Ursane-Type Triterpenes, Phenolics and Phenolic Derivatives from Globimetula braunii Leaf.

Globimetula braunii is a hemi-parasitic plant used in African ethnomedicine for the management of microbial infections, rheumatic pain and tumors amongst others. We report the isolation and characterization of eight compounds with their antioxidant and antimicrobial activities. The air-dried powdered leaf was macerated in EtOH/H20 (4:1). The extract was solvent-partitioned into n-hexane, EtOAc, n-BuOH and aqueous fractions. The fractions were screened for their antioxidant properties, using DPPH, FRAP, TAC and FIC assays. Antimicrobial analysis was performed using the micro-broth dilution method. The active EtOAc fraction was purified for its putative compounds on a repeated silica gel column chromatography monitored with TLC-bioautography. The isolated compounds were characterized using spectroscopic methods of UV, FT-IR, NMR and MS. Eight compounds (1-8) were isolated and characterized as 13,27-cycloursane (1), phyllanthone (2), globraunone (3), three phenolics: methyl 3,5-dihydroxy-4-methoxybenzoate (4), methyl 3-methyl-4-hydroxybenzoate (5) and guaiacol (6), as well as two phenol derivatives: 4-formaldehyde phenone (7) and 6-methoxy-2H-inden-5-ol (8). The study identified 4 and 6 as natural antioxidant compounds with potential as antimicrobial agents.

A Dimer, but Not Monomer, of Tobramycin Potentiates Ceftolozane against Multidrug-Resistant and Extensively Drug-Resistant Pseudomonas aeruginosa and Delays Resistance Development.

Ceftolozane-tazobactam is a potent ß-lactam/ß-lactamase inhibitor combination approved for the treatment of complicated intraabdominal and complicated urinary tract infections and, more recently, the treatment of hospital-acquired and ventilator-associated bacterial pneumonia. Although the activities of ceftolozane are not enhanced by tazobactam against Pseudomonas aeruginosa, it remains the most potent antipseudomonal agent approved to date. Emerging data worldwide has included reports of microbiological failure in patients with serious bacterial infections caused by multidrug-resistant (MDR) P. aeruginosa as a result of ceftolozane resistance developed within therapy. The objective of this study is to compare the efficacy of a tobramycin homodimer plus ceftolozane versus ceftolozane-tazobactam alone against MDR and extensively drug-resistant (XDR) P. aeruginosa Tobramycin homodimer, a synthetic dimer of two monomeric units of tobramycin, was developed to abrogate the ribosomal properties of tobramycin with a view to mitigating aminoglycoside-related toxicity and resistance. Herein, we report that tobramycin homodimer, a nonribosomal aminoglycoside derivative, potentiates the activities of ceftolozane versus MDR/XDR P. aeruginosain vitro and delays the emergence of resistance to ceftolozane-tazobactam in the wild-type PAO1 strain. This combination is also more potent than a standard ceftazidime-avibactam combination against these isolates. Conversely, a tobramycin monomer with intrinsic ribosomal properties does not potentiate ceftolozane under similar conditions. Susceptibility and checkerboard studies were assessed using serial 2-fold dilution assays, following the Clinical and Laboratory Standards Institute (CLSI) guidelines. This strategy provides an avenue to further preserve the clinical utility of ceftolozane and enhances its spectrum of activity against one of the most difficult-to-treat pathogens in hospitals.

Overcoming ß-Lactam resistance in Pseudomonas aeruginosa using non-canonical tobramycin-based antibiotic adjuvants.

