Creation of an NCI comparative brain tumor consortium: informing the translation of new knowledge from canine to human brain tumor patients

Cancer vaccines: Target antigens, vaccine platforms and preclinical models

This review provides a comprehensive overview of the evolving landscape of cancer vaccines, highlighting their potential to revolutionize tumor prevention. Building on the success of vaccines against virus-related cancers, such as HPV- and HBV-associated cervical and liver cancers, the current challenge is to extend these achievements to the prevention of non-viral tumors and the treatment of preneoplastic or early neoplastic lesions. This review analyzes the critical aspects of preventive anti-cancer vaccination, focusing on the choice of target antigens, the development of effective vaccine platforms and technologies, and the use of various model systems for preclinical testing, from laboratory rodents to companion animals.

A diffusion tensor imaging white matter atlas of the domestic canine brain

There is increasing reliance on magnetic resonance imaging (MRI) techniques in both research and clinical settings. However, few standardized methods exist to permit comparative studies of brain pathology and function. To help facilitate these studies, we have created a detailed, MRI-based white matter atlas of the canine brain using diffusion tensor imaging. This technique, which relies on the movement properties of water, permits the creation of a three-dimensional diffusivity map of white matter brain regions that can be used to predict major axonal tracts. To generate an atlas of white matter tracts, thirty neurologically and clinically normal dogs underwent MRI imaging under anesthesia. High-resolution, three-dimensional T1-weighted sequences were collected and averaged to create a population average template. Diffusion-weighted imaging sequences were collected and used to generate diffusivity maps, which were then registered to the T1-weighted template. Using these diffusivity maps, individual white matter tracts-including association, projection, commissural, brainstem, olfactory, and cerebellar tracts-were identified with reference to previous canine brain atlas sources. To enable the use of this atlas, we created downloadable overlay files for each white matter tract identified using manual segmentation software. In addition, using diffusion tensor imaging tractography, we created tract files to delineate major projection pathways. This comprehensive white matter atlas serves as a standard reference to aid in the interpretation of quantitative changes in brain structure and function in clinical and research settings.

Cancer Immunotherapy

The enhanced understanding of immunology experienced over the last 5 decades afforded through the tools of molecular biology has recently translated into cancer immunotherapy becoming one of the most exciting and rapidly expanding fields. Human cancer immunotherapy is now recognized as one of the pillars of treatment alongside surgery, radiation, and chemotherapy. The field of veterinary cancer immunotherapy has also rapidly advanced in the last decade with a handful of commercially available products and a plethora of investigational cancer immunotherapies, which will hopefully expand our veterinary oncology treatment toolkit over time.

Phase I/II Trial of Urokinase Plasminogen Activator-Targeted Oncolytic Newcastle Disease Virus for Canine Intracranial Tumors

Neurotropic oncolytic viruses are appealing agents to treat brain tumors as they penetrate the blood-brain barrier and induce preferential cytolysis of neoplastic cells. The pathobiological similarities between human and canine brain tumors make immunocompetent dogs with naturally occurring tumors attractive models for the study of oncolytic virotherapies. In this dose-escalation/expansion study, an engineered Lasota NDV strain targeting the urokinase plasminogen activator system (rLAS-uPA) was administered by repetitive intravenous infusions to 20 dogs with intracranial tumors with the objectives of characterizing toxicities, immunologic responses, and neuroradiological anti-tumor effects of the virus for up to 6 months following treatment. Dose-limiting toxicities manifested as fever, hematologic, and neurological adverse events, and the maximum tolerated dose (MTD) of rLAS-uPA was 2 × 107 pfu/mL. Mild adverse events, including transient infusion reactions, diarrhea, and fever were observed in 16/18 of dogs treated at or below MTD. No infectious virus was recoverable from body fluids. Neutralizing antibodies to rLAS-uPA were present in all dogs by 2 weeks post-treatment, and viral genetic material was detected in post-treatment tumors from six dogs. Tumor volumetric reductions occurred in 2/11 dogs receiving the MTD. Systemically administered rLAS-uPA NDV was safe and induced anti-tumor effects in canine brain tumors, although modifications to evade host anti-viral immunity are needed to optimize this novel therapy.

Domestic Animal Models of Central Nervous System Tumors: Focus on Meningiomas

Intracranial primary tumors (IPTs) are aggressive forms of malignancies that cause high mortality in both humans and domestic animals. Meningiomas are frequent adult IPTs in humans, dogs, and cats, and both benign and malignant forms cause a decrease in life quality and survival. Surgery is the primary therapeutic approach to treat meningiomas, but, in many cases, it is not resolutive. The chemotherapy and targeted therapy used to treat meningiomas also display low efficacy and many side effects. Therefore, it is essential to find novel pharmacological approaches to increase the spectrum of therapeutic options for meningiomas. This review analyzes the similarities between human and domestic animal (dogs and cats) meningiomas by evaluating the molecular and histological characteristics, diagnosis criteria, and treatment options and highlighting possible research areas to identify novel targets and pharmacological approaches, which are useful for the diagnosis and therapy of this neoplasia to be used in human and veterinary medicine.

A review of primary central nervous system neoplasms of cats

Primary central nervous system (CNS) neoplasms are uncommonly diagnosed in cats. The majority of primary feline CNS neoplasms described in the veterinary literature consist of meningioma and glioma occurring mainly in the brain and less often in the spinal cord. Although most neoplasms can be diagnosed based on routine histologic evaluation, less typical tumors need to be further characterized using immunohistochemistry. This review compiles the relevant information about the most common primary CNS neoplasms of cats available in the veterinary literature, aiming to serve as a converging source of information for the topic.

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.

Pre-clinical models for evaluating glioma targeted immunotherapies

Gliomas have an extremely poor prognosis in both adult and pediatric patient populations as these tumors are known to grow aggressively and respond poorly to standard of care treatment. Currently, treatment for gliomas involves surgical resection followed by chemoradiation therapy. However, some gliomas, such as diffuse midline glioma, have more limited treatment options such as radiotherapy alone. Even with these interventions, the prognosis for those diagnosed with a glioma remains poor. Immunotherapy is highly effective for some cancers and there is great interest in the development of effective immunotherapies for the treatment of gliomas. Clinical trials evaluating the efficacy of immunotherapies targeted to gliomas have largely failed to date, and we believe this is partially due to the poor choice in pre-clinical mouse models that are used to evaluate these immunotherapies. A key consideration in evaluating new immunotherapies is the selection of pre-clinical models that mimic the glioma-immune response in humans. Multiple pre-clinical options are currently available, each one with their own benefits and limitations. Informed selection of pre-clinical models for testing can facilitate translation of more promising immunotherapies in the clinical setting. In this review we plan to present glioma cell lines and mouse models, as well as alternatives to mouse models, that are available for pre-clinical glioma immunotherapy studies. We plan to discuss considerations of model selection that should be made for future studies as we hope this review can serve as a guide for investigators as they choose which model is best suited for their study.

