Neural stem cell-based cell carriers enhance therapeutic efficacy of an oncolytic adenovirus in an orthotopic mouse model of human glioblastoma. Mol Ther. 2011;19:1714-1726. [PMID: 21629227 DOI: 10.1038/mt.2011.100]

Cancer therapy with the viral and bacterial pathogens: The past enemies can be considered the present allies

Cancer continues to be one of the leading causes of mortality worldwide despite significant advancements in cancer treatment. Many difficulties have arisen as a result of the detrimental consequences of chemotherapy and radiotherapy as a common cancer therapy, such as drug inability to penetrate deep tumor tissue, and also the drug resistance in tumor cells continues to be a major concern. These obstacles have increased the need for the development of new techniques that are more selective and effective against cancer cells. Bacterial-based therapies and the use of oncolytic viruses can suppress cancer in comparison to other cancer medications. The tumor microenvironment is susceptible to bacterial accumulation and proliferation, which can trigger immune responses against the tumor. Oncolytic viruses (OVs) have also gained considerable attention in recent years because of their potential capability to selectively target and induce apoptosis in cancer cells. This review aims to provide a comprehensive summary of the latest literature on the role of bacteria and viruses in cancer treatment, discusses the limitations and challenges, outlines various strategies, summarizes recent preclinical and clinical trials, and emphasizes the importance of optimizing current strategies for better clinical outcomes.

Emerging delivery strategy for oncolytic virotherapy

Oncolytic virotherapy represents a promising approach in cancer immunotherapy. The primary delivery method for oncolytic viruses (OVs) is intratumoral injection, which apparently limits their clinical application. For patients with advanced cancer with disseminated metastasis, systemic administration is considered the optimal approach. However, the direct delivery of naked viruses through intravenous injection presents challenges, including rapid clearance by the immune system, inadequate accumulation in tumors, and significant side effects. Consequently, the development of drug delivery strategies has led to the emergence of various bio-materials serving as viral vectors, thereby improving the anti-tumor efficacy of oncolytic virotherapy. This review provides an overview of innovative strategies for delivering OVs, with a focus on nanoparticle-based or cell-based delivery systems. Recent pre-clinical and clinical studies are examined to highlight the enhanced efficacy of systemic delivery using these novel platforms. In addition, prevalent challenges in current research are briefly discussed, and potential solutions are proposed.

A viral attack on brain tumors: the potential of oncolytic virus therapy

Managing malignant brain tumors remains a significant therapeutic hurdle that necessitates further research to comprehend their treatment potential fully. Oncolytic viruses (OVs) offer many opportunities for predicting and combating tumors through several mechanisms, with both preclinical and clinical studies demonstrating potential. OV therapy has emerged as a potent and effective method with a dual mechanism. Developing innovative and effective strategies for virus transduction, coupled with immune checkpoint inhibitors or chemotherapy drugs, strengthens this new technique. Furthermore, the discovery and creation of new OVs that can seamlessly integrate gene therapy strategies, such as cytotoxic, anti-angiogenic, and immunostimulatory, are promising advancements. This review presents an overview of the latest advancements in OVs transduction for brain cancer, focusing on the safety and effectiveness of G207, G47Δ, M032, rQNestin34.5v.2, C134, DNX-2401, Ad-TD-nsIL12, NSC-CRAd-S-p7, TG6002, and PVSRIPO. These are evaluated in both preclinical and clinical models of various brain tumors.

Glioblastoma microenvironment and its reprogramming by oncolytic virotherapy

Glioblastoma (GBM), a highly aggressive form of brain tumor, responds poorly to current conventional therapies, including surgery, radiation therapy, and systemic chemotherapy. The reason is that the delicate location of the primary tumor and the existence of the blood-brain barrier limit the effectiveness of traditional local and systemic therapies. The immunosuppressive status and multiple carcinogenic pathways in the complex GBM microenvironment also pose challenges for immunotherapy and single-targeted therapy. With an improving understanding of the GBM microenvironment, it has become possible to consider the immunosuppressive and highly angiogenic GBM microenvironment as an excellent opportunity to improve the existing therapeutic efficacy. Oncolytic virus therapy can exert antitumor effects on various components of the GBM microenvironment. In this review, we have focused on the current status of oncolytic virus therapy for GBM and the related literature on antitumor mechanisms. Moreover, the limitations of oncolytic virus therapy as a monotherapy and future directions that may enhance the field have also been discussed.

Magnetic-Powered Janus Cell Robots Loaded with Oncolytic Adenovirus for Active and Targeted Virotherapy of Bladder Cancer

A unique robotic medical platform is designed by utilizing cell robots as the active "Trojan horse" of oncolytic adenovirus (OA), capable of tumor-selective binding and killing. The OA-loaded cell robots are fabricated by entirely modifying OA-infected 293T cells with cyclic arginine-glycine-aspartic acid tripeptide (cRGD) to specifically bind with bladder cancer cells, followed by asymmetric immobilization of Fe₃ O₄ nanoparticles (NPs) on the cell surface. OA can replicate in host cells and induce cytolysis to release the virus progeny to the surrounding tumor sites for sustainable infection and oncolysis. The asymmetric coating of magnetic NPs bestows the cell robots with effective movement in various media and wireless manipulation with directional migration in a microfluidic device and bladder mold under magnetic control, further enabling steerable movement and prolonged retention of cell robots in the mouse bladder. The biorecognition of cRGD and robust, controllable propulsion of cell robots work synergistically to greatly enhance their tissue penetration and anticancer efficacy in the 3D cancer spheroid and orthotopic mouse bladder tumor model. Overall, this study integrates cell-based microrobots with virotherapy to generate an attractive robotic system with tumor specificity, expanding the operation scope of cell robots in biomedical community.

Recent advances in the therapeutic strategies of glioblastoma multiforme

Glioblastoma multiforme (GBM) is one of the most common, most formidable, and deadliest malignant types of primary astrocytoma with a poor prognosis. At present, the standard of care includes surgical tumor resection, followed by radiation therapy concomitant with chemotherapy and temozolomide. New developments and significant advances in the treatment of GBM have been achieved in recent decades. However, despite the advances, recurrence is often inevitable, and the survival of patients remains low. Various factors contribute to the difficulty in identifying an effective therapeutic option, among which are tumor complexity, the presence of the blood-brain barrier (BBB), and the presence of GBM cancer stem cells, prompting the need for improving existing treatment approaches and investigating new treatment alternatives for ameliorating the treatment strategies of GBM. In this review, we outline some of the most recent literature on the various available treatment options such as surgery, radiotherapy, cytotoxic chemotherapy, gene therapy, immunotherapy, phototherapy, nanotherapy, and tumor treating fields in the treatment of GBM, and we list some of the potential future directions of GBM. The reviewed studies confirm that GBM is a sophisticated disease with several challenges for scientists to address. Hence, more studies and a multimodal therapeutic approach are crucial to yield an effective cure and prolong the survival of GBM patients.

