Neural stem cells display extensive tropism for pathology in adult brain: evidence from intracranial gliomas

Targeting post-translational histone modifying enzymes in glioblastoma

Glioblastoma (GBM) is the most common primary brain tumor in adults, and the most lethal form of glioma, characterized by variable histopathology, aggressiveness and poor clinical outcome and prognosis. GBMs constitute a challenge for oncologists because of their molecular heterogeneity, extensive invasion, and tendency to relapse. Glioma cells demonstrate a variety of deregulated genomic pathways and extensive interplay with epigenetic alterations. Epigenetic modifications have emerged as essential players in GBM research, with biomarker potential for tumor classification and prognosis and for drug targeting. Histone posttranslational modifications (PTMs) are crucial regulators of chromatin architecture and gene expression, playing a pivotal role in malignant transformation, tumor development and progression. Alteration in the expression of genes coding for lysine and arginine methyltransferases (G9a, SUV39H1 and SETDB1) and acetyltransferases and deacetylases (KAT6A, SIRT2, SIRT7, HDAC4, 6, 9) contribute to GBM pathogenesis. In addition, proteins of the sumoylation pathway are upregulated in GBM cell lines, including E1 (SAE1), E2 (Ubc9) components, and a SUMO-specific protease (SENP1). Preclinical and clinical studies are currently in progress targeting epigenetic enzymes in gliomas, including a new generation of histone deacetylase (HDAC), protein arginine methyltransferase (PRMT) and bromodomain (BRD) inhibitors. Herein, we provide an update on recent advances in glioma epigenetic research, focusing on the role of histone modifications and the use of epigenetic therapy as a valid treatment option for glioblastoma.

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.

A facile and scalable in production non-viral gene engineered mesenchymal stem cells for effective suppression of temozolomide-resistant (TMZR) glioblastoma growth

BACKGROUND

Mesenchymal stem cells (MSCs) serve as an attractive vehicle for cell-directed enzyme prodrug therapy (CDEPT) due to their unique tumour-nesting ability. Such approach holds high therapeutic potential for treating solid tumours including glioblastoma multiforme (GBM), a devastating disease with limited effective treatment options. Currently, it is a common practice in research and clinical manufacturing to use viruses to deliver therapeutic genes into MSCs. However, this is limited by the inherent issues of safety, high cost and demanding manufacturing processes. The aim of this study is to identify a facile, scalable in production and highly efficient non-viral method to transiently engineer MSCs for prolonged and exceptionally high expression of a fused transgene: yeast cytosine deaminase::uracil phosphoribosyl-transferase::green fluorescent protein (CD::UPRT::GFP).

METHODS

MSCs were transfected with linear polyethylenimine using a cpg-free plasmid encoding the transgene in the presence of a combination of fusogenic lipids and β tubulin deacetylase inhibitor (Enhancer). Process scalability was evaluated in various planar vessels and microcarrier-based bioreactor. The transfection efficiency was determined with flow cytometry, and the therapeutic efficacy of CD::UPRT::GFP expressing MSCs was evaluated in cocultures with temozolomide (TMZ)-sensitive or TMZ-resistant human glioblastoma cell lines. In the presence of 5-fluorocytosine (5FC), the 5-fluorouracil-mediated cytotoxicity was determined by performing colometric MTS assay. In vivo antitumor effects were examined by local injection into subcutaneous TMZ-resistant tumors implanted in the athymic nude mice.

RESULTS

At > 90% transfection efficiency, the phenotype, differentiation potential and tumour tropism of MSCs were unaltered. High reproducibility was observed in all scales of transfection. The therapeutically modified MSCs displayed strong cytotoxicity towards both TMZ-sensitive and TMZ-resistant U251-MG and U87-MG cell lines only in the presence of 5FC. The effectiveness of this approach was further validated with other well-characterized and clinically annotated patient-derived GBM cells. Additionally, a long-term suppression (> 30 days) of the growth of a subcutaneous TMZ-resistant U-251MG tumour was demonstrated.

CONCLUSIONS

Collectively, this highly efficient non-viral workflow could potentially enable the scalable translation of therapeutically engineered MSC for the treatment of TMZ-resistant GBM and other applications beyond the scope of this study.

Feasibility of intracerebrally administering multiple doses of genetically modified neural stem cells to locally produce chemotherapy in glioma patients

Neural stem cells (NSCs) are tumor tropic and can be genetically modified to produce anti-cancer therapies locally in the brain. In a prior first-in-human study we demonstrated that a single dose of intracerebrally administered allogeneic NSCs, which were retrovirally transduced to express cytosine deaminase (CD), tracked to glioma sites and converted oral 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU). The next step in the clinical development of this NSC-based anti-cancer strategy was to assess the feasibility of administering multiple intracerebral doses of CD-expressing NSCs (CD-NSCs) in patients with recurrent high grade gliomas. CD-NSCs were given every 2 weeks using an indwelling brain catheter, followed each time by a 7-day course of oral 5-FC (and leucovorin in the final patient cohort). Fifteen evaluable patients received a median of 4 (range 2–10) intracerebral CD-NSC doses; doses were escalated from 50 x 10⁶ to 150 x 10⁶ CD-NSCs. Neuropharmacokinetic data confirmed that CD-NSCs continuously produced 5-FU in the brain during the course of 5-FC. There were no clinical signs of immunogenicity, and only three patients developed anti-NSC antibodies. Our results suggest intracerebral administration of serial doses of CD-NSCs is safe and feasible and identified a recommended dose for phase II testing of 150 x 10⁶ CD-NSCs.

Cell-Based Therapy for Stroke: Musing With Muse Cells

Stem cell-based regenerative therapies may rescue the central nervous system following ischemic stroke. Mesenchymal stem cells exhibit promising regenerative capacity in in vitro studies but display little to no incorporation in host tissue after transplantation in in vivo models of stroke. Despite these limitations, clinical trials using mesenchymal stem cells have produced some functional benefits ascribed to their ability to modulate the host's inflammatory response coupled with their robust safety profile. Regeneration of ischemic brain tissue using stem cells, however, remains elusive in humans. Multilineage-differentiating stress-enduring (Muse) cells are a distinct subset of mesenchymal stem cells found sporadically in connective tissue of nearly every organ. Since their discovery in 2010, these endogenous reparative stem cells have been investigated for their therapeutic potential against a variety of diseases, including acute myocardial infarction, stroke, chronic kidney disease, and liver disease. Preclinical studies have exemplified Muse cells' unique ability mobilize, differentiate, and engraft into damaged host tissue. Intravenously transplanted Muse cells in mouse lacunar stroke models afforded functional recovery and long-term engraftment into the host neural network. This mini-review article highlights these biological properties that make Muse cells an exceptional candidate donor source for cell therapy in ischemic stroke. Elucidating the mechanism behind the therapeutic potential of Muse cells will undoubtedly help optimize stem cell therapy for stroke and advance the field of regenerative medicine.

