High-Resolution Structures and Orientations of Antimicrobial Peptides Piscidin 1 and Piscidin 3 in Fluid Bilayers Reveal Tilting, Kinking, and Bilayer Immersion

While antimicrobial peptides (AMPs) have been widely investigated as potential therapeutics, high-resolution structures obtained under biologically relevant conditions are lacking. Here, the high-resolution structures of the homologous 22-residue long AMPs piscidin 1 (p1) and piscidin 3 (p3) are determined in fluid-phase 3:1 phosphatidylcholine/phosphatidylglycerol (PC/PG) and 1:1 phosphatidylethanolamine/phosphatidylglycerol (PE/PG) bilayers to identify molecular features important for membrane destabilization in bacterial cell membrane mimics. Structural refinement of 1H–15N dipolar couplings and 15N chemical shifts measured by oriented sample solid-state NMR and all-atom molecular dynamics (MD) simulations provide structural and orientational information of high precision and accuracy about these interfacially bound α-helical peptides. The tilt of the helical axis, τ, is between 83° and 93° with respect to the bilayer normal for all systems and analysis methods. The average azimuthal rotation, ρ, is 235°, which results in burial of hydrophobic residues in the bilayer. The refined NMR and MD structures reveal a slight kink at G13 that delineates two helical segments characterized by a small difference in their τ angles (<10°) and significant difference in their ρ angles (∼25°). Remarkably, the kink, at the end of a G(X)4G motif highly conserved among members of the piscidin family, allows p1 and p3 to adopt ρ angles that maximize their hydrophobic moments. Two structural features differentiate the more potent p1 from p3: p1 has a larger ρ angle and less N-terminal fraying. The peptides have comparable depths of insertion in PC/PG, but p3 is 1.2 Å more deeply inserted than p1 in PE/PG. In contrast to the ideal α-helical structures typically assumed in mechanistic models of AMPs, p1 and p3 adopt disrupted α-helical backbones that correct for differences in the amphipathicity of their N- and C-ends, and their centers of mass lie ∼1.2–3.6 Å below the plane defined by the C2 atoms of the lipid acyl chains

High Affinity Dopamine D₃ Receptor (D₃R)-Selective Antagonists Attenuate Heroin Self-Administration in Wild-Type but not D₃R Knockout Mice

The dopamine D₃ receptor (D₃R) is a promising target for the development of pharmacotherapeutics to treat substance use disorders. Several D₃R-selective antagonists are effective in animal models of drug abuse, especially in models of relapse. Nevertheless, poor bioavailability, metabolic instability, and/or predicted toxicity have impeded success in translating these drug candidates to clinical use. Herein, we report a series of D₃R-selective 4-phenylpiperazines with improved metabolic stability. A subset of these compounds was evaluated for D₃R functional efficacy and off-target binding at selected 5-HT receptor subtypes, where significant overlap in SAR with D₃R has been observed. Several high affinity D₃R antagonists, including compounds <b>16</b> (<i>K_i</i> = 0.12 nM) and <b>32</b> (<i>K_i</i> = 0.35 nM), showed improved metabolic stability compared to the parent compound, PG648 (<b>6</b>). Notably, <b>16</b> and the classic D₃R antagonist SB277011A (<b>2</b>) were effective in reducing self-administration of heroin in wild-type but not D₃R knockout mice

High Affinity Dopamine D₃ Receptor (D₃R)-Selective Antagonists Attenuate Heroin Self-Administration in Wild-Type but not D₃R Knockout Mice

The dopamine D₃ receptor (D₃R) is a promising target for the development of pharmacotherapeutics to treat substance use disorders. Several D₃R-selective antagonists are effective in animal models of drug abuse, especially in models of relapse. Nevertheless, poor bioavailability, metabolic instability, and/or predicted toxicity have impeded success in translating these drug candidates to clinical use. Herein, we report a series of D₃R-selective 4-phenylpiperazines with improved metabolic stability. A subset of these compounds was evaluated for D₃R functional efficacy and off-target binding at selected 5-HT receptor subtypes, where significant overlap in SAR with D₃R has been observed. Several high affinity D₃R antagonists, including compounds <b>16</b> (<i>K_i</i> = 0.12 nM) and <b>32</b> (<i>K_i</i> = 0.35 nM), showed improved metabolic stability compared to the parent compound, PG648 (<b>6</b>). Notably, <b>16</b> and the classic D₃R antagonist SB277011A (<b>2</b>) were effective in reducing self-administration of heroin in wild-type but not D₃R knockout mice

High Affinity Dopamine D₃ Receptor (D₃R)-Selective Antagonists Attenuate Heroin Self-Administration in Wild-Type but not D₃R Knockout Mice