Combination of tucatinib and neural stem cells secreting anti-HER2 antibody prolongs survival of mice with metastatic brain cancer

Brain metastases are among the most severe complications of systemic breast cancer, and overexpression of the human epidermal growth factor receptor 2 (HER2) in breast cancer cells increases the incidence of brain metastases in patients. In this study, we engineered the human-derived, tumor cell tropic neural stem cells LM-NSC008 (LM008) to continuously secrete antibodies against HER2. These anti-HER2 antibodies impaired tumor cell proliferation by inhibiting the PI3K-Akt signaling pathway in HER2+ breast cancer cells in vitro. Importantly, our results demonstrate that the therapeutic combinatorial regimen consisting of LM-NSC008 anti-HER2 antibody-secreting cells and the HER2 kinase inhibitor tucatinib provide therapeutic benefit and prolong survival in preclinical models of HER2+ breast cancer brain metastases.

Brain metastases are a leading cause of death in patients with breast cancer. The lack of clinical trials and the presence of the blood–brain barrier limit therapeutic options. Furthermore, overexpression of the human epidermal growth factor receptor 2 (HER2) increases the incidence of breast cancer brain metastases (BCBM). HER2-targeting agents, such as the monoclonal antibodies trastuzumab and pertuzumab, improved outcomes in patients with breast cancer and extracranial metastases. However, continued BCBM progression in breast cancer patients highlighted the need for novel and effective targeted therapies against intracranial metastases. In this study, we engineered the highly migratory and brain tumor tropic human neural stem cells (NSCs) LM008 to continuously secrete high amounts of functional, stable, full-length antibodies against HER2 (anti-HER2Ab) without compromising the stemness of LM008 cells. The secreted anti-HER2Ab impaired tumor cell proliferation in vitro in HER2+ BCBM cells by inhibiting the PI3K-Akt signaling pathway and resulted in a significant benefit when injected in intracranial xenograft models. In addition, dual HER2 blockade using anti-HER2Ab LM008 NSCs and the tyrosine kinase inhibitor tucatinib significantly improved the survival of mice in a clinically relevant model of multiple HER2+ BCBM. These findings provide compelling evidence for the use of HER2Ab-secreting LM008 NSCs in combination with tucatinib as a promising therapeutic regimen for patients with HER2+ BCBM.

Multiple Treatment Cycles of Neural Stem Cell Delivered Oncolytic Adenovirus for the Treatment of Glioblastoma

Tumor tropic neural stem cells (NSCs) can improve the anti-tumor efficacy of oncovirotherapy agents by protecting them from rapid clearance by the immune system and delivering them to multiple distant tumor sites. We recently completed a first-in-human trial assessing the safety of a single intracerebral dose of NSC-delivered CRAd-Survivin-pk7 (NSC.CRAd-S-pk7) combined with radiation and chemotherapy in newly diagnosed high-grade glioma patients. The maximum feasible dose was determined to be 150 million NSC.CRAd-Sp-k7 (1.875 × 1011 viral particles). Higher doses were not assessed due to volume limitations for intracerebral administration and the inability to further concentrate the study agent. It is possible that therapeutic efficacy could be maximized by administering even higher doses. Here, we report IND-enabling studies in which an improvement in treatment efficacy is achieved in immunocompetent mice by administering multiple treatment cycles intracerebrally. The results imply that pre-existing immunity does not preclude therapeutic benefits attainable by administering multiple rounds of an oncolytic adenovirus directly into the brain.

Coating an adenovirus with functionalized gold nanoparticles favors uptake, intracellular trafficking and anti-cancer therapeutic efficacy

Adenoviral (Ad) vectors have proven to be important tools for gene and cell therapy, although some issues still need to be addressed, such as undesired interactions with blood components and off-target sequestration that ultimately hamper efficacy. In the past years, several organic and inorganic materials have been developed to reduce immunogenicity and improve biodistribution of Ad vectors. Here we investigated the influence of the functionalization of 14 nm PEGylated gold nanoparticles (AuNPs) with quaternary ammonium groups and an arginine-glycine-aspartic acid (RGD)-motif on the uptake and biodistribution of Ad vectors. We report the formation of Ad@AuNPs complexes that promote cell attachment and uptake, independently of the presence of the coxsackievirus and adenovirus receptor (CAR) and α_vβ₃ and α_vβ₅ integrins, significantly improving transduction without limiting Ad bioactivity. Besides, the presence of the RGD peptide favors tumor targeting and decreases Ad sequestration in the liver. Additionally, tumor delivery of a coated Ad vector expressing the human sodium iodide symporter (hNIS) by mesenchymal stem cells induces increased accumulation of radioactive iodine (¹³¹I) and tumor volume reduction compared to naked Ad-hNIS, highlighting the promising potential of our coating formulation in cancer gene therapy. STATEMENT OF SIGNIFICANCE: Modification of adenoviral vectors with lipids and polymers can reduce interactions with blood components and increase tumor accumulation; however, increased toxicity and reduced transduction efficiency were indicated. Coating with gold nanoparticles has proven to be a successful strategy for increasing the efficiency of transduction of receptor-defective cell lines. Here we explore the contribution of cell surface receptors on the mechanisms of entry of Ad vectors coated with gold nanoparticles in cell lines with varying degrees of resistance to infection. The enhancement of the anti-tumoral effect shown in this work provides new evidence for the potential of our formulation.

Concepts in Oncolytic Adenovirus Therapy

Oncolytic adenovirus therapy is gaining importance as a novel treatment option for the management of various cancers. Different concepts of modification within the adenovirus vector have been identified that define the mode of action against and the interaction with the tumour. Adenoviral vectors allow for genetic manipulations that restrict tumour specificity and also the expression of specific transgenes in order to support the anti-tumour effect. Additionally, replication of the virus and reinfection of neighbouring tumour cells amplify the therapeutic effect. Another important aspect in oncolytic adenovirus therapy is the virus induced cell death which is a process that activates the immune system against the tumour. This review describes which elements in adenovirus vectors have been identified for modification not only to utilize oncolytic adenovirus vectors into conditionally replicating adenoviruses (CRAds) that allow replication specifically in tumour cells but also to confer specific characteristics to these viruses. These advances in development resulted in clinical trials that are summarized based on the conceptual design.

Glioblastoma Multiforme-A Look at the Past and a Glance at the Future

Gliomas are the most common type of brain tumor that occur in adults and children. Glioblastoma multiforme (GBM) is the most common, aggressive form of brain cancer in adults and is universally fatal. The current standard-of-care options for GBM include surgical resection, radiotherapy, and concomitant and/or adjuvant chemotherapy. One of the major challenges that impedes success of chemotherapy is the presence of the blood–brain barrier (BBB). Because of the tightly regulated BBB, immune surveillance in the central nervous system (CNS) is poor, contributing to unregulated glioma cell growth. This review gives a comprehensive overview of the latest advances in treatment of GBM with emphasis on the significant advances in immunotherapy and novel therapeutic delivery strategies to enhance treatment for GBM.

Glioblastoma Multiforme-A Look at the Past and a Glance at the Future

Gliomas are the most common type of brain tumor that occur in adults and children. Glioblastoma multiforme (GBM) is the most common, aggressive form of brain cancer in adults and is universally fatal. The current standard-of-care options for GBM include surgical resection, radiotherapy, and concomitant and/or adjuvant chemotherapy. One of the major challenges that impedes success of chemotherapy is the presence of the blood-brain barrier (BBB). Because of the tightly regulated BBB, immune surveillance in the central nervous system (CNS) is poor, contributing to unregulated glioma cell growth. This review gives a comprehensive overview of the latest advances in treatment of GBM with emphasis on the significant advances in immunotherapy and novel therapeutic delivery strategies to enhance treatment for GBM.

