Intracerebral infusion of an EGFR-targeted toxin in recurrent malignant brain tumors

Overcoming Resistance to Temozolomide in Glioblastoma: A Scoping Review of Preclinical and Clinical Data

Glioblastoma (GB) is the most common and most aggressive primary brain tumor in adults, with an overall survival almost 14.6 months. Optimal resection followed by combined temozolomide chemotherapy and radiotherapy, also known as Stupp protocol, remains the standard of treatment; nevertheless, resistance to temozolomide, which can be obtained throughout many molecular pathways, is still an unsurpassed obstacle. Several factors influence the efficacy of temozolomide, including the involvement of other DNA repair systems, aberrant signaling pathways, autophagy, epigenetic modifications, microRNAs, and extracellular vesicle production. The blood-brain barrier, which serves as both a physical and biochemical obstacle, the tumor microenvironment's pro-cancerogenic and immunosuppressive nature, and tumor-specific characteristics such as volume and antigen expression, are the subject of ongoing investigation. In this review, preclinical and clinical data about temozolomide resistance acquisition and possible ways to overcome chemoresistance, or to treat gliomas without restoration of chemosensitinity, are evaluated and presented. The objective is to offer a thorough examination of the clinically significant molecular mechanisms and their intricate interrelationships, with the aim of enhancing understanding to combat resistance to TMZ more effectively.

Brain-targeted drug delivery - nanovesicles directed to specific brain cells by brain-targeting ligands

Neurodegenerative diseases are characterized by extensive loss of function or death of brain cells, hampering the life quality of patients. Brain-targeted drug delivery is challenging, with a low success rate this far. Therefore, the application of targeting ligands in drug vehicles, such as lipid-based and polymeric nanoparticles, holds the promise to overcome the blood-brain barrier (BBB) and direct therapies to the brain, in addition to protect their cargo from degradation and metabolization. In this review, we discuss the barriers to brain delivery and the different types of brain-targeting ligands currently in use in brain-targeted nanoparticles, such as peptides, proteins, aptamers, small molecules, and antibodies. Moreover, we present a detailed review of the different targeting ligands used to direct nanoparticles to specific brain cells, like neurons (C4-3 aptamer, neurotensin, Tet-1, RVG, and IKRG peptides), astrocytes (Aquaporin-4, D4, and Bradykinin B2 antibodies), oligodendrocytes (NG-2 antibody and the biotinylated DNA aptamer conjugated to a streptavidin core Myaptavin-3064), microglia (CD11b antibody), neural stem cells (QTRFLLH, VPTQSSG, and NFL-TBS.40-63 peptides), and to endothelial cells of the BBB (transferrin and insulin proteins, and choline). Reports demonstrated enhanced brain-targeted delivery with improved transport to the specific cell type targeted with the conjugation of these ligands to nanoparticles. Hence, this strategy allows the implementation of high-precision medicine, with reduced side effects or unwanted therapy clearance from the body. Nevertheless, the accumulation of some of these nanoparticles in peripheral organs has been reported indicating that there are still factors to be improved to achieve higher levels of brain targeting. This review is a collection of studies exploring targeting ligands for the delivery of nanoparticles to the brain and we highlight the advantages and limitations of this type of approach in precision therapies.

Toxic warhead-armed antibody for targeted treatment of glioblastoma

Glioblastoma is a fatal intracranial tumor with a poor prognosis, exhibiting uninterrupted malignant progression, widespread invasion throughout the brain leading to the destruction of normal brain tissue and inevitable death. Monoclonal antibodies alone or conjugated with cytotoxic payloads to treat patients with different solid tumors showed effective. This treatment strategy is being explored for patients with glioblastoma (GBM) to obtain meaningful clinical responses and offer new drug options for the treatment of this devastating disease. In this review, we summarize clinical data (from pubmed.gov database and clinicaltrial.gov database) on the efficacy and toxicity of naked antibodies and antibody-drug conjugates (ADCs) against multiple targets on GBM, elucidate the mechanisms that ADCs act at the site of GBM lesions. Finally, we discuss the potential strategies for ADC therapies currently used to treat GBM patients.

Antibody drug conjugates for glioblastoma: current progress towards clinical use

INTRODUCTION

Antibody drug conjugates (ADCs) are now a proven therapeutic class for many cancers, combining highly specific targeting with the potency of high effective payloads. This review summarizes the experience with ADCs in brain tumors and examines future paths for their use in these tumors.

AREAS COVERED

This review will cover all the key classes of ADCs which have been tested in primary brain tumors, including commentary on the major trials to date. The efficacy of these trials, as well as their limitations, will put in context of the overall landscape of drug development in brain tumors. Importantly, this review will summarize key learnings and insights from these trials that help provide the basis for rational ways in which these drugs can be effectively and appropriate developed for patients with primary brain tumors.

EXPERT OPINION

ADC development in brain tumors has occurred in two major phases to date. Key learnings from previous trials provide a strong rationale for the continued development of these drugs for primary brain tumors. However, the unique biology of these tumors requires development strategies specifically tailored to maximize their optimal development.

Local Delivery Strategies for Peptides and Proteins into the CNS: Status Quo, Challenges, and Future Perspectives

Over the past decades, peptides and proteins have been increasingly important in the treatment of various human diseases and conditions owing to their specificity, potency, and minimized off-target toxicity. However, the existence of the practically impermeable blood brain barrier (BBB) limits the entry of macromolecular therapeutics into the central nervous systems (CNS). Consequently, clinical translation of peptide/protein therapeutics for the treatment of CNS diseases has been limited. Over the past decades, developing effective delivery strategies for peptides and proteins has gained extensive attention, in particular with localized delivery strategies, due to the fact that they are capable of circumventing the physiological barrier to directly introduce macromolecular therapeutics into the CNS to improve therapeutic effects and reduce systemic side effects. Here, we discuss various local administration and formulation strategies that have shown successes in the treatment of CNS diseases using peptide/protein therapeutics. Lastly, we discuss challenges and future perspectives of these approaches.

