Development of Hsp90 Isoform- Selective Inhibitors as a Novel Opioid Dose-Reduction Therapy - ABSTRACT The management of chronic pain is clinically challenging, and relies heavily on opioid drugs like morphine and oxycodone. However, opioids are plagued by numerous side effects that impact quality of life, like tolerance, constipation, and reward/addiction, contributing to an opioid abuse, addiction, and overdose crisis. These clinical and social challenges highlight the vast medical need for new approaches to pain management. To this end, we have pioneered an investigation into the role of Heat shock protein 90 (Hsp90) in regulating opioid signal transduction, anti-nociception, and side effects. We have found that Hsp90 regulates mu opioid receptor (MOR) signal transduction to different effect in brain vs. spinal cord. In brain, Hsp90 promotes MOR signaling and anti- nociception, so that Hsp90 inhibition in brain blocks opioid anti-nociception. In spinal cord, Hsp90 blocks MOR signaling and anti-nociception, so that Hsp90 inhibition in spinal cord enhances opioid anti-nociception. In further studies, we found that Hsp90 inhibition in spinal cord increases morphine anti-nociceptive potency 2-3 fold in acute and chronic pain, reduces tolerance and rescues established tolerance, all without altering the potency of constipation and reward. These results suggest that spinal Hsp90 inhibition could be used as an opioid dose-reduction strategy, to improve or maintain analgesic efficacy while reducing side effects. However, one challenge to this approach is our finding that non-selective Hsp90 inhibitors, when given systemically, gave results similar to the brain, blocking opioid anti-nociception. Seeking a way around this limitation, we found that Hsp90 isoforms differ between brain and spinal cord, with Hsp90α alone acting in brain while Hsp90α, Hsp90β, and Grp94 all act in spinal cord. Hypothesizing that an isoform-selective Hsp90 inhibitor could be used to target spinal cord-specific isoforms, we found that the Hsp90β-selective inhibitor KUNB106 enhanced morphine anti- nociception while rescuing established morphine tolerance when given systemically. These results strongly suggest that Hsp90β-selective inhibitors could be used as a novel, first-in-class opioid dose-reduction therapy. However, KUNB106 is a first generation compound, with poor solubility and pharmacokinetics (PK) and an uncertain therapeutic profile. In this proposal, we will thus optimize KUNB106 to create a new therapeutic to enhance opioid therapy and reduce opioid side effects like reward/addiction. In Aim 1 we will utilize cutting edge medicinal chemistry approaches using Hsp90 isoform co-crystallized structures to create optimized compounds based on the KUNB106 scaffold. In Aim 2, we will test these compounds for Hsp90 isoform selectivity, ADMET parameters, off-target interactions, and in vivo PK in mice, aiming to identify highly selective, soluble, and orally bioavailable compounds. In Aim 3, we will test the best of these compounds for their efficacy in enhancing opioid anti-nociception in acute and chronic pain models in mice, while reducing tolerance, constipation, reward, and respiratory depression. Top candidates will be tested for off-target side effects and toxicity. Through this project, we aim to create optimized candidates for further development as new therapeutics for patient pain management.