Stem cells for the treatment of glioblastoma: a 20-year perspective

Glioblastoma, the deadliest form of primary brain tumor, remains a disease without cure. Treatment resistance is in large part attributed to limitations in the delivery and distribution of therapeutic agents. Over the last 20 years, numerous preclinical studies have demonstrated the feasibility and efficacy of stem cells as antiglioma agents, leading to the development of trials to test these therapies in the clinic. In this review we present and analyze these studies, discuss mechanisms underlying their beneficial effect and highlight experimental progress, limitations and the emergence of promising new therapeutic avenues. We hope to increase awareness of the advantages brought by stem cells for the treatment of glioblastoma and inspire further studies that will lead to accelerated implementation of effective therapies.

Glioblastoma is the deadliest and most common form of brain tumor, for which there is no cure. It is very difficult to deliver medicine to the tumor cells, because they spread out widely into the normal brain, and local blood vessels represent a barrier that most medicines cannot cross. It was shown, in many studies over the last 20 years, that stem cells are attracted toward the tumor and that they can deliver many kinds of therapeutic agents directly to brain cancer cells and shrink the tumor. In this review we analyze these studies and present new discoveries that can be used to make stem cell therapies for glioblastoma more effective to prolong the life of patients with brain tumors.

Contemporary Mouse Models in Glioma Research

Despite advances in understanding of the molecular pathogenesis of glioma, outcomes remain dismal. Developing successful treatments for glioma requires faithful in vivo disease modeling and rigorous preclinical testing. Murine models, including xenograft, syngeneic, and genetically engineered models, are used to study glioma-genesis, identify methods of tumor progression, and test novel treatment strategies. Since the discovery of highly recurrent isocitrate dehydrogenase (IDH) mutations in lower-grade gliomas, there is increasing emphasis on effective modeling of IDH mutant brain tumors. Improvements in preclinical models that capture the phenotypic and molecular heterogeneity of gliomas are critical for the development of effective new therapies. Herein, we explore the current status, advancements, and challenges with contemporary murine glioma models.

Stem cell-based therapy treating glioblastoma multiforme

Glioblastoma (GB) is one of the most malignant types of central nervous system tumours, classified as grade IV by the World Health Organization. Despite the therapeutic advances, the prognosis is ominous, with a median survival of about 12-15 months post diagnosis. Although therapeutic options available can increase the survival, they are ineffective in treating patients with GB. Impairing factors such as the blood-brain barrier, cancer stem cells, and infiltration into brain parenchyma lead to failure of current therapies. Therefore, clinicians need novel/alternative effective strategies to treat GB. Due to their ability to preserve healthy tissues and to provide an effective and long-lasting response, stem cells (SCs) with tropism for tumour cells have attracted considerable attention in the scientific community. As is the case here, SCs can be used to target brain tumour cancer cells, especially high-grade malignant gliomas like GB, by overcoming the resistance and exerting benefits for patients affected with such lethal disease. Herein, we will discuss the research knowledge regarding SC-based therapy for the treatment of GB, focalising our attention on SCs and SC-released extracellular vesicles modified to express/load different antitumour payloads, as well as on SCs exploited as a diagnostic tool. Advantages and unresolved issues of anticancer SC-based therapy will also be considered.

Neural Stem Cell-Based Therapies and Glioblastoma Management: Current Evidence and Clinical Challenges

Gliomas, which account for nearly a quarter of all primary CNS tumors, present significant contemporary therapeutic challenges, particularly the highest-grade variant (glioblastoma multiforme), which has an especially poor prognosis. These difficulties are due to the tumor's aggressiveness and the adverse effects of radio/chemotherapy on the brain. Stem cell therapy is an exciting area of research being explored for several medical issues. Neural stem cells, normally present in the subventricular zone and the hippocampus, preferentially migrate to tumor masses. Thus, they have two main advantages: They can minimize the side effects associated with systemic radio/chemotherapy while simultaneously maximizing drug delivery to the tumor site. Another feature of stem cell therapy is the variety of treatment approaches it allows. Stem cells can be genetically engineered into expressing a wide variety of immunomodulatory substances that can inhibit tumor growth. They can also be used as delivery vehicles for oncolytic viral vectors, which can then be used to combat the tumorous mass. An alternative approach would be to combine stem cells with prodrugs, which can subsequently convert them into the active form upon migration to the tumor mass. As with any therapeutic modality still in its infancy, much of the research regarding their use is primarily based upon knowledge gained from animal studies, and a number of ongoing clinical trials are currently investigating their effectiveness in humans. The aim of this review is to highlight the current state of stem cell therapy in the treatment of gliomas, exploring the different mechanistic approaches, clinical applicability, and the existing limitations.

The Potentials and Pitfalls of Using Adult Stem Cells in Cancer Treatment

Stem cells play a pivotal role in the developmental stages of an organism and in adulthood as well. Therefore, it is not surprising that stem cells constitute a focus of extensive research. Indeed, several decades of stem cell research have tremendously increased our knowledge on the mechanistic understandings of stem cell biology. Interestingly, revealing the fundamental principles of stem cell biology has also fostered its application for therapeutic purposes. Many of the attributes that the stem cells possess, some of which are unique, allow multifaceted exploitation of stem cells in the treatment of various diseases. Cancer, the leading cause of mortality worldwide, is one of the disease groups that has been benefited by the potentials of therapeutic applications of the stem cells. While the modi operandi of how stem cells contribute to cancer treatment are many-sided, two major principles can be conceived. One mode involves harnessing the regenerative power of the stem cells to promote the generation of blood-forming cells in cancer patients after cytotoxic regimens. A totally different kind of utility of stem cells has been exercised in another mode where the stem cells can potentially deliver a plethora of anti-cancer therapeutics in a tumor-specific manner. While both these approaches can improve the treatment of cancer patients, there exist several issues that warrant further research. This review summarizes the basic principles of the utility of the stem cells in cancer treatment along with the current trends and pinpoints the major obstacles to focus on in the future for further improvement.

NSCs are permissive to oncolytic Myxoma virus and provide a delivery method for targeted ovarian cancer therapy

Despite the development of many anticancer agents over the past 20 years, ovarian cancer remains the most lethal gynecologic malignancy. Due to a lack of effective screening, the majority of patients with ovarian cancer are diagnosed at an advanced stage, and only ~20% of patients are cured. Thus, in addition to improved screening methods, there is an urgent need for novel anticancer agents that are effective against late-stage, metastatic disease. Oncolytic virotherapy is a promising approach; unfortunately, systemic delivery of viruses to tumors remains a major challenge. In this regard, neural stem/progenitor cells (NSCs) with well-established tumor-homing properties may serve as an effective delivery platform for oncolytic viruses. In this study, we tested the efficacy of myxoma virus (MYXV), a rabbit-specific poxvirus that has demonstrated efficacy against a variety of tumors, using human and mouse ovarian cancer cell lines. We showed that MYXV effectively lysed ovarian cancer cells in vitro, reducing their viability. We also demonstrated that MYXV can infect human NSCs, specifically the clonal HB1.F3.CD21 NSC line. Taken together, these results suggest that NSC-mediated delivery of MYXV may be a promising strategy for achieving more selectively targeted anti-tumor efficacy.

