Prevalence of polymyxin-resistant bacterial strains in India: a systematic review and meta-analysis.

INTRODUCTION: Polymyxins, the cationic lipopeptide antibiotics, are the last line of therapeutics against the MDR Gram-negative bacterial (GNB) pathogens. Unfortunately, the rising cases of polymyxin-resistant strains from across the globe have adversely impacted their utility. While the molecular mechanisms responsible for developing polymyxin resistance (PolR) are largely understood, the prevalence of PolR strains in India has not been investigated systematically. The current study was undertaken to primarily determine the prevalence of PolR strains in India. Moreover, the extent of the spread of mobile colistin resistance (mcr) genes among the GNB strains in India was also determined. METHOD: A systematic search for articles using the relevant inclusion and exclusion criteria was performed in the applicable databases for the period January 2015 to December 2023. The included 41 studies were subjected to a meta-analysis using the Comprehensive Meta-Analysis software (V4.0). Publication biases were assessed using funnel plots and Egger's regression analysis. RESULT: Considering a total of 41 studies including 24 589 bacterial isolates the present meta-analysis found the rate of PolR bacteria in India to be at 15.0% (95% CI: 11.2 to 19.8). Among the Indian States, Tamil Nadu topped with the highest prevalence of PolR at 28.3%. Investigating the contribution of the mcr genes, it was observed that among the PolR strains, 8.4% (95% CI: 4.8 to 14.3) were mcr positive. CONCLUSION: The study determined the prevalence of PolR strains in India at 15.0%, which is higher than that of the global average at 10%. The study also determined that 8.4% of the PolR strains carried the mcr genes. The mcr-positive strains reported from India could be an underestimation of the actual numbers due to the non-inclusion of mcr screening in many previous studies. This study provides insight into the state of the PolR situation in India, which may be useful to develop a monitoring strategy to contain the spread of such strains and preserve the efficacy of the polymyxins.

Methylation-dependent transcriptional regulation of crescentin gene (creS) by GcrA in Caulobacter crescentus.

In Caulobacter crescentus the combined action of chromosome replication and the expression of DNA methyl-transferase CcrM at the end of S-phase maintains a cyclic alternation between a full- to hemi-methylated chromosome. This transition of the chromosomal methylation pattern affects the DNA-binding properties of the transcription factor GcrA that controls the several key cell cycle functions. However, the molecular mechanism by which GcrA and methylation are linked to transcription is not fully elucidated yet. Using a combination of cell biology, genetics, and in vitro analysis, we deciphered how GcrA integrates the methylation pattern of several S-phase expressed genes to their transcriptional output. We demonstrated in vitro that transcription of ctrA from the P1 promoter in its hemi-methylated state is activated by GcrA, while in its fully methylated state GcrA had no effect. Further, GcrA and methylation together influence a peculiar distribution of creS transcripts, encoding for crescentin, the protein responsible for the characteristic shape of Caulobacter cells. This gene is duplicated at the onset of chromosome replication and the two hemi-methylated copies are spatially segregated. Our results indicated that GcrA transcribed only the copy where coding strand is methylated. In vitro transcription assay further substantiated this finding. As several of the cell cycle-regulated genes are also under the influence of methylation and GcrA-dependent transcriptional regulation, this could be a mechanism responsible for maintaining the gene transcription dosage during the S-phase.

Spatial Position Regulates Power of Tryptophan: Discovery of a Major-Groove-Specific Nuclear-Localizing, Cell-Penetrating Tetrapeptide.