Collective invasion of glioma cells through OCT1 signalling and interaction with reactive astrocytes after surgery

Glioblastoma multiforme (GBM) is the most aggressive form of brain cancer with a short median survival time. GBM is characterized by the hallmarks of aggressive proliferation and cellular infiltration of normal brain tissue. miR-451 and its downstream molecules are known to play a pivotal role in regulation of the balance of proliferation and aggressive invasion in response to metabolic stress in the tumour microenvironment (TME). Surgery-induced transition in reactive astrocyte populations can play a significant role in tumour dynamics. In this work, we develop a multi-scale mathematical model of miR-451-LKB1-AMPK-OCT1-mTOR pathway signalling and individual cell dynamics of the tumour and reactive astrocytes after surgery. We show how the effects of fluctuating glucose on tumour cells need to be reprogrammed by taking into account the recent history of glucose variations and an AMPK/miR-451 reciprocal feedback loop. The model shows how variations in glucose availability significantly affect the activity of signalling molecules and, in turn, lead to critical cell migration. The model also predicts that microsurgery of a primary tumour induces phenotypical changes in reactive astrocytes and stem cell-like astrocytes promoting tumour cell proliferation and migration by Cxcl5. Finally, we investigated a new anti-tumour strategy by Cxcl5-targeting drugs. This article is part of the theme issue 'Multi-scale analysis and modelling of collective migration in biological systems'.

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.

Engineering Circulating Tumor Cells as Novel Cancer Theranostics

New ways to target and treat metastatic disease are urgently needed. Tumor “self-homing” describes the recruitment of circulating tumor cells (CTCs) back to a previously excised primary tumor location, contributing to tumor recurrence, as well as their migration to established metastatic lesions. Recently, self-homing CTCs have been exploited as delivery vehicles for anti-cancer therapeutics in preclinical primary tumor models. However, the ability of CTCs to self-home and treat metastatic disease is largely unknown.

Methods: Here, we used bioluminescence imaging (BLI) to explore whether systemically administered CTCs home to metastatic lesions and if CTCs armed with both a reporter gene and a cytotoxic prodrug gene therapy can be used to visualize and treat metastatic disease.

Results: BLI performed over time revealed a remarkable ability of CTCs to home to and treat tumors throughout the body. Excitingly, metastatic tumor burden in mice that received therapeutic CTCs was lower compared to mice receiving control CTCs.

Conclusion: This study demonstrates the noteworthy ability of experimental CTCs to home to disseminated breast cancer lesions. Moreover, by incorporating a prodrug gene therapy system into our self-homing CTCs, we show exciting progress towards effective and targeted delivery of gene-based therapeutics to treat both primary and metastatic lesions.

Nicotine does not affect stem cell properties requisite for suicide gene therapy against glioma

OBJECTIVE: 

Glioblastoma is one of the most lethal tumors in adult central nervous system with a median survival of a year and half and effective therapeutic strategy is urgently needed. For that reason, stem cell-based suicide gene therapies have attracted much interest because of potent tumor tropism of stem cells and bystander effect. In this current clinical situation, stem cells are promising delivery tool of suicide genes for glioma therapy. Since habitual cigarette smoking still prevails worldwide, we investigated the effect of nicotine on stem cell tropism toward glioma and gap junctional intercellular communication (GJIC) function between glioma and stem cells, both of which are important for suicide gene therapies. Methods: Mouse induced pluripotent stem cell-derived neural stem cells (iPS-NSCs) and human dental pulp mesenchymal stem cells (DPSCs) were used. The effect of nicotine on tumor tropism to glioma-conditioned medium (CM) at a non-cytotoxic concentration was assessed with Matrigel invasion assay. Nicotine effect on GJIC was assessed with the scrape loading/dye transfer (SL/DT) assay for co-culture of glioma and stem cells and the parachute assay among glioma cells using high-content analysis. Results: Tumor tropism of iPS-NSCs toward GL261-CM and DPSCs toward U251-CM was not affected by nicotine (0.1 and 1 µM). Nicotine at the concentrations equivalent to habitual smoking (1 µM) did not affect GJIC of iPS-NSC/GL261 and DPSC/U251 and GJIC among each glioma cells. Conclusions: The study demonstrated that non-cytotoxic concentrations of nicotine did not significantly change the stem cell properties requisite for stem cell-based suicide gene therapy.

Polymeric Biomaterial Scaffolds for Tumoricidal Stem Cell Glioblastoma Therapy

Glioblastoma (GBM) is the most common primary brain tumor and has a poor prognosis; as such, there is an urgent need to develop innovative new therapies. Tumoricidal stem cells are an emerging therapy that has the potential to combat limitations of traditional local and systemic chemotherapeutic strategies for GBM by providing a source for high, sustained concentrations of tumoricidal agents locally to the tumor. One major roadblock for tumoricidal stem cell therapy is that the persistence of tumoricidal stem cells injected as a cell suspension into the GBM surgical resection cavity is limited. Polymeric biomaterial scaffolds have been utilized to enhance the delivery of tumoricidal stem cells in the surgical resection cavity and extend their persistence in the brain, ultimately increasing their therapeutic efficacy against GBM. In this review, we examine three main scaffold categories explored for tumoricidal stem cell therapy: microcapsules, hydrogels, and electrospun scaffolds. Furthermore, considering the significant impact of surgery on the brain and recurrent GBM, we survey a brief history of orthotopic models of GBM surgical resection.

Neuronal signatures in cancer

Despite advances in the treatment of solid tumors, the prognosis of patients with many cancers remains poor, particularly of those with primary and metastatic brain tumors. In the last years, "Cancer Neuroscience" emerged as novel field of research at the crossroads of oncology and classical neuroscience. In primary brain tumors, including glioblastoma (GB), communicating networks that render tumor cells resistant against cytotoxic therapies were identified. To build these networks, GB cells extend neurite-like protrusions called tumor microtubes (TMs). Synapses on TMs allow tumor cells to retrieve neuronal input that fosters growth. Single cell sequencing further revealed that primary brain tumors recapitulate many steps of neurodevelopment. Interestingly, neuronal characteristics, including the ability to extend neurite-like protrusions, neuronal gene expression signatures and interactions with neurons, have now been found not only in brain and neuroendocrine tumors but also in some cancers of epithelial origin. In this review, we will provide an overview about neurite-like protrusions as well as neurodevelopmental origins, hierarchies and gene expression signatures in cancer. We will also discuss how "Cancer Neuroscience" might provide a framework for the development of novel therapies.

