Therapeutic effect of genetically modified human neural stem cells encoding cytosine deaminase on experimental glioma

Advances in stem cell-based therapeutic transfers for glioblastoma treatment

INTRODUCTION

Glioblastoma (GBM), a highly malignant brain tumor, has a poor prognosis despite standard treatments like surgery, chemotherapy, and radiation. Glioblastoma stem cells (GSCs) play a critical role in recurrence and therapy resistance. Stem cell-based therapies have emerged as innovative approaches, leveraging the tumor-targeting abilities of stem cells to deliver treatments directly to GBM.

AREAS COVERED

This review focuses on using intact stem cells or subtypes for GBM therapy, excluding antigenic characteristics. The stem cell-based therapies explored include neural, mesenchymal, glioblastoma, hematopoietic and adipose-derived stem cells that have been investigated in both clinical and preclinical settings. A systematic search in PubMed, EMBASE, ClinicalTrials.gov, and Scopus had identified research up until January 2024. Key mechanisms reviewed include immune modulation, angiogenesis inhibition, and apoptosis induction. Discussion of completed and ongoing trials include emphasis on safety, efficacy, challenges, and study design limitations.

EXPERT OPINION

Stem cell-based therapies hold promise for treating GBM by targeting GSCs and improving treatment outcomes. Despite some potential advantages, challenges such as tumorigenesis risks, delivery complexities, and sustained therapeutic effects persist. Future research should prioritize optimizing stem cell modifications, combining them with current treatments, and conducting large-scale trials to ensure safety and efficacy. Integrating stem cell therapies into GBM treatment could provide more effective and less invasive options for patients.

Intravenously Infused Stem Cells for Cancer Treatment

Despite the recent influx of immunotherapies and small molecule drugs to treat tumors, cancer remains a leading cause of death in the United States, in large part due to the difficulties of treating metastatic cancer. Stem cells, which are inherently tumoritropic, provide a useful drug delivery vehicle to target both primary and metastatic tumors. Intravenous infusions of stem cells carrying or secreting therapeutic payloads show significant promise in the treatment of cancer. Stem cells may be engineered to secrete cytotoxic products, loaded with oncolytic viruses or nanoparticles containing small molecule drugs, or conjugated with immunotherapies. Herein we describe these preclinical and clinical studies, discuss the distribution and migration of stem cells following intravenous infusion, and examine both the limitations of and the methods to improve the migration and therapeutic efficacy of tumoritropic, therapeutic stem cells.

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.

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.

Tumor-specific gene therapy for pancreatic cancer using human neural stem cells encoding carboxylesterase

Advanced pancreatic cancer is one of the most lethal malignant human diseases lacking effective treatment. Its extremely low survival rate necessitates development of novel therapeutic approach. Human neural stem cells (NSCs) are known to have tumor-tropic effect. We genetically engineered them to express rabbit carboxyl esterase (F3.CE), which activates prodrug CPT-11(irinotecan) into potent metabolite SN-38. We found significant inhibition of the growth of BxPC3 human pancreatic cancer cell line in vitro by F3.CE in presence of CPT-11. Apoptosis was also markedly increased in BxPC3 cells treated with F3.CE and CPT-11. The ligand VEGF and receptor VEGF-1(Flt1) were identified to be the relevant tumor-tropic chemoattractant. We confirmed in vivo that in mice injected with BxPC3 on their skin, there was significant reduction of tumor size in those treated with both F3.CE and BxPC3 adjacent to the cancer mass. Administration of F3.CE in conjunction with CPT-11 could be a new possibility as an effective treatment regimen for patients suffering from advanced pancreatic cancer.

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.

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.