Identification of key amino acids is required for development of efficient cell-penetrating peptides (CPPs) and has tremendous implications in medicine. Extensive research work has enlightened us about the importance of two amino acids, arginine and tryptophan, in cell penetration. Here, we present a top-down approach to show how spatial positions of two tryptophans regulate the cellular entry and nuclear localization. This enables us to develop short, non-toxic tetrapeptides with excellent potential for cell penetration and nuclear localization. Among them, Glu-Thr-Trp-Trp (ETWW) emerges as the most promising. Results suggest that it enters into cancer cells following an endocytic pathway and binds at the major groove of nuclear DNA, where successive tryptophan plays major role. We subsequently show that it is not a P-glycoprotein substrate and is non-toxic to PC12-derived neurons, suggesting its excellent potential as a CPP. Furthermore, its potential as a CPP is validated in multi-cellular 3D cell culture (spheroid) and in in vivo mice model. This study provides major fundamental insights about the positional importance of tryptophan and opens new avenues toward the development of next-generation CPPs and major-groove-specific anticancer drugs.

Role of CovR phosphorylation in gene transcription in Streptococcus mutans.

Streptococcus mutans, the primary aetiological agent of dental caries, is one of the major bacteria of the human oral cavity. The pathogenicity of this bacterium is attributed not only to the expression of virulence factors, but also to its ability to respond and adapt rapidly to the ever-changing conditions of the oral cavity. The two-component signal transduction system (TCS) CovR/S plays a crucial role in virulence and stress response in many streptococci. Surprisingly, in S. mutans the response regulator CovR appears to be an orphan, as the cognate sensor kinase, CovS, is absent in all the strains. We found that acetyl phosphate, an intracellular phosphodonor molecule known to act in signalling, might play a role in CovR phosphorylation in vivo. We also found that in vitro, upon phosphorylation by potassium phosphoramide (a high-energy phophodonor) CovR formed a dimer and showed altered electrophoretic mobility. As expected, we found that the conserved aspartic acid residue at position 53 (D53) was the site of phosphorylation, since neither phosphorylation nor dimerization was seen when an alanine-substituted CovR mutant (D53A) was used. Surprisingly, we found that the ability of CovR to act as a transcriptional regulator does not depend upon its phosphorylation status, since the D53A mutant behaved similarly to the wild-type protein in both in vivo and in vitro DNA-binding assays. This unique phosphorylation-mediated inhibition of CovR function in S. mutans sheds light on an unconventional mechanism of the signal transduction pathway.

Designed Tetrapeptide Interacts with Tubulin and Microtubule.

Microtubules regulate eukaryotic cell functions, which have tremendous implication in tumor progression. Thus, the design of novel approaches for controlling microtubule function is extremely important. In this manuscript, a novel tetrapeptide Ser-Leu-Arg-Pro (SLRP) has been designed and synthesized from a small peptide library consisting of 14 tetrapeptides, which perturbs microtubule function through interaction in the "anchor region". We have studied the role of peptides on microtubule function on a chemically functionalized 2D platform. Interestingly, we have found that SLRP binds with tubulin and inhibits the kinesin-driven microtubule motility on a kinesin-immobilized chemically functionalized 2D platform. Further, this peptide modulator interacts with intracellular tubulin/microtubule and depolymerizes the microtubule networks. These interesting findings of perturbation of microtubule function both on engineered platforms and inside the cell by this small peptide modulator inspired us to study the effect of this tetrapeptide on cancer cell proliferation. We found that the novel tetrapeptide modulator causes moderate cytotoxicity to the human breast cancer cell (MCF-7 cell), induces the apoptotic death of MCF-7 cell, and activates the tumor suppressor proteins p53 and cyclin-dependent kinase inhibitor 1 (p21). To the best of our knowledge, this is the shortest peptide discovered, which perturbs microtubule function both on an engineered 2D platform and inside the cell.

Cancer Cell Imaging Using in Situ Generated Gold Nanoclusters.

