Delivery of hypoxia and glioma dual-specific suicide gene using dexamethasone conjugated polyethylenimine for glioblastoma-specific gene therapy

Glucocorticoids-based prodrug design: Current strategies and research progress

Attributing to their broad pharmacological effects encompassing anti-inflammation, antitoxin, and immunosuppression, glucocorticoids (GCs) are extensively utilized in the clinic for the treatment of diverse diseases such as lupus erythematosus, nephritis, arthritis, ulcerative colitis, asthma, keratitis, macular edema, and leukemia. However, long-term use often causes undesirable side effects, including metabolic disorders-induced Cushing's syndrome (buffalo back, full moon face, hyperglycemia, etc.), osteoporosis, aggravated infection, psychosis, glaucoma, and cataract. These notorious side effects seriously compromise patients' quality of life, especially in patients with chronic diseases. Therefore, glucocorticoid-based advanced drug delivery systems for reducing adverse effects have received extensive attention. Among them, prodrugs have the advantages of low investment, low risk, and high success rate, making them a promising strategy. In this review, we propose the strategies for the design and summarize current research progress of glucocorticoid-based prodrugs in recent decades, including polymer-based prodrugs, dendrimer-based prodrugs, antibody-drug conjugates, peptide-drug conjugates, carbohydrate-based prodrugs, aliphatic acid-based prodrugs and so on. Besides, we also raise issues that need to be focused on during the development of glucocorticoid-based prodrugs. This review is expected to be helpful for the research and development of novel GCs and prodrugs.

Nucleic acid therapies for CNS diseases: Pathophysiology, targets, barriers, and delivery strategies

Nucleic acid therapeutics have emerged as one of the very advanced and efficacious treatment approaches for debilitating health conditions, including those diseases affecting the central nervous system (CNS). Precise targeting with an optimal control over gene regulation confers long-lasting benefits through the administration of nucleic acid payloads via viral, non-viral, and engineered vectors. The current review majorly focuses on the development and clinical translational potential of non-viral vectors for treating CNS diseases with a focus on their specific design and targeting approaches. These carriers must be able to surmount the various intracellular and extracellular barriers, to ensure successful neuronal transfection and ultimately attain higher therapeutic efficacies. Additionally, the specific challenges associated with CNS administration also include the presence of blood-brain barrier (BBB), the complex pathophysiological and biochemical changes associated with different disease conditions and the existence of non-dividing cells. The advantages offered by lipid-based or polymeric systems, engineered proteins, particle-based systems coupled with various approaches of neuronal targeting have been discussed in the context of a variety of CNS diseases. The possibilities of rapid yet highly efficient gene modifications rendered by the breakthrough methodologies for gene editing and gene manipulation have also opened vast avenues of research in neuroscience and CNS disease therapy. The current review also underscores the extensive scientific efforts to optimize specialized, efficacious yet non-invasive and safer administration approaches to overcome the therapeutic delivery challenges specifically posed by the CNS transport barriers and the overall obstacles to clinical translation.

Advantages and drawbacks of dexamethasone in glioblastoma multiforme

The most widespread, malignant, and deadliest type of glial tumor is glioblastoma multiforme (GBM). Despite radiation, chemotherapy, and radical surgery, the median survival of afflicted individuals is about 12 months. Unfortunately, existing therapeutic interventions are abysmal. Dexamethasone (Dex), a synthetic glucocorticoid, has been used for many years to treat brain edema and inflammation caused by GBM. Several investigations have recently shown that Dex also exerts antitumoral effects against GBM. On the other hand, more recent disputed findings have questioned the long-held dogma of Dex treatment for GBM. Unfortunately, steroids are associated with various undesirable side effects, including severe immunosuppression and metabolic changes like hyperglycemia, which may impair the survival of GBM patients. Current ideas and concerns about Dex's effects on GBM cerebral edema, cell proliferation, migration, and its clinical outcomes were investigated in this study.