Intraductal administration of transferrin receptor-targeted immunotoxin clears ductal carcinoma in situ in mouse models of breast cancer-a preclinical study

The human transferrin receptor (TFR) is overexpressed in most breast cancers, including preneoplastic ductal carcinoma in situ (DCIS). HB21(Fv)-PE40 is a single-chain immunotoxin (IT) engineered by fusing the variable region of a monoclonal antibody (HB21) against a TFR with a 40 kDa fragment of Pseudomonas exotoxin (PE). In humans, the administration of other TFR-targeted immunotoxins intrathecally led to inflammation and vascular leakage. We proposed that for treatment of DCIS, intraductal (i.duc) injection of HB21(Fv)-PE40 could avoid systemic toxicity while retaining its potent antitumor effects on visible and occult tumors in the entire ductal tree. Pharmacokinetic studies in mice showed that, in contrast to intravenous injection, IT was undetectable by enzyme-linked immunosorbent assay in blood following i.duc injection of up to 3.0 μg HB21(Fv)-PE40. We demonstrated the antitumor efficacy of HB21(Fv)-PE40 in two mammary-in-duct (MIND) models, MCF7 and SUM225, grown in NOD/SCID/gamma mice. Tumors were undetectable by In Vivo Imaging System (IVIS) imaging in intraductally treated mice within 1 wk of initiation of the regimen (IT once weekly/3 wk, 1.5 μg/teat). MCF7 tumor-bearing mice remained tumor free for up to 60 d of observation with i.duc IT, whereas the HB21 antibody alone or intraperitoneal IT treatment had minimal/no antitumor effects. These and similar findings in the SUM225 MIND model were substantiated by analysis of mammary gland whole mounts, histology, and immunohistochemistry for the proteins Ki67, CD31, CD71 (TFR), and Ku80. This study provides a strong preclinical foundation for conducting feasibility and safety trials in patients with stage 0 breast cancer.

Antibody Drug Conjugates in Glioblastoma - Is There a Future for Them?

Glioblastoma (GBM) is an aggressive and fatal malignancy that despite decades of trials has limited therapeutic options. Antibody drug conjugates (ADCs) are composed of a monoclonal antibody which specifically recognizes a cellular surface antigen linked to a cytotoxic payload. ADCs have demonstrated superior efficacy and/or reduced toxicity in a range of haematological and solid tumors resulting in nine ADCs receiving regulatory approval. ADCs have also been explored in patients with brain tumours but with limited success to date. While earlier generations ADCs in glioma patients have had limited success and high toxicity, newer and improved ADCs characterised by low immunogenicity and more effective payloads have shown promise in a range of tumour types. These newer ADCs have also been tested in glioma patients, however, with mixed results. Factors affecting the effectiveness of ADCs to target the CNS include the blood brain barrier which acts as a physical and biochemical barrier, the pro-cancerogenic and immunosuppressive tumor microenvironment and tumour characteristics like tumour volume and antigen expression. In this paper we review the data regarding the ongoing the development of ADCs in glioma patients as well as potential strategies to overcome these barriers to maximise their therapeutic potential.

Convection-enhanced delivery for high-grade glioma

Glioblastoma (GBM) is the most common adult primary malignant brain tumor and is associated with a dire prognosis. Despite multi-modality therapies of surgery, radiation, and chemotherapy, its 5-year survival rate is 6.8%. The presence of the blood-brain barrier (BBB) is one factor that has made GBM difficult to treat. Convection-enhanced delivery (CED) is a modality that bypasses the BBB, which allows the intracranial delivery of therapies that would not otherwise cross the BBB and avoids systemic toxicities. This review will summarize prior and ongoing studies and highlights practical considerations related to clinical care to aid providers caring for a high-grade glioma patient being treated with CED. Although not the main scope of this paper, this review also touches upon relevant technical considerations of using CED, an area still under much development.

Convection-Enhanced Delivery and Principles of Extracellular Transport in the Brain

Stereotactic neurosurgery involves a targeted intervention based on congruence of image guidance to a reference fiducial system. This discipline has widespread applications in radiosurgery, tumor therapy, drug delivery, functional lesioning, and neuromodulation. In this article, we focused on convection-enhanced delivery to deliver therapeutic agents to the brain addressing areas of research and clinical development. We performed a robust literature review of all relevant articles highlighting current efforts and challenges of making this delivery technique more widely understood. We further described key biophysical properties of molecular transport in the extracellular space that may impact the efficacy and control of drug delivery using stereotactic methods. Understanding these principles is critical for further refinement of predictive models that can inform advances in stereotactic techniques for convection-enhanced delivery of therapeutic agents to the brain.

Breaching the Blood-Brain Tumor Barrier for Tumor Therapy

Tumors affecting the central nervous system (CNS), either primary or secondary, are highly prevalent and represent an unmet medical need. Prognosis of these tumors remains poor, mostly due to the low intrinsic chemo/radio-sensitivity of tumor cells, a meagerly known role of the microenvironment and the poor CNS bioavailability of most used anti-cancer agents. The BBTB is the main obstacle for anticancer drugs to achieve therapeutic concentrations in the tumor tissues. During the last decades, many efforts have been devoted to the identification of modalities allowing to increase drug delivery into brain tumors. Until recently, success has been modest, as few of these approaches reached clinical testing and even less gained regulatory approval. In recent years, the scenario has changed, as various conjugates and drug delivery technologies have advanced into clinical testing, with encouraging results and without being burdened by a heavy adverse event profile. In this article, we review the different approaches aimed at increasing drug delivery to brain tumors, with particular attention to new, promising approaches that increase the permeability of the BBTB or exploit physiological transport mechanisms.

Evolution of the Neurosurgeon's Role in Clinical Trials for Glioblastoma: A Systematic Overview of the Clinicaltrials.Gov Database

BACKGROUND

The therapeutic challenge of glioblastoma (GBM) has catalyzed the development of clinical trials to evaluate novel interventions. With increased understanding of GBM biology and technological advances, the neurosurgeon's role in neuro-oncology has evolved.

OBJECTIVE

To evaluate the current landscape of procedure-based clinical trials for GBM to characterize this evolution, gain insight into past failures, and accordingly outline implications for future research and practice that may inform future studies.

METHODS

The ClinicalTrials.gov database was searched for surgical/procedural trials in individuals with GBM. Demographics, specific intervention, trial phase, and main outcome measures were abstracted.

RESULTS

A total of 224 of 2311 GBM trials (9.7%) were identified as procedural, with the majority being based in the United States (155/224, 69.2%), single-center (155/224, 69.2%), and not randomized (176/224, 78.6%). Primary and recurrent GBMs were evenly addressed. The leading interventions were local delivery of therapeutics (50.0%), surgical techniques (33.9%), such as image-guided surgery, and novel device applications (14.3%). Phase I designs predominated (82/224, 36.6%). The top primary outcome was safety/tolerability/feasibility (88/224, 39.3%), followed by survival (46/224, 20.5%). Approximately 17% of studies were terminated, withdrawn, or suspended. Fifty-two linked publications were identified, among which 42 were classified as having a positive result.

CONCLUSION

Procedural interventions comprised ∼10% of all registered GBM trials. Local delivery of therapeutics, use of surgical imaging techniques and novel device applications, predominantly through phase I designs, represent the evolved role of the neurosurgeon in neuro-oncology. Improved reporting of trial designs, outcomes, and results are needed to better inform the field and increase efficiency.

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.