Delivery systems for enhancing oncolytic adenoviruses efficacy

Oncolytic adenovirus (OAds) has long been considered a promising biotherapeutic agent against various types of cancer owing to selectively replicate in and lyse cancer cells, while remaining dormant in healthy cells. In the last years, multiple (pre)clinical studies using genetic engineering technologies enhanced OAds anti-tumor effects in a broad range of cancers. However, poor targeting delivery, tropism toward healthy tissues, low-level expression of Ad receptors on tumor cells, and pre-existing neutralizing antibodies are major hurdles for systemic administration of OAds. Different vehicles have been developed for addressing these obstacles, such as stem cells, nanoparticles (NPs) and shielding polymers, extracellular vesicles (EVs), hydrogels, and microparticles (MPs). These carriers can enhance the therapeutic efficacy of OVs through enhancing transfection, circulatory longevity, cellular interactions, specific targeting, and immune responses against cancer. In this paper, we reviewed adenovirus structure and biology, different types of OAds, and the efficacy of different carriers in systemic administration of OAds.

Developing Bioinspired Three-Dimensional Models of Brain Cancer to Evaluate Tumor-Homing Neural Stem Cell Therapy

Engineered neural stem cells (NSCs) have recently emerged as a promising therapy. Acting as a tumor-homing drug-delivery system, NSCs migrate through brain tissue to seek out primary and invasive tumor foci. NSCs can deliver therapeutic agents, such as TNFα-related apoptosis-inducing ligand, directly to the tumor and suppress glioblastoma (GBM) in murine models. While the mainstays for evaluating NSC migration and efficacy have been two-dimensional chemotaxis assays and mouse models, these low-throughput and small-scale systems limit our ability to implant and track these cells for human translation. To circumvent these challenges, we developed a three-dimensional culture system using a matrix of poly-l-lactic acid 6100 microfibers suspended in agar. These bioinspired brain matrices were used to model tumor growth, NSC migration, and efficacy of NSC therapy at small and human scale. Kinetic fluorescent imaging confirmed growth of tumors in both small and human-sized bioinspired brain matrix. Tumors proliferated 50-fold and 3-fold for GBM and human metastatic breast cancer, respectively, over 7 days. We next explored the impact of tumor location on NSC migration. When NSCs were implanted 2 mm lateral from the tumor foci, NSCs colocalized with the GBM within 7 days. In models of multifocal disease, NSCs were found to colocalize with multiple tumors, preferentially migrating to tumor foci closest to the site of NSC implantation. Lastly, therapeutic NSCs were implanted at increasing distances (0, 2, 5, or 10 mm) laterally from GBM foci to investigate the effects of distance on NSC efficacy. Serial imaging showed reduced fluorescence at tumor sites, implicating GBM apoptosis across all distances. NSCs coinjected with tumor induced a near-complete response in <10 days, while NSCs implanted 10 mm laterally from the tumor induced a near-complete response by day 30. Lastly, GBM foci were established in each hemisphere of the model and control or therapeutic NSCs were implanted adjacent to tumor cells in the right hemisphere. Kinetic imaging showed that NSC therapy attenuated progression of GBM foci, while GBM cells treated with control NSC expanded rapidly over 21 days. In conclusion, we developed a new bioinspired model that supports growth of human brain cancer cells and enables rapid tracking of NSC therapy. Impact statement Tumor-homing and tumor-killing-engineered neural stem cell (NSC) therapies have shown immense promise in both preclinical and clinical trials. However, as cell therapies continue to evolve, cost-effective and high-throughput screening assays are needed to assess the proliferation, migration, and efficacy of these cells. In this study, we developed a bioinspired brain matrix for the evaluation of engineered NSCs. Importantly, this matrix is easy to fabricate, scalable, and allows for sterile real-time, noninvasive imaging using our custom bioreactor. We then utilized the bioinspired brain matrix system to answer key questions around the tumor-homing migration and efficacy of engineered NSC therapies that are challenging to address with traditional models.

Neural Stem Cells Improve the Delivery of Oncolytic Chimeric Orthopoxvirus in a Metastatic Ovarian Cancer Model

Oncolytic virotherapy represents a promising approach for treating recurrent and/or drug-resistant ovarian cancer. However, its successful application in the clinic has been hampered by rapid immune-mediated clearance, which reduces viral delivery to the tumor. Patient-derived mesenchymal stem cells that home to tumors have been used as viral delivery tools, but variability associated with autologous cell isolations limits the clinical applicability of this approach. We previously developed an allogeneic, clonal neural stem cell (NSC) line (HB1.F3.CD21) that can be used to deliver viral cargo. Here, we demonstrate that this NSC line can improve the delivery of a thymidine kinase gene-deficient conditionally replication-competent orthopoxvirus, CF33, in a preclinical cisplatin-resistant peritoneal ovarian metastases model. Overall, our findings provide the basis for using off-the-shelf allogeneic cell-based delivery platforms for oncolytic viruses, thus providing a more efficient delivery alternative compared with the free virus administration approach.

The impact of stem cells in neuro-oncology: applications, evidence, limitations and challenges

BACKGROUND

Stem cells (SCs) represent a recent and attractive therapeutic option for neuro-oncology, as well as for treating degenerative, ischemic and traumatic pathologies of the central nervous system. This is mainly because of their homing capacity, which makes them capable of reaching the inaccessible SC niches of the tumor, therefore, acting as living drugs. The target of the study is a comprehensive overview of the SC-based therapies in neuro-oncology, also highlighting the current translational challenges of this type of approach.

METHODS

An online search of the literature was carried out on the PubMed/MEDLINE and ClinicalTrials.gov websites, restricting it to the most pertinent keywords regarding the systematization of the SCs and their therapeutic use for malignant brain tumors. A large part of the search was dedicated to clinical trials. Only preclinical and clinical data belonging to the last 5 years were shortlisted. A further sorting was implemented based on the best match and relevance.

RESULTS

The results consisted in 96 relevant articles and 31 trials. Systematization involves a distinction between human embryonic, fetal and adult, but also totipotent, pluripotent or multipotent SCs. Mesenchymal and neuronal SCs were the most studied for neuro-oncological illnesses. 30% and 50% of the trials were phase I and II, respectively.

CONCLUSION

Mesenchymal and neuronal SCs are ideal candidates for SCs-based therapy of malignant brain tumors. The spectrum of their possible applications is vast and is mainly based on the homing capacity toward the tumor microenvironment. Availability, delivery route, oncogenicity and ethical issues are the main translational challenges concerning the use of SCs in neuro-oncology.

Research Progress in Bioinspired Drug Delivery Systems

INTRODUCTION

To tackle challenges associated with traditional drug carriers, investigators have explored cells, cellular membrane, and macromolecular components including proteins and exosomes for the fabrication of delivery vehicles, owing to their excellent biocompatibility, lower toxicity, lower immunogenicity and similarities with the host. Biomacromolecule- and biomimetic nanoparticle (NP)-based drug/gene carriers are drawing immense attention, and biomimetic drug delivery systems (BDDSs) have been conceived and constructed.

AREAS COVERED

This review focuses on BDDS based on mammalian cells, including blood cells, cancer cells, adult stem cells, endogenous proteins, pathogens and extracellular vesicles (EVs).

