Chronic Drug Delivery Research Articles

DDEL-06. CONVECTION-ENHANCED DELIVERY OF SEVEN DIFFERENT MOLECULES SHOW LARGE DIFFERENCES IN CONVECTIVE PROPERTIES BETWEEN MOLECULES. INFORMED DECISION MAKING FOR OPTIMIZED CATHETER PLACEMENT AND SUBSEQUENT INFUSION STRATEGIES

Abstract INTRODUCTION Glioblastoma (GBM) trials based on convection-enhanced drug delivery (CED) bypassing the blood-brain barrier have failed to prove efficient until now. Many factors influence CED. In this study we evaluated CED of seven different molecules using dynamic PET/MRI during infusion. This enabled in-depth evaluation of drug distribution and concentration gradients providing a more precise understanding of the Vd/Vi ratio and the extent of efficacy level across the Vd zone. Novel surgical catheter placement software algorithms, results in more informed-decision-making for catheter positioning and subsequent infusion planning strategies. METHODS Pigs were implanted with neuroinfuse™ drug delivery systems enabling intermittent drug infusions. Gadolinium, [124I]-UdR, [55Co]Co-DOTA-hEGF, [55Co]Co-DOTA-SP4, [18F]PSMA-1007 and three differently sized [64Cu]-labelled nanocarriers were evaluated in both pigs with and without a brain resection cavity. Gadolinium distribution was followed by MRI. PET imaging was used for the rest. To inform clinical trial design, strategic catheter placement and volumes to be infused, planning was investigated on several historical GBM cases. RESULTS Vd/Vi ratios ranged between 1.00 – 3.77. where large-sized liposomes performed best. Catheters stayed patent during weeks of repeated infusions. In the resected animals no leakage of drugs into the brain resection cavity was observed. Effective 3D modelling of novel catheter infusion planning aids provided visualized representations of tailor-made infusion plumes, capable of being suitably positioned to optimize surgical planning of catheters and transcutaneous reaccess port. CONCLUSION Large differences in convective properties between different molecules were observed. Large-sized liposomes as drug-carrier system showed superior performance to all other molecules. Vd/Vi ratios for promising drugs should be determined before initiating future clinical CED trials. Infusion concentration gradients to facilitate more precise Vd/Vi ratios provided important performance metrics for visualised infusion planning aids of a novel chronic drug delivery system, illustrating informed decision making for optimised catheter placement and subsequent infusion strategies is clinically translatable for GBM indications.

3D Printed Cell Culture Chamber for Testing the Effect of Pump-Based Chronic Drug Delivery on Inner Ear Tissue.

Cochlear hair cell damage and spiral ganglion neuron (SGN) degeneration are the main causes of sensory neural hearing loss. Cochlear implants (CIs) can replace the function of the hair cells and stimulate the SGNs electrically. The condition of the SGNs and their spatial distance to the CI are key factors for CI-functionality. For a better performance, a high number of neurons and a closer contact to the electrode are intended. Neurotrophic factors are able to enhance SGN survival and neurite outgrowth, and thereby might optimize the electrode-nerve interaction. This would require chronic factor treatment, which is not yet established for the inner ear. Investigations on chronic drug delivery to SGNs could benefit from an appropriate in vitro model. Thus, an inner ear inspired Neurite Outgrowth Chamber (NOC), which allows the incorporation of a mini-osmotic pump for long-term drug delivery, was designed and three-dimensionally printed. The NOC’s function was validated using spiral ganglion explants treated with ciliary neurotrophic factor, neurotrophin-3, or control fluid released via pumps over two weeks. The NOC proved to be suitable for explant cultivation and observation of pump-based drug delivery over the examined period, with neurotrophin-3 significantly increasing neurite outgrowth compared to the other groups.

Implantation of Osmotic Pumps and Induction of Stress to Establish a Symptomatic, Pharmacological Mouse Model for DYT/PARK-ATP1A3 Dystonia.

