LCB01-0371 is a new oxazolidinone with cyclic amidrazone. In vitro activity of LCB01-0371 against 624 clinical isolates was evaluated and compared with those of linezolid, vancomycin, and other antibiotics. LCB01-0371 showed good activity against Gram-positive pathogens. In vivo activity of LCB01-0371 against systemic infections in mice was also evaluated. LCB01-0371 was more active than linezolid against these systemic infections. LCB01-0371 showed bacteriostatic activity against Staphylococcus aureus.The emergence of multidrug-resistant (MDR) pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant coagulase-negative staphylococci (MRCNS), penicillin-resistant Streptococcus pneumoniae (PRSP), and vancomycinresistant enterococci (VRE), has generated worldwide concern in the medical community (11). The requirement for effective new antimicrobial agents to treat infections caused by Gram-positive organisms is becoming urgent as resistance to existing agents arises and spreads around the world.The oxazolidinones, a totally synthetic class of novel antibiotics, have strong activity against nearly all Gram-positive organisms, including those resistant to other agents (1, 10). They inhibit protein synthesis by binding to domain V of the 23S rRNA and thereby blocking formation of the initiation complex (6). Linezolid is the first member of the oxazolidinone class approved by the FDA in the United States. The success of linezolid and the occurrence of strains resistant to linezolid in clinical isolates of Enterococcus faecium (4, 5) and S. aureus (12) have inspired further efforts toward developing new oxazolidinones with improved safety and antibacterial activity.LCB01-0371 ( Fig. 1), a novel oxazolidinone with cyclic amidrazone, was synthesized by LegoChem BioSciences Inc. (Daejeon, Republic of Korea). In this study, in vitro activity of LCB01-0371 was compared with those of eight different antibacterial agents against 624 clinical isolates that were collected from several general hospitals in the Republic of Korea. In vivo activity of LCB01-0371 against systemic infections in mice and time-kill studies of LCB01-0371 against S. aureus giorgio (methicillin-susceptible S. aureus [MSSA]) and S. aureus p125 (MRSA) were also investigated.(This study was presented in part at the 49th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, CA, 2009 [7].)In vitro MICs were determined by the 2-fold agar dilution method as described by the Clinical and Laboratory Standards Institute (CLSI) (3). Mueller-Hinton agar (MHA) medium was used for testing aerobic and facultative organisms. Streptococcus pneumoniae, Streptococcus pyogenes, and Moraxella catarrhalis were grown on Mueller-Hinton agar supplemented with 5% defibrinated sheep blood (Hanil Komed Ltd., Sungnam City, Republic of Korea). Mueller-Hinton agar supplemented with 3% Fildes enrichment (Oxoid Ltd., Basingstoke, Hampshire, England) was used for Haemophilus influenzae. Bacteria (10 4 to 10 5 CFU) were s...

Mycobacterium abscessus is a highly pathogenic drug-resistant rapidly growing mycobacterium. In this study, we evaluated the in vitro, intracellular, and in vivo activities of LCB01-0371, a novel and safe oxazolidinone derivative, for the treatment of M. abscessus infection and compared its resistance to that of other oxazolidinone drugs. LCB01-0371 was effective against several M. abscessus strains in vitro and in a macrophage model of infection. In the murine model, a similar efficacy to linezolid was achieved, especially in the lungs. We induced laboratory-generated resistance to LCB01-0371; sequencing analysis revealed mutations in rplC of T424C and G419A and a nucleotide insertion at the 503 position. Furthermore, LCB01-0371 inhibited the growth of amikacin-, cefoxitin-, and clarithromycin-resistant strains. Collectively, our data indicate that LCB01-0371 might represent a promising new class of oxazolidinones with improved safety, which may replace linezolid for the treatment of M. abscessus.

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Single-molecule fluorescence resonance energy transfer (smFRET) measurement provides a unique and powerful approach to understand complex biological processes including conformational and structural dynamics of individual biomolecules. For effective smFRET analysis of protein, site-specific dual-labeling with two fluorophores as an energy donor and an acceptor is crucial. Here we demonstrate that site-specific dual-labeling of protein via incorporation of unnatural amino acid provides a clearer picture for the folded and unfolded states of the protein in smFRET analysis than conventional labeling using double cysteines. As a model study, maltose-binding protein (MBP) was dually labeled via incorporation of ρ-azido-l-phenylalanine and cysteine at specific positions, immobilized on a surface, and subjected to smFRET analysis under native and denaturing conditions. The resulting histograms show that site-specific dual-labeling results in a more homogeneous distribution in protein populations, enabling a precise smFRET analysis of protein.

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