Inhibition of protein kinase C by dequalinium analogues: Structure–activity studies on head group variations

Pyrimido[5,4-c]quinolines: Synthesis from 3,4-Di-functionallized Quinoline, Reactivity and Biological Activities

Quinoline and pyrimidine moieties are ubiquitous components in both natural and synthetic compounds, showcasing diverse applications. The fusion of these well-known structures into hybrid molecules has garnered attention due to their intriguing biological properties. Particularly in the field of medicinal chemistry, numerous studies in the last decade have focused on pyrimido[5,4-c]quinoline ring systems (PyQs5,4-c). This review elucidates the synthesis of PyQs5,4-c and their derivatives using 3,4-difunctionalized quinoline as a key starting material. The preparation of PyQs5,4-c involves a series of chemical transformations, including the Friedländer, Ullmann and Biginelli reaction, Vilsmeier-Haack formylation, Suzuki coupling, and a one-pot three-component reaction. These synthetic routes not only offer access to diverse PyQs5,4-c derivatives.

Development of Single-Stranded DNA Bisintercalating Inhibitors of Primase DnaG as Antibiotics

Many essential enzymes in bacteria remain promising potential targets of antibacterial agents. In this study, we discovered that dequalinium, a topical antibacterial agent, is an inhibitor of Staphylococcus aureus primase DnaG (SaDnaG) with low-micromolar minimum inhibitory concentrations against several S. aureus strains, including methicillin-resistant bacteria. Mechanistic studies of dequalinium and a series of nine of its synthesized analogues revealed that these compounds are single-stranded DNA bisintercalators that penetrate a bacterium by compromising its membrane. The best compound of this series likely interacts with DnaG directly, inhibits both staphylococcal cell growth and biofilm formation, and displays no significant hemolytic activity or toxicity to mammalian cells. This compound is an excellent lead for further development of a novel anti-staphylococcal therapeutic.

Medicinal applications and molecular targets of dequalinium chloride

For more than 60 years dequalinium chloride (DQ) has been used as anti-infective drug, mainly to treat local infections. It is a standard drug to treat bacterial vaginosis and an active ingredient of sore-throat lozenges. As a lipophilic bis-quaternary ammonium molecule, the drug displays membrane effects and selectively targets mitochondria to deplete DNA and to block energy production in cells. But beyond its mitochondriotropic property, DQ can interfere with the correct functioning of diverse proteins. A dozen of DQ protein targets have been identified and their implication in the antibacterial, antiviral, antifungal, antiparasitic and anticancer properties of the drug is discussed here. The anticancer effects of DQ combine a mitochondrial action, a selective inhibition of kinases (PKC-α/β, Cdc7/Dbf4), and a modulation of Ca²⁺-activated K⁺ channels. At the bacterial level, DQ interacts with different multidrug transporters (QacR, AcrB, EmrE) and with the transcriptional regulator RamR. Other proteins implicated in the antiviral (MPER domain of gp41 HIV-1) and antiparasitic (chitinase A from Vibrio harveyi) activities have been identified. DQ also targets α -synuclein oligomers to restrict protofibrils formation implicated in some neurodegenerative disorders. In addition, DQ is a typical bolaamphiphile molecule, well suited to form liposomes and nanoparticules useful for drug entrapment and delivery (DQAsomes and others). Altogether, the review highlights the many pharmacological properties and therapeutic benefits of this old 'multi-talented' drug, which may be exploited further. Its multiple sites of actions in cells should be kept in mind when using DQ in experimental research.

Inhibition of porcine reproductive and respiratory syndrome virus by PKC inhibitor dequalinium chloride in vitro

As a severe disease characterized by reproductive failure and respiratory distress, porcine reproductive and respiratory syndrome (PRRS) is one of the most leading threats to the swine industry worldwide. Highly evolving porcine reproductive and respiratory syndrome virus (PRRSV) strains with distinct genetic diversity make the current vaccination strategy much less cost-effective and thus urge alternative protective host directed therapeutic approaches. RACK1-PKC-NF-κB signalling axis was suggested as a potential therapeutic target for PRRS control, therefore we tested the inhibitory effect of PKC inhibitor dequalinium chloride (DECA) on the PRRSV infection in vitro. RT-qPCR, western blot, Co-IP and cytopathic effect (CPE) observations revealed that DECA suppressed PRRSV infection and protected Marc-145 cells and porcine alveolar macrophages (PAMs) from severe cytopathic effects, by repressing the PKCα expression, the interaction between RACK1 and PKCα, and subsequently the NF-κB activation. In conclusion, the data presented in this study shed more light on deeper understanding of the molecular pathogenesis upon PRRSV infection and more importantly suggested DECA as a potential promising drug candidate for PRRS control.