Genetically modified mouse models face limitations, especially when studying movement disorders, where most of the available transgenic rodent models do not present a motor phenotype resembling the clinical aspects of the human disease. Pharmacological mouse models allow for a more direct study of the pathomechanisms and their effect on the behavioral phenotype. Osmotic pumps connected to brain cannulas open up the possibility of creating pharmacological mouse models via local and chronic drug delivery. For the hereditary movement disorder of rapid-onset dystonia-parkinsonism, the loss-of-function mutation in the α3-subunit of the Na+/K+-ATPase can be simulated by a highly specific blockade via the glycoside ouabain. In order to locally block the α3-subunit in the basal ganglia and the cerebellum, which are the two brain structures believed to be heavily involved in the pathogenesis of rapid-onset dystonia-parkinsonism, a bilateral cannula is stereotaxically implanted into the striatum and an additional single cannula is introduced into the cerebellum. The cannulas are connected via vinyl tubing to two osmotic pumps, which are subcutaneously implanted on the back of the animals and allow for the chronic and precise delivery of ouabain. The pharmacological mouse model for rapid-onset dystonia-parkinsonism carries the additional advantage of recapitulating the clinical and pathological features of asymptomatic and symptomatic mutation carriers. Just like mutation carriers of rapid-onset dystonia parkinsonism, the ouabain-perfused mice develop dystonia-like movements only after additional exposure to stress. We demonstrate a mild stress paradigm and introduce two modified scoring systems for the assessment of a motor phenotype.

SCIDOT-36. PREDICTIVE CED INFUSION VOLUMES FOR SURGICAL PLANNING AND INFUSION REGIME STRATEGIES

Abstract Previous research and clinical trials have highlighted the utility of convection-enhanced delivery (CED) to directly administer therapeutics to the brain. This method bypasses the blood-brain barrier, which is a major obstacle in systemic drug delivery. The Renishaw Neuroinfuse™ recessed step catheter has been developed to utilise a mechanism we have termed “controlled reflux” to maximise distribution within brain targets, whereby the infusate tracks to a flow inhibiting feature. Once in contact with this feature, the flow pathway is initiated radially along the step region, facilitating a low-pressure infusion profile that minimises fast flow-rate tissue damage at the catheter tip whilst maximising coverage. This can be demonstrated through in vitro studies, in vivo preclinical work and humanitarian cases treating DIPG. The controlled reflux mechanism provides a level of infusion prediction, which can be used for catheter placement planning in order to optimize infusion distribution within a chosen target area. The Neuroinfuse™ catheter is delivered through an implantable guide tube whereby the guide tube and the catheter lengths are cut to provide bespoke features within the controlled reflux zone. By manipulating catheter step lengths this way, catheters can be designed to achieve target distribution volumes within an individual’s unique brain anatomy. Here we will present data demonstrating the utility of the acute catheter system, and its additional use as a modular component of the chronic drug delivery system. This modularisation strategy provides attributes for catheter placement and infusion distribution planning that spans across multiple indications for neuro-oncology and neurodegenerative diseases.

