An unbiased highthroughput behavior based screen for small molecule analgesics

University Of Washington, Seattle WA

Investigators

Abstract

? DESCRIPTION (provided by applicant): Sensation of painful stimuli is critical for the survival. However, acute and chronic pain affects hundreds of millions of people as a result of injury, and is a debilitating symptom in many illnesses. Unfortunately, currently available drug based therapies have numerous deleterious side effects and/or potential for abuse and addiction, while also not being effective in the treatment of persistent pain. Despite massive investment, there has been limited success in the development of novel analgesic compounds. The dominant drug development model follows a predictable preclinical path in which a selected target is subjugated to high-throughput in vitro screens, the generation of lead compounds, and finally testing in disease model systems for safety and efficacy assessments. While this approach can be successful, it often leads to failure due to poor target selection, the inability to model complx pain behaviors using in vitro testing and/or ineffectiveness and unforeseen side effects in animal model testing. An alternative approach to analgesic development would be to develop low cost, high throughput, untargeted animal based behavioral screens that model complex nociceptive behaviors in which to screen for analgesic compounds. In fact the most commonly used analgesics were identified due to their analgesic properties prior to target identification. Here w propose to use an alternative analgesic drug discovery approach by utilizing a novel zebrafish based behavioral assay to conduct a small molecule screen to identify novel analgesic compounds. The zebrafish provides an intriguing model system to study nociception. The neural circuits underling nociception in zebrafish larvae are highly analogous to those found in higher vertebrates such as rodents and humans. Furthermore we've shown that zebrafish larvae have a functionally diverse peripheral and central nervous system and respond robustly to noxious stimuli. Additionally zebrafish can be generated in large numbers at low costs and their small size allows for rapid upscaling using existing high throughput platforms, which is not possible with other vertebrate systems such as rodents. We will utilize a place aversion assay, which likely utilizes supraspinal nociceptive neuronal circuitry since the larvae must choose to avoid the noxious stimulus, to model sensitized thermal hyperalgesia, a symptom of many chronic pain diseases. In this assay individually arrayed zebrafish larvae show profound aversion to noxious temperature. Demonstrating that our place aversion reflects nociceptive behavior, small molecules with known analgesic properties potently reverse thermal aversion. In this exploratory study, utilizing the described assay, we propose to screen a 10,000 compound small molecule library for novel analgesic compounds. Identified molecules will be evaluated for their analgesic properties in future studies utilizing rodent model systems as well as for their site of action and could lead to the generation of novel analgesics. Findings from this proposal could provide a way forward for analgesic discovery that may offer a complementary parallel pathway to target-based drug development.