Epidermal Growth Factor Receptor: Key to Selective Intracellular Delivery

Epidermal growth factor receptor (EGFR) is an integral surface protein mediating cellular response to a number of growth factors. Its overexpression and increased activation due to mutations is one of the most common traits of many types of cancer. Development and clinical use of the agents, which block EGFR activation, became a prime example of the personalized targeted medicine. However, despite the obvious success in this area, cancer cure remains unattainable in most cases. Because of that, as well as the result of the search for possible ways to overcome the difficulties of treatment, a huge number of new treatment methods relying on the use of EGFR overexpression and its changes to destroy cancer cells. Modern data on the structure, functioning, and intracellular transport of EGFR, its natural ligands, as well as signaling cascades triggered by the EGFR activation, peculiarities of the EGFR expression and activation in oncological disorders, as well as applied therapeutic approaches aimed at blocking EGFR signaling pathway are summarized and analyzed in this review. Approaches to the targeted delivery of various chemotherapeutic agents, radionuclides, immunotoxins, photosensitizers, as well as the prospects for gene therapy aimed at cancer cells with EGFR overexpression are reviewed in detail. It should be noted that increasing attention is being paid nowadays to the development of multifunctional systems, either carrying several different active agents, or possessing several environment-dependent transport functions. Potentials of the systems based on receptor-mediated endocytosis of EGFR and their possible advantages and limitations are discussed.

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.

Adult precision medicine: learning from the past to enhance the future

Despite therapeutic advances for other malignancies, gliomas remain challenging solid tumors to treat. Complete surgical resection is nearly impossible due to gliomas’ diffuse infiltrative nature, and treatment is hampered by restricted access to the tumors due to limited transport across the blood–brain barrier. Recent advances in genomic studies and next-generation sequencing techniques have led to a better understanding of gliomas and identification of potential aberrant signaling pathways. Targeting the specific genomic abnormalities via novel molecular therapies has opened a new avenue in the management of gliomas, with encouraging results in preclinical studies and early clinical trials. However, molecular characterization of gliomas revealed significant heterogeneity, which poses a challenge for targeted therapeutic approaches. In this context, leading neuro-oncology researchers and clinicians, industry innovators, and patient advocates convened at the inaugural annual Remission Summit held in Orlando, FL in February 2019 to discuss the latest advances in immunotherapy and precision medicine approaches for the treatment of adult and pediatric brain tumors and outline the unanswered questions, challenges, and opportunities that lay ahead for advancing the duration and quality of life for patients with brain tumors. Here, we provide historical context for precision medicine in other cancers, present emerging approaches for gliomas, discuss their limitations, and outline the steps necessary for future success. We focus on the advances in small molecule targeted therapy, as the use of immunotherapy as an emerging precision medicine modality for glioma treatment has recently been reviewed by our colleagues.

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.

Disentangling the therapeutic tactics in GBM: From bench to bedside and beyond

Glioblastoma multiforme (GBM) is one of the most common and malignant form of adult brain tumor with a high mortality rate and dismal prognosis. The present standard treatment comprising surgical resection followed by radiation and chemotherapy using temozolomide can broaden patient's survival to some extent. However, the advantages are not palliative due to the development of resistance to the drug and tumor recurrence following the multimodal treatment approaches due to both intra- and intertumoral heterogeneity of GBM. One of the major contributors to temozolomide resistance is O⁶ -methylguanine-DNA methyltransferase. Furthermore, deficiency of mismatch repair, base excision repair, and cytoprotective autophagy adds to temozolomide obstruction. Rising proof additionally showed that a small population of cells displaying certain stem cell markers, known as glioma stem cells, adds on to the resistance and tumor progression. Collectively, these findings necessitate the discovery of novel therapeutic avenues for treating glioblastoma. As of late, after understanding the pathophysiology and biology of GBM, some novel therapeutic discoveries, such as drug repurposing, targeted molecules, immunotherapies, antimitotic therapies, and microRNAs, have been developed as new potential treatments for glioblastoma. To help illustrate, "what are the mechanisms of resistance to temozolomide" and "what kind of alternative therapeutics can be suggested" with this fatal disease, a detailed history of these has been discussed in this review article, all with a hope to develop an effective treatment strategy for GBM.

Targeting Receptors on Cancer Cells with Protein Toxins

Cancer cells frequently upregulate surface receptors that promote growth and survival. These receptors constitute valid targets for intervention. One strategy involves the delivery of toxic payloads with the goal of killing those cancer cells with high receptor levels. Delivery can be accomplished by attaching a toxic payload to either a receptor-binding antibody or a receptor-binding ligand. Generally, the cell-binding domain of the toxin is replaced with a ligand or antibody that dictates a new binding specificity. The advantage of this “immunotoxin” approach lies in the potency of these chimeric molecules for killing cancer cells. However, receptor expression on normal tissue represents a significant obstacle to therapeutic intervention.

Strategies for Improved Intra-arterial Treatments Targeting Brain Tumors: a Systematic Review

Conventional treatments for brain tumors relying on surgery, radiation, and systemic chemotherapy are often associated with high recurrence and poor prognosis. In recent decades, intra-arterial administration of anti-cancer drugs has been considered a suitable alternative drug delivery route to intravenous and oral administration. Intra-arterial administration is believed to offer increasing drug responses by primary and metastatic brain tumors, and to be associated with better median overall survival. By directly injecting therapeutic agents into carotid or vertebral artery, intra-arterial administration rapidly increases intra-tumoral drug concentration but lowers systemic exposure. However, unexpected vascular or neural toxicity has questioned the therapeutic safety of intra-arterial drug administration and limits its widespread clinical application. Therefore, improving targeting and accuracy of intra-arterial administration has become a major research focus. This systematic review categorizes strategies for optimizing intra-arterial administration into five categories: (1) transient blood-brain barrier (BBB)/blood-tumor barrier (BTB) disruption, (2) regional cerebral hypoperfusion for peritumoral hemodynamic changes, (3) superselective endovascular intervention, (4) high-resolution imaging techniques, and (5) others such as cell and gene therapy. We summarize and discuss both preclinical and clinical research, focusing on advantages and disadvantages of different treatment strategies for a variety of cerebral tumor types.

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.

Antiangiogenic Targets for Glioblastoma Therapy from a Pre-Clinical Approach, Using Nanoformulations

Glioblastoma (GBM) is the most aggressive tumor type whose resistance to conventional treatment is mediated, in part, by the angiogenic process. New treatments involving the application of nanoformulations composed of encapsulated drugs coupled to peptide motifs that direct drugs to specific targets triggered in angiogenesis have been developed to reach and modulate different phases of this process. We performed a systematic review with the search criterion (Glioblastoma OR Glioma) AND (Therapy OR Therapeutic) AND (Nanoparticle) AND (Antiangiogenic OR Angiogenesis OR Anti-angiogenic) in Pubmed, Scopus, and Cochrane databases, in which 312 articles were identified; of these, only 27 articles were included after selection and analysis of eligibility according to the inclusion and exclusion criteria. The data of the articles were analyzed in five contexts: the characteristics of the tumor cells; the animal models used to induce GBM for antiangiogenic treatment; the composition of nanoformulations and their physical and chemical characteristics; the therapeutic anti-angiogenic process; and methods for assessing the effects on antiangiogenic markers caused by therapies. The articles included in the review were heterogeneous and varied in practically all aspects related to nanoformulations and models. However, there was slight variance in the antiangiogenic effect analysis. CD31 was extensively used as a marker, which does not provide a view of the effects on the most diverse aspects involved in angiogenesis. Therefore, the present review highlighted the need for standardization between the different approaches of antiangiogenic therapy for the GBM model that allows a more effective meta-analysis and that helps in future translational studies.

