Marcella Wyatt

An evaluation of the relationships between catheter design and tissue mechanics in achieving high-flow convection-enhanced delivery

Convection-enhanced delivery (CED) is a rational technique for the direct intracranial administration of a range of therapeutic agents. CED critically depends on the use of a catheter with a narrow outer diameter and low infusion rate. Failure to adhere to these requirements can lead to reflux of infusate along the catheter-brain interface and damage at the catheter-tip. In this study we have tested the hypothesis that the relationship between infusion parameters and infusate distribution, including reflux, is critically dependent on the occurrence of tissue damage. The relationship between catheter outer diameter and the extent of blood-brain barrier disruption and subsequent tissue oedema was evaluated following catheter insertion into the striatum of rats. Three patterns of infusate distribution were observed: (1) Reflux restricted to the traumatised tissue around the catheter site. (2) Distribution in the white matter beyond the area of tissue trauma. (3) Widespread distribution in the striatum, which occurred only with catheters of an outer diameter of 0.35 mm or less. Extensive tissue damage occurred with a 0.2mm outer diameter catheter. This damage was completely prevented by rounding the catheter-tip. Infusions into pig brain demonstrated that high-flow CED could be performed in a large brain in both grey and white matter using a 0.2mm outer diameter catheter, with minimal reflux or MRI-evidence of tissue damage. This study demonstrates that by minimising tissue damage from catheter design and insertion, high flow-rate CED can be utilised to distribute therapeutic agents over large volumes of brain within clinically practical timescales.

PEGylation improves the receptor-mediated transfection efficiency of peptide-targeted, self-assembling, anionic nanocomplexes

Non-viral vector formulations comprise typically complexes of nucleic acids with cationic polymers or lipids. However, for in vivo applications cationic formulations suffer from problems of poor tissue penetration, non-specific binding to cells, interaction with serum proteins and cell adhesion molecules and can lead to inflammatory responses. Anionic formulations may provide a solution to these problems but they have not been developed to the same extent as cationic formulations due to difficulties of nucleic acid packaging and poor transfection efficiency. We have developed novel PEGylated, anionic nanocomplexes containing cationic targeting peptides that act as a bridge between PEGylated anionic liposomes and plasmid DNA. At optimized ratios, the components self-assemble into anionic nanocomplexes with a high packaging efficiency of plasmid DNA. Anionic PEGylated nanocomplexes were resistant to aggregation in serum and transfected cells with a far higher degree of receptor-targeted specificity than their homologous non-PEGylated anionic and cationic counterparts. Gadolinium-labeled, anionic nanoparticles, administered directly to the brain by convection-enhanced delivery displayed improved tissue penetration and dispersal as well as more widespread cellular transfection than cationic formulations. Anionic PEGylated nanocomplexes have widespread potential for in vivo gene therapy due to their targeted transfection efficiency and ability to penetrate tissues.

Intrastriatal convection-enhanced delivery results in widespread perivascular distribution in a pre-clinical model

BackgroundConvection-enhanced delivery (CED), a direct method for drug delivery to the brain through intraparenchymal microcatheters, is a promising strategy for intracerebral pharmacological therapy. By establishing a pressure gradient at the tip of the catheter, drugs can be delivered in uniform concentration throughout a large volume of interstitial fluid. However, the variables affecting perivascular distribution of drugs delivered by CED are not fully understood. The aim of this study was to determine whether the perivascular distribution of solutes delivered by CED into the striatum of rats is affected by the molecular weight of the infused agent, by co-infusion of vasodilator, alteration of infusion rates or use of a ramping regime. We also wanted to make a preliminary comparison of the distribution of solutes with that of nanoparticles.MethodsWe analysed the perivascular distribution of 4, 10, 20, 70, 150 kDa fluorescein-labelled dextran and fluorescent nanoparticles at 10 min and 3 h following CED into rat striatum. We investigated the effect of local vasodilatation, slow infusion rates and ramping on the perivascular distribution of solutes. Co-localisation with perivascular basement membranes and vascular endothelial cells was identified by immunohistochemistry. The uptake of infusates by perivascular macrophages was quantified using stereological methods.ResultsWidespread perivascular distribution and macrophage uptake of fluorescein-labelled dextran was visible 10 min after cessation of CED irrespective of molecular weight. However, a significantly higher proportion of perivascular macrophages had taken up 4, 10 and 20 kDa fluorescein-labelled dextran than 150 kDa dextran (p < 0.05, ANOVA). Co-infusion with vasodilator, slow infusion rates and use of a ramping regime did not alter the perivascular distribution. CED of fluorescent nanoparticles indicated that particles co-localise with perivascular basement membranes throughout the striatum but, unlike soluble dextrans, are not taken up by perivascular macrophages after 3 h.ConclusionsThis study suggests that widespread perivascular distribution and interaction with perivascular macrophages is likely to be an inevitable consequence of CED of solutes. The potential consequences of perivascular distribution of therapeutic agents, and in particular cytotoxic chemotherapies, delivered by CED must be carefully considered to ensure safe and effective translation to clinical trials.

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.

The development of an implantable catheter system for chronic or intermittent convection-enhanced delivery

Convection-enhanced delivery (CED) is a promising technique for the administration of therapeutic agents such as cytotoxics, neurotrophins and enzymes to the brain. In this study we describe the development of an implantable catheter system that is compatible with long-term intermittent CED. Catheters made from fused silica, PEEK or carbothane, and of various internal and external diameters were implanted in the striatum of rats and assessed for patency at 21 or 28 days. A high-rate of catheter blockage was observed with all fused silica and PEEK catheters. Carbothane catheters with an outer diameter of 0.6mm and an inner diameter of 0.35 mm had significantly lower rates of blockage (P≤0.01). Carbothane catheters were then implanted into 4 Large White/Landrace pigs and 4 NIH miniature pigs and infusions undertaken at monthly intervals to evaluate catheter patency and infusate distribution. Catheter patency was demonstrated for a maximum period of 163 days in one animal. Widespread and reproducible intraputamenal CED could be achieved with intermittent drug delivery at flow-rates as high as 5 μl/min. Problems were encountered using the pig model due to catheter distortion from rapid animal growth. In conclusion, it is possible to achieve intermittent high-flow CED with a chronic implanted carbothane catheter with a low rate of catheter blockage.

A robust MRI-compatible system to facilitate highly accurate stereotactic administration of therapeutic agents to targets within the brain of a large animal model

Research highlights ▶ Development of a highly accurate and robust method for MRI-guided, stereotactic delivery of catheters into the brain of pigs. ▶ Reliable head immobilisation, acquisition of high-resolution MR images, precise co-registration of MRI and stereotactic spaces to facilitate accurate burr hole-generation and catheter implantation. ▶ Implants were accurately placed into the putamen with a mean Euclidean distance of 0.623 mm (standard deviation of 0.33 mm).

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.

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.