(T1130-06-36) Synthesis and Biological Evaluation of Dual Acting Sigma Receptor Ligands and Dopamine Transporter Ligands as Potential Treatment Cocaine Misuse

Purpose: Cocaine addiction remains a worldwide public health crisis with no effective pharmacotherapies for treatment. Cocaine stimulates the brain’s reward pathway, the mesolimbic system, by inhibiting the uptake of all monoamine neurotransmitters and leading to a buildup of monoamine neurotransmitters in the synapse.^1–3Cocaine’s mechanism of action is poorly understood, but it is largely believed that dopamine transporter (DAT) plays a primary role.^1,4 In addition to DAT, literature has demonstrated the involvement of the sigma 1 receptor (S1R) in cocaine’s mechanism of action through the modulation of DAT.^3,5–7 At this time, the mechanism of this interaction is unknown. Despite this, the blockade of S1Rs and DAT significantly attenuates cocaine self-administration in rodent models.^2,6,7 Our lab has brought forth a novel lead compound, SBS-518 (K_i S1R = 7.46 ± 0.556 nM, K_i DAT = 875.46 nM), that functions as a S1R antagonist and a DAT inhibitor. Alone, it produces no significant effect on dopamine concentrations in the brain and is not self-administered by rodents, suggesting low abuse potential. SBS-518 dose-dependently decreased cocaine self-administration at doses that did not affect responding maintained by food reinforcement. Unfortunately, SBS-518 suffers from several unfavorable characteristics, including poor half-life, poor metabolic stability, poor bioavailability, and issues with first-pass metabolism. Our lab developed a series of novel analogs that maintain activity at S1R and DAT, comparable to SBS-518 to address the stability concerns.

Methods: The 1-(4-bromobutyl)-1,3,4,5-tetrahydro-2H-benzo[b]azepin-2-one derivatives (4-6), were prepared by alkylating the 1,3,4,5-tetrahydro-2H-benzo[b]azepin-2-one derivatives (1-3) with 1,4-dibromobutane. The spiro-secondary amine (7) was prepared with a modified Grignard reaction using 1-chloro-2-(iodomethyl)benzene, i-PrMgCl•LiCl, and 1-benzylpiperidin-4-one. The resulting compound was then debenzylated using HCl. The secondary piperazines (8-10) were obtained commercially. The final compounds (11-15) were prepared by linking the 1-(4-bromobutyl)-1,3,4,5-tetrahydro-2H-benzo[b]azepin-2-one derivatives (4-6) and the secondary amines (7-10) using K₂CO₃ in DMF followed by salt formation using oxalic acid. The final compounds (11-15) were evaluated for their in vitro binding affinities at S1R and DAT. The S1R binding affinities were evaluated in guinea pig brain homogenate⁷ using [³H](+)-pentazocine as the radioligand. The DAT binding affinities were evaluated in hDAT-HEK293 cells⁸ using [³H]WIN35,428 as the radioligand. All binding data was analyzed using GraphPad Prism.

Results: Overall, the expansion of the five-membered ring to the seven-membered ring decreased DAT affinity by as much as 2.7-fold in our derivatives. However, the seven-membered ring improved S1R affinity seen with STG187 (K_i S1R = < 3 nM, K_i DAT = 1658.8 ± 376.5 nM). The addition of electronegativity to the seven-membered ring decreased activity at DAT seen with STG191 (K_i S1R = < 3 nM, K_i DAT = 2393.2 ± 317.7 nM) and SMB108 (K_i S1R = 18.25 ± 1.73 nM, K_i DAT = 2183.5 ± 301.8 nM). Additionally, our data suggests that the movement of the chlorine from the meta to ortho position had a marginal effect on the DAT affinity (STG188 K_iS1R = < 3 nM, K_i DAT = 1671.7 ± 186.2 nM), SMB107 K_i S1R = < 3 nM, K_i DAT = 1345.0 ± 13.14 nM).

Conclusion: Given the effects seen with SBS-518 on cocaine self-administration, we designed and synthesized a series of SBS-518 analogs that were evaluated in radioligand binding assays at S1R and DAT. Some of the analogs resulted in binding affinities at S1R and DAT that were comparable to SBS-518. Metabolic stability studies are currently underway. In vivo testing of these compounds in rat cocaine self-administration assays and pharmacokinetic paradigms are still needed. Our current results suggest that SMB107, SMB108, STG188, and STG191 may be useful in developing new pharmacological treatments for cocaine abuse. This novel approach could offer insights into new developments in pharmacotherapy for drug abuse.

References: 1 Simon DP, Kreek MJ. Cocaine: Usage, Misuse, and Addiction Processes. An Overview. In: Preedy V, editor. Neuropathology of drug addictions and substance misuse. Volume 2, Stimulants, club and dissociative drugs, hallucinogens, steroids, inhalants, and international aspects, vol. 2. 1st ed. Academic Press; 2016.
2 Hong WC, Yano H, Hiranita T, Chin FT, McCurdy CR, Su TP, et al. The sigma-1 receptor modulates dopamine transporter conformation and cocaine binding and may thereby potentiate cocaine self-administration in rats. Journal of Biological Chemistry 2017;292:11250–61. https://doi.org/10.1074/jbc.M116.774075.
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5 Sambo DO, Lebowitz JJ, Khoshbouei H. The sigma-1 receptor as a regulator of dopamine neurotransmission: A potential therapeutic target for methamphetamine addiction. Pharmacol Ther 2018;186:152–67. https://doi.org/10.1016/j.pharmthera.2018.01.009.
6 Hiranita T, Soto PL, Kohut SJ, Kopajtic T, Cao J, Newman AH, et al. Decreases in cocaine self-administration with dual inhibition of the dopamine transporter and σ receptors. Journal of Pharmacology and Experimental Therapeutics 2011;339:662–77. https://doi.org/10.1124/jpet.111.185025.
7 Katz JL, Hiranita T, Kopajtic TA, Rice KC, Mesangeau C, Narayanan S, et al. Blockade of cocaine or σ receptor agonist self administration by subtype-selective σ receptor antagonists. Journal of Pharmacology and Experimental Therapeutics 2016;358:109–24. https://doi.org/10.1124/jpet.116.232728.
8 Eshleman AJ, Carmolli M, Cumbay M, Martens CR, Neve KA, Janowsky A. Characteristics of Drug Interactions with Recombinant Biogenic Amine Transporters Expressed in the Same Cell Type 1. J Pharmacol Exp Ther 1999;289:877–85.

Acknowledgements: This study was supported, in part, by the National Institutes of Health, National Institutes on Drug Abuse Grants R01 DA023205 (CRM), UG3 DA058553 (JR), the National Institutes of General Medical Sciences Grant P20 GM104932 (CRM), and the Intramural Research Program of the National Institutes of Health, National Institutes on Drug Abuse. The hDAT-HEK293 cells were a gift from Dr. Amy Newman.

Synthesis of SBS-518 analogs.

Binding affinities of SBS-518 analogs.