Biomimetic cell membrane-coated DNA nanoparticles for gene delivery to glioblastoma

Gene therapy has been introduced as an alternative to radiation and chemical therapy for glioblastoma. Biomimetic nanoparticles coated with cell membranes (CM) have advantages such as high biocompatibility and prolong half-life. To apply CM coated nanoparticles to gene delivery, the polyethylenimine (PEI25k)/plasmid DNA (pDNA) complexes were coated with CM from C6 rat glioblastoma cells. With the CM covering, the PEI25k/pDNA complexes formed stable nanoparticles with negative surface charge. The PEI25k/pDNA/CM nanoparticles had high colloidal stability and could be stored for approximately 20 days without aggregation. The transfection efficiency of the PEI25k/pDNA/CM nanoparticles was higher than that of the PEI25k/pDNA complex in serum-containing medium. This suggests that serum does not interfere with transfection efficiency of the nanoparticles. Moreover, the PEI25k/pDNA/CM nanoparticles had lower toxicity than the PEI25k/DNA complex in vitro and in vivo. The PEI25k/pDNA/CM nanoparticles prepared with CMs of different types of cells were transfected into cells. The results showed that the PEI25k/pDNA/CM nanoparticles with the C6 CM had the highest transfection efficiency to C6 cells, suggesting the homotypic targeting effect. The therapeutic effects of the nanoparticles were evaluated in intracranial C6 transplanted glioblastoma animal models. The PEI25k/pDNA/CM nanoparticles were prepared with herpes simplex virus thymidine kinase plasmid (pHSVtk) and injected into the tumor locally. The results showed that the PEI25k/pHSVtk/CM nanoparticles induced higher HSVtk expression compared with the PEI25k/pHSVtk complex. Furthermore, tumor size was reduced more efficiently by the PEI25k/pHSVtk/CM nanoparticles than by the PEI25k/pHSVtk complex. Overall results indicate that PEI25k/pDNA/CM nanoparticles are suitable for pDNA delivery to glioblastoma.

Dexamethasone Conjugates: Synthetic Approaches and Medical Prospects

Dexamethasone (DEX) is the most commonly prescribed glucocorticoid (GC) and has a wide spectrum of pharmacological activity. However, steroid drugs like DEX can have severe side effects on non-target organs. One strategy to reduce these side effects is to develop targeted systems with the controlled release by conjugation to polymeric carriers. This review describes the methods available for the synthesis of DEX conjugates (carbodiimide chemistry, solid-phase synthesis, reversible addition fragmentation-chain transfer [RAFT] polymerization, click reactions, and 2-iminothiolane chemistry) and perspectives for their medical application as GC drug or gene delivery systems for anti-tumor therapy. Additionally, the review focuses on the development of DEX conjugates with different physical-chemical properties as successful delivery systems in the target organs such as eye, joint, kidney, and others. Finally, polymer conjugates with improved transfection activity in which DEX is used as a vector for gene delivery in the cell nucleus have been described.

Biocompatible copolymer formulations to treat glioblastoma multiforme

The treatment for glioblastoma multiforme (GBM) has not changed for more than 20 years while the prognosis for the patients is still poor and most of them survive less than 1 year after diagnosis. The standard of care for GBM is comprised of surgical resection followed by radiotherapy and oral chemotherapy with temozolomide. The placement of carmustine wafers in the brain after tumour removal is added in cases of recurrent glioma. Significant research is underway to improve the GBM therapy outcome and patient quality of life. Biomaterials are in the front line of the research focus for new treatment options. Specially, biocompatible polymers have been proposed in hydrogel-based formulations aiming at injectable and localized therapies. These formulations can comprise many different pharmacological agents such as chemotherapeutic drugs, nanoparticles, cells, nucleic acids, and diagnostic agents. In this manuscript, we review the most recent formulations developed and tested both in vitro and in vivo using different types of hydrogels. Firstly, we describe three common types of thermo-responsive polymers addressing the advantages and drawbacks of their formulations. Then, we focus on formulations specifically developed for GBM treatment.

Combination Therapy by Tissue-Specific Suicide Gene and Bevacizumab in Intramedullary Spinal Cord Tumor

PURPOSE

Malignant gliomas are aggressive spinal cord tumors. In this study, we hypothesized that combination therapy using an anti-angiogenic agent, bevacizumab, and hypoxia-inducible glioblastoma-specific suicide gene could reduce tumor growth.

