Rational molecular design converting fascaplysin derivatives to potent broad-spectrum inhibitors against bacterial pathogens via targeting FtsZ

The filamentous temperature-sensitive mutant Z protein (FtsZ), a key player in bacterial cell division machinery, emerges as an attractive target to tackle the plight posed by the ever growing antibiotic resistance over the world. Therefore in this regard, agents with scaffold diversities and broad-spectrum antibacterial activity against Gram-positive and Gram-negative pathogens are highly needed. In this study, a new class of marine-derived fascaplysin derivatives has been designed and synthesized by Suzuki-Miyaura cross-coupling. Some compounds exhibited potent bactericidal activities against a panel of Gram-positive (MIC = 0.024-6.25 μg/mL) and Gram-negative (MIC = 1.56-12.5 μg/mL) bacteria including methicillin-resistant S. aureus (MRSA). They exerted their effects by dual action mechanism via disrupting the integrity of the bacterial cell membrane and targeting FtsZ protein. These compounds stimulated polymerization of FtsZ monomers and bundling of the polymers, and stabilized the resulting polymer network, thus leading to the dysfunction of FtsZ in cell division. In addition, these agents showed negligible hemolytic activity and low cytotoxicity to mammalian cells. The studies on docking and molecular dynamics simulations suggest that these inhibitors bind to the hydrophilic inter-domain cleft of FtsZ protein and the insights obtained in this study would facilitate the development of potential drugs with broad-spectrum bioactivities.

The bacterial division protein MinDE has an independent function in flagellation

Before preparing for division, bacteria stop their motility. During the exponential growth phase in Escherichia coli, when the rate of bacterial division is highest, the expression of flagellar genes is repressed and bacterial adhesion is enhanced. Hence, it is evident that cell division and motility in bacteria are linked; however, the specific molecular mechanism by which these two processes are linked is not known. While observing E. coli, we found that compared to the WT, the E. coli (Δmin) cells show higher motility and flagellation. We demonstrated that the higher motility was due to the absence of the Min system and can be restored to normal in the presence of Min proteins, where Min system negatively regulates flagella formation. The Min system in E. coli is widely studied for its role in the inhibition of polar Z-ring formation through its pole-to-pole oscillation. However, its role in bacterial motility is not explored. MinD homologs, FlhG and FleN, are known to control flagellar expression through their interaction with FlrA and FleQ, respectively. AtoC, a part of the two-component system AtoSC complex, is homologous to FlrA/FleQ, and the complex is involved in E. coli flagellation via its interaction with the fliA promoter. We have shown that MinD interacts directly with the AtoS of AtoSC complex and controls the fliA expression. Our findings suggest that the Min system acts as a link between cell division and motility in E. coli.

An adamantyl-caffeoyl-anilide exhibits broad-spectrum antibacterial activity by inhibiting FtsZ assembly and Z-ring formation

Several harmful bacteria have evolved resistance to conventional antibiotics due to their extensive usage. FtsZ, a principal bacterial cell division protein, is considered as an important drug target to combat resistance. We identified a caffeoyl anilide derivative, (E)-N-(4-(3-(3,4-dihydroxyphenyl)acryloyl)phenyl)-1-adamantylamide (compound 11) as a new antimicrobial agent targeting FtsZ. Compound 11 caused cell elongation in Mycobacterium smegmatis, Bacillus subtilis, and Escherichia coli cells, indicating that it inhibits cell partitioning. Compound 11 inhibited the assembly of Mycobacterium smegmatis FtsZ (MsFtsZ), forming short and thin filaments in vitro. Interestingly, the compound increased the rate of GTP hydrolysis of MsFtsZ. Compound 11 also impeded the assembly of Mycobacterium tuberculosis FtsZ. Fluorescence and absorption spectroscopic analysis suggested that compound 11 binds to MsFtsZ and produces conformational changes in FtsZ. The docking analysis indicated that the compound binds at the interdomain cleft of MsFtsZ. Further, it caused delocalization of the Z-ring in Mycobacterium smegmatis and Bacillus subtilis without affecting DNA segregation. Notably, compound 11 did not inhibit tubulin polymerization, the eukaryotic homolog of FtsZ, suggesting its specificity on bacteria. The evidence indicated that compound 11 exerts its antibacterial effect by impeding FtsZ assembly and has the potential to be developed as a broad-spectrum antimicrobial agent.

Filamentous temperature sensitive mutant Z: a putative target to combat antibacterial resistance

In the pre-antibiotic era, common bacterial infections accounted for high mortality and morbidity. Moreover, the discovery of penicillin in 1928 marked the beginning of an antibiotic revolution, and this antibiotic era witnessed the discovery of many novel antibiotics, a golden era. However, the misuse or overuse of these antibiotics, natural resistance that existed even before the antibiotics were discovered, genetic variations in bacteria, natural selection, and acquisition of resistance from one species to another consistently increased the resistance to the existing antibacterial targets. Antibacterial resistance (ABR) is now becoming an ever-increasing concern jeopardizing global health. Henceforth, there is an urgent unmet need to discover novel compounds to combat ABR, which act through untapped pathways/mechanisms. Filamentous Temperature Sensitive mutant Z (FtsZ) is one such unique target, a tubulin homolog involved in developing a cytoskeletal framework for the cytokinetic ring. Additionally, its pivotal role in bacterial cell division and the lack of homologous structural protein in mammals makes it a potential antibacterial target for developing novel molecules. Approximately 2176 X-crystal structures of FtsZ were available, which initiated the research efforts to develop novel antibacterial agents. The literature has reported several natural, semisynthetic, peptides, and synthetic molecules as FtsZ inhibitors. This review provides valuable insights into the basic crystal structure of FtsZ, its inhibitors, and their inhibitory activities. This review also describes the available in vitro detection and quantification methods of FtsZ-drug complexes and the various approaches for determining drugs targeting FtsZ polymerization.

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.

Models versus pathogens: how conserved is the FtsZ in bacteria?

