Browsing by Author "Taylor, Michelle"
Now showing 1 - 5 of 5
- Results Per Page
- Sort Options
Item Design and Synthesis of Conformationally Flexible Scaffold as Bitopic Ligands for Potent D(3)-Selective Antagonists(MDPI, 2023-01-09) Kim, Ho Young; Lee, Ji Youn; Hsieh, Chia-Ju; Taylor, Michelle; Luedtke, Robert R.; Mach, Robert H.Previous studies have confirmed that the binding of D(3) receptor antagonists is competitively inhibited by endogenous dopamine despite excellent binding affinity for D(3) receptors. This result urges the development of an alternative scaffold that is capable of competing with dopamine for binding to the D(3) receptor. Herein, an SAR study was conducted on metoclopramide that incorporated a flexible scaffold for interaction with the secondary binding site of the D(3) receptor. The alteration of benzamide substituents and secondary binding fragments with aryl carboxamides resulted in excellent D(3) receptor affinities (Ki = 0.8-13.2 nM) with subtype selectivity to the D(2) receptor ranging from 22- to 180-fold. The beta-arrestin recruitment assay revealed that 21c with 4-(pyridine-4-yl)benzamide can compete well against dopamine with the highest potency (IC(50) = 1.3 nM). Computational studies demonstrated that the high potency of 21c and its analogs was the result of interactions with the secondary binding site of the D(3) receptor. These compounds also displayed minimal effects for other GPCRs except moderate affinity for 5-HT(3) receptors and TSPO. The results of this study revealed that a new class of selective D(3) receptor antagonists should be useful in behavioral pharmacology studies and as lead compounds for PET radiotracer development.Item Design and Synthesis of D(3)R Bitopic Ligands with Flexible Secondary Binding Fragments: Radioligand Binding and Computational Chemistry Studies(MDPI, 2024-01-11) Tian, Gui-Long; Hsieh, Chia-Ju; Taylor, Michelle; Lee, Ji Youn; Luedtke, Robert R.; Mach, Robert H.A series of bitopic ligands based on Fallypride with a flexible secondary binding fragment (SBF) were prepared with the goal of preparing a D(3)R-selective compound. The effect of the flexible linker ((R,S)-trans-2a-d), SBFs ((R,S)-trans-2h-j), and the chirality of orthosteric binding fragments (OBFs) ((S,R)-trans-d, (S,R)-trans-i, (S,S)-trans-d, (S,S)-trans-i, (R,R)-trans-d, and (R,R)-trans-i) were evaluated in in vitro binding assays. Computational chemistry studies revealed that the interaction of the fragment binding to the SBF increased the distance between the pyrrolidine nitrogen and ASP110(3.32) of the D(3)R, thereby reducing the D(3)R affinity to a suboptimal level.Item Evaluation of Substituted N-Phenylpiperazine Analogs as D3 vs. D2 Dopamine Receptor Subtype Selective Ligands(MDPI, 2021-05-26) Lee, Boeun; Taylor, Michelle; Griffin, Suzy A.; McInnis, Tamara; Sumien, Nathalie; Mach, Robert H.; Luedtke, Robert R.N-phenylpiperazine analogs can bind selectively to the D3 versus the D2 dopamine receptor subtype despite the fact that these two D2-like dopamine receptor subtypes exhibit substantial amino acid sequence homology. The binding for a number of these receptor subtype selective compounds was found to be consistent with their ability to bind at the D3 dopamine receptor subtype in a bitopic manner. In this study, a series of the 3-thiophenephenyl and 4-thiazolylphenyl fluoride substituted N-phenylpiperazine analogs were evaluated. Compound 6a was found to bind at the human D3 receptor with nanomolar affinity with substantial D3 vs. D2 binding selectivity (approximately 500-fold). Compound 6a was also tested for activity in two in-vivo assays: (1) a hallucinogenic-dependent head twitch response inhibition assay using DBA/2J mice and (2) an L-dopa-dependent abnormal involuntary movement (AIM) inhibition assay using unilateral 6-hydroxydopamine lesioned (hemiparkinsonian) rats. Compound 6a was found to be active in both assays. This compound could lead to a better understanding of how a bitopic D3 dopamine receptor selective ligand might lead to the development of pharmacotherapeutics for the treatment of levodopa-induced dyskinesia (LID) in patients with Parkinson's disease.Item In vitro characterization of [(125)I]HY-3-24, a selective ligand for the dopamine D3 receptor(Frontiers Media S.A., 2024-04-24) Lee, Ji Youn; Kim, Ho Young; Martorano, Paul; Riad, Aladdin; Taylor, Michelle; Luedtke, Robert