Combination Suicide Gene Delivery with an Adeno-Associated Virus Vector Encoding Inducible Caspase-9 and a Chemical Inducer of Dimerization Is Effective in a Xenotransplantation Model of Hepatocellular Carcinoma

Development of an Optimized Promoter System for Exosomal and Naked AAV Vector-Based Suicide Gene Therapy in Hepatocellular Carcinoma

Suicide gene therapy is a promising strategy for the potential treatment of hepatocellular carcinoma (HCC). However, the lack of high transduction efficiency and targeted vectors in delivering the suicide genes to only the HCC cells is a major impediment. In the present study, we utilized an adeno-associated virus serotype 6 (AAV6) and its exosomal counterpart (exo-AAV) comprising of an inducible Caspase 9 (iCasp9) gene under the control of different promoter systems for targeting HCC cells. We employed a ubiquitous cytomegalovirus immediate early enhancer/chicken β actin promoter (CAG), a liver-specific promoter (LP1), and a baculoviral IAP repeat-containing protein 5 (BIRC5) promoter for liver and cancer cell-specific expression of iCasp9, respectively. We further evaluated these vectors in Huh7 cells for their ability to kill the target cells. BIRC5 and LP1 promoter-driven iCasp9 vectors demonstrated superior cytotoxicity when compared to CAG promoter-driven iCasp9 vectors. Further validation in a murine model of HCC demonstrated that the LP1-iCasp9 or Birc5-iCasp9-based AAV6 vectors contributed to tumor regression (∼2 fold) as effectively as the AAV6-CAG-iCasp9 vectors (∼1.9 fold). Similarly, exo-AAV6 vectors showed ∼2.1 to 2.8 fold superior in vivo tumor regression when compared to mock-treated animals. Our study has developed two novel promoters (LP1 or BIRC5) whose efficacy is comparable to a strong ubiquitous promoter in both AAV and exo-AAV systems. This expands the toolkit of AAV vectors for safe and effective treatment of HCC.

Recent advances in various adeno-associated viruses (AAVs) as gene therapy agents in hepatocellular carcinoma

Primary liver cancer, which is scientifically referred to as hepatocellular carcinoma (HCC), is a significant concern in the field of global health. It has been demonstrated that conventional chemotherapy, chemo-hormonal therapy, and conformal radiotherapy are ineffective against HCC. New therapeutic approaches are thus urgently required. Identifying single or multiple mutations in genes associated with invasion, metastasis, apoptosis, and growth regulation has resulted in a more comprehensive comprehension of the molecular genetic underpinnings of malignant transformation, tumor advancement, and host interaction. This enhanced comprehension has notably propelled the development of novel therapeutic agents. Therefore, gene therapy (GT) holds great promise for addressing the urgent need for innovative treatments in HCC. However, the complexity of HCC demands precise and effective therapeutic approaches. The adeno-associated virus (AAV) distinctive life cycle and ability to persistently infect dividing and nondividing cells have rendered it an alluring vector. Another appealing characteristic of the wild-type virus is its evident absence of pathogenicity. As a result, AAV, a vector that lacks an envelope and can be modified to transport DNA to specific cells, has garnered considerable interest in the scientific community, particularly in experimental therapeutic strategies that are still in the clinical stage. AAV vectors emerge as promising tools for HCC therapy due to their non-immunogenic nature, efficient cell entry, and prolonged gene expression. While AAV-mediated GT demonstrates promise across diverse diseases, the current absence of ongoing clinical trials targeting HCC underscores untapped potential in this context. Furthermore, gene transfer through hepatic AAV vectors is frequently facilitated by GT research, which has been propelled by several congenital anomalies affecting the liver. Notwithstanding the enthusiasm associated with this notion, recent discoveries that expose the integration of the AAV vector genome at double-strand breaks give rise to apprehensions regarding their enduring safety and effectiveness. This review explores the potential of AAV vectors as versatile tools for targeted GT in HCC. In summation, we encapsulate the multifaceted exploration of AAV vectors in HCC GT, underlining their transformative potential within the landscape of oncology and human health.

