Prolonged intracerebral convection-enhanced delivery of topotecan with a subcutaneously implantable infusion pump

Dual drug-loaded PLGA fibrous scaffolds for effective treatment of breast cancer in situ

Advanced metastatic breast cancer remains nearly an incurable disease. In situ therapy may help patients with worse prognoses have better clinical outcomes by significantly reducing systematic toxicity. Dural-drug fibrous scaffold was created and assessed using an in-situ therapeutic strategy, simulating the preferred regimens advised by the National Comprehensive Cancer Network. DOX, a once-used chemotherapy drug is embedded into scaffolds and produces a fast release for two cycles to kill tumor cells. PTX, a hydrophobic drug is continuously injected and produces a gradual release for up to two cycles to treat long cycles. Chosen drug loading system and the designated fabrication parameter controlled the releasing profile. Drug carrier system complied with the clinical regimen. It demonstrated both in vitro and in vivo anti-proliferative effects on the breast cancer model. The dosage of an intratumoral injection to drug capsules, the local tissue toxicity could be significantly reduced. To optimized intravenous injection with dual drugs, fewer side effects and a higher survival rate were seen even in the large tumor model (450-550 mm³). Drug delivery system makes the precise accumulation of the topical drug concentration possible, simulating clinically successful therapy and possibly offering better clinical treatment options for solid tumors.

Childhood Brain Tumors: A Review of Strategies to Translate CNS Drug Delivery to Clinical Trials

Brain and spinal tumors affect 1 in 1000 people by 25 years of age, and have diverse histological, biological, anatomical and dissemination characteristics. A mortality of 30-40% means the majority are cured, although two-thirds have life-long disability, linked to accumulated brain injury that is acquired prior to diagnosis, and after surgery or chemo-radiotherapy. Only four drugs have been licensed globally for brain tumors in 40 years and only one for children. Most new cancer drugs in clinical trials do not cross the blood-brain barrier (BBB). Techniques to enhance brain tumor drug delivery are explored in this review, and cover those that augment penetration of the BBB, and those that bypass the BBB. Developing appropriate delivery techniques could improve patient outcomes by ensuring efficacious drug exposure to tumors (including those that are drug-resistant), reducing systemic toxicities and targeting leptomeningeal metastases. Together, this drug delivery strategy seeks to enhance the efficacy of new drugs and enable re-evaluation of existing drugs that might have previously failed because of inadequate delivery. A literature review of repurposed drugs is reported, and a range of preclinical brain tumor models available for translational development are explored.

H3K27-altered diffuse midline glioma: a paradigm shifting opportunity in direct delivery of targeted therapeutics

INTRODUCTION

Despite much progress, the prognosis for H3K27-altered diffuse midline glioma (DMG), previously known as diffuse intrinsic pontine glioma when located in the brainstem, remains dark and dismal.

AREAS COVERED

A wealth of research over the past decade has revolutionized our understanding of the molecular basis of DMG, revealing potential targetable vulnerabilities for treatment of this lethal childhood cancer. However, obstacles to successful clinical implementation of novel therapies remain, including effective delivery across the blood-brain barrier (BBB) to the tumor site. Here, we review relevant literature and clinical trials and discuss direct drug delivery via convection-enhanced delivery (CED) as a promising treatment modality for DMG. We outline a comprehensive molecular, pharmacological, and procedural approach that may offer hope for afflicted patients and their families.

EXPERT OPINION

Challenges remain in successful drug delivery to DMG. While CED and other techniques offer a chance to bypass the BBB, the variables influencing successful intratumoral targeting are numerous and complex. We discuss these variables and potential solutions that could lead to the successful clinical implementation of preclinically promising therapeutic agents.

Convection-enhanced delivery of immunomodulatory therapy for high-grade glioma

The prognosis for glioblastoma has remained poor despite multimodal standard of care treatment, including temozolomide, radiation, and surgical resection. Further, the addition of immunotherapies, while promising in a number of other solid tumors, has overwhelmingly failed in the treatment of gliomas, in part due to the immunosuppressive microenvironment and poor drug penetrance to the brain. Local delivery of immunomodulatory therapies circumvents some of these challenges and has led to long-term remission in select patients. Many of these approaches utilize convection-enhanced delivery (CED) for immunological drug delivery, allowing high doses to be delivered directly to the brain parenchyma, avoiding systemic toxicity. Here, we review the literature encompassing immunotherapies delivered via CED-from preclinical model systems to clinical trials-and explore how their unique combination elicits an antitumor response by the immune system, decreases toxicity, and improves survival among select high-grade glioma patients.

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.

Chronic convection-enhanced delivery of topotecan for patients with recurrent glioblastoma: a first-in-patient, single-centre, single-arm, phase 1b trial

BACKGROUND

Topotecan is cytotoxic to glioma cells but is clinically ineffective because of drug delivery limitations. Systemic delivery is limited by toxicity and insufficient brain penetrance, and, to date, convection-enhanced delivery (CED) has been restricted to a single treatment of restricted duration. To address this problem, we engineered a subcutaneously implanted catheter-pump system capable of repeated, chronic (prolonged, pulsatile) CED of topotecan into the brain and tested its safety and biological effects in patients with recurrent glioblastoma.

