Progress and problems with the use of suicide genes for targeted cancer therapy

Nanotechnology and bioengineering approaches to improve the potency of mesenchymal stem cell as an off-the-shelf versatile tumor delivery vehicle

Targeting actionable mutations in oncogene-driven cancers and the evolution of immuno-oncology are the two prominent revolutions that have influenced cancer treatment paradigms and caused the emergence of precision oncology. However, intertumoral and intratumoral heterogeneity are the main challenges in both fields of precision cancer treatment. In other words, finding a universal marker or pathway in patients suffering from a particular type of cancer is challenging. Therefore, targeting a single hallmark or pathway with a single targeted therapeutic will not be efficient for fighting against tumor heterogeneity. Mesenchymal stem cells (MSCs) possess favorable characteristics for cellular therapy, including their hypoimmune nature, inherent tumor-tropism property, straightforward isolation, and multilineage differentiation potential. MSCs can be loaded with various chemotherapeutics and oncolytic viruses. The combination of these intrinsic features with the possibility of genetic manipulation makes them a versatile tumor delivery vehicle that can be used for in vivo selective tumor delivery of various chemotherapeutic and biological therapeutics. MSCs can be used as biofactory for the local production of chemical or biological anticancer agents at the tumor site. MSC-mediated immunotherapy could facilitate the sustained release of immunotherapeutic agents specifically at the tumor site, and allow for the achievement of therapeutic concentrations without the need for repetitive systemic administration of high therapeutic doses. Despite the enthusiasm evoked by preclinical studies that used MSC in various cancer therapy approaches, the translation of MSCs into clinical applications has faced serious challenges. This manuscript, with a critical viewpoint, reviewed the preclinical and clinical studies that have evaluated MSCs as a selective tumor delivery tool in various cancer therapy approaches, including gene therapy, immunotherapy, and chemotherapy. Then, the novel nanotechnology and bioengineering approaches that can improve the potency of MSC for tumor targeting and overcoming challenges related to their low localization at the tumor sites are discussed.

Designing cytochrome P450 enzymes for use in cancer gene therapy

Cancer is a significant global socioeconomic burden, as millions of new cases and deaths occur annually. In 2020, almost 10 million cancer deaths were recorded worldwide. Advancements in cancer gene therapy have revolutionized the landscape of cancer treatment. An approach with promising potential for cancer gene therapy is introducing genes to cancer cells that encode for chemotherapy prodrug metabolizing enzymes, such as Cytochrome P450 (CYP) enzymes, which can contribute to the effective elimination of cancer cells. This can be achieved through gene-directed enzyme prodrug therapy (GDEPT). CYP enzymes can be genetically engineered to improve anticancer prodrug conversion to its active metabolites and to minimize chemotherapy side effects by reducing the prodrug dosage. Rational design, directed evolution, and phylogenetic methods are some approaches to developing tailored CYP enzymes for cancer therapy. Here, we provide a compilation of genetic modifications performed on CYP enzymes aiming to build highly efficient therapeutic genes capable of bio-activating different chemotherapeutic prodrugs. Additionally, this review summarizes promising preclinical and clinical trials highlighting engineered CYP enzymes' potential in GDEPT. Finally, the challenges, limitations, and future directions of using CYP enzymes for GDEPT in cancer gene therapy are discussed.

Oncolytic viral therapy for gliomas: Advances in the mechanisms and approaches to delivery

Glioma is a diverse category of tumors originating from glial cells encompasses various subtypes, based on the specific type of glial cells involved. The most aggressive is glioblastoma multiforme (GBM), which stands as the predominant primary malignant tumor within the central nervous system in adults. Despite the application of treatment strategy, the median survival rate for GBM patients still hovers around 15 months. Oncolytic viruses (OVs) are artificially engineered viruses designed to selectively target and induce apoptosis in cancer cells. While clinical trials have demonstrated encouraging results with intratumoral OV injections for some cancers, applying this approach to GBM presents unique challenges. Here we elaborate on current trends in oncolytic viral therapy and their delivery methods. We delve into the various methods of delivering OVs for therapy, exploring their respective advantages and disadvantages and discussing how selecting the optimal delivery method can enhance the efficacy of this innovative treatment approach.

Mesenchymal stem cells as therapeutic vehicles for glioma

Glioma is a disease with a poor prognosis despite the availability of multimodality treatments, and the development of novel therapies is urgently needed. Challenges in glioma treatment include the difficulty for drugs to cross the blood-brain barrier when administered systemically and poor drug diffusion when administered locally. Mesenchymal stem cells exhibit advantages for glioma therapy because of their ability to pass through the blood-brain barrier and migrate to tumor cells and their tolerance to the immune system. Therefore, mesenchymal stem cells have been explored as vehicles for various therapeutic agents for glioma treatment. Mesenchymal stem cells loaded with chemotherapeutic drugs show improved penetration and tumor accumulation. For gene therapy, mesenchymal stem cells can be used as vehicles for suicide genes, the so-called gene-directed enzyme prodrug therapy. Mesenchymal stem cell-based oncolytic viral therapies have been attempted in recent years to enhance the efficacy of infection against the tumor, viral replication, and distribution of viral particles. Many uncertainties remain regarding the function and behavior of mesenchymal stem cells in gliomas. However, strategies to increase mesenchymal stem cell migration to gliomas may improve the delivery of therapeutic agents and enhance their anti-tumor effects, representing promising potential for patient treatment.

Beneath the radar: immune-evasive cell sources for stroke therapy

Stem cell therapy is an emerging treatment paradigm for stroke patients with remaining neurological deficits. While allogeneic cell transplants overcome the manufacturing constraints of autologous grafts, they can be rejected by the recipient's immune system, which identifies foreign cells through the human leukocyte antigen (HLA) system. The heterogeneity of HLA molecules in the human population would require a very high number of cell lines, which may still be inadequate for patients with rare genetic HLAs. Here, we outline key progress in genetic HLA engineering in pluripotent stem and derived cells to evade the host's immune system, reducing the number of allogeneic cell lines required, and examine safety measures explored in both preclinical studies and upcoming clinical trials.

Ganciclovir as a potential treatment for glioma: a systematic review and meta-analysis

BACKGROUND

Glioma is a challenging malignant tumor with a low survival rate and no effective treatment. Recently, ganciclovir, an antiviral drug, combined with gene therapy and its own antiviral ability, has been proposed as a potential treatment for glioma. However, there are differences in the results of various clinical trials. In this study, we conducted a systematic review and meta-analysis to evaluate the efficacy of ganciclovir in treating glioma.

METHODS

We searched databases such as PubMed, EMBASE, and Cochrane Library before March 30, 2023. The search terms included glioma, ganciclovir, valganciclovir and treatment. Calculated 1, 2 and 4-year survival rate by risk difference (RD), and overall survival (OS) by odds ratio (OR).

RESULTS

Five randomized controlled trials (RCTs) with a total of 606 high-grade glioma patients were included. The results showed that ganciclovir can improve 2-yeaer (RD = 0.179, 95% CI 0.012-0.346, P = 0.036) and 4-year survival rate (RD = 0.185, 95% CI 0.069-0.3, P = 0.002) and OS (OR 2.393, 95% CI 1.212-4.728, P = 0.012) compared with the control group.

CONCLUSIONS

This meta-analysis showed that ganciclovir significantly improved the prognosis of glioma patients. Therefore, we suggest that more cases of ganciclovir as a glioma treatment can be conducted, or a large clinical trial can be designed.

