William F. Goins

A new transgene reporter for in vivo magnetic resonance imaging

We report a new platform technology for visualizing transgene expression in living subjects using magnetic resonance imaging (MRI). Using a vector, we introduced an MRI reporter, a metalloprotein from the ferritin family, into specific host tissues. The reporter is made superparamagnetic as the cell sequesters endogenous iron from the organism. In this new approach, the cells construct the MRI contrast agent in situ using genetic instructions introduced by the vector. No exogenous metal-complexed contrast agent is required, thereby simplifying intracellular delivery. We used a replication-defective adenovirus vector to deliver the ferritin transgenes. Following focal inoculation of the vector into the mouse brain, we monitored the reporter activity using in vivo time-lapse MRI. We observed robust contrast in virus-transduced neurons and glia for several weeks. This technology is adaptable to monitor transgene expression in vivo in many tissue types and has numerous biomedical applications, such as visualizing preclinical therapeutic gene delivery.

Deletion of multiple immediate-early genes from herpes simplex virus reduces cytotoxicity and permits long-term gene expression in neurons.

Herpes simplex virus type 1 (HSV-1) has many attractive features that suggest its utility for gene transfer to neurons. However, viral cytotoxicity and transient transgene expression limit practical applications even in the absence of viral replication. Mutant viruses deleted for the immediate–early (IE) gene, ICP4, an essential transcriptional transactivator, are toxic to many cell types in culture in which only the remaining IE genes are expressed. In order to test directly the toxicity of other IE gene products in neurons and develop a mutant background capable of long-term transgene expression, we generated mutants deleted for multiple IE genes in various combinations and tested their relative cytotoxicity in 9L rat gliosarcoma cells, Vero monkey kidney cells, and primary rat cortical and dorsal root neurons in culture. Viral mutants deleted simultaneously for the IE genes encoding ICP4, ICP22 and ICP27 showed substantially reduced cytotoxicity compared with viruses deleted for ICP4 alone or ICP4 in combination with either ICP22, ICP27 or ICP47. Infection of neurons in culture with these triple IE deletion mutants substantially enhanced cell survival and permitted transgene expression for over 21 days. Such mutants may prove useful for efficient gene transfer and extended transgene expression in neurons in vitro and in vivo.

Antinociceptive effect of a genomic herpes simplex virus-based vector expressing human proenkephalin in rat dorsal root ganglion

Endogenous opiate peptides acting pre- and post-synaptically in the dorsal horn of spinal cord inhibit transmission of nociceptive stimuli. We transfected neurons of the dorsal root ganglion in vivo by footpad inoculation with 30 μl (3 × 107 p.f.u.) of a replication-incompetent (ICP4-deleted) herpes simplex virus (HSV) vector with a cassette containing a portion of the human proenkephalin gene coding for 5 met- and 1 leu-enkephalin molecules under the control of the human cytomegalovirus immediate–early promoter (HCMV IEp) inserted in the HSV thymidine kinase (tk) locus. Vector-directed expression of enkephalin produced a significant antinociceptive effect measured by the formalin footpad test, that was most prominent in the delayed (‘tonic’) phase 20–70 min after the administration of formalin. The magnitude of the antinociceptive effect diminished over 4 weeks after transduction, but reinoculation of the vector reestablished the analgesic effect, without evidence for the development of tolerance. The antinociceptive effect was blocked completely by intrathecal naltrexone. These results suggest that gene therapy with an enkephalin-producing herpes-based vector may prove useful in the treatment of pain.

Transgene-mediated enkephalin release enhances the effect of morphine and evades tolerance to produce a sustained antiallodynic effect in neuropathic pain

&NA; We examined the pharmacologic characteristics of herpes simplex virus (HSV) vector‐mediated expression of proenkephalin in the dorsal root ganglion in a rodent model of neuropathic pain. We found that: (i) vector‐mediated enkephalin produced an antiallodynic effect that was reversed by naloxone; (ii) vector‐mediated enkephalin production in animals with spinal nerve ligation prevented the induction of c‐fos expression in second order sensory neurons in the dorsal horn of spinal cord; (iii) the effect of vector‐mediated enkephalin enhanced the effect of morphine, reducing the ED50 of morphine 10‐fold; (iv) animals did not develop tolerance to the continued production of vector‐mediated enkephalin over a period of several weeks; and, (v) vector transduction continued to provide an analgesic effect despite the induction of tolerance to morphine. This is the first demonstration of gene transfer to provide an analgesic effect in neuropathic pain. The pharmacologic analysis demonstrates that transgene‐mediated expression and local release of opioid peptides produce some effects that are distinct from peptide analogues delivered pharmacologically.

