Neuropathic chronic pain affects ~20 million of Americans and bears more than US$500 Billion burden on the US economy. Moreover, the widespread use of addictive opioid painkillers for chronic pain is the major root of the opioid abuse epidemics threatening the whole society. As only one in four patients with neuropathic pain experiences pain relief with the current treatment options, discovery of new approaches to treating neuropathic pain is an unmet medical need with a major impact on society. Targeting pain in peripheral neurons is a key paradigm for effective and safe analgesia, which can naturally bypass the CNS-mediated side effects and addiction. One of the most promising and advanced peripheral targets, angiotensin AT2 receptor is involved in regulations of neuronal membrane excitability and neurite outgrowth of peripheral sensory neurons. Inhibition of AT2R in PNS has shown effect in preclinical models of neuropathic pain, as well as in phase II clinical trials, where the EMA401 drug demonstrated analgesia in patients with post-herpetic neuralgia. However, EMA401, which had modest potency and suboptimal drug-like properties, has been terminated in May 2019 due to off- target hepatotoxicity at high therapeutic doses. Lack of suitable AT2R candidates in pipeline calls for discovery and development of new highly potent and safe AT2R antagonists for neuropathic pain. We have established a structure-based drug discovery platform and used it to identify new lead chemotypes for AT2R antagonists. Our current lead has affinity (Ki =56 nM) on par with the previous clinical candidate, but much higher ligand efficiency, better drug-like properties and initial SAR suggesting high optimization potential. Moreover, recent breakthroughs in understanding the neuroimmune functional role of AT2R in neuropathic pain helped us to establish a set of cell-based functional assays, lack of which hampered previous development efforts. Using these platforms, we plan to establish comprehensive SAR for our main and backup lead series, and develop a screening funnel in the 1-year UG3 phase of the project. In close collaboration with the BPN steering committee, consultants and contractors, this screening funnel will then be employed in UH3 phase to optimize the lead potency, selectivity, ADMET and PK properties relevant for AT2R lead development, including peripheral restriction that precludes CNS side effects. This would allow selection of clinical development candidate for pre- development, IND-enabling studies and preparation of IND targeting post-herpetic neuralgia.
Neuropathic pain affects most people at some point in their lives, often as a burning or tingling sensations from shingles, excruciating back pain, postoperative pain or hypersensitivity caused by chemotherapy or diabetes. Apart from direct personal and economic burden of chronic pain, widespread treatment with opioid painkillers is a major cause of the ongoing epidemics of opioid abuse. We propose development of pain therapies based on a newly non-opioid target, angiotensin receptor AT2R, which could relieve pain directly in peripheral sensory neurons, without affecting brain function or causing drug addiction.