Therapeutic potential of FtsZ inhibition: a patent perspective

Targeting Filamenting temperature-sensitive mutant Z (FtsZ) with bioactive phytoconstituents: An emerging strategy for antibacterial therapy

The rise and widespread occurrence of bacterial resistance has created an evident need for novel antibacterial drugs. Filamenting temperature-sensitive mutant Z (FtsZ) is a crucial bacterial protein that forms a ring-like structure known as the Z-ring, playing a significant role in cell division. Targeting FtsZ is an effective approach for developing antibiotics that disrupt bacterial cell division and halt growth. This study aimed to use a virtual screening approach to search for bioactive phytoconstituents with the potential to inhibit FtsZ. The screening process proceeded with the filtering compounds from the IMPPAT library of phytochemicals based on their physicochemical properties using the Lipinski rule of five. This was followed by molecular docking, Pan-assay interference compounds (PAINS) filter, absorption, distribution, metabolism, excretion, and toxicity (ADMET), prediction of activity spectra for biologically active substances (PASS), and molecular dynamics (MD) simulations. These filters ensured that any adverse effects that could impede the identification of potential inhibitors of FtsZ were eliminated. Following this, two phytocompounds, Withaperuvin C and Trifolirhizin, were selected after the screening, demonstrating noteworthy binding potential with FtsZ's GTP binding pocket, acting as potent GTP-competitive inhibitors of FtsZ. The study suggested that these compounds could be further investigated for developing a novel class of antibiotics after required studies.

Design and synthesis of fascaplysin derivatives as inhibitors of FtsZ with potent antibacterial activity and mechanistic study

The increase in antibiotic resistance has made it particularly urgent to develop new antibiotics with novel antibacterial mechanisms. Inhibition of bacterial cell division by disrupting filamentous temperature-sensitive mutant Z (FtsZ) function is an effective and promising approach. A series of novel fascaplysin derivatives with tunable hydrophobicity were designed and synthesized here. The in vitro bioactivity assessment revealed that these compounds could inhibit the tested Gram-positive bacteria including methicillin-resistant S. aureus (MRSA) (MIC = 0.049-25 μg/mL), B. subtilis (MIC = 0.024-12.5 μg/mL) and S. pneumoniae (MIC = 0.049-50 μg/mL). Among them, compounds B3 (MIC = 0.098 μg/mL), B6 (MIC = 0.098 μg/mL), B8 (MIC = 0.049 μg/mL) and B16 (MIC = 0.098 μg/mL) showed the best bactericidal activities against MRSA and no significant tendency to trigger bacterial resistance as well as rapid bactericidal properties. The cell surface integrity of bacteria was significantly disrupted by hydrophobic tails of fascaplysin derivatives. Further studies revealed that these highly active amphiphilic compounds showed low hemolytic activity and cytotoxicity to mammalian cells. Preliminary mechanistic exploration suggests that B3, B6, B8 and B16 are potent FtsZ inhibitors to promote FtsZ polymerization and inhibit GTPase activity of FtsZ, leading to the death of bacterial cells by inhibiting bacterial division. Molecular docking simulations and structure-activity relationship (SAR) study reveal that appropriate increase in the hydrophobicity of fascaplysin derivatives and the addition of additional hydrogen bonds facilitated their binding to FtsZ proteins. These amphiphilic fascaplysin derivatives could serve as a novel class of FtsZ inhibitors, which not only gives new prospects for the application of compounds containing this skeleton but also provides new ideas for the discovery of new antibiotics.

Bacterial FtsZ inhibition by benzo[d]imidazole-2-carboxamide derivative with anti-TB activity

Aims: The present study aimed to assess the mode of action of previously reported anti- Mycobacterium tuberculosis benzo[ d]imidazole-2-carboxamides against FtsZ along with their antibacterial potential. Materials & methods: The anti-mycobacterial action of benzo[ d]imidazole-2-carboxamides against FtsZ was evaluated using inhibition of Bacillus subtilis 168, light scattering assay, circular dichroism spectroscopy, in silico molecular docking and molecular dynamics simulations. Results & conclusion: Three compounds (1k, 1o and 1e) were active against isoniazid-resistant strains. Four compounds (1h, 1i, 1o and 4h) showed >70% inhibition against B. subtilis 168. Compound 1o was the most potent inhibitor (91 ± 5% inhibition) of  B. subtilis 168 FtsZ and perturbed its secondary structure. Molecular docking and molecular dynamics simulation of complexed 1o suggested M. tuberculosis FtsZ as a possible target for antitubercular activity.

Tackling Multiple-Drug-Resistant Bacteria With Conventional and Complex Phytochemicals

Emerging antibiotic resistance in bacteria endorses the failure of existing drugs with chronic illness, complicated treatment, and ever-increasing expenditures. Bacteria acquire the nature to adapt to starving conditions, abiotic stress, antibiotics, and our immune defense mechanism due to its swift evolution. The intense and inappropriate use of antibiotics has led to the development of multidrug-resistant (MDR) strains of bacteria. Phytochemicals can be used as an alternative for complementing antibiotics due to their variation in metabolic, genetic, and physiological fronts as well as the rapid evolution of resistant microbes and lack of tactile management. Several phytochemicals from diverse groups, including alkaloids, phenols, coumarins, and terpenes, have effectively proved their inhibitory potential against MDR pathogens through their counter-action towards bacterial membrane proteins, efflux pumps, biofilms, and bacterial cell-to-cell communications, which are important factors in promoting the emergence of drug resistance. Plant extracts consist of a complex assortment of phytochemical elements, against which the development of bacterial resistance is quite deliberate. This review emphasizes the antibiotic resistance mechanisms of bacteria, the reversal mechanism of antibiotic resistance by phytochemicals, the bioactive potential of phytochemicals against MDR, and the scientific evidence on molecular, biochemical, and clinical aspects to treat bacterial pathogenesis in humans. Moreover, clinical efficacy, trial, safety, toxicity, and affordability investigations, current status and developments, related demands, and future prospects are also highlighted.

