Repurposed Antimicrobial Combination Therapy: Tobramycin-Ciprofloxacin Hybrid Augments Activity of the Anticancer Drug Mitomycin C Against Multidrug-Resistant Gram-Negative Bacteria.

The lack of therapeutic options to treat infections caused by multidrug-resistant (MDR) pathogens, especially Gram-negative bacteria, is apparent. Therefore, it is imperative to develop new strategies to address the problem of antimicrobial resistance. Repurposing non-antibiotic commercial drugs for antimicrobial therapy presents a viable option. We screened six anticancer drugs for their potential use in antimicrobial therapy. Here, we provide in vitro evidence that suggests feasibility to repurpose the anticancer drug mitomycin C against MDR Gram-negative bacteria. We also demonstrated that mitomycin C, etoposide and doxorubicin were affected by drug efflux in Pseudomonas aeruginosa. In combination with a tobramycin-ciprofloxacin antibiotic hybrid (TOB-CIP), the antibacterial activity of mitomycin C was enhanced against MDR clinical isolates of P. aeruginosa, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae. In fact, 4 µg/mL (3 µM) TOB-CIP reduced the minimum inhibitory concentration of mitomycin C to ≤1 µg/mL against MDR Gram-negative bacteria, except A. baumannii. We showed that synergy was inherent to TOB-CIP and that neither tobramycin nor ciprofloxacin individually synergized with mitomycin C. Our finding supports identifying adjuvant partners for mitomycin C, such as TOB-CIP, to enhance suitability for antimicrobial therapy.

Amphiphilic Tobramycin-Lysine Conjugates Sensitize Multidrug Resistant Gram-Negative Bacteria to Rifampicin and Minocycline.

Chromosomally encoded low membrane permeability and highly efficient efflux systems are major mechanisms by which Pseudomonas aeruginosa evades antibiotic actions. Our previous reports have shown that amphiphilic tobramycin-fluoroquinolone hybrids can enhance efficacy of fluoroquinolone antibiotics against multidrug-resistant (MDR) P. aeruginosa isolates. Herein, we report on a novel class of tobramycin-lysine conjugates containing an optimized amphiphilic tobramycin-C12 tether that sensitize Gram-negative bacteria to legacy antibiotics. Combination studies indicate the ability of these conjugates to synergize rifampicin and minocycline against MDR and extensively drug resistant (XDR) P. aeruginosa isolates and enhance efficacy of both antibiotics in the Galleria mellonella larvae in vivo infection model. Mode of action studies indicate that the amphiphilic tobramycin-lysine adjuvants enhance outer membrane cell penetration and affect the proton motive force, which energizes efflux pumps. Overall, this study provides a strategy for generating effective antibiotic adjuvants that overcome resistance of rifampicin and minocycline in MDR and XDR Gram-negative bacteria including P. aeruginosa.

A Tobramycin Vector Enhances Synergy and Efficacy of Efflux Pump Inhibitors against Multidrug-Resistant Gram-Negative Bacteria.

Drug efflux mechanisms interact synergistically with the outer membrane permeability barrier of Gram-negative bacteria, leading to intrinsic resistance that presents a major challenge for antibiotic drug development. Efflux pump inhibitors (EPIs) which block the efflux of antibiotics synergize antibiotics, but the clinical development of EPI/antibiotic combination therapy to treat multidrug-resistant (MDR) Gram-negative infections has been challenging. This is in part caused by the inefficiency of current EPIs to penetrate the outer membrane and resist efflux. We demonstrate that conjugation of a tobramycin (TOB) vector to EPIs like NMP, paroxetine, or DBP enhances synergy and efficacy of EPIs in combination with tetracycline antibiotics against MDR Gram-negative bacteria including Pseudomonas aeruginosa. Besides potentiating tetracycline antibiotics, TOB-EPI conjugates can also suppress resistance development to the tetracycline antibiotic minocycline, thereby providing a strategy to develop more effective adjuvants to rescue tetracycline antibiotics from resistance in MDR Gram-negative bacteria.

Solithromycin: A Novel Fluoroketolide for the Treatment of Community-Acquired Bacterial Pneumonia.