Combating anti-microbial resistance by developing alternative strategies is the need of the hour. Cell division, particularly FtsZ, is being extensively studied for its potential as an alternative target for anti-bacterial therapy. Bacillus subtilis and Escherichia coli are the two well-studied models for research on FtsZ, the leader protein of the cell division machinery. As representatives of gram-positive and gram-negative bacteria, respectively, these organisms have provided an extensive outlook into the process of cell division in rod-shaped bacteria. However, research on other shapes of bacteria, like cocci and ovococci, lags behind that of model rods. Even though most regions of FtsZ show sequence and structural conservation throughout bacteria, the differences in FtsZ functioning and interacting partners establish several different modes of division in different bacteria. In this review, we compare the features of FtsZ and cell division in the model rods B. subtilis and E. coli and the four pathogens: Staphylococcus aureus, Streptococcus pneumoniae, Mycobacterium tuberculosis, and Pseudomonas aeruginosa. Reviewing several recent articles on these pathogenic bacteria, we have highlighted the functioning of FtsZ, the unique roles of FtsZ-associated proteins, and the cell division processes in them. Further, we provide a detailed look at the anti-FtsZ compounds discovered and their target bacteria, emphasizing the need for elucidation of the anti-FtsZ mechanism of action in different bacteria. Current challenges and opportunities in the ongoing journey of identifying potent anti-FtsZ drugs have also been described.

Design and synthesis of quinolinium-based derivatives targeting FtsZ for antibacterial evaluation and mechanistic study

The discovery of small molecular inhibitors targeting essential and conserved bacterial drug targets such as FtsZ protein is a promising approach to fight against multi-drug resistant bacteria. In the present study, two new series of FtsZ inhibitors based on a 1-methylquinolinium scaffold were synthesized. The inhibitors possess a variety of substituent groups including the cyclic or linear amine skeleton at the 2- and 4-position of the quinolinium ring for structure-activity relationship study. In general, the inhibitors bearing a cyclic amine substituent at the 4-position of the quinolinium ring showed better antibacterial activity (MIC down to 0.25 μg/mL) than that at the 2-position, especially against Gram-positive bacteria. Among the twenty FtsZ inhibitors examined in various assays, A3 was identified to exhibit excellent antibacterial activity against S. aureus (MIC = 0.5-1 μg/mL), S. epidermidis (MIC = 0.25 μg/mL) and E. faecium (MIC = 1-8 μg/mL). More importantly, A3 showed low hemolytic toxicity (IC₅ = 64 μg/mL) and was found not readily to induce drug resistance. A3 at 2-8 μg/mL promoted the polymerization of FtsZ and interrupted the bacterial division. Furthermore, the ligand-FtsZ interaction study conducted with circular dichroism and molecular docking revealed that A3 induced secondary structure changes of FtsZ protein upon binding to the interdomain cleft of the protein. A3 is thus a potent inhibitor of FtsZ and shows potential to be used as a new antibacterial agent against drug-resistant bacteria.

Targeting the Achilles Heel of FtsZ: The Interdomain Cleft

Widespread antimicrobial resistance among bacterial pathogens is a serious threat to public health. Thus, identification of new targets and development of new antibacterial agents are urgently needed. Although cell division is a major driver of bacterial colonization and pathogenesis, its targeting with antibacterial compounds is still in its infancy. FtsZ, a bacterial cytoskeletal homolog of eukaryotic tubulin, plays a highly conserved and foundational role in cell division and has been the primary focus of research on small molecule cell division inhibitors. FtsZ contains two drug-binding pockets: the GTP binding site situated at the interface between polymeric subunits, and the inter-domain cleft (IDC), located between the N-terminal and C-terminal segments of the core globular domain of FtsZ. The majority of anti-FtsZ molecules bind to the IDC. Compounds that bind instead to the GTP binding site are much less useful as potential antimicrobial therapeutics because they are often cytotoxic to mammalian cells, due to the high sequence similarity between the GTP binding sites of FtsZ and tubulin. Fortunately, the IDC has much less sequence and structural similarity with tubulin, making it a better potential target for drugs that are less toxic to humans. Over the last decade, a large number of natural and synthetic IDC inhibitors have been identified. Here we outline the molecular structure of IDC in detail and discuss how it has become a crucial target for broad spectrum and species-specific antibacterial agents. We also outline the drugs that bind to the IDC and their modes of action.

Modification of 5-methylphenanthridium from benzothiazoles to indoles as potent FtsZ inhibitors: Broadening the antibacterial spectrum toward vancomycin-resistant enterococci

The death caused by pathogenic bacteria has always been a severe threat to mankind. The prevalence of drug resistance among bacteria underscores an urgent goal for new antibacterial agents with novel mode of action. Here we first designed and synthesized a class of benzothiazolyl-5-methylphenanthridium derivatives and evaluated their antibacterial activity. On this basis, we further designed and synthesized another class of novel indolyl-5-methylphenanthridium derivatives by optimizing the benzothiazolyl-5-methylphenanthridium core and evaluated their antibacterial activity targeting the bacterial cell division protein FtsZ. The results showed that the indolyl-5-methylphenanthridium derivatives had greatly improved activity against various drug-resistant bacterial strains including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus (VRE). Among them, compound C5 displayed excellent antibacterial activity against susceptible (MIC = 1 μg/mL), methicillin-resistant and clinical isolated S. aureus (MIC = 2 μg/mL). With low hemolytic activity towards mice red blood cells, C5 exhibited good antibacterial effect in vivo in preliminary pharmacodynamic assay. More importantly, C5 was difficult to induce bacterial resistance. Further mechanism studies proved that C5 could inhibit bacterial cell division by promoting FtsZ polymerization, leading to disorderly polymerization and disordered knots. Therefore, our findings suggest that this class of novel indolyl-5-methylphenanthridium derivatives are promising for future antibacterial agents.