EXPERT OPINION

Compared with traditional drug delivery systems (DDSs), BDDSs are based on biological nanocarriers, exhibiting superior biocompatibility, fewer side effects, natural targeting, and diverse modifications. In addition to directly employing natural biomaterials such as cells, proteins, pathogens and EVs as carriers, BDDSs offer these advantages by mimicking the structure of natural nanocarriers through bioengineering technologies. Furthermore, BDDSs demonstrate fewer limitations and irregularities than natural materials and can overcome several shortcomings associated with natural carriers. Although research remains ongoing to resolve these limitations, it is anticipated that BDDSs possess the potential to overcome challenges associated with traditional DDS, with a promising future in the treatment of human diseases.

Advances and potential pitfalls of oncolytic viruses expressing immunomodulatory transgene therapy for malignant gliomas

Glioblastoma (GBM) is an immunosuppressive, lethal brain tumor. Despite advances in molecular understanding and therapies, the clinical benefits have remained limited, and the life expectancy of patients with GBM has only been extended to ~15 months. Currently, genetically modified oncolytic viruses (OV) that express immunomodulatory transgenes constitute a research hot spot in the field of glioma treatment. An oncolytic virus is designed to selectively target, infect, and replicate in tumor cells while sparing normal tissues. Moreover, many studies have shown therapeutic advantages, and recent clinical trials have demonstrated the safety and efficacy of their usage. However, the therapeutic efficacy of oncolytic viruses alone is limited, while oncolytic viruses expressing immunomodulatory transgenes are more potent inducers of immunity and enhance immune cell-mediated antitumor immune responses in GBM. An increasing number of basic studies on oncolytic viruses encoding immunomodulatory transgene therapy for malignant gliomas have yielded beneficial outcomes. Oncolytic viruses that are armed with immunomodulatory transgenes remain promising as a therapy against malignant gliomas and will undoubtedly provide new insights into possible clinical uses or strategies. In this review, we summarize the research advances related to oncolytic viruses that express immunomodulatory transgenes, as well as potential treatment pitfalls in patients with malignant gliomas.

Expanding the Spectrum of Adenoviral Vectors for Cancer Therapy

Adenoviral vectors (AdVs) have attracted much attention in the fields of vaccine development and treatment for diseases such as genetic disorders and cancer. In this review, we discuss the utility of AdVs in cancer therapies. In recent years, AdVs were modified as oncolytic AdVs (OAs) that possess the characteristics of cancer cell-specific replication and killing. Different carriers such as diverse cells and extracellular vesicles are being explored for delivering OAs into cancer sites after systemic administration. In addition, there are also various strategies to improve cancer-specific replication of OAs, mainly through modifying the early region 1 (E1) of the virus genome. It has been documented that oncolytic viruses (OVs) function through stimulating the immune system, resulting in the inhibition of cancer progression and, in combination with classical immune modulators, the anti-cancer effect of OAs can be even further enforced. To enhance the cancer treatment efficacy, OAs are also combined with other standard treatments, including surgery, chemotherapy and radiotherapy. Adenovirus type 5 (Ad5) has mainly been explored to develop vectors for cancer treatment with different modulations. Only a limited number of the more than 100 identified AdV types were converted into OAs and, therefore, the construction of an adenovirus library for the screening of potential novel OA candidates is essential. Here, we provide a state-of-the-art overview of currently performed and completed clinic trials with OAs and an adenovirus library, providing novel possibilities for developing innovative adenoviral vectors for cancer treatment.

Established and Emerging Strategies for Drug Delivery Across the Blood-Brain Barrier in Brain Cancer

Brain tumors are characterized by very high mortality and, despite the continuous research on new pharmacological interventions, little therapeutic progress has been made. One of the main obstacles to improve current treatments is represented by the impermeability of the blood vessels residing within nervous tissue as well as of the new vascular net generating from the tumor, commonly referred to as blood-brain barrier (BBB) and blood-brain tumor barrier (BBTB), respectively. In this review, we focused on established and emerging strategies to overcome the blood-brain barrier to increase drug delivery for brain cancer. To date, there are three broad strategies being investigated to cross the brain vascular wall and they are conceived to breach, bypass, and negotiate the access to the nervous tissue. In this paper, we summarized these approaches highlighting their working mechanism and their potential impact on the quality of life of the patients as well as their current status of development.

The vitamin K-dependent factor, protein S, regulates brain neural stem cell migration and phagocytic activities towards glioma cells

Malignant gliomas are the most common primary brain tumors. Due to both their invasive nature and resistance to multimodal treatments, these tumors have a very high percentage of recurrence leading in most cases to a rapid fatal outcome. Recent data demonstrated that neural stem/progenitor cells possess an inherent ability to migrate towards glioma cells, track them in the brain and reduce their growth. However, mechanisms involved in these processes have not been explored in-depth. In the present report, we investigated interactions between glioma cells and neural stem/progenitor cells derived from the subventricular zone, the major brain stem cell niche. Our data show that neural stem/progenitor cells are attracted by cultured glioma-derived factors. Using multiple approaches, we demonstrate for the first time that the vitamin K-dependent factor protein S produced by glioma cells is involved in tumor tropism through a mechanism involving the tyrosine kinase receptor Tyro3 that, in turn, is expressed by neural stem/progenitor cells. Neural stem/progenitor cells decrease the growth of both glioma cell cultures and clonogenic population. Cultured neural stem/progenitor cells also engulf, by phagocytosis, apoptotic glioma cell-derived fragments and this mechanism depends on the exposure of phosphatidylserine eat-me signal and is stimulated by protein S. The disclosure of a role of protein S/Tyro3 axis in neural stem/progenitor cell tumor-tropism and the demonstration of a phagocytic activity of neural stem/progenitor cells towards dead glioma cells that is regulated by protein S open up new perspectives for both stem cell biology and brain physiopathology.

Pharmacologic modulation of nasal epithelium augments neural stem cell targeting of glioblastoma

Glioblastoma (GBM) remains the most lethal and untreatable central nervous system malignancy. The challenges to devise novel and effective anti-tumor therapies include difficulty in locating the precise tumor border for complete surgical resection, and rapid regrowth of residual tumor tissue after standard treatment. Repeatable and non-invasive intranasal application of neural stem cells (NSCs) was recently shown to enable clinically relevant delivery of therapy to tumors. Treatment with chemotactic NSCs demonstrated significant survival benefits when coupled with radiation and oncolytic virotherapy in preclinical models of GBM. In order to further augment the clinical applicability of this novel therapeutic platform, we postulate that the FDA-approved compound, methimazole (MT), can be safely utilized to delay the nasal clearance and improve the ability of NSCs to penetrate the olfactory epithelium for robust in vivo brain tumor targeting and therapeutic actions. METHODS: To examine the role of reversible reduction of the olfactory epithelial barrier in non-invasive intranasal delivery, we explored the unique pharmacologic effect of MT at a single dosage regimen. In our proof-of-concept studies, quantitative magnetic resonance imaging (MRI), immunocytochemistry, and survival analysis were performed on glioma-bearing mice treated with a single dose of MT prior to intranasal anti-GBM therapy using an oncolytic virus (OV)-loaded NSCs. RESULTS: Based on histology and in vivo imaging, we found that disrupting the olfactory epithelium with MT effectively delays clearance and allows NSCs to persist in the nasal cavity for at least 24 h. MT pretreatment amplified the migration of NSCs to the tumor. The therapeutic advantage of this enhancement was quantitatively validated by tissue analysis and MRI tracking of NSCs loaded with superparamagnetic iron oxide nanoparticles (SPIOs) in live animals. Moreover, we observed significant survival benefits in GBM-bearing mice treated with intranasal delivery of oncolytic virus-loaded NSCs following MT injection. Conclusion: Our work identified a novel pharmacologic strategy to accelerate the clinical application of the non-invasive NSCs-based therapeutic platform to tackle aggressive brain tumors.