Evaluation of 2,6-difluoro-3-(oxazol-2-ylmethoxy)benzamide chemotypes as Gram-negative FtsZ inhibitors

FtsZ inhibitors represent a new drug class as no drugs using this mode of action (MOA) have been approved by regulators. 3-alkoxy substituted 2,6-difluorobenzamide scaffold is one of the most studied FtsZ inhibitors among which the most promising anti-MRSA candidate TXA709 is in clinical trial. In this paper, we present the screening and evaluation of a benzamide class that is functionalized at the alkoxy fragment targeting Gram-negative bacteria. The variations in 3-alkoxy substitutions, specifically the hydroxylated alkyl residues to the secondary and stereogenic pseudo-benzylic carbon of their methyleneoxy linker, are particularly active against K. pneumoniae ATCC 10031 in marked contrast to the derivatives related to PC190723, all of which were inactive against Gram-negative bacteria. The two lead molecules TXA6101 and TXY6129 inhibit the polymerization of E. coli FtsZ in a concentration-dependent manner and induce changes in the morphology of E. coli and K. pneumoniae consistent with inhibition of cell division. These classes of compounds, however, were found to be substrates for efflux pumps in Gram-negative bacteria.

Discovery of FtsZ inhibitors by virtual screening as antibacterial agents and study of the inhibition mechanism

Inhibition of bacterial cell division is a novel mechanistic action in the development of new antimicrobial agents. The FtsZ protein is an important antimicrobial drug target because of its essential role in bacterial cell division. In the present study, potential inhibitors of FtsZ were identified by virtual screening followed by in vivo and in vitro bioassays. One of the candidates, Dacomitinib (S2727), shows for the first time its potent inhibitory activity against the MRSA strains. The binding mode of Dacomitinib in FtsZ was analyzed by docking, and Asp199 and Thr265 are thought to be essential residues involved in the interactions.

Phytochemicals: A Promising Weapon in the Arsenal against Antibiotic-Resistant Bacteria

The extensive usage of antibiotics and the rapid emergence of antimicrobial-resistant microbes (AMR) are becoming important global public health issues. Many solutions to these problems have been proposed, including developing alternative compounds with antimicrobial activities, managing existing antimicrobials, and rapidly detecting AMR pathogens. Among all of them, employing alternative compounds such as phytochemicals alone or in combination with other antibacterial agents appears to be both an effective and safe strategy for battling against these pathogens. The present review summarizes the scientific evidence on the biochemical, pharmacological, and clinical aspects of phytochemicals used to treat microbial pathogenesis. A wide range of commercial products are currently available on the market. Their well-documented clinical efficacy suggests that phytomedicines are valuable sources of new types of antimicrobial agents for future use. Innovative approaches and methodologies for identifying plant-derived products effective against AMR are also proposed in this review.

Design, synthesis and evaluation of novel 9-arylalkyl-10-methylacridinium derivatives as highly potent FtsZ-targeting antibacterial agents

With the increasing incidence of antibiotic resistance, new antibacterial agents having novel mechanisms of action hence are in an urgent need to combat infectious diseases caused by multidrug-resistant (MDR) pathogens. Four novel series of substituted 9-arylalkyl-10-methylacridinium derivatives as FtsZ inhibitors were designed, synthesized and evaluated for their antibacterial activities against various Gram-positive and Gram-negative bacteria. The results demonstrated that they exhibited broad-spectrum activities with substantial efficacy against MRSA and VRE, which were superior or comparable to the berberine, sanguinarine, linezolid, ciprofloxacin and vancomycin. In particular, the most promising compound 15f showed rapid bactericidal properties, which avoid the emergence of drug resistance. However, 15f showed no inhibitory effect on Gram-negative bacteria but biofilm formation study gave possible answers. Further target identification and mechanistic studies revealed that 15f functioned as an effective FtsZ inhibitor to alter the dynamics of FtsZ self-polymerization, which resulted in termination of the cell division and caused cell death. Further cytotoxicity and animal studies demonstrated that 15f not only displayed efficacy in a murine model of bacteremia in vivo, but also no significant hemolysis to mammalian cells. Overall, this compound with novel skeleton could serve as an antibacterial lead of FtsZ inhibitor for further evaluation of drug-likeness.

Computational studies of the properties and activities of selected trisubstituted benzimidazoles as potential antitubercular drugs inhibiting MTB-FtsZ polymerization

Trisubstituted benzimidazoles (trisbenz) are significantly active against nonreplicating Mycobacterium tuberculosis (MTB) by inhibiting the polymerization of Filamentous Temperature Sensitive Mutant Z (FtsZ), an essential bacteria cell division protein. In-depth in-silico study of 5 of the most active trisubstituted benzimidazoles; trisbenz 1, 2, 3, 4 and 5, giving insight into their properties, such as stability, bioavailability, interactions with residues at the binding site of MTB-FtsZ and their influence on structural dynamics of the protein have been conducted. This was achieved through the application of in-silico methods including density functional theory (DFT) calculations, ADME properties calculations, molecular docking and molecular dynamics simulations. A DFT approach was applied to predict reactivity properties of potent FtsZ inhibitors, and the results reveal the relative reactivity of these inhibitors as bioactive moieties. The estimated ADME properties predicted all 5 compounds to be bioavailable and suitable for oral administration. Molecular docking, binding free energy, RMSD, RMSF, and hydrogen bond analysis confirmed these 5 compounds as potent MTB-FtsZ inhibitors. Although analyses proved these compounds to be bioactive and potent MTB-FtsZ inhibitors, however, trisbenz 1 appeared to be the most active against this protein while trisbenz 5 was the least active. This study further confirms the experimental study while also giving insight on the compounds mechanism of action and presents their bioavailability properties.

