Peripherally Delivered Glutamic Acid Decarboxylase Gene Therapy for Spinal Cord Injury Pain

Abstract

Neuropathic pain after spinal cord injury (SCI) represents a difficult problem that is commonly refractory to conventional medical management. To determine if spinal release of gamma-amino butyric acid (GABA) could reduce below-level central neuropathic pain after SCI, we constructed a replication-incompetent herpes simplex virus (HSV)-based vector encoding one isoform of human glutamic acid decarboxylase (GAD67). Dorsal root ganglion (DRG) neurons transduced in vitro or in vivo by subcutaneous inoculation produced GAD and released GABA constitutively. T13 spinal cord hemisection resulted in central neuropathic pain manifested by mechanical allodynia and thermal hyperalgesia. Subcutaneous inoculation of the vector into both feet reduced both manifestations of below-level SCI pain; the vector-mediated effect was partially reversed by intrathecal bicuculline or phaclofen at doses that did not affect thresholds in normal or injured uninoculated animals. Vector-mediated GABA release attenuated the increase in spinal calcitonin gene-related peptide immunoreactivity caused by cord hemisection. These results suggest that HSV-mediated gene transfer to DRG could be used to treat below-level central neuropathic pain after incomplete SCI.

HSV-mediated transfer of interleukin-10 reduces inflammatory pain through modulation of membrane tumor necrosis factor α in spinal cord microglia

“…11,12,17,18 For the purposes of this study we constructed a non-replicating vector (QHIL10) that contains two copies of a hemagglutinin (HA)-tagged rat IL-10 gene, each under the control of the human cytomegalovirus immediate-early promoter (HCMV IEp; Figure 1a). Control vector QHGFP contains two copies of the green fluorescent protein (GFP) gene under the control of the same promoter (Figure 1b).…”

“…15,16 In previous studies we have shown that vectors constructed from nonreplicating herpes simplex virus (HSV) recombinants can be used effectively to transfer genes into DRG neurons from subcutaneous inoculation, and that release of inhibitory neurotransmitters or antiinflammatory proteins from the central afferent terminals of transduced DRG neurons in vivo can be used to modulate pain-related behaviors. 11,12,17,18 In this study, we used a nonreplicating HSV vector constructed to express and release IL-10 in the formalin model of inflammatory pain. We report that prolonged expression and transport of IL-10 by primary afferents to dorsal horn prevents the activation of p38 mitogen-activated protein kinase (MAPK) and decreases expression of mTNFa in microglia with concomitant reduction in pain-related behaviors during the delayed phase of the formalin test.…”

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

“…These initial studies have been extended in a variety of animal models, including a formalin model of chronic pain, 136 and models of bone metastasis pain, 137 bladder pain, 138 and spinal cord injury pain, 139 using a variety of different analgesic transgenes including opioid receptor ligands 136 and glutamic acid decarboxylase. 140 Furthermore, in one paradigm, the waning analgesic effect associated with declining transgene expression several weeks after initial inoculation was re-established following repeat inoculation, indicating that tolerance to the transgene product did not develop. 136 In view of these promising results in preclinical studies, it is possible that HSV gene therapy clinical trials for chronic pain will commence in the foreseeable future.…”

Viral Vector-based Gene Transfer for Treatment of Chronic Pain

“…64 We demonstrated that subcutaneous inoculation of this glutamic acid decarboxylase-expressing vector into both feet reduced mechanical allodynia and thermal hyperalgesia characteristic in spinal cord injury pain model. 65 The vector-mediated effect was partially reversed by intrathecal bicuculline or phaclofen indicating that the effect was mediated in part by both GABAA receptors and GABAB receptors. 65 Proinflammatory and anti-inflammatory cytokines and chemokines are endogenous small protein mediators released by local or migrating cells whose balance modulates the intensity of inflammatory response.…”

“…65 The vector-mediated effect was partially reversed by intrathecal bicuculline or phaclofen indicating that the effect was mediated in part by both GABAA receptors and GABAB receptors. 65 Proinflammatory and anti-inflammatory cytokines and chemokines are endogenous small protein mediators released by local or migrating cells whose balance modulates the intensity of inflammatory response. The inflammatory stimuli or tissue injury induces the release of characteristic cytokine cascades, which ultimately triggers the release of final mediators responsible for inflammatory pain.…”