Practical Issues with the Use of Stem Cells for Cancer Gene Therapy

Stem cell-based drug delivery for cancer therapy has steadily gained momentum in the past decade as several studies have reported stem cells' inherent tropism towards tumors. Since this science is still in its early stages and there are many factors that could significantly impact tumor tropism of stem cells, some contradictory results have been observed. This review starts by examining a number of proof-of-concept studies that demonstrate the potential application of stem cells in cancer therapy. Studies that illustrate stem cells' tumor tropism and discuss the technical difficulties that could impact the therapeutic outcome are also highlighted. The discussion also emphasizes stem cell imaging/tracking, as it plays a crucial role in performing reliable dose-response studies and evaluating the therapeutic outcome of treatment protocols. In each section, the pros and cons associated with each method are highlighted, limitations are underlined, and potential solutions are discussed. The overall intention is to familiarize the reader with important practical issues related to stem cell cancer tropism and in vivo tracking, underline the shortcomings, and emphasize critical factors that need to be considered for effective translation of this science into the clinic.

Targeted Treatment of Experimental Spinal Cord Glioma With Dual Gene-Engineered Human Neural Stem Cells

BACKGROUND

There are currently no satisfactory treatments or experimental models showing autonomic dysfunction for intramedullary spinal cord gliomas (ISCG).

OBJECTIVE

To develop a rat model of ISCG and investigate whether genetically engineered human neural stem cells (F3.hNSCs) could be developed into effective therapies for ISCG.

METHODS

Immunodeficient/Rowett Nude rats received C6 implantation of G55 human glioblastoma cells (10K/each). F3.hNSCs engineered to express either cytosine deaminase gene only (i.e., F3.CD) or dual genes of CD and thymidine kinase (i.e., F3.CD-TK) converted benign 5-fluorocytosine and ganciclovir into oncolytic 5-fluorouracil and ganciclovir-triphosphate, respectively. ISCG rats received injection of F3.CD-TK, F3.CD, or F3.CD-TK debris near the tumor epicenter 7 days after G55 seeding, followed with 5-FC (500 mg/kg/5 mL) and ganciclovir administrations (25 mg/kg/1 mL/day × 5/each repeat, intraperitoneal injection). Per humane standards for animals, loss of weight-bearing stepping in the hindlimb was used to determine post-tumor survival. Also evaluated were autonomic functions and tumor growth rate in vivo.

RESULTS

ISCG rats with F3.CD-TK treatment survived significantly longer (37.5 ± 4.78 days) than those receiving F3.CD (21.5 ± 1.75 days) or F3.CD-TK debris (19.3 ± 0.85 days; n = 4/group; P <.05, median rank test), with significantly improved autonomic function and reduced tumor growth rate. F3.DC-TK cells migrated diffusively into ISCG clusters to mediate oncolytic effect.

CONCLUSION

Dual gene-engineered human neural stem cell regimen markedly prolonged survival in a rat model that emulates somatomotor and autonomic dysfunctions of human cervical ISCG. F3.CD-TK may provide a novel approach to treating clinical ISCG.

Mesenchymal stem cells secretome as a modulator of the neurogenic niche: basic insights and therapeutic opportunities

Neural stem cells (NSCs) and mesenchymal stem cells (MSCs) share few characteristics apart from self-renewal and multipotency. In fact, the neurogenic and osteogenic stem cell niches derive from two distinct embryonary structures; while the later originates from the mesoderm, as all the connective tissues do, the first derives from the ectoderm. Therefore, it is highly unlikely that stem cells isolated from one niche could form terminally differentiated cells from the other. Additionally, these two niches are associated to tissues/systems (e.g., bone and central nervous system) that have markedly different needs and display diverse functions within the human body. Nevertheless they do share common features. For instance, the differentiation of both NSCs and MSCs is intimately associated with the bone morphogenetic protein family. Moreover, both NSCs and MSCs secrete a panel of common growth factors, such as nerve growth factor (NGF), glial derived neurotrophic factor (GDNF), and brain derived neurotrophic factor (BDNF), among others. But it is not the features they share but the interaction between them that seem most important, and worth exploring; namely, it has already been shown that there are mutually beneficially effects when these cell types are co-cultured in vitro. In fact the use of MSCs, and their secretome, become a strong candidate to be used as a therapeutic tool for CNS applications, namely by triggering the endogenous proliferation and differentiation of neural progenitors, among other mechanisms. Quite interestingly it was recently revealed that MSCs could be found in the human brain, in the vicinity of capillaries. In the present review we highlight how MSCs and NSCs in the neurogenic niches interact. Furthermore, we propose directions on this field and explore the future therapeutic possibilities that may arise from the combination/interaction of MSCs and NSCs.