ß-Lactam antibiotics have for long been a mainstay in antimicrobial chemotherapy. However, due to its ubiquitous usage, bacteria have evolved multiple concerted pathways to evade its actions, underscoring the complexity of resistance to this class of drug. Current strategies to mitigate this problem are geared towards developing inhibitors that can shield the ß-lactam core from enzymatic hydrolysis. In reality, a combination of factors including porin loss, overexpressed efflux pumps, expression of ß-lactamases, reduced outer membrane permeability, and target modifications are characteristics of phenotypes that are microbiologically resistant to ß-lactam antibiotics, especially Pseudomonas aeruginosa. Herein, we describe a strategy that may simultaneously address multiple mechanisms of resistance to ß-lactams. A triple combination with ß-lactam/ß-lactamase inhibitors offers better microbiological response against carbapenem-resistant P. aeruginosa than the current standard of care. The observed interactions are also unaffected by efflux pumps. We conclude that a multicomponent combination therapy may be the way forward in addressing the myriads of emerging therapy failure associated with ß-lactam resistance.

Syntheses of L-Rhamnose-Linked Amino Glycerolipids and Their Cytotoxic Activities against Human Cancer Cells.

A major impediment to successful cancer treatment is the inability of clinically available drugs to kill drug-resistant cancer cells. We recently identified metabolically stable L-glucosamine-based glycosylated antitumor ether lipids (GAELs) that were cytotoxic to chemotherapy-resistant cancer cells. In the absence of commercially available L-glucosamine, many steps were needed to synthesize the compound and the overall yield was poor. To overcome this limitation, a facile synthetic procedure using commercially available L-sugars including L-rhamnose and L-glucose were developed and the L-GAELs tested for anticancer activity. The most potent analog synthesized, 3-amino-1-O-hexadecyloxy-2R-(O-α-L-rhamnopyranosyl)-sn- glycerol 3, demonstrated a potent antitumor effect against human cancer cell lines derived from breast, prostate, and pancreas. The activity observed was superior to that observed with clinical anticancer agents including cisplatin and chlorambucil. Moreover, like other GAELs, 3 induced cell death by a non-membranolytic caspase-independent pathway.

Antibiotic Hybrids: the Next Generation of Agents and Adjuvants against Gram-Negative Pathogens?

The global incidence of drug-resistant Gram-negative bacillary infections has been increasing, and there is a dire need to develop novel strategies to overcome this problem. Intrinsic resistance in Gram-negative bacteria, such as their protective outer membrane and constitutively overexpressed efflux pumps, is a major survival weapon that renders them refractory to current antibiotics. Several potential avenues to overcome this problem have been at the heart of antibiotic drug discovery in the past few decades. We review some of these strategies, with emphasis on antibiotic hybrids either as stand-alone antibacterial agents or as adjuvants that potentiate a primary antibiotic in Gram-negative bacteria. Antibiotic hybrid is defined in this review as a synthetic construct of two or more pharmacophores belonging to an established agent known to elicit a desired antimicrobial effect. The concepts, advances, and challenges of antibiotic hybrids are elaborated in this article. Moreover, we discuss several antibiotic hybrids that were or are in clinical evaluation. Mechanistic insights into how tobramycin-based antibiotic hybrids are able to potentiate legacy antibiotics in multidrug-resistant Gram-negative bacilli are also highlighted. Antibiotic hybrids indeed have a promising future as a therapeutic strategy to overcome drug resistance in Gram-negative pathogens and/or expand the usefulness of our current antibiotic arsenal.

Potentiation of ß-lactam antibiotics and ß-lactam/ß-lactamase inhibitor combinations against MDR and XDR Pseudomonas aeruginosa using non-ribosomal tobramycin-cyclam conjugates.

