Inhibition of cocaine self‐administration by a novel mutant cocaine esterase (ET CocE) in rats
Authors: Jimenez Karen , Nichols Joey , Woods James H. , Sunahara Roger K. , Collins Gregory T. 
Published: June 2021

Cocaine abuse is a serious public health problem for which there are currently no approved therapies. Cocaine esterase (CocE) is a bacterially‐derived esterase capable of rapidly metabolizing cocaine to the inactive metabolites ecgonine methyl ester, and benzoylecgonine; however, CocE is not stable at body temperature resulting in a very short in vivo duration of action. Previous mutagenesis studies have improved the thermostability of CocE, resulting in longer acting mutant forms of CocE (e.g., RQ CocE) capable of inhibiting the reinforcing, discriminative stimulus, cardiovascular, convulsant, and lethal effects of cocaine in both rodents and rhesus monkeys. Despite a ~500‐fold improvement in the in vivo duration of action, incorporation of the T172R/G173Q mutations did not enhance the catalytic efficiency (Kcat/Km) of CocE (~100 uM/min). Recent studies aimed to improve the catalytic efficiency of CocE by mutating both the binding site (A51E) and active site (S288T), resulting a CocE (ET CocE) with a catalytic efficiency (157 uM/min) ~1.6‐fold greater than that of RQ CocE. This study aimed to characterize the potency and effectiveness of ET CocE to decrease cocaine self‐administration. Male Sprague‐Dawley (n=12) rats were trained to self‐administer 0.32 mg/kg/inf cocaine under a fixed ratio (FR) 5 schedule of reinforcement. Half of these rats transitioned to a multiple component FR5 schedule capable of evaluating the reinforcing effects of multiple doses of cocaine (0.032–1 mg/kg/inf) in a single session, and the following tests were performed: saline was substituted for cocaine, pretreatment with ET CocE (0.1–3.2 mg/kg; IV) and RQ CocE (3.2 mg/kg; IV) prior to cocaine self‐administration sessions. The other 6 rats were used to test the effects of ET CocE (1 mg/kg; IV) during 90 min sessions in which either cocaine (0.1 and 1.0 mg/kg/inf) or MDPV (0.01 and 0.1 mg/kg/inf) were available for infusion. Pretreatment with 3.2 mg/kg RQ CocE resulted in a ~3‐fold rightward shift in the cocaine dose‐response curve. Pretreatment with ET CocE produced dose‐dependent rightward shifts in the cocaine dose‐response curve, with a doses of 1 and 3.2 mg/kg ET CocE producing ~3‐fold and ~10‐fold rightward shifts, respectively; low rates of responding were observed when saline was substituted for cocaine. When ET CocE (1 mg/kg) was evaluated in sessions in which rats could respond for either cocaine or MDPV, ET CocE decreased responding for the small dose of cocaine and increased responding for the large dose of cocaine, but failed to alter responding for MDPV. Together, these data show that the incorporation of novel mutations to the binding site (A51E) and active site (S288T) of CocE results in an enzyme (ET CocE) that is ~1.6‐fold more efficient at metabolizing cocaine and ~3‐fold more potent at inhibiting the self‐administration of cocaine, and provide additional strong support for the continued development of cocaine metabolizing enzymes, such as ET CocE, for treatment of cocaine abuse in humans.Support or Funding InformationSupported by a NIDA research grant (R01DA039146; GTC) and the ASPET SURF program (KJ).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.