In situ generated fluorescent gold nanoclusters (Au-NCs) are used for bio-imaging of three human cancer cells, namely, lung (A549), breast (MCF7), and colon (HCT116), by confocal microscopy. The amount of Au-NCs in non-cancer cells (WI38 and MCF10A) is 20-40 times less than those in the corresponding cancer cells. The presence of a larger amount of glutathione (GSH) capped Au-NCs in the cancer cell is ascribed to a higher glutathione level in cancer cells. The Au-NCs exhibit fluorescence maxima at 490-530 nm inside the cancer cells. The fluorescence maxima and matrix-assisted laser desorption ionization (MALDI) mass spectrometry suggest that the fluorescent Au-NCs consist of GSH capped clusters with a core structure (Au8-13). Time-resolved confocal microscopy indicates a nanosecond (1-3 ns) lifetime of the Au-NCs inside the cells. This rules out the formation of aggregated Au-thiolate complexes, which typically exhibit microsecond (≈1000 ns) lifetimes. Fluorescence correlation spectroscopy (FCS) in live cells indicates that the size of the Au-NCs is ≈1-2 nm. For in situ generation, we used a conjugate consisting of a room-temperature ionic liquid (RTIL, [pmim][Br]) and HAuCl4. Cytotoxicity studies indicate that the conjugate, [pmim][AuCl4], is non-toxic for both cancer and non-cancer cells.

Selective Killing of Breast Cancer Cells by Doxorubicin-Loaded Fluorescent Gold Nanoclusters: Confocal Microscopy and FRET.

Fluorescent gold nanoclusters (AuNCs) capped with lysozymes are used to deliver the anticancer drug doxorubicin to cancer and noncancer cells. Doxorubicin-loaded AuNCs cause the highly selective and efficient killing (90 %) of breast cancer cells (MCF7) (IC50 =155 nm). In contrast, the killing of the noncancer breast cells (MCF10A) by doxorubicin-loaded AuNCs is only 40 % (IC50 =4500 nm). By using a confocal microscope, the fluorescence spectrum and decay of the AuNCs were recorded inside the cell. The fluorescence maxima (at ≈490-515 nm) and lifetime (≈2 ns), of the AuNCs inside the cells correspond to Au10-13 . The intracellular release of doxorubicin from AuNCs is monitored by Förster resonance energy transfer (FRET) imaging.

Spectral mapping of 3D multi-cellular tumor spheroids: time-resolved confocal microscopy.

A tumor-like multi-cellular spheroid (3D) differs from a 2D cell in a number of ways. This is demonstrated using time resolved confocal microscopy. Two different tumor spheroids - HeLa (cervical cancer) and A549 (lung cancer) - are studied using 3 different fluorescent dyes - C153 (non-covalent), CPM (covalent) and doxorubicin (non-covalent, anti-cancer drug). The pattern of localization of these three fluorescent probes in the 3D tumor cell exhibits significant differences from that in the conventional 2D cells. For both the cells (HeLa and A549), the total uptake of doxorubicin in the 3D cell is much lower than that in the 2D cell. The uptake of doxorubicin molecules in the A549 spheroid is significantly different compared to the HeLa spheroid. The local polarity (i.e. emission maxima) and solvation dynamics in the 3D tumor cell differ from those in 2D cells. The covalent probe CPM exhibits intermittent fluorescence oscillations in the 1-2 s time scale. This is attributed to redox processes. These results may provide new insights into 3D tumors.

DNA binding of the cell cycle transcriptional regulator GcrA depends on N6-adenosine methylation in Caulobacter crescentus and other Alphaproteobacteria.

Several regulators are involved in the control of cell cycle progression in the bacterial model system Caulobacter crescentus, which divides asymmetrically into a vegetative G1-phase (swarmer) cell and a replicative S-phase (stalked) cell. Here we report a novel functional interaction between the enigmatic cell cycle regulator GcrA and the N6-adenosine methyltransferase CcrM, both highly conserved proteins among Alphaproteobacteria, that are activated early and at the end of S-phase, respectively. As no direct biochemical and regulatory relationship between GcrA and CcrM were known, we used a combination of ChIP (chromatin-immunoprecipitation), biochemical and biophysical experimentation, and genetics to show that GcrA is a dimeric DNA-binding protein that preferentially targets promoters harbouring CcrM methylation sites. After tracing CcrM-dependent N6-methyl-adenosine promoter marks at a genome-wide scale, we show that these marks recruit GcrA in vitro and in vivo. Moreover, we found that, in the presence of a methylated target, GcrA recruits the RNA polymerase to the promoter, consistent with its role in transcriptional activation. Since methylation-dependent DNA binding is also observed with GcrA orthologs from other Alphaproteobacteria, we conclude that GcrA is the founding member of a new and conserved class of transcriptional regulators that function as molecular effectors of a methylation-dependent (non-heritable) epigenetic switch that regulates gene expression during the cell cycle.

