Bis-imidazolinylindoles are active against methicillin-resistant Staphylococcus aureus and multidrug-resistant Mycobacterium tuberculosis

Recent advances and challenges of revolutionizing drug-resistant tuberculosis treatment

Tuberculosis (TB), an infectious disease induced by Mycobacterium tuberculosis, is one of the primary public health threats all over the world. Since the prevalence of first-line anti-TB agents, the morbidity and mortality issues of TB descended obviously. Nevertheless, the emergences of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains, the double prevalence of HIV-TB co-infection, and the insufficiency of plentiful health care have led to an increased incidence of TB. It is noted that current drugs for treating TB have proved unsustainable in the face of highly resistant strains. Fortunately, five categories of new drugs and candidates with new mechanisms of action have emerged in the field of anti-TB research after decades of stagnation in the progression of anti-TB drugs. In this paper, the research status of these promising anti-TB drugs and candidates are reviewed, emphasizing the challenges to be addressed for efficient development of future TB therapies.

Recent advances in indole dimers and hybrids with antibacterial activity against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA), one of the major and most dangerous pathogens in humans, is a causative agent of severe pandemic of mainly skin and soft tissue and occasionally fatal infections. Therefore, it is imperative to develop potent and novel anti-MRSA agents. Indole derivatives could act against diverse enzymes and receptors in bacteria, occupying a salient place in the development of novel antibacterial agents. Dimerization and hybridization are common strategies to discover new drugs, and a number of indole dimers and hybrids possess potential antibacterial activity against a panel of clinically important pathogens including MRSA. Accordingly, indole dimers and hybrids are privileged scaffolds for the discovery of novel anti-MRSA agents. This review outlines the recent development of indole dimers and hybrids with a potential activity against MRSA, covering articles published between 2010 and 2020. The structure-activity relationship and the mechanism of action are also discussed to facilitate further rational design of more effective candidates.

DNA Targeting as a Likely Mechanism Underlying the Antibacterial Activity of Synthetic Bis-Indole Antibiotics

We previously reported the synthesis and biological activity of a series of cationic bis-indoles with potent, broad-spectrum antibacterial properties. Here, we describe mechanism of action studies to test the hypothesis that these compounds bind to DNA and that this target plays an important role in their antibacterial outcome. The results reported here indicate that the bis-indoles bind selectively to DNA at A/T-rich sites, which is correlated with the inhibition of DNA and RNA synthesis in representative Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) organisms. Further, exposure of E. coli and S. aureus to representative bis-indoles resulted in induction of the DNA damage-inducible SOS response. In addition, the bis-indoles were found to be potent inhibitors of cell wall biosynthesis; however, they do not induce the cell wall stress stimulon in S. aureus, suggesting that this pathway is inhibited by an indirect mechanism. In light of these findings, the most likely basis for the observed activities of these compounds is their ability to bind to the minor groove of DNA, resulting in the inhibition of DNA and RNA synthesis and other secondary effects.

Novel synthetic bis-indolic derivatives with antistaphylococcal activity, including against MRSA and VISA strains

OBJECTIVES

We report the synthesis, antibacterial activity and toxicity of 24 bis-indolic derivatives obtained during the development of new ways of synthesis of marine bis-indole alkaloids from the spongotine, topsentin and hamacanthin classes.

METHODS

Innovative ways of synthesis and further structural optimizations led to bis-indoles presenting either the 1-(1H-indol-3'-yl)-1,2-diaminoethane unit or the 1-(1H-indol-3-yl)ethanamine unit. MIC determination was performed for reference and clinical strains of Staphylococcus aureus and CoNS species. MBC, time-kill kinetics, solubility, hydrophobicity index, plasma protein-binding and cytotoxicity assays were performed for lead compounds. Inhibition of the S. aureus NorA efflux pump was also tested for bis-indoles with no antistaphylococcal activity.

RESULTS

Lead compounds were active against both S. aureus and CoNS species, with MICs between 1 and 4 mg/L. Importantly, the same MICs were found for MRSA and vancomycin-intermediate S. aureus strains. Early concentration-dependent bactericidal activity was observed for lead derivatives. Compounds with no intrinsic antibacterial activity could inhibit the S. aureus NorA efflux pump, which is involved in resistance to fluoroquinolones. At 0.5 mg/L, the most effective compound led to an 8-fold reduction of the ciprofloxacin MIC for the SA-1199B S. aureus strain, which overexpresses NorA. However, the bis-indole compounds displayed a high hydrophobicity index and high plasma protein binding, which significantly reduced antibacterial activity.

CONCLUSIONS

We have synthesized and characterized novel bis-indole derivatives as promising candidates for the development of new antistaphylococcal treatments, with preserved activity against MDR S. aureus strains.

A Molecular Dynamics Investigation of Mycobacterium tuberculosis Prenyl Synthases: Conformational Flexibility and Implications for Computer-aided Drug Discovery

With the rise in antibiotic resistance, there is interest in discovering new drugs active against new targets. Here, we investigate the dynamic structures of three isoprenoid synthases from Mycobacterium tuberculosis using molecular dynamics (MD) methods with a view to discovering new drug leads. Two of the enzymes, cis-farnesyl diphosphate synthase (cis-FPPS) and cis-decaprenyl diphosphate synthase (cis-DPPS), are involved in bacterial cell wall biosynthesis, while the third, tuberculosinyl adenosine synthase (Rv3378c), is involved in virulence factor formation. The MD results for these three enzymes were then compared with previous results on undecaprenyl diphosphate synthase (UPPS) by means of active site volume fluctuation and principal component analyses. In addition, an analysis of the binding of prenyl diphosphates to cis-FPPS, cis-DPPS, and UPPS utilizing the new MD results is reported. We also screened libraries of inhibitors against cis-DPPS, finding ~1 μm inhibitors, and used the receiver operating characteristic-area under the curve (ROC-AUC) method to test the predictive power of X-ray and MD-derived cis-DPPS receptors. We found that one compound with potent M. tuberculosis cell growth inhibition activity was an IC(50) ~0.5- to 20-μm inhibitor (depending on substrate) of cis-DPPS, a ~660-nm inhibitor of Rv3378c as well as a 4.8-μm inhibitor of cis-FPPS, opening up the possibility of multitarget inhibition involving both cell wall biosynthesis and virulence factor formation.

Antibiotics and bacterial resistance in the 21st century

Dangerous, antibiotic resistant bacteria have been observed with increasing frequency over the past several decades. In this review the factors that have been linked to this phenomenon are addressed. Profiles of bacterial species that are deemed to be particularly concerning at the present time are illustrated. Factors including economic impact, intrinsic and acquired drug resistance, morbidity and mortality rates, and means of infection are taken into account. Synchronously with the waxing of bacterial resistance there has been waning antibiotic development. The approaches that scientists are employing in the pursuit of new antibacterial agents are briefly described. The standings of established antibiotic classes as well as potentially emerging classes are assessed with an emphasis on molecules that have been clinically approved or are in advanced stages of development. Historical perspectives, mechanisms of action and resistance, spectrum of activity, and preeminent members of each class are discussed.