MATERIALS AND METHODS

In the present study, we evaluated the effect of combination therapy using bevacizumab and pEpo-NI2-SV-TK in reducing the proliferation of C6 cells and tumor growth in the spinal cord. Spinal cord tumor was generated by the injection of C6 cells into the T5 level of the spinal cord. Complexes of branched polyethylenimine (bPEI)/pEpo-NI2-SV-TK were injected into the spinal cord tumor. Bevacizumab was then administered by an intraperitoneal injection at a dose of 7 mg/kg. The anti-cancer effects of combination therapy were analyzed by histological analyses and magnetic resonance imaging (MRI). The Basso, Beattie and Bresnahan scale scores for all of the treatment groups were recorded every other day for 15 days to assess the rat hind-limb strength.

RESULTS

The complexes of bPEI/pEpo-NI2-SV-TK inhibited the viability of C6 cells in the hypoxia condition at 5 days after treatment with ganciclovir. Bevacizumab was decreased in the cell viability of human umbilical vein endothelial cells. Combination therapy reduced the tumor size by histological analyses and MRI. The combination therapy group showed improved hind-limb function compared to the other groups that were administered pEpo-NI2-SV-TK alone or bevacizumab alone.

CONCLUSION

This study suggests that combination therapy using bevacizumab with the pEpo-NI2-SV-TK therapeutic gene could be useful for increasing its therapeutic benefits for intramedullary spinal cord tumors.

Non-viral nucleic acid delivery to the central nervous system and brain tumors

Gene therapy is a rapidly emerging remedial route for many serious incurable diseases, such as central nervous system (CNS) diseases. Currently, nucleic acid medicines, including DNAs encoding therapeutic or destructive proteins, small interfering RNAs or microRNAs, have been successfully delivered to the CNS with gene delivery vectors using various routes of administration and have subsequently exhibited remarkable therapeutic efficiency. Among these vectors, non-viral vectors are favorable for delivering genes into the CNS as a result of their many special characteristics, such as low toxicity and pre-existing immunogenicity, high gene loading efficiency and easy surface modification. In this review, we highlight the main types of therapeutic genes that have been applied in the therapy of CNS diseases and then outline non-viral gene delivery vectors.

Second near-infrared photodynamic therapy and chemotherapy of orthotopic malignant glioblastoma with ultra-small Cu2-xSe nanoparticles

The treatment of malignant glioblastoma is a huge challenge due to the existence of the blood-brain barrier. Herein, we report the treatment of orthotopic malignant glioblastoma with imaging guided second near-infrared (NIR-II) photodynamic therapy and chemotherapy by using drug-loaded ultra-small Cu2-xSe theranostic nanoparticles (NPs). Ultra-small Cu2-xSe NPs possess a strong absorbance in the NIR-II window, and their absorption at 1064 nm is around 2 times that at 808 nm. Their strong NIR-II absorbance and the deeper-tissue penetration of NIR-II light ensure excellent photodynamic therapy performance under irradiation with a 1064 nm laser. We also demonstrate that ultra-small Cu2-xSe NPs can produce vast amounts of reactive oxygen species via electron transfer (for ˙OH generation) and energy transfer (for 1O2 generation) mechanisms under irradiation. In addition, these NPs can be effectively and locally transported into orthotopic malignant glioblastoma with the assistance of focused ultrasound. The deposited Cu2-xSe NPs can be used for photoacoustic imaging to guide the combined NIR-II photodynamic therapy and chemotherapy. The results show that the tumor growth can be significantly suppressed. This work demonstrates the great potential of drug-loaded ultra-small Cu2-xSe NPs as a promising therapeutic agent for the treatment of orthotopic malignant glioblastoma.

