This study was a phase 1, single-center, randomized, double-blind, placebo-controlled, single-dosing, and dose-escalating study of intravenous SAL200. It is a new candidate drug for the treatment of antibiotic-resistant staphylococcal infections based on a recombinant form of the phage endolysin SAL-1. The study evaluated the pharmacokinetics, pharmacodynamics, and tolerance among healthy male volunteers after the intravenous infusion of single ascending doses of SAL200 (0.1, 0.3, 1, 3, and 10 mg/kg of body weight). SAL200 was well tolerated, and no serious adverse events (AEs) were observed in this clinical study. Most AEs were mild, self-limiting, and transient. The AEs reported in more than three participants were fatigue, rigors, headache, and myalgia. No clinically significant values with respect to the findings of clinical chemistry, hematology, and coagulation analyses, urinalysis, vital signs, and physical examinations were observed, and no notable trends in our electrocardiogram (ECG) results for any tested dose were noticed. A greater-than-dose-proportional increase with regard to systemic exposure and the maximum serum concentration was observed when the SAL200 dose was increased from 0.1 mg/kg to 10 mg/kg. This investigation constitutes the first-in-human phase 1 study of an intravenously administered, phage endolysin-based drug. (This study has been registered at ClinicalTrials.gov under identifier NCT01855048 and at the Clinical Research Information Service [https://cris.nih.go.kr/cris/] under identifier KCT0000968.).

Antibacterial and biofilm removal activity of a new podoviridae Staphylococcus aureus bacteriophage (SAP-2), which belongs to the phi29-like phage genus of the Podoviridae family, and a cell-wall-degrading enzyme (SAL-2), which is derived from bacteriophage SAP-2, have been characterized. The cell-wall-degrading enzyme SAL-2 was expressed in Escherichia coli in a soluble form using a low-temperature culture. The cell-wall-degrading enzyme SAL-2 had specific lytic activity against S. aureus, including methicillin-resistant strains, and showed a minimum inhibitory concentration of about 1 microg/ml. In addition, this enzyme showed a broader spectrum of activity within the Staphylococcus genus compared with bacteriophage SAP-2 in its ability to remove the S. aureus biofilms. Thus, the cell-wall-degrading enzyme SAL-2 can be used to prevent and treat biofilm-associated S. aureus infections either on its own or in combination with other cell-wall-degrading enzymes with anti-S. aureus activity.

dPhage endolysins have received increasing attention as potent antibacterial agents. However, although safety evaluation is a prerequisite for the drug development process, a good laboratory practice (GLP)-compliant safety evaluation has not been reported for phage endolysins. A safety evaluation of intravenously administered SAL200 (containing phage endolysin SAL-1) was conducted according to GLP standards. No animals died in any of the safety evaluation studies. In general toxicity studies, intravenously administered SAL200 showed no sign of toxicity in rodent single-and repeated-dose toxicity studies. In the dog repeateddose toxicity test, there were no abnormal findings, with the exception of transient abnormal clinical signs that were observed in some dogs when daily injection of SAL200 was continued for more than 1 week. In safety pharmacology studies, there were also no signs of toxicity in the central nervous and respiratory system function tests. In the cardiovascular function test, there were no abnormal findings in all tested dogs after the first and second administrations, but transient abnormalities were observed after the third and fourth administrations (2 or 3 weeks after the initial administration). All abnormal findings observed in these safety evaluation studies were slight to mild, were apparent only transiently after injection, and resolved quickly. The safety evaluation results for SAL200 support the implementation of an exploratory phase I clinical trial and underscore the potential of SAL200 as a new drug. We have designed an appropriate phase I clinical trial based on the results of this study.

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In spite of the high degree of amino acid sequence similarity between the newly discovered phage endolysin SAL-1 and the phage endolysin LysK, SAL-1 has an approximately 2-fold-lower MIC against several Staphylococcus aureus strains and higher bacterial cell-wall-hydrolyzing activity than LysK. The amino acid residue change contributing the most to this enhanced enzymatic activity is a change from glutamic acid to glutamine at the 114th residue.Staphylococcus aureus is a highly virulent human pathogen, and S. aureus infections are a significant cause of morbidity and mortality, particularly in settings such as hospitals, nursing homes, and infirmaries (24). In addition to the more severe consequences of contact with S. aureus, this pathogen is also responsible for many cases of food poisoning (14). Many recent isolates of S. aureus show innate resistance to currently available antibiotics (18), leading to challenges in managing S. aureus infections.Since the discovery of bacteriophages, their destructive effect on their host organisms has been exploited as a way of treating infectious bacteria (10). In addition, phage endolysins, also termed lysins, have been proposed as potent antibacterial agents (15,17). Phage endolysins derived from bacteriophages are bacteriophage-encoded peptidoglycan hydrolases that have evolved to rapidly break down the bacterial cell wall, thereby allowing the release of phage progeny (30). Many phage endolysins have shown promise in preclinical trials involving animal models of human diseases (3,5,7,16,20,27), and they thus constitute a promising route for the discovery and development of novel antibacterial therapeutic agents.The phage endolysin LysK from staphylococcal phage K (22) is a valuable endolysin due to its broad-spectrum activity against the staphylococcal genus (23). A large number of articles have been published about this phage endolysin (2, 6, 11) due to its potency and promise as an antibacterial agent.The present study was prompted by the serendipitous observation that phage endolysin SAL-1, derived from the bacteriophage SAP-1 recently isolated in our laboratory, had a significantly lower MIC than phage endolysin LysK in spite of the high level of amino acid sequence similarity between the two proteins. Based on sequencing studies, we determined that phage endolysin SAL-1 only differs from LysK at three residues: isoleucine instead of valine at the 26th residue, glutamine instead of glutamic acid at the 114th residue, and histidine instead of glutamine at the 486th residue.This article describes a comparative study of the newly discovered phage endolysin SAL-1 and the well-studied phage endolysin LysK.An S. aureus bacteriophage was isolated from an environmental sample by a conventional method (29) and designated bacteriophage SAP-1. The gene encoding the endolysin of bacteriophage SAP-1 was identified by comparison with reported sequences and subcloned into the pBAD-TOPO vector (Invitrogen, Carlsbad, CA) by conventional PCR cloning methods. Escherichia coli TOP10 (I...