Developing Scotland's First Green Health Prescription Pathway: A One-Stop Shop for Nature-Based Intervention Referrals

Introduction

Lifestyle modifications are part of comprehensive treatment plans to help manage the symptoms of pre-existing chronic conditions. However, behavior change is notoriously difficult as patients often lack the necessary support. The present manuscript outlines the development of a Green Health Prescription pathway that was designed to link patients with appropriate lifestyle interventions (i.e., nature-based interventions) and to support attendance. Strengths, Weaknesses, Opportunities, and Threats (SWOT) analysis was undertaken in three focus groups (i.e., National Health Service healthcare professionals, service-users, and nature-based intervention delivery partners) to highlight areas of strength and weakness within the proposed pathway prior to delivery. The SWOT analyses revealed that the pathway was supported by all three focus groups. Weaknesses and threats were identified including sustainability of nature-based interventions in terms of funding, the need to connect patients with appropriate interventions based on their physical and mental health needs, and the requirement to have a “one-stop shop” for information to ensure that the pathway was accessible for all service-users and healthcare professionals. Results were addressed and considered throughout the development of the pathway.

Discussion

The Green Health Prescription pathway was launched in 2019 and gave patients the ability to receive a prescription from a healthcare professional, community service, or to self-refer. The pathway allows patients to contact a consultant, via a telephone service, who is trained to match them with a programme that the patient believes will be enjoyable and that fits their treatment needs. Data collection to assess the efficacy of the pathway is ongoing.

Use of Handheld Raman Spectroscopy for Intraoperative Differentiation of Normal Brain Tissue From Intracranial Neoplasms in Dogs

The aim of this study was to assess feasibility and accuracy of a hand-held, intraoperative Raman spectroscopy device as a neuronavigation aid to accurately detect neoplastic tissue from adjacent normal gray and white matter. Although Raman spectra are complicated fingerprints of cell signature, the relative shift corresponding to lipid and protein content (2,845 and 2,930 cm−1, respectively), can provide a rapid assessment of whether tissue is normal white or gray matter vs. neoplasia for real-time guidance of tumor resection. Thirteen client-owned dogs were initially enrolled in the study. Two were excluded from final analysis due to incomplete data acquisition or lack of neoplastic disease. The diagnoses of the remaining 11 dogs included six meningiomas, two histiocytic sarcomas, and three gliomas. Intraoperatively, interrogated tissues included normal gray and/or white matter and tumor. A total of five Raman spectra readings were recorded from the interrogated tissues, and samples were submitted for confirmation of Raman spectra by histopathology. A resultant total of 24 samples, 13 from neoplastic tissue and 11 from normal gray or white matter, were used to calculate sensitivity and specificity of Raman spectra compared to histopathology. The handheld Raman spectroscopy device had sensitivity of 85.7% and specificity of 90% with a positive predictive value of 92.3% and negative predictive value of 81.6%. The Raman device was feasible to use intraoperatively with rapid interpretation of spectra. Raman spectroscopy may be useful for intraoperative guidance of tumor resection.

European Mistletoe (Viscum album) Extract Is Cytotoxic to Canine High-Grade Astrocytoma Cells In Vitro and Has Additive Effects with Mebendazole

Malignant gliomas are associated with extremely poor clinical outcomes in both humans and dogs, and novel therapies are needed. Glioma-bearing canine patients may serve as promising preclinical models for human therapies, including complementary medicine. The objective of this study was to evaluate the effects of mistletoe extract (Viscum album) alone and in combination with mebendazole in an in vitro model of canine high-grade astrocytoma using the cell line SDT-3G. SDT-3G cells were exposed to a range of concentrations of mistletoe extract alone to obtain an IC50. In separate experiments, cells were exposed to mebendazole at a previously determined IC50 (0.03 µM) alone or in conjunction with varying concentrations of mistletoe extract to determine the additive effects. The IC50 for mistletoe alone was 5.644 ± 0.09 SD μg/mL. The addition of mistletoe at 5 μg/mL to mebendazole at 0.03 µM led to increased cell death compared to what would be expected for each drug separately. The cytotoxicity of mistletoe in vitro and its additive effect with mebendazole support future expanded in vitro and in vivo studies in dogs and supply early evidence that this may be a useful adjunct therapeutic agent for use in glioma-bearing dogs. To the authors’ knowledge, this is the first published report of Viscum album extract in canine glioma.

Conjugation of glucosylated polymer chains to checkpoint blockade antibodies augments their efficacy and specificity for glioblastoma

Because of the blood-tumour barrier and cross-reactivity with healthy tissues, immune checkpoint blockade therapy against glioblastoma has inadequate efficacy and is associated with a high risk of immune-related adverse events. Here we show that anti-programmed death-ligand 1 antibodies conjugated with multiple poly(ethylene glycol) (PEG) chains functionalized to target glucose transporter 1 (which is overexpressed in brain capillaries) and detaching in the reductive tumour microenvironment augment the potency and safety of checkpoint blockade therapy against glioblastoma. In mice bearing orthotopic glioblastoma tumours, a single dose of glucosylated and multi-PEGylated antibodies reinvigorated antitumour immune responses, induced immunological memory that protected the animals against rechallenge with tumour cells, and suppressed autoimmune responses in the animals' healthy tissues. Drug-delivery formulations leveraging multivalent ligand interactions and the properties of the tumour microenvironment to facilitate the crossing of blood-tumour barriers and increase drug specificity may enhance the efficacy and safety of other antibody-based therapies.