METHODS

We did a single-centre, open-label, single-arm, phase 1b clinical trial at Columbia University Irving Medical Center (New York, NY, USA). Eligible patients were at least 18 years of age with solitary, histologically confirmed recurrent glioblastoma showing radiographic progression after surgery, radiotherapy, and chemotherapy, and a Karnofsky Performance Status of at least 70. Five patients had catheters stereotactically implanted into the glioma-infiltrated peritumoural brain and connected to subcutaneously implanted pumps that infused 146 μM topotecan 200 μL/h for 48 h, followed by a 5-7-day washout period before the next infusion, with four total infusions. After the fourth infusion, the pump was removed and the tumour was resected. The primary endpoint of the study was safety of the treatment regimen as defined by presence of serious adverse events. Analyses were done in all treated patients. The trial is closed, and is registered with ClinicalTrials.gov, NCT03154996.

FINDINGS

Between Jan 22, 2018, and July 8, 2019, chronic CED of topotecan was successfully completed safely in all five patients, and was well tolerated without substantial complications. The only grade 3 adverse event related to treatment was intraoperative supplemental motor area syndrome (one [20%] of five patients in the treatment group), and there were no grade 4 adverse events. Other serious adverse events were related to surgical resection and not the study treatment. Median follow-up was 12 months (IQR 10-17) from pump explant. Post-treatment tissue analysis showed that topotecan significantly reduced proliferating tumour cells in all five patients.

INTERPRETATION

In this small patient cohort, we showed that chronic CED of topotecan is a potentially safe and active therapy for recurrent glioblastoma. Our analysis provided a unique tissue-based assessment of treatment response without the need for large patient numbers. This novel delivery of topotecan overcomes limitations in delivery and treatment response assessment for patients with glioblastoma and could be applicable for other anti-glioma drugs or other CNS diseases. Further studies are warranted to determine the effect of this drug delivery approach on clinical outcomes.

FUNDING

US National Institutes of Health, The William Rhodes and Louise Tilzer Rhodes Center for Glioblastoma, the Michael Weiner Glioblastoma Research Into Treatment Fund, the Gary and Yael Fegel Foundation, and The Khatib Foundation.

Spermidine/Spermine N1-Acetyltransferase 1 (SAT1)-A Potential Gene Target for Selective Sensitization of Glioblastoma Cells Using an Ionizable Lipid Nanoparticle to Deliver siRNA

Spermidine/spermine N1-acetyltransferase 1 (SAT1) responsible for cell polyamine catabolism is overexpressed in glioblastoma multiforme (GB). Its role in tumor survival and promoting resistance towards radiation therapy has made it an interesting target for therapy. In this study, we prepared a lipid nanoparticle-based siRNA delivery system (LNP-siSAT1) to selectively knockdown (KD) SAT1 enzyme in a human glioblastoma cell line. The LNP-siSAT1 containing ionizable DODAP lipid was prepared following a microfluidics mixing method and the resulting nanoparticles had a hydrodynamic size of around 80 nm and a neutral surface charge. The LNP-siSAT1 effectively knocked down the SAT1 expression in U251, LN229, and 42MGBA GB cells, and other brain-relevant endothelial (hCMEC/D3), astrocyte (HA) and macrophage (ANA-1) cells at the mRNA and protein levels. SAT1 KD in U251 cells resulted in a 40% loss in cell viability. Furthermore, SAT1 KD in U251, LN229 and 42MGBA cells sensitized them towards radiation and chemotherapy treatments. In contrast, despite similar SAT1 KD in other brain-relevant cells no significant effect on cytotoxic response, either alone or in combination, was observed. A major roadblock for brain therapeutics is their ability to cross the highly restrictive blood-brain barrier (BBB) presented by the brain microcapillary endothelial cells. Here, we used the BBB circumventing approach to enhance the delivery of LNP-siSAT1 across a BBB cell culture model. A cadherin binding peptide (ADTC5) was used to transiently open the BBB tight junctions to promote paracellular diffusion of LNP-siSAT1. These results suggest LNP-siSAT1 may provide a safe and effective method for reducing SAT1 and sensitizing GB cells to radiation and chemotherapeutic agents.

Convection-Enhanced Delivery in Children: Techniques and Applications

Since its first description in 1994, convection-enhanced delivery (CED) has become a reliable method of administering drugs directly into the brain parenchyma. More predictable and effective than simple diffusion, CED bypasses the challenging boundary of the blood brain barrier, which has frustrated many attempts at delivering large molecules or polymers into the brain parenchyma. Although most of the clinical work with CED has been carried out on adults with incurable neoplasms, principally glioblastoma multiforme, an increasing number of studies have recognized its potential for paediatric applications, which now include treatment of currently incurable brain tumours such as diffuse intrinsic pontine glioma (DIPG), as well as metabolic and neurotransmitter diseases. The roadmap for the development of hardware and use of pharmacological agents in CED has been well-established, and some neurosurgical centres throughout the world have successfully undertaken clinical trials, admittedly mostly early phase, on the basis of in vitro, small animal and large animal pre-clinical foundations. However, the clinical efficacy of CED, although theoretically logical, has yet to be unequivocally demonstrated in a clinical trial; this applies particularly to neuro-oncology.This review aims to provide a broad description of the current knowledge of CED as applied to children. It reviews published studies of paediatric CED in the context of its wider history and developments and underlines the challenges related to the development of hardware, the selection of pharmacological agents, and gene therapy. It also reviews the difficulties related to the development of clinical trials involving CED and looks towards its potential disease-modifying opportunities in the future.

Pre- and Post-Treatment Imaging of Primary Central Nervous System Tumors in the Molecular and Genetic Era

Recent advances in the molecular and genetic characterization of central nervous system (CNS) tumors have ushered in a new era of tumor classification, diagnosis, and prognostic assessment. In this emerging and rapidly evolving molecular genetic era, imaging plays a critical role in the preoperative diagnosis and surgical planning, molecular marker prediction, targeted treatment planning, and post-therapy assessment of CNS tumors. This review provides an overview of the current imaging methods relevant to the molecular genetic classification of CNS tumors. Specifically, we focused on 1) the correlates between imaging features and specific molecular genetic markers and 2) the post-therapy imaging used for therapeutic assessment.