Recent advances of imidazole-containing derivatives as anti-tubercular agents

Tuberculosis still remains one of the most common, communicable, and leading deadliest diseases known to mankind throughout the world. Drug-resistance in Mycobacterium tuberculosis which threatens to worsen the global tuberculosis epidemic has caused great concern in recent years. To overcome the resistance, the development of new drugs with novel mechanisms of actions is of great importance. Imidazole-containing derivatives endow with various biological properties, and some of them demonstrated excellent anti-tubercular activity. As the most emblematic example, 4-nitroimidazole delamanid has already received approval for treatment of multidrug-resistant tuberculosis infected patients. Thus, imidazole-containing derivatives have caused great interests in discovery of new anti-tubercular agents. Numerous of imidazole-containing derivatives were synthesized and screened for their in vitro and in vivo anti-mycobacterial activities against both drug-sensitive and drug-resistant Mycobacterium tuberculosis pathogens. This review aims to outline the recent advances of imidazole-containing derivatives as anti-tubercular agents, and summarize the structure-activity relationship of these derivatives. The enriched structure-activity relationship may pave the way for the further rational development of imidazole-containing derivatives as anti-tubercular agents.

Design and development of novel antibiotics based on FtsZ inhibition – in silico studies

QSAR models, computer-aided drug design and the application of molecular docking were used to evaluate benzamide analogues as FtsZ inhibitors.

Comparative proteomics analysis of Neisseria gonorrhoeae strains in response to extended-spectrum cephalosporins

Neisseria gonorrhoeae strains displaying reduced susceptibility and resistance to extended-spectrum cephalosporins (ESCs) are major public health concerns. Although resistance mechanisms of ESCs have extensively been studied, the proteome-wide investigation on the biological response to the antibiotic stress is still limited. Herein, a proteomics approach based on two-dimensional gel electrophoresis and MALDI-TOF/TOF-MS analysis was applied to investigate the global protein expression under ESC stresses of ESC-susceptible and ESC-reduced susceptible N. gonorrhoeae strains. Upon exposure to ceftriaxone, 14 and 21 proteins of ESC-susceptible and ESC-reduced susceptible strains, respectively, were shown to be differentially expressed. In the meanwhile, differential expressions of 13 and 17 proteins were detected under cefixime stress for ESC-susceptible and ESC-reduced susceptible strains, respectively. ESC antibiotics have been proven to trigger the expression of several proteins implicated in a variety of biological functions including transport system, energy metabolism, stress response and pathogenic virulence factors. Interestingly, macrophage infectivity potentiators (Ng-MIP) showed increased expression for ESC-reduced susceptible strain under ESC stress. The altered expression of Ng-MIP was found to be a unique response to ESC stresses. Our finding proposes a broad view on proteomic changes in N. gonorrhoeae in response to ESC antibiotics that provides further insights into the gonococcal antimicrobial resistance and physiological adaptation mechanism.

Structural Flexibility of an Inhibitor Overcomes Drug Resistance Mutations in Staphylococcus aureus FtsZ

In the effort to combat antibiotic resistance, inhibitors of the essential bacterial protein FtsZ have emerged as a promising new class of compounds with clinical potential. One such FtsZ inhibitor (TXA707) is associated with potent activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) that are resistant to current standard-of-care antibiotics. However, mutations in S. aureus FtsZ (SaFtsZ) that confer resistance to TXA707 have been observed, with mutations in the Gly196 and Gly193 residues being among the most prevalent. Here, we describe structural studies of an FtsZ inhibitor, TXA6101, which retains activity against MRSA isolates that express either G196S or G193D mutant FtsZ. We present the crystal structures of TXA6101 in complex with both wild-type SaFtsZ and G196S mutant SaFtsZ, as well the crystal structure of TXA707 in complex with wild-type SaFtsZ. Comparison of the three structures reveals a molecular basis for the differential targeting abilities of TXA6101 and TXA707. The greater structural flexibility of TXA6101 relative to TXA707 enables TXA6101 to avoid steric clashes with Ser196 and Asp193. Our structures also demonstrate that the binding of TXA6101 induces previously unobserved conformational rearrangements of SaFtsZ residues in the binding pocket. In aggregate, the structures reported in this work reveal key factors for overcoming drug resistance mutations in SaFtsZ and offer a structural basis for the design of FtsZ inhibitors with enhanced antibacterial potency and reduced susceptibility to mutational resistance.