MazEF-rifampicin interaction suggests a mechanism for rifampicin induced inhibition of persisters

Background

Persistence is a natural phenomenon whereby a subset of a population of isogenic bacteria either grow slow or become dormant conferring them with the ability to withstand various stresses including antibiotics. In a clinical setting bacterial persistence often leads to the recalcitrance of various infections increasing the treatment time and cost. Additionally, some studies also indicate that persistence can also pave way for the emergence of resistant strains. In a laboratory setting this persistent phenotype is enriched in nutritionally deprived environments. Consequently, in a batch culture the late stationary phase is enriched with persistent bacteria. The mechanism of persister cell formation and its regulation is not well understood. Toxin-antitoxin (TA) systems have been implicated to be responsible for bacterial persistence and rifampicin is used to treat highly persistent bacterial strains. The current study tries to explore a possible interaction between rifampicin and the MazEF TA system that furthers the former’s success rate in treating persistent bacteria.

Results

In the current study we found that the population of bacteria in the death phase of a batch culture consists of metabolically inactive live cells resembling persisters, which showed higher membrane depolarization as compared to the log phase bacteria. We also observed an increase in the expression of the MazEF TA modules in this phase. Since rifampicin is used to kill the persisters, we assessed the interaction of rifampicin with MazEF complex. We showed that rifampicin moderately interacts with MazEF complex with 1:1 stoichiometry.

Conclusion

Our study suggests that the interaction of rifampicin with MazEF complex might play an important role in inhibition of persisters.

Supplementary information

The online version contains supplementary material available at 10.1186/s12860-020-00316-8.

Recent progress of bacterial FtsZ inhibitors with a focus on peptides

In recent years, the rise of antibiotic resistance has become a primary health problem. With the emergence of bacterial resistance, the need to explore and develop novel antibacterial drugs has become increasingly urgent. Filamentous temperature-sensitive mutant Z (FtsZ), a crucial cell division protein of bacteria, has become a vital antibacterial target. FtsZ is a filamentous GTPase; it is highly conserved in bacteria and shares less than 20% sequence identity with the eukaryotic cytoskeleton protein tubulin, indicating that FtsZ-targeting antibacterial agents may have a low cytotoxicity toward eukaryotes. FtsZ can form a dynamic Z-ring in the center of the cell resulting in cell division. Furthermore, disturbance in the assembly of FtsZ may affect cellular dynamics and bacterial cell survival, making it a fascinating target for drug development. This review focuses on the recent discovery of FtsZ inhibitors, including peptides, natural products, and other synthetic small molecules, as well as their mechanism of action, which could facilitate the discovery of novel FtsZ-targeting clinical drugs in the future.

Novel targets of pentacyclic triterpenoids in Staphylococcus aureus: A systematic review

BACKGROUND

Staphylococcus aureus is an important pathogen both in community-acquired and healthcare-associated infections, and has successfully evolved numerous strategies for resisting the action to practically all antibiotics. Resistance to methicillin is now widely described in the community setting (CMRSA), thus the development of new drugs or alternative therapies is urgently necessary. Plants and their secondary metabolites have been a major alternative source in providing structurally diverse bioactive compounds as potential therapeutic agents for the treatment of bacterial infections. One of the classes of natural secondary metabolites from plants with the most bioactive compounds are the triterpenoids, which comprises structurally diverse organic compounds. In nature, triterpenoids are often found as tetra- or penta-cyclic structures.

AIM

This review highlights the anti-staphylococcal activities of pentacyclic triterpenoids, particularly α-amyrin (AM), betulinic acid (BA) and betulinaldehyde (BE). These compounds are based on a 30-carbon skeleton comprising five six-membered rings (ursanes and lanostanes) or four six-membered rings and one five-membered ring (lupanes and hopanes).

METHODS

Electronic databases such as ScienceDirect, PubMed and Scopus were used to search scientific contributions until March 2018, using relevant keywords. Literature focusing on the antimicrobial and antibiofilms of effects of pentacyclic triterpenoids on S. aureus were identified and summarized.

RESULTS

Pentacyclic triterpenoids can be divided into three representative classes, namely ursane, lupane and oleananes. This class of compounds have been shown to exhibit analgesic, immunomodulatory, anti-inflammatory, anticancer, antioxidant, antifungal and antibacterial activities. In studies of the antimicrobial activities and targets of AM, BA and BE in sensitive and multidrug-resistant S. aureus, these compounds acted synergistically and have different targets from the conventional antibiotics.

CONCLUSION

The inhibitory mechanisms of S. aureus in novel targets and pathways should stimulate further researches to develop AM, BA and BE as therapeutic agents for infections caused by S. aureus. Continued efforts to identify and exploit synergistic combinations by the three compounds and peptidoglycan inhibitors, are also necessary as alternative treatment options for S. aureus infections.

Drug repurposing approach to target FtsZ cell division protein from Salmonella Typhi

Drug repurposing is an efficient alternative approach to counter the increasing drug-resistant pathogens to treat infectious diseases. FtsZ is an essential bacterial cytokinesis protein involved in the formation of cell-division complex and targeting FtsZ using FDA approved drugs is a promising strategy to identify and develop a new antibacterial drug. Using in silico pharmacophore-based screening of drug bank, molecular docking and molecular dynamics simulations, we identified six drugs inhibiting the function of stFtsZ from Salmonella Typhi. The selected drugs target stFtsZ at the hydrophobic cleft formed between the C-terminal domain and helix α7 with binding energy better than -8 kcal/mol. Out of these six drugs, benzethonium chloride showed promising results at 8 μM concentration where it inhibits stFtsZ GTPase activity by 80% and prevents polymerization. Benzethonium chloride also possesses an excellent antibacterial activity against the bacterial culture of Salmonella Typhi (ATCC 19430), Staphylococcus aureus (ATCC 43300) and Escherichia coli (ATCC 25922) with the MIC values of 8 μg/mL, 1 μg/mL and 12 μg/mL, respectively. Based on our current study, the scaffold of benzethonium chloride can be used for the development of broad-spectrum antibacterial agents against drug-resistant pathogens.

Antibacterial activity evaluation and mode of action study of novel thiazole-quinolinium derivatives

A new series of thiazole-quinolinium derivatives perturb the polymerization of FtsZ with strong antibacterial activities.

