Attempted gene therapy for intractable pain: dexamethasone-mediated exogenous control of beta-endorphin secretion in genetically modified cells and intrathecal transplantation

Recent Advances in Management of Neuropathic, Nociceptive, and Chronic Pain: A Narrative Review with Focus on Nanomedicine, Gene Therapy, Stem Cell Therapy, and Newer Therapeutic Options

PURPOSE OF REVIEW

This manuscript summarizes novel clinical and interventional approaches in the management of chronic, nociceptive, and neuropathic pain.

RECENT FINDINGS

Pain can be defined as a feeling of physical or emotional distress caused by an external stimulus. Pain can be grouped into distinct types according to characteristics including neuropathic pain, which is a pain caused by disease or lesion in the sensory nervous system; nociceptive pain, which is pain that can be sharp, aching, or throbbing and is caused by injury to bodily tissues; and chronic pain, which is long lasting or persisting beyond 6 months. With improved understanding of different signaling systems for pain in recent years, there has been an upscale of methods of analgesia to counteract these pathological processes. Novel treatment methods such as use of cannabinoids, stem cells, gene therapy, nanoparticles, monoclonal antibodies, and platelet-rich plasma have played a significant role in improved strategies for therapeutic interventions. Although many management options appear to be promising, extensive additional clinical research is warranted to determine best practice strategies in the future for clinicians.

An Engineered Endomorphin-2 Gene for Morphine Withdrawal Syndrome

An optimal therapeutics to manage opioid withdrawal syndrome is desired for opioid addiction treatment. Down-regulation of endogenous endomorphin-2 (EM2) level in the central nervous system after continuous morphine exposure was observed, which suggested that increase of EM2 could be an alternative novel method for opioid dependence. As a short peptide, the short half-life of EM2 limits its clinical usage through conventional administration. In the present study, we engineered an EM2 gene using a signal peptide of mouse growth factor for an out-secretory expression of EM2 and an adenovirus as a vector, which ultimately sustained the release of EM-2. After administration of the adenovirus in central nervous system, a sustained increase of EM2 level in the cerebral spinal fluid (CSF) was observed along with a reduction of morphine withdrawal syndrome. These findings suggest that the engineered EM2 gene delivered to the central nervous system could be a novel therapeutics for withdrawal syndrome in opioid dependent subjects.

Herpes simplex virus-based nerve targeting gene therapy in pain management

Chronic pain represents a major medical burden not only in terms of suffering but also in terms of economic costs. Traditional medical approaches have so far proven insufficient in treating chronic pain and new approaches are necessary. Gene therapy with herpes simplex virus (HSV)-based vectors offers the ability to directly target specific regions of the neuraxis involved in pain transmission including the primary afferent nociceptor. This opens up new targets to interact with that are either not available to traditional systemic drugs or cannot be adequately acted upon without substantial adverse off-target effects. Having access to the entire neuron, which HSV-based vector gene therapy enables, expands treatment options beyond merely treating symptoms and allows for altering the basic biology of the nerve. In this paper, we discuss several HSV-based gene therapy vectors that our group and others have used to target specific neuronal functions involved in the processing of nociception in order to develop new therapies for the treatment of chronic pain.

Cell transplantation as a pain therapy targets both analgesia and neural repair

Cell transplantation is a potentially powerful approach for the alleviation of chronic pain. The strategy of cell transplantation for the treatment of pain is focused on cell-based analgesia and neural repair. (1) Adrenal medullary chromaffin cells and the PC12 cell line have been used to treat cancer pain and neuropathic pain in both animal models and human cases. As biological or living minipumps, these cells produce and secrete pain-reducing neuroactive substances if administered directly into the spinal subarachnoid space. (2) Cell implantation for pain neurorestorative therapy is a new concept and an emerging research field for pain control along with neural repair. Possible neurorestorative mechanisms include neuroprotective, neurotrophic, neuroreparative, neuroregenerative, neuromodulation, or neuroconstructive interventions, as well as immunomodulation and enhancing the microcirculation. These factors may ultimately restore the damaged or irritated condition of the lesioned nerves. The growing preclinical and clinical data show that neural stem/progenitor cells, olfactory ensheathing cells, mesenchymal stromal cells, and CD34(+) cells have the capacity to manage intractable pain and improve neurological functions. Cell delivery routes include local, intrathecal, or intravascular implants. Although these strategies are still in their infancy phase for pain neurorestoratology, cell-based therapies could open up new avenues for the relief of pain. In this review, these aspects are critically analyzed based on our own investigations. This manuscript is published as part of the International Association of Neurorestoratology (IANR) supplement issue of Cell Transplantation.

