Structure–Activity Relationship Study of <i>N</i>⁶-(2-(4-(1<i>H</i>-Indol-5-yl)piperazin-1-yl)ethyl)-<i>N</i>⁶-propyl-4,5,6,7-tetrahydrobenzo[<i>d</i>]thiazole-2,6-diamine Analogues: Development of Highly Selective D3 Dopamine Receptor Agonists along with a Highly Potent D2/D3 Agonist and Their Pharmacological Characterization

In our effort to develop multifunctional drugs against Parkinson’s disease, a structure–activity-relationship study was carried out based on our hybrid molecular template targeting D2/D3 receptors. Competitive binding with [³H]­spiroperidol was used to evaluate affinity (<i>K</i>_i) of test compounds. Functional activity of selected compounds in stimulating [³⁵S]­GTPγS binding was assessed in CHO cells expressing either human D2 or D3 receptors. Our results demonstrated development of highly selective compounds for D3 receptor (for (−)-<b>40</b> <i>K</i>_i, D3 = 1.84 nM, D2/D3 = 583.2; for (−)-<b>45</b> <i>K</i>_i, D3 = 1.09 nM, D2/D3 = 827.5). Functional data identified (−)-<b>40</b> (EC₅₀, D2 = 114 nM, D3 = 0.26 nM, D2/D3 = 438) as one of the highest D3 selective agonists known to date. In addition, high affinity, nonselective D3 agonist (−)-<b>19</b> (EC₅₀, D2 = 2.96 nM and D3 = 1.26 nM) was also developed. Lead compounds with antioxidant activity were evaluated using an in vivo PD animal model

Development of a Highly Potent D₂/D₃ Agonist and a Partial Agonist from Structure–Activity Relationship Study of <i>N</i>⁶‑(2-(4-(1<i>H</i>‑Indol-5-yl)piperazin-1-yl)ethyl)‑<i>N</i>⁶‑propyl-4,5,6,7-tetrahydrobenzo[<i>d</i>]thiazole-2,6-diamine Analogues: Implication in the Treatment of Parkinson’s Disease

Our structure–activity relationship studies with <i>N</i>⁶-(2-(4-(1<i>H</i>-indol-5-yl)­piperazin-1-yl)­ethyl)-<i>N</i>⁶-propyl-4,5,6,7-tetrahydrobenzo­[<i>d</i>]­thiazole-2,6-diamine derivatives led to development of a lead compound (−)-<b>21a</b> which exhibited very high affinity (<i>K</i>_i, D₂ = 16.4 nM, D₃ = 1.15 nM) and full agonist activity (EC₅₀ (GTPγS); D₂ = 3.23 and D₃ = 1.41 nM) at both D₂ and D₃ receptors. A partial agonist molecule (−)-<b>34</b> (EC₅₀ (GTPγS); D₂ = 21.6 (<i>E</i>_max = 27%) and D₃ = 10.9 nM) was also identified. In a Parkinson’s disease (PD) animal model, (−)-<b>21a</b> was highly efficacious in reversing hypolocomotion in reserpinized rats with a long duration of action, indicating its potential as an anti-PD drug. Compound (−)-<b>34</b> was also able to elevate locomotor activity in the above PD animal model significantly, implying its potential application in PD therapy. Furthermore, (−)-<b>21a</b> was shown to be neuroprotective in protecting neuronal PC12 from toxicity of 6-OHDA. This report, therefore, underpins the notion that a multifunctional drug like (−)-<b>21a</b> might have the potential not only to ameliorate motor dysfunction in PD patients but also to modify disease progression by protecting DA neurons from progressive degeneration

Novel Bivalent Ligands for D2/D3 Dopamine Receptors: Significant Cooperative Gain in D2 Affinity and Potency