Personalized therapy and stem cell transplantation for pro-inflammatory modulation of cancer stem cells microenvironment in glioblastoma: Review

Glioblastoma multiforme (GBM) is one of the most aggressive types of brain tumor in humans. The prognosis for patients with GBM is unfavorable and treatment is largely ineffective, where modern treatment regimens typically increase survival by 15 months. GBM relapse and progression are associated with cancer stem cells (CSCs). The present review provides a critical analysis of the primary reasons underlying the lack of effectiveness of modern CSC management methods. An emphasis is placed on the role of the blood-brain barrier in the development of treatment resistance. The existing methods for increasing the efficiency of antitumor genotoxic therapy are also described, and a strategy for personalized regulation of CSC based on post-genome technologies is suggested. The hypothesis that GBM cells employ a special mechanism for DNA repair based on their interactions with normal stem cells, is presented and the function of the tumor microenvironment in fulfilling the antitumor potential of normal stem cells is explained. Additionally, the mechanisms by which cancer stem cells regulate glioblastoma progression and recurrence are described based on novel biomedical technologies.

Adult Stem Cell-Derived Extracellular Vesicles in Cancer Treatment: Opportunities and Challenges

Adult stem cells (SCs) participate in tissue repair and homeostasis regulation. The relative ease of SC handling and their therapeutic effect has made of these cell popular candidates for cellular therapy. However, several problems interfere with their clinical application in cancer treatment, like safety issues, unpredictable pro-tumour effects, and tissue entrapment. Therefore cell-free therapies that exhibit SC properties are being investigated. It is now well known that adult SCs exhibit their therapeutic effect via paracrine mechanisms. In addition to secretory proteins, SCs also release extracellular vesicles (EV) that deliver their contents to the target cells. Cancer treatment is one of the most promising applications of SC-EVs. Moreover, SC-EVs could be modified to improve targeted drug delivery. The aim of the review is to summarise current knowledge of adult SC-EV application in cancer treatment and to emphasise future opportunities and challenges in cancer treatment.

Generation and Profiling of Tumor-Homing Induced Neural Stem Cells from the Skin of Cancer Patients

The conversion of human fibroblasts into personalized induced neural stem cells (iNSCs) that actively seek out tumors and deliver cytotoxic agents is a highly promising approach for treating various types of cancer. However, the ability to generate iNSCs from the skin of cancer patients has not been explored. Here, we take an important step toward clinical application by generating iNSCs from skin biopsies of human patients undergoing treatment for the aggressive brain cancer, glioblastoma (GBM). We then utilized a panel of functional and genomic studies to investigate the efficacy and tumor-homing capacity of these patient-derived cells, as well as genomic analysis, to characterize the impact of interpatient variability on this personalized cell therapy. From the skin-tissue biopsies, we established fibroblasts and transdifferentiated the cells into iNSCs. Genomic and functional testing revealed marked variability in growth rates, therapeutic agent production, and gene expression during fibroblast-to-iNSC conversion among patient lines. In vivo testing showed patient-derived iNSCs home to tumors, yet rates and expression of homing-related pathways varied among patients. With the use of surgical-resection mouse models of invasive human cluster of differentiation 133⁺ (CD133⁺) GBM cells and serial kinetic imaging, we found that "high-performing" patient-derived iNSC lines reduced the volume of GBM cells 60-fold and extended survival from 28 to 45 days. Treatment with "low-performing" patient lines had minimal effect on tumor growth, but the anti-tumor effect could be rescued by increasing the intracavity dose. Together, these data show, for the first time, that tumor-homing iNSCs can be generated from the skin of cancer patients and efficaciously suppress tumor growth. We also begin to define genetic markers that could be used to identify cells that will contain the most effective attributes for tumor homing and kill in human patients, including high gene expression of the semaphorin-3B (SEMA3B), which is known to be involved in neuronal cell migration. These studies should serve as an important guide toward clinical GBM therapy, where the personalized nature of optimized iNSC therapy has the potential to avoid transplant rejection and maximize treatment durability.

Impact of composite scaffold degradation rate on neural stem cell persistence in the glioblastoma surgical resection cavity

Tumoricidal neural stem cells (NSCs) are an emerging therapy to combat glioblastoma (GBM). This therapy employs genetically engineered NSCs that secrete tumoricidal agents to seek out and kill tumor foci remaining after GBM surgical resection. Biomaterial scaffolds have previously been utilized to deliver NSCs to the resection cavity. Here, we investigated the impact of scaffold degradation rate on NSC persistence in the brain resection cavity. Composite acetalated dextran (Ace-DEX) gelatin electrospun scaffolds were fabricated with two distinct degradation profiles created by changing the ratio of cyclic to acyclic acetal coverage of Ace-DEX. In vitro, fast degrading scaffolds were fully degraded by one week, whereas slow degrading scaffolds had a half-life of >56 days. The scaffolds also retained distinct degradation profiles in vivo. Two different NSC lines readily adhered to and remained viable on Ace-DEX gelatin scaffolds, in vitro. Therapeutic NSCs secreting tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) had the same TRAIL output as tissue culture treated polystyrene (TCPS) when seeded on both scaffolds. Furthermore, secreted TRAIL was found to be highly potent against the human derived GBM cell line, GBM8, in vitro. Firefly luciferase expressing NSCs were seeded on scaffolds, implanted in a surgical resection cavity and their persistence in the brain was monitored by bioluminescent imaging (BLI). NSC loaded scaffolds were compared to a direct injection (DI) of NSCs in suspension, which is the current clinical approach to NSC therapy for GBM. Fast and slow degrading scaffolds enhanced NSC implantation efficiency 2.87 and 3.08-fold over DI, respectively. Interestingly, scaffold degradation profile did not significantly impact NSC persistence. However, persistence and long-term survival of NSCs was significantly greater for both scaffolds compared to DI, with scaffold implanted NSCs still detected by BLI at day 120 in most mice. Overall, these results highlight the benefit of utilizing a scaffold for application of tumoricidal NSC therapy for GBM.

Olfactory Ensheathing Cells: A Trojan Horse for Glioma Gene Therapy

BACKGROUND

The olfactory ensheathing cells (OECs) migrate from the peripheral nervous system to the central nervous system (CNS), a critical process for the development of the olfactory system and axonal extension after injury in neural regeneration. Because of their ability to migrate to the injury site and anti-inflammatory properties, OECs were tested against different neurological pathologies, but were never studied in the context of cancer. Here, we evaluated OEC tropism to gliomas and their potential as a "Trojan horse" to deliver therapeutic transgenes through the nasal pathway, their natural route to CNS.

METHODS

OECs were purified from the mouse olfactory bulb and engineered to express a fusion protein between cytosine deaminase and uracil phosphoribosyltransferase (CU), which convert the prodrug 5-fluorocytosine (5-FC) into cytotoxic metabolite 5-fluorouracil, leading to a bystander killing of tumor cells. These cells were injected into the nasal cavity of mice bearing glioblastoma tumors and OEC-mediated gene therapy was monitored by bioluminescence imaging and confirmed with survival and ex vivo histological analysis. All statistical tests were two-sided.

