Neuronal specificity of HSV/sleeping beauty amplicon transduction in utero is driven primarily by tropism and cell type composition

HMGB1 Protein: A Therapeutic Target Inside and Outside the Cell

High-mobility group box 1 protein (HMGB1) is a nonhistone chromosomal protein discovered more than 30 years ago. It is an abundant nuclear protein that has a dual function-in the nucleus, it binds DNA and participates in practically all DNA-dependent processes serving as an architectural factor. Outside the cell, HMGB1 plays a different role-it acts as an alarmine that activates a large number of HMGB1-"competent" cells and mediates a broad range of physiological and pathological responses. This universality makes it an attractive target for innovative therapeutic strategies in the treatment of various diseases. Here we present an overview of the major nuclear and extracellular properties of HMGB1 and describe its interaction with different molecular partners as specific receptors or inhibitors, which are important for its role as a target in multiple diseases. We highlight its pivotal role as a target for cancer treatment at two aspects: first in terms of its substantial impact on the repair capacity of cancer cells, thus affecting the effectiveness of chemotherapy with the antitumor drug cis-platinum and, second, the possibility to be targeted by microRNAs influencing different pathways of human diseases, thus making it a promising candidate for a new strategy for therapeutic interventions against various pathological conditions but mainly cancer.

Sleeping Beauty transposition: from biology to applications

Sleeping Beauty (SB) is the first synthetic DNA transposon that was shown to be active in a wide variety of species. Here, we review studies from the last two decades addressing both basic biology and applications of this transposon. We discuss how host-transposon interaction modulates transposition at different steps of the transposition reaction. We also discuss how the transposon was translated for gene delivery and gene discovery purposes. We critically review the system in clinical, pre-clinical and non-clinical settings as a non-viral gene delivery tool in comparison with viral technologies. We also discuss emerging SB-based hybrid vectors aimed at combining the attractive safety features of the transposon with effective viral delivery. The success of the SB-based technology can be fundamentally attributed to being able to insert fairly randomly into genomic regions that allow stable long-term expression of the delivered transgene cassette. SB has emerged as an efficient and economical toolkit for safe and efficient gene delivery for medical applications.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Comparative genomic integration profiling of Sleeping Beauty transposons mobilized with high efficacy from integrase-defective lentiviral vectors in primary human cells

It has been previously shown that integrase-defective HIV-1-based gene vectors can serve, with moderate efficiency, as substrate for DNA transposition by a transiently expressed Sleeping Beauty (SB) transposase. Here, we describe the enhanced gene transfer properties of a HIV-1/SB hybrid vector that allows efficient DNA transposition, facilitated by the hyperactive SB100X transposase, from vector DNA intermediates in primary human cells. Potent transposase-dependent integration of genetic cargo carried by the hybrid HIV-1/SB vector (up to 160-fold above background) is reported in human cell lines as well as in primary human fibroblasts and keratinocytes. The efficiency of transgene integration in context of the newly developed hybrid vector is comparable with that of conventional lentiviral vectors (LVs). Integration profiles of integrating HIV-1-derived vectors and SB transposons mobilized from LVs are investigated by deep sequencing of a large number of integration sites. A significant bias of lentiviral integrations in genes is reported, confirming that biological properties of the viral integration machinery facilitate preferred insertion into actively transcribed genomic regions. In sharp contrast, lentiviral insertions catalyzed by the SB100X transposase are far more random with respect to genes. Based on these properties, HIV-1/SB vectors may become valuable tools for genetic engineering and therapeutic gene transfer.

In utero gene transfer to the mouse nervous system

The cellular and molecular environment present in the fetus and early newborn provides an excellent opportunity for effective gene transfer. Innate and pre-existing anti-vector immunity may be attenuated or absent and the adaptive immune system predisposed to tolerance towards xenoproteins. Stem cell and progenitor cell populations are abundant, active and accessible. In addition, for treatment of early lethal genetic diseases of the nervous system, the overarching advantage may be that early gene supplementation prevents the onset of irreversible pathological changes. Gene transfer to the fetal mouse nervous system was achieved, albeit inefficiently, as far back as the mid-1980s. Recently, improvements in vector design and production have culminated in near-complete correction of a mouse model of spinal muscular atrophy. In the present article, we review perinatal gene transfer from both a therapeutic and technological perspective.