Strategic incorporation of fluorine in the drug discovery of new-generation antitubercular agents targeting bacterial cell division protein FtsZ

This article presents an account of our research on the discovery and development of new-generation fluorine-containing antibacterial agents against drug-resistant tuberculosis, targeting FtsZ. FtsZ is an essential protein for bacterial cell division and a highly promising therapeutic target for antibacterial drug discovery. Through design, synthesis and semi-HTP screening of libraries of novel benzimidazoles, followed by SAR studies, we identified highly potent lead compounds. However, these lead compounds were found to lack sufficient metabolic and plasma stabilities. Accordingly, we have performed extensive study on the strategic incorporation of fluorine into lead compounds to improve pharmacological properties. This study has led to the development of highly efficacious fluorine-containing benzimidazoles as potential drug candidates. We have also performed computational docking analysis of these novel FtsZ inhibitors to identify their putative binding site. Based on the structural data and docking analysis, a plausible mode-of-action for this novel class of FtsZ inhibitors is proposed.

FtsZ inhibition and redox modulation with one chemical scaffold: Potential use of dihydroquinolines against mycobacteria

The dual effect of FtsZ inhibition and oxidative stress by a group of 1,2-dihydroquinolines that culminate in bactericidal effect on mycobacterium strains is demonstrated. They inhibited the non-pathogenic Mycobacterium smegmatis mc(2) 155 with MIC as low as 0.9 μg/mL and induced filamentation. Detailed studies revealed their ability to inhibit polymerization and GTPase activity of MtbFtsZ (Mycobacterial filamentous temperature sensitive Z) with an IC50 value of ∼40 μM. In addition to such target specific effects, these compounds exerted a global cellular effect by causing redox-imbalance that was evident from overproduction of ROS in treated cells. Such multi-targeting effect with one chemical scaffold has considerable significance in this era of emerging drug resistance and could offer promise in the development of new therapeutic agents against tuberculosis.

In Vivo Pharmacodynamic Evaluation of an FtsZ Inhibitor, TXA-709, and Its Active Metabolite, TXA-707, in a Murine Neutropenic Thigh Infection Model

Antibiotics with novel mechanisms of action are urgently needed. Processes of cellular division are attractive targets for new drug development. FtsZ, an integral protein involved in cell cytokinesis, is a representative example. In the present study, the pharmacodynamic (PD) activity of an FtsZ inhibitor, TXA-709, and its active metabolite, TXA-707, was evaluated in the neutropenic murine thigh infection model against 5 Staphylococcus aureus isolates, including both methicillin-susceptible and methicillin-resistant isolates. The pharmacokinetics (PK) of the TXA-707 active metabolite were examined after oral administration of the TXA-709 prodrug at 10, 40, and 160 mg/kg of body weight. The half-life ranged from 3.2 to 4.4 h, and the area under the concentration-time curve (AUC) and maximum concentration of drug in serum (Cmax) were relatively linear over the doses studied. All organisms exhibited an MIC of 1 mg/liter. Dose fractionation demonstrated the area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC ratio) to be the PD index most closely linked to efficacy (R(2) = 0.72). Dose-dependent activity was demonstrated against all 5 isolates, and the methicillin-resistance phenotype did not alter the pharmacokinetic/pharmacodynamic (PK/PD) targets. Net stasis was achieved against all isolates and a 1-log10 kill level against 4 isolates. PD targets included total drug 24-h AUC/MIC values of 122 for net stasis and 243 for 1-log10 killing. TXA-709 and TXA-707 are a promising novel antibacterial class and compound for S. aureus infections. These results should prove useful for design of clinical dosing regimen trials.

TXA709, an FtsZ-Targeting Benzamide Prodrug with Improved Pharmacokinetics and Enhanced In Vivo Efficacy against Methicillin-Resistant Staphylococcus aureus

The clinical development of FtsZ-targeting benzamide compounds like PC190723 has been limited by poor drug-like and pharmacokinetic properties. Development of prodrugs of PC190723 (e.g., TXY541) resulted in enhanced pharmaceutical properties, which, in turn, led to improved intravenous efficacy as well as the first demonstration of oral efficacy in vivo against both methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA). Despite being efficacious in vivo, TXY541 still suffered from suboptimal pharmacokinetics and the requirement of high efficacious doses. We describe here the design of a new prodrug (TXA709) in which the Cl group on the pyridyl ring has been replaced with a CF3 functionality that is resistant to metabolic attack. As a result of this enhanced metabolic stability, the product of the TXA709 prodrug (TXA707) is associated with improved pharmacokinetic properties (a 6.5-fold-longer half-life and a 3-fold-greater oral bioavailability) and superior in vivo antistaphylococcal efficacy relative to PC190723. We validate FtsZ as the antibacterial target of TXA707 and demonstrate that the compound retains potent bactericidal activity against S. aureus strains resistant to the current standard-of-care drugs vancomycin, daptomycin, and linezolid. These collective properties, coupled with minimal observed toxicity to mammalian cells, establish the prodrug TXA709 as an antistaphylococcal agent worthy of clinical development.

Inhibiting the growth of methicillin-resistant Staphylococcus aureus in vitro with antisense peptide nucleic acid conjugates targeting the ftsZ gene

BACKGROUND

The increasing emergence of clinical infections caused by methicillin-resistant Staphylococcus aureus (MRSA) challenges existing therapeutic options and highlights the need to develop novel treatment strategies. The ftsZ gene is essential to bacterial cell division.

METHODS

In this study, two antisense peptide nucleic acids (PNAs) conjugated to a cell-penetrating peptide were used to inhibit the growth of MRSA. PPNA1, identified with computational prediction and dot-blot hybridization, is complementary to nucleotides 309-323 of the ftsZ mRNA. PPNA2 was designed to target the region that includes the translation initiation site and the ribosomal-binding site (Shine-Dalgarno sequence) of the ftsZ gene. Scrambled PPNA was constructed with mismatches to three bases within the antisense PPNA1 sequence.