RESULTS

OECs migrated from the nasal pathway to the primary glioma site, tracked infiltrative glioma stemlike cells, and delivered therapeutic transgene, leading to a slower tumor growth and increased mice survival. At day 28, bioluminescence imaging revealed that mice treated with a single injection of OEC-expressing CU and 5-FC had tumor-associated photons (mean [SD]) of 1.08E + 08 [9.7E + 07] vs 4.1E + 08 [2.3E + 08] for control group (P < .001), with a median survival of 41 days vs 34 days, respectively (ratio = 0.8293, 95% confidence interval = 0.4323 to 1.226, P <  .001) (n = 9 mice per group).

CONCLUSIONS

We show for the first time that autologous transplantation of OECs can target and deliver therapeutic transgenes to brain tumors upon intranasal delivery, the natural route of OECs to the CNS, which could be extended to other types of cancer.

Developing Implantable Scaffolds to Enhance Neural Stem Cell Therapy for Post-Operative Glioblastoma

Pre-clinical and clinical studies have shown that engineered tumoricidal neural stem cells (tNSCs) are a promising treatment strategy for the aggressive brain cancer glioblastoma (GBM). Yet, stabilizing human tNSCs within the surgical cavity following GBM resection is a significant challenge. As a critical step toward advancing engineered human NSC therapy for GBM, we used a preclinical variant of the clinically utilized NSC line HB1.F3.CD and mouse models of human GBM resection/recurrence to identify a polymeric scaffold capable of maximizing the transplant, persistence, and tumor kill of NSC therapy for post-surgical GBM. Using kinetic bioluminescence imaging, we found that tNSCs delivered into the mouse surgical cavity wall by direct injection persisted only 3 days. We found that delivery of tNSCs into the cavity on nanofibrous electrospun poly-l-lactic acid scaffolds extended tNSC persistence to 8 days. Modifications to fiber surface coating, diameter, and morphology of the scaffold failed to significantly extend tNSC persistence in the cavity. In contrast, tNSCs delivered into the post-operative cavity on gelatin matrices (GEMs) persisted 8-fold longer as compared to direct injection. GEMs remained permissive to tumor-tropic homing, as tNSCs migrated off the scaffolds and into invasive tumor foci both in vitro and in vivo. To mirror envisioned human brain tumor trials, we engineered tNSCs to express the prodrug/enzyme thymidine kinase (tNSCs^tk) and transplanted the therapeutic cells in the post-operative cavity of mice bearing resected orthotopic patient-derived GBM xenografts. Following administration of the prodrug ganciclovir, residual tumor volumes in mice receiving GEM/tNSCs were reduced by 10-fold at day 35, and median survival was extended from 31 to 46 days. Taken together, these data begin to define design parameters for effective scaffold/tNSC composites and suggest a new approach to maximizing the efficacy of tNSC therapy in human patient trials.

Suicide gene therapy for the treatment of high-grade glioma: past lessons, present trends, and future prospects

Suicide gene therapy has represented an experimental cancer treatment modality for nearly 40 years. Among the various cancers experimentally treated by suicide gene therapy, high-grade gliomas have been the most prominent both in preclinical and clinical settings. Failure of a number of promising suicide gene therapy strategies in the clinic pointed toward a bleak future of this approach for the treatment of high-grade gliomas. Nevertheless, the development of new vectors and suicide genes, better prodrugs, more efficient delivery systems, and new combinatorial strategies represent active research areas that may eventually lead to better efficacy of suicide gene therapy. These trends are evident by the current increasing focus on suicide gene therapy for high-grade glioma treatment both in the laboratory and in the clinic. In this review, we give an overview of different suicide gene therapy approaches for glioma treatment and discuss clinical trials, delivery issues, and immune responses.

Intravenously Transplanted Human Multilineage-Differentiating Stress-Enduring Cells Afford Brain Repair in a Mouse Lacunar Stroke Model

Background and Purpose—

Multilineage-differentiating stress-enduring cells are endogenous nontumorigenic reparative pluripotent-like stem cells found in bone marrow, peripheral blood, and connective tissues. Topically administered human multilineage-differentiating stress-enduring cells into rat/mouse stroke models differentiated into neural cells and promoted clinically relevant functional recovery. However, critical questions on the appropriate timing and dose, and safety of the less invasive intravenous administration of clinical-grade multilineage-differentiating stress-enduring cell–based product CL2020 remain unanswered.

Methods—

Using an immunodeficient mouse lacunar model, CL2020 was administered via the cervical vein in different doses (high dose=5×10 4 cells/body; medium dose=1×10 4 cells/body; low dose=5×10 3 cells/body) at subacute phase (≈9 days after onset) and chronic phase (≈30 days). Cylinder test, depletion of human cells by diphtheria toxin administration, immunohistochemistry, and human specific-genome detection were performed.

Results—

Tumorigenesis and adverse effects were not detected for up to 22 weeks. The high-dose group displayed significant functional recovery compared with the vehicle group in cylinder test in subacute-phase–treated and chronic-phase–treated animals after 6 weeks and 8 weeks post-injection, respectively. In the high-dose group of subacute-phase–treated animals, robust and stable recovery in cylinder test persisted up to 22 weeks compared with the vehicle group. In both groups, intraperitoneal injection of diphtheria toxin abrogated the functional recovery. Anti-human mitochondria revealed CL2020 distributed mainly in the peri-infarct area at 1, 10, and 22 weeks and expressed NeuN (neuronal nuclei)- and MAP-2 (microtubule-associated protein-2)-immunoreactivity.

Conclusions—

Intravenously administered CL2020 was safe, migrated to the peri-infarct area, and afforded functional recovery in experimental stroke.

Advances in living cell-based anticancer therapeutics

This review summarizes recent advances in the applications of living cells as drug carriers or active drugs for anticancer drug delivery and cancer therapy.

Engineered stem cells targeting multiple cell surface receptors in tumors

Multiple stem cell types exhibit inherent tropism for cancer, and engineered stem cells have been used as therapeutic agents to specifically target cancer cells. Recently, stem cells have been engineered to target multiple surface receptors on tumor cells, as well as endothelial and immune cells in the tumor microenvironment. In this review, we discuss the rationales and strategies for developing multiple receptor-targeted stem cells, their mechanisms of action, and the promises and challenges they hold as cancer therapeutics.

