Antibodies to nerve growth factor reverse established tactile allodynia in rodent models of neuropathic pain without tolerance

A considerable body of evidence implicates endogenous nerve growth factor ( NGF) in conditions in which pain is a prominent feature, including neuropathic pain. However, previous studies of NGF antagonism in animal models of neuropathic pain have examined only the prevention of hyperalgesia and allodynia after injury, whereas the more relevant issue is whether treatment can provide relief of established pain, particularly without tolerance. In the current work, we studied the effects of potent, neutralizing anti- NGF antibodies on the reversal of tactile allodynia and thermal hyperalgesia in established models of neuropathic and inflammatory pain in rats and mice. In the complete Freund's adjuvant- induced hind- paw inflammation, spinal nerve ligation and streptozotocin- induced neuropathic pain models, a single intraperitoneal injection of a polyclonal anti-NGF antibody reversed established tactile allodynia from approximately day 3 to day 7 after treatment. Effects on thermal hyperalgesia were variable with a significant effect observed only in the spinal nerve ligation model. In the mouse chronic constriction injury ( CCI) model, a mouse monoclonal anti- NGF antibody reversed tactile allodynia when administered 2 weeks after surgery. Repeated administration of this antibody to CCI mice for 3 weeks produced a sustained reversal ( days 4 to 21) of tactile allodynia that returned 5 days after the end of dosing. In conclusion, NGF seems to play a critical role in models of established neuropathic and inflammatory pain in both rats and mice, with no development of tolerance to antagonism. Antagonists of NGF, such as fully human monoclonal anti- NGF antibodies, may have therapeutic utility in analogous human pain conditions.