RESULTS

PPNA1 and PPNA2 caused concentration-dependent growth inhibition and had bactericidal effects. The minimal bactericidal concentrations of antisense PPNA1 and PPNA2 were 30μmol/l and 40μmol/l, respectively. The scrambled PPNA had no effect on bacterial growth, even at higher concentrations, confirming the sequence specificity of the probes. RT-PCR showed that the antisense PPNAs suppressed ftsZ mRNA expression in a dose-dependent manner.

CONCLUSION

Our results demonstrate that the potent effects of PNAs on bacterial growth and cell viability were mediated by the down-regulation or even knock-out of ftsZ gene expression. This highlights the utility of ftsZ as a promising target for the development of new antisense antibacterial agents to treat MRSA infections.

Drug discovery targeting cell division proteins, microtubules and FtsZ

Eukaryotic cell division or cytokinesis has been a major target for anticancer drug discovery. After the huge success of paclitaxel and docetaxel, microtubule-stabilizing agents (MSAs) appear to have gained a premier status in the discovery of next-generation anticancer agents. However, the drug resistance caused by MDR, point mutations, and overexpression of tubulin subtypes, etc., is a serious issue associated with these agents. Accordingly, the discovery and development of new-generation MSAs that can obviate various drug resistances has a significant meaning. In sharp contrast, prokaryotic cell division has been largely unexploited for the discovery and development of antibacterial drugs. However, recent studies on the mechanism of bacterial cytokinesis revealed that the most abundant and highly conserved cell division protein, FtsZ, would be an excellent new target for the drug discovery of next-generation antibacterial agents that can circumvent drug-resistances to the commonly used drugs for tuberculosis, MRSA and other infections. This review describes an account of our research on these two fronts in drug discovery, targeting eukaryotic as well as prokaryotic cell division.

Design, synthesis and evaluation of novel 2,5,6-trisubstituted benzimidazoles targeting FtsZ as antitubercular agents

Filamenting temperature-sensitive protein Z (FtsZ), an essential cell division protein, is a promising target for the drug discovery of new-generation antibacterial agents against various bacterial pathogens. As a part of SAR studies on benzimidazoles, we have synthesized a library of 376 novel 2,5,6-trisubstituted benzimidazoles, bearing ether or thioether linkage at the 6-position. In a preliminary HTP screening against Mtb H37Rv, 108 compounds were identified as hits at a cut off concentration of 5 μg/mL. Among those hits, 10 compounds exhibited MIC values in the range of 0.63-12.5 μg/mL. Light scattering assay and TEM analysis with the most potent compound 5a clearly indicate that its molecular target is Mtb-FtsZ. Also, the Kd of 5a with Mtb-FtsZ was determined to be 1.32 μM.

Characterization and in vitro inhibition studies of Bacillus anthracis FtsZ: a potential antibacterial target

FtsZ is an essential bacterial cell division protein that is an attractive target for the development of antibacterial agents. FtsZ is a homologue of eukaryotic tubulin, has GTPase activity, and forms a ring-type structure to initiate cell division. In this study, the FtsZ of Bacillus anthracis was cloned into a bacterial expression vector and overexpressed into Escherichia coli BL21 (DE3) cells. The overexpressed B. anthracis FtsZ was soluble and purified to homogeneity using Ni-His-tag affinity chromatography. Like other known FtsZs, the recombinant B. anthracis FtsZ also showed GTP-dependent polymerization, which was analyzed using both spectrophotometric and Transmission Electronic Microscopic (TEM) analysis. Using the purified FtsZ, we screened a naturally extracted chemical library to identify potent and novel inhibitors. The screening yielded three chemicals, SA-011, SA-059, and SA-069, that inhibited the in vitro polymerization activity of FtsZ in the micromolar range (IC50 of 55-168 μM). The inhibition potency was significantly comparable with that of berberine, a known potential inhibitor of FtsZ. Understanding the biochemical basis of the effect of these inhibitors on B. anthracis growth would provide a promising path for the development of new antianthracis drugs.

SAR studies on trisubstituted benzimidazoles as inhibitors of Mtb FtsZ for the development of novel antitubercular agents

FtsZ, an essential protein for bacterial cell division, is a highly promising therapeutic target, especially for the discovery and development of new-generation anti-TB agents. Following up the identification of two lead 2,5,6-trisubstituted benzimidazoles, 1 and 2, targeting Mtb-FtsZ in our previous study, an extensive SAR study for optimization of these lead compounds was performed through systematic modification of the 5 and 6 positions. This study has successfully led to the discovery of a highly potent advanced lead 5f (MIC = 0.06 μg/mL) and several other compounds with comparable potencies. These advanced lead compounds possess a dimethylamino group at the 6 position. The functional groups at the 5 position exhibit substantial effects on the antibacterial activity as well. In vitro experiments such as the FtsZ polymerization inhibitory assay and TEM analysis of Mtb-FtsZ treated with 5f and others indicate that Mtb-FtsZ is the molecular target for their antibacterial activity.

Design, synthesis and structure-activity relationships of substituted oxazole-benzamide antibacterial inhibitors of FtsZ

The design, synthesis and structure-activity relationships of a series of oxazole-benzamide inhibitors of the essential bacterial cell division protein FtsZ are described. Compounds had potent anti-staphylococcal activity and inhibited the cytokinesis of the clinically-significant bacterial pathogen Staphylococcus aureus. Selected analogues possessing a 5-halo oxazole also inhibited a strain of S. aureus harbouring the glycine-to-alanine amino acid substitution at residue 196 of FtsZ which conferred resistance to previously reported inhibitors in the series. Substitutions to the pseudo-benzylic carbon of the scaffold improved the pharmacokinetic properties by increasing metabolic stability and provided a mechanism for creating pro-drugs. Combining multiple substitutions based on the findings reported in this study has provided small-molecule inhibitors of FtsZ with enhanced in vitro and in vivo antibacterial efficacy.