Convection Enhanced Delivery in the Setting of High-Grade Gliomas

Development of effective treatments for high-grade glioma (HGG) is hampered by (1) the blood–brain barrier (BBB), (2) an infiltrative growth pattern, (3) rapid development of therapeutic resistance, and, in many cases, (4) dose-limiting toxicity due to systemic exposure. Convection-enhanced delivery (CED) has the potential to significantly limit systemic toxicity and increase therapeutic index by directly delivering homogenous drug concentrations to the site of disease. In this review, we present clinical experiences and preclinical developments of CED in the setting of high-grade gliomas.

Against the Resilience of High-Grade Gliomas: The Immunotherapeutic Approach (Part I)

The resilience of high-grade gliomas (HGGs) against conventional chemotherapies is due to their heterogeneous genetic landscape, adaptive phenotypic changes, and immune escape mechanisms. Innovative immunotherapies have been developed to counteract the immunosuppressive capability of gliomas. Nevertheless, further research is needed to assess the efficacy of the immuno-based approach. The aim of this study is to review the newest immunotherapeutic approaches for glioma, focusing on the drug types, mechanisms of action, clinical pieces of evidence, and future challenges. A PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis)-based literature search was performed on PubMed/Medline and ClinicalTrials.gov databases using the keywords “active/adoptive immunotherapy,” “monoclonal antibodies,” “vaccine,” and “engineered T cell.”, combined with “malignant brain tumor”, “high-grade glioma.” Only articles written in English published in the last 10 years were selected, filtered based on best relevance. Active immunotherapies include systemic temozolomide, monoclonal antibodies, and vaccines. In several preclinical and clinical trials, adoptive immunotherapies, including T, natural killer, and natural killer T engineered cells, have been shown to be potential treatment options for relapsing gliomas. Systemic temozolomide is considered the backbone for newly diagnosed HGGs. Bevacizumab and rindopepimut are promising second-line treatments. Adoptive immunotherapies have been proven for relapsing tumors, but further evidence is needed.

Real-Time Positron Emission Tomography Evaluation of Topotecan Brain Kinetics after Ultrasound-Mediated Blood-Brain Barrier Permeability

Glioblastoma (GBM) is the most common primary adult brain malignancy with an extremely poor prognosis and a median survival of fewer than two years. A key reason for this high mortality is that the blood-brain barrier (BBB) significantly restricts systemically delivered therapeutics to brain tumors. High-intensity focused ultrasound (HIFU) with microbubbles is a methodology being used in clinical trials to noninvasively permeabilize the BBB for systemic therapeutic delivery to GBM. Topotecan is a topoisomerase inhibitor used as a chemotherapeutic agent to treat ovarian and small cell lung cancer. Studies have suggested that topotecan can cross the BBB and can be used to treat brain metastases. However, pharmacokinetic data demonstrated that topotecan peak concentration in the brain extracellular fluid after systemic injection was ten times lower than in the blood, suggesting less than optimal BBB penetration by topotecan. We hypothesize that HIFU with microbubbles treatment can open the BBB and significantly increase topotecan concentration in the brain. We radiolabeled topotecan with 11C and acquired static and dynamic positron emission tomography (PET) scans to quantify [11C] topotecan uptake in the brains of normal mice and mice after HIFU treatment. We found that HIFU treatments significantly increased [11C] topotecan brain uptake. Moreover, kinetic analysis of the [11C] topotecan dynamic PET data demonstrated a substantial increase in [11C] topotecan volume of distribution in the brain. Furthermore, we found a decrease in [11C] topotecan brain clearance, confirming the potential of HIFU to aid in the delivery of topotecan through the BBB. This opens the potential clinical application of [11C] topotecan as a tool to predict topotecan loco-regional brain concentration in patients with GBMs undergoing experimental HIFU treatments.

Convection-enhanced drug delivery for glioblastoma: a review

INTRODUCTION

Convection-enhanced delivery (CED) is a method of targeted, local drug delivery to the central nervous system (CNS) that bypasses the blood-brain barrier (BBB) and permits the delivery of high-dose therapeutics to large volumes of interest while limiting associated systemic toxicities. Since its inception, CED has undergone considerable preclinical and clinical study as a safe method for treating glioblastoma (GBM). However, the heterogeneity of both, the surgical procedure and the mechanisms of action of the agents studied-combined with the additional costs of performing a trial evaluating CED-has limited the field's ability to adequately assess the durability of any potential anti-tumor responses. As a result, the long-term efficacy of the agents studied to date remains difficult to assess.

MATERIALS AND METHODS

We searched PubMed using the phrase "convection-enhanced delivery and glioblastoma". The references of significant systematic reviews were also reviewed for additional sources. Articles focusing on physiological and physical mechanisms of CED were included as well as technological CED advances.

RESULTS

We review the history and principles of CED, procedural advancements and characteristics, and outcomes from key clinical trials, as well as discuss the potential future of this promising technique for the treatment of GBM.

CONCLUSION

While the long-term efficacy of the agents studied to date remains difficult to assess, CED remains a promising technique for the treatment of GBM.

Convection Enhanced Delivery of Topotecan for Gliomas: A Single-Center Experience

A key limitation to glioma treatment involves the blood brain barrier (BBB). Convection enhanced delivery (CED) is a technique that uses a catheter placed directly into the brain parenchyma to infuse treatments using a pressure gradient. In this manuscript, we describe the physical principles behind CED along with the common pitfalls and methods for optimizing convection. Finally, we highlight our institutional experience using topotecan CED for the treatment of malignant glioma.

