Moonlighting proteins: beacon of hope in era of drug resistance in bacteria.

Moonlighting proteins (MLPs) are ubiquitous and provide a unique advantage to bacteria performing multiple functions using the same genomic content. Targeting MLPs can be considered as a futuristic approach in fighting drug resistance problem. This review follows the MLP trail from its inception to the present-day state, describing a few bacterial MLPs, viz., glyceraldehyde 3'-phosphate dehydrogenase, phosphoglucose isomerase glutamate racemase (GR), and DNA gyrase. Here, we carve out that targeting MLPs are the beacon of hope in an era of increasing drug resistance in bacteria. Evolutionary stability, structure-functional relationships, protein diversity, possible drug targets, and identification of new drugs against bacterial MLP are given due consideration. Before the final curtain calls, we provide a comprehensive list of small molecules that inhibit the biochemical activity of MLPs, which can aid the development of novel molecules to target MLPs for therapeutic applications.

Bronsted Acid-Catalyzed Regioselective Carboxamidation of 2-Indolylmethanols with Isonitriles.

A regioselective direct carboxamidation reaction of 2-indolylmethanols with readily available isocyanoesters/isocyanides has been reported in this work. The reaction was catalyzed by Bronsted acid such as p-TsOH to deliver the benzylic regioselective amides in 67-86% yield under mild conditions. The developed methodology provides alternative access to traditional metal-free carboxamidation via C-C and C-O bond formation with high atom economy. Furthermore, the developed approach was diversified to synthesize chiral indole-2-carboxamide derivatives with a moderate enantiomeric excess (61-73% ee) using an (R)-chiral phosphoric acid.

Multistep Synthesis of Analogues of Remdesivir: Incorporating Heterocycles at the C-1' Position.

Studies suggest that the 1'ß-CN moiety in remdesivir sterically clashes with the Ser861 residue of the RNA-dependent-RNA polymerase (RdRp), causing a delayed chain termination in the RNA replication process. Replacing C1'ß-CN with 5-membered heterocycles such as tetrazoles, oxadiazoles, and triazoles can augment the inhibitory activity and pharmacokinetic profile of C-nucleotides. Synthesis of tetrazole-, triazole-, and oxadiazole-integrated C1' analogues of remdesivir was attempted using general synthetic routes. The final compounds 26, 28, and 29 did not inhibit viral replication; however, the synthetic intermediates, i.e., 27 and 50, exhibited an IC90 = 14.1 µM each. The trifluoromethyl-substituted 1,2,4-oxadiazole 59 showed an IC90 of 33.5 µM. This work adds to the growing evidence of the beneficial medicinal impact of C1,1'-disubstituted C-nucleotides.

Strategic Advances in Sequential C-Arylations of Heteroarenes.

Sequence-specific C-arylation strategies have important applications in medicinal and material research. These strategies allow C-C bond formations in a regioselective manner to synthesize large molecular libraries for studying structure-activity profiles. The past decade has seen the development of single C-C bond forming reactions using various transition-metal catalysts, cryogenic metalation strategies, and metal-free methods. Sequential arylations of heterocycles allow for the formation of multiaryl derivatives and are a preferred choice over de novo synthetic routes. This perspective sheds light on recent strategic advances to develop various sequential synthetic routes for the multiarylation of heteroarenes. This perspective addresses many challenges in optimizing sequential routes with respect to catalysts, reaction parameters, and various strategies adopted to obtain diversely arylated products.

Recent approaches to the synthesis of tetrahydrocarbazoles.

The tetrahydrocarbazole (THC) motif is ubiquitous in natural products and biologically active compounds. THCs can serve as favorable synthetic intermediates or precursors en-route to desired complex natural products. Despite a considerable number of strategies for the synthesis of THCs that have emerged in the last two decades, only a handful of reviews have been published on the subject. Herein, we have summarized synthetic methodologies published in the last ten years for the benefit of organic chemists. The review focuses on non-enantioselective syntheses of THCs, and encompasses ring opening reactions of donor-acceptor cyclopropanes, metal-catalyzed C-C/C-N bond formation, cycloaddition, conjugate addition, and miscellaneous reactions employed for accessing the THC framework.