Proceedings of the 2021 National Toxicology Program Satellite Symposium

The 2021 annual National Toxicology Program (NTP) Satellite Symposium, entitled "Pathology Potpourri," was the 20th anniversary of the symposia and held virtually on June 25th, in advance of the Society of Toxicologic Pathology's 40th annual meeting. The goal of this symposium was to present and discuss challenging diagnostic pathology and/or nomenclature issues. This article presents summaries of the speakers' talks along with select images that were presented to the audience for voting and discussion. Various lesions and topics covered during the symposium included differentiation of canine oligodendroglioma, astrocytoma, and undefined glioma with presentation of the National Cancer Institute's updated diagnostic terminology for canine glioma; differentiation of polycystic kidney, dilated tubules and cystic tubules with a discussion of human polycystic kidney disease; a review of various rodent nervous system background lesions in control animals from NTP studies with a focus on incidence rates and potential rat strain differences; vehicle/excipient-related renal lesions in cynomolgus monkeys with a discussion on the various cyclodextrins and their bioavailability, toxicity, and tumorigenicity; examples of rodent endometrial tumors including intestinal differentiation in an endometrial adenocarcinoma that has not previously been reported in rats; a review of various rodent adrenal cortex lesions including those that represented diagnostic challenges with multiple processes such as vacuolation, degeneration, necrosis, hyperplasia, and hypertrophy; and finally, a discussion of diagnostic criteria for uterine adenomyosis, atypical hyperplasia, and adenocarcinoma in the rat.

Models for Translational Proton Radiobiology-From Bench to Bedside and Back

The number of proton therapy centers worldwide are increasing steadily, with more than two million cancer patients treated so far. Despite this development, pending questions on proton radiobiology still call for basic and translational preclinical research. Open issues are the on-going discussion on an energy-dependent varying proton RBE (relative biological effectiveness), a better characterization of normal tissue side effects and combination treatments with drugs originally developed for photon therapy. At the same time, novel possibilities arise, such as radioimmunotherapy, and new proton therapy schemata, such as FLASH irradiation and proton mini-beams. The study of those aspects demands for radiobiological models at different stages along the translational chain, allowing the investigation of mechanisms from the molecular level to whole organisms. Focusing on the challenges and specifics of proton research, this review summarizes the different available models, ranging from in vitro systems to animal studies of increasing complexity as well as complementing in silico approaches.

The One Medicine concept: its emergence from history as a systematic approach to re-integrate human and veterinary medicine

The COVID-19 pandemic has resulted in the global recognition for greater inter-disciplinary and multi-disciplinary working, and the need for systematic approaches which recognise the interconnectedness and interactions between human, animal and environmental health. The notion of such a One Team/One science approach is perhaps best exemplified by the One Health concept, a systematic approach which is rapidly entering into the mainstream. However, the concept of One Health, as we presently know it, originated from One Medicine, a notion which is much older and which emerged to promote collaboration between the human and veterinary medicine professions and the allied health/scientific disciplines. Whilst One Medicine is perhaps better known by the veterinary community, some misconceptions of what One Medicine is have arisen. Therefore, this review introduces this emerging concept and how it can help to address overlapping (communicable and non-communicable disease) health challenges faced by both human and veterinary medicine.

Man's best friend in life and death: scientific perspectives and challenges of dog brain banking

Biobanking refers to the systematic collection, storage, and distribution of pre- or post-mortem biological samples derived from volunteer donors. The demand for high-quality human specimens is clearly demonstrated by the number of newly emerging biobanking facilities and large international collaborative networks. Several animal species are relevant today in medical research; therefore, similar initiatives in comparative physiology could be fruitful. Dogs, in particular, are gaining increasing attention in translational research on complex phenomena, like aging, cancer, and neurodegenerative diseases. Therefore, biobanks gathering and storing dog biological materials together with related data could play a vital role in translational and veterinary research projects. To achieve these aims, a canine biobank should meet the same standards in sample quality and data management as human biobanks and should rely on well-designed collaborative networks between different professionals and dog owners. While efforts to create dog biobanks could face similar financial and technical challenges as their human counterparts, they can widen the spectrum of successful collaborative initiatives towards a better picture of dogs’ physiology, disease, evolution, and translational potential. In this review, we provide an overview about the current state of dog biobanking and introduce the “Canine Brain and Tissue Bank” (CBTB)—a new, large-scale collaborative endeavor in the field.

Translational oncotargets for immunotherapy: From pet dogs to humans

Preclinical studies in rodent models have been a pivotal role in human clinical research, but many of them fail in the translational process. Spontaneous tumors in pet dogs have the potential to bridge the gap between preclinical models and human clinical trials. Their natural occurrence in an immunocompetent system overcome the limitations of preclinical rodent models. Due to its reasonable cellular, molecular, and genetic homology to humans, the pet dog represents a valuable model to accelerate the translation of preclinical studies to clinical trials in humans, actually with benefits for both species. Moreover, their unique genetic features of breeding and breed-related mutations have contributed to assess and optimize therapeutics in individuals with different genetic backgrounds. This review aims to outline four main immunotherapy approaches - cancer vaccines, adaptive T-cell transfer, antibodies, and cytokines -, under research in veterinary medicine and how they can serve the clinical application crosstalk with humans.

Phase I trial of convection-enhanced delivery of IL13RA2 and EPHA2 receptor targeted cytotoxins in dogs with spontaneous intracranial gliomas

Background

The interleukin-13 receptor alpha 2 (IL13RA2) and ephrin type A receptor 2 (EPHA2) are attractive therapeutic targets, being expressed in ~90% of canine and human gliomas, and absent in normal brain. Clinical trials using an earlier generation IL-13 based cytotoxin showed encouraging clinical effects in human glioma, but met with technical barriers associated with the convection-enhanced delivery (CED) method. In this study, IL-13 mutant and ephrin A1 (EFNA1)–based bacterial cytotoxins targeted to IL13RA2 and EPHA2 receptors, respectively, were administered locoregionally by CED to dogs with intracranial gliomas to evaluate their safety and preliminary efficacy.

Methods

In this phase I, 3 + 3 dose escalation trial, cytotoxins were infused by CED in 17 dogs with gliomas expressing IL13RA2 or EPHA2 receptors. CED was performed using a shape-fitting therapeutic planning algorithm, reflux-preventing catheters, and real-time intraoperative MRI monitoring. The primary endpoint was to determine the maximum tolerated dose of the cytotoxic cocktail in dogs with gliomas.

Results

Consistent intratumoral delivery of the cytotoxic cocktail was achieved, with a median target coverage of 70% (range, 40–94%). Cytotoxins were well tolerated over a dose range of 0.012–1.278 μg/mL delivered to the target volume (median, 0.099 μg/mL), with no dose limiting toxicities observed. Objective tumor responses, up to 94% tumor volume reduction, were observed in 50% (8/16) of dogs, including at least one dog in each dosing cohort >0.05 μg/mL.