The blood-brain barrier and blood-tumour barrier in brain tumours and metastases

For a blood-borne cancer therapeutic agent to be effective, it must cross the blood vessel wall to reach cancer cells in adequate quantities, and it must overcome the resistance conferred by the local microenvironment around cancer cells. The brain microenvironment can thwart the effectiveness of drugs against primary brain tumours as well as brain metastases. In this Review, we highlight the cellular and molecular components of the blood-brain barrier (BBB), a specialized neurovascular unit evolved to maintain brain homeostasis. Tumours are known to compromise the integrity of the BBB, resulting in a vasculature known as the blood-tumour barrier (BTB), which is highly heterogeneous and characterized by numerous distinct features, including non-uniform permeability and active efflux of molecules. We discuss the challenges posed by the BBB and BTB for drug delivery, how multiple cell types dictate BBB function and the role of the BTB in disease progression and treatment. Finally, we highlight emerging molecular, cellular and physical strategies to improve drug delivery across the BBB and BTB and discuss their impact on improving conventional as well as emerging treatments, such as immune checkpoint inhibitors and engineered T cells. A deeper understanding of the BBB and BTB through the application of single-cell sequencing and imaging techniques, and the development of biomarkers of BBB integrity along with systems biology approaches, should enable new personalized treatment strategies for primary brain malignancies and brain metastases.

Recent progress in the research of suicide gene therapy for malignant glioma

Malignant glioma, which is characterized by diffuse infiltration into the normal brain parenchyma, is the most aggressive primary brain tumor with dismal prognosis. Over the past 40 years, the median survival has only slightly improved. Therefore, new therapeutic modalities must be developed. In the 1990s, suicide gene therapy began attracting attention for the treatment of malignant glioma. Some clinical trials used a viral vector for suicide gene transduction; however, it was found that viral vectors cannot cover the large invaded area of glioma cells. Interest in this therapy was recently revived because some types of stem cells possess a tumor-tropic migratory capacity, which can be used as cellular delivery vehicles. Immortalized, clonal neural stem cell (NSC) line has been used for patients with recurrent high-grade glioma, which showed safety and efficacy. Embryonic and induced pluripotent stem cells may be considered as sources of NSC because NSC is difficult to harvest, and ethical issues have been raised. Mesenchymal stem cells are alternative candidates for cellular vehicle and are easily harvested from the bone marrow. In addition, a new type of nonlytic, amphotropic retroviral replicating vector encoding suicide gene has shown efficacy in patients with recurrent high-grade glioma in a clinical trial. This replicating viral capacity is another possible candidate as delivery vehicle to tackle gliomas. Herein, we review the concept of suicide gene therapy, as well as recent progress in preclinical and clinical studies in this field.

Biological intratumoral therapy for the high-grade glioma part II: vector- and cell-based therapies and radioimmunotherapy

Management of high-grade gliomas (HGGs) remains a complex challenge with an overall poor prognosis despite aggressive multimodal treatment. New translational research has focused on maximizing tumor cell eradication through improved tumor cell targeting while minimizing collateral systemic side effects. In particular, biological intratumoral therapies have been the focus of novel translational research efforts due to their inherent potential to be both dynamically adaptive and target specific. This two part review will provide an overview of biological intratumoral therapies that have been evaluated in human clinical trials in HGGs, and summarize key advances and remaining challenges in the development of these therapies as a potential new paradigm in the management of HGGs. Part II discusses vector-based therapies, cell-based therapies and radioimmunotherapy.

Biomimetic drug-delivery systems for the management of brain diseases

Acting as a double-edged sword, the blood-brain barrier (BBB) is essential for maintaining brain homeostasis by restricting the entry of small molecules and most macromolecules from blood. However, it also largely limits the brain delivery of most drugs. Even if a drug can penetrate the BBB, its accumulation in the intracerebral pathological regions is relatively low. Thus, an optimal drug-delivery system (DDS) for the management of brain diseases needs to display BBB permeability, lesion-targeting capability, and acceptable safety. Biomimetic DDSs, developed by directly utilizing or mimicking the biological structures and processes, provide promising approaches for overcoming the barriers to brain drug delivery. The present review summarizes the biological properties and biomedical applications of the biomimetic DDSs including the cell membrane-based DDS, lipoprotein-based DDS, exosome-based DDS, virus-based DDS, protein template-based DDS and peptide template-based DDS for the management of brain diseases.

The cell-based approach in neurosurgery: ongoing trends and future perspectives

OBJECTIVE

Examination of the current trends and future perspectives of the cell-based therapies in neurosurgery.

METHODS

A PubMed/MEDLINE-based systematic review has been performed combining the main Medical Subject Headings (MeSH) regarding the cell- and tissue-based therapies with the "Brain", "Spinal Cord", "Spine" and "Skull" MeSH terms. Only articles in English published in the last 10 years and pertinent to neurosurgery have been selected.

RESULTS

A total of 1,173 relevant articles have been chosen. Somatic cells and gene-modification technologies have undergone the greatest development. Immunotherapies and gene therapies have been tested for the cure of glioblastoma, stem cells mainly for brain and spinal cord traumatic injuries. Stem cells have also found a rationale in the treatment of the cranial and spinal bony defects, and of the intervertebral disc degeneration, as well.Most of the completed or ongoing trials concerning the cell-based therapies in neurosurgery are on phase 2. Future perspectives involve the need to overcome issues related to immunogenicity, oncogenicity and routes for administration. Refinement and improvement of vector design and delivery are required within the gene therapies.

CONCLUSION

The last decade has been characterised by a progressive evolution of neurosurgery from a purely mechanical phase to a new biological one. This trend has followed the rapid and parallel development of translational medicine and nanotechnologies.The introduction of new technologies, the optimisation of the already existing ones, and the reduction of costs are among the main challenges of the foreseeable future.

Preclinical And Clinical Development Of Oncolytic Adenovirus For The Treatment Of Malignant Glioma

Replication conditional oncolytic human adenovirus has long been considered a promising biological therapeutic to target high-grade gliomas (HGG), a group of essentially lethal primary brain cancer. The last decade has witnessed initiation and some completion of a number of Phase I and II clinical investigations of oncolytic adenovirus for HGG in the US and Europe. Results of these trials in patients are pivotal for not only federal approval but also filling an existing knowledge gap that primarily derives from the stark differences in permissivity to human adenovirus between humans and preclinical mouse models. DNX-2401 (Delta-24-RGD), the current mainstream oncolytic adenovirus with modifications in E1A and the fiber, has been shown to induce impressive objective response and long-term survival (>3 years) in a fraction of patients with recurrent HGG. Responders exhibited initial enlargement of the treated lesions for a few months post treatment, followed by shrinkage and near complete resolution. In accord with preclinical research, post-treatment specimens revealed virus-mediated alteration of the immune tumor microenvironment as evidenced by infiltration of CD8+ T cells and M1-polarized macrophages. These findings are encouraging and together with further information from ongoing studies have a potential to make oncolytic adenovirus a viable option for clinical management of HGG. This review deals with this timely topic; we will describe both preclinical and clinical development of oncolytic adenovirus therapy for HGG, summarize updated knowledge on clinical trials and discuss challenges that the field currently faces.

