Sensitization of Gram-Negative Bacteria to Aminoglycosides with 2-Aminoimidazole Adjuvants

In 2019, five million deaths associated with antimicrobial resistance were reported by The Centers for Disease Control and Prevention (CDC). Acinetobacter baumannii, a Gram-negative bacterial pathogen, is among the list of urgent threats. Previously, we reported 2-aminoimidazole (2-AI) adjuvants that potentiate macrolide activity against A. baumannii. In this study, we identify several of these adjuvants that sensitize A. baumannii to aminoglycoside antibiotics. Lead compounds 1 and 7 lower the tobramycin (TOB) minimum inhibitory concentration (MIC) against the TOB-resistant strain AB5075 from 128 μg/mL to 2 μg/mL at 30 μM. In addition, the lead compounds lower the TOB MIC against the TOB-susceptible strain AB19606 from 4 μg/mL to 1 μg/mL and 0.5 μg/mL, respectively, at 30 μM and 15 μM. The evolution of resistance to TOB and 1 in AB5075 revealed mutations in genes related to protein synthesis, the survival of bacteria under environmental stressors, bacteriophages, and proteins containing Ig-like domains.

6-Bromoindirubin-3'-oxime derivatives are highly active colistin adjuvants against Klebsiella pneumoniae

Multidrug resistant (MDR) bacterial infections have become increasingly common, leading clinicians to rely on last-resort antibiotics such as colistin. However, the utility of colistin is becoming increasingly compromised as a result of increasing polymyxin resistance. Recently we discovered that derivatives of the eukaryotic kinase inhibitor meridianin D abrogate colistin resistance in several Gram-negative species. A subsequent screen of three commercial kinase inhibitor libraries led to the identification of several scaffolds that potentiate colistin activity, including 6-bromoindirubin-3'-oxime, which potently suppresses colistin resistance in Klebsiella pneumoniae. Herein we report the activity of a library of 6-bromoindirubin-3'-oxime analogs and identify four derivatives that show equal or increased colistin potentiation activity compared to the parent compound.

Overcoming intrinsic resistance in gram-negative bacteria using small molecule adjuvants

Gram-negative bacteria are intrinsically resistant to many classes of antibiotics, predominantly due to the impermeability of the outer membrane and the presence of efflux pumps. Small molecule adjuvants that circumvent these resistance mechanisms have the potential to expand therapeutic options for treating Gram-negative infections to encompass antibiotic classes that are otherwise limited to treating Gram-positive infections. Adjuvants that effect increased antibiotic permeation, either by physical disruption of the outer membrane or through interference with synthesis, transport, or assembly of membrane components, and adjuvants that limit efflux, are discussed as potential avenues to overcoming intrinsic resistance in Gram-negative bacteria.

Benzimidazole Isosteres of Salicylanilides Are Highly Active Colistin Adjuvants

Multidrug-resistant bacterial infections have become a global threat. We recently disclosed that the known IKK-β inhibitor IMD-0354 and subsequent analogues abrogate colistin resistance in several Gram-negative strains. Herein, we report the activity of a second-generation library of IMD-0354 analogues incorporating a benzimidazole moiety as an amide isostere. We identified several analogues that show increased colistin potentiation activity against Gram-negative bacteria.

Phenotypic screening of compound libraries as a platform for the identification of antibiotic adjuvants: Identification of colistin adjuvants from a natural product library

The identification of antibiotic adjuvants, small molecules that potentiate the activity of conventional antibiotics, provides an orthogonal approach to the development of new antibiotics in the fight against drug resistant bacterial infections. Methods to identify novel adjuvants could potentially aid efforts to overcome the increasing prevalence of resistance and stave off the onset of a "post-antibiotic era." Phenotypic whole cell screens allow for the identification of hits with the necessary properties to access their biomolecular target, and may also facilitate the discovery of novel adjuvant targets. A phenotypic screening platform is outlined, in which a natural product library was explored for activity with antibiotics from several mechanistically distinct classes against clinically important bacterial species. General approaches to delineating the mechanism of action of hit compounds identified from phenotypic screens are described, followed by specific approaches to uncovering the mechanism of action of the colistin adjuvants identified from the natural product screen.