The DivJ, CbrA and PleC system controls DivK phosphorylation and symbiosis in Sinorhizobium meliloti.

Sinorhizobium meliloti is a soil bacterium that invades the root nodules it induces on Medicago sativa, whereupon it undergoes an alteration of its cell cycle and differentiates into nitrogen-fixing, elongated and polyploid bacteroid with higher membrane permeability. In Caulobacter crescentus, a related alphaproteobacterium, the principal cell cycle regulator, CtrA, is inhibited by the phosphorylated response regulator DivK. The phosphorylation of DivK depends on the histidine kinase DivJ, while PleC is the principal phosphatase for DivK. Despite the importance of the DivJ in C. crescentus, the mechanistic role of this kinase has never been elucidated in other Alphaproteobacteria. We show here that the histidine kinases DivJ together with CbrA and PleC participate in a complex phosphorylation system of the essential response regulator DivK in S. meliloti. In particular, DivJ and CbrA are involved in DivK phosphorylation and in turn CtrA inactivation, thereby controlling correct cell cycle progression and the integrity of the cell envelope. In contrast, the essential PleC presumably acts as a phosphatase of DivK. Interestingly, we found that a DivJ mutant is able to elicit nodules and enter plant cells, but fails to establish an effective symbiosis suggesting that proper envelope and/or low CtrA levels are required for symbiosis.

Assembly of an injectable noncytotoxic peptide-based hydrogelator for sustained release of drugs.

A new synthetic tripeptide-based hydrogel has been discovered at physiological pH and temperature. This hydrogel has been thoroughly characterized using different techniques including field emission scanning electron microscopic (FE-SEM) and high-resolution transmission electron microscopic (HR-TEM) imaging, small- and wide-angle X-ray diffraction analyses, FT-IR, circular dichroism, and rheometric analyses. Moreover, this gel exhibits thixotropy and injectability. This hydrogel has been used for entrapment and sustained release of an antibiotic vancomycin and vitamin B12 at physiological pH and temperature for about 2 days. Interestingly, MTT assay of these gelator molecules shows almost 100% cell viability of this peptide gelator, indicating its noncytotoxicity.

A molecular overview of the polymyxin-LPS interaction in the context of its mode of action and resistance development.

With the rising incidences of antimicrobial resistance (AMR) and the diminishing options of novel antimicrobial agents, it is paramount to decipher the molecular mechanisms of action and the emergence of resistance to the existing drugs. Polymyxin, a cationic antimicrobial lipopeptide, is used to treat infections by Gram-negative bacterial pathogens as a last option. Though polymyxins were identified almost seventy years back, their use has been restricted owing to toxicity issues in humans. However, their clinical use has been increasing in recent times resulting in the rise of polymyxin resistance. Moreover, the detection of "mobile colistin resistance (mcr)" genes in the environment and their spread across the globe have complicated the scenario. The mechanism of polymyxin action and the development of resistance is not thoroughly understood. Specifically, the polymyxin-bacterial lipopolysaccharide (LPS) interaction is a challenging area of investigation. The use of advanced biophysical techniques and improvement in molecular dynamics simulation approaches have furthered our understanding of this interaction, which will help develop polymyxin analogs with better bactericidal effects and lesser toxicity in the future. In this review, we have delved deeper into the mechanisms of polymyxin-LPS interactions, highlighting several models proposed, and the mechanisms of polymyxin resistance development in some of the most critical Gram-negative pathogens.

Colistin resistance among the Gram-negative nosocomial pathogens in India: a systematic review and meta-analysis.

