Evaluating the Killing Dynamics of Polymyxin B and Meropenem as Monotherapy and Combination Therapy Against Hypermutable Pseudomonas aeruginosa

Conserving the activity of the remaining viable last line antibiotic agents for the treatment of highly resistant Pseudomonas aeruginosa (PSA) is a critical challenge and data regarding treatment that is effective against hypermutant PSA is limited. To help overcome this challenge, the objective of this study is to perform phenotypic characterization of 33 PSA clinical isolates from cystic fibrosis (CF) patients, and evaluate the killing dynamics of monotherapy and combination therapy against hypermutable PSA. Phenotypic characterization was performed to detect hypermutators and bacterial susceptibilities for colistin (COL), polymyxin B (PMB), and meropenem (MEM) were evaluated. Static time–kill experiments were performed to determine the rate and extent of bacterial killing using PMB and MEM as monotherapy and combination therapy against hypermutatant and non-hypermutatant strains, PSA 203 and PSA 205, respectively. 6 out of the 33 (18%) PSA clinical isolates obtained from CF patients were determined to be hypermutators. Time-kill results demonstrated poor sustained killing of PMB monotherapy for both isolates. MEM 10 mg/L and MEM 40 mg/L concentrations in combination with PMB 0.5 mg/L and 1 mg/L resulted in regrowth at 8 h for both PSA 203 and PSA 205 isolates, while combination of PMB 2 mg/L and 4 mg/L resulted in sustained bactericidal killing. PMB based combination therapy resulted in superior pharmacodynamic activity compared to monotherapy with either drug, which is consistent with previous in vitro studies that have evaluated polymyxins in combination with carbapenems against highly resistant Gram-negative bacteria in non-CF patients.Doctor of Pharmac

Structural determinants of 5-HT2B receptor activation and biased agonism

Serotonin (5-hydroxytryptamine; 5-HT) receptors modulate a variety of physiological processes ranging from perception, cognition and emotion to vascular and smooth muscle contraction, platelet aggregation, gastrointestinal function and reproduction. Drugs that interact with 5-HT receptors effectively treat diseases as diverse as migraine headaches, depression and obesity. Here we present four structures of a prototypical serotonin receptor—the human 5-HT2B receptor—in complex with chemically and pharmacologically diverse drugs, including methysergide, methylergonovine, lisuride and LY266097. A detailed analysis of these structures complemented by comprehensive interrogation of signaling illuminated key structural determinants essential for activation. Additional structure-guided mutagenesis experiments revealed binding pocket residues that were essential for agonist-mediated biased signaling and β-arrestin2 translocation. Given the importance of 5-HT receptors for a large number of therapeutic indications, insights derived from these studies should accelerate the design of safer and more effective medications. © 2018, The Author(s)