OBJECTIVES: To develop a multifunctional adjuvant molecule that can rescue ß-lactam antibiotics and ß-lactam/ß-lactamase inhibitor combinations from resistance in carbapenem-resistant Pseudomonas aeruginosa clinical isolates. METHODS: Preparation of adjuvant was guided by structure-activity relationships, following standard protocols. Susceptibility and chequerboard studies were assessed using serial 2-fold dilution assays. Toxicity was evaluated against porcine erythrocytes, human embryonic kidney (HEK293) cells and liver carcinoma (HepG2) cells via MTS assay. Preliminary in vivo efficacy was evaluated using a Galleria mellonella infection model. RESULTS: Conjugation of tobramycin and cyclam abrogates the ribosomal effects of tobramycin but confers a potent adjuvant property that restores full antibiotic activity of meropenem and aztreonam against carbapenem-resistant P. aeruginosa. Therapeutic levels of susceptibility, as determined by CLSI susceptibility breakpoints, were attained in several MDR clinical isolates, and time-kill assays revealed a synergistic dose-dependent pharmacodynamic relationship. A triple combination of the adjuvant with ceftazidime/avibactam (approved), aztreonam/avibactam (Phase III) and meropenem/avibactam enhances the efficacies of ß-lactam/ß-lactamase inhibitors against recalcitrant strains, suggesting rapid access of the combination to their periplasmic targets. The newly developed adjuvants, and their combinations, were non-haemolytic and non-cytotoxic, and preliminary in vivo evaluation in G. mellonella suggests therapeutic potential for the double and triple combinations. CONCLUSIONS: Non-ribosomal tobramycin-cyclam conjugate mitigates the effect of OprD/OprF porin loss in P. aeruginosa and potentiates ß-lactam/ß-lactamase inhibitors against carbapenem-resistant clinical isolates, highlighting the complexity of resistance to ß-lactam antibiotics. Our strategy presents an avenue to further preserve the therapeutic utility of ß-lactam antibiotics.

Investigating the anti-cancer potential of pyrimethamine analogues through a modern chemical biology lens.

Pharmacological inhibition of dihydrofolate reductase (DHFR) is an established approach for treating a variety of human diseases, including foreign infections and cancer. However, treatment with classic DHFR inhibitors, such as methotrexate (MTX), are associated with negative side-effects and resistance mechanisms that have prompted the search for alternatives. The DHFR inhibitor pyrimethamine (Pyr) has compelling anti-cancer activity in in vivo models, but lacks potency compared to MTX, thereby requiring higher concentrations to induce therapeutic responses. The purpose of this work was to investigate structural analogues of Pyr to improve its in vitro and cellular activity. A series of 36 Pyr analogues were synthesized and tested in a sequence of in vitro and cell-based assays to monitor their DHFR inhibitory activity, cellular target engagement, and impact on breast cancer cell viability. Ten top compounds were identified, two of which stood out as potential lead candidates, 32 and 34. These functionalized Pyr analogues potently engaged DHFR in cells, at concentrations as low as 1 nM and represent promising DHFR inhibitors that could be further explored as potential anti-cancer agents.

Disrupting TSLP-TSLP receptor interactions via putative small molecule inhibitors yields a novel and efficient treatment option for atopic diseases.

Thymic stromal lymphopoietin (TSLP) is a key player in atopic diseases, which has sparked great interest in therapeutically targeting TSLP. Yet, no small-molecule TSLP inhibitors exist due to the challenges of disrupting the protein-protein interaction between TSLP and its receptor. Here, we report the development of small-molecule TSLP receptor inhibitors using virtual screening and docking of >1,000,000 compounds followed by iterative chemical synthesis. BP79 emerged as our lead compound that effectively abrogates TSLP-triggered cytokines at low micromolar concentrations. For in-depth analysis, we developed a human atopic disease drug discovery platform using multi-organ chips. Here, topical application of BP79 onto atopic skin models that were co-cultivated with lung models and Th2 cells effectively suppressed immune cell infiltration and IL-13, IL-4, TSLP, and periostin secretion, while upregulating skin barrier proteins. RNA-Seq analysis corroborate these findings and indicate protective downstream effects on the lungs. To the best of our knowledge, this represents the first report of a potent putative small molecule TSLPR inhibitor which has the potential to expand the therapeutic and preventive options in atopic diseases.

Heterodimeric Rifampicin-Tobramycin conjugates break intrinsic resistance of Pseudomonas aeruginosa to doxycycline and chloramphenicol in vitro and in a Galleria mellonella in vivo model.