SCIDOT-35. A NOVEL MODEL FOR THE OPTIMIZATION OF DRUG-DEVICE COMBINATIONS FOR THE TREATMENT OF BRAIN TUMORS

Abstract BACKGROUND Failure of many brain tumor treatments has been attributed to the inability of a compound to cross the blood-brain barrier. Convection-enhanced delivery (CED) offers a method to administer drugs directly to the tumor site, thereby mitigating this limitation. CED has been used in several preclinical and clinical studies, though an approved treatment is yet to come to fruition. A medical device suitable for repeated intraparenchymal delivery is valuable for brain tumor treatment strategies, but a lack of appropriate preclinical models capable of infusing clinically relevant volumes has hindered progress in clinical translation. Currently utilized preclinical models include porcine, which have limited use due to their growth rates and canine and non-human primates, which are restricted by ethical considerations. This study investigates the functional characteristics and stability of the Renishaw clinical Neuroinfuse™ drug delivery system in an ovine model. METHODS A head fixation frame was refined for ovine stereotactic surgery. Eight Romney ewes were implanted with the drug delivery system, comprising of four catheters and a transcutaneous port allowing chronic re-access infusions without repeated surgery. A maximum of four infusions were performed per subject, at four to eight-week intervals. RESULTS The implantation of the Neuroinfuse™ drug delivery system was well-tolerated in all subjects, without serious device related adverse events. Artificial CSF/gadolinium infusions were performed on five subjects. Three subjects were maintained for a follow-up study. Putaminal and thalamic distribution volumes remained stable over the re-access period of up to six months post-implantation. CONCLUSION Romney ewes are suitable for the stereotactic implantation of the Neuroinfuse™ chronic drug delivery system. Transcutaneous ports remained integrated for the study duration, allowing repeated intraparenchymal delivery. This novel preclinical model provides a stable platform for infusion regime optimization of drug-device combinations for chronic CED, which will undoubtably de-risk clinical translation in the neuro-oncology CED field.

Producing new bacteriocins using recombinant microorganisms

There are multiple challenges for neuropharmacology in the future. Undoubtedly, one of the greatest challenges is the development of strategies for pharmacological targeting of specific brain regions for treatment of diseases. GABA is the main inhibitory neurotransmitter in the central nervous system, and dysfunction of GABAergic mechanisms is associated with different neurological conditions. Liposomes are lipid vesicles that are able to encapsulate chemical compounds and are used for chronic drug delivery. This short review reports our experience with the development of liposomes for encapsulation and chronic delivery of GABA to sites within the brain. Directions for future research regarding the efficacy and practical use of GABA-containing liposomes for extended periods of time as well as understanding and targeting neurological conditions are discussed.

Design of a neural probe using localised cooling and long term delivery of anti-inflammatory factors to reduce glial scar formation and improve the chronic efficacy of therapeutic probes

Event Abstract Back to Event Design of a neural probe using localised cooling and long term delivery of anti-inflammatory factors to reduce glial scar formation and improve the chronic efficacy of therapeutic probes Laura Frey1, 2, 3, 4, Su Ryon Shin2, 3, 4, Kevin O'Kelly1 and Ali Khademhosseini2, 3, 4 1 Trinity College Dublin, Trinity Centre for Bioengineering, TBSI, Ireland 2 Massachusetts Institute of Technology, Harvard-MIT Division of Health Sciences and Technology, United States 3 Brigham and Women's Hospital, Harvard Medical School, Biomaterials Innovation Research Center, Department of Medicine, United States 4 Harvard University, Wyss Institute for Biologically Inspired Engineering, United States Introduction: Considerable advancements have been made using neural electrodes to minimise the effects of debilitating neural conditions[1],[2]. However, the chronic implantation of these electrodes into the brain has proven to be problematic, with most failing after 5-6 months due to the formation of an inhibitory glial scar[2]-[4]. Researchers at Trinity College Dublin are developing an alternative strategy using highly localized cooling and are collaborating with Harvard-MIT to design a coating with a long term microfluidic drug delivery system. This presentation will discuss our preliminary results on integrating the two systems into a single design to reduce the formation of a glial scar and extend the efficacy of these probes. Experimental Methods: Required ceramic coating thickness for thermal insulation was modelled in silico and validated with an in vitro model. Microfluidic channels were fabricated in a photocrosslinkable methacryloyl gelatin (GelMA) and polyethylene glycol (PEG) hydrogel and covered with a PDMS membrane with micropores (100μm). The effects of the release of anti-inflammatory drugs or factors such as dexamethasone and cytokine IL4 were tested in vitro on monocytes and astrocytes encapsulated in a brain-like hydrogel model to determine cell behaviour over 4 weeks. Adhesion tests were carried out to ensure the stability of both coatings on a probe surface. Results and Discussion: An insulating ceramic coating was designed to allow cooling of brain tissue by 10°C at a depth of up to 10cm and provide easy probe insertion. For the drug delivery system, microfluidic channels of <100µm diameter were successfully created in GelMA/PEG. This hydrogel can be inserted in its thin dry state and allowed to reswell to reduce micromotion. The coupling of GelMA/PEG with a PDMS membrane allowed 4 days of slow steady diffusion of anti-inflammatory cytokines into the in vitro brain model from one infusion (Fig 1). Burst release of small drug like molecules was also minimal. These active particles significantly reduced the presence of inflammatory markers 27E10 in monocytes and GFAP in astrocytes and increased the presence of anti-inflammatory marker CD206 which implies that a larger proportion of monocytes have differentiated into prohealing M2 macrophages because of the anti-inflammatory particles delivered to them(Fig 2). This implies that, in an in vivo environment, chronic drug delivery could potentially reduce the body’s immune response against the implants and ensure they function better during long term implantation. Conclusion: An insulating ceramic coating was developed to allow cooling of brain tissue by 10°C. The addition of a microfluidic coating to this allowed repeated infusions of anti-inflammatory factors which were shown to reduce the inflammatory response of monocytes and astrocytes in vitro. The mechanical properties of the hydrogel reduced micromotion of the probe and the mechanical mismatch between probe and brain tissue. Further work to miniaturise the system is required before moving to in vivo trials. The combination of our therapeutic cooling with prolonged anti-inflammatory treatment could increase the chronic efficacy of these probes in patients. This work was funded by the Higher Education Authority (HEA) Ireland (PRTLI5 GREP) and supported by Fulbright Ireland

