Currently, the contribution of trace amine-associated receptors (TAARs) to breast cancer (BC) is recognized, but their associations with various pathological characteristics are not yet understood. There is accumulated transcriptomic data for BC tumors, which are represented in publicly accessible databases. We estimated TAARs’ (including TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9) associations with BC stage, grade, and molecular subtypes in these data and identified that the expression of all TAARs was associated with more unfavorable cancer subtypes, including basal-like and HER2-positive tumors. Also, the significant upregulation of all TAARs was demonstrated in circulating tumor cells compared to the metastatic lesions. Considering that co-expressed genes are more likely to be involved in the same biologic processes, we analyzed genes that are co-expressed with TAARs in BC. These gene sets were enriched with the genes of the olfactory transduction pathway and neuroactive ligand–receptor interaction participants. TAARs are co-expressed with G-protein-coupled receptors of monoamine neurotransmitters including dopamine, norepinephrine, and serotonin as well as with other neuroactive ligand-specific receptors. Since TAAR1 is able to modulate the activity of monoamine receptors that are involved in the regulation of BC growth, TAAR1 and potentially other TAARs may be regarded as prospective therapeutic targets for breast cancer.

Starting from a screening hit, a set of analogs was synthesized based on a 4-(2-aminoethyl)piperidine core not associated previously with trace amine-associated receptor 1 (TAAR1) modulation in the literature. Several structure–activity relationship generalizations have been drawn from the observed data, some of which were corroborated by molecular modeling against the crystal structure of TAAR1. The four most active compounds (EC₅₀ for TAAR1 agonistic activity ranging from 0.033 to 0.112 μM) were nominated for evaluation in vivo. The dopamine transporter knockout (DAT-KO) rat model of dopamine-dependent hyperlocomotion was used to evaluate compounds’ efficacy in vivo. Out of four compounds, only one compound (AP163) displayed a statistically significant and dose-dependent reduction in hyperlocomotion in DAT-KO rats. As such, compound AP163 represents a viable lead for further preclinical characterization as a potential novel treatment option for disorders associated with increased dopaminergic function, such as schizophrenia.

The search for novel effective TAAR1 ligands continues to draw great attention due to the wide range of pharmacological applications related to TAAR1 targeting. Herein, molecular docking studies of known TAAR1 ligands, characterized by an oxazoline core, have been performed in order to identify novel promising chemo-types for the discovery of more active TAAR1 agonists. In particular, the oxazoline-based compound S18616 has been taken as a reference compound for the computational study, leading to the development of quite flat and conformationally locked ligands. The choice of a “Y-shape” conformation was suggested for the design of TAAR1 ligands, interacting with the protein cavity delimited by ASP103 and aromatic residues such as PHE186, PHE195, PHE268, and PHE267. The obtained results allowed us to preliminary in silico screen an in-house series of pyrimidinone-benzimidazoles (1a–10a) as a novel scaffold to target TAAR1. Combined ligand-based (LBCM) and structure based (SBCM) computational methods suggested the biological evaluation of compounds 1a–10a, leading to the identification of derivatives 1a–3a (hTAAR1 EC₅₀ = 526.3–657.4 nM) as promising novel TAAR1 agonists.

Trace amine-associated receptor 1 (TAAR1) is an attractive target for the design of innovative drugs to be applied in diverse pharmacological settings. Due to a non-negligible structural similarity with endogenous ligands, most of the agonists developed so far resulted in being affected by a low selectivity for TAAR1 with respect to other monoaminergic G protein-coupled receptors, like the adrenoreceptors. This study utilized comparative molecular docking studies and quantitative–structure activity relationship (QSAR) analyses to unveil key structural differences between TAAR1 and alpha2-adrenoreceptor (α₂-ADR), with the aim to design novel TAAR1 agonists characterized by a higher selectivity profile and reduced off-target effects. While the presence of hydrophobic motives is encouraged towards both the two receptors, the introduction of polar/positively charged groups and the ligand conformation deeply affect the TAAR1 or α₂-ADR putative selectivity. These computational methods allowed the identification of the α₂A-ADR agonist guanfacine as an attractive TAAR1-targeting lead compound, demonstrating nanomolar activity in vitro. In vivo exploration of the efficacy of guanfacine showed that it is able to decrease the locomotor activity of dopamine transporter knockout (DAT-KO) rats. Therefore, guanfacine can be considered as an interesting template molecule worthy of structural optimization. The dual activity of guanfacine on both α₂-ADR and TAAR1 signaling and the related crosstalk between the two pathways will deserve more in-depth investigation.