Solithromycin is a novel fluoroketolide developed in both oral and intravenous formulations to address increasing macrolide resistance in pathogens causing community-acquired bacterial pneumonia (CABP). When compared with its macrolide and ketolide predecessors, solithromycin has several structural modifications which increase its ribosomal binding and reduce its propensity to known macrolide resistance mechanisms. Solithromycin, like telithromycin, affects 50S ribosomal subunit formation and function, as well as causing frame-shift errors during translation. However, unlike telithromycin, which binds to two sites on the ribosome, solithromycin has three distinct ribosomal binding sites. Its desosamine sugar interacts at the A2058/A2059 cleft in domain V (as all macrolides do), an extended alkyl-aryl side chain interacts with base pair A752-U2609 in domain II (similar to telithromycin), and a fluorine at C-2 of solithromycin provides additional binding to the ribosome. Studies describing solithromycin activity against Streptococcus pneumoniae have reported that it does not induce erm-mediated resistance because it lacks a cladinose moiety, and that it is less susceptible than other macrolides to mef-mediated efflux due to its increased ribosomal binding and greater intrinsic activity. Solithromycin has demonstrated potent in vitro activity against the most common CABP pathogens, including macrolide-, penicillin-, and fluoroquinolone-resistant isolates of S. pneumoniae, as well as Haemophilus influenzae and atypical bacterial pathogens. Solithromycin displays multi-compartment pharmacokinetics, a large volume of distribution (>500 L), approximately 67% bioavailability when given orally, and serum protein binding of 81%. Its major metabolic pathway appears to follow cytochrome P450 (CYP) 3A4, with metabolites of solithromycin undergoing biliary excretion. Its serum half-life is approximately 6-9 h, which is sufficient for once-daily administration. Pharmacodynamic activity is best described as fAUC0-24/MIC (the ratio of the area under the free drug concentration-time curve from 0 to 24 h to the minimum inhibitory concentration of the isolate). Solithromycin has completed one phase II and two phase III clinical trials in patients with CABP. In the phase II trial, oral solithromycin was compared with oral levofloxacin and demonstrated similar clinical success rates in the intention-to-treat (ITT) population (84.6 vs 86.6%). Clinical success in the clinically evaluable patients group was 83.6% of patients receiving solithromycin compared with 93.1% for patients receiving levofloxacin. In SOLITAIRE-ORAL, a phase III trial which assessed patients receiving oral solithromycin or oral moxifloxacin for CABP, an equivalent (non-inferior) early clinical response in the ITT population was demonstrated for patients receiving either solithromycin (78.2%) or moxifloxacin (77.9%). In a separate phase III trial, SOLITAIRE-IV, patients receiving intravenous-to-oral solithromycin (79.3%) demonstrated non-inferiority as the primary outcome of early clinical response in the ITT population compared with patients receiving intravenous-to-oral moxifloxacin (79.7%). Overall, solithromycin has been well tolerated in clinical trials, with gastrointestinal adverse events being most common, occurring in approximately 10% of patients. Transaminase elevation occurred in 5-10% of patients and generally resolved following cessation of therapy. None of the rare serious adverse events that occurred with telithromycin (i.e., hepatotoxicity) have been noted with solithromycin, possibly due to the fact that solithromycin (unlike telithromycin) does not possess a pyridine moiety in its chemical structure, which has been implicated in inhibiting nicotinic acetylcholine receptors. Because solithromycin is a possible substrate and inhibitor of both CYP3A4 and P-glycoprotein (P-gp), it may display drug interactions similar to macrolides such as clarithromycin. Overall, the in vitro activity, clinical efficacy, tolerability, and safety profile of solithromycin demonstrated to date suggest that it continues to be a promising treatment for CABP.

Hybrid Antibiotic Overcomes Resistance in P. aeruginosa by Enhancing Outer Membrane Penetration and Reducing Efflux.

Therapeutic interventions to treat multidrug-resistant (MDR) Pseudomonas aeruginosa infections are severely limited and often require the use of colistin as drug of last resort. The major challenges impeding the development of novel antipseudomonal agents are the lack of cell penetration and extensive efflux. We have discovered a tobramycin-moxifloxacin hybrid core structure which enhances outer membrane permeability and reduces efflux by dissipating the proton motive force of the cytoplasmic membrane in P. aeruginosa. The optimized hybrid protects Galleria mellonella larvae from the lethal effects of MDR P. aeruginosa. Attempts to select for resistance over a period of 25 days resulted in a 2-fold increase in the minimal inhibitory concentration (MIC) for the hybrid, while moxifloxacin or tobramycin resulted in a 16- and 512-fold increase in MIC. Although the hybrid possesses potent activity against MDR, P. aeruginosa isolates the activity that can be synergized when used in combination with other classes of antibiotics.