Benzimidazoles: Selective Inhibitors of Topoisomerase I with Differential Modes of Action.

DNA topoisomerases are unique enzymes that alter the topology of DNA by cleavage and religation mechanisms. Small molecules such as camptothecins and noncamptothecins are reported to inhibit different classes of topoisomerases. Benzimidazole, 2-(3,4-dimethoxyphenyl)-5-[5-(4-methylpiperazin-1-yl)-1 H-benzimidazol-2-yl]-1 H benzimidazole (DMA), a new analogue of Hoechst 33342, was observed as a selective and differential inhibitor of human and Escherichia coli DNA topoisomerase I. In this study, we have concluded that DMA and Hoechst 33342 have differential binding toward human and E. coli topoisomerase I. We also dissected the mechanism of differential binding, as DMA and Hoechst 33342 bind to human topoisomerase I with linear kinetics with reversible binding, whereas the same molecules bind to E. coli topoisomerase I in a nonlinear and irreversible manner, which contributes to higher affinity and comparatively good IC50 values toward E. coli topoisomerase I. Interestingly, DMA and Hoechst 33342 showed inhibition of mutant human topoisomerases I, i.e., A653P, N722S, and T729P, whereas these clinically relevant mutants are resistant to camptothecins.

Interaction of HIV-1 integrase with polypyrimidine tract binding protein and associated splicing factor (PSF) and its impact on HIV-1 replication.

BACKGROUND: The different interactions between viral proteins and cellular host proteins are required for efficient replication of HIV-1. Various reports implicated host cellular proteins as a key factor that either interact directly with HIV-1 integrase (IN) or get involved in the integration process of virus resulting in the modulation of integration step. Polypyrimidine tract binding protein and associated splicing factor (PSF) has diverse functions inside the cell such as transcriptional regulation, DNA repair, acts as nucleic acids binding protein and regulate replication and infectivity of different viruses. RESULTS: The protein binding study identified the association of host protein PSF with HIV-1 integrase. The siRNA knockdown (KD) of PSF resulted in increased viral replication in TZM-bl cells, suggesting PSF has negative influence on viral replication. The quantitative PCR of virus infected PSF knockdown TZM-bl cells showed more integrated DNA and viral cDNA as compared to control cells. We did not observe any significant difference between the amount of early reverse transcription products as well as infectivity of virus in the PSF KD and control TZM-bl cells. Molecular docking study supported the argument that PSF hinders the binding of viral DNA with IN. CONCLUSION: In an attempt to study the host interacting protein of IN, we have identified a new interacting host protein PSF which is a splicing factor and elucidated its role in integration and viral replication. Experimental as well as in silico analysis inferred that the host protein causes not only change in the integration events but also targets the incoming viral DNA or the integrase-viral DNA complex. The role of PSF was also investigated at early reverse transcript production as well as late stages. The PSF is causing changes in integration events, but it does not over all make any changes in the virus infectivity. MD trajectory analyses provided a strong clue of destabilization of Integrase-viral DNA complex occurred due to PSF interaction with the conserved bases of viral DNA ends that are extremely crucial contact points with integrase and indispensable for integration. Thus our study emphasizes the negative influence of PSF on HIV-1 replication.

Pd-Catalyzed Sequential Arylation of 7-Azaindoles: Aggregate-Induced Emission of Tetra-Aryl 7-Azaindoles.

Pd-catalyzed synthesis of multi-aryl 7-azaindoles using sequential arylation of 5-bromo-6-chloro-3-iodo-1-methyl-1H-pyrrolo[2,3-b] pyridine is established. Four diverse aryl groups are installed in a chemo-selective fashion providing a general method to synthesize sterically encumbered compounds and extended 7-azaindoles in 48-95% yields. Three-selective sequential arylations at C-3, C-5, and C-6 via Suzuki-Miyaura cross-coupling followed by direct C-2 arylation using a Pd catalyst and AgOTf as an additive are highlights of the present work. Interestingly, the tetra-aryl 7-azaindoles showed aggregate-induced emission (AIE) making it potentially useful as fluorophores in OLEDs, sensors, and bio-imaging tools.