Through Scalp and Skull NIR-II Photothermal Therapy of Deep Orthotopic Brain Tumors with Precise Photoacoustic Imaging Guidance

Brain tumor is one of the most lethal cancers owing to the existence of blood-brain barrier and blood-brain tumor barrier as well as the lack of highly effective brain tumor treatment paradigms. Herein, cyclo(Arg-Gly-Asp-D-Phe-Lys(mpa)) decorated biocompatible and photostable conjugated polymer nanoparticles with strong absorption in the second near-infrared (NIR-II) window are developed for precise photoacoustic imaging and spatiotemporal photothermal therapy of brain tumor through scalp and skull. Evidenced by the higher efficiency to penetrate scalp and skull for 1064 nm laser as compared to common 808 nm laser, NIR-II brain-tumor photothermal therapy is highly effective. In addition, via a real-time photoacoustic imaging system, the nanoparticles assist clear pinpointing of glioma at a depth of almost 3 mm through scalp and skull with an ultrahigh signal-to-background ratio of 90. After spatiotemporal photothermal treatment, the tumor progression is effectively inhibited and the survival spans of mice are significantly extended. This study demonstrates that NIR-II conjugated polymer nanoparticles are promising for precise imaging and treatment of brain tumors.

A ternary-complex of a suicide gene, a RAGE-binding peptide, and polyethylenimine as a gene delivery system with anti-tumor and anti-angiogenic dual effects in glioblastoma

The receptor for advanced glycation end-products (RAGE) is involved in tumor angiogenesis. Inhibition of RAGE might be an effective anti-angiogenic therapy for cancer. In this study, a cationic RAGE-binding peptide (RBP) was produced as an antagonist of RAGE, and a ternary-complex consisting of RBP, polyethylenimine (2 kDa, PEI2k), and a suicide gene (pHSVtk) was developed as a gene delivery system with dual functions: the anti-tumor effect of pHSVtk and anti-angiogenic effect of RBP. As an antagonist of RAGE, RBP decreased the secretion of vascular-endothelial growth factor (VEGF) in activated macrophages and reduced the tube-formation of endothelial cells in vitro. In in vitro transfection assays, the RBP/PEI2k/plasmid DNA (pDNA) ternary-complex had higher transfection efficiency than the PEI2k/pDNA binary-complex. In an intracranial glioblastoma animal model, the RBP/PEI2k/pHSVtk ternary-complex reduced α-smooth muscle actin expression, suggesting that the complex has an anti-angiogenic effect. In addition, the ternary-complex had higher pHSVtk delivery efficiency than the PEI2k/pHSVtk and PEI25k/pHSVtk binary-complexes in an animal model. As a result, the ternary-complex induced apoptosis and reduced tumor volume more effectively than the PEI2k/pHSVtk and PEI25k/pHSVtk binary-complexes. In conclusion, due to its dual anti-tumor and anti-angiogenesis effects, the RBP/PEI2k/pHSVtk ternary-complex might be an efficient gene delivery system for the treatment of glioblastoma.

Hypoxia-inducible tumour-specific promoters as a dual-targeting transcriptional regulation system for cancer gene therapy

Transcriptional targeting is the best approach for specific gene therapy. Hypoxia is a common feature of the tumour microenvironment. Therefore, targeting gene expression in hypoxic cells by placing transgene under the control of a hypoxia-responsive promoter can be a good strategy for cancer-specific gene therapy. The hypoxia-inducible gene expression system has been investigated more in suicide gene therapy and it can also be of great help in knocking down cancer gene therapy with siRNAs. However, this system needs to be optimised to have maximum efficacy with minimum side effects in normal tissues. The combination of tissue-/tumour-specific promoters with HRE core sequences has been found to enhance the specificity and efficacy of this system. In this review, hypoxia-inducible gene expression system as well as gene therapy strategies targeting tumour hypoxia will be discussed. This review will also focus on hypoxia-inducible tumour-specific promoters as a dual-targeting transcriptional regulation systems developed for cancer-specific gene therapy.

Combined delivery of temozolomide and the thymidine kinase gene for treatment of glioblastoma

