lysocin-e and Staphylococcal-Infections

In this symposium, we reported the identification and mechanistic analysis of a novel antibiotic named lysocin E. Lysocin E was identified by screening for therapeutic effectiveness in a silkworm Staphylococcus aureus infection model. The advantages of the silkworm infection model for screening and purification of antibiotics from the culture supernatant of soil bacteria are: 1) low cost; 2) no ethical issues; 3) convenient for evaluation of the therapeutic effectiveness of antibiotics; and 4) pharmacokinetics similar to those of mammals. Lysocin E has remarkable features compared with known antibiotics such as a novel mechanism of action and target. Here, we summarize our reports presented in this symposium.

Topics: Animals; Anti-Bacterial Agents; Bombyx; Disease Models, Animal; Drug Evaluation, Preclinical; Peptides, Cyclic; Staphylococcal Infections

Development of novel medicines is an important responsibility of researchers in the field of pharmaceutical sciences. However, the discovery of new therapeutically effective without side effects is not an easy job. I think the limiting step of drug discovery is the process of evaluating the therapeutic effects of candidate drugs. To overcome this problem, I would like to propose a novel approach, "drug discovery with silkworms".

Topics: Animals; Anti-Bacterial Agents; Bombyx; Diabetes Mellitus; Disease Models, Animal; Drug Discovery; Humans; Methicillin-Resistant Staphylococcus aureus; Mice; Models, Animal; Peptides, Cyclic; Pharmacokinetics; Staphylococcal Infections; Virulence

Lysocin E is a lipopeptide with antibiotic activity against methicillin-resistant Staphylococcus aureus. For unclear reasons, the antibacterial activity of lysocin E in a mouse systemic infection model is higher than expected from in vitro results, and the in vitro activity is enhanced by addition of bovine serum. Here, we confirm that serum from various species, including humans, increases lysocin E antimicrobial activity, and identify apolipoprotein A-I (ApoA-I) as an enhancing factor. ApoA-I increases the antibacterial activity of lysocin E when added in vitro, and the antibiotic displays reduced activity in ApoA-I gene knockout mice. Binding of ApoA-I to lysocin E is enhanced by lipid II, a cell-wall synthesis precursor found in the bacterial membrane. Thus, the antimicrobial activity of lysocin E is potentiated through interactions with host serum proteins and microbial components.

Topics: Animals; Anti-Bacterial Agents; Apolipoprotein A-I; Disease Models, Animal; Female; Lipopeptides; Methicillin-Resistant Staphylococcus aureus; Mice; Mice, Inbred C57BL; Mice, Inbred ICR; Microbial Sensitivity Tests; Peptides, Cyclic; Staphylococcal Infections

Lysocin E, a 37-membered natural depsipeptide, induces rapid bacteriolysis in methicillin-resistant Staphylococcus aureus via a unique menaquinone-dependent mechanism, presenting a promising therapeutic lead. Despite the great medical importance, exploring the potential utility of its derivatives as new platform structures for antibiotic development has remained a significant challenge. Here, we report a high-throughput strategy that enabled the preparation of thousands of analogues of lysocin E and large-scale structure-activity relationship analyses. We integrate 26-step total synthesis of 2401 cyclic peptides, tandem mass spectrometry-sequencing, and two microscale activity assays to identify 23 candidate compounds. Re-synthesis of these candidates shows that 11 of them (A1-A11) exhibit antimicrobial activity superior or comparable to that of lysocin E, and that lysocin E and A1-A11 share L-Leu-6 and L-Ile-11. Therefore, the present strategy allows us to efficiently decipher biologically crucial residues and identify potentially useful agents for the treatment of infectious diseases.

Topics: Anti-Bacterial Agents; Chemistry, Pharmaceutical; Drug Discovery; High-Throughput Screening Assays; Methicillin-Resistant Staphylococcus aureus; Microbial Sensitivity Tests; Molecular Structure; Peptides, Cyclic; Staphylococcal Infections; Structure-Activity Relationship; Tandem Mass Spectrometry

To obtain therapeutically effective new antibiotics, we first searched for bacterial culture supernatants with antimicrobial activity in vitro and then performed a secondary screening using the silkworm infection model. Through further purification of the in vivo activity, we obtained a compound with a previously uncharacterized structure and named it 'lysocin E'. Lysocin E interacted with menaquinone in the bacterial membrane to achieve its potent bactericidal activity, a mode of action distinct from that of any other known antibiotic, indicating that lysocin E comprises a new class of antibiotic. This is to our knowledge the first report of a direct interaction between a small chemical compound and menaquinone that leads to bacterial killing. Furthermore, lysocin E decreased the mortality of infected mice. To our knowledge, lysocin E is the first compound identified and purified by quantitative measurement of therapeutic effects in an invertebrate infection model that exhibits robust in vivo effects in mammals.

Topics: Animals; Anti-Bacterial Agents; Bacterial Proteins; Bacteriolysis; Bombyx; Cell Membrane; Disease Models, Animal; Drug Discovery; Gram-Positive Bacteria; Lysobacter; Membrane Potentials; Mice; Mice, Inbred ICR; Microbial Sensitivity Tests; Molecular Structure; Peptides, Cyclic; Staphylococcal Infections; Staphylococcus aureus; Vitamin K 2