This report describes development of a series of novel bivalent molecules with a pharmacophore derived from the D2/D3 agonist 5-OH-DPAT. The spacer length in the bivalent compounds had a pronounced influence on affinity for D2 receptors. A 23-fold increase of D2 affinity was observed at a spacer length of 9 or 10 (compounds <b>11d</b> and <b>14b</b>) as compared to monovalent 5-OH-DPAT (<i>K</i>_i; 2.5 and 2.0 vs 59 nM for <b>11d</b> and <b>14b</b> vs 5-OH-DPAT, respectively). The functional potency of <b>11d</b> and <b>14b</b> indicated a 24- and 94-fold increase in potency at the D2 receptor as compared to 5-OH-DPAT (EC₅₀; 1.7 and 0.44 vs 41 nM for <b>11d</b> and <b>14b</b> vs 5-OH-DPAT, respectively). These are the most potent bivalent agonists for the D2 receptor known to date. This synergism is consonant with cooperative interaction at the two orthosteric binding sites in the homodimeric receptor

Development of a Highly Potent D₂/D₃ Agonist and a Partial Agonist from Structure–Activity Relationship Study of <i>N</i>⁶‑(2-(4-(1<i>H</i>‑Indol-5-yl)piperazin-1-yl)ethyl)‑<i>N</i>⁶‑propyl-4,5,6,7-tetrahydrobenzo[<i>d</i>]thiazole-2,6-diamine Analogues: Implication in the Treatment of Parkinson’s Disease

Our structure–activity relationship studies with <i>N</i>⁶-(2-(4-(1<i>H</i>-indol-5-yl)­piperazin-1-yl)­ethyl)-<i>N</i>⁶-propyl-4,5,6,7-tetrahydrobenzo­[<i>d</i>]­thiazole-2,6-diamine derivatives led to development of a lead compound (−)-<b>21a</b> which exhibited very high affinity (<i>K</i>_i, D₂ = 16.4 nM, D₃ = 1.15 nM) and full agonist activity (EC₅₀ (GTPγS); D₂ = 3.23 and D₃ = 1.41 nM) at both D₂ and D₃ receptors. A partial agonist molecule (−)-<b>34</b> (EC₅₀ (GTPγS); D₂ = 21.6 (<i>E</i>_max = 27%) and D₃ = 10.9 nM) was also identified. In a Parkinson’s disease (PD) animal model, (−)-<b>21a</b> was highly efficacious in reversing hypolocomotion in reserpinized rats with a long duration of action, indicating its potential as an anti-PD drug. Compound (−)-<b>34</b> was also able to elevate locomotor activity in the above PD animal model significantly, implying its potential application in PD therapy. Furthermore, (−)-<b>21a</b> was shown to be neuroprotective in protecting neuronal PC12 from toxicity of 6-OHDA. This report, therefore, underpins the notion that a multifunctional drug like (−)-<b>21a</b> might have the potential not only to ameliorate motor dysfunction in PD patients but also to modify disease progression by protecting DA neurons from progressive degeneration

A Novel Iron(II) Preferring Dopamine Agonist Chelator as Potential Symptomatic and Neuroprotective Therapeutic Agent for Parkinson’s Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder, and development of disease-modifying treatment is still an unmet medical need. Considering the implication of free iron­(II) in PD, we report here the design and characterization of a novel hybrid iron chelator, (−)-<b>12</b> (D-607) as a multitarget-directed ligand against PD. Binding and functional assays at dopamine D₂/D₃ receptors indicate potent agonist activity of (−)-<b>12</b>. The molecule displayed an efficient preferential iron­(II) chelation properties along with potent in vivo activity in a reserpinized PD animal model. The compound also rescued PC12 cells from toxicity induced by iron delivered intracellularly in a dose-dependent manner. However, Fe³⁺ selective dopamine agonist 1 and a well-known antiparkinsonian drug pramipexole produced little to no neuroprotection effect under the same experimental condition. These observations strongly suggest that (−)-<b>12</b> should be a promising multifunctional lead molecule for a viable symptomatic and disease modifying therapy of PD