Bacterial amidohydrolases and modified 5-fluorocytidine compounds: Novel enzyme-prodrug pairs

Gene-directed enzyme prodrug therapy is an emerging strategy for cancer treatment based on the delivery of a gene that encodes an enzyme that is able to convert a prodrug into a potent cytotoxin exclusively in target cancer cells. However, it is limited by the lack of suitable enzyme variants and a scarce choice of chemical bonds that could be activated. Therefore, this study is aimed to determine the capability of bacterial amidohydrolases YqfB and D8_RL to activate novel prodrugs and the effect such system has on the viability of eukaryotic cancer cells. We have established cancer cell lines that stably express the bacterial amidohydrolase genes and selected several N4-acylated cytidine derivatives as potential prodrugs. A significant decrease in the viability of HCT116 human colon cancer cell lines expressing either the YqfB or the D8_RL was observed after exposure to the novel prodrugs. The data we acquired suggests that bacterial YqfB and D8_RL amidohydrolases, together with the modified cytidine-based prodrugs, may serve as a promising enzyme-prodrug system for gene-directed enzyme prodrug therapy.

Bacterial enzymes: powerful tools for protein labeling, cell signaling, and therapeutic discovery

Bacteria have evolved a diverse set of enzymes that enable them to subvert host defense mechanisms as well as to form part of the prokaryotic immune system. Due to their unique and varied biochemical activities, these bacterial enzymes have emerged as key tools for understanding and investigating biological systems. In this review, we summarize and discuss some of the most prominent bacterial enzymes used for the site-specific modification of proteins, in vivo protein labeling, proximity labeling, interactome mapping, signaling pathway manipulation, and therapeutic discovery. Finally, we provide a perspective on the complementary advantages and limitations of using bacterial enzymes compared with chemical probes for exploring biological systems.

Suicide gene-enabled cell therapy: A novel approach to scalable human pluripotent stem cell quality control

There are an increasing number of cell therapy approaches being studied and employed world-wide. An emerging area in this field is the use of human pluripotent stem cell (hPSC) products for the treatment of injuries/diseases that cannot be effectively managed through current approaches. However, as with any cell therapy, vast numbers of functional and safe cells are required. Bioreactors provide an attractive avenue to generate clinically relevant cell numbers with decreased labour and decreased batch to batch variation. Yet, current methods of performing quality control are not readily scalable to the cell densities produced during bioreactor scale-up. One potential solution is the application of inducible/controllable suicide genes that can trigger cell death in unwanted cell types. These types of approaches have been demonstrated to increase the quality and safety of the resultant cell products. In this review, we will provide background on these approaches and how they could be used together with bioreactor technology to create effective bioprocesses for the generation of high quality and safe hPSCs for use in regenerative medicine approaches.

Advancement in precision diagnosis and therapeutic for triple-negative breast cancer: Harnessing diagnostic potential of CRISPR-cas & engineered CAR T-cells mediated therapeutics

Cancer is characterized by uncontrolled cell growth, disrupted regulatory pathways, and the accumulation of genetic mutations. These mutations across different types of cancer lead to disruptions in signaling pathways and alterations in protein expression related to cellular growth and proliferation. This review highlights the AKT signaling cascade and the retinoblastoma protein (pRb) regulating cascade as promising for novel nanotheranostic interventions. Through synergizing state-of-the-art gene editing tools like the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas system with nanomaterials and targeting AKT, there is potential to enhance cancer diagnostics significantly. Furthermore, the integration of modified CAR-T cells into multifunctional nanodelivery systems offers a promising approach for targeted cancer inhibition, including the eradication of cancer stem cells (CSCs). Within the context of highly aggressive and metastatic Triple-negative Breast Cancer (TNBC), this review specifically focuses on devising innovative nanotheranostics. For both pre-clinical and post-clinical TNBC detection, the utilization of the CRISPR-Cas system, guided by RNA (gRNA) and coupled with a fluorescent reporter specifically designed to detect TNBC's mutated sequence, could be promising. Additionally, a cutting-edge approach involving the engineering of TNBC-specific iCAR and syn-Notch CAR T-cells, combined with the co-delivery of a hybrid polymeric nano-liposome encapsulating a conditionally replicative adenoviral vector (CRAdV) against CSCs, could present an intriguing intervention strategy. This review thus paves the way for exciting advancements in the field of nanotheranostics for the treatment of TNBC and beyond.

Immunotherapy: a promising approach for glioma treatment

Gliomas are the most prevalent primary malignant brain tumors worldwide, with glioblastoma (GBM) being the most common and aggressive type. Despite two decades of relentless pursuit in exploring novel therapeutic approaches for GBM, there is limited progress in improving patients' survival outcomes. Numerous obstacles impede the effective treatment of GBM, including the immunosuppressive tumor microenvironment (TME), the blood-brain barrier, and extensive heterogeneity. Despite these challenges, immunotherapies are emerging as a promising avenue that may offer new hope for the treatment of gliomas. There are four main types of immunotherapies for gliomas, immune checkpoint blockades, chimeric antigen receptor T-cell therapies, vaccines, and oncolytic viruses. In addition, gene therapy, bispecific antibody therapy, and combine therapy are also briefly introduced in this review. The significant role of TME in the process of immunotherapies has been emphasized in many studies. Although immunotherapy is a promising treatment for gliomas, enormous effort is required to overcome the existing barriers to its success. Owing to the rapid development and increasing attention paid to immunotherapies for gliomas, this article aims to review the recent advances in immunotherapies for gliomas.

RapaCaspase-9-based suicide gene applied to the safety of IL-1RAP CAR-T cells

Even if adoptive cell transfer (ACT) has already shown great clinical efficiency in different types of disease, such as cancer, some adverse events consistently occur, and suicide genes are an interesting system to manage these events. Our team developed a new medical drug candidate, a chimeric antigen receptor (CAR) targeting interleukin-1 receptor accessory protein (IL-1RAP), which needs to be evaluated in clinical trials with a clinically applicable suicide gene system. To prevent side effects and ensure the safety of our candidate, we devised two constructs carrying an inducible suicide gene, RapaCasp9-G or RapaCasp9-A, containing a single-nucleotide polymorphism (rs1052576) affecting the efficiency of endogenous caspase 9. These suicide genes are activated by rapamycin and based on the fusion of human caspase 9 with a modified human FK-binding protein, allowing conditional dimerization. RapaCasp9-G- and RapaCasp9-A-expressing gene-modified T cells (GMTCs) were produced from healthy donors (HDs) and acute myeloid leukemia (AML) donors. The RapaCasp9-G suicide gene demonstrated better efficiency, and we showed its in vitro functionality in different clinically relevant culture conditions. Moreover, as rapamycin is not pharmacologically inert, we also demonstrated its safe use as part of our therapy.

Liposomal delivery of gene therapy for ovarian cancer: a systematic review

OBJECTIVE

To systematically identify and narratively synthesize the evidence surrounding liposomal delivery of gene therapy and the outcome for ovarian cancer.

METHODS

An electronic database search of the Embase, MEDLINE and Web of Science from inception until July 7, 2023, was conducted to identify primary studies that investigated the effect of liposomal delivery of gene therapy on ovarian cancer outcomes. Retrieved studies were assessed against the eligibility criteria for inclusion.

RESULTS

The search yielded 564 studies, of which 75 met the inclusion criteria. Four major types of liposomes were identified: cationic, neutral, polymer-coated, and ligand-targeted liposomes. The liposome with the most evidence involved cationic liposomes which are characterized by their positively charged phospholipids (n = 37, 49.3%). Similarly, those with neutrally charged phospholipids, such as 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine, were highly researched as well (n = 25, 33.3%). Eight areas of gene therapy research were identified, evaluating either target proteins/transcripts or molecular pathways: microRNAs, ephrin type-A receptor 2 (EphA2), interleukins, mitogen-activated protein kinase (MAPK), human-telomerase reverse transcriptase/E1A (hTERT/EA1), suicide gene, p53, and multidrug resistance mutation 1 (MDR1).