Anticancer effects of the engineered stem cells transduced with therapeutic genes via a selective tumor tropism caused by vascular endothelial growth factor toward HeLa cervical cancer cells

The aim of the present study was to investigate the therapeutic efficacy of genetically engineered stem cells (GESTECs) expressing bacterial cytosine deaminase (CD) and/or human interferon-beta (IFN-β) gene against HeLa cervical cancer and the migration factors of the GESTECs toward the cancer cells. Anticancer effect of GESTECs was examined in a co-culture with HeLa cells using MTT assay to measure cell viability. A transwell migration assay was performed so as to assess the migration capability of the stem cells to cervical cancer cells. Next, several chemoattractant ligands and their receptors related to a selective migration of the stem cells toward HeLa cells were determined by real-time PCR. The cell viability of HeLa cells was decreased in response to 5-fluorocytosine (5-FC), a prodrug, indicating that 5-fluorouracil (5-FU), a toxic metabolite, was converted from 5-FC by CD gene and it caused the cell death in a co-culture system. When IFN-β was additionally expressed with CD gene by these GESTECs, the anticancer activity was significantly increased. In the migration assay, the GESTECs selectively migrated to HeLa cervical cancer cells. As results of real-time PCR, chemoattractant ligands such as MCP-1, SCF, and VEGF were expressed in HeLa cells, and several receptors such as uPAR, VEGFR2, and c-kit were produced by the GESTECs. These GESTECs transduced with CD gene and IFN-β may provide a potential of a novel gene therapy for anticervical cancer treatments via their selective tumor tropism derived from VEGF and VEGFR2 expressions between HeLa cells and the GESTECs.

[Mesenchymal stem cells as an antitumor therapy tool]

Development of antitumor preparations with low toxicity and high selectivity of action is one of the top priorities of cancer gene therapy. Mesenchymal stem cells possess natural tropism towards tumors, a property that makes possible their use as a vehicle for targeted delivery of therapeutic genes into tumors of various etiologies. At present, genes encoding enzymes (cytosine deaminase, thymidine kinase, carboxyl esterase), cytokines (IL-2, IL-4, IL-12, IFN-beta) and apoptosis inducing factors (TRAIL) are used as therapeutic genes. Mesenchymal stem cells, as demonstrated using experimental models of tumors of various etiologies as well as animals with metastases in brain and lungs, are able to successfully deliver therapeutic genes into tumors and produce significant antitumor effect. However, to effectively use this therapeutic strategy in clinic, one still has to solve a number of technical problems.

Adenosine potentiates the therapeutic effects of neural stem cells expressing cytosine deaminase against metastatic brain tumors

Tumor-tropic properties of neural stem cells (NSCs) provide a novel approach with which to deliver targeting therapeutic genes to brain tumors. Previously, we developed a therapeutic strategy against metastatic brain tumors using a human NSC line (F3) expressing cytosine deaminase (F3.CD). F3.CD converts systemically administered 5-fluorocytosine (5-FC), a blood-brain barrier permeable nontoxic prodrug, into the anticancer agent 5-fluorouracil (5-FU). In this study, we potentiated a therapeutic strategy of treatment with nucleosides in order to chemically facilitate the endogenous conversion of 5-FU to its toxic metabolite 5-FU ribonucleoside (5-FUR). In vitro, 5-FUR showed superior cytotoxic activity against MDA-MB-435 cancer cells when compared to 5-FU. Although adenosine had little cytotoxic activity, the addition of adenosine significantly potentiated the in vitro cytotoxicity of 5-FU. When MDA-MB‑435 cells were co-cultured with F3.CD cells, F3.CD cells and 5-FC inhibited the growth of MDA-MB-435 cells more significantly in the presence of adenosine. Facilitated 5-FUR production by F3.CD was confirmed by an HPLC analysis of the conditioned media derived from F3.CD cells treated with 5-FC and adenosine. In vivo systemic adenosine treatment also significantly potentiated the therapeutic effects of F3.CD cells and 5-FC in an MDA-MB-435 metastatic brain tumor model. Simple adenosine addition improved the antitumor activity of the NSCs carrying the therapeutic gene. Our results demonstrated an increased therapeutic potential, and thereby, clinical applicability of NSC-based gene therapy.