Topoisomerases: Resistance versus Sensitivity, How Far We Can Go?

DNA topoisomerases are ubiquitously present remarkable molecular machines that help in altering topology of DNA in living cells. The crucial role played by these nucleases during DNA replication, transcription, and recombination vis-à-vis less sequence similarity among different species makes topoisomerases unique and attractive targets for different anticancer and antibacterial drugs. However, druggability of topoisomerases by the existing class of molecules is increasingly becoming questationable due to resistance development predominated by mutations in the corresponding genes. The current scenario facing a decline in the development of new molecules further comprises an important factor that may challenge topoisomerase-targeting therapy. Thus, it is imperative to wisely use the existing inhibitors lest with this rapid rate of losing grip over the target we may not go too far. Furthermore, it is important not only to design new molecules but also to develop new approaches that may avoid obstacles in therapies due to multiple resistance mechanisms. This review provides a succinct account of different classes of topoisomerase inhibitors, focuses on resistance acquired by mutations in topoisomerases, and discusses the various approaches to increase the efficacy of topoisomerase inhibitors. In a later section, we also suggest the possibility of using bisbenzimidazoles along with efflux pump inhibitors for synergistic bactericidal effects.

Facile access to functionalized indenes and fused quinolines by regioselective 5-enolexo-dig Michael addition and cyclization reactions.

Herein we report a facile approach to synthesise multi-substituted indenes and cyclopenta[b]quinolines under mild conditions. The reaction proceeds via Michael addition between commercially available cyanoacetate/malonic esters and α,ß-unsaturated ketones. The synthetic methodology involves enolate mediated regio- and stereoselective intramolecular 5-enolexo-dig cyclization promoted by a catalytic base. The products stereoselectively form cis-isomers for indenes and trans-isomers for cyclopenta[b]quinolines, albeit with the presence of steric hindrance at a quaternary carbon substituted by active methylene compounds. The reaction pathway was investigated by isolating the reaction intermediate. This synthetic transformation was achieved with various aromatic and heteroaromatic Michael acceptors and the desired products were obtained in high to excellent yields. The reaction is scalable up to gram level with only 10 mol% of base.

Radioprotective Agents: Strategies and Translational Advances.

Radioprotectors are agents required to protect biological system exposed to radiation, either naturally or through radiation leakage, and they protect normal cells from radiation injury in cancer patients undergoing radiotherapy. It is imperative to study radioprotectors and their mechanism of action comprehensively, looking at their potential therapeutic applications. This review intimately chronicles the rich intellectual, pharmacological story of natural and synthetic radioprotectors. A continuous effort is going on by researchers to develop clinically promising radioprotective agents. In this article, for the first time we have discussed the impact of radioprotectors on different signaling pathways in cells, which will create a basis for scientific community working in this area to develop novel molecules with better therapeutic efficacy. The bright future of exceptionally noncytotoxic derivatives of bisbenzimidazoles is also described as radiomodulators. Amifostine, an effective radioprotectant, has been approved by the FDA for limited clinical use. However, due to its adverse side effects, it is not routinely used clinically. Recently, CBLB502 and several analog of a peptide are under clinical trial and showed high success against radiotherapy in cancer. This article reviews the different types of radioprotective agents with emphasis on the strategies for the development of novel radioprotectors for drug development. In addition, direction for future strategies relevant to the development of radioprotectors is also addressed.

Regioselective synthesis of functionalized dihydroisoquinolines from o-alkynylarylaldimines via the Reformatsky reaction.

