Targeted Cholera Toxin for Treatment of Hyperalgesia

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DESCRIPTION (provided by applicant): In a study conducted by the American Pain Society it was demonstrated that 9 percent of the United States population suffers from moderate to severe chronic pain. Current methods to treat chronic pain are in many instances not effective or produce a wide range of side effects that limit their utility. In this project we are going to take advantage of the recent discoveries that intrathecally administered cholera toxin blocks hyperalgesia and allodynia in rodent models of chronic pain, and that toxins can be directly targeted to nociceptive neurons in the spinal cord via the neurokinin 1 (NK1) receptor. We will conjugate the catalytic portion of cholera toxin to substance P in order to direct the cholera toxin to NK1 receptor expressing cells in the spinal cord. This conjugate will be tested for activity in NK1 expressing cell lines and in rodent models of chronic pain for its ability to stimulate cAMP production, suppress the expression of Gs g-proteins and to inhibit hyperalgesia and allodynia. The unique aspect of this conjugate is that cholera toxin will not kill the NK1 expressing cells in the spinal cord like saporin, diphtheria toxin and pseudomonas exotoxin, which have previously been used in NK1 receptor targeting strategies. Instead, cholera toxin will uncouple opioid receptors from Gs, thus enhancing their inhibitory actions, and will reduce the activity of Gs coupled receptor systems, which would further suppress nociceptive transmission. Thus, this project will be the first, to the best our knowledge, to produce a therapeutic effect by directly manipulating g-protein function in an identified population of neurons in vivo. If successful, this project will produce a novel agent for the control of pain and will open up an entire new dimension in therapeutics by making g-proteins in specific cells the pharmacological target.