Inducible caspase 9-mediated suicide gene therapy using AAV6 vectors in a murine model of breast cancer

Breast carcinoma has one of the highest incidence rates (11.7%), with significant clinical heterogeneity. Although conventional chemotherapy and surgical resection are the current standard of care, the resistance and recurrence, after these interventions, necessitate alternate therapeutic approaches. Cancer gene therapy for breast cancer with the suicide gene is an attractive option due to their directed delivery into the tumor. In this study, we have developed a novel treatment strategy against breast cancer with recombinant adeno-associated virus (AAV) serotype 6 vectors carrying a suicide gene, inducible Caspase 9 (iCasp9). Upon treatment with AAV6-iCasp9 vectors and the chemical inducer of dimerizer, AP20187, the viability of murine breast cancer cells (4T1) was significantly reduced to ∼40%-60% (mock control 100%). Following intratumoral delivery of AAV6-iCasp9 vectors in an orthotopic breast cancer mouse model, we observed a significant increase in iCasp9 transgene expression and a significant reduction in tumor growth rate. At the molecular level, immunohistochemical analysis demonstrated subsequent activation of the effector caspase 3 and cellular death. These data highlight the potential of AAV6-iCasp9-based suicide gene therapy for aggressive breast cancer in patients.

Caspase-9 driven murine model of selective cell apoptosis and efferocytosis

Apoptosis and efficient efferocytosis are integral to growth, development, and homeostasis. The heterogeneity of these mechanisms in different cells across distinct tissues renders it difficult to develop broadly applicable in vivo technologies. Here, we introduced a novel inducible caspase-9 (iCasp9) mouse model which allowed targeted cell apoptosis and further facilitated investigation of concomitant efferocytosis. We generated iCasp9+/+ mice with conditional expression of chemically inducible caspase-9 protein that is triggered in the presence of Cre recombinase. In vitro, bone marrow cells from iCasp9+/+ mice showed expression of the iCasp9 protein when transduced with Cre-expressing adenovirus. Treatment of these cells with the chemical dimerizer (AP20187/AP) resulted in iCasp9 processing and cleaved caspase-3 upregulation, indicating successful apoptosis induction. The in vivo functionality and versatility of this model was demonstrated by crossing iCasp9+/+ mice with CD19-Cre and Osteocalcin (OCN)-Cre mice to target CD19+ B cells or OCN+ bone-lining osteoblasts. Immunofluorescence and/or immunohistochemical staining in combination with histomorphometric analysis of EGFP, CD19/OCN, and cleaved caspase-3 expression demonstrated that a single dose of AP effectively induced apoptosis in CD19+ B cells or OCN+ osteoblasts. Examination of the known efferocytes in the target tissues showed that CD19+ cell apoptosis was associated with infiltration of dendritic cells into splenic B cell follicles. In the bone, where efferocytosis remains under-explored, the use of iCasp9 provided direct in vivo evidence that macrophages are important mediators of apoptotic osteoblast clearance. Collectively, this study presented the first mouse model of iCasp9 which achieved selective apoptosis, allowing examination of subsequent efferocytosis. Given its unique feature of being controlled by any Cre-expressing mouse lines, the potential applications of this model are extensive and will bring forth more insights into the diversity of mechanisms and cellular effects induced by apoptosis including the physiologically important efferocytic process that follows.

Vector engineering, strategies and targets in cancer gene therapy

Understanding the molecular basis of disease and the design of rationally designed molecular therapies has been the holy grail in the management of human cancers. Gene-based therapies are an important avenue for achieving a possible cure. Focused research in the last three decades has provided significant clues to optimize the potential of cancer gene therapy. The development of gene therapies with a high potential to kill the target cells at the lowest effective dose possible, the development of vectors with significant ability to target cancer-associated antigen, the application of adjunct therapies to target dysregulated microRNA, and embracing a hybrid strategy with a combination of gene therapy and low-dose chemotherapy in a disease-specific manner will be pivotal. This article outlines the advances and challenges in the field with emphasis on the biology and scope of vectors used for gene transfer, newer targets identified, and their outcome in preclinical and clinical studies.

Hepatocellular Carcinoma Is a Natural Target for Adeno-Associated Virus (AAV) 2 Vectors

Simple Summary

Gene therapy is a novel approach to treat diseases by introducing corrective genetic information into target cells. Adeno-associated virus vectors are the most frequently applied gene delivery tools for in vivo gene therapy and are also studied as part of innovative anticancer strategies. Here, we report on the natural preference of AAV2 vectors for hepatocellular carcinoma (HCC) compared to nonmalignant liver cells in mice and human tissue. This preference in transduction is due to the improved intracellular processing of AAV2 vectors in HCC, resulting in significantly more vector genomes serving as templates for transcription in the cell nucleus. Based on this natural tropism for HCC, novel therapeutic strategies can be designed or existing therapeutic approaches can be strengthened as they currently result in only a minor improvement of the poor prognosis for most liver cancer patients.