The dopamine D₃ receptor (D₃R) is a promising target for the development of pharmacotherapeutics to treat substance use disorders. Several D₃R-selective antagonists are effective in animal models of drug abuse, especially in models of relapse. Nevertheless, poor bioavailability, metabolic instability, and/or predicted toxicity have impeded success in translating these drug candidates to clinical use. Herein, we report a series of D₃R-selective 4-phenylpiperazines with improved metabolic stability. A subset of these compounds was evaluated for D₃R functional efficacy and off-target binding at selected 5-HT receptor subtypes, where significant overlap in SAR with D₃R has been observed. Several high affinity D₃R antagonists, including compounds <b>16</b> (<i>K_i</i> = 0.12 nM) and <b>32</b> (<i>K_i</i> = 0.35 nM), showed improved metabolic stability compared to the parent compound, PG648 (<b>6</b>). Notably, <b>16</b> and the classic D₃R antagonist SB277011A (<b>2</b>) were effective in reducing self-administration of heroin in wild-type but not D₃R knockout mice

Novel and High Affinity 2‑[(Diphenylmethyl)sulfinyl]acetamide (Modafinil) Analogues as Atypical Dopamine Transporter Inhibitors

The development of pharmacotherapeutic treatments of psychostimulant abuse has remained a challenge, despite significant efforts made toward relevant mechanistic targets, such as the dopamine transporter (DAT). The atypical DAT inhibitors have received attention due to their promising pharmacological profiles in animal models of cocaine and methamphetamine abuse. Herein, we report a series of modafinil analogues that have an atypical DAT inhibitor profile. We extended SAR by chemically manipulating the oxidation states of the sulfoxide and the amide functional groups, halogenating the phenyl rings, and/or functionalizing the terminal nitrogen with substituted piperazines, resulting in several novel leads such as <b>11b</b>, which demonstrated high DAT affinity (<i>K</i>_i = 2.5 nM) and selectivity without producing concomitant locomotor stimulation in mice, as compared to cocaine. These results are consistent with an atypical DAT inhibitor profile and suggest that <b>11b</b> may be a potential lead for development as a psychostimulant abuse medication

Novel and High Affinity 2‑[(Diphenylmethyl)sulfinyl]acetamide (Modafinil) Analogues as Atypical Dopamine Transporter Inhibitors

The development of pharmacotherapeutic treatments of psychostimulant abuse has remained a challenge, despite significant efforts made toward relevant mechanistic targets, such as the dopamine transporter (DAT). The atypical DAT inhibitors have received attention due to their promising pharmacological profiles in animal models of cocaine and methamphetamine abuse. Herein, we report a series of modafinil analogues that have an atypical DAT inhibitor profile. We extended SAR by chemically manipulating the oxidation states of the sulfoxide and the amide functional groups, halogenating the phenyl rings, and/or functionalizing the terminal nitrogen with substituted piperazines, resulting in several novel leads such as <b>11b</b>, which demonstrated high DAT affinity (<i>K</i>_i = 2.5 nM) and selectivity without producing concomitant locomotor stimulation in mice, as compared to cocaine. These results are consistent with an atypical DAT inhibitor profile and suggest that <b>11b</b> may be a potential lead for development as a psychostimulant abuse medication

Novel Analogues of (<i>R</i>)‑5-(Methylamino)-5,6-dihydro‑4<i>H</i>‑imidazo[4,5,1-<i>ij</i>]quinolin-2(1<i>H</i>)‑one (Sumanirole) Provide Clues to Dopamine D₂/D₃ Receptor Agonist Selectivity

Novel 1-, 5-, and 8-substituted analogues of sumanirole (<b>1</b>), a dopamine D₂/D₃ receptor (D₂R/D₃R) agonist, were synthesized. Binding affinities at both D₂R and D₃R were higher when determined in competition with the agonist radioligand [³H]­7-hydroxy-<i>N</i>,<i>N</i>-dipropyl-2-aminotetralin (7-OH-DPAT) than with the antagonist radioligand [³H]<i>N</i>-methylspiperone. Although <b>1</b> was confirmed as a D₂R-preferential agonist, its selectivity in binding and functional studies was lower than previously reported. All analogues were determined to be D₂R/D₃R agonists in both G_oBRET and mitogenesis functional assays. Loss of efficacy was detected for the <i>N</i>-1-substituted analogues at D₃R. In contrast, the <i>N</i>-5-alkyl-substituted analogues, and notably the <i>n</i>-butyl-arylamides (<b>22b</b> and <b>22c</b>), all showed improved affinity at D₂R over <b>1</b> with neither a loss of efficacy nor an increase in selectivity. Computational modeling provided a structural basis for the D₂R selectivity of <b>1</b>, illustrating how subtle differences in the highly homologous orthosteric binding site (OBS) differentially affect D₂R/D₃R affinity and functional efficacy