CONCLUSION

Liposomal delivery of gene therapy for ovarian cancer shows promise in many in vivo studies. Emerging polymer-coated and ligand-targeted liposomes have been gaining interest as they have been shown to have more stability and specificity. We found that gene therapy involving microRNAs was the most frequently studied. Overall, liposomal genetic therapy has been shown to reduce tumor size and weight and improve survivability. More research involving the delivery and targets of gene therapy for ovarian cancer may be a promising avenue to improve patient outcomes.

Lipid nanoparticles-loaded with toxin mRNA represents a new strategy for the treatment of solid tumors

Background and rationale: Cancer therapy have evolved remarkably over the past decade, providing new strategies to inhibit cancer cell growth using immune modulation, with or without gene therapy. Specifically, suicide gene therapies and immunotoxins have been investigated for the treatment of tumors by direct cancer cell cytotoxicity. Recent advances in mRNA delivery also demonstrated the potential of mRNA-based vaccines and immune-modulators for cancer therapeutics by utilizing nanocarriers for mRNA delivery. Methods: We designed a bacterial toxin-encoding modified mRNA, delivered by lipid nanoparticles into a B16-melanoma mouse model. Results: We showed that local administration of LNPs entrapping a modified mRNA that encodes for a bacterial toxin, induced significant anti-tumor effects and improved overall survival of treated mice. Conclusions: We propose mmRNA-loaded LNPs as a new class of anti-tumoral, toxin-based therapy.

Repurposing antifungal drugs for cancer therapy

BACKGROUND

Repurposing antifungal drugs in cancer therapy has attracted unprecedented attention in both preclinical and clinical research due to specific advantages, such as safety, high-cost effectiveness and time savings compared with cancer drug discovery. The surprising and encouraging efficacy of antifungal drugs in cancer therapy, mechanistically, is attributed to the overlapping targets or molecular pathways between fungal and cancer pathogenesis. Advancements in omics, informatics and analytical technology have led to the discovery of increasing "off-site" targets from antifungal drugs involved in cancerogenesis, such as smoothened (D477G) inhibition from itraconazole in basal cell carcinoma.

AIM OF REVIEW

This review illustrates several antifungal drugs repurposed for cancer therapy and reveals the underlying mechanism based on their original target and "off-site" target. Furthermore, the challenges and perspectives for the future development and clinical applications of antifungal drugs for cancer therapy are also discussed, providing a refresh understanding of drug repurposing.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review may provide a basic understanding of repurposed antifungal drugs for clinical cancer management, thereby helping antifungal drugs broaden new indications and promote clinical translation.

Engineering the Active Site Lid Dynamics to Improve the Catalytic Efficiency of Yeast Cytosine Deaminase

Conformational dynamics is important for enzyme catalysis. However, engineering dynamics to achieve a higher catalytic efficiency is still challenging. In this work, we develop a new strategy to improve the activity of yeast cytosine deaminase (yCD) by engineering its conformational dynamics. Specifically, we increase the dynamics of the yCD C-terminal helix, an active site lid that controls the product release. The C-terminal is extended by a dynamical single α-helix (SAH), which improves the product release rate by up to ~8-fold, and the overall catalytic rate kcat by up to ~2-fold. It is also shown that the kcat increase is due to the favorable activation entropy change. The NMR H/D exchange data indicate that the conformational dynamics of the transition state analog complex increases as the helix is extended, elucidating the origin of the enhanced catalytic entropy. This study highlights a novel dynamics engineering strategy that can accelerate the overall catalysis through the entropy-driven mechanism.

Stem cell-assisted enzyme/prodrug therapy makes drug-resistant ovarian cancer cells vulnerable to natural killer cells through upregulation of NKG2D ligands

Cancer stem-like cells (CSCs) are believed to be responsible for cancer recurrence and metastasis. Therefore, a therapeutic approach is needed to eliminate both rapidly proliferating differentiated cancer cells and slow-growing drug-resistant CSCs. Using established ovarian cancer cells lines as well as ovarian cancer cells isolated from a patient with high-grade drug-resistant ovarian carcinoma, we demonstrate that ovarian CSCs consistently express lower levels of NKG2D ligands (MICA/B and ULBPs) on their surfaces, a mechanism by which they evade natural killer (NK) cells' surveillance. Here, we discovered that exposure of ovarian cancer (OC) cells to SN-38 followed by 5-FU not only acts synergistically to kill the OC cells, but also makes the CSCs vulnerable to NK92 cells through upregulation of NKG2D ligands. Since systemic administration of these two drugs is marred by intolerance and instability, we engineered and isolated an adipose-derived stem cell (ASC) clone, which stably expresses carboxylesterase-2 and yeast cytosine deaminase enzymes to convert irinotecan and 5-FC prodrugs into SN-38 and 5-FU cytotoxic drugs, respectively. Co-incubation of ASCs and prodrugs with drug-resistant OC cells not only led to the death of the drug-resistant OC cells but also made them significantly vulnerable to NK92 cells. This study provides proof of principle for a combined ASC-directed targeted chemotherapy with NK92-assisted immunotherapy to eradicate drug-resistant OC cells.

Inhibition of human oral squamous cell carcinoma proliferation and migration by prodrug-activating suicide gene therapies

Head and neck squamous cell carcinoma (HNSCC), which originates from mucosal epithelium in the oral cavity, pharynx and larynx, is the sixth most common malignancy in the world. The prognosis of HNSCC is not satisfactory due to metastasis, resulting in 5-year survival rates ranging from 65.9 to 67.2%. Previously, we developed a method to evaluate the effect prodrug-activating suicide gene (PA-SG) therapy on the proliferation of HNSCC. The present study investigated PA-SG therapy on metastatic HNSCC by wound-healing assay and our previously established method. HSC-3 cells with stable expression of suicide genes thymidine kinase (TK) or cytosine deaminase (CD) were treated with prodrugs ganciclovir (GCV) or 5-fluorocytosine (5-FC), respectively. Both GCV and 5-FC inhibited HSC-3 proliferation while the bystander effect of CD/5-FC was greater compared with that of TK/GCV. GCV showed a greater anti-migration effect compared with that of 5-FC. To the best of our knowledge, the present study is the first to evaluate the anti-migratory and anti-proliferative effects of PA-SG therapies on metastatic HNSCC. This may also serve as a general method to quantify other types of PA-SC therapy. The present results demonstrated that PA-SG therapy is a promising treatment for anti-metastatic HNSCC therapy development.

Suicide gene strategies applied in ovarian cancer studies

Ovarian cancer represents the most lethal gynecological malignancy among women in developed countries. Despite the recent innovations, the improvements in the 5-year survival rate have been insufficient and the management of this disease still remains a challenge. The fact that the majority of patients experience recurrent or resistant disease have substantiated the necessity of an innovative treatment. Among various strategies investigated, the recent strides made in gene delivery techniques have made gene therapy, including suicide gene strategies, a potential alternative for treating ovarian cancer. Various suicide gene candidates, which are capable of promoting cancer cell apoptosis directly after its entry or indirectly by prodrug administration, can be separated into three systems using enzyme-coding, toxin or pro-apoptotic genes. With this review, we aim to provide an overview of different suicide genes depending on therapeutic strategies, the vectors used to deliver these transgenes specifically to malignant cells, and the combined treatments of these genes with various therapeutic regimens.