Conclusions

This study provides preclinical data fundamental to the translation of this multireceptor targeted therapeutic approach to the human clinic.

Pre-clinical tumor models of primary brain tumors: Challenges and opportunities

Primary brain tumors are a heterogeneous group of malignancies that originate in cells of the central nervous system. A variety of models tractable for preclinical studies have been developed to recapitulate human brain tumors, allowing us to understand the underlying pathobiology and explore potential treatments. However, many promising therapeutic strategies identified using preclinical models have shown limited efficacy or failed at the clinical trial stage. The inability to develop therapeutic strategies that significantly improve survival rates in patients highlight the compelling need to revisit the design of currently available animal models and explore the use of new models that allow us to bridge the gap between promising preclinical findings and clinical translation. In this review, we discuss current strategies used to model glioblastoma, the most malignant brain tumor in adults and highlight the shortcomings of specific models that must be circumvented for the development of innovative therapeutic strategies.

Canine Gliomatosis Cerebri: Morphologic and Immunohistochemical Characterization Is Supportive of Glial Histogenesis

Gliomatosis cerebri (GC) is a glioma subtype with diffuse neuroparenchymal infiltration without architectural distortion. GC was first used in human neuropathology and remained controversial until its elimination from the diagnostic lexicon in 2016. GC is currently defined as a diffuse growth pattern of glioma rather than a distinct entity. In this article, we characterize 24 cases of canine GC and classify these neoplasms as diffuse gliomas. Selected cases of canine GC were reviewed and immunolabeled for oligodendrocyte lineage transcription factor 2 (Olig2), glial fibrillary acidic protein (GFAP), and 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase). The mean age of affected dogs was 7 years, and 9 were brachycephalic. Gross lesions (8 cases) consisted mainly of parenchymal swelling. Histologically, of the 24 cases, there was widespread infiltration of neoplastic cells with astrocytic (12 cases), oligodendroglial (8 cases), or mixed morphology (4 cases) in the brain (18 cases), spinal cord (4 cases), or both (2 cases). Secondary structures occurred across different tumor grades and were not restricted to high-grade neoplasms. Astrocytic neoplasms had moderate nuclear immunolabeling for Olig2 and robust cytoplasmic immunolabeling for GFAP. Oligodendroglial neoplasms had robust nuclear immunolabeling for Olig2, moderate or absent cytoplasmic immunolabeling for GFAP, and moderate cytoplasmic immunolabeling for CNPase. Tumors with mixed morphology had robust nuclear immunolabeling for Olig2 and variable cytoplasmic immunolabeling for GFAP and CNPase. Morphologic and immunohistochemical features confirmed a glial histogenesis for all tumors and allowed for their classification as diffuse, low- or high-grade astrocytoma; oligodendroglioma; or undefined glioma. Further research is needed to confirm or refute the hypothesis that canine GC represents an infiltrative growth pattern of canine glioma.

Development and Evaluation of a Caregiver Reported Quality of Life Assessment Instrument in Dogs With Intracranial Disease

In veterinary medicine, quality of life (QOL) assessment instruments, which are important components of the holistic evaluation of treatment success, have largely not included organ-specific concerns that may be broadly relevant to caregivers of dogs with intracranial disease. The objective of this study was to identify core questionnaire items and domains that contribute to health-related QOL (HRQOL) in dogs with intracranial disease. A questionnaire was developed that contained 39 QOL-related items encompassing physical, social/companionship, and brain-specific domains associated with the treatment of dogs with intracranial disease, and administered to caregivers of 56 dogs diagnosed with genetic, inflammatory, neoplastic, traumatic, and vascular brain diseases, 52 healthy dogs, and 20 dogs with non-neurological illnesses. Clinician derived functional measures of each dog's health status including chronic pain, Karnofsky performance, and modified Glasgow coma scale scores were also recorded. Principal component analysis refined the final questionnaire, termed the CanBrainQOL-24, to 24-items within the three domains with a minimum Cronbach's alpha of 0.7, indicative of good internal consistency. The CanBrainQOL-24 discriminated between healthy and diseased dogs. Physical and brain-specific domains were significantly different between dogs with intracranial and non-neurological diseases. Significant correlations were observed between owner reported visual analog scores and CanBrainQOL-24 scores, as well between clinician derived functional status measures and owner reported QOL. The CanBrainQOL-24 contains core questions relevant to caregiver assessment of HRQOL in dogs with a variety of intracranial diseases, and provides information that is complementary to clinician derived functional outcome measures.

Predictive modeling for cancer drug discovery using canine models

INTRODUCTION

Rodent models of cancer lack many features associated with the disease in humans. Because dogs closely share an environment with humans, as well as comparable pathophysiology of cancer, they represent a powerful model with which to study novel approaches to cancer treatment.

AREAS COVERED

The authors summarize the weaknesses of rodent models of cancer and the ongoing need for better animal models with which to study potential therapeutic approaches. The homology of cancer in dogs and humans is described, along with examples specific to several common cancer types.

EXPERT OPINION

Laboratory mice and rats will continue to play a central role in cancer research; however, because of a variety of limitations, pet dogs with spontaneous cancer offer unique opportunities for research and should be included in the preclinical development of therapeutic compounds. Environmental homology between dogs and humans, along with biological and molecular similarities present circumstances that strengthen the translational rigor of studies conducted using canine patients. Progress will depend on a sufficient number of dogs to be diagnosed with cancer and available for use in studies; and essential to this will be the availability of enhanced resources for diagnosis of cancer in canine patients and reliable coordination between research scientists, veterinarians, and physicians.

Differential Expression of miRNAs in Hypoxia ("HypoxamiRs") in Three Canine High-Grade Glioma Cell Lines

Dogs with spontaneous high-grade gliomas increasingly are being proposed as useful large animal pre-clinical models for the human disease. Hypoxia is a critical microenvironmental condition that is common in both canine and human high-grade gliomas and drives increased angiogenesis, chemo- and radioresistance, and acquisition of a stem-like phenotype. Some of this effect is mediated by the hypoxia-induced expression of microRNAs, small (~22 nucleotides long), non-coding RNAs that can modulate gene expression through interference with mRNA translation. Using an in vitro model with three canine high-grade glioma cell lines (J3T, SDT3G, and G06A) exposed to 72 h of 1.5% oxygen vs. standard 20% oxygen, we examined the global “hypoxamiR” profile using small RNA-Seq and performed pathway analysis for targeted genes using both Panther and NetworkAnalyst. Important pathways include many that are well-established as being important in glioma biology, general cancer biology, hypoxia, angiogenesis, immunology, and stem-ness, among others. This work provides the first examination of the effect of hypoxia on miRNA expression in the context of canine glioma, and highlights important similarities with the human disease.