Abstract

Although therapeutic options are gradually improving, the overall prognosis for patients with hepatocellular carcinoma (HCC) is still poor. Gene therapy-based strategies are developed to complement the therapeutic armamentarium, both in early and late-stage disease. For efficient delivery of transgenes with antitumor activity, vectors demonstrating preferred tumor tropism are required. Here, we report on the natural tropism of adeno-associated virus (AAV) serotype 2 vectors for HCC. When applied intravenously in transgenic HCC mouse models, similar amounts of vectors were detected in the liver and liver tumor tissue. In contrast, transduction efficiency, as indicated by the level of transgene product, was moderate in the liver but was elevated up to 19-fold in mouse tumor tissue. Preferred transduction of HCC compared to hepatocytes was confirmed in precision-cut liver slices from human patient samples. Our mechanistic studies revealed that this preference is due to the improved intracellular processing of AAV2 vectors in HCC, resulting, for example, in nearly 4-fold more AAV vector episomes that serve as templates for gene transcription. Given this background, AAV2 vectors ought to be considered to strengthen current—or develop novel—strategies for treating HCC.

The Application of the CRISPR/Cas9 System in the Treatment of Hepatitis B Liver Cancer

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system was originally discovered in prokaryotes and functions as part of the adaptive immune system. The experimental research of many scholars, as well as scientific and technological advancements, has allowed prokaryote-derived CRISPR/Cas genome-editing systems to transform our ability to manipulate, detect, image, and annotate specific DNA and RNA sequences in the living cells of diverse species. Through modern genetic engineering editing technology and high-throughput gene sequencing, we can edit and splice covalently closed circular DNA to silence it, and correct the mutation and deletion of liver cancer genes to achieve precise in situ repair of defective genes and prohibit viral infection or replication. Such manipulations do not destroy the structure of the entire genome and facilitate the cure of diseases. In this review, we discussed the possibility that CRISPR/Cas could be used as a treatment for patients with liver cancer caused by hepatitis B virus infection, and reviewed the challenges incurred by this effective gene-editing technology.

Delivery of cancer therapies by synthetic and bio-inspired nanovectors

BACKGROUND

As a complement to the clinical development of new anticancer molecules, innovations in therapeutic vectorization aim at solving issues related to tumor specificity and associated toxicities. Nanomedicine is a rapidly evolving field that offers various solutions to increase clinical efficacy and safety. MAIN: Here are presented the recent advances for different types of nanovectors of chemical and biological nature, to identify the best suited for translational research projects. These nanovectors include different types of chemically engineered nanoparticles that now come in many different flavors of 'smart' drug delivery systems. Alternatives with enhanced biocompatibility and a better adaptability to new types of therapeutic molecules are the cell-derived extracellular vesicles and micro-organism-derived oncolytic viruses, virus-like particles and bacterial minicells. In the first part of the review, we describe their main physical, chemical and biological properties and their potential for personalized modifications. The second part focuses on presenting the recent literature on the use of the different families of nanovectors to deliver anticancer molecules for chemotherapy, radiotherapy, nucleic acid-based therapy, modulation of the tumor microenvironment and immunotherapy.

CONCLUSION

This review will help the readers to better appreciate the complexity of available nanovectors and to identify the most fitting "type" for efficient and specific delivery of diverse anticancer therapies.

MicroRNA-based recombinant AAV vector assembly improves efficiency of suicide gene transfer in a murine model of lymphoma

Recent success in clinical trials with recombinant Adeno-associated virus (AAV)-based gene therapy has redirected efforts in optimizing AAV assembly and production, to improve its potency. We reasoned that inclusion of a small RNA during vector assembly, which specifically alters the phosphorylation status of the packaging cells may be beneficial. We thus employed microRNAs (miR-431, miR-636) identified by their ability to bind AAV genome and also dysregulate Mitogen-activated protein kinase (MAPK) signaling during vector production, by a global transcriptome study in producer cells. A modified vector assembly protocol incorporating a plasmid encoding these microRNAs was developed. AAV2 vectors packaged in the presence of microRNA demonstrated an improved gene transfer potency by 3.7-fold, in vitro. Furthermore, AAV6 serotype vectors encoding an inducible caspase 9 suicide gene, packaged in the presence of miR-636, showed a significant tumor regression (~2.2-fold, P < .01) in a syngeneic murine model of T-cell lymphoma. Taken together, we have demonstrated a simple but effective microRNA-based approach to improve the assembly and potency of suicide gene therapy with AAV vectors.