Spotlight on CYP4B1

The mammalian cytochrome P450 monooxygenase CYP4B1 can bioactivate a wide range of xenobiotics, such as its defining/hallmark substrate 4-ipomeanol leading to tissue-specific toxicities. Similar to other members of the CYP4 family, CYP4B1 has the ability to hydroxylate fatty acids and fatty alcohols. Structural insights into the enigmatic role of CYP4B1 with functions in both, xenobiotic and endobiotic metabolism, as well as its unusual heme-binding characteristics are now possible by the recently solved crystal structures of native rabbit CYP4B1 and the p.E310A variant. Importantly, CYP4B1 does not play a major role in hepatic P450-catalyzed phase I drug metabolism due to its predominant extra-hepatic expression, mainly in the lung. In addition, no catalytic activity of human CYP4B1 has been observed owing to a unique substitution of an evolutionary strongly conserved proline 427 to serine. Nevertheless, association of CYP4B1 expression patterns with various cancers and potential roles in cancer development have been reported for the human enzyme. This review will summarize the current status of CYP4B1 research with a spotlight on its roles in the metabolism of endogenous and exogenous compounds, structural properties, and cancer association, as well as its potential application in suicide gene approaches for targeted cancer therapy.

The roles of connexins and gap junctions in the progression of cancer

Gap junctions (GJs), which are composed of connexins (Cxs), provide channels for direct information exchange between cells. Cx expression has a strong spatial specificity; however, its influence on cell behavior and information exchange between cells cannot be ignored. A variety of factors in organisms can modulate Cxs and subsequently trigger a series of responses that have important effects on cellular behavior. The expression and function of Cxs and the number and function of GJs are in dynamic change. Cxs have been characterized as tumor suppressors in the past, but recent studies have highlighted the critical roles of Cxs and GJs in cancer pathogenesis. The complex mechanism underlying Cx and GJ involvement in cancer development is a major obstacle to the evolution of therapy targeting Cxs. In this paper, we review the post-translational modifications of Cxs, the interactions of Cxs with several chaperone proteins, and the effects of Cxs and GJs on cancer. Video Abstract.

Development of Synthetic mRNAs Encoding Split Cytotoxic Proteins for Selective Cell Elimination Based on Specific Protein Detection

For the selective elimination of deleterious cells (e.g., cancer cells and virus-infected cells), the use of a cytotoxic gene is a promising approach. DNA-based systems have achieved selective cell elimination but risk insertional mutagenesis. Here, we developed a synthetic mRNA-based system to selectively eliminate cells expressing a specific target protein. The synthetic mRNAs used in the system are designed to express an engineered protein pair that are based on a cytotoxic protein, Barnase. Each engineered protein is composed of an N- or C-terminal fragment of Barnase, a target protein binding domain, and an intein that aids in reconstituting full-length Barnase from the two fragments. When the mRNAs are transfected to cells expressing the target protein, both N- and C-terminal Barnase fragments bind to the target protein, causing the intein to excise itself and reconstitute cytotoxic full-length Barnase. In contrast, when the target protein is not present, the reconstitution of full-length Barnase is not induced. Four candidate constructs containing split Barnase were evaluated for the ability to selectively eliminate target protein-expressing cells. One of the candidate sets demonstrated highly selective cell death. This system will be a useful therapeutic tool to selectively eliminate deleterious cells.

Suicide Gene Delivery System Mediated by Ultrasound-Targeted Microbubble Destruction: A Promising Strategy for Cancer Therapy

The treatment of malignant tumors has always been one of the challenges that have plagued researchers and clinicians. The ideal status in cancer treatment is to eliminate tumor cells while avoiding damage to normal tissues. Different approaches have been investigated to achieve such a goal, and suicide gene therapy has emerged as a novel mode of cancer treatment. This approach involves the delivery of genes encoding enzymes that activate non-toxic prodrugs into cytotoxic metabolites that cause the death of transfected cancer cells. Despite promising results obtained both in vitro and in vivo, this innovative approach has long been stalled in the clinic due to the lack of a suitable delivery system to introduce the suicide gene into cancer cells. Ultrasound-targeted microbubble destruction (UTMD) represents a valuable non-viral vector system for site-specific and noninvasive gene therapy. Ultrasound promotes intracellular uptake of therapeutic agents by increasing vascular and cell membrane permeability, especially in the presence of microbubbles. In this scenario, the true potential of suicide genes can be translated into clinically valuable treatments for patients. This review provides background information on suicide gene therapy and UTMD technology, summarizes the current state of knowledge about UTMD-mediated suicide gene delivery in cancer treatment, and presents an outlook on its future development.

Editing a gateway for cell therapy across the blood-brain barrier

Stem cell therapy has been shown to improve stroke outcomes in animal models and is currently advancing towards clinical practice. However, uncertainty remains regarding the optimal route for cell delivery to the injured brain. Local intracerebral injections are effective in precisely delivering cells into the stroke cavity but carry the risk of damaging adjacent healthy tissue. Systemic endovascular injections, meanwhile, are minimally invasive, but most injected cells do not cross CNS barriers and become mechanically trapped in peripheral organs. Although the blood-brain barrier and the blood-CSF barrier tightly limit the entrance of cells and molecules into the brain parenchyma, immune cells can cross these barriers especially under pathological conditions, such as stroke. Deciphering the cell surface signature and the molecular mechanisms underlying this pathophysiological process holds promise for improving the targeted delivery of systemic injected cells to the injured brain. In this review, we describe experimental approaches that have already been developed in which (i) cells are either engineered to express cell surface proteins mimicking infiltrating immune cells; or (ii) cell grafts are preconditioned with hypoxia or incubated with pharmacological agents or cytokines. Modified cell grafts can be complemented with strategies to temporarily increase the permeability of the blood-brain barrier. Although these approaches could significantly enhance homing of stem cells into the injured brain, cell entrapment in off-target organs remains a non-negligible risk. Recent developments in safety-switch systems, which enable the precise elimination of transplanted cells on the administration of a drug, represent a promising strategy for selectively removing stem cells stuck in untargeted organs. In sum, the techniques described in this review hold great potential to substantially improve efficacy and safety of future cell therapies in stroke and may be relevant to other brain diseases.

Ultrasonically Enhanced ZD2767P–Carboxypeptidase G2 Deactivates Cisplatin-Resistant Human Lung Cancer Cells

The prodrug–enzyme regimen ZD2767P+CPG2 is limited by low efficacy. Here, ultrasound was used to modulate ZD2767P+CPG2 (i.e., ZD2767P+CPG2+US) against cisplatin-resistant human lung cancer cells. A549 and A549/DDP (resistant subline) cells received ZD2767P+CPG2 or ZD2767P+CPG2+US. Either ZD2767P+CPG2 or ZD2767P+CPG2+US led to cell death and apoptosis, and ZD2767P+CPG2+US produced stronger effects; comet assays revealed that these two means directly caused DNA double-strand break. Z-VAD-fmk and/or ferrostatin-1 increased the cell survival percentage, and Z-VAD-fmk decreased the apoptosis percentage. The level of transferrin was increased in treated cells, but those of ferroportin and glutathione peroxidase 4 (GPX4) were reduced, with higher intracellular levels of reactive oxygen species and of iron. Intracellular pharmacokinetics of ZD2767D (activated drug) indicated that the peak level, area under the drug level vs. time curve, and mean residence time in ZD2767P+CPG2+US were higher than those in ZD2767P+CPG2. Both ZD2767P+CPG2 and ZD2767P+CPG2+US were effective on xenograft tumors in nude mice; inhibitory rates were 39.7% and 63.5% in A549 tumors and 50.0% and 70.1% in A549/DDP tumors, respectively. A higher apoptosis level and a lower GPX4 level were noted in tumors receiving treatments. No severe adverse events were observed. These data demonstrated that ZD2767P+CPG2+US deactivated cancer cells via apoptosis and ferroptosis pathways, being a candidate therapy for cisplatin-resistant lung cancer.