Preclinical analysis of human mesenchymal stem cells: tumor tropism and therapeutic efficiency of local HSV-TK suicide gene therapy in glioblastoma

Glioblastoma are highly invasive and associated with limited therapeutic options and a grim prognosis. Using stem cells to extend current therapeutic strategies by targeted drug delivery to infiltrated tumors cells is highly attractive. This study analyzes the tumor homing and therapeutic abilities of clinical grade human mesenchymal stem cells (MSCs) in an orthotopic glioblastoma mouse model. Our time course analysis demonstrated that MSCs display a rapid targeted migration to intracerebral U87 glioma xenografts growing in the contralateral hemisphere within the first 48h hours after application as assessed by histology and 7T magnetic resonance imaging. MSCs accumulated predominantly peritumorally but also infiltrated the main tumor mass and targeted distant tumor satellites while no MSCs were found in other regions of the brain. Intratumoral application of MSCs expressing herpes simplex virus thymidine kinase followed by systemic prodrug application of ganciclovir led to a significant tumor growth inhibition of 86% versus the control groups (p<0.05), which translated in a significant prolonged survival time (p<0.05). This study demonstrates that human MSCs generated according to apceth’s GMP process from healthy donors are able to target and provide a significant growth inhibition in a glioblastoma model supporting a potential clinical translation.

Glioblastoma extracellular vesicles induce the tumour-promoting transformation of neural stem cells

Recurrent glioblastomas are frequently found near subventricular zone (SVZ) areas of the brain where neural stem cells (NSCs) reside, and glioblastoma-derived extracellular vesicles (EVs) are reported to play important roles in tumour micro-environment, but the details are not clear. Here, we investigated the possibility that NSCs are involved in glioblastoma relapse mediated by glioblastoma-derived EVs. We studied changes to NSCs by adding glioblastoma-derived EVs into a culture system of NSCs, and found that NSCs differentiated into a type of tumour-promoting cell. These transformed cells had distinguished proliferation activity, a high migration rate, and clone-forming ability revealed by CCK-8, wound healing and soft agar clone formation assays, respectively. In vivo assays indicated that these cells could accelerate tumour formation by Ln229 cells in nude mice. Moreover, to explore the mechanisms underlying NSC transformation, single cell transcriptome sequencing was performed; our results suggest that several key genes such as S100B, CXCL14, EFEMP1, SCRG1, GLIPR1, HMGA1 and CD44 and dysregulated signalling may be important for the transformation of NSCs. It is also indicated that NSCs may be involved in glioblastoma recurrence through EV release by glioblastoma in this work. This could help to illuminate the mechanism of glioblastoma relapse, which occurs in a brief period after surgical excision, and contribute to finding new ways to treat this disease.

High dose vs low dose irradiation of the subventricular zone in patients with glioblastoma-a systematic review and meta-analysis

PURPOSE

The published data indicate that the irradiation of the subventricular zone (SVZ) might play a role in the treatment of patients with glioblastoma (GBM). We aimed to determine whether radiation treatment doses (high vs low) applied to the SVZ can lead to an increase in progression free survival (PFS) and overall survival (OS).

PATIENTS AND METHODS

We undertook a systematic review and meta-analysis according to the PICOS research criteria of patients with glioblastoma which received high doses compared to low doses in order to determine if they have a better survival in observational and experimental studies.

RESULTS

Our survey of the literature yielded 2573 unique records. After screening, 17 were assessed for eligibility, and in the end 8 were included in the qualitative and 4 in the quantitative analysis. Subjects who received higher doses of ipsilateral SVZ (iSVZ) irradiation had a statistically significant better PFS than those receiving lower doses (HR 0.58 [95% CI 0.42-0.82], p=0.002). Subjects receiving higher doses of contralateral SVZ (cSVZ) irradiation did not have a statistically significant better PFS than those receiving lower doses (HR =0.89 [95% CI 0.35-2.26], p=0.81). Also for OS the subjects receiving higher doses to the iSVZ did not have a statistically significant better survival than those receiving lower doses (HR =0.75 [95% CI 0.51-1.11], p=0.15).

CONCLUSION

The data indicate a possible involvement of the SVZ in the onset and progression of the GBM, as well as a possible role of the SVZ in radiation therapy.

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.

Neural stem cells promote glioblastoma formation in nude mice

PURPOSE

Neural stem cells (NSCs) have been characterized with the ability of self-renewal and neurogenesis, which has inspired lots of studies to clarify the functions of NSCs in neural injury, ischemic stroke, brain inflammation and neurodegenerative diseases. We focused on the relationship of NSCs with glioblastoma, since we have discovered that recurrent glioblastomas were inclined to be derived from subventricular zone (SVZ), where NSCs reside. We want to clarify whether NSCs are involved in glioblastoma relapse.

METHODS

Immunocytochemistry was used to confirm the stemness of NSCs. The Cell Counting Kit-8 was used to measure the proliferation of cells. Migration abilities were examined by wound healing and transwell assays, and tumor formation abilities were confirmed in nude mice.

RESULTS

We found in experiments that NSCs promoted proliferation of a glioblastoma cell line-Ln229, the migration ability of Ln229 cells was motivated by co-cultured with NSCs. Tumor formation of Ln229 cells was also accelerated in nude mice when co-transplanted with NSCs. In immunohistochemistry, we found that the Sox2- and Ki67-positive cells were much higher in co-transplanted groups than that of control groups.

CONCLUSIONS

These results imply the potential role that NSCs play in speeding up tumor formation in the process of glioblastoma relapse, providing the basis for dealing with newly diagnosed glioblastoma patients, which may help postpone the recurrence of glioblastoma as far as possible through preprocessing the tumor-adjacent SVZ tissue.

Stem cell-mediated delivery of nanogels loaded with ultrasmall iron oxide nanoparticles for enhanced tumor MR imaging

The development of new nanoplatforms with enhanced tumor accumulation for accurate diagnosis still remains a great challenge in current precision nanomedicine. Herein, we report the design of stem cell-mediated delivery of nanogels (NGs) loaded with ultrasmall iron oxide (Fe3O4) nanoparticles (NPs) for enhanced magnetic resonance (MR) imaging of tumors. In this study, sodium citrate-stabilized ultrasmall Fe3O4 NPs with a size of 3.16 ± 1.30 nm were first synthesized using a solvothermal route, coated with polyethyleneimine (PEI), and used as crosslinkers to crosslink alginate (AG) NGs formed via a double emulsion approach, where the AG carboxyl groups were pre-activated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The thus prepared Fe3O4 NP-loaded NGs (AG/PEI-Fe3O4 NGs) with a size of 47.68 ± 3.41 nm are water-dispersible, colloidally stable, cytocompatible in a given concentration range, display a relatively high r1 relaxivity (r1 = 1.5 mM-1 s-1), and are able to be taken up by bone mesenchymal stem cells without compromising cell viability and stem cell characteristics. Due to the tumor-chemotaxis or tumor tropism, the BMSCs are able to mediate the enhanced delivery of AG/PEI-Fe3O4 NGs to the tumor site after intravenous injection, thus enabling significantly strengthened MR imaging of tumors when compared to free NGs. These findings suggest that the developed AG/PEI-Fe3O4NGs, once mediated by stem cells may serve as a novel, safe, effective and targeted platform for enhanced MR imaging of tumors.