Pharmacokinetics and in vivo antistaphylococcal efficacy of TXY541, a 1-methylpiperidine-4-carboxamide prodrug of PC190723

The benzamide derivative PC190723 was among the first of a promising new class of FtsZ-directed antibacterial agents to be identified that exhibit potent antistaphylococcal activity. However, the compound is associated with poor drug-like properties. As part of an ongoing effort to develop FtsZ-targeting antibacterial agents with increased potential for clinical utility, we describe herein the pharmacodynamics, pharmacokinetics, in vivo antistaphylococcal efficacy, and mammalian cytotoxicity of TXY541, a novel 1-methylpiperidine-4-carboxamide prodrug of PC190723. TXY541 was found to be 143-times more soluble than PC190723 in an aqueous acidic vehicle (10mM citrate, pH 2.6) suitable for both oral and intravenous in vivo administration. In staphylococcal growth media, TXY541 converts to PC190723 with a half-life of approximately 8h. In 100% mouse serum, the TXY541-to-PC190723 conversion was much more rapid (with a half-life of approximately 3min), suggesting that the conversion of the prodrug in serum is predominantly enzyme-catalyzed. Pharmacokinetic analysis of both orally and intravenously administered TXY541 in mice yielded a half-life for the PC190723 conversion product of 0.56h and an oral bioavailability of 29.6%. Whether administered orally or intravenously, TXY541 was found to be efficacious in vivo in mouse models of systemic infection with both methicillin-sensitive and methicillin-resistant S. aureus. Toxicological assessment of TXY541 against mammalian cells revealed minimal detectable cytotoxicity. The results presented here highlight TXY541 as a potential therapeutic agent that warrants further pre-clinical development.

An FtsZ-targeting prodrug with oral antistaphylococcal efficacy in vivo

The bacterial cell division protein FtsZ represents a novel antibiotic target that has yet to be exploited clinically. The benzamide PC190723 was among the first FtsZ-targeting compounds to exhibit in vivo efficacy in a murine infection model system. Despite its initial promise, the poor formulation properties of the compound have limited its potential for clinical development. We describe here the development of an N-Mannich base derivative of PC190723 with enhanced drug-like properties and oral in vivo efficacy. The N-Mannich base derivative (TXY436) is ∼100-fold more soluble than PC190723 in an acidic aqueous vehicle (10 mM citrate, pH 2.6) suitable for oral in vivo administration. At physiological pH (7.4), TXY436 acts as a prodrug, converting to PC190723 with a conversion half-life of 18.2 ± 1.6 min. Pharmacokinetic analysis following intravenous administration of TXY436 into mice yielded elimination half-lives of 0.26 and 0.96 h for the TXY436 prodrug and its PC190723 product, respectively. In addition, TXY436 was found to be orally bioavailable and associated with significant extravascular distribution. Using a mouse model of systemic infection with methicillin-sensitive Staphylococcus aureus or methicillin-resistant S. aureus, we show that TXY436 is efficacious in vivo upon oral administration. In contrast, the oral administration of PC190723 was not efficacious. Mammalian cytotoxicity studies of TXY436 using Vero cells revealed an absence of toxicity up to compound concentrations at least 64 times greater than those associated with antistaphylococcal activity. These collective properties make TXY436 a worthy candidate for further investigation as a clinically useful agent for the treatment of staphylococcal infections.

Antibacterial activity of quinoxalines, quinazolines, and 1,5-naphthyridines

Several phenyl substituted naphthalenes and isoquinolines have been identified as antibacterial agents that inhibit FtsZ-Zing formation. In the present study we evaluated the antibacterial of several phenyl substituted quinoxalines, quinazolines and 1,5-naphthyridines against methicillin-sensitive and methicillin-resistant Staphylococcusaureus and vancomycin-sensitive and vancomycin-resistant Enterococcusfaecalis. Some of the more active compounds against S. aureus were evaluated for their effect on FtsZ protein polymerization. Further studies were also performed to assess their relative bactericidal and bacteriostatic activities. The notable differences observed between nonquaternized and quaternized quinoxaline derivatives suggest that differing mechanisms of action are associated with their antibacterial properties.

Enterococcal and streptococcal resistance to PC190723 and related compounds: molecular insights from a FtsZ mutational analysis

New antibiotics with novel mechanisms of action are urgently needed to overcome the growing bacterial resistance problem faced by clinicians today. PC190723 and related compounds represent a promising new class of antibacterial compounds that target the essential bacterial cell division protein FtsZ. While this family of compounds exhibits potent antistaphylococcal activity, they have poor activity against enterococci and streptococci. The studies described herein are aimed at investigating the molecular basis of the enterococcal and streptococcal resistance to this family of compounds. We show that the poor activity of the compounds against enterococci and streptococci correlates with a correspondingly weak impact of the compounds on the self-polymerization of the FtsZ proteins from those bacteria. In addition, computational and mutational studies identify two key FtsZ residues (E34 and R308) as being important determinants of enterococcal and streptococcal resistance to the PC190723-type class of compounds.