Virus-inspired strategies for cancer therapy

The intentional use of viruses for cancer therapy dates back over a century. As viruses are inherently immunogenic and naturally optimized delivery vehicles, repurposing viruses for drug delivery, tumor antigen presentation, or selective replication in cancer cells represents a simple and elegant approach to cancer treatment. While early virotherapy was fraught with harsh side effects and low response rates, virus-based therapies have recently seen a resurgence due to newfound abilities to engineer and tune oncolytic viruses, virus-like particles, and virus-mimicking nanoparticles for improved safety and efficacy. However, despite their great potential, very few virus-based therapies have made it through clinical trials. In this review, we present an overview of virus-inspired approaches for cancer therapy, discuss engineering strategies to enhance their mechanisms of action, and highlight their application for overcoming the challenges of traditional cancer therapies.

Variants of the adeno-associated virus serotype 9 with enhanced penetration of the blood-brain barrier in rodents and primates

The development of gene therapies for the treatment of diseases of the central nervous system has been hindered by the limited availability of adeno-associated viruses (AAVs) that efficiently traverse the blood-brain barrier (BBB). Here, we report the rational design of AAV9 variants displaying cell-penetrating peptides on the viral capsid and the identification of two variants, AAV.CPP.16 and AAV.CPP.21, with improved transduction efficiencies of cells of the central nervous system on systemic delivery (6- to 249-fold across 4 mouse strains and 5-fold in cynomolgus macaques, with respect to the AAV9 parent vector). We also show that the neurotropism of AAV.CPP.16 is retained in young and adult macaques, that this variant displays enhanced transcytosis at the BBB as well as increased efficiency of cellular transduction relative to AAV9, and that it can be used to deliver antitumour payloads in a mouse model of glioblastoma. AAV capsids that can efficiently penetrate the BBB will facilitate the clinical translation of gene therapies aimed at the central nervous system.

Biocompatible Iron Oxide Nanoparticles for Targeted Cancer Gene Therapy: A Review

In recent years, gene therapy has made remarkable achievements in tumor treatment. In a successfully cancer gene therapy, a smart gene delivery system is necessary for both protecting the therapeutic genes in circulation and enabling high gene expression in tumor sites. Magnetic iron oxide nanoparticles (IONPs) have demonstrated their bright promise for highly efficient gene delivery target to tumor tissues, partly due to their good biocompatibility, magnetic responsiveness, and extensive functional surface modification. In this review, the latest progress in targeting cancer gene therapy is introduced, and the unique properties of IONPs contributing to the efficient delivery of therapeutic genes are summarized with detailed examples. Furthermore, the diagnosis potentials and synergistic tumor treatment capacity of IONPs are highlighted. In addition, aiming at potential risks during the gene delivery process, several strategies to improve the efficiency or reduce the potential risks of using IONPs for cancer gene therapy are introduced and addressed. The strategies and applications summarized in this review provide a general understanding for the potential applications of IONPs in cancer gene therapy.

Governing HPV-related carcinoma using vaccines: Bottlenecks and breakthroughs

Human papillomavirus (HPV) contributes to sexually transmitted infection, which is primarily associated with pre-cancerous and cancerous lesions in both men and women and is among the neglected cancerous infections in the world. At global level, two-, four-, and nine-valent pure L1 protein encompassed vaccines in targeting high-risk HPV strains using recombinant DNA technology are available. Therapeutic vaccines are produced by early and late oncoproteins that impart superior cell immunity to preventive vaccines that are under investigation. In the current review, we have not only discussed the clinical significance and importance of both preventive and therapeutic vaccines but also highlighted their dosage and mode of administration. This review is novel in its way and will pave the way for researchers to address the challenges posed by HPV-based vaccines at the present time.

Microbial cytosine deaminase is a programmable anticancer prodrug mediating enzyme: antibody, and gene directed enzyme prodrug therapy

Cytosine deaminase (CDA) is a non-mammalian enzyme with powerful activity in mediating the prodrug 5-fluorcytosine (5-FC) into toxic drug 5-fluorouracil (5-FU), as an alternative directed approach for the traditional chemotherapies and radiotherapies of cancer. This enzyme has been frequently reported and characterized from various microorganisms. The therapeutic strategy of 5-FC-CDA involves the administration of CDA followed by the prodrug 5-FC injection to generate cytotoxic 5-FU. The antiproliferative activity of CDA-5-FC elaborates from the higher activity of uracil pathway in tumor cells than normal ones. The main challenge of the therapeutic drug 5-FU are the short half-life, lack of selectivity and emergence of the drug resistance, consistently to the other chemotherapies. So, mediating the 5-FU to the tumor cells by CDA is one of the most feasible approaches to direct the drug to the tumor cells, reducing its toxic effects and improving their pharmacokinetic properties. Nevertheless, the catalytic efficiency, stability, antigenicity and targetability of CDA-5-FC, are the major challenges that limit the clinical application of this approach. Thus, exploring the biochemical properties of CDA from various microorganisms, as well as the approaches for localizing the system of CDA-5-FC to the tumor cells via the antibody directed enzyme prodrug therapy (ADEPT) and gene directed prodrug therapy (GDEPT) were the objectives of this review. Finally, the perspectives for increasing the therapeutic efficacy, and targetability of the CDA-5-FC system were described.

From Immunotoxins to Suicide Toxin Delivery Approaches: Is There a Clinical Opportunity?

Suicide gene therapy is a relatively novel form of cancer therapy in which a gene coding for enzymes or protein toxins is delivered through targeting systems such as vesicles, nanoparticles, peptide or lipidic co-adjuvants. The use of toxin genes is particularly interesting since their catalytic activity can induce cell death, damaging in most cases the translation machinery (ribosomes or protein factors involved in protein synthesis) of quiescent or proliferating cells. Thus, toxin gene delivery appears to be a promising tool in fighting cancer. In this review we will give an overview, describing some of the bacterial and plant enzymes studied so far for their delivery and controlled expression in tumor models.

Hypoxia-directed tumor targeting of CRISPR-Cas9 and HSV-TK suicide gene therapy using lipid nanoparticles

Hypoxia is a characteristic feature of solid tumors that contributes to tumor aggressiveness and is associated with resistance to cancer therapy. The hypoxia inducible factor-1 (HIF-1) transcription factor complex mediates hypoxia-specific gene expression by binding to hypoxia-responsive element (HRE) sequences within the promoter of target genes. HRE-driven expression of therapeutic cargo has been widely explored as a strategy to achieve cancer-specific gene expression. By utilizing this system, we achieve hypoxia-specific expression of two therapeutically relevant cargo elements: the herpes simplex virus thymidine kinase (HSV-tk) suicide gene and the CRISPR-Cas9 nuclease. Using an expression vector containing five copies of the HRE derived from the vascular endothelial growth factor gene, we are able to show high transgene expression in cells in a hypoxic environment, similar to levels achieved using the cytomegalovirus (CMV) and CBh promoters. Furthermore, we are able to deliver our therapeutic cargo to tumor cells with high efficiency using plasmid-packaged lipid nanoparticles (LNPs) to achieve specific killing of tumor cells in hypoxic conditions while maintaining tight regulation with no significant changes to cell viability in normoxia.

Therapeutic potential of the cytosine deaminase::uracil phosphoribosyl transferase/5-fluorocytosine suicide system for canine melanoma

We tested the efficacy of a yeast cytosine deaminase::uracil phosphoribosyl transferase/5-fluorocytosine (CDU/5-FC) non-viral suicide system on eight established canine melanoma cell lines. Albeit with different degree of sensitivity 5 days after lipofection, this system was significantly efficient killing melanoma cells, being four cell lines highly, two fairly and two not very sensitive to CDU/5-FC (their respective IC50 ranging from 0.20 to 800 μM 5-FC). Considering the relatively low lipofection efficiencies, a very strong bystander effect was verified in the eight cell lines: depending on the cell line, this effect accounted for most of the induced cell death (from 70% to 95%). In our assay conditions, we did not find useful interactions either with the herpes simplex thymidine kinase/ganciclovir suicide system (in sequential or simultaneous modality) or with cisplatin and bleomycin chemotherapeutic drugs. Furthermore, only two cell lines displayed limited useful interactions of the CDU/5-FC either with interferon-β gene transfer or the proteasome inhibitor bortezomib respectively. These results would preclude a wide use of these combinations. However, the fact that all the tested cells were significantly sensitive to the CDU/5-FC system encourages further research as a gene therapy tool for local control of canine melanoma.