Herpes vector-mediated expression of proenkephalin reduces bone cancer pain.

We examined whether a herpes simplex virus vector that expresses human proenkephalin could be used to attenuate nociception in a model of bone cancer pain in mice. Osteolytic sarcoma cells were implanted into the medullary space of the right femur, followed by a subcutaneous inoculation of a replication‐defective herpes simplex virus vector expressing human proenkephalin (vector SHPE) or a lacZ‐expressing control vector (vector SHZ). SHPE‐inoculated mice demonstrated a significant, naltrexone‐reversible decrease in pain‐related behavior assessed during open‐field motor activity. These results suggest that gene transfer with an enkephalin‐expressing vector may be used to treat pain resulting from cancer in bone.

Progress in gene therapy for neurological disorders

Diseases of the nervous system have devastating effects and are widely distributed among the population, being especially prevalent in the elderly. These diseases are often caused by inherited genetic mutations that result in abnormal nervous system development, neurodegeneration, or impaired neuronal function. Other causes of neurological diseases include genetic and epigenetic changes induced by environmental insults, injury, disease-related events or inflammatory processes. Standard medical and surgical practice has not proved effective in curing or treating these diseases, and appropriate pharmaceuticals do not exist or are insufficient to slow disease progression. Gene therapy is emerging as a powerful approach with potential to treat and even cure some of the most common diseases of the nervous system. Gene therapy for neurological diseases has been made possible through progress in understanding the underlying disease mechanisms, particularly those involving sensory neurons, and also by improvement of gene vector design, therapeutic gene selection, and methods of delivery. Progress in the field has renewed our optimism for gene therapy as a treatment modality that can be used by neurologists, ophthalmologists and neurosurgeons. In this Review, we describe the promising gene therapy strategies that have the potential to treat patients with neurological diseases and discuss prospects for future development of gene therapy.

Herpes simplex virus mediated nerve growth factor expression in bladder and afferent neurons: Potential treatment for diabetic bladder dysfunction

PURPOSE Diabetic cystopathy resulting from sensory neuropathy may potentially be treated by direct gene therapy. It has been suggested that nerve growth factor (NGF) has an ameliorative effect in preventing the death in diabetes of afferent dorsal root ganglion neurons, which control bladder function. We investigated NGF gene transfer to the bladder and bladder afferent pathways for treating diabetic cystopathy. We used replication competent and replication defective herpes simplex virus type 1 (HSV-1) vectors that express a functionally active form of the beta-subunit of mouse NGF (beta-NGF) to examine the level and duration of therapeutic gene expression after administration of the vectors. MATERIALS AND METHODS NGF expression during acute (3 days) and latent (21 days) infections was assessed by enzyme-linked immunosorbent assay (ELISA) and immunohistochemical testing after the injection of 1 x 106 to 1 x 108 pfu HSV-NGF expression vectors into the bladder wall of adult rats. RESULTS HSV vectors with the strong human cytomegalovirus immediate early promoter used to drive beta-NGF gene expression exhibited increased NGF 3 days after infection in the bladder and L6 to S1 dorsal root ganglia, where bladder afferent neurons are located. ELISA analysis revealed that NGF in the bladder tissue and dorsal root ganglia was increased 7 to 9 and 2 to 4-fold, respectively, over the control vector. Increased NGF expression in L6 to S1 dorsal root ganglia neurons was also detected by immunohistochemical staining with antiNGF antibodies. Extended NGF expression was detected by ELISA 21 days after injection. Replication defective vectors containing HSV-1 latency promoter (LAP-2) driving NGF expressed NGF in the bladder and dorsal root ganglia 21 days after bladder injection. ELISA analysis confirmed an approximate 2 to 3-fold increase of NGF expression in the bladder and L6 to S1 dorsal root ganglia. CONCLUSIONS The NGF gene may be transferred and expressed in the bladder and bladder afferent pathways using HSV vectors. To our knowledge our study represents the first demonstration of the effectiveness of gene therapy for altering neurotrophic expression in visceral sensory neurons. This technique of gene transfer may be useful for treating certain types of neurogenic bladder dysfunction, such as diabetic cystopathy, in which decreased NGF transport may be a causative factor.