Comparative Molecular Life History of Spontaneous Canine and Human Gliomas

Sporadic gliomas in companion dogs provide a window on the interaction between tumorigenic mechanisms and host environment. We compared the molecular profiles of canine gliomas with those of human pediatric and adult gliomas to characterize evolutionarily conserved mammalian mutational processes in gliomagenesis. Employing whole-genome, exome, transcriptome, and methylation sequencing of 83 canine gliomas, we found alterations shared between canine and human gliomas such as the receptor tyrosine kinases, TP53 and cell-cycle pathways, and IDH1 R132. Canine gliomas showed high similarity with human pediatric gliomas per robust aneuploidy, mutational rates, relative timing of mutations, and DNA-methylation patterns. Our cross-species comparative genomic analysis provides unique insights into glioma etiology and the chronology of glioma-causing somatic alterations.

Advanced Cancer Imaging Applied in the Comparative Setting

The potential for companion (pet) species with spontaneously arising tumors to act as surrogates for preclinical development of advanced cancer imaging technologies has become more apparent in the last decade. The utility of the companion model specifically centers around issues related to body size (including spatial target/normal anatomic characteristics), physical size and spatial distribution of metastasis, tumor heterogeneity, the presence of an intact syngeneic immune system and a syngeneic tumor microenvironment shaped by the natural evolution of the cancer. Companion species size allows the use of similar equipment, hardware setup, software, and scan protocols which provide the opportunity for standardization and harmonization of imaging operating procedures and quality assurance across imaging protocols, imaging hardware, and the imaged species. Murine models generally do not replicate the size and spatial distribution of human metastatic cancer and these factors strongly influence image resolution and dosimetry. The following review will discuss several aspects of comparative cancer imaging in more detail while providing several illustrative examples of investigational approaches performed or currently under exploration at our institutions. Topics addressed include a discussion on interested consortia; image quality assurance and harmonization; image-based biomarker development and validation; contrast agent and radionuclide tracer development; advanced imaging to assess and predict response to cytotoxic and immunomodulatory anticancer agents; imaging of the tumor microenvironment; development of novel theranostic approaches; cell trafficking assessment via non-invasive imaging; and intraoperative imaging to inform surgical oncology decision making. Taken in totality, these comparative opportunities predict that safety, diagnostic and efficacy data generated in companion species with naturally developing and progressing cancers would better recapitulate the human cancer condition than that of artificial models in small rodent systems and ultimately accelerate the integration of novel imaging technologies into clinical practice. It is our hope that the examples presented should serve to provide those involved in cancer investigations who are unfamiliar with available comparative methodologies an understanding of the potential utility of this approach.

Companion animal models of neurological disease

Clinical translation of novel therapeutics that improve the survival and quality of life of patients with neurological disease remains a challenge, with many investigational drug and device candidates failing in advanced stage clinical trials. Naturally occurring inherited and acquired neurological diseases, such as epilepsy, inborn errors of metabolism, brain tumors, spinal cord injury, and stroke occur frequently in companion animals, and many of these share epidemiologic, pathophysiologic and clinical features with their human counterparts. As companion animals have a relatively abbreviated lifespan and genetic background, are immunocompetent, share their environment with human caregivers, and can be clinically managed using techniques and tools similar to those used in humans, they have tremendous potential for increasing the predictive value of preclinical drug and device studies. Here, we review comparative features of spontaneous neurological diseases in companion animals with an emphasis on neuroimaging methods and features, illustrate their historical use in translational studies, and discuss inherent limitations associated with each disease model. Integration of companion animals with naturally occurring disease into preclinical studies can complement and expand the knowledge gained from studies in other animal models, accelerate or improve the manner in which research is translated to the human clinic, and ultimately generate discoveries that will benefit the health of humans and animals.

Urological Sequelae to Acute Spinal Cord Injury in Pet Dogs: A Natural Disease Model of Neuropathic Bladder Dysfunction

The authors review urologic dysfunction, including urine retention, incontinence, and recurrent and resistant urinary tract infection, in dogs as a sequela to acute spinal cord injury. Urologic sequelae to acute spinal cord injury (SCI) pose significant complications in human and canine patients impacting quality of life and long-term cost of treatment. Dogs with intervertebral disc extrusion may serve as a natural disease model of acute SCI for investigating translational interventions, both prophylactic and therapeutic, for urologic dysfunction in human SCI patients.

Of Mice, Dogs, Pigs, and Men: Choosing the Appropriate Model for Immuno-Oncology Research

The immune system plays dual roles in response to cancer. The host immune system protects against tumor formation via immunosurveillance; however, recognition of the tumor by immune cells also induces sculpting mechanisms leading to a Darwinian selection of tumor cell variants with reduced immunogenicity. Cancer immunoediting is the concept used to describe the complex interplay between tumor cells and the immune system. This concept, commonly referred to as the three E's, is encompassed by 3 distinct phases of elimination, equilibrium, and escape. Despite impressive results in the clinic, cancer immunotherapy still has room for improvement as many patients remain unresponsive to therapy. Moreover, many of the preclinical results obtained in the widely used mouse models of cancer are lost in translation to human patients. To improve the success rate of immuno-oncology research and preclinical testing of immune-based anticancer therapies, using alternative animal models more closely related to humans is a promising approach. Here, we describe 2 of the major alternative model systems: canine (spontaneous) and porcine (experimental) cancer models. Although dogs display a high rate of spontaneous tumor formation, an increased number of genetically modified porcine models exist. We suggest that the optimal immuno-oncology model may depend on the stage of cancer immunoediting in question. In particular, the spontaneous canine tumor models provide a unique platform for evaluating therapies aimed at the escape phase of cancer, while genetically engineered swine allow for elucidation of tumor-immune cell interactions especially during the phases of elimination and equilibrium.