A novel approach for the synthesis of functionalized 1,2-dihydroisoquinolines from o-alkynylarylaldimines via the Reformatsky reaction without the aid of an external Lewis acid has been described. The chemistry involves the dual role of the Reformatsky reagent which has been generated in situ in the reaction. We propose that one molecule of the Reformatsky reagent is being utilised for the activation of alkynes, whereas the second molecule acts as a nucleophile on the iminium carbon. This synthetic pathway has high functional group tolerance, and can be utilized on a gram scale. The proposed mechanistic pathway is well supported by the control experiments. The 1,2-dihydroisoquinoline derivatives showed up to 90% inhibition of the strand transfer activity of the HIV integrase enzyme.

Design, synthesis, cytotoxicity, HuTopoIIα inhibitory activity and molecular docking studies of pyrazole derivatives as potential anticancer agents.

In an attempt to find potential anticancer agents, a series of novel ethyl 4-(3-(aryl)-1-phenyl-1H-pyrazol-4-yl)-2-oxo-6-(pyridin-3-yl)cyclohex-3-enecarboxylates 5a-i and 5-(3-(4-fluorophenyl)-1-phenyl-1H-pyrazol-4-yl)-3-(pyridin-3-yl)-4,5-dihydropyrazole-1-carbothioamides 6a-i were designed, synthesized and evaluated for their topoisomerase IIα inhibitory activity and in vitro cytotoxicity against a panel of cancerous cell lines (MCF-7, NCI-H460, HeLa) and a normal cell line (HEK-293T). Molecular docking studies of all the synthesized compounds into the binding site of topoisomerase IIα protein (PDB ID: 1ZXM) were performed to gain a comprehensive understanding into plausible binding modes. These compounds were also screened for in silico drug-likeliness properties on the basis of the absorption, distribution, metabolism and excretion (ADME) prediction. Among all the synthesized compounds, analogue 5d showed superior cytotoxicity with an IC50 value of 7.01±0.60µM for HeLa, 8.55±0.35µM for NCI-H460 and 14.31±0.90 for MCF-7 cancer cell lines. Further, compound 5d showed 70.82% inhibition of topoisomerase IIα at a concentration of 100µM with maximum docking score of -8.24. Results of ADME prediction revealed that most of these compounds showed in silico drug-likeliness properties within the ideal range.

Preclinical Evaluation of DMA, a Bisbenzimidazole, as Radioprotector: Toxicity, Pharmacokinetics, and Biodistribution Studies in Balb/c Mice.

Radiotherapy, a therapeutic modality of cancer treatment, nonselectively damages normal tissues as well as tumor tissues. The search is ongoing for therapeutic agents that selectively reduce radiation-induced normal tissue injury without reducing tumoricidal effect, thereby increasing the therapeutic ratio of radiation therapy. Our laboratory established 5-(4-methylpiperazin-1-yl)-2-[2'-(3,4-dimethoxyphenyl)-5'benzimidazolyl] benzimidazole (DMA) as noncytotoxic radioprotector in mammalian cells. DMA showed an excellent radioprotection in mice at single nontoxic oral dose by a dose-reduction factor of 1.28. An oxygen radical absorbing capacity assay confirmed its free-radical quenching ability. Single bolus dose and 28-days of repeated administration of DMA in mice for toxicity studies determined an LD50 of >2000 mg/kg body weight (bw) and 225 mg/kg bw, respectively, suggesting DMA is safe. Histopathology, biochemical parameters, and relative organ weight analysis revealed insignificant changes in the DMA-treated animals. The pharmacokinetic study of DMA at oral and intravenous doses showed its C(max) = 1 hour, bioavailability of 8.84%, elimination half-life of 4 hours, and an enterohepatic recirculation. Biodistribution study in mice with Ehrlich ascites tumors showed that (99m)Tc-DMA achieved its highest concentration in 1 hour and was retained up to 4 hours in the lungs, liver, kidneys, and spleen, and in a low concentration in the tumor, a solicited property of any radioprotector to protect normal cells over cancerous cells. We observed that the single-dose treatment of tumor-bearing mice with DMA 2 hours before 8 Gy total body irradiation showed an impressive rescue of radiation-induced morbidity in terms of weight loss and mortality without a change in tumor response.