Virus oncolíticos: un arma contra el cáncer

Introducción. Los virus oncolíticos son virus atenuados, mutados o que por naturaleza se dirigen y matan específicamente células tumorales, sin afectar a las células normales. La administración intratumoral del virus ofrece la oportunidad de tratar el tumor primario pero no focos metastásicos, los cuales pueden ser alcanzados mediante la administración intravenosa. Sin embargo, su eficiencia puede disminuir por la presencia de una respuesta inmunológica preexistente en los sujetos tratados.Objetivo. Exponer las técnicas utilizadas para envolver y transportar los virus con el fin de eludir el sistema inmunológico antes de que el virus llegue al tumor.Materiales y métodos. Se realizó una búsqueda narrativa de la literatura original y de revisión en las bases de datos PubMed, JSTOR y EBSCO sobre métodos o técnicas utilizadas para el tratamiento del cáncer mediante el uso de virus oncolíticos.Resultados. La formación de nanocomplejos entre los virus oncolíticos y biopolímeros —ya sea mediante la unión química o mediante la unión a través de interacciones electrostáticas o el uso de micropartículas, células transportadoras, liposomas, ultrasonido o terapias combinadas– es eficaz para evitar la respuesta inmunológica del huésped contra el virus.Conclusión. Para evitar la respuesta inmunológica del huésped contra los virus oncolíticos se han desarrollo diversos métodos que permiten la liberación controlada y especifica de los mismos. Sin embargo, debido a la diversidad de los virus, se debe tener en cuenta que la eficacia de los métodos de protección y transporte depende de las características bioquímicas tanto del biomaterial como del virus.

Oncolytic viruses: overcoming translational challenges

Oncolytic virotherapy (OVT) is a promising approach in which WT or engineered viruses selectively replicate and destroy tumor cells while sparing normal ones. In the last two decades, different oncolytic viruses (OVs) have been modified and tested in a number of preclinical studies, some of which have led to clinical trials in cancer patients. These clinical trials have revealed several critical limitations with regard to viral delivery, spread, resistance, and antiviral immunity. Here, we focus on promising research strategies that have been developed to overcome the aforementioned obstacles. Such strategies include engineering OVs to target a broad spectrum of tumor cells while evading the immune system, developing unique delivery mechanisms, combining other immunotherapeutic agents with OVT, and using clinically translatable mouse tumor models to potentially translate OVT more readily into clinical settings.

Modified cells as potential ocular drug delivery systems

Drug delivery to ocular targets is problematic, especially in retinal disease treatment. Therefore, targeted drug delivery, prolonged drug action, and minimally invasive treatments are needed. In this review, we describe cell technologies for drug delivery. These technologies are based on genetic engineering and nongenetic-based approaches for cell modification. In principle, cell technologies enable targeted delivery, long drug action, and minimally invasive administration, but they have only been sparsely studied for ocular drug delivery. Herein, these technologies are discussed in the ocular context.

Enhanced Delivery of Oncolytic Adenovirus by Neural Stem Cells for Treatment of Metastatic Ovarian Cancer

Oncolytic virotherapy is a promising approach for treating recurrent and/or drug-resistant ovarian cancer. However, its successful application in the clinic has been hampered by rapid immune-mediated clearance or neutralization of the virus, which reduces viral access to tumor foci. To overcome this barrier, patient-derived mesenchymal stem cells have been used to deliver virus to tumors, but variability associated with autologous cell isolations prevents this approach from being broadly clinically applicable. Here, we demonstrate the ability of an allogeneic, clonal neural stem cell (NSC) line (HB1.F3.CD21) to protect oncolytic viral cargo from neutralizing antibodies within patient ascites fluid and to deliver it to tumors within preclinical peritoneal ovarian metastases models. The viral payload used is a conditionally replication-competent adenovirus driven by the survivin promoter (CRAd-S-pk7). Because the protein survivin is highly expressed in ovarian cancer, but not in normal differentiated cells, viral replication should occur selectively in ovarian tumor cells. We found this viral agent was effective against cisplatin-resistant ovarian tumors and could be used as an adjunct treatment with cisplatin to decrease tumor burden without increasing toxicity. Collectively, our data suggest NSC-delivered CRAd-S-pk7 virotherapy holds promise for improving clinical outcome, reducing toxicities, and improving quality of life for patients with advanced ovarian cancer.

Concise Review: Neural Stem Cell-Mediated Targeted Cancer Therapies

Cancer is one of the leading causes of morbidity and mortality worldwide, with 1,688,780 new cancer cases and 600,920 cancer deaths projected to occur in 2017 in the U.S. alone. Conventional cancer treatments including surgical, chemo-, and radiation therapies can be effective, but are often limited by tumor invasion, off-target toxicities, and acquired resistance. To improve clinical outcomes and decrease toxic side effects, more targeted, tumor-specific therapies are being developed. Delivering anticancer payloads using tumor-tropic cells can greatly increase therapeutic distribution to tumor sites, while sparing non-tumor tissues therefore minimizing toxic side effects. Neural stem cells (NSCs) are tumor-tropic cells that can pass through normal organs quickly, localize to invasive and metastatic tumor foci throughout the body, and cross the blood-brain barrier to reach tumors in the brain. This review focuses on the potential use of NSCs as vehicles to deliver various anticancer payloads selectively to tumor sites. The use of NSCs in cancer treatment has been studied most extensively in the brain, but the findings are applicable to other metastatic solid tumors, which will be described in this review. Strategies include NSC-mediated enzyme/prodrug gene therapy, oncolytic virotherapy, and delivery of antibodies, nanoparticles, and extracellular vesicles containing oligonucleotides. Preclinical discovery and translational studies, as well as early clinical trials, will be discussed. Stem Cells Translational Medicine 2018;7:740-747.

Autophagy in glioma cells: An identity crisis with a clinical perspective

Over the last decade, autophagy has emerged as one of the critical cellular systems that control homeostasis. Besides management of normal homeostatic processes, autophagy can also be induced by tissue damage stress or by rapidly progressing tumors. During tumor progression, autophagy mediates a cellular reaction to the changes inside and outside of cells, which leads to tumor adaptation. Even though the regulation of autophagy seems universal and is a well-described process, its dysregulation and role in glioma progression remain an important topic of investigation. In this review, we summarize recent evidence of autophagy regulation in brain tumor tissues and possible interconnection between signaling pathways that govern cellular responses. This perspective may help to assess the qualitative differences and various outcomes in response to autophagy stimulation.

A Survey of the Neuro-Oncology Landscape

The field of neuro-oncology is evolving rapidly. Many important advances have recently been reported, and other promising investigations have the potential to soon make substantial impacts in the field, especially in the areas of high-grade gliomas and brain metastases. We present an overview of the current status of this field, highlighting the key recent advances as well as representative work of key clinical investigations, since these concepts have the potential to influence clinical management if they are demonstrated to be safe and efficacious. This overview includes some work that has only appeared in abstract form in order to provide a timely understanding of how the field is actively changing and what may lie on the horizon. We focus on both medical and surgical neuro-oncology advances in this highly multidisciplinary subspecialty.

