Streptococcus mutans is a keystone pathogen that promotes caries by acidifying the dental biofilm... more Streptococcus mutans is a keystone pathogen that promotes caries by acidifying the dental biofilm milieu. The collagen- and laminin-binding glycoprotein Cnm is a virulence factor of S. mutans . Expression of Cnm by S. mutans is hypothesized to contribute to niche expansion, allowing colonization of multiple sites in the body, including collagen-rich surfaces such as dentin and heart valves.
Here we report the design of membrane-active peptidomimetic molecules with a tunable arrangement ... more Here we report the design of membrane-active peptidomimetic molecules with a tunable arrangement of hydrophobic and polar groups.
More than 80% of the bacterial infections are associated with biofilm formation. To combat infect... more More than 80% of the bacterial infections are associated with biofilm formation. To combat infections, amphiphilic small molecules have been developed as promising antibiofilm agents. However, cytotoxicity of such molecules still remains a major problem. Herein we demonstrate a concept in which antibacterial versus cytotoxic activities of cationic small molecules are tuned by spatial positioning of hydrophobic moieties while keeping positive charges constant. Compared to the molecules with more pendent hydrophobicity from positive centers (MIC = 1-4 μg/mL and HC50 = 60-65 μg/mL), molecules with more confined hydrophobicity between two centers show similar antibacterial activity but significantly less toxicity toward human erythrocytes (MIC = 1-4 μg/mL and HC50 = 805-1242 μg/mL). Notably, the optimized molecule is shown to be nontoxic toward human cells (HEK 293) at a concentration at which it eradicates established bacterial biofilms. The molecule is also shown to eradicate preformed bacterial biofilm in vivo in a murine model of superficial skin infection.
The continuous rise of antimicrobial resistance and the dearth of new antibiotics in the clinical... more The continuous rise of antimicrobial resistance and the dearth of new antibiotics in the clinical pipeline raise an urgent call for the development of potent antimicrobial agents. Cationic chitosan derivatives, N-(2-hydroxypropyl)-3-trimethylammonium chitosan chlorides (HTCC), have been widely studied as potent antibacterial agents. However, their systemic structure-activity relationship, activity towards drug-resistant bacteria and fungi and mode of action are very rare. Moreover, toxicity and efficacy of these polymers under in vivo conditions are yet to be established. Herein, we investigated antibacterial and antifungal efficacies of the HTCC polymers against multi-drug resistant bacteria including clinical isolates and pathogenic fungi, studied their mechanism of action and evaluated cytotoxic and microbial activities in vitro and in vivo. The polymers were found to be active against both bacteria and fungi (MIC = 125-250 µg/mL) and displayed rapid microbicidal kinetics, killin...
Staphylococcus aureus is a facultative intracellular pathogen and there are limited options for t... more Staphylococcus aureus is a facultative intracellular pathogen and there are limited options for the treatment of severe intracellular bacterial infections. The membrane-active glycopeptide antibiotic Van-QC8 is a permanent positively charged lipophilic vancomycin analogue that demonstrates high activity against clinically relevant drug-resistant Gram-positive bacteria both in vitro and in vivo. In this study, the intracellular activity of Van-QC8 was evaluated against meticillin-resistant S. aureus (MRSA) infection in RAW macrophages. Furthermore, the mechanism of intracellular uptake of Van-QC8 was investigated. Van-QC8 showed time- and concentration-dependent bactericidal activity against intracellular MRSA. Van-QC8 displayed significantly higher intracellular activity compared with vancomycin and linezolid. Cellular uptake of Van-QC8 was found to be through clathrin-dependent and -independent and caveolin-dependent and -independent endocytic pathways. The findings of this study suggest that Van-QC8 could be translated clinically for the treatment of intracellular infections due to MRSA.
Angewandte Chemie (International ed. in English), Jan 24, 2016
Vancomycin, the drug of last resort for Gram-positive bacterial infections, has also been rendere... more Vancomycin, the drug of last resort for Gram-positive bacterial infections, has also been rendered ineffective by the emergence of resistance in such bacteria. To combat the threat of vancomycin-resistant bacteria (VRB), we report the development of a dipicolyl-vancomycin conjugate (Dipi-van), which leads to enhanced inhibition of cell-wall biosynthesis in VRB and displays in vitro activity that is more than two orders of magnitude higher than that of vancomycin. Conjugation of the dipicolyl moiety, which is a zinc-binding ligand, endowed the parent drug with the ability to bind to pyrophosphate groups of cell-wall lipids while maintaining the inherent binding affinity for pentapeptide termini of cell-wall precursors. Furthermore, no detectable resistance was observed after several serial passages, and the compound reduced the bacterial burden by a factor of 5 logs at 12 mg kg(-1) in a murine model of VRB kidney infection. The findings presented in this report stress the potential o...