Intrinsic resistance in Pseudomonas aeruginosa, defined by chromosomally encoded low outer membrane permeability and constitutively over-expressed efflux pumps, is a major reason why the pathogen is refractory to many antibiotics. Herein, we report that heterodimeric rifampicin-tobramycin conjugates break this intrinsic resistance and sensitize multidrug and extensively drug-resistant P. aeruginosa to doxycycline and chloramphenicol in vitro and in vivo. Tetracyclines and chloramphenicol are model compounds for bacteriostatic effects, but when combined with rifampicin-tobramycin adjuvants, their effects became bactericidal at sub MIC levels. Potentiation of tetracyclines correlates with the SAR of this class of drugs and is consistent with outer membrane permeabilization and efflux pump inhibition. Overall, this strategy finds new uses for old drugs and presents an avenue to expand the therapeutic utility of legacy antibiotics to recalcitrant pathogens such as P. aeruginosa.

Development of a nebramine-cyclam conjugate as an antibacterial adjuvant to potentiate ß-lactam antibiotics against multidrug-resistant P. aeruginosa.

The ß-lactams are the most widely used class of antibiotics due to their safety, effectiveness, and spectrum of activity. As a result of their ubiquitous usage, there has been a steady rise in ß-lactam resistant Gram-negative bacteria, especially Pseudomonas aeruginosa, resulting in limited treatment options. P. aeruginosa can develop multidrug-resistant phenotypes using a multifaceted approach of ß-lactamase expression, decreased porin production and increased efflux. Current ß-lactamase inhibitors address drug hydrolyzing enzymes but may not be as effective in phenotypes with reduced permeability and/or overexpressed efflux pumps. Herein, we present the synthesis and biological evaluation of a nebramine-cyclam conjugate molecule that is able to potentiate ß-lactam antibiotics, as well as other legacy antibiotics, against P. aeruginosa in vitro. Combination studies show that this adjuvant is able to synergize with ß-lactams such as aztreonam and ceftazidime against multidrug-resistant and extremely drug-resistant clinical isolates through a hypothesized mechanism of outer membrane permeabilization. Importantly, the addition of low concentrations (8 µM) of the nontoxic nebramine-cyclam conjugate is able to further potentiate existing ß-lactam/ß-lactamase inhibitor combinations in ß-lactamase-harboring P. aeruginosa strains. These data support a potential application of the nebramine-cyclam conjugate as an adjuvant for treating infections caused by P. aeruginosa strains that utilize multiple mechanisms of resistance.

Homodimeric Tobramycin Adjuvant Repurposes Novobiocin as an Effective Antibacterial Agent against Gram-Negative Bacteria.

Low permeability across the outer membrane is a major reason why most antibiotics are ineffective against Gram-negative bacteria. Agents that permeabilize the outer membrane are typically toxic at their effective concentrations. Here, we report the development of a broad-spectrum homodimeric tobramycin adjuvant that is nontoxic and more potent than the gold standard permeabilizing agent, polymyxin B nonapeptide. In pilot studies, the adjuvant confers potent bactericidal activity on novobiocin against Gram-negative bacteria, including carbapenem-resistant and colistin-resistant strains bearing plasmid-borne mcr-1 genes. Resistance development to the combination was significantly reduced, relative to novobiocin alone, and there was no induction of cross-resistance to other antibiotics, including the gyrase-acting fluoroquinolones. Tobramycin homodimer may allow the use of lower doses of novobiocin, overcoming its twin problem of efficacy and toxicity.

Amphiphilic nebramine-based hybrids Rescue legacy antibiotics from intrinsic resistance in multidrug-resistant Gram-negative bacilli.

