The COVID-19 (Coronavirus disease-2019) pandemic, caused by the SARS-CoV-2 coronavirus, is a significant threat to public health and the global economy. SARS-CoV-2 is closely related to the more lethal but less transmissible coronaviruses SARS-CoV-1 and MERS-CoV. Here, we have carried out comparative viral-human protein-protein interaction and viral protein localization analysis for all three viruses. Subsequent functional genetic screening identified host factors that functionally impinge on coronavirus proliferation, including Tom70, a mitochondrial chaperone protein that interacts with both SARS-CoV-1 and SARS-CoV-2 Orf9b, an interaction we structurally characterized using cryo-EM. Combining genetically-validated host factors with both COVID-19 patient genetic data and medical billing records identified important molecular mechanisms and potential drug treatments that merit further molecular and clinical study.

To establish the activity of sigma ligands at sigma1 and sigma2 receptor, we chose two tumour cell lines, the human SK-N-SH neuroblastoma and the rat C6 glioma lines, which express sigma2 receptors at a high density and sigma1 receptors in their high-affinity or low-affinity state. We tested the sigma2 receptor agonist PB28 and the sigma2 antagonist AC927, and (+)-pentazocine and NE100 as agonist and antagonist, respectively, at sigma1 receptors, with regard to antiproliferative and cytotoxic effects. In addition, 1,3-di(2-tolyl)guanidine (DTG) and haloperidol were tested as reference compounds displaying nearly equipotent sigma affinity (sigma2>sigma1 and sigma1>sigma2, respectively). In both SK-N-SH and C6 cells, PB28 and NE100 displayed the most potent results both in antiproliferative and cytotoxic assay while AC927 and (+)-pentazocine were inactive in both assays. The cytotoxic and antiproliferative effects of DTG and haloperidol reflected their sigma1 antagonist activity and sigma2 agonist activity. Moreover, our results in the tumour cell lines correlated well with those for sigma2 activity found previously in a functional assay in the guinea-pig bladder. These findings establish a new model for evaluating both sigma2 and sigma1 receptor activity of sigma ligands, which could be useful for developing new ligands having mixed sigma2 agonist/sigma1 antagonist activity as potential antineoplastic agents.

Several 1-cyclohexylpiperazine derivatives related to sigma(2) receptor ligand 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine (33, K(i) = 0.34 nM) were synthesized and tested in radioligand binding assays, to attempt a structure-affinity relationship study. Intermediate alkyl chain length and methoxyl group position on the tetralin nucleus were varied. A few naphthalene analogues were also prepared. High affinities were found in sigma(2) receptor binding for almost all compounds, some of which displayed K(i) values in subnanomolar range, but low sigma(2)/sigma(1) selectivities were found. The highest sigma(2) affinities were displayed by compounds with an intermediate alkyl chain of three (32 and 43) or five methylenes (39 and 46). Quite high sigma(1) receptor affinity was found for compounds with a four-methylene chain; 36 (K(i) = 0.036 nM) and 45 (K(i) = 0.22 nM) displaying good sigma(1)/sigma(2) selectivity (406- and 139-fold, respectively). Moreover, homologues of compound 33 displayed also satisfactory selectivities over dopamine D(2)-like, serotonin 5-HT(3), and adrenergic alpha(1) receptors. These compounds and a few others were tested in the inhibition of the electrically evoked contractions in guinea pig bladder and were demonstrated to be full sigma(2) agonists. The activity values correlated well to the affinity scale (EC(50) in microM range). 33 and related compounds are proposed as a class of potential antineoplastic and PET diagnosis agents.