Review of Eravacycline, a Novel Fluorocycline Antibacterial Agent.

Eravacycline is an investigational, synthetic fluorocycline antibacterial agent that is structurally similar to tigecycline with two modifications to the D-ring of its tetracycline core: a fluorine atom replaces the dimethylamine moiety at C-7 and a pyrrolidinoacetamido group replaces the 2-tertiary-butyl glycylamido at C-9. Like other tetracyclines, eravacycline inhibits bacterial protein synthesis through binding to the 30S ribosomal subunit. Eravacycline demonstrates broad-spectrum antimicrobial activity against Gram-positive, Gram-negative, and anaerobic bacteria with the exception of Pseudomonas aeruginosa. Eravacycline is two- to fourfold more potent than tigecycline versus Gram-positive cocci and two- to eightfold more potent than tigecycline versus Gram-negative bacilli. Intravenous eravacycline demonstrates linear pharmacokinetics that have been described by a four-compartment model. Oral bioavailability of eravacycline is estimated at 28 % (range 26-32 %) and a single oral dose of 200 mg achieves a maximum plasma concentration (C max) and area under the plasma concentration-time curve from 0 to infinity (AUC0-∞) of 0.23 ± 0.04 mg/L and 3.34 ± 1.11 mg·h/L, respectively. A population pharmacokinetic study of intravenous (IV) eravacycline demonstrated a mean steady-state volume of distribution (V ss) of 320 L or 4.2 L/kg, a mean terminal elimination half-life (t ½) of 48 h, and a mean total clearance (CL) of 13.5 L/h. In a neutropenic murine thigh infection model, the pharmacodynamic parameter that demonstrated the best correlation with antibacterial response was the ratio of area under the plasma concentration-time curve over 24 h to the minimum inhibitory concentration (AUC0-24h/MIC). Several animal model studies including mouse systemic infection, thigh infection, lung infection, and pyelonephritis models have been published and demonstrated the in vivo efficacy of eravacycline. A phase II clinical trial evaluating the efficacy and safety of eravacycline in the treatment of community-acquired complicated intra-abdominal infection (cIAI) has been published as well, and phase III clinical trials in cIAI and complicated urinary tract infection (cUTI) have been completed. The eravacycline phase III program, known as IGNITE (Investigating Gram-Negative Infections Treated with Eravacycline), investigated its safety and efficacy in cIAI (IGNITE 1) and cUTI (IGNITE 2). Eravacycline met the primary endpoint in IGNITE 1, while data analysis for IGNITE 2 is currently ongoing. Common adverse events reported in phase I-III studies included gastrointestinal effects such as nausea and vomiting. Eravacycline is a promising intravenous and oral fluorocycline that may offer an alternative treatment option for patients with serious infections, particularly those caused by multidrug-resistant Gram-negative pathogens.

Adjuvants Based on Hybrid Antibiotics Overcome Resistance in Pseudomonas aeruginosa and Enhance Fluoroquinolone Efficacy.

The use of adjuvants that rescue antibiotics against multidrug-resistant (MDR) pathogens is a promising combination strategy for overcoming bacterial resistance. While the combination of ß-lactam antibiotics and ß-lactamase inhibitors has been successful in restoring antibacterial efficacy in MDR bacteria, the use of adjuvants to restore fluoroquinolone efficacy in MDR Gram-negative pathogens has been challenging. We describe tobramycin-ciprofloxacin hybrid adjuvants that rescue the activity of fluoroquinolone antibiotics against MDR and extremely drug-resistant Pseudomonas aeruginosa isolates in vitro and enhance fluoroquinolone efficacy in vivo. Structure-activity studies reveal that the presence of both tobramycin and ciprofloxacin, which are separated by a C12 tether, is critical for the function of the adjuvant. Mechanistic studies indicate that the antibacterial modes of ciprofloxacin are retained while the role of tobramycin is limited to destabilization of the outer membrane in the hybrid.