Herpes simplex virus/Sleeping Beauty vector-based embryonic gene transfer using the HSB5 mutant: loss of apparent transposition hyperactivity in vivo

The Sleeping Beauty (SB) transposon system has been successfully used as a gene delivery tool in nonviral and viral vector platforms. Since its initial reconstruction, a series of hyperactive mutants of SB have been generated. Questions remain as to whether the enhanced in vitro activities of these SB transposase mutants translate to the in vivo setting, and whether such increased integration efficiencies will ultimately compromise the safety profile of the transposon platform by raising the risk of genomic insertional mutagenesis. Herein, we compared the in vivo impact of a herpes simplex virus (HSV) amplicon-vectored "wild-type" SB transposase (SB10) and a "hyperactive" SB mutant (HSB5), codelivered in utero with the HSVT-βgeo transposable reporter amplicon vector to embryonic day 14.5 C57BL/6 mice. The SB10 and HSB5 transposases do not disparately affect the viability and development of injected mouse embryos. Quantitation of brain-resident βgeo expression on postnatal day 21 revealed that mice receiving HSB5 exhibited only a trending increase in transgene expression compared with the SB10-infused group, an outcome that did not mirror the marked enhancement of HSB5-mediated transposition observed in vitro. These findings indicate that in vivo application of hyperactive SB mutants, although not differentially genotoxic to the developing mouse embryo, does not necessarily provide a significant therapeutic advantage over the employment of a lesser active SB when delivered in the context of the HSV/SB amplicon platform.

Virion-associated cofactor high-mobility group DNA-binding protein-1 facilitates transposition from the herpes simplex virus/Sleeping Beauty amplicon vector platform

The development of the integration-competent, herpes simplex virus/Sleeping Beauty (HSV/SB) amplicon vector platform has created a means to efficiently and stably deliver therapeutic transcription units (termed "transgenons") to neurons within the mammalian brain. Furthermore, an investigation into the transposition capacity of the HSV/SB vector system revealed that the amplicon genome provides an optimal substrate for the transposition of transgenons at least 12 kb in length [de Silva, S., Mastrangelo, M.A., Lotta, L.T., Jr., Burris, C.A., Federoff, H.J., and Bowers, W.J. ( 2010 ). Gene Ther. 17, 424-431]. These results prompted an investigation into the factors that may contribute toward efficient transposition from the HSV/SB amplicon. One of the cellular cofactors known to play a key role during SB-mediated transposition is the high-mobility group DNA-binding protein-1 (HMGB1). Our present investigation into the role of HMGB1 during amplicon-based transposition revealed that transposition is not strictly dependent on the presence of cellular HMGB1, contrary to what had been previously demonstrated with plasmid-based SB transposition. We have shown for the first time that during amplicon preparation, biologically active HMGB1 derived from the packaging cell line is copackaged into amplicon vector particles. As a result, HSV/SB amplicon virions arrive prearmed with HMGB1 protein at levels sufficient for facilitating SB-mediated transposition in the transduced mammalian cell.

Early oligodendrocyte/myelin pathology in Alzheimer's disease mice constitutes a novel therapeutic target

The detection of myelin disruptions in Alzheimer's disease (AD)-affected brain raises the possibility that oligodendrocytes undergo pathophysiological assault over the protracted course of this neurodegenerative disease. Oligodendrocyte compromise arising from direct toxic effects imparted by pathological amyloid-beta peptides and/or through signals derived from degenerating neurons could play an important role in the disease process. We previously demonstrated that 3xTg-AD mice, which harbor the human amyloid precursor protein Swedish mutant transgene, presenilin knock-in mutation, and tau P301L mutant transgene, exhibit significant alterations in overall myelination patterns and oligodendrocyte status at time points preceding the appearance of amyloid and tau pathology. Herein, we demonstrate that Abeta(1-42) leads to increased caspase-3 expression and apoptotic cell death of both nondifferentiated and differentiated mouse oligodendrocyte precursor (mOP) cells in vitro. Through use of a recombinant adeno-associated virus serotype-2 (rAAV2) vector expressing an Abeta(1-42)-specific intracellular antibody (intrabody), oligodendrocyte and myelin marker expression, as well as myelin integrity, were restored in the vector-infused brain regions of 3xTg-AD mice. Overall, this work provides further insights into the impact of Abeta(1-42)-mediated toxicity on the temporal and spatial progression of subtle myelin disruption during the early presymptomatic stages of AD and may help to validate new therapeutic options designed to avert these early impairments.

