Optimization of 4-arylthiophene-3-carboxylic acid derivatives as inhibitors of ANO1: Lead optimization studies toward their analgesic efficacy for inflammatory pain

Current pain management is largely limited to opioids and non-steroidal anti-inflammatory drugs. Developing new analgesic drugs remains important to address the unmet medical needs of chronic pain patients. Calcium-activated Chloride Channel anoctamin-1 (ANO1) is a potential analgesic target. ANO1 is activated by noxious stimuli in peripheral sensory neurons and further induced neural depolarization. Downregulation of ANO1 reduced hyperalgesia and allodynia caused by inflammation and nerve injury. Here we developed a series of 4-arylthiophene-3-carboxylic acid derivatives for proof-of-concept studies of ANO1-targeted analgesia. These efforts led to the identification of the compound DFBTA, 4-(4-chlorophenyl)-2-(2,5-difluorobenzamido)thiophene-3-carboxylic acid, which displays dramatic ANO1 inhibition with IC₅₀ of 24 nM. DFBTA displays very weak cytotoxicity, cardiotoxicity, and acute toxicity (HEK293 proliferation IC₅₀ > 30 μM, hERG IC₅₀ > 30 μM, mouse minimum lethal dosage, MLD>1000 mg/kg), as well as excellent pharmacokinetics properties with oral bioavailability >75% and little brain penetration (<1.5% brain/plasma). Finally, the analgesic efficacy of ANO1 inhibitor was evaluated in animal models. DFBTA shown comparable efficacy to clinical drugs in all inflammatory pain models induced by complete Freund's adjuvant, formalin, and capsaicin. These works provide a useful tool compound and promising results for ANO1-targenting analgesic development.