AAV6 Vexosomes Mediate Robust Suicide Gene Delivery in a Murine Model of Hepatocellular Carcinoma

During recombinant Adeno-associated virus (AAV) production, a proportionately large amount of vectors is released in the culture supernatant, which is often discarded. It has been shown that these vectors often associate with vesiculated structures, such as exosomes. Exosome-associated AAV (vexosomes) represent an additional gene-delivery platform. The efficiency of such vexosomes in suicide gene therapy is unexplored. In the present study, we have generated AAV serotype 6 vexosomes containing an inducible caspase 9 (iCasp9) suicide gene by a differential ultracentrifugation-based protocol. We further tested the cytotoxic potential of these vexosomes in a human hepatocellular carcinoma (HCC) model in vitro and in vivo. The AAV6-iCasp9 containing vexosomes, when primed with a pro-drug (AP20187), demonstrated a significant loss in cell viability (57% ± 8% versus 100% ± 4.8%, p < 0.001) in comparison to mock-treated Huh7 cells. An intratumoral administration of AAV6-iCasp9 vexosomes and AP20187 in a murine xenograft model revealed a 2.3-fold increase in tumor regression in comparison to untreated animals. These findings were further corroborated by histological analysis and apoptosis assays. In conclusion, our data demonstrate the therapeutic potential of AAV6 vexosomes in a xenotransplantation model of HCC. Furthermore, the simplicity in production and isolation of vexosomes should further facilitate its application in other malignancies.

Targeting apoptotic caspases in cancer

Members of the caspase family of proteases play essential roles in the initiation and execution of apoptosis. These caspases are divided into two groups: the initiator caspases (caspase-2, -8, -9 and -10), which are the first to be activated in response to a signal, and the executioner caspases (caspase-3, -6, and -7) that carry out the demolition phase of apoptosis. Many conventional cancer therapies induce apoptosis to remove the cancer cell by engaging these caspases indirectly. Newer therapeutic applications have been designed, including those that specifically activate individual caspases using gene therapy approaches and small molecules that repress natural inhibitors of caspases already present in the cell. For such approaches to have maximal clinical efficacy, emerging insights into non-apoptotic roles of these caspases need to be considered. This review will discuss the roles of caspases as safeguards against cancer in the context of the advantages and potential limitations of targeting apoptotic caspases for the treatment of cancer.

A CD33 Antigen-Targeted AAV6 Vector Expressing an Inducible Caspase-9 Suicide Gene Is Therapeutic in a Xenotransplantation Model of Acute Myeloid Leukemia

Current chemotherapeutic regimens for acute myeloid leukemia (AML) have been modestly effective in patients and are associated with poor long-term survival (<30% at 5 years). Viral vector-based suicide gene therapy is an attractive option, if these vectors can target the AML cells with high specificity and efficiency. In this study, we have developed a receptor-specific adeno-associated virus (AAV) based vector to target the CD33 antigen which is overexpressed in leukemic cells. A targeting peptide was rationally designed from the antigen-binding regions of a CD33 monoclonal antibody. This peptide was further expressed on the capsid of the AAV6 vector, since this serotype was most efficient among AAV1-rh10 vectors to infect the pro-monocytic, human myeloid leukemia cells (U937). AAV6-CD33 vectors expressing a suicide gene, the inducible caspase 9 (iCasp9), and its prodrug AP20187 significantly reduced (∼59%) the viability of U937 cells. To further test its efficacy and specificity in vivo, AAV6-CD33 vectors were administered into a xenotransplantation model of AML in zebrafish through systemic delivery. We observed a significant antileukemic effect with AAV6-CD33 vectors, with a markedly higher survival (100% for AAV6-CD33 vectors vs 15% for mock-treated) and a higher number of TUNEL positive apoptotic cells after systemic vector delivery. Taken together, our work demonstrates the efficacy and translational potential of CD33-targeted AAV6 vectors for cytotoxic gene therapy in AML.