PET, image-guided HDAC inhibition of pediatric diffuse midline glioma improves survival in murine models

Efforts at altering the dismal prognosis of pediatric midline gliomas focus on direct delivery strategies like convection-enhanced delivery (CED), where a cannula is implanted into tumor. Successful CED treatments require confirmation of tumor coverage, dosimetry, and longitudinal in vivo pharmacokinetic monitoring. These properties would be best determined clinically with image-guided dosimetry using theranostic agents. In this study, we combine CED with novel, molecular-grade positron emission tomography (PET) imaging and show how PETobinostat, a novel PET-imageable HDAC inhibitor, is effective against DIPG models. PET data reveal that CED has significant mouse-to-mouse variability; imaging is used to modulate CED infusions to maximize tumor saturation. The use of PET-guided CED results in survival prolongation in mouse models; imaging shows the need of CED to achieve high brain concentrations. This work demonstrates how personalized image-guided drug delivery may be useful in potentiating CED-based treatment algorithms and supports a foundation for clinical translation of PETobinostat.

Lentiviral Vector Induced Modeling of High-Grade Spinal Cord Glioma in Minipigs

BACKGROUND

Prior studies have applied driver mutations targeting the RTK/RAS/PI3K and p53 pathways to induce the formation of high-grade gliomas in rodent models. In the present study, we report the production of a high-grade spinal cord glioma model in pigs using lentiviral gene transfer.

METHODS

Six Gottingen Minipigs received thoracolumbar (T14-L1) lateral white matter injections of a combination of lentiviral vectors, expressing platelet-derived growth factor beta (PDGF-B), constitutive HRAS, and shRNA-p53 respectively. All animals received injection of control vectors into the contralateral cord. Animals underwent baseline and endpoint magnetic resonance imaging (MRI) and were evaluated daily for clinical deficits. Hematoxylin and eosin (H&E) and immunohistochemical analysis was conducted. Data are presented using descriptive statistics including relative frequencies, mean, standard deviation, and range.

RESULTS

100% of animals (n = 6/6) developed clinical motor deficits ipsilateral to the oncogenic lentiviral injections by a three-week endpoint. MRI scans at endpoint demonstrated contrast enhancing mass lesions at the site of oncogenic lentiviral injection and not at the site of control injections. Immunohistochemistry demonstrated positive staining for GFAP, Olig2, and a high Ki-67 proliferative index. Histopathologic features demonstrate consistent and reproducible growth of a high-grade glioma in all animals.

CONCLUSIONS

Lentiviral gene transfer represents a feasible pathway to glioma modeling in higher order species. The present model is the first lentiviral vector induced pig model of high-grade spinal cord glioma and may potentially be used in preclinical therapeutic development programs.

Longitudinal Monitoring of Gd-DTPA Following Convection Enhanced Delivery in the Brainstem

BACKGROUND

Convection-enhanced delivery (CED) has been introduced into contemporary therapeutic strategies for incurable brain neoplasms as diffuse intrinsic pontine glioma. Therapeutic benefit in part is predictably dependent on drug distribution within tumors. However, therapeutics can rarely be detected through conventional imaging techniques. Coinfusion of the tracer gadolinium-diethylenetriaminepentacetate (Gd-DTPA) has been advocated to monitor drug distributive features including volume, tumor coverage, and efflux during and after administration. The kinetics of Gd-DTPA are unclear as longitudinal magnetic resonance imaging is rarely performed. Understanding these changes would have important implications related to the timing of diagnostic imaging and reliance on tracers as surrogates of pharmacokinetic drug monitoring.

CASE DESCRIPTION

The behavior of Gd-DTPA as a surrogate is presented in a time-dependent fashion as measured by repeated magnetic resonance imaging based on the case of a child with recurrent diffuse intrinsic pontine glioma treated with an oncolytic virus (ICOVIR-5) delivered by CED with coinfused Gd-DTPA (1 mM, for a volume of 2000 μL). Initial Vd/Vi was 1.46. Gd-DTPA was observed up to 18 hours post CED but not thereafter.

CONCLUSIONS

This longitudinal imaging assessment provides a rare opportunity to better characterize the kinetics of surrogate tracers delivered by CED to the brainstem, highlighting the importance of immediate and longitudinal monitoring.

Validation of an effective implantable pump-infusion system for chronic convection-enhanced delivery of intracerebral topotecan in a large animal model

OBJECTIVE

Intracerebral convection-enhanced delivery (CED) has been limited to short durations due to a reliance on externalized catheters. Preclinical studies investigating topotecan (TPT) CED for glioma have suggested that prolonged infusion improves survival. Internalized pump-catheter systems may facilitate chronic infusion. The authors describe the safety and utility of long-term TPT CED in a porcine model and correlation of drug distribution through coinfusion of gadolinium.

METHODS

Fully internalized CED pump-catheter systems were implanted in 12 pigs. Infusion algorithms featuring variable infusion schedules, flow rates, and concentrations of a mixture of TPT and gadolinium were characterized over increasing intervals from 4 to 32 days. Therapy distribution was measured using gadolinium signal on MRI as a surrogate. A 9-point neurobehavioral scale (NBS) was used to identify side effects.