A method for reliable voluntary oral administration of a fixed dosage (mg/kg) of chronic daily medication to rats

Stress can influence a number of physiological processes including adult neurogenesis, metabolism, cardiovascular function, immune function, neurophysiological function, endocrine function and inflammatory processes following injury. In testing drugs which may be used to treat various diseases or injuries, reducing stress associated with chronic drug delivery to animal models should then be an imperative, which led us to design a reliable voluntary oral drug delivery method. Various drug combinations were tested versus vehicle controls in four different rat stocks or strains (Wistar, Fisher, Long Evans and Sprague Dawley) with our voluntary oral delivery system. Oral medications were placed into a store-bought sugar cookie dough ball (~4 g), thoroughly integrating the dry drugs with the dough. This method has worked consistently to deliver the medication (complete ingestion) in four different stocks or strains of rats, with reliabilities ranging from 98.6% to 100%. The percentage of rats in each stock or strain that have at any time during the study had incomplete ingestion of the drugs ranged from 1% in Sprague Dawley, approximately 4% in Wistar and Fisher, to approximately 16% in Long Evans. Both serum and brain samples were analysed for high-performance liquid chromatography (HPLC) detection of one of our administered drugs: 5 mg/kg fluoxetine. HPLC analysis shows that serum levels are detectable 2-4 h after ingestion, but not 24 h after ingestion. Brain samples however, showed detectable levels of both fluoxetine and norfluoxetine more than a week following ingestion of a single dose, with higher norfluoxetine levels seen following a month of daily administered drugs.

Local drug delivery with a self-contained, programmable, microfluidic system

The development and optimization of many new drug therapies requires long-term local delivery with controlled, but variable dosage. Current methods for chronic drug delivery have limited utility because they either cannot deliver drugs locally to a specific organ or tissue, do not permit changes in delivery rate in situ, or cannot be used in clinical trials in an untethered, wearable configuration. Here, we describe a small, self-contained system for liquid-phase drug delivery. This system enables studies lasting several months and infusion rates can be programmed and modified remotely. A commercial miniature pump is integrated with microfabricated components to generate ultralow flow rates and stroke volumes. Solutions are delivered in pulses as small as 370 nL, with pulses delivered at any interval of 1 min or longer. A unique feature of the system is the ability to infuse and immediately withdraw liquid, resulting in zero net volume transfer while compounds are exchanged by mixing and diffusion with endogenous fluid. We present in vitro results demonstrating repeatability of the delivered pulse volume for nearly 3 months. Furthermore, we present in vivo results in an otology application, infusing into the cochlea of a guinea pig a glutamate receptor antagonist, which causes localized and reversible changes in auditory sensitivity.

