations of GDNF, with dosing intervals determined by tissue clearance, has most potential for effective clinical translation by optimising distribution and minimising the risk of toxic accumulation.

Intermittent convection-enhanced delivery to the brain through a novel transcutaneous bone-anchored port

Convection-enhanced delivery (CED) describes a novel method of drug delivery to the brain through intraparenchymal microcatheters. One of the barriers to effective translation of CED to clinical trials is the requirement for intermittent delivery over prolonged periods. This is particularly relevant for delivery of neurotrophins for the treatment of Parkinsons disease where chronic infusion of glial cell-line derived neurotrophic factor (GDNF) with subcutaneously implanted pumps has been associated with poor distribution and local toxicity due to point source accumulation. We have previously described the development of an implantable catheter for CED which facilitates repeated drug administrations at intervals of up to one month. The aim of this study was to determine the feasibility of implanting a transcutaneous bone-anchored port (TBAP) which facilitates chronic intermittent drug delivery to the brain. We describe the design and development of a titanium port which was implanted in Large White and NIH miniature pigs for periods of up to three months. By intermittently accessing the port with a needle administration set it was possible to repeatedly perform CED infusions at one month intervals. This study confirms the safety and feasibility of performing intermittent CED through a transcutaneous bone-anchored port. The use of a transcutaneous port has the potential to facilitate clinical translation of CED of therapeutics requiring intermittent delivery to achieve optimum efficacy whilst negating the need for subcutaneously implanted pumps.

Convection-enhanced delivery of AAV2 in white matter—A novel method for gene delivery to cerebral cortex

BACKGROUND Convection-enhanced delivery (CED) is currently under investigation for delivering therapeutic agents to subcortical targets in the brain. Direct delivery of therapies to the cerebral cortex, however, remains a significant challenge. NEW METHOD We describe a novel method of targeting adeno-associated viral vector (AAV) mediated gene therapies to specific cerebral cortical regions by performing high volume, high flow rate infusions into underlying white matter in a large animal (porcine) model. RESULTS Infusion volumes of up to 700 μl at flow rates as high as 10 μl/min were successfully performed in white matter without adverse neurological sequelae. Co-infusion of AAV2/5-GFP with 0.2% Gadolinium in artificial CSF confirmed transgene expression in the deep layers of cerebral cortex overlying the infused areas of white matter. COMPARISON WITH EXISTING METHODS AAV-mediated gene therapies have been previously targeted to the cerebral cortex by performing intrathalamic CED and exploiting axonal transport. The novel method described in this study facilitates delivery of gene therapies to specific regions of the cerebral cortex without targeting deep brain structures. CONCLUSIONS AAV-mediated gene therapies can be targeted to specific cortical regions by performing CED into underlying white matter. This technique could be applied to the treatment of neurological disorders characterised by cerebral cortical degeneration.

Convection enhanced delivery of panobinostat (LBH589)-loaded pluronic nano-micelles prolongs survival in the F98 rat glioma model

Background The pan-histone deacetylase inhibitor panobinostat is a potential therapy for malignant glioma, but it is water insoluble and does not cross the blood–brain barrier when administered systemically. In this article, we describe the in vitro and in vivo efficacy of a novel water-soluble nano-micellar formulation of panobinostat designed for administration by convection enhanced delivery (CED). Materials and methods The in vitro efficacy of panobinostat-loaded nano-micelles against rat F98, human U87-MG and M059K glioma cells and against patient-derived glioma stem cells was measured using a cell viability assay. Nano-micelle distribution in rat brain was analyzed following acute CED using rhodamine-labeled nano-micelles, and toxicity was assayed using immunofluorescent microscopy and synaptophysin enzyme-linked immunosorbent assay. We compared the survival of the bioluminescent syngenic F98/Fischer344 rat glioblastoma model treated by acute CED of panobinostat-loaded nano-micelles with that of untreated and vehicle-only-treated controls. Results Nano-micellar panobinostat is cytotoxic to rat and human glioma cells in vitro in a dose-dependent manner following short-time exposure to drug. Fluorescent rhodamine-labelled nano-micelles distribute with a volume of infusion/volume of distribution (Vi/Vd) ratio of four and five respectively after administration by CED. Administration was not associated with any toxicity when compared to controls. CED of panobinostat-loaded nano-micelles was associated with significantly improved survival when compared to controls (n=8 per group; log-rank test, P<0.001). One hundred percent of treated animals survived the 60-day experimental period and had tumour response on post-mortem histological examination. Conclusion CED of nano-micellar panobinostat represents a potential novel therapeutic option for malignant glioma and warrants translation into the clinic.