Glioblastoma is the most malignant form of brain tumor. In this study, combination therapy with temozolomide (TMZ) and the herpes simplex virus thymidine kinase (HSVtk) gene was evaluated in glioblastoma models. The R7L10 peptide was used as a carrier of TMZ and the HSVtk gene. TMZ was loaded into R7L10 micelles using the oil-in-water emulsion/solvent evaporation method. The TMZ-loaded R7L10 (R7L10-TMZ) micelles formed a complex with the HSVtk gene, pHSVtk. The formation of the R7L10-TMZ/pHSVtk complex was confirmed by gel retardation and heparin competition assays. An in vitro transfection assay demonstrated that the transfection efficiency of R7L10-TMZ was similar to that of R7L10 in C6 glioblastoma cells. R7L10-TMZ had greater anti-tumor effects than TMZ alone in C6 cells in vitro, suggesting that R7L10 is an efficient carrier of TMZ. The in vivo efficacy of the R7L10-TMZ/pHSVtk complex was evaluated in the intracranial glioblastoma model. HSVtk expression in tumors was confirmed by immunohistochemistry. Furthermore, a greater anti-tumor effect was observed in the R7L10-TMZ/pHSVtk group compared with the TMZ or R7L10/pHSVtk single injection group. In conclusion, combined delivery of TMZ and the HSVtk gene using R7L10 peptides may be useful for the treatment of glioblastoma.

Development of bioactive materials for glioblastoma therapy

Glioblastoma is the most common and deadly human brain cancers. Unique barriers hinder the drug delivering pathway due to the individual position of glioblastoma, including blood-brain barrier and blood-brain tumor barrier. Numerous bioactive materials have been exploited and applied as the transvascular delivery carriers of therapeutic drugs. They promote site-specific accumulation and long term release of the encapsulated drugs at the tumor sites and reduce side effects with systemic delivery. And the delivery systems exhibit a certain extent of anti-glioblastoma effect and extend the median survival time. However, few of them step into the clinical trials. In this review, we will investigate the recent studies of bioactive materials for glioblastoma chemotherapy, including the inorganic materials, lipids and polymers. These bioactive materials construct diverse delivery vehicles to trigger tumor sites in brain intravenously. Herein, we exploit their functionality in drug delivery and discuss the deficiency for the featured tumors, to provide guidance for establishing optimized therapeutic drug formulation for anti-glioblastoma therapy and pave the way for clinical application.

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Numerous bioactive materials have been exploited as delivery carriers of therapeutic drugs for glioblastoma chemotherapy.

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The functionality and deficiency of the bioactive materials are discussed.

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Combing the chemo- and immunotherapy will provide a promising strategy for glioblastoma therapy and inhibiting recurrence.

Targeted delivery of growth factors in ischemic stroke animal models

INTRODUCTION

Ischemic stroke is caused by reduced blood supply and leads to loss of brain function. The reduced oxygen and nutrient supply stimulates various physiological responses, including induction of growth factors. Growth factors prevent neuronal cell death, promote neovascularization, and induce cell growth. However, the concentration of growth factors is not sufficient to recover brain function after the ischemic damage, suggesting that delivery of growth factors into the ischemic brain may be a useful treatment for ischemic stroke.

AREAS COVERED

In this review, various approaches for the delivery of growth factors to ischemic brain tissue are discussed, including local and targeting delivery systems.

EXPERT OPINION

To develop growth factor therapy for ischemic stroke, important considerations should be taken into account. First, growth factors may have possible side effects. Thus, concentration of growth factors should be restricted to the ischemic tissues by local administration or targeted delivery. Second, the duration of growth factor therapy should be optimized. Growth factor proteins may be degraded too fast to have a high enough therapeutic effect. Therefore, delivery systems for controlled release or gene delivery may be useful. Third, the delivery systems to the brain should be optimized according to the delivery route.

Reducible Poly(Oligo-D-Arginine) as an Efficient Carrier of the Thymidine Kinase Gene in the Intracranial Glioblastoma Animal Model