The rapid rise of nosocomial infections and the growing ineffectiveness of frontline antibiotics against Gram-negative bacteria (GNB) have put the healthcare sector under unprecedented stress. In this scenario, colistin, an antibiotic of the polymyxin class, has become the last resort treatment option. However, the unrestricted use of colistin in the preceding decades has led to the emergence of colistin-resistant (ColR) bacterial strains. Unfortunately, comprehensive data on the prevalence of ColR nosocomial pathogens in India are scarce. This study was conducted to address this information gap. A systematic review and meta-analysis were conducted to determine the prevalence of ColR among the nosocomial GNB species in India and their geographical distribution. A systematic search of the online databases was performed and eligible studies meeting the inclusion criteria were used for qualitative synthesis. The combined event rate and 95% confidence interval were estimated using a forest plot with a random-effect model. Cochrane Q statistics and I2 statistics were used to detect possible heterogeneity. From a total of 1865 retrieved records from 4 databases, 33 studies were included in the study. Among the most common nosocomial pathogens, Klebsiella pneumoniae showed a rate of ColR at 16.1% (95% CI: 10.1 to 24.6), followed by Pseudomonas aeruginosa (13.3%) (95% CI: 9.1 to 19.2), Acinetobacter baumannii (10%) (95% CI: 7.5 to 13.2), and Escherichia coli (7.8%) (95% CI: 5.3 to 11.2). Interestingly, our analysis revealed that Enterobacter cloacae have the highest rate of ColR at 27.9% (95% CI: 12.7 to 50.9). The results indicate that the prevalence of ColR nosocomial pathogens vary among regions and over time; however, continuous monitoring, and sustained efforts are crucial to ensure the effectiveness of colistin antibiotic.

NPEPPS Is a Druggable Driver of Platinum Resistance.

There is an unmet need to improve the efficacy of platinum-based cancer chemotherapy, which is used in primary and metastatic settings in many cancer types. In bladder cancer, platinum-based chemotherapy leads to better outcomes in a subset of patients when used in the neoadjuvant setting or in combination with immunotherapy for advanced disease. Despite such promising results, extending the benefits of platinum drugs to a greater number of patients is highly desirable. Using the multiomic assessment of cisplatin-responsive and -resistant human bladder cancer cell lines and whole-genome CRISPR screens, we identified puromycin-sensitive aminopeptidase (NPEPPS) as a driver of cisplatin resistance. NPEPPS depletion sensitized resistant bladder cancer cells to cisplatin in vitro and in vivo. Conversely, overexpression of NPEPPS in sensitive cells increased cisplatin resistance. NPEPPS affected treatment response by regulating intracellular cisplatin concentrations. Patient-derived organoids (PDO) generated from bladder cancer samples before and after cisplatin-based treatment, and from patients who did not receive cisplatin, were evaluated for sensitivity to cisplatin, which was concordant with clinical response. In the PDOs, depletion or pharmacologic inhibition of NPEPPS increased cisplatin sensitivity, while NPEPPS overexpression conferred resistance. Our data present NPEPPS as a druggable driver of cisplatin resistance by regulating intracellular cisplatin concentrations. SIGNIFICANCE: Targeting NPEPPS, which induces cisplatin resistance by controlling intracellular drug concentrations, is a potential strategy to improve patient responses to platinum-based therapies and lower treatment-associated toxicities.

CovR alleviates transcriptional silencing by a nucleoid-associated histone-like protein in Streptococcus mutans.

