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.).

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...

SAL200 is a new phage endolysin-based candidate drug for the treatment of staphylococcal infections. An intravenous administration study was conducted in monkeys to obtain pharmacokinetic information on SAL200 and to assess the safety of a short SAL200 dosing period (<1 week). Maximum serum drug concentrations and systemic SAL200 exposure were proportional to the dose and comparable in male and female monkeys. SAL200 was well tolerated, and no adverse events or laboratory abnormalities were detected after injection of a single dose of up to 80 mg/kg per day, or injection of multiple doses of up to 40 mg/kg per day.

The recombinant phage endolysins AP50-31 and LysB4 were developed using genetic information from bacteriophages AP50 and B4 and were produced by microbial cultivation followed by chromatographic purification. Subsequently, appropriate formulations were developed that provided an acceptable stability of the recombinant endolysins. The bacteriolytic properties of the formulated endolysins AP50-31 and LysB4 against several bacterial strains belonging to the Bacillus genus including Bacillus anthracis (anthrax) strains were examined. AP50-31 and LysB4 displayed rapid bacteriolytic activity and broad bacteriolytic spectra within the Bacillus genus, including bacteriolytic activity against all the B. anthracis strains tested. When administered intranasally, LysB4 completely protected A/J mice from lethality after infection with the spores of B. anthracis Sterne. When examined at 3 days post-infection, bacterial counts in the major organs (lung, liver, kidney, and spleen) were significantly lower compared with those of the control group that was not treated with endolysin. In addition, histopathological examinations revealed a marked improvement of pathological features in the LysB4-treated group. The results of this study support the idea that phage endolysins are promising candidates for developing therapeutics against anthrax infection.

High‐dose radiation‐induced tissue damage is a major limiting factor in the medical application of nuclear technology. Herein, we tested 28‐day repeated‐dose toxicity of KMRC011, an agonist of toll‐like receptor (TLR) 5, which is being developed as a medical countermeasure for radiation, using cynomolgus monkeys. KMRC011 (0.01, 0.02 or 0.04 mg/kg/day) was intramuscularly injected once daily for 4 weeks, and each two monkeys in both control and 0.04 mg/kg/day group were observed for an additional 2‐week recovery period. There were no dose‐related toxicological changes in mortality, clinical observations, body weight, food consumption, ophthalmological findings, electrocardiographs, coagulation, serum chemistry, organ weights, or urinalysis and urine chemistry. Although treatment‐related changes, such as increased white blood cells, increased absolute and relative neutrophils, decreased relative lymphocytes and inflammatory lesions, were noted in the maximum dose group, these findings were not observed after the 2‐week recovery period. Further, we considered that the kidneys and heart may be target organs of TLR5 agonists, as well as the spleen, and that autophagic signals can be triggered in tissue damage and the repair process. Importantly, accumulation of p62 protein, an indicator of autophagy, and a decrease of caveolin‐1 protein, a regulator of TLR5 protein half‐life, were found in both tissues from the highest dose group. Therefore, we conclude that the no‐observed‐adverse‐effect level for KMRC011 may be greater than 0.04 mg/kg/day in male and female monkeys. Additionally, we propose that further studies are needed to identify the molecular signals, which are related to KMRC011‐induced adverse effects.