R.; Mach, Robert H.INTRODUCTION: Dopamine D3 receptor (D3R) ligands have been studied for the possible treatment of neurological and neuropsychiatric disorders. However, selective D3R radioligands for in vitro binding studies have been challenging to identify due to the high structural similarity between the D2R and D3R. In a prior study, we reported a new conformationally-flexible benzamide scaffold having a high affinity for D3R and excellent selectivity vs. D2R. In the current study, we characterized the in vitro binding properties of a new radioiodinated ligand, [(125)I]HY-3-24. METHODS: In vitro binding studies were conducted in cell lines expressing D3 receptors, rat striatal homogenates, and rat and non-human primate (NHP) brain tissues to measure regional brain distribution of this radioligand. RESULTS: HY-3-24 showed high potency at D3R (K(i) = 0.67 +/- 0.11 nM, IC(50) = 1.5 +/- 0.58 nM) compared to other D2-like dopamine receptor subtypes (D2R K(i) = 86.7 +/- 11.9 nM and D4R K(i) > 1,000). The K(d) (0.34 +/- 0.22 nM) and B(max) (38.91 +/- 2.39 fmol/mg) values of [(125)I]HY-3-24 were determined. In vitro binding studies in rat striatal homogenates using selective D2R and D3R antagonists confirmed the D3R selectivity of [(125)I]HY-3-24. Autoradiography results demonstrated that [(125)I]HY-3-24 specifically binds to D3Rs in the nucleus accumbens, islands of Calleja, and caudate putamen in rat and NHP brain sections. CONCLUSION: These results suggest that [(125)I]HY-3-24 appears to be a novel radioligand that exhibits high affinity binding at D3R, with low binding to other D2-like dopamine receptors. It is anticipated that [(125)I]HY-3-24 can be used as the specific D3R radioligand.Item Neuroprotection by Novel Sigma 1 ligands(2024-03-21) Kinariwala, Kush; Taylor, Michelle; Schreihofer, DerekPurpose: Identify neuroprotective compounds that could potentially be used for conditions like Alzheimer’s disease. Sigma 1 receptors are an intracellular chaperone protein involved in endoplasmic reticulum stress response. Ligands of sigma 1 receptor have been shown to be acutely neuroprotective in a number of in vitro and in vivo brain injury models including stroke and traumatic brain injury. We are examining potential for novel sigma 1 compounds to protect the mouse hippocampal cell line HT22 from oxidative stress and endoplasmic reticulum stress. Among the compounds tested are haloperidol, cutamesine, oxeladin which are neuroprotective in stroke, and additional proprietary ligands derived from substituted haloperidol. Methods: Cell death in HT22 cells was determined using Cell Counting Kit 8. Cells were plated in quadruplicate in 96 well plates for 24 hours in DMEM/10%FBS. Cells were then treated with either hydrogen peroxide (H2O2, 0.5 mM) or Tunicamycin (50 ng/mL) for 24 hours with or without sigma 1 ligands (100 nM). Results: Haloperidol, a mixed sigma 1 and dopamine agonist, dose dependently protected cells from both H2O2 and Tunicamycin induced cell death. However, the sedative actions of Haloperidol make it unsuitable for use against neuroprotective diseases in vivo. We tested 3 sigma 1 compounds without dopamine activity to determine whether sigma 1 activity would protect cells against these insults. Preliminary results suggests that all sigma 1 compounds tested show some efficacy against oxidative stress and ER stress dependent cell death. Average percent live cells after treatment with 0.5 mM hydrogen peroxide was 59.55% (n = 3) and average percent live cells after treatment with 0.5 mM hydrogen peroxide and 100 nM Haloperidol was 101.06% (n = 5). Average percent live cells after treatment with 50 ng/mL Tunicamycin and 100 nM Haloperidol was 85.8% (n = 2). Average percent live cells after treatment with 50 ng/mL Tunicamycin and 100 nM Oxeladin was 49.7% (n = 2). Average percent live cells after treatment with 50 ng/mL Tunicamycin and 100 nM Cutamesine was 74.4% (n = 2). Average percent live cells after treatment with 50 ng/mL Tunicamycin and 100 nM of a novel sigma 1 agonist was 85.7% (n = 2). Ongoing studies are examining the intracellular pathways responsible for neuroprotective effects. Conclusion: Novel sigma 1 agonists may be suitable for protecting neurons against neurodegenerative diseases like Alzheimer’s. In terms of examining mechanisms, we are exploring endoplasmic reticulum stress pathways and more traditional apoptotic signaling.