Screening an Established Natural Product Library Identifies Secondary Metabolites That Potentiate Conventional Antibiotics

Health organizations worldwide have warned that we are on the cusp of a "post-antibiotic era," necessitating new approaches to combat antibiotic resistant infections. One such approach is the development of antibiotic adjuvants, which have little or no inherent antibiotic activity at their active concentrations but instead potentiate the activity of antibiotics against antibiotic-resistant bacteria. Recently, we demonstrated that meridianin D, a natural product originally reported to have activity against Staphylococcus aureus and Mycobacterium tuberculosis, possesses the ability to reverse colistin resistance in colistin resistant bacteria. As most natural product screens typically involve screening for only certain activities (anticancer, antiviral, and antimicrobial are typical), we posited that the meridianin D discovery was not unique and there are potentially many natural products that have adjuvant activity. To explore this, the National Cancer Institute (NCI) Natural Product Library Set IV was screened for adjuvant activity using four classes of antibiotics (β-lactams, aminoglycosides, macrolides, and polymyxins) against three bacterial pathogens (methicillin-resistant Staphylococcus aureus (MRSA), Acinetobacter baumannii, and Klebsiella pneumoniae). Sixteen compounds suppressed β-lactam resistance in MRSA, five of which effected a 16-fold reduction in the oxacillin minimum inhibitory concentration (MIC). Two natural products effectively suppressed aminoglycoside resistance in both of the Gram-negative species tested, and no hits were observed with macrolides. In contrast, a larger number of natural product adjuvants were identified when screening against colistin-resistant strains of A. baumannii and K. pneumoniae. Nine compounds reduced the colistin MIC to its breakpoint or lower (up to a 1024-fold reduction). Clorobiocin, novobiocin, and prodigiosin were most effective, reducing the colistin MIC in K. pneumoniae strain B9 to 2 μg/mL at concentrations as low as 0.625, 2.5, and 1.25 μM, respectively. Restored sensitivity to colistin with these compounds does not appear to coincide with known mechanisms of colistin resistance.

Augmenting the Activity of Macrolide Adjuvants against Acinetobacter baumannii

Approximately 1.7 million Americans develop hospital associated infections each year, resulting in more than 98,000 deaths. One of the main contributors to such infections is the Gram-negative pathogen Acinetobacter baumannii. Recently, it was reported that aryl 2-aminoimidazole (2-AI) compounds potentiate macrolide antibiotics against a highly virulent strain of A. baumannii, AB5075. The two lead compounds in that report increased clarithromycin (CLR) potency against AB5075 by 16-fold, lowering the minimum inhibitory concentration (MIC) from 32 to 2 μg/mL at a concentration of 10 μM. Herein, we report a structure-activity relationship study of a panel of derivatives structurally inspired by the previously reported aryl 2-AI leads. Substitutions around the core phenyl ring yielded a lead that potentiates clarithromycin by 64- and 32-fold against AB5075 at 10 and 7.5 μM, exceeding the dose response of the original lead. Additional probing of the amide linker led to the discovery of two urea containing adjuvants that suppressed clarithromycin resistance in AB5075 by 64- and 128-fold at 7.5 μM. Finally, the originally reported adjuvant was tested for its ability to suppress the evolution of resistance to clarithromycin over the course of nine consecutive days. At 30 μM, the parent compound reduced the CLR MIC from 512 to 2 μg/mL, demonstrating that the original lead remained active against a more CLR resistant strain of AB5075.

Assessing Travel Conditions: Environmental and Host Influences On Bacterial Surface Motility

The degree to which surface motile bacteria explore their surroundings is influenced by aspects of their local environment. Accordingly, regulation of surface motility is controlled by numerous chemical, physical, and biological stimuli. Discernment of such regulation due to these multiple cues is a formidable challenge. Additionally inherent ambiguity and variability from the assays used to assess surface motility can be an obstacle to clear delineation of regulated surface motility behavior. Numerous studies have reported single environmental determinants of microbial motility and lifestyle behavior but the translation of these data to understand surface motility and bacterial colonization of human host or environmental surfaces is unclear. Here, we describe the current state of the field and our understanding of exogenous factors that influence bacterial surface motility.