Canine Primary Intracranial Cancer: A Clinicopathologic and Comparative Review of Glioma, Meningioma, and Choroid Plexus Tumors

In the dog, primary intracranial neoplasia represents ~2-5% of all cancers and is especially common in certain breeds including English and French bulldogs and Boxers. The most common types of primary intracranial cancer in the dog are meningioma, glioma, and choroid plexus tumors, generally occurring in middle aged to older dogs. Much work has recently been done to understand the characteristic imaging and clinicopathologic features of these tumors. The gross and histologic landscape of these tumors in the dog compare favorably to their human counterparts with many similarities noted in histologic patterns, subtype, and grades. Data informing the underlying molecular abnormalities in the canine tumors have only begun to be unraveled, but reveal similar pathways are mutated between canine and human primary intracranial neoplasia. This review will provide an overview of the clinicopathologic features of the three most common forms of primary intracranial cancer in the dog, delve into the comparative aspects between the dog and human neoplasms, and provide an introduction to current standard of care while also highlighting novel, experimental treatments that may help bridge the gap between canine and human cancer therapies.

Clinical, Pathological, and Ethical Considerations for the Conduct of Clinical Trials in Dogs with Naturally Occurring Cancer: A Comparative Approach to Accelerate Translational Drug Development

The role of comparative oncology in translational research is receiving increasing attention from drug developers and the greater biomedical research community. Pet dogs with spontaneous cancer are important and underutilized translational models, owing to dogs' large size and relative outbreeding, combined with their high incidence of certain tumor histotypes with significant biological, genetic, and histological similarities to their human tumor counterparts. Dogs with spontaneous tumors naturally develop therapy resistance and spontaneous metastasis, all in the context of an intact immune system. These fundamental features of cancer biology are often lacking in induced or genetically engineered preclinical tumor models and likely contribute to their poor predictive value and the associated overall high failure rate in oncology drug development. Thus, the conduct of clinical trials in pet dogs with naturally occurring cancer represents a viable surrogate and valuable intermediary step that should be increasingly incorporated into the cancer drug discovery and development pipeline. The development of molecular-targeted therapies has resulted in an expanded role of the pathologist in human oncology trials, and similarly the expertise of veterinary pathologists will be increasingly valuable to all phases of comparative oncology trial design and conduct. In this review, we provide a framework of clinical, ethical, and pathology-focused considerations for the increasing integration of translational research investigations in dogs with spontaneous cancer as a means to accelerate clinical cancer discovery and drug development.

A Revised Diagnostic Classification of Canine Glioma: Towards Validation of the Canine Glioma Patient as a Naturally Occurring Preclinical Model for Human Glioma

The National Cancer Institute-led multidisciplinary Comparative Brain Tumor Consortium (CBTC) convened a glioma pathology board, comprising both veterinarian and physician neuropathologists, and conducted a comprehensive review of 193 cases of canine glioma. The immediate goal was to improve existing glioma classification methods through creation of a histologic atlas of features, thus yielding greater harmonization of phenotypic characterization. The long-term goal was to support future incorporation of clinical outcomes and genomic data into proposed simplified diagnostic schema, so as to further bridge the worlds of veterinary and physician neuropathology and strengthen validity of the dog as a naturally occurring, translationally relevant animal model of human glioma. All cases were morphologically reclassified according to a new schema devised by the entire board, yielding a majority opinion diagnosis of astrocytoma (43, 22.3%), 19 of which were low-grade and 24 high-grade, and oligodendroglioma (134, 69.4%), 35 of which were low-grade and 99 were high-grade. Sixteen cases (8.3%) could not be classified as oligodendroglioma or astrocytoma based on morphology alone and were designated as undefined gliomas. The simplified classification scheme proposed herein provides a tractable means for future addition of molecular data, and also serves to highlight histologic similarities and differences between human and canine glioma.

Common Molecular Alterations in Canine Oligodendroglioma and Human Malignant Gliomas and Potential Novel Therapeutic Targets

Spontaneous canine (Canis lupus) oligodendroglioma (ODG) holds tremendous potential as an immunocompetent large animal model of human malignant gliomas (MG). However, the feasibility of utilizing this model in pre-clinical studies depends on a thorough understanding of the similarities and differences of the molecular pathways associated with gliomas between the two species. We have previously shown that canine ODG has an immune landscape and expression pattern of commonly described oncogenes similar to that of human MG. In the current study, we performed a comprehensive analysis of canine ODG RNAseq data from 4 dogs with ODG and 2 normal controls to identify highly dysregulated genes in canine tumors. We then evaluated the expression of these genes in human MG using Xena Browser, a publicly available database. STRING-database inquiry was used in order to determine the suggested protein associations of these differentially expressed genes as well as the dysregulated pathways commonly enriched by the protein products of these genes in both canine ODG and human MG. Our results revealed that 3,712 (23%) of the 15,895 differentially expressed genes demonstrated significant up- or downregulation (log2-fold change > 2.0). Of the 3,712 altered genes, ~50% were upregulated (n = 1858) and ~50% were downregulated (n = 1854). Most of these genes were also found to have altered expression in human MG. Protein association and pathway analysis revealed common pathways enriched by members of the up- and downregulated gene categories in both species. In summary, we demonstrate that a similar pattern of gene dysregulation characterizes both human MG and canine ODG and provide additional support for the use of the canine model in order to therapeutically target these common genes. The results of such therapeutic targeting in the canine model can serve to more accurately predict the efficacy of anti-glioma therapies in human patients.

Clinicopathologic Features, Diagnosis, and Characterization of the Immune Cell Population in Canine Choroid Plexus Tumors

The World Health Organization characterizes human choroid plexus tumor (CPT) as papilloma (CPP), atypical CPP (ACPP), and carcinoma (CPC). CPCs can disseminate via cerebrospinal fluid and be mistaken for metastatic carcinoma, creating a diagnostic challenge. Kir7.1 immunohistochemistry (IHC) is a highly reliable tool for diagnostic confirmation of CPTs and their differentiation from metastatic carcinomas in human beings and dogs. This study describes the neuropathology, Kir7.1 staining profile, and the immune cell population within the tumor microenvironment in 11 CPTs in dogs. Archived tissue sections with a diagnosis of CPT were examined and immunolabelled with Kir7.1 for diagnostic confirmation. The number of Ki67-positive neoplastic cells was calculated in 2.4 mm² (equivalent to 10 FN22/40X fields), and a mean value was generated for each neoplasm. IHC for CD3, CD20, MAC387, and Iba1 was performed for immune cell characterization, and the number of stained cells for each antibody was counted in 2.4 mm², generating individual cumulative values for each antibody. T-tests with Bonferroni correction evaluated IHC differences between tumor types, and Spearman's rank correlations evaluated relationships among IHC markers. Kir7.1 immunoreactivity was intense at the apical cell membrane in CPPs and ACPPs, and at the apical cell membrane and cytoplasm in CPCs. Ki67 immunoreactivity was detected in all cases. CD3+ and CD20+ lymphocytes trended together (p = 0.005) and were present within and around all CPTs. Five cases had intravascular MAC387+ monocytes. Iba1 immunoreactivity was robust within and around all tumors. Statistical differences in immune cell markers were not found among tumor types. As previously reported, Kir7.1 is a reliable antibody for the diagnosis of canine CPTs. Although immune cells were present in all cases, no significant associations were found between the type of cells and tumor diagnosis. The characterization of the immune cells within CPTs could be useful in future studies involving immunotherapy.

