Selective Monoamine Release as a Treatment for Cocaine Use Disorders

Cocaine (COC) addiction is an unrelenting public health concern. An effective medication has not been identified for COC dependence despite being a high priority for the National Institute on Drug Abuse for nearly 30 years and extensive efforts by the scientific and treatment communities. The results of preclinical studies have shown that monoamine releasers attenuate the reinforcing effects of COC. The results of human laboratory studies also suggest that monoamine releasers attenuate the reinforcing effects of COC although the effects are small in magnitude and dependent on the methods used to assess drug reinforcement. The results of clinical trials that tested monoamine releasers for COC abuse are mixed. Monoamine releasers vary along a continuum from DA/NE selective to 5-HT selective. Theoreticians have postulated that the 5-HT/DA releasing ratio is a critical determinant of the efficacy and selectivity of a monoamine releaser to attenuate the reinforcing effects of COC. Compounds with intermediate 5-HT/DA release ratios (i.e., 30-40) were the most effective and specific terms of reducing cocaine taking. Methamphetamine (5-HT/DA ratio = 31) completely and specifically eliminated responding for COC. Consistent with these findings, methamphetamine dramatically reduced COC use in a clinical trial although it is NOT a viable option for managing COC abuse because of its high abuse and diversion potential. Compounds with a desirable 5-HT/DA releasing ratio and minimal abuse potential need to be tested for COC dependence. Phendimetrazine (PHEN) is indicated for treating obesity. After oral administration, PHEN is converted to phenmetrazine, which is largely responsible for its behavioral and neuropharmacological effects. Consistent with the notion that compounds with intermediate 5-HT/DA release ratios selectively attenuate the reinforcing effects of COC, also phenmetrazine (5-HT/DA ratio = 37) completely and specifically eliminated COC-maintained responding. Moreover, PHEN also reduces COC-maintained responding, but does not maintain self-administration or produce high magnitude positive subjective effects, which suggests that its abuse potential is low. Although PHEN has not yet been tested as a potential pharmacotherapy for COC dependence in human laboratory experiments or clinical trials to our knowledge, the results of extant preclinical experiments suggest it may be a viable option. We will conduct two rigorous within-subject experiments to fill this gap. These studies will 1) establish the safety and tolerability of PHEN-COC combinations and 2) demonstrate that PHEN reduces COC self-administration. The results of project will provide critical information regarding the initial efficacy of PHEN for COC dependence, which will enhance the probability of success when advanced to a clinical trial.