RESULTS

All animals tolerated infusion without serious adverse events. The average NBS score was 8.99. The average maximum volume of distribution (Vdmax) in chronically infused animals was 11.30 mL and represented 32.73% of the ipsilateral cerebral hemispheric volume. Vdmax was achieved early during infusions and remained relatively stable despite a slight decline as the infusion reached steady state. Novel tissue TPT concentrations measured by liquid chromatography mass spectroscopy correlated with gadolinium signal intensity on MRI (p = 0.0078).

CONCLUSIONS

Prolonged TPT-gadolinium CED via an internalized system is safe and well tolerated and can achieve a large Vdmax, as well as maintain a stable Vd for up to 32 days. Gadolinium provides an identifiable surrogate for measuring drug distribution. Extended CED is potentially a broadly applicable and safe therapeutic option in select patients.

Continuous and bolus intraventricular topotecan prolong survival in a mouse model of leptomeningeal medulloblastoma

Leptomeningeal metastasis remains a difficult clinical challenge. Some success has been achieved by direct administration of therapeutics into the cerebrospinal fluid (CSF) circumventing limitations imposed by the blood brain barrier. Here we investigated continuous infusion versus bolus injection of therapy into the CSF in a preclinical model of human Group 3 medulloblastoma, the molecular subgroup with the highest incidence of leptomeningeal disease. Initial tests of selected Group 3 human medulloblastoma cell lines in culture showed that D283 Med and D425 Med were resistant to cytosine arabinoside and methotrexate. D283 Med cells were also resistant to topotecan, whereas 1 μM topotecan killed over 99% of D425 Med cells. We therefore introduced D425 Med cells, modified to express firefly luciferase, into the CSF of immunodeficient mice. Mice were then treated with topotecan or saline in five groups: continuous intraventricular (IVT) topotecan via osmotic pump (5.28 μg/day), daily bolus IVT topotecan injections with a similar daily dose (6 μg/day), systemic intraperitoneal injections of a higher daily dose of topotecan (15 μg/day), daily IVT pumped saline and daily intraperitoneal injections of saline. Bioluminescence analyses revealed that both IVT topotecan treatments effectively slowed leptomeningeal tumor growth in the brains. Histological analysis showed that they were associated with localized brain necrosis, possibly due to backtracking of topotecan around the catheter. In the spines, bolus IVT topotecan showed a trend towards slower tumor growth compared to continuous (pump) IVT topotecan, as measured by bioluminescence. Both continuous and bolus topotecan IVT showed longer survival compared to other groups. Thus, both direct IVT topotecan CSF delivery methods produced better anti-medulloblastoma effect compared to systemic therapy at the dosages used here.

Drug-carrying microbubbles as a theranostic tool in convection-enhanced delivery for brain tumor therapy

Convection-enhanced delivery (CED) is a promising technique for infusing a therapeutic agent through a catheter with a pressure gradient to create bulk flow for improving drug spread into the brain. So far, gadopentetate dimeglumine (Gd-DTPA) is the most commonly applied surrogate agent for predicting drug distribution through magnetic resonance imaging (MRI). However, Gd-DTPA provides only a short observation duration, and concurrent infusion provides an indirect measure of the exact drug distribution. In this study, we propose using microbubbles as a contrast agent for MRI monitoring, and evaluate their use as a drug-carrying vehicle to directly monitor the infused drug. Results show that microbubbles can provide excellent detectability through MRI relaxometry and accurately represent drug distribution during CED infusion. Compared with the short half-life of Gd-DTPA (1-2 hours), microbubbles allow an extended observation period of up to 12 hours. Moreover, microbubbles provide a sufficiently high drug payload, and glioma mice that underwent a CED infusion of microbubbles carrying doxorubicin presented considerable tumor growth suppression and a significantly improved survival rate. This study recommends microbubbles as a new theranostic tool for CED procedures.

Volume of distribution and clearance of peptide-based nanofiber after convection-enhanced delivery

OBJECTIVE Drug clearance may be a limiting factor in the clinical application of convection-enhanced delivery (CED). Peptide-based nanofibers (NFPs) have a high aspect ratio, and NFPs loaded with drugs could potentially maintain effective drug concentrations for an extended period sufficient for cancer therapy. The objective of this study was to assess the volume of distribution (Vd) and clearance of variable lengths of NFPs when administered using CED. METHODS NFPs composed of multiple methoxypolyethylene glycol (mPEG)-conjugated constructs (mPEG₂₀₀₀-KLDLKLDLKLDL-K( FITC)-CONH₂, for which FITC is fluorescein isothiocyanate) were assembled in an aqueous buffer. The NFPs were approximately 5 nm in width and were formulated into different lengths: 100 nm (NFP-100), 400 nm (NFP-400), and 1000 nm (NFP-1000). The NFP surface was covalently conjugated with multiple Cy5.5 fluorophores as the optical reporters to track the post-CED distribution. Forty-two 6- to 8-week-old Ntv-a;p53^fl/fl mice underwent CED to the striatum. Animals were killed immediately, 24 hours or 72 hours after CED. The brains were extracted and sectioned for assessing NFP Vd to volume of infusion (Vi) ratio, and clearance using fluorescence microscopy. RESULTS CED of NFPs was well tolerated by all the animals. The average Vd/Vi ratios for NFP-100, NFP-400, NFP-1000, and unconjugated positive control (free Cy5.5) were 1.87, 2.47, 1.07, and 3.0, respectively, which were statistically different (p = 0.003). The percentages remaining of the original infusion volume at 24 hours for NFP-100, -400, and -1000 were 40%, 90%, and 74%, respectively. The percentages remaining at 72 hours for NFP-100, -400, and -1000 were 15%, 30%, and 46%, respectively. Unconjugated Cy5.5 was not detected at 24 or 72 hours after CED. CONCLUSIONS CED of NFPs is feasible with Vd/Vi ratios and clearance rates comparable to other nanocarriers. Of the 3 NFPs, NFP-400 appears to provide the best distribution and slowest clearance after 24 hours. NFP provides a dynamic theranostic platform, with the potential to deliver clinically efficacious drug payload to brain tumor after CED.