Review of the history and current status of cell-transplant approaches for the management of neuropathic pain

Treatment of sensory neuropathies, whether inherited or caused by trauma, the progress of diabetes, or other disease states, are among the most difficult problems in modern clinical practice. Cell therapy to release antinociceptive agents near the injured spinal cord would be the logical next step in the development of treatment modalities. But few clinical trials, especially for chronic pain, have tested the transplant of cells or a cell line to treat human disease. The history of the research and development of useful cell-transplant-based approaches offers an understanding of the advantages and problems associated with these technologies, but as an adjuvant or replacement for current pharmacological treatments, cell therapy is a likely near future clinical tool for improved health care.

Suppression of acute morphine withdrawal syndrome by adenovirus-mediated β-endorphin in rats

BACKGROUND

Endogenous β-endorphin (β-EP) in the central nervous system (CNS) is decreased upon opioid addiction. The current study examined whether exogenous β-EP, delivered using an adenoviral vector into the CNS could attenuate morphine withdrawal syndrome in rats.

METHODS

The model of opioid-dependent rats was set up by receiving subcutaneous injection of morphine using an escalating regimen for 6days (5, 10, 20, 40, 50, 60mg/kg, three times/day). The adenovirus mediated β-EP gene was constructed based on our previous work. The ilea of opioid-dependent rats were isolated and treated with the supernatant of Ad-NEP. The basic and naloxone-induced (4μm/l) contractions of dependent ilea were recorded. The Ad-NEP was injected into the left lateral ventricle of the addition rats. The expression of the β-EP gene was verified by radioimmunoassay of the cerebrospinal fluid (CSF) and immunocytochemistry for β-EP. Withdrawal syndrome was evaluated after intraperitoneal injection of naloxone.

RESULTS

The contractions of dependent ilea were attenuated with supernatant containing β-EP expressed by Ad-NEP. Injection of the Ad-NEP resulted in significant increases in β-EP level in the CSF and β-EP-positive neurons. Rats receiving adenovirus carrying the β-EP gene had significantly less severe withdrawal symptoms upon naloxone challenge.

CONCLUSIONS

Exogenous β-EP mediated by adenovirus could attenuate withdrawal syndrome in morphine-dependent rats.

Headache attributed to non-vascular intracranial disorder

This chapter deals with non-vascular intracranial disorders resulting in headache. Headache attributed to high or low cerebrospinal fluid pressure is separated into headache attributed to idiopathic intracranial hypertension (IIH), headache attributed to intracranial hypertension secondary to metabolic, toxic, or hormonal causes, headache attributed to intracranial hypertension secondary to hydrocephalus, post-dural puncture headache, cerebrospinal fluid (CSF) fistula headache, headache attributed to spontaneous (or idiopathic) low CSF pressure. Headache attributed to non-infectious inflammatory disease can be caused by neurosarcoidosis, aseptic (non-infectious) meningitis or lymphocytic hypophysitis. Headache attributed to intracranial neoplasm can be caused by increased intracranial pressure or hydrocephalus caused by neoplasm or attributed directly to neoplasm or carcinomatous meningitis. Other causes of headache include hypothalamic or pituitary hyper- or hyposecretion and intrathecal injection. Headache attributed to epileptic seizure is separated into hemicrania epileptica and post-seizure headache. Finally headache attributed to Chiari malformation type I (CM1) and the syndrome of transient headache and neurological deficits with cerebrospinal fluid lymphocytosis (HaNDL) are described.