Cancer Immunotherapies

The enhanced understanding of immunology experienced over the last 4 decades afforded through the tools of molecular biology has recently translated into cancer immunotherapy becoming one of the most exciting and rapidly expanding fields. Human cancer immunotherapy is now recognized as one of the pillars of treatment alongside surgery, radiation, and chemotherapy. The field of veterinary cancer immunotherapy has also rapidly advanced in the last decade with a handful of commercially available products and a plethora of investigational cancer immunotherapies that will hopefully expand the veterinary oncology treatment toolkit over time.

Nanomedicine for Spontaneous Brain Tumors: A Companion Clinical Trial

Nanoparticles' enhanced permeation and retention (EPR) variations due to tumor heterogeneity in naturally occurring brain tumors are commonly neglected in preclinical nanomedicine studies. Recent pathological studies have shown striking similarities between brain tumors in humans and dogs, indicating that canine brain tumors may be a valuable model to evaluate nanoparticles' EPR in this context. We recruited canine clinical cases with spontaneous brain tumors to investigate nanoparticles' EPR in different brain tumor pathologies using surface-enhanced Raman spectroscopy (SERS). We used gold nanoparticles due to their surface plasmon effect that enables their sensitive and microscopic resolution detection using the SERS technique. Raman microscopy of the resected tumors showed heterogeneous EPR of nanoparticles into oligodendrogliomas and meningiomas of different grades, without any detectable traces in necrotic parts of the tumors or normal brain. Raman observations were confirmed by scanning electron microscopy (SEM) and X-ray elemental analyses, which enabled localization of individual nanoparticles embedded in tumor tissues. Our results demonstrate nanoparticles' EPR and its variations in clinically relevant, spontaneous brain tumors. Such heterogeneities should be considered alongside routine preoperative imaging and histopathological analyses in order to accelerate clinical management of brain tumors using nanomedicine approaches.

Immunohistochemical Characterization of Procaspase-3 Overexpression as a Druggable Target With PAC-1, a Procaspase-3 Activator, in Canine and Human Brain Cancers

Gliomas and meningiomas are the most common brain neoplasms affecting both humans and canines, and identifying druggable targets conserved across multiple brain cancer histologies and comparative species could broadly improve treatment outcomes. While satisfactory cure rates for low grade, non-invasive brain cancers are achievable with conventional therapies including surgery and radiation, the management of non-resectable or recurrent brain tumors remains problematic and necessitates the discovery of novel therapies that could be accelerated through a comparative approach, such as the inclusion of pet dogs with naturally-occurring brain cancers. Evidence supports procaspase-3 as a druggable brain cancer target with PAC-1, a pro-apoptotic, small molecule activator of procaspase-3 that crosses the blood-brain barrier. Procaspase-3 is frequently overexpressed in malignantly transformed tissues and provides a preferential target for inducing cancer cell apoptosis. While preliminary evidence supports procaspase-3 as a viable target in preclinical models, with PAC-1 demonstrating activity in rodent models and dogs with spontaneous brain tumors, the broader applicability of procaspase-3 as a target in human brain cancers, as well as the comparability of procaspase-3 expressions between differing species, requires further investigation. As such, a large-scale validation of procaspase-3 as a druggable target was undertaken across 651 human and canine brain tumors. Relative to normal brain tissues, procaspase-3 was overexpressed in histologically diverse cancerous brain tissues, supporting procaspase-3 as a broad and conserved therapeutic target. Additionally, procaspase-3 expressing glioma and meningioma cell lines were sensitive to the apoptotic effects of PAC-1 at biologically relevant exposures achievable in cancer patients. Importantly, the clinical relevance of procaspase-3 as a potential prognostic variable was demonstrated in human astrocytomas of variable histologic grades and associated clinical outcomes, whereby tumoral procaspase-3 expression was negatively correlated with survival; findings which suggest that PAC-1 might provide the greatest benefit for patients with the most guarded prognoses.

Checkpoint Blockade Reverses Anergy in IL-13Rα2 Humanized scFv-Based CAR T Cells to Treat Murine and Canine Gliomas

We generated two humanized interleukin-13 receptor α2 (IL-13Rα2) chimeric antigen receptors (CARs), Hu07BBz and Hu08BBz, that recognized human IL-13Rα2, but not IL-13Rα1. Hu08BBz also recognized canine IL-13Rα2. Both of these CAR T cell constructs demonstrated superior tumor inhibitory effects in a subcutaneous xenograft model of human glioma compared with a humanized EGFRvIII CAR T construct used in a recent phase 1 clinical trial (ClinicalTrials.gov: NCT02209376). The Hu08BBz demonstrated a 75% reduction in orthotopic tumor growth using low-dose CAR T cell infusion. Using combination therapy with immune checkpoint blockade, humanized IL-13Rα2 CAR T cells performed significantly better when combined with CTLA-4 blockade, and humanized EGFRvIII CAR T cells' efficacy was improved by PD-1 and TIM-3 blockade in the same mouse model, which was correlated with the levels of checkpoint molecule expression in co-cultures with the same tumor in vitro. Humanized IL-13Rα2 CAR T cells also demonstrated benefit from a self-secreted anti-CTLA-4 minibody in the same mouse model. In addition to a canine glioma cell line (J3T), canine osteosarcoma lung cancer and leukemia cell lines also express IL-13Rα2 and were recognized by Hu08BBz. Canine IL-13Rα2 CAR T cell was also generated and tested in vitro by co-culture with canine tumor cells and in vivo in an orthotopic model of canine glioma. Based on these results, we are designing a pre-clinical trial to evaluate the safety of canine IL-13Rα2 CAR T cells in dog with spontaneous IL-13Rα2-positive glioma, which will help to inform a human clinical trial design for glioblastoma using humanized scFv-based IL-13Rα2 targeting CAR T cells.