Recent advances in intradural spinal tumors

Intradural spinal tumors are rare tumors of the central nervous system. Due to the eloquence of the spinal cord and its tracts, the compact architecture of the cord and nerves, and the infiltrative nature of some of these tumors, surgical resection is difficult to achieve without causing neurological deficits. Likewise, chemotherapy and radiotherapy are utilized more cautiously in the treatment of intradural spinal tumors than their cranial counterparts. Targeted therapies aimed at the genetic alterations and molecular biology tailored to these tumors would be helpful but are lacking.Here, we review the major types of intradural spinal tumors, with an emphasis on genetic alterations, molecular biology, and experimental therapies for these difficult to treat neoplasms.

Tracking Neural Progenitor Cell Migration in the Rodent Brain Using Magnetic Resonance Imaging

The study of neurogenesis and neural progenitor cells (NPCs) is important across the biomedical spectrum, from learning about normal brain development and studying disease to engineering new strategies in regenerative medicine. In adult mammals, NPCs proliferate in two main areas of the brain, the subventricular zone (SVZ) and the subgranular zone, and continue to migrate even after neurogenesis has ceased within the rest of the brain. In healthy animals, NPCs migrate along the rostral migratory stream (RMS) from the SVZ to the olfactory bulb, and in diseased animals, NPCs migrate toward lesions such as stroke and tumors. Here we review how MRI-based cell tracking using iron oxide particles can be used to monitor and quantify NPC migration in the intact rodent brain, in a serial and relatively non-invasive fashion. NPCs can either be labeled directly in situ by injecting particles into the lateral ventricle or RMS, where NPCs can take up particles, or cells can be harvested and labeled in vitro, then injected into the brain. For in situ labeling experiments, the particle type, injection site, and image analysis methods have been optimized and cell migration toward stroke and multiple sclerosis lesions has been investigated. Delivery of labeled exogenous NPCs has allowed imaging of cell migration toward more sites of neuropathology, which may enable new diagnostic and therapeutic opportunities for as-of-yet untreatable neurological diseases.

Targeted Delivery to Tumors: Multidirectional Strategies to Improve Treatment Efficiency

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

A promising therapeutic strategy for metastatic gestational trophoblastic disease: Engineered anticancer gene-expressing stem cells to selectively target choriocarcinoma

Gestational trophoblastic disease (GTD) is an unusual disease occurring in pregnancy that originates from abnormal trophoblastic cells and comprises a group of diseases with different properties of invasion, metastasis and recurrence. The GTD group includes hydatidiform moles and gestational trophoblastic neoplasms (GTNs), with GTNs being divided into invasive moles, choriocarcinoma, placental site trophoblastic tumors and epithelioid trophoblastic tumors. The present review focuses on current effective treatments for GTD, including conventional and novel promising direct enzyme prodrug therapies (DEPTs). Conventional therapies, such as chemotherapy and hysterectomy, are currently used in a clinical setting; however, the use of diverse DEPTs, including antibody-DEPT and gene-DEPT is also being attempted to cure GTNs. In addition, gene delivery tools using genetically engineered neural stem cells (NSCs) are presently being examined for the treatment of GTNs. The tumor-tropism of NSCs by chemoattractant factors is a unique characteristic of these cells and can serve as a vehicle to deliver anticancer agents. Previous studies have demonstrated that injection with NSC-expressing suicide genes into xenograft animal models has a significant inhibitory effect on tumor growth. Stem cells can be genetically engineered to express anticancer genes, which migrate to the metastatic sites and selectively target cancer cells, and are considered to effectively target metastatic GTNs. However, the safety issue of stem cell therapy, such as tumorigenesis, remains a challenge. Novel therapies comprising a combination of conventional and novel promising treatments are anticipated to be definitive treatments for metastasized and/or recurrent patients with GTNs.

Insulin-like Growth Factor-1 Receptor Dictates Beneficial Effects of Treadmill Training by Regulating Survival and Migration of Neural Stem Cell Grafts in the Injured Spinal Cord

Survival and migration of transplanted neural stem cells (NSCs) are prerequisites for therapeutic benefits in spinal cord injury. We have shown that survival of NSC grafts declines after transplantation into the injured spinal cord, and that combining treadmill training (TMT) enhances NSC survival via insulin-like growth factor-1 (IGF-1). Here, we aimed to obtain genetic evidence that IGF-1 signaling in the transplanted NSCs determines the beneficial effects of TMT. We transplanted NSCs heterozygous (+/-) for Igf1r, the gene encoding IGF-1 receptor, into the mouse spinal cord after injury, with or without combining TMT. We analyzed the influence of genotype and TMT on locomotor recovery and survival and migration of NSC grafts. In vitro experiments were performed to examine the potential roles of IGF-1 signaling in the migratory ability of NSCs. Mice receiving +/- NSC grafts showed impaired locomotor recovery compared with those receiving wild-type (+/+) NSCs. Locomotor improvement by TMT was more pronounced with +/+ grafts. Deficiency of one allele of Igf1r significantly reduced survival and migration of the transplanted NSCs. Although TMT did not significantly influence NSC survival, it substantially enhanced the extent of migration for only +/+ NSCs. Cultured neurospheres exhibited dynamic motility with cytoplasmic protrusions, which was regulated by IGF-1 signaling. IGF-1 signaling in transplanted NSCs may be essential in regulating their survival and migration. Furthermore, TMT may promote NSC graft-mediated locomotor recovery via activation of IGF-1 signaling in transplanted NSCs. Dynamic NSC motility via IGF-1 signaling may be the cellular basis for the TMT-induced enhancement of migration.

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.

Neural stem cell-derived factors inhibit the growth and invasion of U87 stem-like cells in vitro

Glioma is one of the most common and aggressive tumors in the brain. Significant attention has been paid to the potential use of neural stem/progenitor cells (NSCs/NPCs) as delivery vehicles to cure gliomas. However, whether the NSCs/NPCs or the factors they produced could make a contribution still remains to be seen. In this study, we focused on the inhibitory effects of the factors produced by NSCs/NPCs on the biological behavior of the glioma stem-like cell in vitro. The human glioma cell line U87 was selected and the U87 stem-like cells were addressed. After being cultured in the NSC condition medium (NSC-CM), the viability and proliferation of U87 stem-like cells were significantly reduced. The invasion of U87 stem-like cells and the migration of U87 cells were also significantly decreased. However, no significant change was observed in regard to the astrocytic differentiation of U87 stem-like cells. These indicated that NSCs/NPCs produced some factors and had an inhibitory effect on the growth and invasion but not the terminal differentiation of U87 stem-like cells. It is worth paying attention to NSCs/NPCs as a high-potential candidate for glioma treatment.