Slow, continuous enzyme replacement via spinal CSF in dogs with the paediatric-onset neurodegenerative disease, MPS IIIA

Intra-cerebrospinal fluid (CSF) injection of recombinant human lysosomal enzyme is a potential treatment strategy for several neurodegenerative lysosomal storage disorders including Sanfilippo syndrome (Mucopolysaccharidosis type IIIA; MPS IIIA). Here we have utilised the MPS IIIA Huntaway dog model to compare the effectiveness of the repeated intermittent bolus injection strategy being used in the trials with an alternate approach; slow, continual infusion of replacement enzyme (recombinant human sulphamidase; rhSGSH) into the spinal CSF using a SynchroMed II® pump attached to a spinal infusion cannula. The ability of each enzyme delivery strategy to ameliorate lesions in MPS IIIA brain was determined in animals treated from ∼three- to six-months of age. Controls received buffer or no treatment. Significant reductions in heparan sulphate (primary substrate) were observed in brain samples from dogs treated via either cisternal or lumbar spinal CSF bolus injection methods and also in slow intra-spinal CSF infusion-treated dogs. The extent of the reduction differed regionally. Pump-delivered rhSGSH was less effective in reducing secondary substrate (G_M3 ganglioside) in deeper aspects of cerebral cortex, and although near-amelioration of microglial activation was seen in superficial (but not deep) layers of cerebral cortex in both bolus enzyme-treated groups, pump-infusion of rhSGSH had little impact on microgliosis. While continual low-dose infusion of rhSGSH into MPS IIIA dog CSF reduces disease-based lesions in brain, it was not as efficacious as repeated cisternal or spinal CSF bolus infusion of rhSGSH over the time-frame of these experiments.

Convection-Enhanced Delivery

Convection-enhanced delivery (CED) is a promising technique that generates a pressure gradient at the tip of an infusion catheter to deliver therapeutics directly through the interstitial spaces of the central nervous system. It addresses and offers solutions to many limitations of conventional techniques, allowing for delivery past the blood-brain barrier in a targeted and safe manner that can achieve therapeutic drug concentrations. CED is a broadly applicable technique that can be used to deliver a variety of therapeutic compounds for a diversity of diseases, including malignant gliomas, Parkinson's disease, and Alzheimer's disease. While a number of technological advances have been made since its development in the early 1990s, clinical trials with CED have been largely unsuccessful, and have illuminated a number of parameters that still need to be addressed for successful clinical application. This review addresses the physical principles behind CED, limitations in the technique, as well as means to overcome these limitations, clinical trials that have been performed, and future developments.

Targeted concurrent and sequential delivery of chemotherapeutic and antiangiogenic agents to the brain by using drug-loaded nanofibrous membranes

Glioblastoma is the most frequent and devastating primary brain tumor. Surgery followed by radiotherapy with concomitant and adjuvant chemotherapy is the standard of care for patients with glioblastoma. Chemotherapy is ineffective, because of the low therapeutic levels of pharmaceuticals in tumor tissues and the well-known tumor-cell resistance to chemotherapy. Therefore, we developed bilayered poly(d,l)-lactide-co-glycolide nanofibrous membranes that enabled the sequential and sustained release of chemotherapeutic and antiangiogenic agents by employing an electrospinning technique. The release characteristics of embedded drugs were determined by employing an in vitro elution technique and high-performance liquid chromatography. The experimental results showed that the fabricated nanofibers showed a sequential drug-eluting behavior, with the release of high drug levels of chemotherapeutic carmustine, irinotecan, and cisplatin from day 3, followed by the release of high concentrations of the antiangiogenic combretastatin from day 21. Biodegradable multidrug-eluting nanofibrous membranes were then dispersed into the cerebral cavity of rats by craniectomy, and the in vivo release characteristics of the pharmaceuticals from the membranes were investigated. The results suggested that the nanofibrous membranes released high concentrations of pharmaceuticals for more than 8 weeks in the cerebral parenchyma of rats. The result of histological analysis demonstrated developmental atrophy of brains with no inflammation. Biodegradable nanofibrous membranes can be manufactured for long-term sequential transport of different chemotherapeutic and anti-angiogenic agents in the brain, which can potentially improve the treatment of glioblastoma multiforme and prevent toxic effects due to systemic administration.

Advances in Molecular Imaging of Locally Delivered Targeted Therapeutics for Central Nervous System Tumors

Thanks to the recent advances in the development of chemotherapeutics, the morbidity and mortality of many cancers has decreased significantly. However, compared to oncology in general, the field of neuro-oncology has lagged behind. While new molecularly targeted chemotherapeutics have emerged, the impermeability of the blood–brain barrier (BBB) renders systemic delivery of these clinical agents suboptimal. To circumvent the BBB, novel routes of administration are being applied in the clinic, ranging from intra-arterial infusion and direct infusion into the target tissue (convection enhanced delivery (CED)) to the use of focused ultrasound to temporarily disrupt the BBB. However, the current system depends on a “wait-and-see” approach, whereby drug delivery is deemed successful only when a specific clinical outcome is observed. The shortcomings of this approach are evident, as a failed delivery that needs immediate refinement cannot be observed and corrected. In response to this problem, new theranostic agents, compounds with both imaging and therapeutic potential, are being developed, paving the way for improved and monitored delivery to central nervous system (CNS) malignancies. In this review, we focus on the advances and the challenges to improve early cancer detection, selection of targeted therapy, and evaluation of therapeutic efficacy, brought forth by the development of these new agents.