FtsZ inhibitors as a new genera of antibacterial agents

The continuous emergence and rapid spread of a multidrug-resistant strain of bacterial pathogens have demanded the discovery and development of new antibacterial agents. A highly conserved prokaryotic cell division protein FtsZ is considered as a promising target by inhibiting bacterial cytokinesis. Inhibition of FtsZ assembly restrains the cell-division complex known as divisome, which results in filamentation, leading to lysis of the cell. This review focuses on details relating to the structure, function, and influence of FtsZ in bacterial cytokinesis. It also summarizes on the recent perspective of the known natural and synthetic inhibitors directly acting on FtsZ protein, with prominent antibacterial activities. A series of benzamides, trisubstituted benzimidazoles, isoquinolene, guanine nucleotides, zantrins, carbonylpyridine, 4 and 5-Substituted 1-phenyl naphthalenes, sulindac, vanillin analogues were studied here and recognized as FtsZ inhibitors that act either by disturbing FtsZ polymerization and/or GTPase activity. Doxorubicin, from a U.S. FDA, approved drug library displayed strong interaction with FtsZ. Several of the molecules discussed, include the prodrugs of benzamide based compound PC190723 (TXA-709 and TXA707). These molecules have exhibited the most prominent antibacterial activity against several strains of Staphylococcus aureus with minimal toxicity and good pharmacokinetics properties. The evidence of research reports and patent documentations on FtsZ protein has disclosed distinct support in the field of antibacterial drug discovery. The pressing need and interest shall facilitate the discovery of novel clinical molecules targeting FtsZ in the upcoming days.

3D QSAR-based design and liquid phase combinatorial synthesis of 1,2-disubstituted benzimidazole-5-carboxylic acid and 3-substituted-5H-benzimidazo[1,2-d][1,4]benzodiazepin-6(7H)-one derivatives as anti-mycobacterial agents

Tuberculosis (TB) is one of the world's deadliest infectious diseases, caused by Mycobacterium tuberculosis (Mtb). In the present study, a 3D QSAR study was performed for the design of novel substituted benzimidazole derivatives as anti-mycobacterial agents. The anti-tubercular activity of the designed compounds was predicted using the generated 3D QSAR models. The designed compounds which showed better activity were synthesized as 1,2-disubstituted benzimidazole-5-carboxylic acid derivatives (series 1) and 3-substituted-5H-benzimidazo[1,2-d][1,4]benzodiazepin-6(7H)-one derivatives (series 2) using the liquid phase combinatorial approach using a soluble polymer assisted support (PEG5000). The compounds were characterized by ¹H-NMR, ¹³C-NMR, FTIR and mass spectrometry. HPLC analysis was carried out to evaluate the purity of the compounds. We observed that the synthesised compounds inhibited the growth of intracellular M. tuberculosis H₃₇Rv in a bactericidal manner. The most active compound 16 displayed an MIC value of 0.0975 μM against the Mtb H₃₇Rv strain in liquid cultures. The lead compound was also able to inhibit the growth of intracellular mycobacteria in THP-1 macrophages.

MinD directly interacting with FtsZ at the H10 helix suggests a model for robust activation of MinC to destabilize FtsZ polymers

Cell division in bacteria is a highly controlled and regulated process. FtsZ, a bacterial cytoskeletal protein, forms a ring-like structure known as the Z-ring and recruits more than a dozen other cell division proteins. The Min system oscillates between the poles and inhibits the Z-ring formation at the poles by perturbing FtsZ assembly. This leads to an increase in the FtsZ concentration at the mid-cell and helps in Z-ring positioning. MinC, the effector protein, interferes with Z-ring formation through two different mechanisms mediated by its two domains with the help of MinD. However, the mechanism by which MinD triggers MinC activity is not yet known. We showed that MinD directly interacts with FtsZ with an affinity stronger than the reported MinC-FtsZ interaction. We determined the MinD-binding site of FtsZ using computational, mutational and biochemical analyses. Our study showed that MinD binds to the H10 helix of FtsZ. Single-point mutations at the charged residues in the H10 helix resulted in a decrease in the FtsZ affinity towards MinD. Based on our findings, we propose a novel model for MinCD-FtsZ interaction, where MinD through its direct interaction with FtsZ would trigger MinC activity to inhibit FtsZ functions.

Lessons from bacterial homolog of tubulin, FtsZ for microtubule dynamics

FtsZ, a homolog of tubulin, is found in almost all bacteria and archaea where it has a primary role in cytokinesis. Evidence for structural homology between FtsZ and tubulin came from their crystal structures and identification of the GTP box. Tubulin and FtsZ constitute a distinct family of GTPases and show striking similarities in many of their polymerization properties. The differences between them, more so, the complexities of microtubule dynamic behavior in comparison to that of FtsZ, indicate that the evolution to tubulin is attributable to the incorporation of the complex functionalities in higher organisms. FtsZ and microtubules function as polymers in cell division but their roles differ in the division process. The structural and partial functional homology has made the study of their dynamic properties more interesting. In this review, we focus on the application of the information derived from studies on FtsZ dynamics to study microtubule dynamics and vice versa. The structural and functional aspects that led to the establishment of the homology between the two proteins are explained to emphasize the network of FtsZ and microtubule studies and how they are connected.

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.

Recent advances in the discovery and development of antibacterial agents targeting the cell-division protein FtsZ

With the emergence of multidrug-resistant bacterial strains, there is a dire need for new drug targets for antibacterial drug discovery and development. Filamentous temperature sensitive protein Z (FtsZ), is a GTP-dependent prokaryotic cell division protein, sharing less than 10% sequence identity with the eukaryotic cell division protein, tubulin. FtsZ forms a dynamic Z-ring in the middle of the cell, leading to septation and subsequent cell division. Inhibition of the Z-ring blocks cell division, thus making FtsZ a highly attractive target. Various groups have been working on natural products and synthetic small molecules as inhibitors of FtsZ. This review summarizes the recent advances in the development of FtsZ inhibitors, focusing on those in the last 5years, but also includes significant findings in previous years.