Overexpression of plasminogen activators in the nucleus accumbens enhances cocaine‐, amphetamine‐ and morphine‐induced reward and behavioral sensitization

Urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) are extracellular proteases that play a role in synaptic plasticity and remodeling. Psychostimulants induce both tPA and uPA in acute and chronic drug delivery, but cocaine induces preferentially uPA, whereas morphine and amphetamine induce preferentially tPA. Specific doxycline-regulatable lentiviruses expressing these extracellular proteases have been prepared and stereotaxically injected into the nucleus accumbens. We show that tPA-overexpressing animals show greater locomotor activity and behavioral sensitization upon morphine and amphetamine treatments. These effects could be fully suppressed by doxycycline or when tPA had been silenced using small interfering RNAs (siRNAs)-expressing lentiviruses. Furthermore, animals infected with lentiviruses expressing uPA show enhanced conditional place preference for cocaine compared with tPA-overexpressing animals. In contrast, tPA-overexpressing animals when administered amphetamine or morphine showed greater place preference compared with uPA-overexpressing animals. The effects are suppressed when tPA has been silenced using specific siRNAs-expressing vectors. Tissue-type plasminogen activator and uPA possibly induce distinct behaviors, which may be interpreted according to their differential pattern of activation and downstream targets. Taken together, these data add further evidence for a significant function of extracellular proteases tPA and uPA in addiction and suggest a differential role of plasminogen activators in this context.

Effects of continuous oral nicotine administration on brain nicotinic receptors and responsiveness to nicotine in C57Bl/6 mice.

The route of drug delivery is an important consideration in studies that evaluate the long-term bio-behavioral adaptations that occur in response to chronic drug administration. Continuous infusions (intravenous or subcutaneous) or intermittent intraperitoneal (or subcutaneous) injections are the most commonly utilized routes of chronic drug delivery in these studies. The purpose of the present study was to determine the effects of chronic oral nicotine exposure on sensitivity to nicotine and brain nicotinic cholinergic receptors in female C57Bl/6 mice. Mice were randomized to different treatment groups that received 2% saccharin, containing 0-200 microg/ml nicotine (free base). In preliminary experiments, radiotelemetry devices were implanted in the mice; consumption of the nicotine-containing drinking solution caused a significant increase in home-cage nocturnal (but not diurnal) activity and also altered circadian alterations in body temperature. Oral nicotine exposure resulted in dose-related elevations in plasma levels of cotinine, a primary nicotine metabolite. Continuous exposure (30 days) to oral nicotine (200 microg/ml) resulted in the expression of significant tolerance to the locomotor depressant and hypothermic actions of acute nicotine challenge. This tolerance was accompanied by a significant increase in brain nicotinic receptor number assessed by quantitative auto-radiography using [3H]-cytisine (alpha4 nAChr) and [125I]-alpha-bungarotoxin (alpha7 nAChr) as radioligands. These results suggest that chronic oral nicotine delivery to female C57Bl/6 mice results in behavioral and biochemical changes that resemble changes that occur following other routes of chronic nicotine delivery.

Strategies for drug delivery through the blood-brain barrier

Strategies for drug delivery through the blood-brain barrier include neurosurgical-based, pharmacologic-based, and physiologic-based approaches. Neurosurgical-based techniques involve the implantation of intraventricular catheters that allow for chronic drug delivery. However, this approach is limited by the much faster rates of bulk flow of CSF through the ventricular compartments as compared to the slow rates of drug diffusion down into brain parenchyma. Pharmacologic-based strategies, e.g., synthesis of lipid soluble pro-drugs, or physiologic-based strategies, e.g., the development of chimeric nutrients or chimeric peptides allow for drug delivery through the brain capillary wall, i.e., the blood-brain barrier, and allow for drug delivery directly into brain parenchyma.