Convection-enhanced delivery in glioblastoma: a review of preclinical and clinical studies

Glioblastoma is the most common malignant brain tumor, and it carries an extremely poor prognosis. Attempts to develop targeted therapies have been hindered because the blood-brain barrier prevents many drugs from reaching tumors cells. Furthermore, systemic toxicity of drugs often limits their therapeutic potential. A number of alternative methods of delivery have been developed, one of which is convection-enhanced delivery (CED), the focus of this review. The authors describe CED as a therapeutic measure and review preclinical studies and the most prominent clinical trials of CED in the treatment of glioblastoma. The utilization of this technique for the delivery of a variety of agents is covered, and its shortcomings and challenges are discussed in detail.

Continuous intraputamenal convection-enhanced delivery in adult rhesus macaques

OBJECT

Assessing the safety and feasibility of chronic delivery of compounds to the brain using convection-enhanced delivery (CED) is important for the further development of this important therapeutic technology. The objective of this study was to follow and model the distribution of a compound delivered by CED into the putamen of rhesus monkeys.

METHODS

The authors sequentially implanted catheters into 4 sites spanning the left and right putamen in each of 6 rhesus monkeys. The catheters were connected to implanted pumps, which were programmed to deliver a 5-mM solution of the MRI contrast agent Gd-DTPA at 0.1 μl/minute for 7 days and 0.3 μl/minute for an additional 7 days. The animals were followed for 28 days per implant cycle during which they were periodically examined with MRI.

RESULTS

All animals survived the 4 surgeries with no deficits in behavior. Compared with acute infusion, the volume of distribution (Vd) increased 2-fold with 7 days of chronic infusion. Increasing the flow rate 3-fold over the next week increased the Vd an additional 3-fold. Following withdrawal of the compound, the half-life of Gd-DTPA in the brain was estimated as 3.1 days based on first-order pharmacokinetics. Histological assessment of the brain showed minimal tissue damage limited to the insertion site.

CONCLUSIONS

These results demonstrate several important features in the development of a chronically implanted pump and catheter system: 1) the ability to place catheters accurately in a predetermined target; 2) the ability to deliver compounds in a chronic fashion to the putamen; and 3) the use of MRI and MR visible tracers to follow the evolution of the infusion volume over time.

Convection-enhanced delivery for the treatment of glioblastoma

Effective treatment of glioblastoma (GBM) remains a formidable challenge. Survival rates remain poor despite decades of clinical trials of conventional and novel, biologically targeted therapeutics. There is considerable evidence that most of these therapeutics do not reach their targets in the brain when administered via conventional routes (intravenous or oral). Hence, direct delivery of therapeutics to the brain and to brain tumors is an active area of investigation. One of these techniques, convection-enhanced delivery (CED), involves the implantation of catheters through which conventional and novel therapeutic formulations can be delivered using continuous, low-positive-pressure bulk flow. Investigation in preclinical and clinical settings has demonstrated that CED can produce effective delivery of therapeutics to substantial volumes of brain and brain tumor. However, limitations in catheter technology and imaging of delivery have prevented this technique from being reliable and reproducible, and the only completed phase III study in GBM did not show a survival benefit for patients treated with an investigational therapeutic delivered via CED. Further development of CED is ongoing, with novel catheter designs and imaging approaches that may allow CED to become a more effective therapeutic delivery technique.

Promising approaches to circumvent the blood-brain barrier: progress, pitfalls and clinical prospects in brain cancer

Brain drug delivery is a major challenge for therapy of central nervous system (CNS) diseases. Biochemical modifications of drugs or drug nanocarriers, methods of local delivery, and blood-brain barrier (BBB) disruption with focused ultrasound and microbubbles are promising approaches which enhance transport or bypass the BBB. These approaches are discussed in the context of brain cancer as an example in CNS drug development. Targeting to receptors enabling transport across the BBB offers noninvasive delivery of small molecule and biological cancer therapeutics. Local delivery methods enable high dose delivery while avoiding systemic exposure. BBB disruption with focused ultrasound and microbubbles offers local and noninvasive treatment. Clinical trials show the prospects of these technologies and point to challenges for the future.

Convection-enhanced delivery for glioblastoma: targeted delivery of antitumor therapeutics

Glioblastoma is the most common primary brain tumor in adults and carries a dismal prognosis despite advancements in treatment. Diffuse tumor infiltration precludes curative surgical resection and necessitates advancements in drug delivery mechanisms. Convection-enhanced delivery (CED) enables continuous local drug delivery for a diverse population of antitumor agents. Importantly, CED circumvents therapeutic challenges posed by the blood-brain barrier by facilitating concentrated local therapeutic drug delivery with limited systemic effects. Here, we present a concise review of properties essential for safe and efficient convection-enhanced drug delivery, as well as a focused review of clinical studies evaluating CED in the treatment of glioblastoma.

Toxicity evaluation of prolonged convection-enhanced delivery of small-molecule kinase inhibitors in naïve rat brainstem

PURPOSE

Convection-enhanced delivery (CED), a local drug delivery technique, is typically performed as a single session and drug concentrations therefore decline quickly post CED. Prolonged CED (pCED) overcomes this problem by performing a long-term infusion to maintain effective drug concentrations for an extended period. The purpose of the current study was to assess the toxicity of using pCED to deliver single and multi-drug therapy in naïve rat brainstem.

