Discovery of GuaB inhibitors with efficacy against Acinetobacter baumannii infection.

Guanine nucleotides are required for growth and viability of cells due to their structural role in DNA and RNA, and their regulatory roles in translation, signal transduction, and cell division. The natural antibiotic mycophenolic acid (MPA) targets the rate-limiting step in de novo guanine nucleotide biosynthesis executed by inosine-5´-monophosphate dehydrogenase (IMPDH). MPA is used clinically as an immunosuppressant, but whether in vivo inhibition of bacterial IMPDH (GuaB) is a valid antibacterial strategy is controversial. Here, we describe the discovery of extremely potent small molecule GuaB inhibitors (GuaBi) specific to pathogenic bacteria with a low frequency of on-target spontaneous resistance and bactericidal efficacy in vivo against Acinetobacter baumannii mouse models of infection. The spectrum of GuaBi activity includes multidrug-resistant pathogens that are a critical priority of new antibiotic development. Co-crystal structures of A. baumannii, Staphylococcus aureus, and Escherichia coli GuaB proteins bound to inhibitors show comparable binding modes of GuaBi across species and identifies key binding site residues that are predictive of whole-cell activity across both Gram-positive and Gram-negative clades of Bacteria. The clear in vivo efficacy of these small molecule GuaB inhibitors in a model of A. baumannii infection validates GuaB as an essential antibiotic target. IMPORTANCE: The emergence of multidrug-resistant bacteria worldwide has renewed interest in discovering antibiotics with novel mechanism of action. For the first time ever, we demonstrate that pharmacological inhibition of de novo guanine biosynthesis is bactericidal in a mouse model of Acinetobacter baumannii infection. Structural analyses of novel inhibitors explain differences in biochemical and whole-cell activity across bacterial clades and underscore why this discovery may have broad translational impact on treatment of the most recalcitrant bacterial infections.

CHIP: a clonal odyssey of the bone marrow niche.

Clonal hematopoiesis of indeterminate potential (CHIP) is characterized by the selective expansion of hematopoietic stem and progenitor cells (HSPCs) carrying somatic mutations. While CHIP is typically asymptomatic, it has garnered substantial attention due to its association with the pathogenesis of multiple disease conditions, including cardiovascular disease (CVD) and hematological malignancies. In this Review, we will discuss seminal and recent studies that have advanced our understanding of mechanisms that drive selection for mutant HSPCs in the BM niche. Next, we will address recent studies evaluating potential relationships between the clonal dynamics of CHIP and hematopoietic development across the lifespan. Next, we will examine the roles of systemic factors that can influence hematopoietic stem cell (HSC) fitness, including inflammation, and exposures to cytotoxic agents in driving selection for CHIP clones. Furthermore, we will consider how - through their impact on the BM niche - lifestyle factors, including diet, exercise, and psychosocial stressors, might contribute to the process of somatic evolution in the BM that culminates in CHIP. Finally, we will review the role of old age as a major driver of selection in CHIP.

Measurements of Ion Binding to Lipid-Hosted Ionophores by Affinity Chromatography.

The binding affinity between antibiotic ionophores and alkali ions within supported lipid bilayers was evaluated using affinity chromatography. We used zonal elution and frontal analysis methods in nanovolume liquid chromatography to characterize the binding selectivity of the carrier and channel ionophores valinomycin and gramicidin A within different phosphatidylcholine bilayers. Distinct binding sensitivity to the lipid phase, both in affinity and selectivity, is observed for valinomycin, whereas gramicidin is less sensitive to changes in a membrane environment, behavior that is consistent with ion binding occurring within the interior of an established channel. There is good agreement between the chromatographic retention and the reported binding selectivity measured by other techniques. Surface potential near the binding site affects ion retention and the apparent association binding constants, but not the binding selectivity or enthalpy measurements. A model accounting for the surface potential contributions of retained ions during frontal analyses yields values close to intrinsic binding constants for gramicidin A (KA for K+ between 70 and 120 M-1) using reasonable estimates of the initial potential that is postulated to arise from the underlying silica.