Design, synthesis and biological evaluation of di-substituted noscapine analogs as potent and microtubule-targeted anticancer agents.

Noscapine is an opium-derived kinder-gentler microtubule-modulating drug, currently in Phase I/II clinical trials for cancer chemotherapy. Here, we report the synthesis of four more potent di-substituted brominated derivatives of noscapine, 9-Br-7-OH-NOS (2), 9-Br-7-OCONHEt-NOS (3), 9-Br-7-OCONHBn-NOS (4), and 9-Br-7-OAc-NOS (5) and their chemotherapeutic efficacy on PC-3 and MDA-MB-231 cells. The four derivatives were observed to have higher tubulin binding activity than noscapine and significantly affect tubulin polymerization. The equilibrium dissociation constant (KD) for the interaction between tubulin and 2, 3, 4, 5 was found to be, 55±6µM, 44±6µM, 26±3µM, and 21±1µM respectively, which is comparable to parent analog. The effects of these di-substituted noscapine analogs on cell cycle parameters indicate that the cells enter a quiescent phase without undergoing further cell division. The varying biological activity of these analogs and bulk of substituent at position-7 of the benzofuranone ring system of the parent molecule was rationalized utilizing predictive in silico molecular modeling. Furthermore, the immunoblot analysis of protein lysates from cells treated with 4 and 5, revealed the induction of apoptosis and down-regulation of survivin levels. This result was further supported by the enhanced activity of caspase-3/7 enzymes in treated samples compared to the controls. Hence, these compounds showed a great potential for studying microtubule-mediated processes and as chemotherapeutic agents for the management of human cancers.

An expedient approach to 1,2-dihydroisoquinoline derivatives via cobalt catalysed 6-endo dig cyclization followed by Mannich condensation of o-alkynylarylaldimines.

A highly effective 6-endo dig cyclisation of o-alkynylaldimines to 1,2-dihydroisoquinolines has been described via direct and nitro Mannich condensation using inexpensive and readily available cobalt chloride as catalyst. This strategy provides an effective procedure for the synthesis of substituted 1,2-dihydroisoquinolines derivatives in moderate to high yields. An addition of pronucleophiles, such as nitromethane, acetone and α-hydroxyacetone, to o-alkynylarylaldimines has been achieved via isoquinolinium intermediate.

HupB, a nucleoid-associated protein of Mycobacterium tuberculosis, is modified by serine/threonine protein kinases in vivo.

HU, a widely conserved bacterial histone-like protein, regulates many genes, including those involved in stress response and virulence. Whereas ample data are available on HU-DNA communication, the knowledge on how HU perceives a signal and transmit it to DNA remains limited. In this study, we identify HupB, the HU homolog of the human pathogen Mycobacterium tuberculosis, as a component of serine/threonine protein kinase (STPK) signaling. HupB is extracted in its native state from the exponentially growing cells of M. tuberculosis H37Ra and is shown to be phosphorylated on both serine and threonine residues. The STPKs capable of modifying HupB are determined in vitro and the residues modified by the STPKs are identified for both in vivo and the in vitro proteins through mass spectrometry. Of the identified phosphosites, Thr(65) and Thr(74) in the DNA-embracing ß-strand of the N-terminal domain of HupB (N-HupB) are shown to be crucial for its interaction with DNA. In addition, Arg(55) is also identified as an important residue for N-HupB-DNA interaction. N-HupB is shown to have a diminished interaction with DNA after phosphorylation. Furthermore, hupB is shown to be maximally expressed during the stationary phase in M. tuberculosis H37Ra, while HupB kinases were found to be constitutively expressed (PknE and PknF) or most abundant during the exponential phase (PknB). In conclusion, HupB, a DNA-binding protein, with an ability to modulate chromatin structure is proposed to work in a growth-phase-dependent manner through its phosphorylation carried out by the mycobacterial STPKs.

Enterohepatic recirculation of bioactive ginger phytochemicals is associated with enhanced tumor growth-inhibitory activity of ginger extract.