Gene therapy has been considered as an alternative treatment for glioblastoma therapy. In this study, a glioblastoma-specific suicide gene, pEpo-NI2-SV-TK, was delivered into the intracranial glioblastoma model using reducible poly(oligo-d-arginines) (rPOA). pEpo-NI2-SV-TK has the erythropoietin (Epo) enhancer and the nestin intron 2 (NI2) for glioblastoma specific gene expression. The in vitro studies showed that the rPOA formed stable complexes with pEpo-NI2-SV-TK. In the MTT and TUNEL assays, rPOA showed lower cytotoxicity than polyethylenimine (25 kDa, PEI25k). In addition, the rPOA/pEpo-NI2-SV-TK complex induced higher glioblastoma cell death under hypoxic condition than normoxic condition, suggesting that pEpo-NI2-SV-TK induced gene expression in the hypoxic tumor tissue. For in vivo therapeutic efficacy evaluation, the rPOA/pEpo-NI2-SV-TK complex was injected into the brains of an intracranial glioblastoma rat model. The rPOA/pEpo-NI2-SV-TK injected group had a significantly reduced tumor size, compared with the control and the PEI25k/pEpo-NI2-SV-TK injected group. The TUNEL assay showed that the rPOA-pEpo-NI2-SV-TK complex had more apoptotic cells than the control and PEI25k/pEpo-NI2-SV-TK injected groups. These results suggest that the rPOA is an efficient carrier for pEpo-NI2-SV-TK and increased the therapeutic efficacy in the intracranial glioblastoma models. Therefore, the rPOA/pEpo-NI2-SV-TK complex may be useful for glioblastoma specific gene therapy.

Roles and potential clinical applications of intermediate filament proteins in brain tumors

Intermediate filament (IF) proteins are cytoplasmic and nuclear cytoskeletal proteins. Of the ~70 IF proteins, nearly 12 are found in the nervous system, where their expression is largely cell-type specific. Astrocytes express glial fibrillary acidic protein (GFAP), whereas different neuron types contain neurofilament proteins, α-internexin, or peripherin. These proteins are often downregulated in brain cancer. In addition, brain cancer cells may also contain vimentin, nestin, and synemin, which are the IF proteins found in neural progenitor cells. In different brain tumor types, the expression of nestin, vimentin, and α-internexin appears to correlate with the clinical outcome. Experimental investigations have also demonstrated that IF proteins have distinct roles in specific brain tumor cell behaviors: nestin, for instance, is important for the proliferation of glioma cells, whereas synemin also affect their mobility. The mechanisms responsible for these effects involve the interaction of IF proteins with specific signaling pathways. Synemin, for instance, positively regulates glioma cell proliferation by antagonizing protein phosphatase 2A. Further evidence for the potential of IF proteins as therapeutic targets derives from animal models showing the influence of IF proteins on tumor growth. Nestin downregulation, for instance, dramatically reduced intracerebral glioma growth. Selective targeted therapies of IFs to date primarily include gene therapy approaches using nestin or GFAP gene promoters to drive transgene expression into glioma cells. Although attempts to identify small molecules specifically antagonizing IF proteins have been unsuccessful to date, it is anticipated that the identification of such compounds will be instrumental in expanding therapeutic approaches for brain tumors.

Peptide micelle-mediated delivery of tissue-specific suicide gene and combined therapy with avastin in a glioblastoma model

Bevacizumab (Avastin) is an angiogenesis inhibitor used as a treatment for various cancers. In this study, the combination therapy of Avastin and glioblastoma-specific thymidine kinase gene [pEpo-NI2-SV-herpes simplex virus thymidine kinase(HSVtk)] was evaluated in a glioblastoma animal model. The R7L10 peptide was used as a gene carrier of pEpo-NI2-SV-HSVtk. Gel retardation assays confirmed that R7L10 formed stable complexes with pEpo-NI2-SV-HSVtk. R7L10 protected DNA from nuclease digestion. R7L10 had lower transfection efficiency than polyethylenimine (PEI; 25 kDa). However, the in vitro and in vivo toxicity assays showed that R7L10 had lower cytotoxicity than PEI, suggesting that R7L10 is safer than PEI. For the combination therapy, Avastin was injected intravenously and the pEpo-NI2-SV-HSVtk/R7L10 complexes were injected intratumorally in the glioblastoma animal model. Tumor growth was most effectively inhibited by the combination therapy of Avastin and the gene. The immunostaining results confirmed that the HSVtk genes were expressed in the groups with the pEpo-NI2-SV-HSVtk/R7L10 complex. The terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed a higher level of apoptotic cells in the combination group than the pEpo-NI2-SV-HSVtk/R7L10 complex or Avastin group. In conclusion, the combination of Avastin and the glioblastoma-specific HSVtk gene has a higher antitumor effect than single therapy of Avastin or HSVtk after intratumoral administration in glioblastoma animal model.