Electrical Stimulation-Induced Release of β-Endorphin from Genetically Modified Neuro-2a Cells

The quantity of therapeutic gene products released from genetically engineered cells can be controlled externally at different levels. The widely used approach of controlling expression, however, generally has the disadvantage that chemical substances must be applied for stimulation. An alternative strategy aims at controlling gene products at posttranslational levels such as secretion. The secretion of a therapeutic agent can be regulated if the agent is targeted to the regulated secretory pathway and stored in the secretory granules until its release. In this article we address the question of whether the release of β-endorphin, an opioid with a potent analgesic effect, could be induced by electrically stimulating stably transfected Neuro-2a cells. Throughout this study we used the human proopiomelanocortin (POMC) gene, which is the precursor molecule for human β-endorphin. We analyzed its subcellular localization and found it in the regulated secretory pathway in Neuro-2a cells. Using electrical field stimulation we were able to identify a stimulation pattern that significantly increased the release of β-endorphin-immunoreactive material, although to a limited extent. This result indicates that electrical stimulation of secretion could be used to manipulate the amount of a therapeutic agent released from transplanted cells.

Gene therapy applications for the treatment of neuropathic pain

Neuropathic pain is notoriously difficult to treat; currently available pharmaceutical drugs result in moderate analgesia in approximately a third of patients. As our understanding of the biological processes involved in the establishment and maintenance of neuropathic pain increases, so does the development of novel treatment options. Significant advancements have been made in the past few years in gene transfer, a very powerful potential therapy that can be used to directly target affected areas of the neuraxis or body tissues involved in neuropathic pain. Candidate gene products include directly analgesic proteins as well as proteins that interfere with pain-associated biochemical changes in nerve or other tissues underlying the disease process.

Intrathecal long-term gene expression by self-complementary adeno-associated virus type 1 suitable for chronic pain studies in rats

Background

Intrathecal (IT) gene transfer is an attractive approach for targeting spinal mechanisms of nociception but the duration of gene expression achieved by reported methods is short (up to two weeks) impairing their utility in the chronic pain setting. The overall goal of this study was to develop IT gene transfer yielding true long-term transgene expression defined as ≥ 3 mo following a single vector administration. We defined "IT" administration as atraumatic injection into the lumbar cerebrospinal fluid (CSF) modeling a lumbar puncture. Our studies focused on recombinant adeno-associated virus (rAAV), one of the most promising vector types for clinical use.

Results

Conventional single stranded rAAV2 vectors performed poorly after IT delivery in rats. Pseudotyping of rAAV with capsids of serotypes 1, 3, and 5 was tested alone or in combination with a modification of the inverted terminal repeat. The former alters vector tropism and the latter allows packaging of self-complementary rAAV (sc-rAAV) vectors. Combining both types of modification led to the identification of sc-rAAV2/l as a vector that performed superiorly in the IT space. IT delivery of 3 × 10e9 sc-rAAV2/l particles per animal led to stable expression of enhanced green fluorescent protein (EGFP) for ≥ 3 mo detectable by Western blotting, quantitative PCR, and in a blinded study by confocal microscopy. Expression was strongest in the cauda equina and the lower sections of the spinal cord and only minimal in the forebrain. Microscopic examination of the SC fixed in situ with intact nerve roots and meninges revealed strong EGFP fluorescence in the nerve roots.

Conclusion

sc-rAAVl mediates stable IT transgene expression for ≥ 3 mo. Our findings support the underlying hypothesis that IT target cells for gene transfer lack the machinery for efficient conversion of the single-stranded rAAV genome into double-stranded DNA and favor uptake of serotype 1 vectors over 2. Experiments presented here will provide a rational basis for utilizing IT rAAV gene transfer in basic and translational studies on chronic pain.