An intravitreal cannula system: long-term follow-up study.

An intravitreal cannula for chronic drug delivery was implanted in the eyes of two rabbits and one monkey. The rabbits were followed up for three years after surgery and the monkey was followed up for two and one-half years. Clinical observations did not reveal any adverse effects from the cannula implantation. Patency of the cannula was demonstrated by using sodium fluorescein. Histopathological studies with light and electron microscopy revealed the scar tissue around the cannula to be minimal and localized to the wound site. The optic nerve and the retina and choroid at the posterior pole did not show any abnormalities. These results suggest that this system can be used for repeated or continuous drug delivery to the vitreous over a long period of time in experimental models.

Intraocular cannula for chronic drug delivery. Method and clinical observation.

An intraocular cannula system for chronic drug delivery was designed and tested in rabbits. The cannula was inserted through the pars plana and the tip positioned in the vitreous cavity (distal tip) in a site close to the retinal area of interest. The cannula was stabilized by a silicone plate that was sutured to the sclera. The proximal end of the cannula was attached to a larger diameter silicone tubing which served as a connector to the reservoir for chronic drug delivery. Rabbit eyes with implanted cannulas were followed clinically and electrophysiologically for up to one and a half years. They showed almost no adverse effects as a result of the implantation and cannula patency was demonstrated by the injection of sodium fluorescein through the cannula at various times following surgery. We believe that the implanted intraocular cannula, which allows chronic drug delivery, will be a valuable asset for research and possibly clinical studies.

Intraocular cannula for continuous, chronic drug delivery. Histopathologic observations and function.

An indwelling cannula for drug delivery was implanted in rabbit eyes. Rabbits were followed up for as long as 1 1/2 years after surgery. They showed almost no adverse effects as a result of the implantation, and cannula patency was demonstrated by the injection of fluorescein sodium through the cannula at various times following surgery. Histopathologic studies using light and electron microscopy were performed at various times to determine the effect of cannula implantation on the eye. Cellular proliferation along the cannula after 1 1/2 years was limited to the region immediately adjacent to the wound and rarely extended to the surrounding retina or ciliary body. The proliferative tissue at the wound site originated mainly from the episclera; the retina and the choroid at the posterior fundus remained intact. Photoreceptor cell metabolism was studied by light microscopic autoradiography following intraocular injection of tritiated leucine to assess photoreceptor outer-segment renewal. Autoradiography showed normal receptor uptake of leucine. A broad band of radioactive labeling of the outer segments resulted from continuous, chronic drug delivery, while a narrow band of labeling resulted from a single intravitreous injection. These data indicate that the cannula system continuously delivered tritiated leucine into the vitreous cavity. We believe that the implanted intraocular cannula, which allows continuous drug delivery on a relatively long-term basis, will be a valuable technique for research and possibly clinical studies.

An indwelling cannula system for the primate eye

An indwelling cannula system was designed as an instrument for chronic drug infusion into the vitreous cavity and tested in the cynomolgus monkey eye with repeated injections or continuous infusion using a pumping device. The cannula was passed through the pars plana and its tip situated in the vitreous cavity close to the macular area. Clinical observations up to 18 months did not reveal any adverse effects due to implantation. Histopathological observations from 1 week to 18 months after surgery revealed tissue proliferation around the cannula was minimal and localized only at the wound site, where proliferative tissue originated from the episclera and ciliary epithelium. Retina and choroid at the posterior pole showed normal morphology. Light microscopic autoradiograms demonstrated the function of this system. Injections of tritiated leucine through the cannula resulted in narrow bands of radioactive labelling of the photoreceptor outer segments corresponding to each injection. In contrast, chronic delivery using the pumping device resulted in a diffuse and wide band of labelling. These results strongly suggest that this system did not adversely affect the eye and that repeated intravitreal injections or chronic drug delivery into the vitreous are feasible using this system. Furthermore, autoradiographic results suggest that the drugs infused into the vitreous cavity spread readily into the retina.