In vitro anti-cancer activity of doxorubicin against human RNA helicase, DDX3

RNA helicase, DDX3 is a multifunctional enzyme and is known to be associated with several diseases like HIV progression, brain and breast cancer. Some of the ring expanded nucleoside compounds such as REN: NZ51, fused di imidazodiazepine ring (RK33), (Z)-3-(5- (3-bromo benzylidene)-4-oxo-2-thioxothiazolidin-3-yl)-N-(2- hydroxy phenyl) propanamide compound (FE15) have been documented to inhibit DDX3 helicase activity. However, synthesis of these drugs is limited to few research groups. Prevalence of literature study, we found that doxorubicin form strong hydrogen bond interactions with crystallized form of DDX3 using in-silico molecular docking approach. To evaluate the biological inhibitory action of doxorubicin, we performed the ATPase activity assay and anti-cancer activity using H357 cancer cell lines. Results showed that doxorubicin continually declined the inorganic phosphate (Pi) release and inhibited the ATP hydrolysis by directly interacting with DDX3. Anticancer activity was detected by MTT assay. The half maximal inhibitory concentrations of doxorubicin (IC50) for H357 cancer cell line is 50 μM and also doxorubicin significantly down regulated the expression of DDX3. Taken together, our results demonstrate, that inhibition of DDX3 expression by using doxorubicin can be used as an ideal drug candidate to treat DDX3 associated cancer disorder by interacting with unique amino acid residues (Thr 198) and common amino acid residues (Tyr 200 and Thr 201).

BT-benzo-29 inhibits bacterial cell proliferation by perturbing FtsZ assembly

We have identified a potent antibacterial agent N-(4-sec-butylphenyl)-2-(thiophen-2-yl)-1H-benzo[d]imidazole-4-carboxamide (BT-benzo-29) from a library of benzimidazole derivatives that stalled bacterial division by inhibiting FtsZ assembly. A short (5 min) exposure of BT-benzo-29 disassembled the cytokinetic Z-ring in Bacillus subtilis cells without affecting the cell length and nucleoids. BT-benzo-29 also perturbed the localization of early and late division proteins such as FtsA, ZapA and SepF at the mid-cell. Further, BT-benzo-29 bound to FtsZ with a dissociation constant of 24 ± 3 μm and inhibited the assembly and GTPase activity of purified FtsZ. A docking analysis suggested that BT-benzo-29 may bind to FtsZ at the C-terminal domain near the T7 loop. BT-benzo-29 displayed significantly weaker inhibitory effects on the assembly and GTPase activity of two mutants (L272A and V275A) of FtsZ supporting the prediction of the docking analysis. Further, BT-benzo-29 did not appear to inhibit DNA duplication and nucleoid segregation and it did not perturb the membrane potential of B. subtilis cells. The results suggested that BT-benzo-29 exerts its potent antibacterial activity by inhibiting FtsZ assembly. Interestingly, BT-benzo-29 did not affect the membrane integrity of mammalian red blood cells. BT-benzo-29 bound to tubulin with a much weaker affinity than FtsZ and exerted significantly weaker effects on mammalian cells than on the bacterial cells indicating that the compound may have a strong antibacterial potential.

Doxorubicin inhibits E. coli division by interacting at a novel site in FtsZ

The increase in antibiotic resistance has become a major health concern in recent times. It is therefore essential to identify novel antibacterial targets as well as discover and develop new antibacterial agents. FtsZ, a highly conserved bacterial protein, is responsible for the initiation of cell division in bacteria. The functions of FtsZ inside cells are tightly regulated and any perturbation in its functions leads to inhibition of bacterial division. Recent reports indicate that small molecules targeting the functions of FtsZ may be used as leads to develop new antibacterial agents. To identify small molecules targeting FtsZ and inhibiting bacterial division, we screened a U.S. FDA (Food and Drug Administration)-approved drug library of 800 molecules using an independent computational, biochemical and microbial approach. From this screen, we identified doxorubicin, an anthracycline molecule that inhibits Escherichia coli division and forms filamentous cells. A fluorescence-binding assay shows that doxorubicin interacts strongly with FtsZ. A detailed biochemical analysis demonstrated that doxorubicin inhibits FtsZ assembly and its GTPase activity through binding to a site other than the GTP-binding site. Furthermore, using molecular docking, we identified a probable doxorubicin-binding site in FtsZ. A number of single amino acid mutations at the identified binding site in FtsZ resulted in a severalfold decrease in the affinity of FtsZ for doxorubicin, indicating the importance of this site for doxorubicin interaction. The present study suggests the presence of a novel binding site in FtsZ that interacts with the small molecules and can be targeted for the screening and development of new antibacterial agents.

Ketorolac salt is a newly discovered DDX3 inhibitor to treat oral cancer

DDX3 belongs to DEAD box RNA helicase family and is involved in the progression of several types of cancer. In this work, we employed a High Throughput Virtual screening approach to identify bioactive compounds against DDX3 from ZINC natural database. Ketorolac salt was selected based on its binding free energy less than or equals to −5 Kcal/mol with reference to existing synthetic DDX3 inhibitors and strong hydrogen bond interactions as similar to crystallized DDX3 protein (2I4I). The anti-cancer activity of Ketorolac salt against DDX3 was tested using oral squamous cell carcinoma (OSCC) cell lines. This compound significantly down regulated the expression of DDX3 in human OSCC line (H357) and the half maximal growth inhibitory concentration (IC₅₀) of Ketorolac salt in H357 cell line is 2.6 µM. Ketorolac salt also inhibited the ATP hydrolysis by directly interacting with DDX3. More importantly, we observed decreased number of neoplastic tongue lesions and reduced lesion severity in Ketorolac salt treated groups in a carcinogen induced tongue tumor mouse model. Taken together, our result demonstrates that Ketorolac salt is a newly discovered bioactive compound against DDX3 and this compound can be used as an ideal drug candidate to treat DDX3 associated oral cancer.

Axial ligand modified high valent tin(iv) porphyrins: synthesis, structure, photophysical studies and photodynamic antimicrobial activities on Candida albicans

Photophysical studies, fluorescence imaging, single crystal X-ray structure analysis and DFT calculations revealed that compounds2and3show enhanced phototoxicity towardsCandida albicanscompared to compound1.