Controlling pathological pain by adenovirally driven spinal production of the anti-inflammatory cytokine, interleukin-10

Gene therapy for the control of pain has, to date, targeted neurons. However, recent evidence supports that spinal cord glia are critical to the creation and maintenance of pain facilitation through the release of proinflammatory cytokines. Because of the ability of interleukin-10 (IL-10) to suppress proinflammatory cytokines, we tested whether an adenoviral vector encoding human IL-10 (AD-h-IL10) would block and reverse pain facilitation. Three pain models were examined, all of which are mediated by spinal pro-inflammatory cytokines. Acute intrathecal administration of rat IL-10 protein itself briefly reversed chronic constriction injury-induced mechanical allodynia and thermal hyperalgesia. The transient reversal caused by IL-10 protein paralleled the half-life of human IL-10 protein in the intrathecal space (t(1/2) approximately 2 h). IL-10 gene therapy both prevented and reversed thermal hyperalgesia and mechanical allodynia, without affecting basal responses to thermal or mechanical stimuli. Extra-territorial, as well as territorial, pain changes were reversed by this treatment. Intrathecal AD-h-IL10 injected over lumbosacral spinal cord led to elevated lumbosacral cerebrospinal fluid (CSF) levels of human IL-10, with far less human IL-10 observed in cervical CSF. In keeping with IL-10's known anti-inflammatory actions, AD-h-IL10 lowered CSF levels of IL-1, relative to control AD. These studies support that this gene therapy approach provides an alternative to neuronally focused drug and gene therapies for clinical pain control.

Cell therapy for neuropathic pain in spinal cord injuries

Cell therapy to treat neuropathic pain after spinal cord injury (SCI) is in its infancy. However, the development of cellular strategies that would replace or be used as an adjunct to existing pharmacological treatments for neuropathic pain have progressed tremendously over the past 20 years. The earliest cell therapy studies for pain relief tested adrenal chromaffin cells from rat or bovine sources, placed in the subarachnoid space, near the spinal cord pain- processing pathways. These grafts functioned as cellular minipumps, secreting a cocktail of antinociceptive agents around the spinal cord for peripheral nerve injury, inflammatory or arthritic pain. These initial animal, and later clinical, studies suggested that the spinal intrathecal space was a safe and accessible location for the placement of cell grafts. However, one major problem was the lack of a homogeneous, expandable cell source to supply the antinociceptive agents. Cell lines that can be reversibly immortalised are the next phase for the development of a practical, homogenous cell source. These technologies have been modelled with a variety of murine cell lines, derived from embryonic adrenal medulla or CNS brainstem, in which cells are transplanted, which downregulate their proliferative, oncogenic phenotype either before or after transplant. An alternative approach for existing human cell lines is the use of neural or adrenal precursors, in which the antinociceptive properties are induced by in vitro treatment with molecules that move the cells to an irreversible neural or chromaffin, and non-oncogenic, phenotype. Although such human cell lines are at an early stage of investigation, their clinical antinociceptive potential is significant given the daunting problem of difficult-to-treat neuropathic SCI pain.

Regulated, electroporation-mediated delivery of pro-opiomelanocortin gene suppresses chronic constriction injury-induced neuropathic pain in rats

We previously reported that intrathecal pro-opiomelanocortin gene electroporation could reduce pain sensitivity induced by chronic constriction injury (CCI) of the sciatic nerve. For optimal use of antinociceptive gene therapy, it might be important to control the expression of the transfected gene extrinsically. For this purpose, a doxycycline-controlled transrepressor system composed of two plasmids coding, respectively, for pro-opiomelanocortin gene (pTRE2-POMC) and the silencer (pTel-off) was employed. The regulation of beta-endorphin expression was first assessed in spinal neuronal culture, then we electrotranfected this plasmid into the spinal cord of mononeuropathic rats and evaluated the analgesic potential of this therapy in vivo by thermal and mechanical withdrawal latency. Intraperitoneal injections of various doses of doxycycline were made to elucidate the possible exogenous downregulation of transfected beta-endorphin gene expression in vivo. The levels of beta-endorphin were analyzed by intrathecal microdialysis and radioimmunoassay. Intrathecal pTRE2-POMC/pTel-off electroporation elevated spinal beta-endorphin levels, as manifested in a significantly elevated pain threshold for chronic constriction injury limbs. Intraperitoneal doxycycline decreased the antinociceptive effect and spinal beta-endorphin levels in a dose-dependent manner. We concluded that intrathecal pTRE2-POMC/pTel-off electroporation alleviates CCI-induced limb pain, and can be controlled by intraperitoneal doxycycline administration.

