Extrahelical Binding Site for a 1H-Imidazo[4,5-c]quinolin-4-amine A3 Adenosine Receptor Positive Allosteric Modulator on Helix 8 and Distal Portions of Transmembrane Domains 1 and 7.

This study describes the localization and computational prediction of a binding site for the A3 adenosine receptor (A3AR) positive allosteric modulator 2-cyclohexyl-1H-imidazo[4,5-c]quinolin-4-(3,4-dichlorophenyl)amine (LUF6000). The work reveals an extrahelical lipid-facing binding pocket disparate from the orthosteric binding site that encompasses transmembrane domain (TMD) 1, TMD7, and Helix (H) 8, which was predicted by molecular modeling and validated by mutagenesis. According to the model, the nearly planar 1H-imidazo[4,5-c]quinolinamine ring system lies parallel to the transmembrane segments, inserted into an aromatic cage formed by π-π stacking interactions with the side chains of Y2847.55 in TMD7 and Y2938.54 in H8 and by π-NH bonding between Y2847.55 and the exocyclic amine. The 2-cyclohexyl group is positioned "upward" within a small hydrophobic subpocket created by residues in TMDs 1 and 7, while the 3,4-dichlorophenyl group extends toward the lipid interface. An H-bond between the N-1 amine of the heterocycle and the carbonyl of G291.49 further stabilizes the interaction. Molecular dynamics simulations predicted two metastable intermediates, one resembling a pose determined by molecular docking and a second involving transient interactions with Y2938.54; in simulations, each of these intermediates converges into the final bound state. Structure-activity-relationships for replacement of either of the identified exocyclic or endocyclic amines with heteroatoms lacking H-bond donating ability were consistent with the hypothetical pose. Thus, we characterized an allosteric pocket for 1H-imidazo[4,5-c]quinolin-4-amines that is consistent with data generated by orthogonal methods, which will aid in the rational design of improved A3AR positive allosteric modulators. SIGNIFICANCE STATEMENT: Orthosteric A3AR agonists have advanced in clinical trials for inflammatory conditions, liver diseases, and cancer. Thus, the clinical appeal of selective receptor activation could extend to allosteric enhancers, which would induce site- and time-specific activation in the affected tissue. By identifying the allosteric site for known positive allosteric modulators, structure-based drug discovery modalities can be enabled to enhance the pharmacological properties of the 1H-imidazo[4,5-c]quinolin-4-amine class of A3AR positive allosteric modulators.

Synthesis of fluorinated triphenylphosphonium analogs that improve cancer cell selectivity and in vivo detection.

Triphenylphosphonium (TPP+) compounds like mito-metformin (MMe) target cancer cells by exploiting their hyperpolarized mitochondrial membrane potential. Here, we present a protocol for synthesizing TPP+ analogs with selectivity for mammalian cancer cells, reduced toxicity, and quantifiability using fluorine-19 nuclear magnetic resonance (19F-NMR). We describe steps for treating mammalian cells with mitochondria-targeted compounds, treating and preparing mouse tissue with these compounds, and 19F-NMR detection of MMe analogs in cells and tissue. TPP+-conjugated metformin analogs include para-methoxy (pMeO-MMe) and para-trifluoromethyl MMe (pCF3-MMe) and meta-trifluoromethyl MMe (mCF3-MMe).

Sulfenylation links oxidative stress to protein disulfide isomerase oxidase activity and thrombus formation.

BACKGROUND: Oxidative stress contributes to thrombosis in atherosclerosis, inflammation, infection, aging, and malignancy. Oxidant-induced cysteine modifications, including sulfenylation, can act as a redox-sensitive switch that controls protein function. Protein disulfide isomerase (PDI) is a prothrombotic enzyme with exquisitely redox-sensitive active-site cysteines. OBJECTIVES: We hypothesized that PDI is sulfenylated during oxidative stress, contributing to the prothrombotic potential of PDI. METHODS: Biochemical and enzymatic assays using purified proteins, platelet and endothelial cell assays, and in vivo murine thrombosis studies were used to evaluate the role of oxidative stress in PDI sulfenylation and prothrombotic activity. RESULTS: PDI exposure to oxidants resulted in the loss of PDI reductase activity and simultaneously promoted sulfenylated PDI generation. Following exposure to oxidants, sulfenylated PDI spontaneously converted to disulfided PDI. PDI oxidized in this manner was able to transfer disulfides to protein substrates. Inhibition of sulfenylation impaired disulfide formation by oxidants, indicating that sulfenylation is an intermediate during PDI oxidation. Agonist-induced activation of platelets and endothelium resulted in the release of sulfenylated PDI. PDI was also sulfenylated by oxidized low-density lipoprotein (oxLDL). In an in vivo model of thrombus formation, oxLDL markedly promoted platelet accumulation following an arteriolar injury. PDI oxidoreductase inhibition blocked oxLDL-mediated augmentation of thrombosis. CONCLUSION: PDI sulfenylation is a critical posttranslational modification that is an intermediate during disulfide PDI formation in the setting of oxidative stress. Oxidants generated by vascular cells during activation promote PDI sulfenylation, and interference with PDI during oxidative stress impairs thrombus formation.