Eliminating the heart from the curcumin molecule: monocarbonyl curcumin mimics (MACs)

Curcumin is a natural product with several thousand years of heritage. Its traditional Asian application to human ailments has been subjected in recent decades to worldwide pharmacological, biochemical and clinical investigations. Curcumin’s Achilles heel lies in its poor aqueous solubility and rapid degradation at pH ~ 7.4. Researchers have sought to unlock curcumin’s assets by chemical manipulation. One class of molecules under scrutiny are the monocarbonyl analogs of curcumin (MACs). A thousand plus such agents have been created and tested primarily against cancer and inflammation. The outcome is clear. In vitro, MACs furnish a 10–20 fold potency gain vs. curcumin for numerous cancer cell lines and cellular proteins. Similarly, MACs have successfully demonstrated better pharmacokinetic (PK) profiles in mice and greater tumor regression in cancer xenografts in vivo than curcumin. The compounds reveal limited toxicity as measured by murine weight gain and histopathological assessment. To our knowledge, MAC members have not yet been monitored in larger animals or humans. However, Phase 1 clinical trials are certainly on the horizon. The present review focuses on the large and evolving body of work in cancer and inflammation, but also covers MAC structural diversity and early discovery for treatment of bacteria, tuberculosis, Alzheimer’s disease and malaria.

Rational design of berberine-based FtsZ inhibitors with broad-spectrum antibacterial activity

Inhibition of the functional activity of Filamenting temperature-sensitive mutant Z (FtsZ) protein, an essential and highly conserved bacterial cytokinesis protein, is a promising approach for the development of a new class of antibacterial agents. Berberine, a benzylisoquinoline alkaloid widely used in traditional Chinese and native American medicines for its antimicrobial properties, has been recently reported to inhibit FtsZ. Using a combination of in silico structure-based design and in vitro biological assays, 9-phenoxyalkyl berberine derivatives were identified as potent FtsZ inhibitors. Compared to the parent compound berberine, the derivatives showed a significant enhancement of antibacterial activity against clinically relevant bacteria, and an improved potency against the GTPase activity and polymerization of FtsZ. The most potent compound 2 strongly inhibited the proliferation of Gram-positive bacteria, including methicillin-resistant S. aureus and vancomycin-resistant E. faecium, with MIC values between 2 and 4 µg/mL, and was active against the Gram-negative E. coli and K. pneumoniae, with MIC values of 32 and 64 µg/mL respectively. The compound perturbed the formation of cytokinetic Z-ring in E. coli. Also, the compound interfered with in vitro polymerization of S. aureus FtsZ. Taken together, the chemical modification of berberine with 9-phenoxyalkyl substituent groups greatly improved the antibacterial activity via targeting FtsZ.

SB-RA-2001 inhibits bacterial proliferation by targeting FtsZ assembly

FtsZ has been recognized as a promising antimicrobial drug target because of its vital role in bacterial cell division. In this work, we found that a taxane SB-RA-2001 inhibited the proliferation of Bacillus subtilis 168 and Mycobacterium smegmatis cells with minimal inhibitory concentrations of 38 and 60 μM, respectively. Cell lengths of these microorganisms increased remarkably in the presence of SB-RA-2001, indicating that it inhibits bacterial cytokinesis. SB-RA-2001 perturbed the formation of the FtsZ ring in B. subtilis 168 cells and also affected the localization of the late cell division protein, DivIVA, at the midcell position. Flow cytometric analysis of the SB-RA-2001-treated cells indicated that the compound did not affect the duplication of DNA in B. subtilis 168 cells. Further, SB-RA-2001 treatment did not affect the localization of the chromosomal partitioning protein, Spo0J, along the two ends of the nucleoids and also had no discernible effect on the nucleoid segregation in B. subtilis 168 cells. The agent also did not appear to perturb the membrane potential of B. subtilis 168 cells. In vitro, SB-RA-2001 bound to FtsZ with modest affinity, promoted the assembly and bundling of FtsZ protofilaments, and reduced the GTPase activity of FtsZ. GTP did not inhibit the binding of SB-RA-2001 to FtsZ, suggesting that it does not bind to the GTP binding site on FtsZ. A computational analysis indicated that SB-RA-2001 binds to FtsZ in the cleft region between the C-terminal domain and helix H7, and the binding site of SB-RA-2001 on FtsZ resembled that of PC190723, a well-characterized inhibitor of FtsZ. The findings collectively suggested that SB-RA-2001 inhibits bacterial proliferation by targeting the assembly dynamics of FtsZ, and this can be exploited further to develop potent FtsZ-targeted antimicrobials.

Bacterial cell division proteins as antibiotic targets

Proteins involved in bacterial cell division often do not have a counterpart in eukaryotic cells and they are essential for the survival of the bacteria. The genetic accessibility of many bacterial species in combination with the Green Fluorescence Protein revolution to study localization of proteins and the availability of crystal structures has increased our knowledge on bacterial cell division considerably in this century. Consequently, bacterial cell division proteins are more and more recognized as potential new antibiotic targets. An international effort to find small molecules that inhibit the cell division initiating protein FtsZ has yielded many compounds of which some are promising as leads for preclinical use. The essential transglycosylase activity of peptidoglycan synthases has recently become accessible to inhibitor screening. Enzymatic assays for and structural information on essential integral membrane proteins such as MraY and FtsW involved in lipid II (the peptidoglycan building block precursor) biosynthesis have put these proteins on the list of potential new targets. This review summarises and discusses the results and approaches to the development of lead compounds that inhibit bacterial cell division.

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.

