A Mechanistic Approach to the Development of Gene Therapy for Chronic Pain

Targeted ubiquitination of sensory neuron calcium channels reduces the development of neuropathic pain

Neuropathic pain caused by lesions to somatosensory neurons due to injury or disease is a widespread public health problem that is inadequately managed by small-molecule therapeutics due to incomplete pain relief and devastating side effects. Genetically encoded molecules capable of interrupting nociception have the potential to confer long-lasting analgesia with minimal off-target effects. Here, we utilize a targeted ubiquitination approach to achieve a unique posttranslational functional knockdown of high-voltage-activated calcium channels (HVACCs) that are obligatory for neurotransmission in dorsal root ganglion (DRG) neurons. CaV-aβlator comprises a nanobody targeted to CaV channel cytosolic auxiliary β subunits fused to the catalytic HECT domain of the Nedd4-2 E3 ubiquitin ligase. Subcutaneous injection of adeno-associated virus serotype 9 encoding CaV-aβlator in the hind paw of mice resulted in the expression of the protein in a subset of DRG neurons that displayed a concomitant ablation of CaV currents and also led to an increase in the frequency of spontaneous inhibitory postsynaptic currents in the dorsal horn of the spinal cord. Mice subjected to spare nerve injury displayed a characteristic long-lasting mechanical, thermal, and cold hyperalgesia underlain by a dramatic increase in coordinated phasic firing of DRG neurons as reported by in vivo Ca2+ spike recordings. CaV-aβlator significantly dampened the integrated Ca2+ spike activity and the hyperalgesia in response to nerve injury. The results advance the principle of targeting HVACCs as a gene therapy for neuropathic pain and demonstrate the therapeutic potential of posttranslational functional knockdown of ion channels achieved by exploiting the ubiquitin-proteasome system.

Cannabinoid receptor agonists from Conus venoms alleviate pain-related behavior in rats

Cannabinoid (CB) receptor agonists show robust antinociceptive effects in various pain models. However, most of the clinically potent CB1 receptor-active drugs derived from cannabis are considered concerning due to psychotomimetic side effects. Selective CB receptor ligands that do not induce CNS side effects are of clinical interest. The venoms of marine snail Conus are a natural source of various potent analgesic peptides, some of which are already FDA approved. In this study we evaluated the ability of several Conus venom extracts to interact with CB1 receptor. HEK293 cells expressing CB1 receptors were treated with venom extracts and CB1 receptor internalization was analyzed by immunofluorescence. Results showed C. textile (C. Tex) and C. miles (C. Mil) samples as the most potent. These were serially subfractionated by HPLC for subsequent analysis by internalization assays and for analgesic potency evaluated in the formalin test and after peripheral nerve injury. Intrathecal injection of C. Tex and C. Mil subfractions reduced flinching/licking behavior during the second phase of formalin test and attenuated thermal and mechanical allodynia in nerve injury model. Treatment with proteolytic enzymes reduced CB1 internalization of subfractions, indicating the peptidergic nature of CB1 active component. Further HPLC purification revealed two potent antinociceptive subfractions within C. Tex with CB1 and possible CB2 activity, with mild to no side effects in the CB tetrad assessment. CB conopeptides can be isolated from these active Conus venom-derived samples and further developed as novel analgesic agents for the treatment of chronic pain using cell based or gene therapy approaches.

The rapidly evolving state of gene therapy

Gene therapy is emerging as a viable option for clinical therapy of monogenic disorders and other genetically defined diseases, with approved gene therapies available in Europe and newly approved gene therapies in the United States. In the past 10 years, gene therapy has moved from a distant possibility, even in the minds of much of the scientific community, to being widely realized as a valuable therapeutic tool with wide-ranging potential. The U.S. Food and Drug Administration has recently approved Luxturna (Spark Therapeutics Inc, Philadelphia, PA, USA), a recombinant adeno-associated virus (rAAV) 2 gene therapy for one type of Leber congenital amaurosis 2 ( 1 , 2 ). The European Medicines Agency (EMA) has approved 3 recombinant viral vector products: Glybera (UniQure, Amsterdam, The Netherlands), an rAAV vector for lipoprotein lipase deficiency; Strimvelis (Glaxo Smith-Kline, Brentford, United Kingdom), an ex vivo gammaretrovirus-based therapy for patients with adenosine deaminase-deficient severe combined immune deficiency (ADA-SCID); and Kymriah (Novartis, Basel, Switzerland), an ex vivo lentivirus-based therapy to engineer autologous chimeric antigen-receptor T (CAR-T) cells targeting CD19-positive cells in acute lymphoblastic leukemia. These examples will be followed by the clinical approval of other gene therapy products as this field matures. In this review we provide an overview of the state of gene therapy by discussing where the field stands with respect to the different gene therapy vector platforms and the types of therapies that are available.-Gruntman, A. M., Flotte, T. R. The rapidly evolving state of gene therapy.