The long-term objectives of this project are to develop long-acting Na+ channel blockers pertinent for pain management and to gain a better understanding of how these blockers work mechanistically. Traditional local anesthetics (LAs) are often inept for chronic or intractable cancer pain due to their insufficient duration of nerve block. Our specific aims are (1) to identify and synthesize compounds that potently block the open and/or inactivated Na+ channels, (2) to assess the use- and state-dependent block of potent Na+ channel blockers, (3) to test their in vivo potency as long-acting LAs, and (4) to map their receptor site within the Na+ channel alpha-subunit. Recent screening has identified several new lead structures that block open Na+ channels with high affinities. Earlier screening demonstrated that drugs taken orally for neuropathic pain, such as amitriptyline, flecainide, and mexiletine, also block open Na+ channels effectively at their therapeutic plasma concentrations. We hypothesize that these drugs alleviate ectopic high-frequency discharges found in injured nerves due to their high-affinity block of open Na+ channels. Amitriptyline, which too potently blocks the inactivated Na+ channels, indeed acts as a long-acting LA. We plan to identify and synthesize novel open and/or inactivated-channel blockers based on these lead structures. Their use-dependent block of Na+ currents during repetitive pulses and the 50% inhibitory concentration (IC50) of resting-, open-, and inactivated-channel block will be determined in wild-type and/or in inactivation-deficient mutant Na+ channels expressed in human HEK293 cells. Sensory and motor functions of nerve block will be evaluated in rats or sheep before and after injection of potent Na + channel blockers via various routes. Finally, we plan to delimit the receptor for selected blockers within the Na+ channel alpha-subunit by site-directed mutagenesis and by computer simulation of the ligand-receptor complex. This information will in turn facilitate receptor-based drug design. Together, these studies should provide us new lead structures for the development of long-acting LAs that selectively target open and/or inactivated Na+ channels. Such drugs, either taken orally or injected locally, may be beneficial for patients with chronic and intractable cancer pain.