Herpes Virus Amplicon Vectors

Since its emergence onto the gene therapy scene nearly 25 years ago, the replication-defective Herpes Simplex Virus Type-1 (HSV-1) amplicon has gained significance as a versatile gene transfer platform due to its extensive transgene capacity, widespread cellular tropism, minimal immunogenicity, and its amenability to genetic manipulation. Herein, we detail the recent advances made with respect to the design of the HSV amplicon, its numerous in vitro and in vivo applications, and the current impediments this virus-based gene transfer platform faces as it navigates a challenging path towards future clinical testing.

Extending the transposable payload limit of Sleeping Beauty (SB) using the Herpes Simplex Virus (HSV)/SB amplicon-vector platform

The ability of a viral vector to safely deliver and stably integrate large transgene units (transgenons), which not only include one or several therapeutic genes, but also requisite native transcriptional regulatory elements, would be of significant benefit for diseases presently refractory to available technologies. The herpes simplex virus type-1 (HSV-1) amplicon vector has the largest known payload capacity of approximately 130 kb, but its episomal maintenance within the transduced cell nucleus and induction of host cell silencing mechanisms limits the duration of the delivered therapeutic gene(s). Our laboratory developed an integration-competent version of the HSV-1 amplicon by adaptation of the Sleeping Beauty (SB) transposon system, which significantly extends transgene expression in vivo. The maximum size limit of the amplicon-vectored transposable element remains unknown, but previously published plasmid-centric studies have established that DNA segments longer than 6-kb are inefficiently transposed. Here, we compared the transposition efficiency of SB transposase in the context of both the HSV amplicon vector as well as the HSV amplicon plasmid harboring 7 and 12-kb transposable reporter transgene units. Our results indicate that the transposition efficiency of the 12-kb transposable unit via SB transposase was significantly reduced as compared with the 7-kb transposable unit when the plasmid version of the HSV amplicon was used. However, the packaged HSV amplicon vector form provided a more amenable platform from which the 12-kb transposable unit was mobilized at efficiency similar to that of the 7-kb transposable unit via the SB transposase. Overall, our results indicate that SB is competent in stably integrating transgenon units of at least 12 kb in size within the human genome upon delivery of the platform via HSV amplicons.

Triple-transgenic Alzheimer's disease mice exhibit region-specific abnormalities in brain myelination patterns prior to appearance of amyloid and tau pathology

Alzheimer's disease (AD) is a progressively debilitating brain disorder pathologically defined by extracellular amyloid plaques, intraneuronal neurofibrillary tangles, and synaptic disintegrity. AD has not been widely considered a disease of white matter, but more recent evidence suggests the existence of abnormalities in myelination patterns and myelin attrition in AD-afflicted human brains. Herein, we demonstrate that triple-transgenic AD (3xTg-AD) mice, which harbor the human amyloid precursor protein Swedish mutant transgene, presenilin knock-in mutation, and tau P301L mutant transgene, exhibit significant region-specific alterations in myelination patterns and in oligodendrocyte marker expression profiles at time points preceding the appearance of amyloid and tau pathology. These immunohistochemical signatures are coincident with age-related alterations in axonal and myelin sheath ultrastructure as visualized by comparative electron microscopic examination of 3xTg-AD and nontransgenic mouse brain tissue. Overall, these findings indicate that 3xTg-AD mice represent a viable model in which to examine mechanisms underlying AD-related myelination and neural transmission defects that occur early during presymptomatic stages of the disease process.

Progress and prospects: biological properties and technological advances of herpes simplex virus type 1-based amplicon vectors

The last two years have seen significant advances in our understanding of the cellular innate responses elicited or activated by the entry of amplicon particles, which may, in part, explain the transient nature of transgene expression often observed in cells infected with helper-free amplicon stocks. At the technological level, the most consistent progress has been in strategies to enhance the stability of transgene cassettes, either through integration into host chromosomes or through the conversion of the amplicon genome into a replication-competent extrachromosomal element.