Current Medicinal Chemistry (v.22, #14)

Meet Our Editorial Board Member by Philippe Cotelle (1639-1639).

Modern Therapeutic Approaches Against Pseudomonas aeruginosa Infections by Agata Dorotkiewicz-Jach, Daria Augustyniak, Tomasz Olszak, Zuzanna Drulis-Kawa (1642-1664).
Despite the enormous progress that has been made in the last few decades in the field of drug design as well as virulence of pathogenic bacteria, the gradual spread of drug resistance can be observed. Only two new classes of antibiotics have been brought to medicine in the last 30 years. The need for novel antibacterial drugs is especially pressing when considering infections caused by multidrug-resistant (MDR) pathogens such as Pseudomonas aeruginosa. The discovery and development of new anti-pseudomonal therapies is one of the main challenges of modern pharmaceutical sciences. The great variety of innovative approaches presented in the current literature is astonishing. In this review, modern, promising strategies against P. aeruginosa infections are described. Antimicrobials, including new antibiotics, β-lactamase and efflux pump inhibitors, quorum quenching molecules and nanoparticles with antibacterial activity are currently being intensively studied. Methods of prevention of infection through vaccines, therapeutic antibodies and development of antimicrobial peptides are discussed as approaches that support the human immunological system. Finally, development of alternative/ supportive therapies such as phage therapy and photodynamic therapy, in which the mechanism of action is completely different from current antibiotic therapy, is of great importance.

Antimicrobial Peptides as an Opportunity Against Bacterial Diseases by Stefania Galdiero, Annarita Falanga, Rita Berisio, Paolo Grieco, Giancarlo Morelli, Massimiliano Galdiero (1665-1677).
Antimicrobial peptides (AMPs) are an heterogeneous group of small amino acidic molecules produced by the innate immune system of a variety of organisms encompassing all orders of life from eukaryotes to amphibians, insects and plants. Numerous AMPs have been isolated from natural sources and many others have been de novo designed and synthetically produced. AMPs have antimicrobial activity in the micromolar range and compared with traditional antibiotics, they kill bacteria very rapidly. They act, principally, by the electrostatic attraction to negatively charged bacterial cells and consequently membrane disruption, but their antibacterial activity may also involve interference with metabolic processes or different cytoplasmic targets. AMPs are a group of unique and incredible compounds that may be directed to a therapeutic use either alone or in combination with existing antibiotics.

The ability to resist the effect of a wide range of antibiotics makes methicillin-resistant Staphylococcus aureus (MRSA) a leading global human pathogen. A key determinant of resistance to β-lactam antibiotics in this organism is penicillin-binding protein 2a (PBP2a), an enzyme that catalyzes the crosslinking reaction between two adjacent peptide stems during the peptidoglycan biosynthesis. The recently published crystal structure of the complex of PBP2a with ceftaroline, a cephalosporin antibiotic that shows efficacy against MRSA, has revealed the allosteric site at 60-Å distance from the transpeptidase domain. Binding of ceftaroline to the allosteric site of PBP2a triggers conformational changes that lead to the opening of the active site from a closed conformation, where a second molecule of ceftaroline binds to give inhibition of the enzyme. The discovery of allostery in MRSA remains the only known example of such regulation of cellwall biosynthesis and represents a new paradigm in fighting MRSA. This review summarizes the present knowledge of the allosteric mechanism, the conformational changes allowing PBP2a catalysis and the means by which some clinical strains have acquired resistance to ceftaroline by disrupting the allosteric mechanism.

Structure and Function of Prokaryotic UDP-Glucose Pyrophosphorylase, A Drug Target Candidate by M. Alvaro Berbis, Jose Maria Sanchez-Puelles, F. Javier Canada, Jesus Jimenez-Barbero (1687-1697).
UDP-glucose is an essential metabolite for a variety of processes in the cell physiology in all organisms. In prokaryotes, it is involved in the synthesis of trehalose, an osmoprotectant, in galactose utilization via the Leloir pathway and it plays a key role in the synthesis of the components of the bacterial envelope, particularly the lipopolysaccharide and the capsule, which represent necessary virulence factors of many bacterial pathogens. UDP-glucose is synthesized in bacteria by the prokaryotic UDP-glucose pyrophosphorylase (UGP, EC 2.7.7.9), an enzyme belonging to the family of sugar:nucleotidyl transferases. Despite the ubiquitous distribution of UGP activity in all domains of life, prokaryotic UGPs are evolutionarily unrelated to their eukaryotic counterparts. Taken together, these features make of bacterial UGP an attractive target candidate for the discovery and development of new generation antibiotics. This review summarizes the current knowledge on structure and function of bacterial UGPs, underlying their potential as drug target candidates.

Exit from Mycobacterial Dormancy: A Structural Perspective by Flavia Squeglia, Alessia Ruggiero, Rita Berisio (1698-1709).
Dormancy in mycobacteria is defined as a stable but reversible non-replicating state in response to stresses. In Mycobacterium tuberculosis, an important human pathogen, this state is responsible for latent Tuberculosis. The current chemotherapy to defeat Tuberculosis while effective in killing growing tubercle bacilli is largely ineffective in killing dormant bacilli. For this reason there is a recent interest to develop new drugs against this disease in the latent form. To this aim, the knowledge of the molecular basis of bacterial resuscitation from dormancy is necessary and of paramount importance. This review summarizes the current knowledge on the complex mechanism of exit from mycobacterial dormancy; the main molecular players responsible for mycobacterial resuscitation from dormancy are described and their role is discussed from a structural perspective.