Symbiosis receptor kinase (SYMRK) is indispensable for activation of root nodule symbiosis (RNS) ... more Symbiosis receptor kinase (SYMRK) is indispensable for activation of root nodule symbiosis (RNS) at both epidermal and cortical levels and is functionally conserved in legumes. Previously we reported SYMRK to be phosphorylated on 'gatekeeper' Tyr both in vitro as well as in planta (Samaddar et al., 2013). Since gatekeeper phosphorylation was not necessary for activity, the significance remained elusive. Herein we show that substituting gatekeeper with non-phosphorylatable residues like Phe or Ala significantly affected autophosphorylation on selected targets on activation segment/αEF and β3 αC loop of SYMRK. In addition, the same gatekeeper mutants failed to restore proper symbiotic features in a symrk null mutant where rhizobial invasion of the epidermis and nodule organogenesis was unaffected but rhizobia remain restricted to the epidermis in infection threads migrating parallel to the longitudinal axis of the root resulting in extensive infection patches at the nodule ape...
Resistance to glycopeptide antibiotics, the drugs of choice for life‐threatening bacterial infect... more Resistance to glycopeptide antibiotics, the drugs of choice for life‐threatening bacterial infections, is on the rise. In order to counter the threat of glycopeptide‐resistant bacteria, we report development of a new class of semi‐synthetic glycopeptide antibiotics, which not only target the bacterial membrane but also display enhanced inhibition of cell‐wall biosynthesis through increased binding affinity to their target peptides. The combined effect of these two mechanisms resulted in improved in vitro activity of two to three orders of magnitude over vancomycin and no propensity to trigger drug resistance in bacteria. In murine model of kidney infection, the optimized compound was able to bring bacterial burden down by about 6 logs at 12 mg kg−1 with no observed toxicity. The results furnished in this report emphasize the potential of this class of compounds as future antibiotics for drug‐resistant Gram‐positive infections.
Streptococcus mutans is a keystone pathogen that promotes caries by acidifying the dental biofilm... more Streptococcus mutans is a keystone pathogen that promotes caries by acidifying the dental biofilm milieu. The collagen- and laminin-binding glycoprotein Cnm is a virulence factor of S. mutans . Expression of Cnm by S. mutans is hypothesized to contribute to niche expansion, allowing colonization of multiple sites in the body, including collagen-rich surfaces such as dentin and heart valves.
Here we report the design of membrane-active peptidomimetic molecules with a tunable arrangement ... more Here we report the design of membrane-active peptidomimetic molecules with a tunable arrangement of hydrophobic and polar groups.
More than 80% of the bacterial infections are associated with biofilm formation. To combat infect... more More than 80% of the bacterial infections are associated with biofilm formation. To combat infections, amphiphilic small molecules have been developed as promising antibiofilm agents. However, cytotoxicity of such molecules still remains a major problem. Herein we demonstrate a concept in which antibacterial versus cytotoxic activities of cationic small molecules are tuned by spatial positioning of hydrophobic moieties while keeping positive charges constant. Compared to the molecules with more pendent hydrophobicity from positive centers (MIC = 1-4 μg/mL and HC50 = 60-65 μg/mL), molecules with more confined hydrophobicity between two centers show similar antibacterial activity but significantly less toxicity toward human erythrocytes (MIC = 1-4 μg/mL and HC50 = 805-1242 μg/mL). Notably, the optimized molecule is shown to be nontoxic toward human cells (HEK 293) at a concentration at which it eradicates established bacterial biofilms. The molecule is also shown to eradicate preformed bacterial biofilm in vivo in a murine model of superficial skin infection.
The continuous rise of antimicrobial resistance and the dearth of new antibiotics in the clinical... more The continuous rise of antimicrobial resistance and the dearth of new antibiotics in the clinical pipeline raise an urgent call for the development of potent antimicrobial agents. Cationic chitosan derivatives, N-(2-hydroxypropyl)-3-trimethylammonium chitosan chlorides (HTCC), have been widely studied as potent antibacterial agents. However, their systemic structure-activity relationship, activity towards drug-resistant bacteria and fungi and mode of action are very rare. Moreover, toxicity and efficacy of these polymers under in vivo conditions are yet to be established. Herein, we investigated antibacterial and antifungal efficacies of the HTCC polymers against multi-drug resistant bacteria including clinical isolates and pathogenic fungi, studied their mechanism of action and evaluated cytotoxic and microbial activities in vitro and in vivo. The polymers were found to be active against both bacteria and fungi (MIC = 125-250 µg/mL) and displayed rapid microbicidal kinetics, killin...