Early Postoperative Complications after Oncoplastic Reduction

BACKGROUND

Breast-conserving surgery with adjuvant radiation therapy (BCT) has been established as safe oncologically. Oncoplastic breast surgery uses both oncologic and plastic surgery techniques for breast conservation to improve cosmetic outcomes. We evaluated the risk factors associated with complications after oncoplastic breast reduction.

METHODS

A single-institution, institutional review board-approved, retrospective review of electronic medical records of female patients with breast cancer who underwent oncoplastic breast reduction from 2008 to 2014. A review of electronic medical records collected relevant medical history, clinical and pathological information, and data on postoperative complications within 6 months stratified into major or minor complications. Categorical variables analyzed with the χ² exact method; continuous variables were analyzed with the Wilcoxon rank sum test exact method.

RESULTS

We identified 59 patients; 4 required re-excision for positive margins, and 1 moved on to completion mastectomy. The overall complication rate was 33.9% (n = 20): 12 major (20.3%) and 8 minor (13.6%). Of the continuous variables (age, body mass index, and tissue removed), increased age was associated with minor complications (P = 0.02). Among the categorical variables (stratified body mass index, prior breast surgery, hypertension, diabetes mellitus, hyperlipidemia, vascular disease, pulmonary disease, and stratified weight of tissue removed), none were associated with overall or major complications. Pulmonary disease was associated with minor complications (P = 0.03). Bilateral versus unilateral oncoplastic breast reduction showed no statistically significant increase in complications.

CONCLUSIONS

The overall complication rate after oncoplastic breast reduction was markedly higher than that in nationally published data for breast-conserving surgery. The complication rate resembled more closely the complication rate after bilateral mastectomy with immediate reconstruction. No risk factors were associated with major or overall complications. Age and pulmonary disease were associated with minor complications. Patients should be selected and counseled appropriately when considering oncoplastic breast reduction.

Clinical Considerations of Risk, Incidence, and Outcomes of Breast Cancer in Sexual Minorities

BACKGROUND

Breast cancer is a leading cause of cancer-related mortality in women. Limited research exists on the impact of sexual orientation on overall risk of and mortality from breast cancer. We sought to summarize the medical literature on breast cancer in sexual minority women and identify possible disparities in this population.

METHODS

A comprehensive literature search was conducted for English-language studies in peer-reviewed medical journals that referenced breast cancer and sexual minority, lesbian, bisexual, or transgender individuals. Articles published between January 2000 and November 2015 were included. They were reviewed for relevance to breast cancer risk stratification, breast cancer mortality, breast reconstruction, and transgender issues.

RESULTS

Behavioral risks, reproductive risks, and risks associated with decreased access to health care may all affect outcomes for sexual minorities with breast cancer. Limited studies have mixed results regarding mortality associated with breast cancer in sexual minorities due to an inconsistent reporting of sexual orientation.

CONCLUSIONS

Overall, the research examining breast cancer in sexual minority women remains limited. This finding is likely due to limitations in the reporting of sexual orientation within large databases, thus making broader-scale research difficult.

Magnetic Resonance Imaging for Axillary Breast Cancer Metastasis in the Neoadjuvant Setting: A Prospective Study

BACKGROUND

Breast magnetic resonance imaging (MRI) for assessment of regional breast cancer metastasis is controversial owing to the variable specificity. We evaluated breast MRI for axillary metastasis in neoadjuvant chemotherapy patients.

MATERIALS AND METHODS

A single-institution, institutional review board-approved prospective trial enrolled female breast cancer patients receiving neoadjuvant chemotherapy from 2008 to 2012 and collected the pre- and post-treatment MRI, pretreatment axillary ultrasound, axillary biopsy, and surgical pathologic findings. The kappa coefficient was used to evaluate the strength of the agreement between the 2 modalities and Fisher's exact test was used to evaluate the association.