Benzimidazole-based antibacterial agents against Francisella tularensis

Francisella tularensis is a highly virulent pathogenic bacterium. In order to identify novel potential antibacterial agents against F. tularensis, libraries of trisubstituted benzimidazoles were screened against F. tularensis LVS strain. In a preliminary screening assay, remarkably, 23 of 2,5,6- and 2,5,7-trisubstituted benzimidazoles showed excellent activity exhibiting greater than 90% growth inhibition at 1 μg/mL. Among those hits, 21 compounds showed MIC90 values in the range of 0.35-48.6 μg/mL after accurate MIC determination. In ex vivo efficacy assays, four of these compounds exhibited 2-3log reduction in colony forming units (CFU) per mL at concentrations of 10 and 50 μg/mL.

Substituted 1,6-diphenylnaphthalenes as FtsZ-targeting antibacterial agents

Bacterial cell division occurs in conjunction with the formation of a cytokinetic Z-ring structure comprised of FtsZ subunits. Agents that disrupt Z-ring formation have the potential, through this unique mechanism, to be effective against several of the newly emerging multidrug-resistant strains of infectious bacteria. Several 1-phenylbenzo[c]phenanthridines exhibit notable antibacterial activity. Based upon their structural similarity to these compounds, a distinct series of substituted 1,6-diphenylnaphthalenes were synthesized and evaluated for antibacterial activity against Staphylococcus aureus and Enterococcus faecalis. In addition, the effect of select 1,6-diphenylnaphthalenes on the polymerization dynamics of S. aureus FtsZ and mammalian β-tubulin was also assessed. The presence of a basic functional group or a quaternary ammonium substituent on the 6-phenylnaphthalene was required for significant antibacterial activity. Diphenylnaphthalene derivatives that were active as antibiotics, did exert a pronounced effect on bacterial FtsZ polymerization and do not appear to cross-react with mammalian tubulin to any significant degree.

Antibacterial activity of alkyl gallates against Xanthomonas citri subsp. citri

The plant-pathogenic bacterium Xanthomonas citri subsp. citri is the causal agent of Asiatic citrus canker, a serious disease that affects all the cultivars of citrus in subtropical citrus-producing areas worldwide. There is no curative treatment for citrus canker; thus, the eradication of infected plants constitutes the only effective control of the spread of X. citri subsp. citri. Since the eradication program in the state of São Paulo, Brazil, is under threat, there is a clear risk of X. citri subsp. citri becoming endemic in the main orange-producing area in the world. Here we evaluated the potential use of alkyl gallates to prevent X. citri subsp. citri growth. These esters displayed a potent anti-X. citri subsp. citri activity similar to that of kanamycin (positive control), as evaluated by the resazurin microtiter assay (REMA). The treatment of X. citri subsp. citri cells with these compounds induced altered cell morphology, and investigations of the possible intracellular targets using X. citri subsp. citri strains labeled for the septum and centromere pointed to a common target involved in chromosome segregation and cell division. Finally, the artificial inoculation of citrus with X. citri subsp. citri cells pretreated with alkyl gallates showed that the bacterium loses the ability to colonize its host, which indicates the potential of these esters to protect citrus plants against X. citri subsp. citri infection.

3-Phenyl substituted 6,7-dimethoxyisoquinoline derivatives as FtsZ-targeting antibacterial agents

The emergence of multidrug-resistant bacteria has created an urgent need for antibiotics with a novel mechanism of action. The bacterial cell division protein FtsZ is an attractive target for the development of novel antibiotics. The benzo[c]phenanthridinium sanguinarine and the dibenzo[a,g]quinolizin-7-ium berberine are two structurally similar plant alkaloids that alter FtsZ function. The presence of a hydrophobic functionality at either the 1-position of 5-methylbenzo[c]phenanthridinium derivatives or the 2-position of dibenzo[a,g]quinolizin-7-ium derivatives is associated with significantly enhanced antibacterial activity. 3-Phenylisoquinoline represents a subunit within the ring-systems of both of these alkaloids. Several 3-phenylisoquinolines and 3-phenylisoquinolinium derivatives have been synthesized and evaluated for antibacterial activity against Staphylococcus aureus and Enterococcus faecalis, including multidrug-resistant strains of methicillin-resistant S. aureus (MRSA) and vancomycin-resistant E. faecalis (VRE). A number of derivatives were found to have activity against both MRSA and VRE. The binding of select compounds to S. aureus FtsZ (SaFtsZ) was demonstrated and characterized using fluorescence spectroscopy. In addition, the compounds were shown to act as stabilizers of SaFtsZ polymers and concomitant inhibitors of SaFtsZ GTPase activity. Toxicological assessment of select compounds revealed minimal cross-reaction mammalian β-tubulin as well as little or no human cytotoxicity.

Chlamydial biology and its associated virulence blockers

Chlamydiales are obligate intracellular parasites of eukaryotic cells. They can be distinguished from other Gram-negative bacteria through their characteristic developmental cycle, in addition to special biochemical and physical adaptations to subvert the eukaryotic host cell. The host spectrum includes humans and other mammals, fish, birds, reptiles, insects and even amoeba, causing a plethora of diseases. The first part of this review focuses on the specific chlamydial infection biology and metabolism. As resistance to classical antibiotics is emerging among Chlamydiae as well, the second part elaborates on specific compounds and tools to block chlamydial virulence traits, such as adhesion and internalization, Type III secretion and modulation of gene expression.