Fourier Transform Infrared Spectroscopy (FTIR) as a Tool for the Identification and Differentiation of Pathogenic Bacteria by Paulina Zarnowiec, Lukasz Lechowicz, Grzegorz Czerwonka, Wiesław Kaca (1710-1718).
Methods of human bacterial pathogen identification need to be fast, reliable, inexpensive, and time efficient. These requirements may be met by vibrational spectroscopic techniques. The method that is most often used for bacterial detection and identification is Fourier transform infrared spectroscopy (FTIR). It enables biochemical scans of whole bacterial cells or parts thereof at infrared frequencies (4,000-600 cm-1). The recorded spectra must be subsequently transformed in order to minimize data variability and to amplify the chemically-based spectral differences in order to facilitate spectra interpretation and analysis. In the next step, the transformed spectra are analyzed by data reduction tools, regression techniques, and classification methods. Chemometric analysis of FTIR spectra is a basic technique for discriminating between bacteria at the genus, species, and clonal levels. Examples of bacterial pathogen identification and methods of differentiation up to the clonal level, based on infrared spectroscopy, are presented below.

The Burkholderia genus is a highly diverse group of species that are distributed throughout a wide range of environments and habitats. Among this group, which is remarkable for its adaptability to a wider range of environmental conditions including disinfectants and organic solvents, are a subgroup that represents some of the most difficult to treat infections. This subgroup includes Burkholderia pseudomallei, the causative agent of melioidosis; B. mallei, the causative agent of glanders and B. cepacia complex (Bcc) which causes opportunistic infections in people with cystic fibrosis and immunocompromised patients. The latter pathogen is itself a group of 18 distinct, but, closely related species. The adaptability of this group allows the expression of a rich selection of molecular virulence determinants to facilitate its survival in the diverse habitats that it colonises. This review will describe a selection of these associated with human infection; comparing them across the three pathogens and highlighting their potential roles as vaccine candidates. Better integration of the knowledge on the pathogenesis and molecular determinants of virulence for these Burkholderia spp may allow the development of more efficacious vaccines.

Role of the Bacterial Type VI Secretion System in the Modulation of Mammalian Host Cell Immunity by Marlies De Ceuleneer, Martine Vanhoucke, Rudi Beyaert (1734-1744).
The type VI Secretion System (T6SS) is a tool for Gram-negative pathogens to interact with other bacteria as well as with the eukaryotic host cell. While the role of T6SS in interbacterial interactions has drawn much attention in recent years, research into the T6SS as a human virulence factor continues at a slower pace. Nevertheless, T6SS has been shown to interfere with eukaryotic host cell immunity at several levels, ranging from direct attack of the host cell to attenuation of disease, allowing the pathogen to survive longer in the host environment. In this review, we aim to give a comprehensive overview focused on the ways bacteria use their T6SS in the modulation of mammalian host cell immunity. While doing so, we attempt to describe potential new avenues of research, as well as outline the ways in which T6SS could become a therapeutic target allowing to circumvent existing antibiotic resistance. Although much work remains to be done, a better comprehension of the T6SS mechanisms of action will undoubtedly lead to new strategies to counteract T6SS-bearing pathogens.

Structure and Function of RNase AS: A Novel Virulence Factor From Mycobacterium tuberculosis by Maria Romano, Flavia Squeglia, Rita Berisio (1745-1756).
The 3′-ends of both prokaryotic and eukaryotic RNA can be polyadenylated and the effect of polyadenylation is known to increase the stability of transcripts in eukaryotes, whereas it promotes instability in prokaryotes. RNAs are considered as key effectors of virulence mechanisms, since they are directly involved in regulatory pathways in pathogenic bacteria. Deadenylation of RNA is thus an important control point and rate-limiting step of its turnover. RNase AS is a novel identified protein of Mycobacterium tuberculosis, which dramatically hampers mycobacterial virulence in vivo, with a mechanism which is still to be fully defined. Phylogenetic analysis identifies orthologs of RNase AS in all mycobacteria. However, functional data only recently clarified that RNase AS is an exo-ribonuclease, which is highly specific in degrading polyadenylate sequences of RNA. This Review summarizes the current knowledge on structure and function of RNase AS and underscores its role in the process of RNA maturation. An overall description of all mycobacterial ribonucleases hitherto characterized is also provided.

Bacteriophages and Phage-Derived Proteins – Application Approaches by Zuzanna Drulis-Kawa, Grazyna Majkowska-Skrobek, Barbara Maciejewska (1757-1773).
Currently, the bacterial resistance, especially to most commonly used antibiotics has proved to be a severe therapeutic problem. Nosocomial and community-acquired infections are usually caused by multidrug resistant strains. Therefore, we are forced to develop an alternative or supportive treatment for successful cure of life-threatening infections. The idea of using natural bacterial pathogens such as bacteriophages is already well known. Many papers have been published proving the high antibacterial efficacy of lytic phages tested in animal models as well as in the clinic. Researchers have also investigated the application of non-lytic phages and temperate phages, with promising results. Moreover, the development of molecular biology and novel generation methods of sequencing has opened up new possibilities in the design of engineered phages and recombinant phage-derived proteins. Encouraging performances were noted especially for phage enzymes involved in the first step of viral infection responsible for bacterial envelope degradation, named depolymerases. There are at least five major groups of such enzymes – peptidoglycan hydrolases, endosialidases, endorhamnosidases, alginate lyases and hyaluronate lyases – that have application potential. There is also much interest in proteins encoded by lysis cassette genes (holins, endolysins, spanins) responsible for progeny release during the phage lytic cycle. In this review, we discuss several issues of phage and phage-derived protein application approaches in therapy, diagnostics and biotechnology in general.