The inability to discover novel class of antibacterial agents, especially against Gram-negative bacteria (GNB), compel us to consider a broader non-conventional approach to treat infections caused by multidrug-resistant (MDR) bacteria. One such approach is the use of adjuvants capable of revitalizing the activity of current existing antibiotics from resistant pathogens. Recently, our group reported a series of tobramycin (TOB)-based hybrid adjuvants that were able to potentiate multiple classes of legacy antibiotics against various MDR GNB. Herein, we report the modification of TOB-based hybrid adjuvants by replacing TOB domain by the pseudo-disaccharide nebramine (NEB) through selective cleavage of the α-d-glucopyranosyl linkage of TOB. Potent synergism was found for combinations of NEB-based hybrid adjuvants with multiple classes of legacy antibiotics including fluoroquinolones (moxifloxacin and ciprofloxacin), tetracyclines (minocycline), or rifamycin (rifampicin) against both wild-type and MDR P. aeruginosa clinical isolates. We also demonstrated that a combination of the optimized NEB-CIP hybrid 1b and rifampicin protects Galleria mellonella larvae from the lethal effects of extensively drug-resistant (XDR) P. aeruginosa. Mechanistic evaluation of NEB-based hybrid adjuvants revealed that the hybrids affect the outer- and inner membranes of wild-type P. aeruginosa PAO1. This study describes an approach to optimize aminoglycoside-based hybrids to yield lead adjuvant candidates that are able to resuscitate the activity of partner antibiotics against MDR GNB.

Cefiderocol: A Siderophore Cephalosporin with Activity Against Carbapenem-Resistant and Multidrug-Resistant Gram-Negative Bacilli.