METHODS

Sixteen rats underwent pCED of three small-molecule kinase inhibitors in the pons. Single and multi-drug combinations were delivered continuously for 7 days using ALZET mini-osmotic pumps (model 2001, rate of 1 μl/h). Rats were monitored daily for neurological signs of toxicity. Rats were sacrificed 10 days post completion of infusion, and appropriate tissue sections were analyzed for histological signs of toxicity.

RESULTS

Two rats exhibited signs of neurological deficits, which corresponded with diffuse inflammation, necrosis, and parenchymal damage on histological analysis. The remaining rats showed no neurological or histological signs of toxicity.

CONCLUSION

The neurological deficits in the two rats were likely due to injury from physical force, such as cannula movement post insertion and subsequent encephalitis. The remaining rats showed no toxicity and therefore brainstem targeting using pCED to infuse single and multi-drug therapy was well tolerated in these rats.

Convection-enhanced delivery of etoposide is effective against murine proneural glioblastoma

BACKGROUND

Glioblastoma subtypes have been defined based on transcriptional profiling, yet personalized care based on molecular classification remains unexploited. Topoisomerase II (TOP2) contributes to the transcriptional signature of the proneural glioma subtype. Thus, we targeted TOP2 pharmacologically with etoposide in proneural glioma models.

METHODS

TOP2 gene expression was evaluated in mouse platelet derived growth factor (PDGF)(+)phosphatase and tensin homolog (PTEN)(-/-)p53(-/-) and PDGF(+)PTEN(-/-) proneural gliomas and cell lines, as well as human glioblastoma from The Cancer Genome Atlas. Correlation between TOP2 transcript levels and etoposide susceptibility was investigated in 139 human cancer cell lines from the Cancer Cell Line Encyclopedia public dataset and in mouse proneural glioma cell lines. Convection-enhanced delivery (CED) of etoposide was tested on cell-based PDGF(+)PTEN(-/-)p53(-/-) and retroviral-based PDGF(+)PTEN(-/-) mouse proneural glioma models.

RESULTS

TOP2 expression was significantly higher in human proneural glioblastoma and in mouse proneural tumors at early as well as late stages of development compared with normal brain. TOP2B transcript correlated with susceptibility to etoposide in mouse proneural cell lines and in 139 human cancer cell lines from the Cancer Cell Line Encyclopedia. Intracranial etoposide CED treatment (680 μM) was well tolerated by mice and led to a significant survival benefit in the PDGF(+)PTEN(-/-)p53(-/-) glioma model. Moreover, etoposide CED treatment at 80 μM but not 4 μM led to a significant survival advantage in the PDGF(+)PTEN(-/-) glioma model.

CONCLUSIONS

TOP2 is highly expressed in proneural gliomas, rendering its pharmacological targeting by intratumoral administration of etoposide by CED effective on murine proneural gliomas. We provide evidence supporting clinical testing of CED of etoposide with a molecular-based patient selection approach.

Convection-enhanced delivery for targeted delivery of antiglioma agents: the translational experience

Recent improvements in the understanding of glioblastoma (GBM) have allowed for increased ability to develop specific, targeted therapies. In parallel, however, there is a need for effective methods of delivery to circumvent the therapeutic obstacles presented by the blood-brain barrier and systemic side effects. The ideal delivery system should allow for adequate targeting of the tumor while minimizing systemic exposure, applicability across a wide range of potential therapies, and have existing safe and efficacious systems that allow for widespread application. Though many alternatives to systemic delivery have been developed, this paper will focus on our experience with convection-enhanced delivery (CED) and our focus on translating this technology from pre-clinical studies to the treatment of human GBM.

Comparison of pulsed versus continuous convective flow for central nervous system tissue perfusion: laboratory investigation

OBJECT

Although pulsatile and continuous infusion paradigms have been described for convective delivery of drugs, the effectiveness and properties of each flow paradigm are unknown. To determine the effectiveness and properties of pulsatile and continuous convective infusion paradigms, the authors compared these convective flow methods in the gray and white matter of primates.

METHODS

Six primates (Macaca mulatta) underwent convective infusion of Gd-DPTA (5 mM) into the cerebral gray matter (thalamus) or white matter (frontal lobe) using pulsed (intermittent pulses of 15 μl/min) or continuous (1 μl/min) convective flow. Results were assessed by clinical MRI and histological analyses.

RESULTS

Distribution of Gd-DTPA infusate in gray and white matter by pulsed and continuous flow was clearly identified using MRI, which revealed that both convective flow methods demonstrated an increase in the volume of distribution (Vd) with increasing volume of infusion (Vi) in the surrounding gray and white matter. Although the mean (± SD) gray matter Vd:Vi ratio for the pulsed infusions (4.2 ± 0.5) was significantly lower than the mean Vd:Vi ratio for continuous infusions (5.4 ± 0.5; a 22% difference [p = 0.0006]), the difference between pulsed (3.8 ± 0.4) and continuous (4.3 ± 1.2) infusions in white matter was not significantly different (p = 0.3). Pulsed infusions were associated with more leakback (12.3% ± 6.4% of Vi) than continuous infusions (3.9% ± 7.8%), although this difference was not significant (p = 0.2). All animals tolerated the infusions and there was no histological evidence of tissue injury at the infusion sites.

CONCLUSIONS

Although pulsed and continuous infusion flow paradigms can be safely and effectively used for convective delivery into both gray and white matter, continuous infusion is associated with a higher Vd:Vi ratio than pulsatile infusion in gray matter. High rates of infusion (15 μl/min) can be used to deliver infusate without any significant leakback and without any clinical or histological evidence of injury.