Tedizolid: a novel oxazolidinone with potent activity against multidrug-resistant gram-positive pathogens.

Tedizolid phosphate is a novel oxazolidinone prodrug (converted to the active form tedizolid by phosphatases in vivo) that has been developed and recently approved (June 2014) by the United States FDA for the treatment of acute bacterial skin and skin structure infections (ABSSSIs) caused by susceptible Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). Tedizolid is an oxazolidinone, but differs from other oxazolidinones by possessing a modified side chain at the C-5 position of the oxazolidinone nucleus which confers activity against certain linezolid-resistant pathogens and has an optimized C- and D-ring system that improves potency through additional binding site interactions. The mechanism of action of tedizolid is similar to other oxazolidinones and occurs through inhibition of bacterial protein synthesis by binding to 23S ribosomal RNA (rRNA) of the 50S subunit of the ribosome. As with other oxazolidinones, the spontaneous frequency of resistance development to tedizolid is low. Tedizolid is four- to eightfold more potent in vivo than linezolid against all species of staphylococci, enterococci, and streptococci, including drug-resistant phenotypes such as MRSA and vancomycin-resistant enterococci (VRE) and linezolid-resistant phenotypes. Importantly, tedizolid demonstrates activity against linezolid-resistant bacterial strains harboring the horizontally transmissible cfr gene, in the absence of certain ribosomal mutations conferring reduced oxazolidinone susceptibility. With its half-life of approximately 12 h, tedizolid is dosed once daily. It demonstrates linear pharmacokinetics, has a high oral bioavailability of approximately 90 %, and is primarily excreted by the liver as an inactive, non-circulating sulphate conjugate. Tedizolid does not require dosage adjustment in patients with any degree of renal dysfunction or hepatic dysfunction. Studies in animals have demonstrated that the pharmacodynamic parameter most closely associated with the efficacy of tedizolid is fAUC(0-24h)/MIC. In non-neutropenic animals, a dose-response enhancement was observed with tedizolid and lower exposures were required compared to neutropenic cohorts. Two Phase III clinical trials have demonstrated non-inferiority of a once-daily tedizolid 200 mg dose for 6-10 days versus twice-daily 600 mg linezolid for the treatment of ABSSSIs. Both trials used the primary endpoint of early clinical response at 48-72 h; however, one trial compared oral formulations while the other initiated therapy with the parenteral formulation and allowed oral sequential therapy following initial clinical response. Throughout its development, tedizolid has demonstrated that it is well tolerated and animal studies have shown a lower propensity for neuropathies with long-term use than its predecessor linezolid. Data from the two completed Phase III clinical trials demonstrated that the studied tedizolid regimen (200 mg once daily for 6 days) had significantly less impact on hematologic parameters as well as significantly less gastrointestinal treatment-emergent adverse effects (TEAEs) than its comparator linezolid. As with linezolid, tedizolid is a weak, reversible MAO inhibitor; however, a murine head twitch model validated to assess serotonergic activity reported no increase in the number of head twitches with tedizolid even at doses that exceeded the C max in humans by up to 25-fold. Tyramine and pseudoephedrine challenge studies in humans have also reported no meaningful MAO-related interactions with tedizolid. With its enhanced in vitro activity against a broad-spectrum of Gram-positive aerobic bacteria, convenient once-daily dosing, a short 6-day course of therapy, availability of both oral and intravenous routes of administration, and an adverse effect profile that appears to be more favorable than linezolid, tedizolid is an attractive agent for use in both the hospital and community settings. Tedizolid is currently undergoing additional Phase III clinical trials for the treatment of hospital-acquired bacterial pneumonia (HABP) and ventilated nosocomial pneumonia (VNP).

Design of a "turn-off/turn-on" biosensor: understanding carbohydrate-lectin interactions for use in noncovalent drug delivery.

A low-cost and highly sensitive biosensor system is designed to investigate carbohydrate-lectin interactions. This combination of glyco-gold nanoparticles and boronic acid biosensor system opens a way to study noncovalent drug delivery.

Stereoselective synthesis of ß-N-glycosides through 2-deoxy-2-nitroglycal.