Cefiderocol is an injectable siderophore cephalosporin discovered and being developed by Shionogi & Co., Ltd., Japan. As with other ß-lactam antibiotics, the principal antibacterial/bactericidal activity of cefiderocol occurs by inhibition of Gram-negative bacterial cell wall synthesis by binding to penicillin binding proteins; however, it is unique in that it enters the bacterial periplasmic space as a result of its siderophore-like property and has enhanced stability to ß-lactamases. The chemical structure of cefiderocol is similar to both ceftazidime and cefepime, which are third- and fourth-generation cephalosporins, respectively, but with high stability to a variety of ß-lactamases, including AmpC and extended-spectrum ß-lactamases (ESBLs). Cefiderocol has a pyrrolidinium group in the side chain at position 3 like cefepime and a carboxypropanoxyimino group in the side chain at position 7 of the cephem nucleus like ceftazidime. The major difference in the chemical structures of cefiderocol, ceftazidime and cefepime is the presence of a catechol group on the side chain at position 3. Together with the high stability to ß-lactamases, including ESBLs, AmpC and carbapenemases, the microbiological activity of cefiderocol against aerobic Gram-negative bacilli is equal to or superior to that of ceftazidime-avibactam and meropenem, and it is active against a variety of Ambler class A, B, C and D ß-lactamases. Cefiderocol is also more potent than both ceftazidime-avibactam and meropenem versus Acinetobacter baumannii, including meropenem non-susceptible and multidrug-resistant (MDR) isolates. Cefiderocol's activity against meropenem-non-susceptible and Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriales is comparable or superior to ceftazidime-avibactam. Cefiderocol is also more potent than both ceftazidime-avibactam and meropenem against all resistance phenotypes of Pseudomonas aeruginosa and against Stenotrophomonas maltophilia. The current dosing regimen being used in phase III studies is 2 g administered intravenously every 8 h (q8 h) using a 3-h infusion. The pharmacokinetics of cefiderocol are best described by a three-compartment linear model. The mean plasma half-life (t½) was ~ 2.3 h, protein binding is 58%, and total drug clearance ranged from 4.6-6.0 L/h for both single- and multi-dose infusions and was primarily renally excreted unchanged (61-71%). Cefiderocol is primarily renally excreted unchanged and clearance correlates with creatinine clearance. Dosage adjustment is thus required for both augmented renal clearance and in patients with moderate to severe renal impairment. In vitro and in vivo pharmacodynamic studies have reported that as with other cephalosporins the pharmacodynamic index that best predicts clinical outcome is the percentage of time that free drug concentrations exceed the minimum inhibitory concentration (%fT > MIC). In vivo efficacy of cefiderocol has been studied in a variety of humanized drug exposure murine and rat models of infection utilizing a variety of MDR and extremely drug resistant strains. Cefiderocol has performed similarly to or has been superior to comparator agents, including ceftazidime and cefepime. A phase II prospective, multicenter, double-blind, randomized clinical trial assessed the safety and efficacy of cefiderocol 2000 mg q8 h versus imipenem/cilastatin 1000 mg q8 h, both administered intravenously for 7-14 days over 1 h, in the treatment of complicated urinary tract infection (cUTI, including pyelonephritis) or acute uncomplicated pyelonephritis in hospitalized adults. A total of 452 patients were initially enrolled in the study, with 303 in the cefiderocol arm and 149 in the imipenem/cilastatin arm. The primary outcome measure was a composite of clinical cure and microbiological eradication at the test-of-cure (TOC) visit, that is, 7 days after the end of treatment in the microbiological intent-to-treat (MITT) population. Secondary outcome measures included microbiological response per pathogen and per patient at early assessment (EA), end of treatment (EOT), TOC, and follow-up (FUP); clinical response per pathogen and per patient at EA, EOT, TOC, and FUP; plasma, urine and concentrations of cefiderocol; and the number of participants with adverse events. The composite of clinical and microbiological response rates was 72.6% (183/252) for cefiderocol and 54.6% (65/119) for imipenem/cilastatin in the MITT population. Clinical response rates per patient at the TOC visit were 89.7% (226/252) for cefiderocol and 87.4% (104/119) for imipenem/cilastatin in the MITT population. Microbiological eradication rates were 73.0% (184/252) for cefiderocol and 56.3% (67/119) for imipenem/cilastatin in the MITT population. Additionally, two phase III clinical trials are currently being conducted by Shionogi & Co., Ltd., Japan. The two trials are evaluating the efficacy of cefiderocol in the treatment of serious infections in adult patients caused by carbapenem-resistant Gram-negative pathogens and evaluating the efficacy of cefiderocol in the treatment of adults with hospital-acquired bacterial pneumonia, ventilator-associated pneumonia or healthcare-associated pneumonia caused by Gram-negative pathogens. Cefiderocol appears to be well tolerated (minor reported adverse effects were gastrointestinal and phlebitis related), with a side effect profile that is comparable to other cephalosporin antimicrobials. Cefiderocol appears to be well positioned to help address the increasing number of infections caused by carbapenem-resistant and MDR Gram-negative bacilli, including ESBL- and carbapenemase-producing strains (including metallo-ß-lactamase producers). A distinguishing feature of cefiderocol is its activity against resistant P. aeruginosa, A. baumannii, S. maltophilia and Burkholderia cepacia.

Ubiquitous Nature of Fluoroquinolones: The Oscillation between Antibacterial and Anticancer Activities.

Fluoroquinolones are synthetic antibacterial agents that stabilize the ternary complex of prokaryotic topoisomerase II enzymes (gyrase and Topo IV), leading to extensive DNA fragmentation and bacteria death. Despite the similar structural folds within the critical regions of prokaryotic and eukaryotic topoisomerases, clinically relevant fluoroquinolones display a remarkable selectivity for prokaryotic topoisomerase II, with excellent safety records in humans. Typical agents that target human topoisomerases (such as etoposide, doxorubicin and mitoxantrone) are associated with significant toxicities and secondary malignancies, whereas clinically relevant fluoroquinolones are not known to exhibit such propensities. Although many fluoroquinolones have been shown to display topoisomerase-independent antiproliferative effects against various human cancer cells, those that are significantly active against eukaryotic topoisomerase show the same DNA damaging properties as other topoisomerase poisons. Empirical models also show that fluoroquinolones mediate some unique immunomodulatory activities of suppressing pro-inflammatory cytokines and super-inducing interleukin-2. This article reviews the extended roles of fluoroquinolones and their prospects as lead for the unmet needs of "small and safe" multimodal-targeting drug scaffolds.