Dioscin potentiates the antitumor effect of suicide gene therapy in melanoma by gap junction intercellular communication-mediated antigen cross-presentation

Dioscin (Dio), steroid saponin, exists in several medicinal herbs with potent anticancer efficacy. This study aimed to explore the effect of Dio on the immune-related modulation and synergistic therapeutic effects of the herpes simplex virus thymidine kinase/ganciclovir (HSV-Tk/GCV) suicide gene therapy system in murine melanoma, thereby providing a research basis to improve the potential immunomodulatory mechanism underlying combination therapy. Using both in vitro and in vivo experiments, we confirmed the immunocidal effect of Dio-potentiated suicide gene therapy on melanoma. The results showed that Dio upregulated connexin 43 (Cx43) expression and improved gap junction intercellular communication (GJIC) in B16 cells while increasing the cross-presentation of antigens by dendritic cells (DCs), eventually promoting the activation and antitumor immune killing effects of CD8⁺ T lymphocytes. In contrast, inhibition or blockade of the GJIC function (overexpression of mutant Cx43 tumor cells/Gap26) partially reversed the potentiating effect. The significant synergistic effect of Dio on HSV-Tk/GCV suicide gene therapy was further investigated in a B16 xenograft mouse model. The increased number and activation ratio of CD8⁺ T lymphocytes and the levels of Gzms-B, IFN-γ, and TNF-α in mice reconfirmed the potential modulatory effects of Dio on the immune system. Taken together, Dio targets Cx43 to enhance GJIC function, improve the antigens cross-presentation of DCs, and activate the antitumor immune effect of CD8⁺ T lymphocytes, thereby providing insights into the potential immunomodulatory mechanism underlying combination therapy.

Mesenchymal stem cells: A living carrier for active tumor-targeted delivery

The strategy of using mesenchymal stem cells (MSCs) as a living carrier for active delivery of therapeutic agents targeting tumor sites has been attempted in a wide range of studies to validate the feasibility and efficacy for tumor treatment. This approach reveals powerful tumor targeting and tumor penetration. In addition, MSCs have been confirmed to actively participate in immunomodulation of the tumor microenvironment. Thus, MSCs are not inert delivery vehicles but have a strong impact on the fate of tumor cells. In this review, these active properties of MSCs are addressed to highlight the advantages and challenges of using MSCs for tumor-targeted delivery. In addition, some of the latest examples of using MSCs to carry a variety of anti-tumor agents for tumor-targeted therapy are summarized. Recent technologies to improve the performance and safety of this delivery strategy will be introduced. The advances, applications, and challenges summarized in this review will provide a general understanding of this promising strategy for actively delivering drugs to tumor tissues.

"PFH/AGM-CBA/HSV-TK/LIPOSOME-Affibody": Novel Targeted Nano Ultrasound Contrast Agents for Ultrasound Imaging and Inhibited the Growth of ErbB2-Overexpressing Gastric Cancer Cells

Objective

Gastric cancer is one of the most lethal malignancies in the world. However, the current research on the diagnosis and treatment of nano-ultrasound contrast agents in the field of tumor is mostly focused on breast cancer, ovarian cancer, prostate cancer, liver cancer, etc. Due to the interference of gas in the stomach, there is no report on the treatment of gastric cancer. Herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) therapy system is the most mature tumor suicide gene in cancer treatment. At the same time, in order to improve its safety and efficiency, we designed a gastric tumor targeted ultrasound-triggered phase-transition nano ultrasound contrast agent PFH/AGM-CBA/HSV-TK/Liposome (PAHL)-Affibody complex.

Methods

In our study, guanidinylated SS-PAAs polymer poly(agmatine/N, N′-cystamine-bis-acrylamide) (AGM-CBA) was used as a nuclear localization vector of suicide gene to form a polyplex, perfluorohexane (PFH) was used as ultrasound contrast agent, liposomes were used to encapsulate perfluorohexane droplets and the polyplexes of AGM-CBA/HSV-TK, and affibody molecules were conjugated to the prepared PAHL in order to obtain a specific targeting affinity to human epidermal growth factor receptor type 2 (ErbB2) at gastric cancer cells. With the aid of ultrasound targeted microbubble destruction technology and the nuclear localization effect of AGM-CBA vector, the transfection efficiency of the suicide gene in gastric cancer cells was significantly increased, leading to significant apoptosis of gastric cancer cells.

Results

It was shown that PAHL-Affibody complex was nearly spherical with an average diameter of 560 ± 28.9 nm, having higher and specific affinity to ErbB2 (+) gastric cells. In vitro experiments further confirmed that PAHL could target gastric cancer cells expressing ErbB2. In a contrast-enhanced ultrasound scanning study, the prepared ultrasound-triggered phase-change nano-ultrasound contrast agent, PAHL, showed improved ultrasound enhancement effects. With the application of the low-frequency ultrasound, the gene transfection efficiency of PAHL was significantly improved,  thereby inducing significant apoptosis in gastric cancer cells.

Conclusion

This study constructs PFH/AGM-CBA/HSV-TK/Liposome-Affibody nano ultrasound contrast agent, which provides new ideas for the treatment strategy of ErbB2-positive gastric cancer and provides some preliminary experimental basis for its inhibitory effect.

Emerging Roles of Green-Synthesized Chalcogen and Chalcogenide Nanoparticles in Cancer Theranostics

The last few decades have seen an overwhelming increase in the amount of research carried out on the use of inorganic nanoparticles. More fascinating is the tremendous progress made in the use of chalcogen and chalcogenide nanoparticles in cancer theranostics. These nanomaterials, which were initially synthesized through chemical methods, have now been efficiently produced using different plant materials. The paradigm shift towards the biogenic route of nanoparticle synthesis stems from its superior advantages of biosafety, eco-friendliness, and simplicity, among others. Despite a large number of reviews available on inorganic nanoparticle synthesis through green chemistry, there is currently a dearth of information on the green synthesis of chalcogens and chalcogenides for cancer research. Nanoformulations involving chalcogens such as sulfur, selenium, and tellurium and their respective chalcogenides have recently emerged as promising tools in cancer therapeutics and diagnosis. Similar to other inorganic nanoparticles, chalcogens and chalcogenides have been synthesized using plant extracts and their purified biomolecules. In this review, we provide an up-to-date discussion of the recent progress that has been made in the plant-mediated synthesis of chalcogens and chalcogenides with a special focus on their application in cancer theranostics.

Research Progress on Gene Editing Based on Nano-Drug Delivery Vectors for Tumor Therapy

Malignant tumors pose a serious threat to human health and have high fatality rates. Conventional clinical anti-tumor treatment is mainly based on traditional surgery, chemotherapy, radiotherapy, and interventional therapy, and even though these treatment methods are constantly updated, a satisfactory efficacy is yet to be obtained. Therefore, research on novel cancer treatments is being actively pursued. We review the classification of gene therapies of malignant tumors and their advantages, as well as the development of gene editing techniques. We further reveal the nano-drug delivery carrier effect in improving the efficiency of gene editing. Finally, we summarize the progress in recent years of gene editing techniques based on nano-drug delivery carriers in the treatment of various malignant tumors, and analyze the prospects of the technique and its restricting factors.