In vivo electroporation of proopiomelanocortin induces analgesia in a formalin-injection pain model in rats

Opioids remain the most efficacious pharmacological agents for various clinical pain syndromes. Recently, various engineered cells capable of secreting opioidergic peptides have been applied to relieve pain in animal models. In vivo gene delivery by viruses encoding endogenous opioids has also been used with success. In this study, we attempted non-viral intrathecal in vivo gene delivery by electroporation to induce analgesia. Thirty Sprague-Dawley rats were used in this study, six in each of five groups. Rats were treated as follows: vehicle without electroporation (group A), vehicle with electroporation (group B), 100 microg of pCMV-hPOMC plasmid without electroporation (group C), or 100 microg of pCMV-hPOMC plasmid with electroporation (group D). Group E was treated with both pCMV-hPOMC plasmid and electroporation, and given naloxone (1mg/kg) 1h before the formalin test. The tail flick, paw withdrawal latency from radiant heat, and formalin test results for each groups were compared. Radioimmunoassay (RIA) and reverse transcription-polymerase chain reaction (RT-PCR) were used to determine the levels of expression of beta-endorphin in the spinal cord. beta-Endorphin expression was localized by immunohistochemistry. A significant decrease in the number of flinches in phase 2 of the formalin test was observed in the group treated with both plasmid and electroporation (group D), whereas the other measures of pain did not differ between groups. RIA and RT-PCR both showed increased expression of beta-endorphin in group D. The expression of beta-endorphin was highest in laminae I and II of the dorsal horn of the spinal cord. We conclude that electroporation successfully delivered intrathecally administered pCMV-hPOMC into the dorsal horn cells of the spinal cord, and induced analgesia in phase 2 of the formalin test in rats.

Molecular biology and gene therapy in the treatment of chronic pain

Technologic advancements have made cell type-specific targeting, expression control, and safe and stable gene transfer possible. Animal research has provided increasing experience with gene transfer to the nervous system and sensory neurons in particular. Gene-based neuromodultion can be achieved through neuronal delivery of transgenes capable of altering synaptic function. Alternatively, ex vivo gene transfer can be used to create cell lines capable of secreting analgesic neurepeptides. Translatation of these grafts and direct gene-based neuromoduation can be applied to the control of pain and the root causes of pain. These approaches combine anatomic and pharmacologic specificity. As the technology continues to improve, clinical application of cellular and molecular pain control is likely.

The impact of gene therapy on dentistry: a revisiting after six years

BACKGROUND

Gene therapy is an emerging field of biomedicine that has commanded considerable scientific and popular attention. The procedure involves the transfer of genes to patients for clinical benefit. Transferred genes can b e used for either reparative or pharmacological purposes.

OVERVIEW

In 1995, the first author and a colleague described the potential impact of gene therapy on dentistry, on the basis of initial studies of gene transfer applications to salivary glands, keratinocytes and cancer cells. Their conclusion was that gene therapy would have a significant impact on the nature of dental practice within 20 years. In this article, the authors consider research progress since 1995 and reexamine the earlier conclusion.

PRACTICE IMPLICATIONS

In the past six years, remarkable progress has been made in the field of gene therapy, including seven areas relevant to dental practice: bone repair, salivary glands, autoimmune disease, pain, DNA vaccinations, keratinocytes and cancer. While considerable problems remain, thus impeding the routine clinical use of gene transfer, gene therapy will have a pervasive and significant impact on areas of dental practice that are based in biological science. By 2015, this will translate into practitioners' having a wide range of novel biological treatment options for their patients.