With the aim of contributing to the development of novel antitumor agents, high-affinity σ2 receptor agonists were developed, with 6,7-dimethoxy-2-[4-[1-(4-fluorophenyl)-1H-indol-3-yl]butyl]-1,2,3,4-tetrahydroisoquinoline (15) and 9-[4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)butyl]-9H-carbazole (25) showing exceptional selectivity for the σ2 subtype. Most of the compounds displayed notable antiproliferative activity in human MCF7 breast adenocarcinoma cells, with similar activity in the corresponding doxorubicin-resistant MCF7adr cell line. Surprisingly, a few compounds, including 25, displayed enhanced activity in MCF7adr cells over parent cells, recalling the phenomenon of collateral sensitivity, which is under study for the treatment of drug-resistant tumors. All of the compounds showed interaction with P-glycoprotein (P-gp), and 15 and 25, with the greatest activity, were able to revert P-gp-mediated resistance and reestablish the antitumor effect of doxorubicin in MCF7adr cells. We therefore identified a series of σ2 receptor agonists endowed with intriguing antitumor properties; these compounds deserve further investigation for the development of alternate strategies against multidrug- resistant cancers.

To find Delta(8)-Delta(7) sterol isomerase (EBP) selective ligands, various arylpiperazines previously studied and structurally related to some sigma receptors ligands were preliminarily screened. Consequently, a novel series of 2- or 2,6-disubstituted (CH(3), CH(3)O, Cl, F) cis- and trans-4-(4-aryl)cyclohexyl-1-(2-pyridyl)piperazines was developed. Radioreceptor binding assays evidenced cis-19, cis-30 and cis-33 as new ligands with nanomolar affinity toward EBP site and a good selectivity relative to EBP-related sigma receptors. The most selective 2,6-dimethoxy derivative (cis-33) demonstrated the highest potency (EC(50) = 12.9 microM) and efficacy (70%) in inhibiting proliferation of human prostate cancer PC-3 cell line. Among the reference compounds, sigma(2) agonist 36 (PB28) reached the maximum efficacy (100%), suggesting the contribution of the sigma(2) receptor to the antiproliferative activity. This novel class of EBP inhibitors represents a valuable tool for investigating the last steps of cholesterol biosynthesis and related pathologies, as well as a starting point for developing new anticancer drugs.

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Fluorescent derivatives of σ2 high affinity ligand 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine 1 (PB28) were synthesized. NBD or Dansyl fluorescent tags were connected through a 5- or 6-atoms linker in two diverse positions of 1 structure. Good σ2 affinities were obtained when the fluorescent tag was linked to 5-methoxytetralin nucleus replacing the methyl function. NBD-bearing compound 16 displayed high σ2 affinity (Ki = 10.8 nM) and optimal fluorescent properties. Its uptake in pancreatic tumor cells was evaluated by flow cytometry showing that it partially occurs through endocytosis. In proliferating cells the uptake was higher supporting that σ2 receptors are markers of cell proliferation and that the higher is the proliferation, the stronger is the antiproliferative effect of σ2 agonists. Colocalization of 16 with subcellular organelles was studied by confocal microscopy: the greatest was in endoplasmic reticulum and lysosomes. Fluorescent σ2 ligands show their potential in clarifying the mechanisms of action of σ2 receptors.

1-Cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine 1 (PB28) represents an excellent lead candidate for therapeutic and/or diagnostic applications in oncology. However, because its utility is limited by its relatively high degree of lipophilicity, novel analogues of 1 with reduced lipophilic character were designed by substituting methylene groups with more polar functional groups in the propylene linker and at the tetralin C4 position. For the chiral analogues, separate enantiomers exhibited substantial and roughly equal affinities within a given receptor subtype, with the greatest difference observed for compound 9 at σ(1) (7.5-fold; (-)-(S)-9 K(i) = 94.6 nM, (+)-(R)-9 K(i) = 12.6 nM). Compound (-)-(S)-9 was also found to be the most σ(2)-selective agent (σ(2) K(i) = 5.92 nM), to possess a lipophilicity consistent with entry into tumor cells (log D(7.4) = 2.38), and to show minimal antiproliferative activity. However, (-)-(S)-9 exhibited moderate activity (EC(50) = 8.1 μM) at the P-gp efflux pump.