Antibiotic discovery in the twenty-first century: current trends and future perspectives

Materials from peptide assembly: towards the treatment of cancer and transmittable disease

As the prevalence of cancer and transmittable disease persists, the development of new and more advanced therapies remains a priority in medical research. An emerging platform for the treatment of these illnesses is the use of materials formed via peptide assembly where the bulk material itself acts as the therapeutic. Higher ordered peptide structures with defined chemistry are capable of cellular targeting, recognition, and internalization. Recent design efforts are being made to exploit the nanoscale definition of the materials formed by assembling peptides to target cancer and microbial cells and to function as vaccines. This review focuses on assembled peptide materials that actively participate in the biological processes important to cancer and transmittable diseases to exert an anticipated functional outcome.

High-throughput profiling of microbial extracts

Microbial culture extracts are used for natural products screening in the drug lead discovery process. An extract of a microbial culture is a complex mixture of organic compounds, making it difficult to evaluate the diversity and redundancy of the compounds. However, having a diverse extract library is a key to success in generating a lead for drug discovery. We have developed a high-throughput and robust LC-MS analysis and data processing method for visualizing sample profile and diversity. In the LC-MS analysis of 16 025 microbial culture extracts, positive and negative ions were acquired simultaneously with an electrospray ionization source. The raw data were processed using ACD IntelliXtract, and peak lists of each extract were generated and stored in the database. The peak list data were binned by nominal mass (m/z 150-1350) and retention time. How frequently the binned peaks, termed peak identifiers, appeared in the extracts library was calculated, and these data were visualized by scattered plots in Spotfire. From 4 to 115 peaks were observed in each sample. As it is easy to eliminate the ubiquitous peaks shown in most samples and simplify the plots, the unique or redundant compounds could be detected.

Synthesis, SAR and antibacterial activity of hybrid chloro, dichloro-phenylthiazolyl-s-triazines

A series of hybrid novel chloro (1a-9a) and dichloro (10b-18b) phenylthiazolyl-s-triazine were synthesized and subsequently subjected to their antibacterial activity against three gram positive viz. Lactobacillus casei (NCIM-2651); Bacillus cereus (NCIM-2458); Staphylococcus aureus (NCIM-2120) and three gram negative viz Salmonella typhimurium (NCIM-2501); Escherichia coli (NCIM-2065); Klebsiella aerogenes (NCIM-2098). The SAR studies around the lead compound revealed that introduction of electron withdrawing groups and amino (-NH-) and mercapto (-S-) linker bridge seemed more promising towards antibacterial activity. Moreover, the virtual Molinspiration screenings are in compliance with Ghose's rule.

Efficacy of the new lantibiotic NAI-107 in experimental infections induced by multidrug-resistant Gram-positive pathogens

NAI-107 is a novel lantibiotic active against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), glycopeptide-intermediate S. aureus (GISA), and vancomycin-resistant enterococci (VRE). The aim of this study was to evaluate the in vivo efficacy of NAI-107 in animal models of severe infection. In acute lethal infections induced with a penicillin-intermediate Streptococcus pneumoniae strain in immunocompetent mice, or with MRSA, GISA, and VRE strains in neutropenic mice, the 50% effective dose (ED(50)) values of NAI-107 were comparable or lower than those of reference compounds, irrespective of the strain and immune status (0.51 to 14.2 mg/kg of body weight for intravenous [i.v.] NAI-107, 5.1 to 22.4 for oral linezolid, and 22.4 for subcutaneous [s.c.] vancomycin). In the granuloma pouch model induced in rats with a MRSA strain, intravenous NAI-107 showed a dose-proportional bactericidal activity that, at a single 40-mg/kg dose, compared with 2 20-mg/kg doses at a 12-h or 24-h interval, caused a 3-log(10)-CFU/ml reduction of viable MRSA in exudates that persisted for more than 72 h. Rat endocarditis was induced with a MRSA strain and treated for five consecutive days. In a first experiment, using 5, 10, or 20 mg/kg/day, and in a second experiment, when 10 mg/kg at 12-h intervals was compared to 20 mg/kg/day, intravenous NAI-107 was effective in reducing the bacterial load in heart vegetations in a dose-proportional manner. Trough plasma levels, as determined on days 2 and 5, were several times higher than the NAI-107 minimal bactericidal concentration (MBC). NAI-107 binding to rat and human serum ranges between 93% and 98.6%. The rapid bactericidal activity of NAI-107 observed in vitro was thus confirmed by the efficacy in several models of experimental infection induced by Gram-positive pathogens, supporting further investigation of the compound.

How to discover new antibiotics: harvesting the parvome

There is a dire need for new antibiotics; commercial discovery programs have essentially dried up and there is talk of 'a return to the pre-antibiotic era'. Natural products are an inexhaustible source of bioactive compounds (antibiotics among them), and recent technical advances such as DNA sequencing and bioinformatics offer new approaches to small molecule discovery. Given that nucleotide sequence studies of actinomycetes genomes reveal the presence of 20 or more pathways for the synthesis of bioactive compounds, 'mining' these sequences offers the potential of expanding the repertoire of antibiotics and other drugs. Combined with advanced chemical separation and characterization techniques, the construction of large chemically diverse libraries of bioactive compounds for therapeutic applications is a realistic near-term goal.