Stem cells in cancer therapy: opportunities and challenges

Metastatic cancer cells generally cannot be eradicated using traditional surgical or chemoradiotherapeutic strategies, and disease recurrence is extremely common following treatment. On the other hand, therapies employing stem cells are showing increasing promise in the treatment of cancer. Stem cells can function as novel delivery platforms by homing to and targeting both primary and metastatic tumor foci. Stem cells engineered to stably express various cytotoxic agents decrease tumor volumes and extend survival in preclinical animal models. They have also been employed as virus and nanoparticle carriers to enhance primary therapeutic efficacies and relieve treatment side effects. Additionally, stem cells can be applied in regenerative medicine, immunotherapy, cancer stem cell-targeted therapy, and anticancer drug screening applications. However, while using stem cells to treat human cancers appears technically feasible, challenges such as treatment durability and tumorigenesis necessitate further study to improve therapeutic performance and applicability. This review focuses on recent progress toward stem cell-based cancer treatments, and summarizes treatment advantages, opportunities, and shortcomings, potentially helping to refine future trials and facilitate the translation from experimental to clinical studies.

Immune System, Friend or Foe of Oncolytic Virotherapy?

Oncolytic viruses (OVs) are an emerging class of targeted anticancer therapies designed to selectively infect, replicate in, and lyse malignant cells without causing harm to normal, healthy tissues. In addition to direct oncolytic activity, OVs have shown dual promise as immunotherapeutic agents. The presence of viral infection and subsequently generated immunogenic tumor cell death trigger innate and adaptive immune responses that mediate further tumor destruction. However, antiviral immune responses can intrinsically limit OV infection, spread, and overall therapeutic efficacy. Host immune system can act both as a barrier as well as a facilitator and sometimes both at the same time based on the phase of viral infection. Thus, manipulating the host immune system to minimize antiviral responses and viral clearance while still promoting immune-mediated tumor destruction remains a key challenge facing oncolytic virotherapy. Recent clinical trials have established the safety, tolerability, and efficacy of virotherapies in the treatment of a variety of malignancies. Most notably, talimogene laherparepvec (T-VEC), a genetically engineered oncolytic herpesvirus-expressing granulocyte macrophage colony stimulating factor, was recently approved for the treatment of melanoma, representing the first OV to be approved by the FDA as an anticancer therapy in the US. This review discusses OVs and their antitumor properties, their complex interactions with the immune system, synergy between virotherapy and existing cancer treatments, and emerging strategies to augment the efficacy of OVs as anticancer therapies.

Human Neural Stem Cell Biodistribution and Predicted Tumor Coverage by a Diffusible Therapeutic in a Mouse Glioma Model

Engineered neural stem cells (NSCs) intrinsically migrating to brain tumors offer a promising mechanism for local therapeutic delivery. However, difficulties in quantitative assessments of NSC migration and in estimates of tumor coverage by diffusible therapeutics have impeded development and refinement of NSC-based therapies. To address this need, we developed techniques by which conventional serial-sectioned formalin-fixed paraffin-embedded (FFPE) brains can be analyzed in their entirety across multiple test animals. We considered a conventional human glioblastoma model: U251 glioma cells orthotopically engrafted in immunodeficient mice receiving intracerebral (i.c.) or intravenous (i.v.) administrations of NSCs expressing a diffusible enzyme to locally catalyze chemotherapeutic formation. NSC migration to tumor sites was dose-dependent, reaching 50%-60% of total administered NSCs for the i.c route and 1.5% for the i.v. route. Curiously, the most efficient NSC homing was seen with smaller NSC doses, implying existence of rate-limiting process active during administration and/or migration. Predicted tumor exposure to a diffusing therapeutic (assuming a 50 µm radius of action) could reach greater than 50% of the entire tumor volume for i.c. and 25% for i.v. administration. Within individual sections, coverage of tumor area could be as high as 100% for i.c. and 70% for i.v. routes. Greater estimated therapeutic coverage was observed for larger tumors and for larger tumor regions in individual sections. Overall, we have demonstrated a framework within which investigators may rationally evaluate NSC migration to, and integration into, brain tumors, and therefore enhance understanding of mechanisms that both promote and limit this therapeutic modality. Stem Cells Translational Medicine 2017;6:1522-1532.

Fibronectin-adherent peripheral blood derived mononuclear cells as Paclitaxel carriers for glioblastoma treatment: An in vitro study

BACKGROUND

Glioblastoma (GBM) represents the most aggressive malignant brain tumor in adults, with a risible median life expectancy despite gold standard treatment. Novel drug-delivery methods have been explored. Here we evaluated the possibility to use mononuclear cells (MCs) belonging to the monocytic-dendritic lineage as drug-carrier.

METHODS

MCs were obtained from 10 patients harboring a GBM, and from healthy volunteers, considered as controls. GBM tissue was also obtained from patients. MCs were cultured and the adherent population on fibronectin (FN-MCs), after immunocytochemistry and flow cytometry characterization, was loaded with Paclitaxel (FN-MCs-PTX). Antiproliferative and migration activity of FN-MCs-PTX was evaluated in two-dimensional (2D) and three-dimensional (3D) co-culture assays with red fluorescent U87 Malignant Glioma cells and primary GBM cells. Antiangiogenic properties of FN-MCs-PTX were tested on cultures with endothelial cells.

RESULTS

Phenotypical characterization showed a high expression of monocytic-dendritic markers in GBM cells and FN-MCs. FN-MCs demonstrated to effectively uptake PTX and to strongly inhibit GBM growth in vitro (P <0.01). Moreover, tumor-induced migration of MCs, although partially affected by the PTX cargo, remained statistically significant when compared with unprimed cells and this was confirmed in a 3D Matrigel model (P <0.01) and in a Trans-well assay (P <0.01). FN-MCs-PTX also disclosed considerable antiangiogenic properties.

DISCUSSION

Our results suggest that the fibronectin-adherent population of MCs isolated from peripheral blood can be an effective tool to inhibit GBM growth. Given the relative facility to obtain such cells and the short time needed for their culture and drug loading this approach may have potential as an adjuvant therapy for GBM.

Mesenchymal stromal cells for the delivery of oncolytic viruses in gliomas

Mesenchymal stromal cells (MSCs) are a type of adult stem cell that has been exploited for the treatment of a variety of diseases, including cancer. In particular, MSCs have been studied extensively for their ability to treat glioblastoma (GBM), the most common and deadly form of brain cancer in adults. MSCs are attractive therapeutics because they can be obtained relatively easily from patients, are capable of being expanded numerically in vitro, can be easily engineered and are inherently capable of homing to tumors, making them ideal vehicles for delivering biological antitumoral agents. Oncolytic viruses are promising biological therapeutic agents that have been used in the treatment of GBMs, and MSCs are currently being explored as a means of delivering these viruses. Here we review the role of MSCs in the treatment of GBMs, focusing on the intersection of MSCs and oncolytic viruses.