Development of Glypican-3 Targeting Immunotoxins for the Treatment of Liver Cancer: An Update

Hepatocellular carcinoma (HCC) accounts for most liver cancers and represents one of the deadliest cancers in the world. Despite the global demand for liver cancer treatments, there remain few options available. The U.S. Food and Drug Administration (FDA) recently approved Lumoxiti, a CD22-targeting immunotoxin, as a treatment for patients with hairy cell leukemia. This approval helps to demonstrate the potential role that immunotoxins can play in the cancer therapeutics pipeline. However, concerns have been raised about the use of immunotoxins, including their high immunogenicity and short half-life, in particular for treating solid tumors such as liver cancer. This review provides an overview of recent efforts to develop a glypican-3 (GPC3) targeting immunotoxin for treating HCC, including strategies to deimmunize immunotoxins by removing B- or T-cell epitopes on the bacterial toxin and to improve the serum half-life of immunotoxins by incorporating an albumin binding domain.

Chronic in vivo exposure to Helicobacter pylori VacA: Assessing the efficacy of automated and long-term intragastric toxin infusion

Helicobacter pylori (Hp) secrete VacA, a diffusible pore-forming exotoxin that is epidemiologically linked to gastric disease in humans. In vitro studies indicate that VacA modulates gastric epithelial and immune cells, but the in vivo contributions of VacA as an important determinant of Hp colonization and chronic infection remain poorly understood. To identify perturbations in the stomachs of C57BL/6 or BALB/C mice that result specifically from extended VacA exposure, we evaluated the efficacy of administering purified toxin using automated infusion via surgically-implanted, intragastric catheters. At 3 and 30 days of interrupted infusion, VacA was detected in association with gastric glands. In contrast to previously-reported tissue damage resulting from short term exposure to Hp extracts administered by oral gavage, extended infusion of VacA did not damage stomach, esophageal, intestinal, or liver tissue. However, several alterations previously reported during Hp infection were detected in animals infused with VacA, including reduction of the gastric mucus layer, and increased vacuolation of parietal cells. VacA infusion invoked an immune response, as indicated by the detection of circulating VacA antibodies. These foundational studies support the use of VacA infusion for identifying gastric alterations that are unambiguously attributable to long-term exposure to toxin.

Multireceptor targeting of glioblastoma

BACKGROUND

Treatment for glioblastoma (GBM) remains an unmet need in medicine. Novel therapies that address GBM complexity and heterogeneity in particular are warranted. To this end, we target 4 tumor-associated receptors at a time that span virtually all of the GBM microenvironment including bulk tumor cells, infiltrating tumor cells, neovasculature, and tumor-infiltrating cells with one pharmaceutical agent delivering a cytotoxic load.

METHODS

We engineered multivalent ligand-based vector proteins termed QUAD with an ability to bind to 4 of the following GBM-associated receptors: IL-13RA2, EphA2, EphA3, and EphB2. We conjugated QUAD with a modified bacterial toxin PE38QQR and tested it in vitro and in vivo.

RESULTS

The QUAD variants preserved functional characteristics of the respective ligands for the 4 receptors. The QUAD 3.0 variant conjugate was highly cytotoxic to GBM cells, but it was nontoxic in mice, and the conjugate exhibited strong antitumor effect in a dog with spontaneous GBM.

CONCLUSION

The QUAD addresses, to a large extent, the issues of intra- and intertumoral heterogeneity and, at the same time, it targets several pathophysiologically important tumor compartments in GBM through multiple receptors overexpressed in tumors allowing for what we call "molecular resection." QUAD-based targeted agents warrant further pre- and clinical development.

Clinical tolerance of corticospinal tracts in convection-enhanced delivery to the brainstem

OBJECTIVE

Convection-enhanced delivery (CED) has been explored as a therapeutic strategy for diffuse intrinsic pontine glioma (DIPG). Variables that may affect tolerance include infusate volume, infusion rate, catheter trajectory, and target position. Supratentorial approaches for catheter placement and infusate distribution patterns may conflict with corticospinal tracts (CSTs). The clinical relevance of these anatomical constraints has not been described. The authors report their experience using CED in the brainstem as it relates to anatomical CST conflict and association with clinical tolerance.

METHODS

In a phase I clinical trial of CED for DIPG (clinical trial registration no. NCT01502917, clinicaltrials.gov), a flexible infusion catheter was placed with MRI guidance for infusion of 124I-8H9, a radioimmunotherapeutic agent. Intra- and postprocedural MR images were analyzed to identify catheter trajectories and changes in T2-weighted signal intensity to approximate volume of distribution (Vd). Intersection of CST by the catheter and overlap between Vd and CST were recorded and their correlation with motor deficits was evaluated.

RESULTS

Thirty-one patients with a mean age of 7.6 years (range 3.2-18 years) underwent 39 catheter insertions for CED between 2012 and 2017. Thirty catheter insertions had tractography data available for analysis. The mean trajectory length was 105.5 mm (range 92.7-121.6 mm). The mean number of intersections of CST by catheter was 2.2 (range 0-3) and the mean intersecting length was 18.9 mm (range 0-44.2 mm). The first 9 infusions in the highest dose level (range 3.84-4.54 ml infusate) were analyzed for Vd overlap with CST. In this group, the mean age was 7.6 years (range 5.8-10.3 years), the mean trajectory length was 109.5 mm (range 102.6-122.3 mm), and the mean overlap between Vd and CST was 5.5 cm3. For catheter placement-related adverse events, 1 patient (3%) had worsening of a contralateral facial nerve palsy following the procedure with two CST intersections, an intersecting distance of 31.7 mm, and an overlap between Vd and CST of 3.64 cm3. For infusion-related adverse events, transient postinfusion deficits were noted in 3 patients in the highest dose level, with a mean number of 2 intersections of CST by catheter, mean intersecting length of 12.9 mm, and mean overlap between Vd and CST of 6.3 cm3.

CONCLUSIONS

A supratentorial approach to the brainstem crossing the CST resulted in one worsened neurological deficit. There does not appear to be a significant risk requiring avoidance of dominant motor fiber tracts with catheter trajectory planning. There was no correlation between Vd-CST overlap and neurological adverse events in this cohort.Clinical trial registration no.: NCT01502917 (clinicaltrials.gov).