Systemic delivery of fusogenic membrane glycoprotein-expressing neural stem cells to selectively kill tumor cells

Intravenously injected neural stem cells (NSCs) can infiltrate both primary and metastatic tumor sites; thus, they are attractive tumor-targeting vehicles for delivering anticancer agents. However, because the systemic distribution of the injected NSCs involves normal organs and might induce off-target actions leading to unintended side effects, clinical applications of this approach is impeded. Given that the vesicular stomatitis virus glycoprotein (VSV-G) can promote the formation of multinucleated syncytia to kill cells in a pH-dependent manner, we engineered a pH sensor of VSV-G and generated a novel VSV-G mutant that efficiently promotes syncytium formation at the tumor extracellular pH (pHe) but not at pH 7.4. Using transduced NSCs derived from induced pluripotent stem cells (iPSCs), the VSV-G mutant was delivered into mice with metastatic breast cancers in the lung through tail vein injection. Compared with the conventional stem cell-based gene therapy that uses the herpes simplex virus thymidine kinase (HSVtk) suicide gene, this treatment did not display toxicity to normal non-targeted organs while retaining therapeutic effects in tumor-bearing organs. Our findings demonstrate the effectiveness of a new approach for achieving tumor-selective killing effects following systemic stem cell administration. Its potential in stem cell-based gene therapy for metastatic cancer is worthy of further exploration.

Current status of gene therapy for brain tumors

Glioblastoma (GBM) is the most common and deadliest primary brain tumor in adults, with current treatments having limited impact on disease progression. Therefore the development of alternative treatment options is greatly needed. Gene therapy is a treatment strategy that relies on the delivery of genetic material, usually transgenes or viruses, into cells for therapeutic purposes, and has been applied to GBM with increasing promise. We have included selectively replication-competent oncolytic viruses within this strategy, although the virus acts directly as a complex biologic anti-tumor agent rather than as a classic gene delivery vehicle. GBM is a good candidate for gene therapy because tumors remain locally within the brain and only rarely metastasize to other tissues; the majority of cells in the brain are post-mitotic, which allows for specific targeting of dividing tumor cells; and tumors can often be accessed neurosurgically for administration of therapy. Delivery vehicles used for brain tumors include nonreplicating viral vectors, normal adult stem/progenitor cells, and oncolytic viruses. The therapeutic transgenes or viruses are typically cytotoxic or express prodrug activating suicide genes to kill glioma cells, immunostimulatory to induce or amplify anti-tumor immune responses, and/or modify the tumor microenvironment such as blocking angiogenesis. This review describes current preclinical and clinical gene therapy strategies for the treatment of glioma.

Advances in stem cell therapy against gliomas

Malignant gliomas are one of the most lethal cancers, and despite extensive research very little progress has been made in improving prognosis. Multimodality treatment combining surgery, radiation, and chemotherapy is the current gold standard, but effective treatment remains difficult due to the invasive nature and high recurrence of gliomas. Stem cell-based therapy using neural, mesenchymal, or hematopoietic stem cells may be an alternative approach because it is tumor selective and allows targeted therapy that spares healthy brain tissue. Stem cells can be used to establish a long-term antitumor response by stimulating the immune system and delivering prodrug, metabolizing genes, or oncolytic viruses. In this review, we discuss current trends and the latest developments in stem cell therapy against malignant gliomas from both the experimental laboratory and the clinic.