Altered mitochondrial function is implicated in disorders characterized by prefrontal cortex activation deficits, including attention deficit hyperactivity disorder (ADHD). The expression of mitochondrial DNA-coded respiratory chain complex I genes (ND1–ND6) in the prefrontal cortex of ADHD animal models was estimated in the present study. ND gene expression was assessed in two publicly available datasets: GSE117357 (Adgrl3 knockout mice) and GSE173926 (MYT1L heterozygous knockout mice). Additionally, we measured NDs gene expression via qPCR in dopamine transporter knockout (DAT-KO) rats and their heterozygous (DAT-Het) littermates. Transcriptomic analysis revealed consistent ND1–ND6 expression profiles across both datasets, and co-expression among ND genes was significantly enhanced in ADHD models compared to wild-type controls. Whole-transcriptome analysis identified associations between ND3 and ND4L expression and genes involved in neural tissue-specific processes, exclusively in ADHD models. In DAT-KO and DAT-Het rats, NDs gene co-expression increased. Furthermore, in DAT-Het rats, which do not exhibit hyperactivity, the upregulation of ND4L expression relative to wild-type littermates was demonstrated. The observed changes in mitochondrial complex I gene co-expression in ADHD models suggest mitochondria may serve as a prospective target for adjuvant therapy. These findings highlight the need for further investigation into mitochondrial contributions to ADHD pathophysiology.

Objective: Triple-negative breast cancer (TNBC) accounts for 10–20% of all invasive breast cancers characterizing by mostly poor outcome and resistance to therapies compared to other breast cancer subtypes. New class monoamine receptors, trace amine-associated ones (TAARs) are known to be associated with overall survival of breast cancer patients, and, for instance, stimulation of trace amine-associated receptor type 1 (TAAR1) in ovarian cancer cell lines with 3-iodothyronamine reduces cell viability in vitro. In this regard, we studied the effects of TAAR1 agonist tyramine hydrochloride and TAAR1 antagonist EPPTB (N-(3-ethoxyphenyl)-4-pyrrolidin-1-yl-3-trifluoromethyl-benzamide) on in vitro proliferation of TNBC-derived cell line BT-20. Methods: To measure in vitro cell proliferation, sulforhodamine B staining assay in 96-well plates was applied. The expression of pro-apoptotic factors BAK and BAX, and anti-apoptotic Bcl2 mRNAs was estimated by qPCR. Results and Discussion: TAAR1 agonist tyramine hydrochloride showed no antiproliferative action at all. In its turn TAAR1 antagonist EPPTB had a weak cytostatic effect (IC₅₀ = 647.2 µM). However, in in vitro combination chemotherapy experiments, EPPTB did not augment the cytostatic effect of classic chemotherapeutic agents 5-fluorouracil and doxorubicin hydrochloride. Treatment of BT-20 cells with IC₅₀ and IC₈₀ of EPPTB did not result in significant changes of BAK and BAX gene expression; however, Bcl2 expression was suppressed by IC₈₀, which may indicate the compound’s slight anti-apoptotic effect. Conclusion: We are able to state the lack of in vitro antiproliferative action of TAAR1 ligands tyramine hydrochloride and EPPTB on triple-negative breast cancer-derived cell line BT-20.