Harnessing the Noncanonical Keap1-Nrf2 Pathway for Human Cytomegalovirus Control.

Host-derived cellular pathways can provide an unfavorable environment for virus replication. These pathways have been a subject of interest for herpesviruses, including the betaherpesvirus human cytomegalovirus (HCMV). Here, we demonstrate that a compound, ARP101, induces the noncanonical sequestosome 1 (SQSTM1)/p62-Keap1-Nrf2 pathway for HCMV suppression. ARP101 increased the levels of both LC3 II and SQSTM1/p62 and induced phosphorylation of p62 at the C-terminal domain, resulting in its increased affinity for Keap1. ARP101 treatment resulted in Nrf2 stabilization and translocation into the nucleus, binding to specific promoter sites and transcription of antioxidant enzymes under the antioxidant response element (ARE), and HCMV suppression. Knockdown of Nrf2 recovered HCMV replication following ARP101 treatment, indicating the role of the Keap1-Nrf2 axis in HCMV inhibition by ARP101. SQSTM1/p62 phosphorylation was not modulated by the mTOR kinase or casein kinase 1 or 2, indicating ARP101 engages other kinases. Together, the data uncover a novel antiviral strategy for SQSTM1/p62 through the noncanonical Keap1-Nrf2 axis. This pathway could be further exploited, including the identification of the responsible kinases, to define the biological events during HCMV replication. IMPORTANCE Antiviral treatment for human cytomegalovirus (HCMV) is limited and suffers from the selection of drug-resistant viruses. Several cellular pathways have been shown to modulate HCMV replication. The autophagy receptor sequestosome 1 (SQSTM1)/p62 has been reported to interact with several HCMV proteins, particularly with components of HCMV capsid, suggesting it plays a role in viral replication. Here, we report on a new and unexpected role for SQSTM1/p62, in HCMV suppression. Using a small-molecule probe, ARP101, we show SQSTM1/p62 phosphorylation at its C terminus domain initiates the noncanonical Keap1-Nrf2 axis, leading to transcription of genes under the antioxidant response element, resulting in HCMV inhibition in vitro. Our study highlights the dynamic nature of SQSTM1/p62 during HCMV infection and how its phosphorylation activates a new pathway that can be exploited for antiviral intervention.

Fluorinated triphenylphosphonium analogs improve cell selectivity and in vivo detection of mito-metformin.

Triphenylphosphonium (TPP+) conjugated compounds selectively target cancer cells by exploiting their hyperpolarized mitochondrial membrane potential. To date, studies have focused on modifying either the linker or the cargo of TPP+-conjugated compounds. Here, we investigated the biological effects of direct modification to TPP+ to improve the efficacy and detection of mito-metformin (MMe), a TPP+-conjugated probe we have shown to have promising preclinical efficacy against solid cancer cells. We designed, synthesized, and tested trifluoromethyl and methoxy MMe analogs (pCF3-MMe, mCF3-MMe, and pMeO-MMe) against multiple distinct human cancer cells. pCF3-MMe showed enhanced selectivity toward cancer cells compared to MMe, while retaining the same signaling mechanism. Importantly, pCF3-MMe allowed quantitative monitoring of cellular accumulation via 19F-NMR in vitro and in vivo. Furthermore, adding trifluoromethyl groups to TPP+ reduced toxicity in vivo while retaining anti-tumor efficacy, opening an avenue to de-risk these next-generation TPP+-conjugated compounds.

Characterization of Dual-Acting A3 Adenosine Receptor Positive Allosteric Modulators That Preferentially Enhance Adenosine-Induced Gαi3 and GαoA Isoprotein Activation.

The A3 adenosine receptor (A3AR) is a promising therapeutic target for inflammatory diseases, cancer, and chronic neuropathic pain, with agonists already in advanced clinical trials. Here we report an in-depth comparison of the pharmacological properties and structure-activity relationships of existing and expanded compound libraries of 2-substituted 1H-imidazo[4,5-c]quinolin-4-amine and 4-amino-substituted quinoline derivatives that function as A3AR positive allosteric modulators (PAMs). We also show that our lead compound from each series enhances adenosine-induced A3AR signaling preferentially toward activation of Gαi3 and GαoA isoproteins, which are coexpressed with the A3AR in immune cells and spinal cord neurons. Finally, utilizing an extracellular/intracellular chimeric A3AR approach composed of sequences from a responding (human) and a nonresponding (mouse) species, we provide evidence in support of the idea that the imidazoquinolin-4-amine class of PAMs variably interacts dually with the orthosteric ligand binding site as well as with a separate allosteric site located within the inner/intracellular regions of the receptor. This study has advanced both structural and pharmacological understanding of these two classes of A3AR PAMs, which includes leads for future pharmaceutical development.

The Synthesis and Anti-Cytomegalovirus Activity of Piperidine-4-Carboxamides.