Phytochemical complexity of plant foods confers health-promoting benefits including chemopreventive and anticancer effects. Isolating single constituents from complex foods may render them inactive, emphasizing the importance of preserving the natural composition of whole extracts. Recently, we demonstrated in vitro synergy among the most abundant bioactive constituents of ginger extract (GE), viz., 6-gingerol (6G), 8-gingerol (8G), 10-gingerol (10G) and 6-shogaol (6S). However, no study has yet examined the in vivo collaboration among ginger phytochemicals or evaluated the importance, if any, of the natural 'milieu' preserved in whole extract. Here, we comparatively evaluated in vivo efficacy of GE with an artificial quasi-mixture (Mix) formulated by combining four most active ginger constituents at concentrations equivalent to those present in whole extract. Orally fed GE showed 2.4-fold higher tumor growth-inhibitory efficacy than Mix in human prostate tumor xenografts. Pharmacokinetic evaluations and bioavailability measurements addressed the efficacy differences between GE and Mix. Plasma concentration-time profiles revealed multiple peaking phenomenon for ginger constituents when they were fed as GE as opposed to Mix, indicating enterohepatic recirculation. Bioavailability of 6G, 8G, 10G and 6S was 1.6-, 1.1-, 2.5- and 3.4-fold higher, respectively, when dosed with GE compared with Mix. In addition, gingerol glucuronides were detected in feces upon intravenous administration confirming hepatobiliary elimination. These data ascribe the superior in vivo efficacy of GE to higher area under the concentration time curves, greater residence time and enhanced bioavailability, of ginger phytochemicals, when fed as a natural extract compared with artificial Mix, emphasizing the usefulness of consuming whole foods over single agents.

Polydispersity-mediated high efficacy of an in-situ aqueous nanosuspension of PPEF.3HCl in methicillin resistant Staphylococcus aureus sepsis model.

Recently, World Health Organization declared antimicrobial resistance as the third greatest threat to human health. Absence of known cross-resistance, new class, new target, and a new mode of action are few major strategies being undertaken by researches to combat multidrug resistant pathogen. PPEF.3HCl, a bisbenzimidazole was developed as highly potent antibacterial agent against ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens, targeting topoisomerase IA. The present work encompasses a radical on-site generation of In-situ nanosuspension of PPEF.3HCl with enhanced efficacy against methicillin resistant S. aureus in septicemia model. We have generated instantaneously a PPEF.3HCl nanosuspension (IsPPEF.3HCl-NS) by mixing optimized monophasic PPEF.3HCl preconcentrate in propylene glycol into an aqueous medium comprising tween 80 as stabilizer. The IsPPEF.3HCl-NS showed precipitation efficiency of > 90 %, average particle size < 500 nm, retained upto 5 h, a negative zeta potential and bi/trimodal particle size distribution. Differential scanning calorimetry, X-ray diffraction confirmed partial amorphization and transmission electron microscopy revealed spherical particles. IsPPEF.3HCl-NS was non-hemolytic and exhibited good stability in serum. More significantly, it exhibited a âˆ¼ 1.6-fold increase in macrophage uptake compared to free PPEF.3HCl in the RAW 264.7 macrophage cell line. Confocal microscopy revealed accumulation of IsPPEF.3HCl-NS within the lysosomal compartment and cell cytosol, proposing high efficacy. In terms of antimicrobial efficacy, IsPPEF.3HCl-NS outperforms free PPEF.3HCl against clinical methicillin sensitive and resistant S. aureus strains. In a pivotal experiment, IsPPEF.3HCl-NS exhibited over 83 % survival at 8 mg/kg.bw and an impressive reduction of âˆ¼ 4-5 log-fold in bacterial load, primarily in the kidney, liver and spleen of septicemia mice. IsPPEF.3HCl-NS prepared by the In-situ approach, coupled with enhanced intramacrophage delivery and superior efficacy, positions IsPPEF.3HCl-NS as a pioneering and highly promising formulation in the battle against antimicrobial resistance.