The intersect of neurosurgery with diffuse intrinsic pontine glioma

An invited article highlighting diffuse intrinsic pontine glioma (DIPG) to celebrate the 75th Anniversary of the Journal of Neurosurgery, a journal known to define surgical nuance and enterprise, is paradoxical since DIPG has long been relegated to surgical abandonment. More recently, however, the neurosurgeon is emerging as a critical stakeholder given our role in tissue sampling, collaborative scientific research, and therapeutic drug delivery. The foundation for this revival lies in an expanding reliance on tissue accession for understanding tumor biology, available funding to fuel research, and strides with interventional drug delivery.

Biological intratumoral therapy for the high-grade glioma part I: intratumoral delivery and immunotoxins

Management of high-grade gliomas remains a complex challenge. Standard of care consists of microsurgical resection, chemotherapy and radiation, but despite these aggressive multimodality therapies the overall prognosis remains poor. A major focus of ongoing translational research studies is to develop novel therapeutic strategies that can maximize tumor cell eradication while minimizing collateral side effects. Particularly, biological intratumoral therapies have been the focus of new translational research efforts due to their inherent potential to be both dynamically adaptive and target specific. This two-part review will provide an overview of biological intratumoral therapies and summarize key advances and remaining challenges in intratumoral biological therapies for high-grade glioma. Part I focuses on discussion of the concepts of intratumoral delivery and immunotoxin therapies.

Convection-Enhanced Delivery: Connection to and Impact of Interstitial Fluid Flow

Convection-enhanced delivery (CED) is a method used to increase transport of therapeutics in and around brain tumors. CED works through locally applying a pressure differential to drive fluid flow throughout the tumor, such that convective forces dominate over diffusive transport. This allows therapies to bypass the blood brain barrier that would otherwise be too large or solely rely on passive diffusion. However, this also drives fluid flow out through the tumor bulk into surrounding brain parenchyma, which results in increased interstitial fluid (IF) flow, or fluid flow within extracellular spaces in the tissue. IF flow has been associated with altered transport of molecules, extracellular matrix rearrangement, and triggering of cellular motility through a number of mechanisms. Thus, the results of a simple method to increase drug delivery may have unintended consequences on tissue morphology. Clinically, prediction of dispersal of agents via CED is important to catheter design, placement, and implementation to optimize contact of tumor cells with therapeutic agent. Prediction software can aid in this problem, yet we wonder if there is a better way to predict therapeutic distribution based simply on IF flow pathways as determined from pre-intervention imaging. Overall, CED based therapy has seen limited success and we posit that integration and appreciation of altered IF flow may enhance outcomes. Thus, in this manuscript we both review the current state of the art in CED and IF flow mechanistic understanding and relate these two elements to each other in a clinical context.

Nanomaterial-based blood-brain-barrier (BBB) crossing strategies

Increasing attention has been paid to the diseases of central nervous system (CNS). The penetration efficiency of most CNS drugs into the brain parenchyma is rather limited due to the existence of blood-brain barrier (BBB). Thus, BBB crossing for drug delivery to CNS remains a significant challenge in the development of neurological therapeutics. Because of the advantageous properties (e.g., relatively high drug loading content, controllable drug release, excellent passive and active targeting, good stability, biodegradability, biocompatibility, and low toxicity), nanomaterials with BBB-crossability have been widely developed for the treatment of CNS diseases. This review summarizes the current understanding of the physiological structure of BBB, and provides various nanomaterial-based BBB-crossing strategies for brain delivery of theranostic agents, including intranasal delivery, temporary disruption of BBB, local delivery, cell penetrating peptide (CPP) mediated BBB-crossing, receptor mediated BBB-crossing, shuttle peptide mediated BBB-crossing, and cells mediated BBB-crossing. Clinicians, biologists, material scientists and chemists are expected to be interested in this review.

Convection-Enhanced Delivery in Malignant Gliomas: A Review of Toxicity and Efficacy

Malignant gliomas are undifferentiated or anaplastic gliomas. They remain incurable with a multitude of modalities, including surgery, radiation, chemotherapy, and alternating electric field therapy. Convection-enhanced delivery (CED) is a local treatment that can bypass the blood-brain barrier and increase the tumor uptake of therapeutic agents, while decreasing exposure to healthy tissues. Considering the multiple choices of drugs with different antitumor mechanisms, the supra-additive effect of concomitant radiation and chemotherapy, CED appears as a promising modality for the treatment of brain tumors. In this review, the CED-related toxicities are summarized and classified into immediate, early, and late side effects based on the time of onset, and local and systemic toxicities based on the location of toxicity. The efficacies of CED of various therapeutic agents including targeted antitumor agents, chemotherapeutic agents, radioisotopes, and immunomodulators are covered. The phase III trial PRECISE compares CED of IL13-PE38QQR, an interleukin-13 conjugated to Pseudomonas aeruginosa exotoxin A, to Gliadel® Wafer, a polymer loaded with carmustine. However, in this case, CED had no significant median survival improvement (11.3 months vs. 10 months) in patients with recurrent glioblastomas. In phase II studies, CED of recombinant poliovirus (PVSRIPO) had an overall survival of 21% vs. 14% for the control group at 24 months, and 21% vs. 4% at 36 months. CED of Tf-diphtheria toxin had a response rate of 35% in recurrent malignant gliomas patients. On the other hand, the TGF-β2 inhibitor Trabedersen, HSV-1-tk ganciclovir, and radioisotope 131I-chTNT-1/B mAb had a limited response rate. With this treatment, patients who received CED of the chemotherapeutic agent paclitaxel and immunomodulator, oligodeoxynucleotides containing CpG motifs (CpG-ODN), experienced intolerable toxicity. Toward the end of this article, an ideal CED treatment procedure is proposed and the methods for quality assurance of the CED procedure are discussed.

Improved efficacy against malignant brain tumors with EGFRwt/EGFRvIII targeting immunotoxin and checkpoint inhibitor combinations

BACKGROUND

D2C7-IT is a novel immunotoxin (IT) targeting wild-type epidermal growth factor receptor (EGFRwt) and mutant EGFR variant III (EGFRvIII) proteins in glioblastoma. In addition to inherent tumoricidal activity, immunotoxins induce secondary immune responses through the activation of T cells. However, glioblastoma-induced immune suppression is a major obstacle to an effective and durable immunotoxin-mediated antitumor response. We hypothesized that D2C7-IT-induced immune response could be effectively augmented in combination with αCTLA-4/αPD-1/αPD-L1 therapies in murine models of glioma.