GTP regulates the interaction between MciZ and FtsZ: a possible role of MciZ in bacterial cell division

MciZ, a peptide with 40 amino acid residues, has been shown to be expressed during bacterial sporulation, to inhibit Z-ring formation in bacteria, and to inhibit the assembly of FtsZ in vitro. Here, MciZ was found to bind to FtsZ in vitro with a dissociation constant of 0.3 ± 0.1 μM. Guanosine nucleotides inhibited the binding of MciZ to FtsZ; however, GTP inhibited the binding of MciZ to FtsZ more strongly than GDP. In addition, MciZ inhibited the binding of 2',3'-O-(2,4,6-trinitrocyclohexadienylidene)-GTP, a fluorescent analogue of GTP, to FtsZ. The results indicated that MciZ shares its binding site on FtsZ with GTP. Furthermore, M19I, an N-terminal 19-residue peptide (MKVHRMPKGVVLVGKAWEI) of MciZ, inhibited the assembly and GTPase activity of FtsZ in vitro. The results suggested that GTP plays an important role in the regulation of the interaction between FtsZ and MciZ and that M19I may be used as a lead peptide to design peptide inhibitors of FtsZ assembly.

Comparison of small molecule inhibitors of the bacterial cell division protein FtsZ and identification of a reliable cross-species inhibitor

FtsZ is a guanosine triphosphatase (GTPase) that mediates cytokinesis in bacteria. FtsZ is homologous in structure to eukaryotic tubulin and polymerizes in a similar head-to-tail fashion. The study of tubulin's function in eukaryotic cells has benefited greatly from specific and potent small molecule inhibitors, including colchicine and taxol. Although many small molecule inhibitors of FtsZ have been reported, none has emerged as a generally useful probe for modulating bacterial cell division. With the goal of establishing a useful and reliable small molecule inhibitor of FtsZ, a broad biochemical cross-comparison of reported FtsZ inhibitors was undertaken. Several of these molecules, including phenolic natural products, are unselective inhibitors that seem to derive their activity from the formation of microscopic colloids or aggregates. Other compounds, including the natural product viriditoxin and the drug development candidate PC190723, exhibit no inhibition of GTPase activity using protocols in this work or under published conditions. Of the compounds studied, only zantrin Z3 exhibits good levels of inhibition, maintains activity under conditions that disrupt small molecule aggregates, and provides a platform for exploration of structure-activity relationships (SAR). Preliminary SAR studies have identified slight modifications to the two side chains of this structure that modulate the inhibitory activity of zantrin Z3. Collectively, these studies will help focus future investigations toward the establishment of probes for FtsZ that fill the roles of colchicine and taxol in studies of tubulin.

An antitubulin agent BCFMT inhibits proliferation of cancer cells and induces cell death by inhibiting microtubule dynamics

Using cell based screening assay, we identified a novel anti-tubulin agent (Z)-5-((5-(4-bromo-3-chlorophenyl)furan-2-yl)methylene)-2-thioxothiazolidin-4-one (BCFMT) that inhibited proliferation of human cervical carcinoma (HeLa) (IC₅₀, 7.2±1.8 µM), human breast adenocarcinoma (MCF-7) (IC₅₀, 10.0±0.5 µM), highly metastatic breast adenocarcinoma (MDA-MB-231) (IC₅₀, 6.0±1 µM), cisplatin-resistant human ovarian carcinoma (A2780-cis) (IC₅₀, 5.8±0.3 µM) and multi-drug resistant mouse mammary tumor (EMT6/AR1) (IC₅₀, 6.5±1µM) cells. Using several complimentary strategies, BCFMT was found to inhibit cancer cell proliferation at G2/M phase of the cell cycle apparently by targeting microtubules. In addition, BCFMT strongly suppressed the dynamics of individual microtubules in live MCF-7 cells. At its half maximal proliferation inhibitory concentration (10 µM), BCFMT reduced the rates of growing and shortening phases of microtubules in MCF-7 cells by 37 and 40%, respectively. Further, it increased the time microtubules spent in the pause (neither growing nor shortening detectably) state by 135% and reduced the dynamicity (dimer exchange per unit time) of microtubules by 70%. In vitro, BCFMT bound to tubulin with a dissociation constant of 8.3±1.8 µM, inhibited tubulin assembly and suppressed GTPase activity of microtubules. BCFMT competitively inhibited the binding of BODIPY FL-vinblastine to tubulin with an inhibitory concentration (K_i) of 5.2±1.5 µM suggesting that it binds to tubulin at the vinblastine site. In cultured cells, BCFMT-treatment depolymerized interphase microtubules, perturbed the spindle organization and accumulated checkpoint proteins (BubR1 and Mad2) at the kinetochores. BCFMT-treated MCF-7 cells showed enhanced nuclear accumulation of p53 and its downstream p21, which consequently activated apoptosis in these cells. The results suggested that BCFMT inhibits proliferation of several types of cancer cells including drug resistance cells by suppressing microtubule dynamics and indicated that the compound may have chemotherapeutic potential.

Inhibitors of bacterial tubulin target bacterial membranes in vivo

FtsZ is a homolog of eukaryotic tubulin that is widely conserved among bacteria and coordinates the assembly of the cell division machinery. FtsZ plays a central role in cell replication and is a target of interest for antibiotic development. Several FtsZ inhibitors have been reported. We characterized the mechanism of these compounds in bacteria and found that many of them disrupt the localization of membrane-associated proteins, including FtsZ, by reducing the transmembrane potential or perturbing membrane permeability. We tested whether the reported phenotypes of a broad collection of FtsZ inhibitors disrupt the transmembrane potential in Bacillus subtilis strain 168. Using a combination of flow cytometry and microscopy, we found that zantrin Z1, cinnamaldehyde, totarol, sanguinarine, and viriditoxin decreased the B. subtilis transmembrane potential or perturbed membrane permeability, and influenced the localization of the membrane-associated, division protein MinD. These studies demonstrate that small molecules that disrupt membrane function in bacterial cells produce phenotypes that are similar to the inhibition of proteins associated with membranes in vivo, including bacterial cytoskeleton homologs, such as FtsZ. The results provide a new dimension for consideration in the design and testing of inhibitors of bacterial targets that are membrane-associated and provide additional insight into the structural characteristics of antibiotics that disrupt the membrane.

