A Selective AC1 Inhibitor as Non‐GPCR‐ or Ion Channel‐Dependent Approach for the Treatment of Pain

Abstract

Adenylyl cyclases (ACs) are enzymes that catalyze the synthesis of cAMP from ATP. The cAMP signaling cascade is involved in a number of physiological processes spanning from breathing to memory and cardiac function. Among the nine different membranous AC isoforms, a role for adenylyl cyclase 1 (AC1) has been suggested in learning, memory, pain, and opioid dependence. AC1 is one of the calcium/calmodulin‐stimulated ACs and previous studies suggest that inhibition AC1 could relieve inflammatory pain and reduce signs of opioid dependence. However, non‐selective inhibition of AC1 and closely related AC8 could lead to learning and memory impairments. We previously identified ST034307 as a selective inhibitor of AC1 and revealed anti‐allodynic activity in the mouse CFA inflammatory pain model. As part of our ongoing studies to identify selective AC inhibitors we developed a novel cellular model that used CRISPR/Cas 9 editing to remove 95% of the forskolin‐stimulated cAMP signal from wild type HEK293 cells (Soto‐Velasquez et al., 2018). We have now used this cellular model to re‐evaluate the AC isoform selectivity of ST034307. The results confirmed unprecedented selective inhibition of AC1 vs the closely related AC8. The development of AC1‐selective inhibitors like ST034307 now provides an opportunity to better study this protein and determine the physiological effects of inhibiting AC1 in additional animal models. The present work represents a comprehensive pre‐clinical study with the selective AC1 inhibitor ST034307. We have determined ST034307’s biodistribution to mouse blood and brain at different time points after injection. In addition, we have shown that the compound is effective and comparable to ketoprofen to relieve visceral and inflammatory pain in mice, and that it does not disrupt mouse innate behavior (nesting) at analgesic doses. In fear extinction experiments with rats ST034307 had no effects on extinction learning. However, the compound disrupted the consolidation of fear extinction compared to vehicle‐treated rats. These data support previous studies suggesting that AC1 inhibitors may be useful to treat pain and also indicates that normal innate behavior is not disrupted at analgesic doses. Moreover, the effect on consolidation of fear extinction may suggest a novel use for these compounds in anxiety disorders, such as post‐traumatic stress disorders (PTSD).Support or Funding InformationThis work was supported by the American Association of Colleges of Pharmacy (New Investigator Award), Palm Beach Atlantic University (Quality Initiative Grant), Lloyd L. Gregory School of Pharmacy (Integra Connect Grant), Purdue College of Pharmacy, and Richard and Anne Borch Award.