In Streptococcus mutans, the global response regulator CovR plays an important role in biofilm formation, stress tolerance response, and caries production. We have previously demonstrated that CovR activates a large gene cluster, which is a part of a genomic island, TnSmu2. In this article, we have further characterized CovR at the molecular level to understand the gene activation mechanism. Toward this end, we mapped the transcription start site of the operon that lies upstream of the SMU.1348 gene (P(SMU.1348)), the first gene of the cluster. We constructed a transcriptional reporter fusion and showed that CovR induces expression from P(SMU.1348). We also demonstrated that purified CovR protects the sequence surrounding the -10 region of P(SMU.1348). In an in vitro transcription assay, we showed that histone-like protein (HLP), a homologue of Escherichia coli HU protein, represses transcription from P(SMU.1348). In vivo overexpression of HLP in trans also represses transcription from P(SMU.1348). Addition of CovR to the HLP-repressed P(SMU.1348) resulted in increased transcription from the promoter, suggesting a role for CovR in countering HLP silencing. Moreover, addition of SMU.1349, a transcriptional activator of the operon, to the in vitro assay further stimulated the transcription. Based on our in vivo and in vitro results, we propose a model for transcriptional activation of the operon.

Designed hybrid anticancer nuclear-localized peptide inhibits aggressive cancer cell proliferation.

Cell proliferation is a crucial step that might promote cancer if deregulated. Therefore, this vital segment is critically controlled by a complicated cell-cycle process in normal cells that is regulated by some regulatory proteins. It has been observed that p16 protein, playing a crucial role in cell-cycle progression/regulation, remains inactivated in different cancer cells. This inactivity of p16 protein leads to the enhancement of cancer cell proliferation by allowing uncontrolled cancer cell division. Hence, the activity of p16 protein needs to be restored using new viral vectors, small molecules as well as peptides to control/suppress this type of abnormal cell proliferation. In this work, we have taken an interesting approach to increase the efficiency and bio-availability of p16 peptide (functional part of p16 protein) to be an aggressive anti-leukemia therapeutic agent by conjugating a nuclear-localized signal (NLS) sequence and a short peptide (AVPI) with it. Moreover, this newly designed NLS attached hybrid peptide greatly affects XIAP expressing but p16 lower expressing human chronic myelogenous leukemia (CML) cell proliferation by targeting both nuclear (CDK4/cyclin D) and cellular factors (XIAP) and promoting the caspase-3 dependent apoptosis pathway.

Re-programming mouse liver-resident invariant natural killer T cells for suppressing hepatic and diabetogenic autoimmunity.

Invariant NKT (iNKT) cells comprise a heterogeneous group of non-circulating, tissue-resident T lymphocytes that recognize glycolipids, including alpha-galactosylceramide (αGalCer), in the context of CD1d, but whether peripheral iNKT cell subsets are terminally differentiated remains unclear. Here we show that mouse and human liver-resident αGalCer/CD1d-binding iNKTs largely correspond to a novel Zbtb16+Tbx21+Gata3+MaflowRorc- subset that exhibits profound transcriptional, phenotypic and functional plasticity. Repetitive in vivo encounters of these liver iNKT (LiNKT) cells with intravenously delivered αGalCer/CD1d-coated nanoparticles (NP) trigger their differentiation into immunoregulatory, IL-10+IL-21-producing Zbtb16highMafhighTbx21+Gata3+Rorc- cells, termed LiNKTR1, expressing a T regulatory type 1 (TR1)-like transcriptional signature. This response is LiNKT-specific, since neither lung nor splenic tissue-resident iNKT cells from αGalCer/CD1d-NP-treated mice produce IL-10 or IL-21. Additionally, these LiNKTR1 cells suppress autoantigen presentation, and recognize CD1d expressed on conventional B cells to induce IL-10+IL-35-producing regulatory B (Breg) cells, leading to the suppression of liver and pancreas autoimmunity. Our results thus suggest that LiNKT cells are plastic for further functional diversification, with such plasticity potentially targetable for suppressing tissue-specific inflammatory phenomena.

Regulation of transcription by SMU.1349, a TetR family regulator, in Streptococcus mutans.