A rhodanine derivative CCR-11 inhibits bacterial proliferation by inhibiting the assembly and GTPase activity of FtsZ

A perturbation of FtsZ assembly dynamics has been shown to inhibit bacterial cytokinesis. In this study, the antibacterial activity of 151 rhodanine compounds was assayed using Bacillus subtilis cells. Of 151 compounds, eight strongly inhibited bacterial proliferation at 2 μM. Subsequently, we used the elongation of B. subtilis cells as a secondary screen to identify potential FtsZ-targeted antibacterial agents. We found that three compounds significantly increased bacterial cell length. One of the three compounds, namely, CCR-11 [(E)-2-thioxo-5-({[3-(trifluoromethyl)phenyl]furan-2-yl}methylene)thiazolidin-4-one], inhibited the assembly and GTPase activity of FtsZ in vitro. CCR-11 bound to FtsZ with a dissociation constant of 1.5 ± 0.3 μM. A docking analysis indicated that CCR-11 may bind to FtsZ in a cavity adjacent to the T7 loop and that short halogen-oxygen, H-bonding, and hydrophobic interactions might be important for the binding of CCR-11 with FtsZ. CCR-11 inhibited the proliferation of B. subtilis cells with a half-maximal inhibitory concentration (IC(50)) of 1.2 ± 0.2 μM and a minimal inhibitory concentration of 3 μM. It also potently inhibited proliferation of Mycobacterium smegmatis cells. Further, CCR-11 perturbed Z-ring formation in B. subtilis cells; however, it neither visibly affected nucleoid segregation nor altered the membrane integrity of the cells. CCR-11 inhibited HeLa cell proliferation with an IC(50) value of 18.1 ± 0.2 μM (∼15 × IC(50) of B. subtilis cell proliferation). The results suggested that CCR-11 inhibits bacterial cytokinesis by inhibiting FtsZ assembly, and it can be used as a lead molecule to develop FtsZ-targeted antibacterial agents.

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.

Targeting the Wolbachia cell division protein FtsZ as a new approach for antifilarial therapy

The use of antibiotics targeting the obligate bacterial endosymbiont Wolbachia of filarial parasites has been validated as an approach for controlling filarial infection in animals and humans. Availability of genomic sequences for the Wolbachia (wBm) present in the human filarial parasite Brugia malayi has enabled genome-wide searching for new potential drug targets. In the present study, we investigated the cell division machinery of wBm and determined that it possesses the essential cell division gene ftsZ which was expressed in all developmental stages of B. malayi examined. FtsZ is a GTPase thereby making the protein an attractive Wolbachia drug target. We described the molecular characterization and catalytic properties of Wolbachia FtsZ. We also demonstrated that the GTPase activity was inhibited by the natural product, berberine, and small molecule inhibitors identified from a high-throughput screen. Furthermore, berberine was also effective in reducing motility and reproduction in B. malayi parasites in vitro. Our results should facilitate the discovery of selective inhibitors of FtsZ as a novel anti-symbiotic approach for controlling filarial infection. NOTE: The nucleotide sequences reported in this paper are available in GenBank™ Data Bank under the accession number wAlB-FtsZ (JN616286).

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.

Discovery of anti-TB agents that target the cell-division protein FtsZ

The emergence of multidrug-resistant Mycobacterium tuberculosis strains has made many of the currently available anti-tuberculosis (TB) drugs ineffective. Accordingly, there is a pressing need to identify new drug targets. Filamentous temperature-sensitive protein Z (FtsZ), a bacterial tubulin homologue, is an essential cell-division protein that polymerizes in a GTP-dependent manner, forming a highly dynamic cytokinetic ring, designated as the Z ring, at the septum site. Other cell-division proteins are recruited to the Z ring and, upon resolution of the septum, two daughter cells are produced. Since inactivation of FtsZ or alteration of FtsZ assembly results in the inhibition of Z-ring and septum formation, FtsZ is a very promising target for novel antimicrobial drug development. This review describes the function and dynamic behaviors of FtsZ and the recent development of FtsZ inhibitors as potential anti-TB agents.

Therapeutic potential of FtsZ inhibition: a patent perspective

INTRODUCTION

Filamentous temperature sensitive mutant Z (FtsZ), an essential protein for bacterial cell division, has emerged as an attractive therapeutic target for the development of efficacious antibacterial agents active against drug-sensitive and drug-resistant bacterial strains. Recently, FtsZ has garnered special attention in the antibacterial research field, which is evident by the amount of research papers and patents disclosed in the public domain. Because of the significance of FtsZ as a highly promising target for the development of novel antibacterial agents, it is timely to review the patents on this subject so far published to date.

AREAS COVERED

This review article covers the patent literature on FtsZ-targeting potential antibacterial agents up to November 2010, including their pharmacological findings.

EXPERT OPINION

Since FtsZ is well preserved in various bacteria, the FtsZ-targeting agents would act as novel broad-spectrum antibacterial drugs in addition to their use against particular bacteria, especially drug-resistant strains. Based on the increasing interest and advancement in this field of research, it looks almost certain that a good number of clinical candidates targeting FtsZ will emerge in the near future.

FtsZ in bacterial cytokinesis: cytoskeleton and force generator all in one

FtsZ, a bacterial homolog of tubulin, is well established as forming the cytoskeletal framework for the cytokinetic ring. Recent work has shown that purified FtsZ, in the absence of any other division proteins, can assemble Z rings when incorporated inside tubular liposomes. Moreover, these artificial Z rings can generate a constriction force, demonstrating that FtsZ is its own force generator. Here we review light microscope observations of how Z rings assemble in bacteria. Assembly begins with long-pitch helices that condense into the Z ring. Once formed, the Z ring can transition to short-pitch helices that are suggestive of its structure. FtsZ assembles in vitro into short protofilaments that are ∼30 subunits long. We present models for how these protofilaments might be further assembled into the Z ring. We discuss recent experiments on assembly dynamics of FtsZ in vitro, with particular attention to how two regulatory proteins, SulA and MinC, inhibit assembly. Recent efforts to develop antibacterial drugs that target FtsZ are reviewed. Finally, we discuss evidence of how FtsZ generates a constriction force: by protofilament bending into a curved conformation.