Treatment options for human cytomegalovirus (CMV) remain limited and are associated with significant adverse effects and the selection of resistant CMV strains in transplant recipients and congenitally infected infants. Although most approved drugs target and inhibit the CMV DNA polymerase, additional agents with distinct mechanisms of action are needed for the treatment and prevention of CMV. In a large high throughput screen using our CMV-luciferase reporter Towne, we identified several unique inhibitors of CMV replication. Here, we synthesize and test in vitro 13 analogs of the original NCGC2955 hit (1). Analogs with no activity against the CMV-luciferase at 10 µM and 30 µM (2-6, 10-14) were removed from further analysis. Three analogs (7-9) inhibited CMV replication in infected human foreskin fibroblasts. The EC50 of (1) was 1.7 ± 0.6 µM and 1.99 ± 0.15 µM, based on luciferase and plaque assay, respectively. Compounds 7, 8, and 9 showed similar activities: the EC50 values of 7 were 0.21 ± 0.06 µM (luciferase) and 0.55 ± 0.06 (plaque), of 8: 0.28 ± 0.06 µM and 0.42 ± 0.07, and of 9: 0.30 ± 0.05 µM (luciferase) and 0.35 ± 0.07 (plaque). The CC50 for 7, 8, and 9 in non-infected human foreskin fibroblasts was > 500µM, yielding a selectivity index of >1500. Compounds 1, 7, and 8 were also tested in CMV-infected primary human hepatocytes and showed a dose-response against CMV by luciferase activity and viral protein expression. None of the active compounds inhibited herpes simplex virus 1 or 2. Compounds 7 and 8 inhibited mouse CMV replication in vitro. Both inhibited CMV at late stages of replication; 7 reduced virus yield at all late time points, although not to the same degree as letermovir. Finally, the activity of analog 8 was additive with newly identified CMV inhibitors (MLS8969, NFU1827, MSL8554, and MSL8091) and with ganciclovir. Further structural activity development should provide promising anti-CMV agents for use in clinical studies.

Validation and Characterization of Five Distinct Novel Inhibitors of Human Cytomegalovirus.

The critical consequences of human cytomegalovirus (HCMV) infection in the transplant population and in congenitally infected infants, the limited treatment options for HCMV, and the rise of resistant mutants toward existing therapies has fueled the search for new anti-HCMV agents. A pp28-luciferase recombinant HCMV was used as a reporter system for high-throughput screening of HCMV inhibitors. Approximately 400 000 compounds from existing libraries were screened. Subsequent validation assays using resynthesized compounds, several virus strains, and detailed virology assays resulted in the identification of five structurally unique and selective HCMV inhibitors, active at sub to low micromolar concentrations. Further characterization revealed that each compound inhibited a specific stage of HCMV replication. One compound was also active against herpes simplex virus (HSV1 and HSV2), and another compound was active against Epstein-Barr virus (EBV). Drug combination studies revealed that all five compounds were additive with ganciclovir or letermovir. Future studies will focus on optimization of these new anti-HCMV compounds along with mechanistic studies.

N-{3-[2-(4-alkoxyphenoxy)thiazol-5-yl]-1-methylprop-2-ynyl}carboxy derivatives as acetyl-coA carboxylase inhibitors--improvement of cardiovascular and neurological liabilities via structural modifications.

A preliminary safety evaluation of ACC2 inhibitor 1-(S) revealed serious neurological and cardiovascular liabilities of this chemotype. A systematic structure-toxicity relationship study identified the alkyne linker as the key motif responsible for these adverse effects. Toxicogenomic studies in rats showed that 1-(R) and 1-(S) induced gene expression patterns similar to that seen with several known cardiotoxic agents such as doxorubicin. Replacement of the alkyne with alternative linker groups led to a new series of ACC inhibitors with drastically improved cardiovascular and neurological profiles.

The synthesis and structure-activity relationship studies of selective acetyl-CoA carboxylase inhibitors containing 4-(thiazol-5-yl)but-3-yn-2-amino motif: polar region modifications.

The structure-activity relationship study focused on the polar region of the HTS hit A-80040 (1) producing several series of potent and selective ACC2 inhibitors. The SAR suggests a compact lipophilic pocket that does not tolerate polar and ionic groups. Replacement of the hydroxyurea group with isoxazoles improves ACC2 selectivity while maintaining potency. Variations at the propargylic site of 11a reduce ACC2 potency.

Short and efficient synthesis of a vinyl-substituted tricyclic erythromycin derivative.

Tricyclic erythromycin A derivatives are known potent antibacterial agents, but the potential of substituted tricyclic erythromycin A derivatives remains largely unexplored. To study this lead, the tricyclic ring system was synthesized by an efficient three-step synthesis starting from the allylic alcohol utilizing a novel azidoisocyanate. These tricyclic analogues can be used as scaffolds to probe secondary ribosomal binding sites. [structure: see text]

Synthesis and antibacterial activity of 6-O-arylbutynyl ketolides with improved activity against some key erythromycin-resistant pathogens.

A series of novel 6-O-substituted homopropargyl ketolides was synthesized and evaluated against various erythromycin-resistant pathogens. Promising in vitro antibacterial activity was demonstrated for compounds bearing this structural motif.