The TetR family of transcriptional regulators is ubiquitous in bacteria, where it plays an important role in bacterial gene expression. Streptococcus mutans, a gram-positive pathogen considered to be the primary etiological agent in the formation of dental caries, encodes at least 18 TetR regulators. Here we characterized one such TetR regulator, SMU.1349, encoded by the TnSmu2 operon, which appeared to be acquired by the organism via horizontal gene transfer. SMU.1349 is transcribed divergently from the rest of the genes encoded by the operon. By the use of a transcriptional reporter system and semiquantitative reverse transcription-PCR (RT-PCR), we demonstrated that SMU.1349 activates the transcription of several genes that are encoded within the TnSmu2 operon. Gel mobility shift and DNase I footprinting assays with purified SMU.1349 protein demonstrated binding to the intergenic region between SMU.1349 and the TnSmu2 operon; therefore, SMU.1349 is directly involved in gene transcription. Using purified S. mutans RpoD and Escherichia coli RNA polymerase, we also demonstrated in an in vitro transcription assay that SMU.1349 could activate transcription from the TnSmu2 operon promoter. Furthermore, we showed that SMU.1349 could also repress transcription from its own promoter by binding to the intergenic region, suggesting that SMU.1349 acts as both an activator and a repressor. Thus, unlike most of the TetR family proteins, which generally function as transcriptional repressors, SMU.1349 is unique in that it can function as both.

Polymyxins, the last-resort antibiotics: Mode of action, resistance emergence, and potential solutions.

Infections caused by multi-drug resistant (MDR) bacterial pathogens are a leading cause of mortality and morbidity across the world. Indiscriminate use of broad-spectrum antibiotics has seriously affected this situation. With the diminishing discovery of novel antibiotics, new treatment methods are urgently required to combat MDR pathogens. Polymyxins, the cationic lipopeptide antibiotics, discovered more than half a century ago, are considered to be the last-line of antibiotics available at the moment. This antibiotic shows a great bactericidal effect against Gram-negative bacteria. Polymyxins primarily target the bacterial membrane and disrupt them, causing lethality. Because of their membrane interacting mode of action, polymyxins cause nephrotoxicity and neurotoxicity in humans, limiting their usability. However, recent modifications in their chemical structure have been able to reduce the toxic effects. The development of better dosing regimens has also helped in getting better clinical outcomes in the infections caused by MDR pathogens. Since the mid1990s the use of polymyxins has increased manifold in clinical settings, resulting in the emergence of polymyxin-resistant strains. The risk posed by the polymyxin-resistant nosocomial pathogens such as the Enterobacteriaceae group, Pseudomonas aeruginosa, and Acinetobacter baumannii, etc. is very serious considering these pathogens are resistant to almost all available antibacterial drugs. In this review article, the mode of action of the polymyxins and the genetic regulatory mechanism responsible for the emergence of resistance are discussed. Specifically, this review aims to update our current understanding in the field and suggest possible solutions that can be pursued for future antibiotic development. As polymyxins primarily target the bacterial membranes, resistance to polymyxins arises primarily by the modification of the lipopolysaccharides (LPS) in the outer membrane (OM). The LPS modification pathways are largely regulated by the bacterial two-component signal transduction (TCS) systems. Therefore, targeting or modulating the TCS signalling mechanisms can be pursued as an alternative to treat the infections caused by polymyxin-resistant MDR pathogens. In this review article, this aspect is also highlighted.

A Small Molecule with Bridged Carbonyl and Tri-fluoro-aceto-phenone Groups Impedes Microtubule Dynamics and Subsequently Triggers Cancer Cell Apoptosis.

We identified a new microtubule targeted small molecule, which showed significant anticancer activity and induced apoptotic death of cancer cells. Precisely the central bridged carbonyl group and trifluoro-acetophenone group of a bis-benzothiazole molecule (BBT) interacts with tubulin close to the curcumin site and perturbs microtubule dynamics as well as causes microtubule depolymerization. We observed a significant enhancement of fluorescence while BBT interacts with the tubulin through bridged carbonyl moiety, a similar phenomenon to colchicine. Further, BBT activates tumor-suppressing bim and p53-puma axes to inhibit cancer survival. It also shows promising results against a tumor spheroid model. BBT is also capable of tumor regression, which shows that this molecule can serve as a potential template for the design of next-generation microtubule targeted anticancer drugs.