Evaluation of the stability and intratumoral delivery of foreign transgenes encoded by an oncolytic Foamy Virus vector

Foamy Viruses are cell cycle-dependent retroviruses capable of persisting unintegrated in quiescent cells until cell division occurs. This unique ability allows them to target slowly dividing human tumor cells which remains an unmet need in oncolytic virotherapy. We have previously reported the generation of oncolytic Foamy Virus (oFV) vector system and demonstrated its superiority over oncolytic Murine Leukemia Virus vectors in infecting slowly dividing cancer cells. In the present study we evaluated (i) the ability of oFV to carry foreign transgenes and (ii) the genetic stability of these vectors upon serial passage. The thymidine kinase (TK) and inducible caspase 9 (iCasp9) cDNAs could be detected in the oFV backbone for up to 3 in vitro passages. In vivo, GFP-, TK- and iCasp9- carrying oFV vectors propagated efficiently in subcutaneous xenograft glioblastoma tumors and drove transgene expression for up to 66 days. However, in vivo oFV vector spread eventually resulted in complete loss of the iCasp9 cDNA, minor loss of the TK cDNA and negligible loss of the GFP. Our results suggest that oFV is a promising gene delivery platform and that transgenes smaller than 1 kb might be most suitable for oFV arming.

Generation and functional characterization of a multigene-modified NK101 cell line exerting diverse mechanisms of antitumor action

Clonal cell line-based, multigene-modified, off-the-shelf NK cell therapeutics are emerging as the new frontier of adoptive cellular immunotherapy. Here, we utilized a newly established NK cell line, NK101, as a backbone to derive multifaceted killer cells armored with various antitumor modalities through repeated cycles of genetic modification and clonal selection. First, NK101 cells were transduced with a tricistronic lentiviral vector expressing CD7, CD28, and cytosine deaminase (CD). The resulting cell line demonstrated enhanced cytotoxicity against B7⁺ tumors and exerted bystander killing effects on neighboring tumor cells upon 5-FC treatment. Second, engineered NK101 cells were again transduced with a bicistronic vector expressing membrane-bound interleukin-15 (mbIL-15) and dominant negative TGFβ type II receptor (DNTβRII). Ectopic expression of mbIL-15 resulted in further augmentation of lytic activities against all tested target cells by inducing upregulation of multiple activating receptors, while that of DNTβRII allowed the cells to maintain heightened cytotoxicity in the presence of TGFβ. Finally, dual-transduced NK101 cells were modified to express chimeric antigen receptors (CARs) targeting either a solid tumor antigen (EpCAM) or a hematologic tumor antigen (FLT3). The final engineered products not only demonstrated antigen-specific killing activities in vitro but also exerted strong tumor-inhibitory effects in preclinical models of metastatic solid tumor and hematologic malignancy. Notably, combined treatment with 5-FC further enhanced antitumor efficacy of engineered NK101 in the solid tumor model. Our results demonstrate successful generation of multigene-modified NK101 cell therapeutics exerting diverse mechanisms of antitumor action - activation receptor-mediated innate killing, antigen-specific killing, and bystander effect-mediated killing.

Cancer Gene Therapy: Development and Production of Lentiviral Vectors for Gene Therapy

Lentiviral vectors are among the most used vectors in gene therapy to treat pathologies of different origins, such as cancers, rare monogenic diseases or neurological disorders. This chapter provides an overview on lentiviral vector developments in terms of vector design and manufacture for gene therapy applications. The state of the art of vector production will be summarized face to the recent developments contributing to improve vector safety, efficacy and manufacturing robustness, focusing on human immunodeficiency virus 1 (HIV-1) based lentiviral vectors. Transient and stable production systems will be discussed highlighting recent advances in producer cell line development. Challenges in lentiviral vector development upstream and downstream will be addressed with a particular focus on the improvements undertaken to increase vector yields and production scalability.

The Potential Applications of Stem Cells for Cancer Treatment

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Scientists encounter many obstacles in traditional cancer therapies, including the side effects on the healthy cells, drug resistance, tumor relapse, the short half-life of employed drugs in the blood circulation, and the improper delivery of drugs toward the tumor site. The unique traits of stem cells (SCs) such as self-renewal, differentiation, tumor tropism, the release of bioactive molecules, and immunosuppression have opened a new window for utilizing SCs as a novel tool in cancer treatment. In this regard, engineered SCs can secrete anti-cancer proteins or express enzymes used in suicide gene therapy which locally induce apoptosis in neoplastic cells via the bystander effect. These cells also stand as proper candidates to serve as careers for drug-loaded nanoparticles or to play suitable hosts for oncolytic viruses. Moreover, they harbor great potential to be employed in immunotherapy and combination therapy. However, tactful strategies should be devised to allow easier transplantation and protection of SCs from in vivo immune responses. In spite of the great hope concerning SCs application in cancer therapy, there are shortcomings and challenges to be addressed. This review tends to elaborate on recent advances on the various applications of SCs in cancer therapy and existing challenges in this regard.

Suicide gene therapy in cancer and HIV-1 infection: An alternative to conventional treatments

Suicide Gene Therapy (SGT) aims to introduce a gene encoding either a toxin or an enzyme making the targeted cell more sensitive to chemotherapy. SGT represents an alternative approach to combat pathologies where conventional treatments fail such as pancreatic cancer or the high-grade glioblastoma which are still desperately lethal. We review the possibility to use SGT to treat these cancers which have shown promising results in vitro and in preclinical trials. However, SGT has so far failed in phase III clinical trials thus further improvements are awaited. We can now take advantages of the many advances made in SGT for treating cancer to combat other pathologies such as HIV-1 infection. In the review we also discuss the feasibility to add SGT to the therapeutic arsenal used to cure HIV-1-infected patients. Indeed, preliminary results suggest that both productive and latently infected cells are targeted by the SGT. In the last section, we address the limitations of this approach and how we might improve it.

Oncolytic Virotherapy: From Bench to Bedside

Oncolytic viruses are naturally occurring or genetically engineered viruses that can replicate preferentially in tumor cells and inhibit tumor growth. These viruses have been considered an effective anticancer strategy in recent years. They mainly function by direct oncolysis, inducing an anticancer immune response and expressing exogenous effector genes. Their multifunctional characteristics indicate good application prospects as cancer therapeutics, especially in combination with other therapies, such as radiotherapy, chemotherapy and immunotherapy. Therefore, it is necessary to comprehensively understand the utility of oncolytic viruses in cancer therapeutics. Here, we review the characteristics, antitumor mechanisms, clinical applications, deficiencies and associated solutions, and future prospects of oncolytic viruses.

Toward Engineered Biosynthesis of Drugs in Human Cells

Biosynthetic genes are not only responsible for the formation of bioactive substances but also suited for other applications including gene therapy. To test the feasibility of human cells producing antibiotics in situ when provided with a heterologous biosynthetic gene, we focused on cytochrome P450, the class of enzymes important in conferring bioactivity to natural product precursors. We selected Fma-P450 that plays a central role in the fumagillin antimicrobial biosynthesis in Aspergillus fumigatus to examine fungal metabolite production by HeLa cells that express fma-P450 heterologously. Here we show that HeLa cells harboring fma-P450 can biosynthesize 5-hydroxyl-β-trans-bergamoten and cytotoxic 5-epi-demethoxyfumagillol when supplemented with the nontoxic precursor β-trans-bergamotene. While the production level was insufficient to effect cell death, we demonstrate that programming human cells to autogenerate antibiotics by introducing a heterologous biosynthetic gene is feasible.