Amphiphilic Modulation of Glycosylated Antitumor Ether Lipids Results in a Potent Triamino Scaffold against Epithelial Cancer Cell Lines and BT474 Cancer Stem Cells.

The problems of resistance to apoptosis-inducing drugs, recurrence, and metastases that have bedeviled cancer treatment have been attributed to the presence of cancer stem cells (CSCs) in tumors, and there is currently no clinically indicated drug for their eradication. We previously reported that glycosylated antitumor ether lipids (GAELs) display potent activity against CSCs. Here, we show that by carefully modulating the amphiphilic nature of a monoamine-based GAEL, we can generate a potent triamino scaffold that is active against a panel of hard-to-kill epithelial cancer cell lines (including triple-negative breast) and BT474 CSCs. The most active compound of this set, which acts via a nonmembranolytic, nonapoptotic caspase-independent mechanism, is more effective than cisplatin and doxorubicin against these cell lines and more potent than salinomycin against BT474 CSCs. Understanding the combination of factors crucial for the enhanced cytotoxicity of GAELs opens new avenues to develop potent compounds against drug-resistant cancer cells and CSCs.

Replacing d-Glucosamine with Its l-Enantiomer in Glycosylated Antitumor Ether Lipids (GAELs) Retains Cytotoxic Effects against Epithelial Cancer Cells and Cancer Stem Cells.

We describe metabolically inert l-glucosamine-based glycosylated antitumor ether lipids (L-GAELs) that retain the cytotoxic effects of the D-GAELs including the ability to kill BT-474 breast cancer stem cells (CSCs). When compared to adriamycin, cisplatin, and the anti-CSC agent salinomycin, L-GAELs display superior activity to kill cancer stem cells (CSCs). Mode of action studies indicate that L-GAELs like the D-GAELs kill cells via an apoptosis-independent mechanism that was not due to membranolytic effects.

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.

Design, synthesis and antitumor properties of glycosylated antitumor ether lipid (GAEL)- chlorambucil-hybrids.

Glycosylated antitumor ether lipids (GAELs) kill cancer cells and cancer stem cells via a novel, apoptosis-independent mechanism. In contrast, chlorambucil, a drug in clinical use for the treatment of chronic lymphocytic leukemia reacts with nucleophiles within the major groove of DNA, leading to apoptosis. We hypothesized that hybrid molecules that combine apoptosis-dependent and apoptosis-independent mode of actions in a single molecule may lead to enhanced antitumor activity. Here, we describe the antitumor activities of chlorambucil-linked glucosamine-derived glycerolipid hybrids and investigate the role of the chlorambucil moiety and the effect of cationic charge on the hybrid molecule. Three hybrids and two control GAELs were synthesized and their activities against breast (JIMT1, MDA-MB-231, BT474), pancreas (MiaPaCa2) and prostate (DU145, PC3) cancer cell lines were determined using MTS assay. Hybrid 3 displayed the most potent activity on DU145 at CC50 of 6.0 µM while hybrid 4 displayed the best activity on JIMT1 at 7.5 µM. Hybrid 5 exhibited no activity at the highest concentration tested (CC50 >20 µM), underscoring the significance of the cationic charge at C-2 position as previously reported. Although chlorambucil (2) itself showed very little activity against all the six cell lines (CC50 >150 µM), GAELs 6 and 7 which lack the chlorambucil moiety were consistently less active than 3 and 4, suggesting that the chlorambucil moiety contributes to the overall activity. The hybrids were however not as active as the parent GAEL 1 against MiaPaCa2 whereas 6 restored activity comparable to 1.