RESULTS

A total of 43 patients were included. Of these 45 patients, 35 had stage N1-N2 before treatment. Comparing the abnormal results on the pretreatment MRI scans and axillary biopsy examinations, a consistent diagnosis was found for 92%, with a moderate strength of agreement (kappa coefficient, 0.54). The pretreatment MRI findings were significantly associated with the axillary biopsy results (P = .014). The false-positive rate, false-negative rate, sensitivity, and specificity were 50%, 3%, 97%, 50%, respectively. Comparing the post-treatment MRI and surgical pathologic findings revealed a consistent diagnosis rate of, with a slight strength of agreement (kappa, 0.16). The false-positive rate, false-negative rate, sensitivity, and specificity were 38%, 46%, 55%, and 63%, respectively. The post-treatment MRI findings were not associated with the pathologic lymph node results (P = .342).

CONCLUSION

Pretreatment breast MRI was more specific for axillary metastasis than was axillary ultrasonography. However, post-treatment breast MRI was not predictive of residual axillary disease and should be used cautiously when altering treatment plans.

Preparation, imaging, and quantification of bacterial surface motility assays

Bacterial surface motility, such as swarming, is commonly examined in the laboratory using plate assays that necessitate specific concentrations of agar and sometimes inclusion of specific nutrients in the growth medium. The preparation of such explicit media and surface growth conditions serves to provide the favorable conditions that allow not just bacterial growth but coordinated motility of bacteria over these surfaces within thin liquid films. Reproducibility of swarm plate and other surface motility plate assays can be a major challenge. Especially for more “temperate swarmers” that exhibit motility only within agar ranges of 0.4%-0.8% (wt/vol), minor changes in protocol or laboratory environment can greatly influence swarm assay results. “Wettability”, or water content at the liquid-solid-air interface of these plate assays, is often a key variable to be controlled. An additional challenge in assessing swarming is how to quantify observed differences between any two (or more) experiments. Here we detail a versatile two-phase protocol to prepare and image swarm assays. We include guidelines to circumvent the challenges commonly associated with swarm assay media preparation and quantification of data from these assays. We specifically demonstrate our method using bacteria that express fluorescent or bioluminescent genetic reporters like green fluorescent protein (GFP), luciferase (lux operon), or cellular stains to enable time-lapse optical imaging. We further demonstrate the ability of our method to track competing swarming species in the same experiment.

Ionotropic glutamate receptors in the ventral tegmental area regulate cocaine-seeking behavior in rats

Drug addiction is characterized by compulsive drug-seeking and drug-taking behavior and by a high rate of relapse even after long periods of abstinence. Although the mesocorticolimbic dopamine (DA) pathway is thought to play a critical role in drug craving and relapse, recent evidence also implicates glutamate, an amino acid known to activate DA neurons in the ventral tegmental area (VTA) via ionotropic receptors. To assess whether increased glutamate transmission in the VTA is involved in cocaine-primed drug-seeking behavior, we tested rats in a between-session reinstatement model. They were trained to press a lever for cocaine infusions (0.25 mg/infusion) accompanied by compound stimuli (light and tone) under a modified fixed-ratio 5 reinforcement schedule. Cocaine-primed reinstatement was conducted after lever pressing was extinguished in the absence of the conditioned stimuli. Blockade of ionotropic glutamate receptors in the VTA by local application of kynurenate (0.0, 1.0, 3.2, and 5.6 microg/side) dose-dependently decreased cocaine-primed reinstatement, whereas sucrose-primed reinstatement of sucrose-seeking behavior was unaffected. In addition, the minimum effective dose for decreasing cocaine-primed reinstatement was ineffective in the substantia nigra. Together, these data indicate that glutamatergic activation of the VTA is critical for cocaine-primed reinstatement. Because such activation can increase impulse flow in DA neurons and thus DA release in mesocorticolimbic targets, this glutamate-DA interaction in the VTA may underlie cocaine-primed relapse to cocaine-seeking behavior.