High-Frequency Irreversible Electroporation for Intracranial Meningioma: A Feasibility Study in a Spontaneous Canine Tumor Model

High-frequency irreversible electroporation is a nonthermal method of tissue ablation that uses bursts of 0.5- to 2.0-microsecond bipolar electric pulses to permeabilize cell membranes and induce cell death. High-frequency irreversible electroporation has potential advantages for use in neurosurgery, including the ability to deliver pulses without inducing muscle contraction, inherent selectivity against malignant cells, and the capability of simultaneously opening the blood–brain barrier surrounding regions of ablation. Our objective was to determine whether high-frequency irreversible electroporation pulses capable of tumor ablation could be delivered to dogs with intracranial meningiomas. Three dogs with intracranial meningiomas were treated. Patient-specific treatment plans were generated using magnetic resonance imaging-based tissue segmentation, volumetric meshing, and finite element modeling. Following tumor biopsy, high-frequency irreversible electroporation pulses were stereotactically delivered in situ followed by tumor resection and morphologic and volumetric assessments of ablations. Clinical evaluations of treatment included pre- and posttreatment clinical, laboratory, and magnetic resonance imaging examinations and adverse event monitoring for 2 weeks posttreatment. High-frequency irreversible electroporation pulses were administered successfully in all patients. No adverse events directly attributable to high-frequency irreversible electroporation were observed. Individual ablations resulted in volumes of tumor necrosis ranging from 0.25 to 1.29 cm³. In one dog, nonuniform ablations were observed, with viable tumor cells remaining around foci of intratumoral mineralization. In conclusion, high-frequency irreversible electroporation pulses can be delivered to brain tumors, including areas adjacent to critical vasculature, and are capable of producing clinically relevant volumes of tumor ablation. Mineralization may complicate achievement of complete tumor ablation.

Intratumoral temozolomide in spontaneous canine gliomas: feasibility of a novel therapy using implanted microcylinders

Entotherapy[Link] an image‐guided drug‐eluting microcylinder platform, has the potential to bypass the limitations of systemic chemotherapy use in the treatment of canine brain tumours. Gliomas, which are common in dogs and also represent the majority of fatal brain tumours in humans, can be amenable to chemotherapy with temozolomide. Biopolymer microcylinders conjugated with temozolomide and gadolinium were implanted into partially resected tumours of four client‐owned dogs with gliomas. All four dogs presented with generalized seizures and had mild to no neurologic deficits at the time of craniotomy. All dogs underwent craniotomy for implantation of the microcylinders into partially resected gliomas (glioblastoma multiforme {n = 1} or oligodendroglioma {n = 3}). All dogs recovered well from the craniotomy and implantation procedure. This novel procedure appears to be feasible and tolerated in tumour‐bearing dogs. A future controlled clinical study can now aim to evaluate the microcylinder implantation for long‐term efficacy.

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.

Canine (Pet Dog) Tumor Microsurgery and Intratumoral Concentration and Safety of Metronomic Chlorambucil for Spontaneous Glioma: A Phase I Clinical Trial

OBJECTIVE

Metronomic (daily low-dose) chlorambucil requires further study before use in human patients with glioma. The aim of this study was to investigate distribution and safety of metronomic chlorambucil in naturally occurring canine glioma.

METHODS

Eight client-owned (pet) dogs with newly diagnosed spontaneous glioma were prospectively enrolled. Chlorambucil was administered preoperatively at 4 mg/m² every 24 hours for ≥3 days and continued postoperatively until death or dose-limiting adverse events. Chlorambucil concentrations in the surgical glioma specimen, cerebrospinal fluid, and serum were analyzed. Dogs additionally received lomustine postoperatively. Dogs were monitored for seizures, myoclonus, cytopenias, and tumor recurrence.

RESULTS

Complete microsurgical resection was achieved in 7 oligodendrogliomas and 1 astrocytoma (6 high grade, 2 low grade). Median surgical glioma specimen chlorambucil concentration was 0.52 ng/g (range, 0-2.62 ng/g), or 37% (range, 0%-178%) of serum concentration. Median cerebrospinal fluid concentration was 0.1 ng/mL (range, 0-0.3 ng/mL). Chlorambucil was not associated with increase in seizure activity. Six dogs displayed prolonged seizure-free intervals. There was no myoclonus. Three dogs developed asymptomatic thrombocytopenia after 8-12 months of chlorambucil. Median progression-free survival was 253 days (range, 63-860 days). Median overall survival was 257 days (range, 64-860 days).

CONCLUSIONS

The presence of intratumoral chlorambucil indicated an altered blood-brain barrier that varied from case to case. Despite sporadic previous reports of neurotoxicity, prolonged seizure-free intervals supported a high safety margin at this dose in this species. Metronomic chlorambucil was well tolerated. Spontaneous canine glioma offers a robust preclinical model.

Consensus recommendations on standardized magnetic resonance imaging protocols for multicenter canine brain tumor clinical trials

The National Cancer Institute Comparative Brain Tumor Consortium, Patient Outcomes Working Group, propose a consensus document in support of standardized magnetic resonance imaging protocols for canine brain tumor clinical trials. The intent of this manuscript is to address the widely acknowledged need to ensure canine brain tumor imaging protocols are relevant and have sufficient equivalency to translate to human studies such that: (1) multi-institutional studies can be performed with minimal inter-institutional variation, and (2) imaging protocols are consistent with human consensus recommendations to permit reliable translation of imaging data to human clinical trials. Consensus recommendations include pre- and postcontrast three-dimensional T1-weighted images, T2-weighted turbo spin echo in all three planes, T2*-weighted gradient recalled echo, T2-weighted fluid attenuated inversion recovery, and diffusion weighted imaging/diffusion tensor imaging in transverse plane; field of view of ≤150 mm; slice thickness of ≤2 mm, matrix ≥ 256 for two-dimensional images, and 150 or 256 for three-dimensional images.

Immunotherapies for malignant glioma

Glioblastoma multiforme (GBM) is a highly malignant primary brain cancer with a dreadful overall survival and for which treatment options are limited. Recent breakthroughs in novel immune-related treatment strategies for cancer have spurred interests in usurping the power of the patient's immune system to recognize and eliminate GBM. Here, we discuss the unique properties of GBM's tumor microenvironment, the effects of GBM standard on care therapy on tumor-associated immune cells, and review several approaches aimed at therapeutically targeting the immune system for GBM treatment. We believe that a comprehensive understanding of the intricate micro-environmental landscape of GBM will abound into the development of novel immunotherapy strategies for GBM patients.