METHODS

To study this, we overexpressed the D2C7-IT antigen, murine EGFRvIII (dmEGFRvIII), in established glioma lines, CT-2A and SMA560. The reactivity and therapeutic efficacy of D2C7-IT against CT-2A-dmEGFRvIII and SMA560-dmEGFRvIII cells was determined by flow cytometry and in vitro cytotoxicity assays, respectively. Antitumor efficacy of D2C7-IT was examined in immunocompetent, intracranial murine glioma models and the role of T cells was assessed by CD4+ and CD8+ T cell depletion. In vivo efficacy of D2C7-IT/αCTLA-4/αPD-1 monotherapy or D2C7-IT+αCTLA-4/αPD-1 combination therapy was evaluated in subcutaneous unilateral and bilateral CT-2A-dmEGFRvIII glioma-bearing immunocompetent mice. Further, antitumor efficacy of D2C7-IT+αCTLA-4/αPD-1/αPD-L1/αTim-3/αLag-3/αCD73 combination therapy was evaluated in intracranial CT-2A-dmEGFRvIII and SMA560-dmEGFRvIII glioma-bearing mice. Pairwise differences in survival curves were assessed using the generalized Wilcoxon test.

RESULTS

D2C7-IT effectively killed CT-2A-dmEGFRvIII (IC₅₀ = 0.47 ng/mL) and SMA560-dmEGFRvIII (IC₅₀ = 1.05 ng/mL) cells in vitro. Treatment of intracranial CT-2A-dmEGFRvIII and SMA560-dmEGFRvIII tumors with D2C7-IT prolonged survival (P = 0.0188 and P = 0.0057, respectively), which was significantly reduced by the depletion of CD4+ and CD8+ T cells. To augment antitumor immune responses, we combined D2C7-IT with αCTLA-4/αPD-1 in an in vivo subcutaneous CT-2A-dmEGFRvIII model. Tumor-bearing mice exhibited complete tumor regressions (4/10 in D2C7-IT+αCTLA-4 and 5/10 in D2C7-IT+αPD-1 treatment groups), and combination therapy-induced systemic antitumor response was effective against both dmEGFRvIII-positive and dmEGFRvIII-negative CT-2A tumors. In a subcutaneous bilateral CT-2A-dmEGFRvIII model, D2C7-IT+αCTLA-4/αPD-1 combination therapies showed dramatic regression of the treated tumors and measurable regression of untreated tumors. Notably, in CT-2A-dmEGFRvIII and SMA560-dmEGFRvIII intracranial glioma models, D2C7-IT+αPD-1/αPD-L1 combinations improved survival, and in selected cases generated cures and protection against tumor re-challenge.

CONCLUSIONS

These data support the development of D2C7-IT and immune checkpoint blockade combinations for patients with malignant glioma.

Advances in Targeting the Epidermal Growth Factor Receptor Pathway by Synthetic Products and Its Regulation by Epigenetic Modulators As a Therapy for Glioblastoma

Glioma is the most common primary tumor of the nervous system, and approximately 50% of patients exhibit the most aggressive form of the cancer, glioblastoma. The biological function of epidermal growth factor receptor (EGFR) in tumorigenesis and progression has been established in various types of cancers, since it is overexpressed, mutated, or dysregulated. Its overexpression has been shown to be associated with enhanced metastatic potential in glioblastoma, with EGFR at the top of a downstream signaling cascade that controls basic functional properties of glioblastoma cells such as survival, cell proliferation, and migration. Thus, EGFR is considered as an important therapeutic target in glioblastoma. Many anti-EGFR therapies have been investigated both in vivo and in vitro, making their way to clinical studies. However, in clinical trials, the potential efficacy of anti-EGFR therapies is low, primarily because of chemoresistance. Currently, a range of epigenetic drugs including histone deacetylase (HDAC) inhibitors, DNA methylation and histone inhibitors, microRNA, and different types of EGFR inhibitor molecules are being actively investigated in glioblastoma patients as therapeutic strategies. Here, we describe recent knowledge on the signaling pathways mediated by EGFR/EGFR variant III (EGFRvIII) with regard to current therapeutic strategies to target EGFR/EGFRvIII amplified glioblastoma.

Nanocarriers and nonviral methods for delivering antiangiogenic factors for glioblastoma therapy: the story so far

Angiogenesis, the formation of new blood vessels, is an essential component of glioblastoma (GB) progression. The development of angiogenesis inhibitor therapy, including treatments targeting vascular endothelial growth factor (VEGF) in particular, raised new hopes for the treatment of GB, but no Phase III clinical trial to date has reported survival benefits relative to standard treatment. There are several possible reasons for this limited efficacy, including VEGF-independent angiogenesis, induction of tumor invasion, and inefficient antiangiogenic factor delivery to the tumor. Efforts have been made to overcome these limitations by identifying new angiogenesis inhibitors that target angiogenesis through different mechanisms of action without inducing tumor invasion, and through the development of viral and nonviral delivery methods to improve antiangiogenic activity. Herein, we describe the nonviral methods, including convection-enhanced delivery devices, implantable polymer devices, nanocarriers, and cellular vehicles, to deliver antiangiogenic factors. We focus on those evaluated in intracranial (orthotopic) animal models of GB, the most relevant models of this disease, as they reproduce the clinical scenario of tumor progression and therapy response encountered in GB patients.

EGFR heterogeneity and implications for therapeutic intervention in glioblastoma

Patients with glioblastoma (GBM) have a universally poor prognosis and are in urgent need of effective treatment strategies. Recent advances in sequencing techniques unraveled the complete genomic landscape of GBMs and revealed profound heterogeneity of individual tumors even at the single cell level. Genomic profiling has detected epidermal growth factor receptor (EGFR) gene alterations in more than half of GBMs. Major genetic events include amplification and mutation of EGFR. Yet, treatment strategies targeting EGFR have thus far failed in clinical trials. In this review, we discuss the clonal and functional heterogeneity of EGFRs in GBM development and critically reassess the potential of EGFRs as therapeutic targets.

Targeted Delivery to Tumors: Multidirectional Strategies to Improve Treatment Efficiency

Malignant tumors are characterized by structural and molecular peculiarities providing a possibility to directionally deliver antitumor drugs with minimal impact on healthy tissues and reduced side effects. Newly formed blood vessels in malignant lesions exhibit chaotic growth, disordered structure, irregular shape and diameter, protrusions, and blind ends, resulting in immature vasculature; the newly formed lymphatic vessels also have aberrant structure. Structural features of the tumor vasculature determine relatively easy penetration of large molecules as well as nanometer-sized particles through a blood⁻tissue barrier and their accumulation in a tumor tissue. Also, malignant cells have altered molecular profile due to significant changes in tumor cell metabolism at every level from the genome to metabolome. Recently, the tumor interaction with cells of immune system becomes the focus of particular attention, that among others findings resulted in extensive study of cells with preferential tropism to tumor. In this review we summarize the information on the diversity of currently existing approaches to targeted drug delivery to tumor, including (i) passive targeting based on the specific features of tumor vasculature, (ii) active targeting which implies a specific binding of the antitumor agent with its molecular target, and (iii) cell-mediated tumor targeting.