Step-by-Step Immune Activation for Suicide Gene Therapy Reinforcement

Gene-directed enzyme prodrug gene therapy (GDEPT) theoretically represents a useful method to carry out chemotherapy for cancer with minimal side effects through the formation of a chemotherapeutic agent inside cancer cells. However, despite great efforts, promising preliminary results, and a long period of time (over 25 years) since the first mention of this method, GDEPT has not yet reached the clinic. There is a growing consensus that optimal cancer therapies should generate robust tumor-specific immune responses. The advent of checkpoint immunotherapy has yielded new highly promising avenues of study in cancer therapy. For such therapy, it seems reasonable to use combinations of different immunomodulators alongside traditional methods, such as chemotherapy and radiotherapy, as well as GDEPT. In this review, we focused on non-viral gene immunotherapy systems combining the intratumoral production of toxins diffused by GDEPT and immunomodulatory molecules. Special attention was paid to the applications and mechanisms of action of the granulocyte-macrophage colony-stimulating factor (GM–CSF), a cytokine that is widely used but shows contradictory effects. Another method to enhance the formation of stable immune responses in a tumor, the use of danger signals, is also discussed. The process of dying from GDEPT cancer cells initiates danger signaling by releasing damage-associated molecular patterns (DAMPs) that exert immature dendritic cells by increasing antigen uptake, maturation, and antigen presentation to cytotoxic T-lymphocytes. We hypothesized that the combined action of this danger signal and GM–CSF issued from the same dying cancer cell within a limited space would focus on a limited pool of immature dendritic cells, thus acting synergistically and enhancing their maturation and cytotoxic T-lymphocyte attraction potential. We also discuss the problem of enhancing the cancer specificity of the combined GDEPT–GM–CSF–danger signal system by means of artificial cancer specific promoters or a modified delivery system.

Against the Resilience of High-Grade Gliomas: Gene Therapies (Part II)

Introduction: High-grade gliomas (HGGs) still have a high rate of recurrence and lethality. Gene therapies were projected to overcome the therapeutic resilience of HGGs, due to the intrinsic genetic heterogenicity and immune evasion pathways. The present literature review strives to provide an updated overview of the novel gene therapies for HGGs treatment, highlighting evidence from clinical trials, molecular mechanisms, and future perspectives. Methods: An extensive literature review was conducted through PubMed/Medline and ClinicalTrials.gov databases, using the keywords “high-grade glioma,” “glioblastoma,” and “malignant brain tumor”, combined with “gene therapy,” “oncolytic viruses,” “suicide gene therapies,” “tumor suppressor genes,” “immunomodulatory genes,” and “gene target therapies”. Only articles in English and published in the last 15 years were chosen, further screened based on best relevance. Data were analyzed and described according to the PRISMA guidelines. Results: Viruses were the most vehicles employed for their feasibility and transduction efficiency. Apart from liposomes, other viral vehicles remain largely still experimental. Oncolytic viruses and suicide gene therapies proved great results in phase I, II preclinical, and clinical trials. Tumor suppressor, immunomodulatory, and target genes were widely tested, showing encouraging results especially for recurrent HGGs. Conclusions: Oncolytic virotherapy and suicide genes strategies are valuable second-line treatment options for relapsing HGGs. Immunomodulatory approaches, tumor suppressor, and target genes therapies may implement and upgrade standard chemoradiotherapy. Future research aims to improve safety profile and prolonging therapeutic effectiveness. Further clinical trials are needed to assess the efficacy of gene-based therapies.

Characterization of a Stable Form of Carboxypeptidase G2 (Glucarpidase), a Potential Biobetter Variant, From Acinetobacter sp. 263903-1

Carboxypeptidase G2 (CPG2) is a bacterial enzyme widely used to detoxify methotrexate (MTX) and in enzyme/prodrug therapy for cancer treatment. However, several drawbacks, such as instability, have limited its efficiency. Herein, we have evaluated the properties of a putative CPG2 from Acinetobacter sp. 263903-1 (AcCPG2). AcCPG2 is compared with a CPG2 derived from Pseudomonas sp. strain RS-16 (PsCPG2), available as an FDA-approved medication called glucarpidase. After modeling AcCPG2 using the I-TASSER program, the refined model was validated by PROCHECK, VERIFY 3D and according to the Z score of the model. Using computational analyses, AcCPG2 displayed higher thermodynamic stability and a lower aggregation propensity than PsCPG2. AcCPG2 showed an optimum pH of 7.5 against MTX and was stable over a pH range of 5-10. AcCPG2 exhibited optimum activity at 50 °C and higher thermal stability at a temperature range of 20-70 °C compared to PsCPG2. The K_m value of the purified AcCPG2 toward folate and MTX was 31.36 µM and 44.99 µM, respectively. The V_max value of AcCPG2 for folate and MTX was 125.80 µmol/min/mg and 48.90  µmol/min/mg, respectively. Accordingly, thermostability and pH versatility makes AcCPG2 a potential biobetter variant for therapeutic applications.

NUDT15 polymorphism influences the metabolism and therapeutic effects of acyclovir and ganciclovir

Nucleobase and nucleoside analogs (NNA) are widely used as anti-viral and anti-cancer agents, and NNA phosphorylation is essential for the activity of this class of drugs. Recently, diphosphatase NUDT15 was linked to thiopurine metabolism with NUDT15 polymorphism associated with drug toxicity in patients. Profiling NNA drugs, we identify acyclovir (ACV) and ganciclovir (GCV) as two new NNAs metabolized by NUDT15. NUDT15 hydrolyzes ACV and GCV triphosphate metabolites, reducing their effects against cytomegalovirus (CMV) in vitro. Loss of NUDT15 potentiates cytotoxicity of ACV and GCV in host cells. In hematopoietic stem cell transplant patients, the risk of CMV viremia following ACV prophylaxis is associated with NUDT15 genotype (P = 0.015). Donor NUDT15 deficiency is linked to graft failure in patients receiving CMV-seropositive stem cells (P = 0.047). In conclusion, NUDT15 is an important metabolizing enzyme for ACV and GCV, and NUDT15 variation contributes to inter-patient variability in their therapeutic effects.

Non-viral Suicide Gene Therapy: Cytosine Deaminase Gene Directed by VEGF Promoter and 5-fluorocytosine as a Gene Directed Enzyme/prodrug System in Breast Cancer Model

The present study investigated the potential of vascular endothelial growth factor (VEGF) promoter to derive cytosine deaminase (CD) transfected by polyamidoamine (G4-PAMAM) dendrimers to 4T1 murine breast cancer cell line as gene-directed enzyme/prodrug therapy. The VEGF promoter and cytosine deaminase gene were cloned into the pEGFP-N1vector from the genomic DNA of 4T1 and E. coli, respectively. The frequency of transfection for VEGF-CD-pEGFP-N1 and pEGFP-N1- CD treated groups was 35±3 and 36±4, respectively. MTT assay was perform to evaluate the cytotoxic effects of converted 5-flurocytosine on 4T1 cells. Also, the optimal concentration of 5-FC in 4T1 cells transfected by VEGF-CD-pEGFP-N1 plasmid was evaluated. The GFP expression of transfected 4T1 cells by VEGF-CD-pEGFP-N1were observed by fluorescent microscopy and flowcytometry. Results demonstrated that the suicide CD gene was successfully expressed in 4T1 cells determined by RT-PCR and GFP expression. A concentration of 200 μg/ml 5-FC was identified as optimal dose of prodrug. Furthermore, the CD/5-FC enzyme/prodrug system not only demonstrated toxicity on transformed 4T1 cells but also exerted a 'bystander effect' determined by MTT assay. The results showed that by 35% transfection with VEGF-CD-pEGFP-N1and CD-pEGFP-N1 plasmids, 80% and 90% inhibition of the cells growth occurred, respectively.