A Novel Iron(II) Preferring Dopamine Agonist Chelator as Potential Symptomatic and Neuroprotective Therapeutic Agent for Parkinson’s Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder, and development of disease-modifying treatment is still an unmet medical need. Considering the implication of free iron­(II) in PD, we report here the design and characterization of a novel hybrid iron chelator, (−)-<b>12</b> (D-607) as a multitarget-directed ligand against PD. Binding and functional assays at dopamine D₂/D₃ receptors indicate potent agonist activity of (−)-<b>12</b>. The molecule displayed an efficient preferential iron­(II) chelation properties along with potent in vivo activity in a reserpinized PD animal model. The compound also rescued PC12 cells from toxicity induced by iron delivered intracellularly in a dose-dependent manner. However, Fe³⁺ selective dopamine agonist 1 and a well-known antiparkinsonian drug pramipexole produced little to no neuroprotection effect under the same experimental condition. These observations strongly suggest that (−)-<b>12</b> should be a promising multifunctional lead molecule for a viable symptomatic and disease modifying therapy of PD

Pharmacological and Behavioral Characterization of D-473, an Orally Active Triple Reuptake Inhibitor Targeting Dopamine, Serotonin and Norepinephrine Transporters

<div><p>Major depressive disorder (MDD) is a debilitating disease affecting a wide cross section of people around the world. The current therapy for depression is less than adequate and there is a considerable unmet need for more efficacious treatment. Dopamine has been shown to play a significant role in depression including production of anhedonia which has been one of the untreated symptoms in MDD. It has been hypothesized that drugs acting at all three monoamine transporters including dopamine transporter should provide more efficacious antidepressants activity. This has led to the development of triple reuptake inhibitor D-473 which is a novel pyran based molecule and interacts with all three monoamine transporters. The monoamine uptake inhibition activity in the cloned human transporters expressed in HEK-293 cells (70.4, 9.18 and 39.7 for DAT, SERT and NET, respectively) indicates a serotonin preferring triple reuptake inhibition profile for this drug. The drug D-473 exhibited good brain penetration and produced efficacious activity in rat forced swim test under oral administration. The optimal efficacy dose did not produce any locomotor activation. Microdialysis experiment demonstrated that systemic administration of D-473 elevated extracellular level of the three monoamines DA, 5-HT, and NE efficaciously in the dorsal lateral striatum (DLS) and the medial prefrontal cortex (mPFC) area, indicating in vivo blockade of all three monoamine transporters by D-473. Thus, the current biological data from D-473 indicate potent antidepressant activity of the molecule.</p></div

Time dependent effect of administration of D-473 (10 mg/kg, i.p) at time 0 (shown by arrow) on extracellular level of DOPAC (Ο), HVA (▪), and 5HIAA (Δ); a) in rats Prefrontal cortex; and b) Dorso lateral striatum.

<p>Results are expressed as percent baseline with baseline values all averaging 100%. Each point represents mean ± standard error (SE) of the percentage of baseline from five rats. Statistical analysis was performed by t-test analysis of every point relative to baseline values (i.e. 100%) using Prism 6 (Graphpad Software Inc, La Jolla, CA). * (DOPAC) p<0.02-0.0004. # (HVA) p<0.02–0.001. P values <0.05 were considered to be statistically significant.</p

Inhibition of [³H]monoamine uptake by D-473 and D-142 in cells heterologously expressing hDAT, hSERT, or hNET (▪-, D-473; Δ-, D-142).

<p>A) Monoamine uptake by DAT, B) Monoamine uptake by SERT, and C) Monoamine uptake by NET was assessed as described in Methods and plotted according to the Logistics equation in the Origin fitting software (see Reith et al., 2012). Points shown are those obtained in a representative experiment, performed in triplicate, which was replicated 8–16 times.</p

Effect of sub-chronic oral administration of vehicle and D-473 on the duration of immobility in the forced swimming test in rats.

<p>One way ANOVA analysis demonstrates significant effect among treatments: F (4, 24) = 10.33 (P<0.0001). Dunnett’s analysis showed that the effect of <b>D-473</b> at three doses (10, 25 and 50 mg/kg) on immobility was statistically significant different compared to vehicle (P<0.01).</p