An efficient, base-free protocol has been developed for the ß-stereoselective synthesis of N-glycosides from 2-nitroglycal and secondary amines. Simple protection and deprotection manipulations on the N-glycosides pave a way for the synthesis of biologically significant1,2-diaminosugars and glycopeptides.

Facile synthesis of carbohydrate-integrated isoxazolines through tandem [4+1] cycloaddition and rearrangement of 2-nitroglycals.

Carbohydrate-integrated isoxazolines were synthesized from 2-nitroglycals and sulfur ylides, with the aid of 1-phenylthiourea catalyst. The reactions proceeded via [4+1] annulations and upon subsequent rearrangement, afforded the corresponding isoxazolines in high yields with excellent diastereoselectivities (up to 95% de).

Ready access to 3-amino-2,3-dideoxysugars via regio- and stereo-selective tandem hydroamination-glycosylation of glycals.

A highly stereoselective BF(3)·OEt(2)-promoted tandem hydroamination-glycosylation on a glycal scaffold has been developed to form 3-amino-2,3-dideoxysugars in a one-pot procedure. This efficient multicomponent reaction protocol offers simplicity and general applicability to a broad range of variations on each component.

[3 + 2] cycloaddition on carbohydrate templates: stereoselective synthesis of pyrrolidines.

Pyrrolidine derivatives were prepared in high diastereoselectivities and good yields via a [3 + 2] cycloaddition of a tert-butyldimethylsilyl protected carbohydrate-based allene with a diverse range of imines. The subsequent removal of the carbohydrate auxiliary afforded a variety of pyrrolidines with excellent enantioselectivities (up to 99% ee). Selective reduction of the pyrrolidines further demonstrated the potential of this strategy.

Quick access to druglike heterocycles: facile silver-catalyzed one-pot multicomponent synthesis of aminoindolizines.

A direct and efficient approach to 1-aminoindolizines through three-component one-pot reaction of heteroaryl aldehydes, secondary amines, and terminal alkynes catalyzed by AgBF(4) has been developed. Desired products were obtained in moderate to excellent yields. Similar aminoindolizines products were afforded from trimethylsilyl protected alkyne substrates as well. This methodology provides a rapid access to construct a diversity-oriented library of indolizines.

Carbohydrate functionalized carbon nanotubes and their applications.

Carbon nanotubes (CNTs) have attracted tremendous attention in biomedical applications due to their molecular size and unique properties. This tutorial review summarizes the strategies to functionalize CNTs with bioactive carbohydrates, which improve their solubility, biocompatibility and biofunctionalities while preserving their desired properties. In addition, studies on the usage of carbohydrate functionalized CNTs to detect bacteria, to bind to specific lectins, to deliver glycomimetic drug molecules into cells and to probe cellular activities as biosensors are reviewed. Improvement in biocompatibility and introduction of bio-functionalities by integration of carbohydrate with CNTs are paving the way to glyconanotechnology and may provide new tools for glycobiological studies.

N-Heterocyclic carbene-catalyzed intramolecular aldehyde-nitrile cross coupling: an easy access to 3- aminochromones.

An immense effort has been made to develop an efficient strategy for the carbon-carbon bond formation between aldehyde and nitrile intramolecularly using an N-heterocyclic carbene catalyst to derive 3-aminochromone derivatives in good to excellent yields (80-95%).

Synthesis of 4-mercapto-L-lysine derivatives: potential building blocks for sequential native chemical ligation.

A general and diastereoselective synthesis of (2S, 4S)-4-mercapto-L-lysine derivative was described. The key features of this synthesis include Zn-mediated diastereoselective Reformatsky reaction and selective reduction of methyl ester with sodium borohydride. Introduction of thiol functional group on lysine side chain proved to be appropriate for dual native chemical ligation. This methodology allows to develop various 4-substituted L-lysine derivatives.

(S)-Camphorsulfonic acid catalyzed highly stereoselective synthesis of pseudoglycosides.

A mild and efficient synthesis of pseudoglycosides has been developed using metal free (S)-camphorsulfonic acid. (S)-CSA acts as an excellent catalyst for conversion of 2,4,6-tri-O-acetyl-D-glucal to 2,3-unsaturated O-glycosides. A wide range of biologically active natural products, alcohols and thiols could be coupled with glucal to give the desired pseudoglycosides in good to excellent yields with exclusive alpha-stereoselectivity.