Pseudomonas Exotoxin Immunotoxins and Anti-Tumor Immunity: From Observations at the Patient's Bedside to Evaluation in Preclinical Models

Immunotoxins are protein drugs composed of a targeting domain genetically fused to a protein toxin. One killing domain being explored is a truncated Pseudomonas exotoxin A (PE). PE based immunotoxins are designed to kill cells directly by inhibiting their ability to synthesize proteins. However, observations from clinical trials suggest that this alone cannot explain their anti-tumor activity. Here we discuss patterns of clinical responses suggesting that PE immunotoxins can provoke anti-tumor immunity, and review murine models that further support this ability. In addition, we describe our preclinical effort to develop a combination therapy of local PE immunotoxins with a systemic anti-CTLA-4 immune check point blocking antibody. The combination eradicated murine tumors and prolonged the survival of mice. Clinical trials that test the ability of immunotoxins to augment immunotherapy have been recently opened.

SS1P Immunotoxin Induces Markers of Immunogenic Cell Death and Enhances the Effect of the CTLA-4 Blockade in AE17M Mouse Mesothelioma Tumors

SS1P is an anti-mesothelin immunotoxin composed of a targeting antibody fragment genetically fused to a truncated fragment of Pseudomonas exotoxin A. Delayed responses reported in mesothelioma patients receiving SS1P suggest that anti-tumor immunity is induced. The goal of this study is to evaluate if SS1P therapy renders mesothelioma tumors more sensitive to cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) immune checkpoint blockade. We evaluated the ability of SS1P to induce adenosine triphosphate (ATP) secretion and calreticulin expression on the surface of AE17M mouse mesothelioma cells. Both properties are associated with immunogenic cell death. Furthermore, we treated these tumors with intra-tumoral SS1P and systemic CTLA-4. We found that SS1P increased the release of ATP from AE17M cells in a dose and time-dependent manner. In addition, SS1P induced calreticulin expression on the surface of AE17M cells. These results suggest that SS1P promotes immunogenic cell death and could sensitize tumors to anti-CTLA-4 based therapy. In mouse studies, we found that the combination of anti-CTLA-4 with intra-tumoral SS1P induced complete regressions in most mice and provided a statistically significant survival benefit compared to monotherapy. The surviving mice were protected from tumor re-challenge, indicating the development of anti-tumor immunity. These findings support the use of intra-tumoral SS1P in combination with anti-CTLA-4.

Receptor-Targeted Glial Brain Tumor Therapies

Among primary brain tumors, malignant gliomas are notably difficult to manage. The higher-grade tumors represent an unmet need in medicine. There have been extensive efforts to implement receptor-targeted therapeutic approaches directed against gliomas. These approaches include immunotherapies, such as vaccines, adoptive immunotherapy, and passive immunotherapy. Targeted cytotoxic radio energy and pro-drug activation have been designed specifically for brain tumors. The field of targeting through receptors progressed significantly with the discovery of an interleukin 13 receptor alpha 2 (IL-13RA2) as a tumor-associated receptor over-expressed in most patients with glioblastoma (GBM) but not in normal brain. IL-13RA2 has been exploited in novel experimental therapies with very encouraging clinical responses. Other receptors are specifically over-expressed in many patients with GBM, such as EphA2 and EphA3 receptors, among others. These findings are important in view of the heterogeneity of GBM tumors and multiple tumor compartments responsible for tumor progression and resistance to therapies. The combined targeting of multiple receptors in different tumor compartments should be a preferred way to design novel receptor-targeted therapeutic approaches in gliomas.

Convection-Enhanced Delivery of Polymeric Nanoparticles Encapsulating Chemotherapy in Canines with Spontaneous Supratentorial Tumors

BACKGROUND

Despite aggressive multimodal treatment, survival for patients with glioblastoma remains dismal. One obstacle to improving patient outcomes is the difficulty in delivering adequate therapeutic to the central nervous system due to the presence of the blood-brain barrier. Although direct drug infusion by convection-enhanced delivery (CED) can bypass the blood-brain barrier and facilitate delivery to intracranial tumors, determining the distribution of delivered therapeutic remains problematic. Image guidance is a strategy that can optimize the accuracy of therapeutic delivery.

METHODS

Here we performed an open-label clinical trial in 10 pet dogs with spontaneous intracranial tumors to examine the target coverage accuracy of delivering polymeric magnetite nanoparticles (PMNPs) encapsulating temozolomide (TMZ). A modified small animal frame was applied to the head of each subject, and PMNPs were delivered stereotactically to the center of the tumor. Magnetic resonance imaging (MRI) was performed immediately postoperatively to examine PMNP distribution, and the animals were followed until death.

RESULTS

Nine of the 10 dogs underwent PMNP infusion without complications. No infusate backflow was observed during any procedure. In 70% of the cases, the infusion accurately targeted the tumor mass, as determined by the presence of PMNP signal in the tumor on immediate postoperative MRI.

CONCLUSIONS

These data suggest that CED of PMNPs carrying TMZ is safe in dogs with intracranial tumors and can lead to nanoparticle distribution in the region of the target. Image guidance is an important adjunct to CED, because distribution is unpredictable, with the potential for missed target delivery.

Duocarmycin SA, a potent antitumor antibiotic, sensitizes glioblastoma cells to proton radiation

New treatment modalities for glioblastoma multiforme (GBM) are urgently needed. Proton therapy is considered one of the most effective forms of radiation therapy for GBM. DNA alkylating agents such as temozolomide (TMZ) are known to increase the radiosensitivity of GBM to photon radiation. TMZ is a fairly impotent agent, while duocarmycin SA (DSA) is an extremely potent cytotoxic agent capable of inducing a sequence-selective alkylation of duplex DNA. Here, the effects of sub-nM concentrations of DSA on the radiosensitivity of a human GBM cell line (U-138) to proton irradiation were examined. Radiation sensitivity was determined by viability, apoptosis, necrosis and clonogenic assays. DSA concentrations as low as 0.001 nM significantly sensitized U-138 cells to proton irradiation. DSA demonstrates synergistic cytotoxicity against GBM cells treated with proton radiation in vitro, which may represent a novel therapeutic alternative for the treatment of GBM.

Evidence and context of use for contrast enhancement as a surrogate of disease burden and treatment response in malignant glioma

The use of contrast enhancement within the brain on CT or MRI has been the gold standard for diagnosis and therapeutic response assessment in malignant gliomas for decades. The use of contrast enhancing tumor size, however, remains controversial as a tool for accurately diagnosing and assessing treatment efficacy in malignant gliomas, particularly in the current, quickly evolving therapeutic landscape. The current article consolidates overwhelming evidence from hundreds of studies in the field of neuro-oncology, providing the necessary evidence base and specific contexts of use for consideration of contrast enhancing tumor size as an appropriate surrogate biomarker for disease burden and as a tool for measuring treatment response in malignant glioma, including glioblastoma.