Herpes simplex virus RNAi and neprilysin gene transfer vectors reduce accumulation of Alzheimer's disease-related amyloid- β peptide in vivo

Accumulation of insoluble aggregates of amyloid-β peptide (Aβ), a cleavage product of amyloid precursor protein (APP), is thought to be central to the pathogenesis of Alzheimers disease (AD). Consequently, downregulation of APP, or enhanced clearance of Aβ, represent possible therapeutic strategies for AD. We generated replication-defective herpes simplex virus (HSV) vectors that inhibit Aβ accumulation, both in vitro and in vivo. In cell culture, HSV vectors expressing either (i) short hairpin RNA directed to the APP transcript (HSV-APP/shRNA), or (ii) neprilysin, an endopeptidase that degrades Aβ (HSV-neprilysin), substantially inhibited accumulation of Aβ. To determine whether these vectors showed similar activity in vivo, we developed a novel mouse model, in which overexpression of a mutant form of APP in the hippocampus, using a lentiviral vector (LV-APPSw), resulted in rapid Aβ accumulation. Co-inoculation of LV-APPSw with each of the HSV vectors showed that either HSV-APP/shRNA or HSV-neprilysin inhibited Aβ accumulation in this model, whereas an HSV control vector did not. These studies demonstrate the utility of HSV vectors for reducing Aβ accumulation in the brain, thus providing useful tools to clarify the role of Aβ in AD that may facilitate the development of novel therapies for this important disease.

HSV trafficking and development of gene therapy vectors with applications in the nervous system

Herpes simplex virus type 1 (HSV-1) is a neurotropic double-stranded DNA virus that causes cold sores, keratitis, and rarely encephalitis in humans. Nonpathogenic HSV-1 gene transfer vectors have been generated by elimination of viral functions necessary for replication. The life cycle of the native virus includes replication in epithelial cells at the site of initial inoculation followed by retrograde axonal transport to the nuclei of sensory neurons innervating the area of cutaneous primary infection. In this review, we summarize the current understanding of the molecular basis for HSV cell entry, nuclear transport of the genome, virion egress following replication, and retrograde and anterograde axonal transport in neurons. We discuss how each of these properties has been exploited or modified to allow the generation of gene transfer vectors with particular utility for neurological applications. Recent advances in engineering virus entry have provided proof of principle that vector targeting is possible. Furthermore, significant and potentially therapeutic modifications to the pathological responses to various noxious insults have been demonstrated in models of peripheral nerve disease. These applications exploit the natural axonal transport mechanism of HSV, allowing transgene expression in the cell nucleus within the inaccessible trigeminal ganglion or dorsal root ganglion, following the noninvasive procedure of subcutaneous vector inoculation. These findings demonstrate the importance of understanding basic virology in the design of vector systems and the powerful approach of exploiting favorable properties of the parent virus in the generation of gene transfer vectors.

Multiple Applications For Replication-Defective Herpes Simplex Virus Vectors

Herpes simplex virus (HSV) is a neurotropic DNA virus. The viral genome is large (152 kb), and many genes are dispensable for viral function, allowing insertion of multiple or large transgene expression cassettes. The virus life cycle includes a latent phase, during which the viral genome remains as a stable episomal element within neuronal nuclei for the lifetime of the host, without disturbing normal function. We have exploited these features of HSV to construct a series of nonpathogenic gene therapy vectors that efficiently deliver therapeutic and experimental transgenes to neural and non‐neural tissue. Importantly, transgene expression may be sustained long term; reporter gene expression has been demonstrated for over a year in the nervous system. This article discusses the generation of replication‐defective HSV vectors and reviews recent studies investigating their use in several animal models of human disease. We have demonstrated correction or prevention of a number of important neurological phenotypes, including neurodegeneration, chronic pain, peripheral neuropathy, and malignancy. In addition, HSV‐mediated transduction of non‐neurological tissues allows their use as depot sites for synthesis of circulating and locally acting secreted proteins. New applications for this vector system include the genetic modification of stem cell populations; this may become an important means to direct cellular differentiation or deliver therapeutic genes systemically. Replication‐defective HSV vectors are an effective and flexible vehicle for the delivery of transgenes to numerous tissues, with multiple applications.