In Vitro Pharmacological Characterization of a Series of 5-Cyano Desnitazene Opioids or "Cyanazenes"

The new synthetic opioid (NSO) market has been reshaped by the emergence of an opioid class known as "nitazenes," 2-benzylbenzimidazole opioids spanning a wide potency range, with several analogues surpassing the potency of fentanyl. The recently identified compound 5-cyano isotodesnitazene, also referred to as isotocyanazene or isotocyanozene, represents a nitazene analogue with a previously unreported 5-cyano substitution. This study determined the in vitro μ-opioid receptor (MOR) activation potential of 5-cyano isotodesnitazene and related "cyanazene" analogues, in comparison with their desnitazene and 5-nitro-substituted counterparts. Using a cell-based β-arrestin 2 recruitment assay, 5-cyano isotodesnitazene (EC₅₀ = 71.5, E_max = 117% vs. fentanyl) demonstrated lower potency than its 5-nitro analogue isotonitazene (EC₅₀ = 2.55, E_max = 130%) and fentanyl (EC₅₀ = 15.1, E_max = 99.9%) while exhibiting comparable activity to isotodesnitazene (EC₅₀ = 49.2, E_max = 113%). Similar in vitro trends were observed for the other three cyanazene analogues examined (5-cyano protodesnitazene, 5-cyano etodesnitazene, and 5-cyano metodesnitazene), indicating that a 5-cyano substitution does not compensate for the potency loss generally associated with removal of the 5-nitro group in the nitazene scaffold. Additionally, MOR activation was confirmed in an authentic 5-cyano isotodesnitazene sample. All cyanazenes and isotodesnitazene were detectable using BTNX nitazene test strips (Version 2.0). The emergence of 5-cyano isotodesnitazene highlights the continued structural diversification of the nitazene scaffold, underscoring the importance of timely pharmacological characterization, targeted harm reduction strategies, and close monitoring of newly emerging NSO.