Intranasal Oncolytic Virotherapy with CXCR4-Enhanced Stem Cells Extends Survival in Mouse Model of Glioma

The challenges to effective drug delivery to brain tumors are twofold: (1) there is a lack of non-invasive methods of local delivery and (2) the blood-brain barrier limits systemic delivery. Intranasal delivery of therapeutics to the brain overcomes both challenges. In mouse model of malignant glioma, we observed that a small fraction of intranasally delivered neural stem cells (NSCs) can migrate to the brain tumor site. Here, we demonstrate that hypoxic preconditioning or overexpression of CXCR4 significantly enhances the tumor-targeting ability of NSCs, but without altering their phenotype only in genetically modified NSCs. Modified NSCs deliver oncolytic virus to glioma more efficiently and extend survival of experimental animals in the context of radiotherapy. Our findings indicate that intranasal delivery of stem cell-based therapeutics could be optimized for future clinical applications, and allow for safe and repeated administration of biological therapies to brain tumors and other CNS disorders.

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Intranasal delivery of NSCs is a promising platform for glioma therapy

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Hypoxia or CXCR4 overexpression enhances NSC migration to glioma

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Oncolytic viruses loaded in CXCR4-enhanced NSCs improve animal survival

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Non-invasive intranasal NSC-based therapies warrant clinical translation

Unlocking the promise of oncolytic virotherapy in glioma: combination with chemotherapy to enhance efficacy

Malignant glioma is a relentless burden to both patients and clinicians, and calls for innovation to overcome the limitations in current management. Glioma therapy using viruses has been investigated to accentuate the nature of a virus, killing a host tumor cell during its replication. As virus mediated approaches progress with promising therapeutic advantages, combination therapy with chemotherapy and oncolytic viruses has emerged as a more synergistic and possibly efficacious therapy. Here, we will review malignant glioma as well as prior experience with oncolytic viruses, chemotherapy and combination of the two, examining how the combination can be optimized in the future.

Single dose GLP toxicity and biodistribution study of a conditionally replicative adenovirus vector, CRAd-S-pk7, administered by intracerebral injection to Syrian hamsters

Background

CRAd-S-pk7 is a conditionally replicative oncolytic adenoviral vector that contains a survivin promoter and a pk7 fiber modification that confer tumor-specific transcriptional targeting and preferential replication in glioma while sparing the surrounding normal brain parenchyma.

Methods

This IND-enabling study performed under GLP conditions evaluated the toxicity and biodistribution of CRAd-S-pk7 administered as a single intracerebral dose to Syrian hamsters, a permissive model of adenoviral replication. Two hundred and forty animals were stereotactically administered either vehicle (n = 60) or CRAd-S-pk7 at 2.5 × 10⁷, 2.5 × 10⁸, or 2.5 × 10⁹ viral particles (vp)/animal (each n = 60) on day 1. The animals were closely monitored for toxicology evaluation, assessment of viral distribution, and immunogenicity of CRAd-S-pk7.

Results

Changes in hematology, clinical chemistry, and coagulation parameters were minor and transient, and consistent with the inflammatory changes observed microscopically. These changes were considered to be of little toxicological significance. The vector remained localized primarily in the brain and to some degree in the tissues at the incision site. Low levels of vector DNA were detected in other tissues in a few animals suggesting systemic circulation of the virus. Viral DNA was detected in brains of hamsters for up to 62 days. However, microscopic changes and virus-related toxicity to the central nervous system were considered minor and decreased in incidence and severity over time. Such changes are not uncommon in studies using adenoviral vectors.

Conclusion

This study provides safety and toxicology data justifying a clinical trial of CRAd-S-pk7 loaded in FDA-approved HB1.F3.CD neural stem cell carriers administered at the tumor resection bed in humans with recurrent malignant glioma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0895-8) contains supplementary material, which is available to authorized users.

Tamoxifen improves cytopathic effect of oncolytic adenovirus in primary glioblastoma cells mediated through autophagy

Oncolytic gene therapy using viral vectors may provide an attractive therapeutic option for malignant gliomas. These viral vectors are designed in a way to selectively target tumor cells and spare healthy cells. To determine the translational impact, it is imperative to assess the factors that interfere with the anti-glioma effects of the oncolytic adenoviral vectors. In the current study, we evaluated the efficacy of survivin-driven oncolytic adenoviruses pseudotyping with adenoviral fiber knob belonging to the adenoviral serotype 3, 11 and 35 in their ability to kill glioblastoma (GBM) cells selectively without affecting normal cells. Our results indicate that all recombinant vectors used in the study can effectively target GBM in vitro with high specificity, especially the 3 knob-modified vector. Using intracranial U87 and U251 GBM xenograft models we have also demonstrated that treatment with Conditionally Replicative Adenovirus (CRAd-S-5/3) vectors can effectively regress tumor. However, in several patient-derived GBM cell lines, cells exhibited resistance to the CRAd infection as evident from the diminishing effects of autophagy. To improve therapeutic response, tumor cells were pretreated with tamoxifen. Our preliminary data suggest that tamoxifen sensitizes glioblastoma cells towards oncolytic treatment with CRAd-S-5/3, which may prove useful for GBM in future experimental therapy.

Controlled Payload Release by Magnetic Field Triggered Neural Stem Cell Destruction for Malignant Glioma Treatment

Stem cells have recently garnered attention as drug and particle carriers to sites of tumors, due to their natural ability to track to the site of interest. Specifically, neural stem cells (NSCs) have demonstrated to be a promising candidate for delivering therapeutics to malignant glioma, a primary brain tumor that is not curable by current treatments, and inevitably fatal. In this article, we demonstrate that NSCs are able to internalize 2 μm magnetic discs (SD), without affecting the health of the cells. The SD can then be remotely triggered in an applied 1 T rotating magnetic field to deliver a payload. Furthermore, we use this NSC-SD delivery system to deliver the SD themselves as a therapeutic agent to mechanically destroy glioma cells. NSCs were incubated with the SD overnight before treatment with a 1T rotating magnetic field to trigger the SD release. The potential timed release effects of the magnetic particles were tested with migration assays, confocal microscopy and immunohistochemistry for apoptosis. After the magnetic field triggered SD release, glioma cells were added and allowed to internalize the particles. Once internalized, another dose of the magnetic field treatment was administered to trigger mechanically induced apoptotic cell death of the glioma cells by the rotating SD. We are able to determine that NSC-SD and magnetic field treatment can achieve over 50% glioma cell death when loaded at 50 SD/cell, making this a promising therapeutic for the treatment of glioma.

Oncolytic viruses for therapy of malignant glioma

Effective treatment of malignant brain tumors is still an open problem. Location of tumor in vital areas of the brain significantly limits capasities of surgical treatment. The presence of tumor stem cells resistant to radiation and anticancer drugs in brain tumor complicates use of chemoradiotherapy and causes a high rate of disease recurrence. A technological improvement in bioselection and production of recombinant resulted in creation of viruses with potent oncolytic properties against glial tumors. Recent studies, including clinical trials, showed, that majority of oncolytic viruses are safe. Despite the impressive results of the viral therapy in some patients, the treatment of other patients is not effective; therefore, further improvement of the methods of oncolytic virotherapy is necessary. High genetic heterogeneity of glial tumor cells even within a single tumor determines differences in individual sensitivity of tumor cells to oncolytic viruses. This review analyses the most successful oncolytic virus strains, including those which had reached clinical trials, and discusses the prospects for new approaches to virotherapy of gliomas.