HIV-1 fusion inhibitors targeting the membrane-proximal external region of Env spikes

Combination antiretroviral therapy has transformed HIV-1 infection, once a fatal illness, into a manageable chronic condition. Drug resistance, severe side effects and treatment noncompliance bring challenges to combination antiretroviral therapy implementation in clinical settings and indicate the need for additional molecular targets. Here, we have identified several small-molecule fusion inhibitors, guided by a neutralizing antibody, against an extensively studied vaccine target-the membrane proximal external region (MPER) of the HIV-1 envelope spike. These compounds specifically inhibit the HIV-1 envelope-mediated membrane fusion by blocking CD4-induced conformational changes. An NMR structure of one compound complexed with a trimeric MPER construct reveals that the compound partially inserts into a hydrophobic pocket formed exclusively by the MPER residues, thereby stabilizing its prefusion conformation. These results suggest that the MPER is a potential therapeutic target for developing fusion inhibitors and that strategies employing an antibody-guided search for novel therapeutics may be applied to other human diseases.

Quaternary ammonium salts and their antimicrobial potential: targets or nonspecific interactions?

For more than 50 years dequalinium chloride has been used successfully as an antiseptic drug and disinfectant, particularly for clinical purposes. Given the success of dequalinium chloride, several series of mono- and bisquaternary ammonium compounds have been designed and reported to have improved antimicrobial activity. Furthermore, many of them exhibit high activity against mycobacteria and protozoa, especially against plasmodia. This review discusses the structure-activity relationships and the modes of action of the various series of (bis)quaternary ammonium compounds.

Synthesis of N-aryl-3-(indol-3-yl)propanamides and their immunosuppressive activities

N-aryl-3-(indol-3-yl)propanamides were synthesized and their immunosuppressive activities were evaluated. This study highlighted the promising potency of 3-[1-(4-chlorobenzyl)-1H-indol-3-yl]-N-(4-nitrophenyl)propanamide 15 which exhibited a significant inhibitory activity on murine splenocytes proliferation assay in vitro and on mice delayed-type hypersensitivity (DTH) assay in vivo.

Dequalinium, a new inhibitor of Mycobacterium tuberculosis mycothiol ligase identified by high-throughput screening

Mycothiol ligase (MshC) is a key enzyme in the biosynthesis of mycothiol, a small molecular weight thiol that is unique to actinomycetes and whose primary role is to maintain intracellular redox balance and remove toxins. MshC catalyzes the adenosine triphosphate (ATP)-dependent condensation of cysteine and glucosamine-inositol (GI) to produce cysteine-glucosamine-inositol (CGI). MshC is essential to Mycobacterium tuberculosis and therefore represents an attractive target for chemotherapeutic intervention. A screening protocol was developed to identify MshC inhibitors based on quantification of residual ATP using a coupled luminescent assay. The protocol was used to screen a library of 3100 compounds in a 384-well plate format (Z'>or=0.65). Fifteen hits (0.48%) were identified from the screen, and 2 hits were confirmed in a secondary assay that measures production of CGI. The structures of both hits contain N-substituted quinolinium moieties, and the more potent of the 2-namely, dequalinium chloride-inhibits MshC with an IC50 value of 24+/-1 microM. Further studies showed dequalinium to be an ATP-competitive inhibitor of MshC, to bind MshC with a KD of 0.22 microM, and to inhibit the growth of M. tuberculosis under aerobic and anaerobic conditions with minimum inhibitory and anaerobic bactericidal concentrations of 1.2 and 0.3 microg/mL, respectively. The screening protocol described is robust and has enabled the identification of new MshC inhibitors.

Protein kinase C intervention: the state of play

Intervention in protein kinase C (PKC) has a chequered history, partly because of the poor selectivity of many inhibitors and partly a reflection of the sometimes antagonistic action of related PKC isoforms. Recent advances in targeting PKC isoforms have come from structural work on isolated kinase domains that have provided opportunities to drive selectivity through structure-based avenues. The promise of isoform selective inhibitors and the rationale for their development are discussed in the broader context of the PKC inhibitor arsenal.