Tumoricidal effect of human olfactory ensheathing cell mediated suicide gene therapy in human glioblastoma cells

The potential of herpes simplex virus type 1 thymidine kinase (HSV-tk)-expressing olfactory ensheathing cells (OEC) treated with ganciclovir (GCV) to induce cell death in adjacent HSV-tk-negative cells (bystander effect) has been well demonstrated. Although it has been shown that bystander effect occurs through the delivery of phosphorylated GCV, the bystander effect mechanism and the role of gap junctions for human OECs mediated suicide gene therapy in primary astrocytes of human glioblastma remain obscure. In the present study, the efficacy of a new method for the transfer of phosphorylated GCV from OECs into primary astrocytes was evaluated. Surgical biopsy of glioblastoma was used to isolate primary astrocyte. Biopsy of olfactory mucosa was applied to isolate olfactory ensheathing cell. Expression of S100-beta antigen was confirmed immunocytochemically in astrocytes and OECs. OECs were transduced to lentiviral containing thymidine kinase gene (TK) and co-cultured with astrocytes. Fluorescent dye transfer and western blot analysis indicated the expression of connexin43 between olfactory ensheathing cells and astrocytes whereas, expression of the gap junction protein connexin43 was inhibited by the gap junction inhibitor 18α-glycyrrhethinic acid (AGA, 20 µg/ml). Furthermore, co-culture of astrocytes with OEC-TK in the presence of concentration of 30 µg/ml GCV led to a decrease in astrocytes survival rate. Also, apoptosis hallmarks, including DNA fragmentation in cell nuclear, expression increase of Bax to Bcl-2 ratio and increase of caspase3 activation were observed in this study. Our findings suggest that human olfactory ensheathing cells can deliver phosphorylated GCV into the glioblastoma derived astrocytes through gap junction communication for apoptosis induction.

Spinal cord astrocytomas: progresses in experimental and clinical investigations for developing recovery neurobiology-based novel therapies

Spinal cord astrocytomas (SCAs) have discernibly unique signatures in regards to epidemiology, clinical oncological features, genetic markers, pathophysiology, and research and therapeutic challenges. Overall, there are presently very limited clinical management options for high grade SCAs despite progresses made in validating key molecular markers and standardizing tumor classification. The endeavors were aimed to improve diagnosis, therapy design and prognosis assessment, as well as to define more effective oncolytic targets. Efficacious treatment for high grade SCAs still remains an unmet medical demand. This review is therefore focused on research state updates that have been made upon analyzing clinical characteristics, diagnostic classification, genetic and molecular features, tumor initiation cell biology, and current management options for SCAs. Particular emphasis was given to basic and translational research endeavors targeting SCAs, including establishment of experimental models, exploration of unique profiles of SCA stem cell-like tumor survival cells, characterization of special requirements for effective therapeutic delivery into the spinal cord, and development of donor stem cell-based gene-directed enzyme prodrug therapy. We concluded that precise understanding of molecular oncology, tumor survival mechanisms (e.g., drug resistance, metastasis, and cancer stem cells/tumor survival cells), and principles of Recovery Neurobiology can help to create clinically meaningful experimental models of SCAs. Establishment of such systems will expedite the discovery of efficacious therapies that not only kill tumor cells but simultaneously preserve and improve residual neural function.

Interaction of hematopoietic CD34+ CD45+ stem cells and cancer cells stimulated by TGF‑β1 in a model of glioblastoma in vitro

The majority of modern treatment methods for malignant brain tumors are not sufficiently effective, with a median survival time varying between 9 and 14 months. Metastatic and invasive processes are the principal characteristics of malignant tumors. The most important pathogenic mechanism is epithelial‑mesenchymal transition (EMT), which causes epithelial cells to become more mobile, and capable of invading the surrounding tissues and migrating to distant organs. Transforming growth factor‑β1 (TGF‑β1) serves a key role in EMT‑inducing mechanisms. The current study presented the interaction between hematopoietic stem cells and glioblastoma cells stimulated by TGF‑β1 in vitro. The materials for the study were hematopoietic progenitor cell antigen CD34+ hematopoietic stem cells (HSCs) and U87 glioblastoma cells. Cell culture methods, automated monitoring of cell‑cell interactions, confocal laser microscopy, flow cytometry and electron microscopy were used. It was demonstrated that U87 cells have a complex communication system, including adhesive intercellular contacts, areas of interdigitation with dissolution of the cytoplasm, cell fusion, communication microtubes and microvesicles. TGF‑β1 affected glioblastoma cells by modifying the cell shape and intensifying their exocrine function. HSCs migrated to glioblastoma cells, interacted with them and exchanged fluorescent tags. Stimulation of cancer cells with TGF‑β1 weakened the ability of glioblastoma cells to attract HSCs and exchange a fluorescent tag. This process stimulated cancer cell proliferation, which is an indication of the ability of HSCs to 'switch' the proliferation and invasion processes in glioblastoma cells.

Mesenchymal stem cells loaded with paclitaxel-poly(lactic-co-glycolic acid) nanoparticles for glioma-targeting therapy

Background

Mesenchymal stem cells (MSCs) possess inherent tropism towards tumor cells, and so have attracted increased attention as targeted-therapy vehicles for glioma treatment.

Purpose

The objective of this study was to demonstrate the injection of MSCs loaded with paclitaxel (Ptx)-encapsulated poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles (NPs) for orthotopic glioma therapy in rats.

Methods

Ptx-PLGA NP-loaded MSC was obtained by incubating MSCs with Ptx-PLGA NPs. The drug transfer and cytotoxicity of Ptx-PLGA NP-loaded MSC against tumor cells were investigated in the transwell system. Biodistribution and antitumor activity was evaluated in the orthotopic glioma rats after contralateral injection.

Results

The optimal dose of MSC-loaded Ptx-PLGA NPs (1 pg/cell Ptx) had little effect on MSC-migration capacity, cell cycle, or multilineage-differentiation potential. Compared with Ptx-primed MSCs, Ptx-PLGA NP-primed MSCs had enhanced sustained Ptx release in the form of free Ptx and Ptx NPs. Ptx transfer from MSCs to glioma cells could induce tumor cell death in vitro. As for distribution in vivo, NP-loaded fluorescent MSCs were tracked throughout the tumor mass for 2 days after therapeutic injection. Survival was significantly longer after contralateral implantation of Ptx-PLGA NP-loaded MSCs than those injected with Ptx-primed MSCs or Ptx-PLGA NPs alone.

Conclusion

Based on timing and sufficient Ptx transfer from the MSCs to the tumor cells, Ptx-PLGA NP-loaded MSC is effective for glioma treatment. Incorporation of chemotherapeutic drug-loaded NPs into MSCs is a promising strategy for tumor-targeted therapy.