Preclinical toxicity evaluation of AAV for pain: evidence from human AAV studies and from the pharmacology of analgesic drugs

Abstract Gene therapy with adeno-associated virus (AAV) has advanced in the last few years from promising results in animal models to >100 clinical trials (reported or under way). While vector availability was a substantial hurdle a decade ago, innovative new production methods now routinely match the scale of AAV doses required for clinical testing. These advances may become relevant to translational research in the chronic pain field. AAV for pain targeting the peripheral nervous system was proven to be efficacious in rodent models several years ago, but has not yet been tested in humans. The present review addresses the steps needed for translation of AAV for pain from the bench to the bedside focusing on pre-clinical toxicology. We break the potential toxicities into three conceptual categories of risk: First, risks related to the delivery procedure used to administer the vector. Second, risks related to AAV biology, i.e., effects of the vector itself that may occur independently of the transgene. Third, risks related to the effects of the therapeutic transgene. To identify potential toxicities, we consulted the existing evidence from AAV gene therapy for other nervous system disorders (animal toxicology and human studies) and from the clinical pharmacology of conventional analgesic drugs. Thereby, we identified required preclinical studies and charted a hypothetical path towards a future phase I/II clinical trial in the oncology-palliative care setting

High cerebrospinal fluid levels of interleukin-10 attained by AAV in dogs

Intrathecal (IT) gene transfer using adeno-associated virus (AAV) may be clinically promising as a treatment for chronic pain if it can produce sufficiently high levels of a transgene product in the cerebrospinal fluid (CSF). Although this strategy was developed in rodents, no studies investigating CSF levels of an analgesic or antiallodynic protein delivered by IT AAV have been performed in large animals. Interleukin-10 (IL-10) is an antiallodynic cytokine for which target therapeutic levels have been established in rats. The present study tested IT AAV8 encoding either human IL-10 (hIL-10) or enhanced green fluorescent protein (EGFP) in a dog model of IT drug delivery. AAV8/hIL-10 at a dose of 3.5 × 10(12) genome copies induced high hIL-10 levels in the CSF, exceeding the target concentration previously found to be antiallodynic in rodents by >1000-fold. AAV8/EGFP targeted the primary sensory and motor neurons and the meninges. hIL-10, a xenogeneic protein in dogs, induced anti-hIL-10 antibodies detectable in the CSF and serum of dogs. The high hIL-10 levels demonstrate the efficacy of AAV for delivery of secreted transgenes into the IT space of large animals, suggesting a strong case for further development toward clinical testing

High cerebrospinal fluid levels of interleukin-10 attained by AAV in dogs

Intrathecal (IT) gene transfer using adeno-associated virus (AAV) may be clinically promising as a treatment for chronic pain if it can produce sufficiently high levels of a transgene product in the cerebrospinal fluid (CSF). While this strategy was developed in rodents, no studies investigating CSF levels of an analgesic or anti-allodynic protein delivered by IT AAV have been performed in large animals. Interleukin-10 (IL-10) is an anti-allodynic cytokine, for which target therapeutic levels have been established in rats. The present study tested IT AAV8 encoding either human IL-10 (hIL-10) or enhanced green fluorescent protein (EGFP) in a dog model of IT drug delivery. AAV8/hIL-10 at a dose of 3.5×10(12) genome copies induced high hIL-10 levels in the CSF, exceeding the target concentration previously found to be anti-allodynic in rodents by >1000-fold. AAV8/EGFP targeted the primary sensory and motor neurons and the meninges. hIL-10, a xenogeneic protein in dogs, induced anti-hIL-10 antibodies detectable in the dogs’ CSF and serum. The high hIL-10 levels demonstrate the efficacy of AAV for delivery of secreted transgenes into the IT space of large animals suggesting a strong case for further development towards clinical testing