Staphylococcus aureus is a facultative intracellular pathogen and there are limited options for t... more Staphylococcus aureus is a facultative intracellular pathogen and there are limited options for the treatment of severe intracellular bacterial infections. The membrane-active glycopeptide antibiotic Van-QC8 is a permanent positively charged lipophilic vancomycin analogue that demonstrates high activity against clinically relevant drug-resistant Gram-positive bacteria both in vitro and in vivo. In this study, the intracellular activity of Van-QC8 was evaluated against meticillin-resistant S. aureus (MRSA) infection in RAW macrophages. Furthermore, the mechanism of intracellular uptake of Van-QC8 was investigated. Van-QC8 showed time- and concentration-dependent bactericidal activity against intracellular MRSA. Van-QC8 displayed significantly higher intracellular activity compared with vancomycin and linezolid. Cellular uptake of Van-QC8 was found to be through clathrin-dependent and -independent and caveolin-dependent and -independent endocytic pathways. The findings of this study suggest that Van-QC8 could be translated clinically for the treatment of intracellular infections due to MRSA.
Angewandte Chemie (International ed. in English), Jan 24, 2016
Vancomycin, the drug of last resort for Gram-positive bacterial infections, has also been rendere... more Vancomycin, the drug of last resort for Gram-positive bacterial infections, has also been rendered ineffective by the emergence of resistance in such bacteria. To combat the threat of vancomycin-resistant bacteria (VRB), we report the development of a dipicolyl-vancomycin conjugate (Dipi-van), which leads to enhanced inhibition of cell-wall biosynthesis in VRB and displays in vitro activity that is more than two orders of magnitude higher than that of vancomycin. Conjugation of the dipicolyl moiety, which is a zinc-binding ligand, endowed the parent drug with the ability to bind to pyrophosphate groups of cell-wall lipids while maintaining the inherent binding affinity for pentapeptide termini of cell-wall precursors. Furthermore, no detectable resistance was observed after several serial passages, and the compound reduced the bacterial burden by a factor of 5 logs at 12 mg kg(-1) in a murine model of VRB kidney infection. The findings presented in this report stress the potential o...
Symbiosis receptor kinase (SYMRK) is indispensable for activation of root nodule symbiosis (RNS) ... more Symbiosis receptor kinase (SYMRK) is indispensable for activation of root nodule symbiosis (RNS) at both epidermal and cortical levels and is functionally conserved in legumes. Previously we reported SYMRK to be phosphorylated on 'gatekeeper' Tyr both in vitro as well as in planta (Samaddar et al., 2013). Since gatekeeper phosphorylation was not necessary for activity, the significance remained elusive. Herein we show that substituting gatekeeper with non-phosphorylatable residues like Phe or Ala significantly affected autophosphorylation on selected targets on activation segment/αEF and β3 αC loop of SYMRK. In addition, the same gatekeeper mutants failed to restore proper symbiotic features in a symrk null mutant where rhizobial invasion of the epidermis and nodule organogenesis was unaffected but rhizobia remain restricted to the epidermis in infection threads migrating parallel to the longitudinal axis of the root resulting in extensive infection patches at the nodule ape...
Resistance to glycopeptide antibiotics, the drugs of choice for life‐threatening bacterial infect... more Resistance to glycopeptide antibiotics, the drugs of choice for life‐threatening bacterial infections, is on the rise. In order to counter the threat of glycopeptide‐resistant bacteria, we report development of a new class of semi‐synthetic glycopeptide antibiotics, which not only target the bacterial membrane but also display enhanced inhibition of cell‐wall biosynthesis through increased binding affinity to their target peptides. The combined effect of these two mechanisms resulted in improved in vitro activity of two to three orders of magnitude over vancomycin and no propensity to trigger drug resistance in bacteria. In murine model of kidney infection, the optimized compound was able to bring bacterial burden down by about 6 logs at 12 mg kg−1 with no observed toxicity. The results furnished in this report emphasize the potential of this class of compounds as future antibiotics for drug‐resistant Gram‐positive infections.
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