This is an amended application seeking continuation of an NIGMS MERIT Award, which has supported a multidisciplinary research program on the studies of mechanisms of general anesthesia and analgesia. In recent years, the research has focused on human glycine receptors (GlyRs) and two bacterial homologues of the pentameric ligand-gated ion channels (pLGICs). High-resolution structural details from the nuclear magnetic resonance and X-ray co-crystallization studies in this project offered mechanistic insights into the role of GlyRs and the related pLGICs in anesthesia and, particularly, in analgesia. In response to a congressional call for the NIH to expand an aggressive basic and clinical research program on the causes and treatments of pain (Section 4305, Patient Protection and Affordable Care Act), this competing renewal will direct a focused research effort towards developing new analgesic therapies in the next funding cycle. A novel strategy based on an unconventional idea for drug discovery is proposed to provide the peripheral nerves with potential analgesic targets through receptor engineering. The central hypothesis is that in certain types of severe and persistent pain, the sensory process of peripheral hypersensitization can be partially controlled by installing non-native chloride (Cl-) channels, thereby creating drug-able modulations of peripheral nociceptors. Two classes of Cl- channels will be developed that will either (a) automatically respond to inflammation-evoked pain by spontaneously mediating Cl- flux in response to changes in tissue pH or (b) serve as exclusive targets for small activating molecules to mediate anti-hyperalgesic actions. Substantive in vitro functional data and in vivo pain behavioral data support the following three specific aims:
Specific Aim #1 : Evaluate the designed receptors and top drug candidates in vivo and devise the best delivery strategies to target peripheral afferents. Two well-established inflammatory rat pain models will be used to test (1) intraneural and perineural injection and (2) intrathecal injection of expression vectors (including plasmid DNA and peripheral nerve/dorsal root ganglion-targeting rival vectors), and (3) systemic intravenous injection of peripheral-nerve-homing nanoparticles carrying the constructs of the engineered receptors. Systemic immune reaction will be profiled, and strategies to evade immune detection will also be developed.
Specific Aim #2 : Continue to optimize two classes of Cl- channels as anti-hyperalgesic targets. Class I will be passive channels that will automatically respond to tissue pH changes proportional to the degree of pain-evoking inflammation. Class II will be activatable channels whose agonist or positive allosteric modulator binding sites will be designed and optimized to match non-psychoactive molecules that would otherwise have little or no analgesic action, thereby turning these molecules into long-acting analgesics.
Specific Aim #3 : Screen and develop non-psychoactive analgesics that act specifically on the optimized Class II channels as exclusive targets. Structure-based in silico screening and in vitro electrophysiology will be combined to search for top candidates. Optimization will be iterated in concert with the receptor designs in Specific Aim #2 and in vivo measurements in Specific Aim #1.
Research for better treatment of chronic pain is rarely in the limelight. Few celebrities find it attractive enough to publicly promote pain research. For over 100 million chronic pain sufferers in our country, we spend merely $4 per year on research to combat this debilitating health problem. Aiming for a major breakthrough, a team of leading scientists is joining forces in this project to find innovative strategies to develop new painkilles that are highly effective but not habit-forming. The research will lead to fundamentally different pain therapies without the risk of drug tolerance, dependence, or abuse.
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