Mesothelin-targeted immunotoxin RG7787 has synergistic anti-tumor activity when combined with taxanes

Recombinant immunotoxins (RITs) are antibody-based therapeutics that carry a toxin payload. The RG7787 RIT targets the cancer antigen mesothelin to deliver a recombinantly-engineered, reduced immunogenicity variant of Pseudomonas exotoxin A (PE) to the cytosol where it inhibits protein synthesis. Here we demonstrate that maximal doses of RG7787 temporarily halt growth of pancreatic cancer tumor xenografts, similar to the approved drugs gemcitabine and nab-paclitaxel, however, combination of the RIT with nab-paclitaxel produces durable complete regressions in most mice. Synergy between taxane and anti-MSLN RITs has been previously demonstrated in mouse models, but direct interaction of the combination in cell culture was not observed. Here, we show that this favorable interaction occurs in cell culture, is dependent on the dose and duration of RG7787 exposure, requires the catalytically active PE, and still occurs with RIT targeting a non-MSLN surface antigen. Unexpectedly, the combination does not increase RG7787-mediated protein synthesis inhibition nor perturb downstream apoptotic markers of RIT-mediated killing, but does augment levels of acetylated tubulin, a marker of taxane activity. Taken together, these data suggest that PE increases cell sensitivity to taxane-mediated killing by increasing taxane-mediated microtubule stability and priming cells for apoptosis by decreasing levels of the pro-survival factor Mcl-1.

Antibody-drug conjugates in glioblastoma therapy: the right drugs to the right cells

Glioblastomas are high-grade brain tumours with a poor prognosis and, currently, few available therapeutic options. This lack of effective treatments has been linked to diverse factors, including target selection, tumour heterogeneity and poor penetrance of therapeutic agents through the blood-brain barrier and into tumours. Therapies using monoclonal antibodies, alone or linked to cytotoxic payloads, have proved beneficial for patients with different solid tumours; these approaches are currently being explored in patients with glioblastoma. In this Review, we summarise clinical data regarding antibody-drug conjugates (ADCs) against a variety of targets in glioblastoma, and compare the efficacy and toxicity of targeting EGFR with ADCs versus naked antibodies in order to illustrate key aspects of the use of ADCs in this malignancy. Finally, we discuss the complex challenges related to the biology and mutational changes of glioblastoma that can affect the use of ADC-based therapies in patients with this disease, and highlight potential strategies to improve efficacy.

Recombinant Immunotoxin Therapy of Glioblastoma: Smart Design, Key Findings, and Specific Challenges

Recombinant immunotoxins (RITs) refer to a group of recombinant protein-based therapeutics, which consists of two components: an antibody variable fragment or a specific ligand that allows RITs to bind specifically to target cells and an engineered toxin fragment that kills the target cells upon internalization. To date, over 1,000 RITs have been generated and significant success has been achieved in the therapy of hematological malignancies. However, the immunogenicity and off-target toxicities of RITs remain as significant barriers for their application to solid tumor therapy. A group of RITs have also been generated for the treatment of glioblastoma multiforme, and some have demonstrated evidence of tumor response and an acceptable profile of toxicity and safety in early clinical trials. Different from other solid tumors, how to efficiently deliver the RITs to intracranial tumors is more critical and needs to be solved urgently. In this article, we first review the design and expression of RITs, then summarize the key findings in the preclinical and clinical development of RIT therapy of glioblastoma multiforme, and lastly discuss the specific issues that still remain to forward RIT therapy to clinical practice.

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

Background

The pan-histone deacetylase inhibitor panobinostat is a potential therapy for malignant glioma, but it is water insoluble and does not cross the blood–brain barrier when administered systemically. In this article, we describe the in vitro and in vivo efficacy of a novel water-soluble nano-micellar formulation of panobinostat designed for administration by convection enhanced delivery (CED).

Materials and methods

The in vitro efficacy of panobinostat-loaded nano-micelles against rat F98, human U87-MG and M059K glioma cells and against patient-derived glioma stem cells was measured using a cell viability assay. Nano-micelle distribution in rat brain was analyzed following acute CED using rhodamine-labeled nano-micelles, and toxicity was assayed using immunofluorescent microscopy and synaptophysin enzyme-linked immunosorbent assay. We compared the survival of the bioluminescent syngenic F98/Fischer344 rat glioblastoma model treated by acute CED of panobinostat-loaded nano-micelles with that of untreated and vehicle-only-treated controls.

Results

Nano-micellar panobinostat is cytotoxic to rat and human glioma cells in vitro in a dose-dependent manner following short-time exposure to drug. Fluorescent rhodamine-labelled nano-micelles distribute with a volume of infusion/volume of distribution (Vi/Vd) ratio of four and five respectively after administration by CED. Administration was not associated with any toxicity when compared to controls. CED of panobinostat-loaded nano-micelles was associated with significantly improved survival when compared to controls (n=8 per group; log-rank test, P<0.001). One hundred percent of treated animals survived the 60-day experimental period and had tumour response on post-mortem histological examination.

Conclusion

CED of nano-micellar panobinostat represents a potential novel therapeutic option for malignant glioma and warrants translation into the clinic.

Convection-Enhanced Delivery for Diffuse Intrinsic Pontine Glioma Treatment

Convection-enhanced delivery (CED) is a technique designed to deliver drugs directly into the brain or tumors. Its ability to bypass the blood-brain barrier (BBB), one of the major hurdles in delivering drugs to the brain, has made it a promising drug delivery method for the treatment of primary brain tumors. A number of clinical trials utilizing CED of various therapeutic agents have been conducted to treat patients with supratentorial high-grade gliomas. Significant responses have been observed in certain patients in all of these trials. However, the insufficient ability to monitor drug distribution and pharmacokinetics hampers CED from achieving its potentials on a larger scale. Brainstem CED for diffuse intrinsic pontine glioma (DIPG) treatment is appealing because this tumor is compact and has no definitive treatment. The safety of brainstem CED has been established in small and large animals, and recently in early stage clinical trials. There are a few current clinical trials of brainstem CED in treating DIPG patients using targeted macromolecules such as antibodies and immunotoxins. Future advances for CED in DIPG treatment will come from several directions including: choosing the right agents for infusion; developing better agents and regimen for DIPG infusion; improving instruments and technique for easier and accurate surgical targeting and for allowing multisession or prolonged infusion to implement optimal time sequence; and better understanding and control of drug distribution, clearance and time sequence. CED-based therapies for DIPG will continue to evolve with new understanding of the technique and the disease.