An improved small-molecule inhibitor of FtsZ with superior in vitro potency, drug-like properties, and in vivo efficacy

The bacterial cell division protein FtsZ is an attractive target for small-molecule antibacterial drug discovery. Derivatives of 3-methoxybenzamide, including compound PC190723, have been reported to be potent and selective antistaphylococcal agents which exert their effects through the disruption of intracellular FtsZ function. Here, we report the further optimization of 3-methoxybenzamide derivatives towards a drug candidate. The in vitro and in vivo characterization of a more advanced lead compound, designated compound 1, is described. Compound 1 was potently antibacterial, with an average MIC of 0.12 μg/ml against all staphylococcal species, including methicillin- and multidrug-resistant Staphylococcus aureus and Staphylococcus epidermidis. Compound 1 inhibited an S. aureus strain carrying the G196A mutation in FtsZ, which confers resistance to PC190723. Like PC190723, compound 1 acted on whole bacterial cells by blocking cytokinesis. No interactions between compound 1 and a diverse panel of antibiotics were measured in checkerboard experiments. Compound 1 displayed suitable in vitro pharmaceutical properties and a favorable in vivo pharmacokinetic profile following intravenous and oral administration, with a calculated bioavailability of 82.0% in mice. Compound 1 demonstrated efficacy in a murine model of systemic S. aureus infection and caused a significant decrease in the bacterial load in the thigh infection model. A greater reduction in the number of S. aureus cells recovered from infected thighs, equivalent to 3.68 log units, than in those recovered from controls was achieved using a succinate prodrug of compound 1, which was designated compound 2. In summary, optimized derivatives of 3-methoxybenzamide may yield a first-in-class FtsZ inhibitor for the treatment of antibiotic-resistant staphylococcal infections.

A bactericidal guanidinomethyl biaryl that alters the dynamics of bacterial FtsZ polymerization

The prevalence of multidrug resistance among clinically significant bacterial pathogens underscores a critical need for the development of new classes of antibiotics with novel mechanisms of action. Here we describe the synthesis and evaluation of a guanidinomethyl biaryl compound {1-((4'-(tert-butyl)-[1,1'-biphenyl]-3-yl)methyl)guanidine} that targets the bacterial cell division protein FtsZ. In vitro studies with various bacterial FtsZ proteins reveal that the compound alters the dynamics of FtsZ self-polymerization via a stimulatory mechanism, while minimally impacting the polymerization of tubulin, the closest mammalian homologue of FtsZ. The FtsZ binding site of the compound is identified through a combination of computational and mutational approaches. The compound exhibits a broad spectrum of bactericidal activity, including activity against the multidrug-resistant pathogens methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE), while also exhibiting a minimal potential to induce resistance. Taken together, our results highlight the compound as a promising new FtsZ-targeting bactericidal agent.

Mechanism of action of the cell-division inhibitor PC190723: modulation of FtsZ assembly cooperativity

The cooperative assembly of FtsZ, the prokaryotic homologue of tubulin, plays an essential role in cell division. FtsZ is a potential drug target, as illustrated by the small-molecule cell-cycle inhibitor and antibacterial agent PC190723 that targets FtsZ. We demonstrate that PC190723 negatively modulates Staphylococcus aureus FtsZ polymerization cooperativity as reflected in polymerization at lower concentrations without a defined critical concentration. The crystal structure of the S. aureus FtsZ-PC190723 complex shows a domain movement that would stabilize the FtsZ protofilament over the monomeric state, with the conformational change mediated from the GTP-binding site to the C-terminal domain via helix 7. Together, the results reveal the molecular mechanism of FtsZ modulation by PC190723 and a conformational switch to the high-affinity state that enables polymer assembly.

Molecular dynamics simulation of GTPase activity in polymers of the cell division protein FtsZ

FtsZ, the prokaryotic ortholog of tubulin, assembles into polymers in the bacterial division ring. The interfaces between monomers contain a GTP molecule, but the relationship between polymerization and GTPase activity is not unequivocally proven. A set of short FtsZ polymers were modelled and the formation of active GTPase structures was monitored using molecular dynamics. Only the interfaces nearest the polymer ends exhibited an adequate geometry for GTP hydrolysis. Simulated conversion of interfaces from close-to-end to internal position and vice versa resulted in their spontaneous rearrangement between active and inactive conformations. This predicted behavior of FtsZ polymer ends was supported by in vitro experiments.

Targeting the assembly of bacterial cell division protein FtsZ with small molecules

FtsZ is the key protein of bacterial cell division and an emergent target for new antibiotics. It is a filament-forming GTPase and a structural homologue of eukaryotic tubulin. A number of FtsZ-interacting compounds have been reported, some of which have powerful antibacterial activity. Here we review recent advances and new approaches in modulating FtsZ assembly with small molecules. This includes analyzing their chemical features, binding sites, mechanisms of action, the methods employed, and computational insights, aimed at a better understanding of their molecular recognition by FtsZ and at rational antibiotic design.

Chemical-biological studies of subcellular organization in bacteria

The subcellular organization of biological molecules is a critical determinant of many bacterial processes, including growth, replication of the genome, and division, yet the details of many mechanisms that control intracellular organization remain unknown. Decoding this information will impact the field of bacterial physiology and can provide insight into eukaryotic biology, including related processes in mitochondria and chloroplasts. Small molecule probes provide unique advantages in studying these mechanisms and manipulating the organization of biomolecules in live bacterial cells. In this review, we describe small molecules that are available for investigating subcellular organization in bacteria, specifically targeting FtsZ, MreB, peptidoglycan, and lipid bilayers. We discuss how these probes have been used to study microbiological questions and conclude by providing suggestions about important areas in which chemical-biological approaches will have a revolutionary impact on the study of bacterial physiology.