In vitro and in vivo characterization of CB-183,315, a novel lipopeptide antibiotic for treatment of Clostridium difficile.

CB-183,315 is a novel lipopeptide antibiotic structurally related to daptomycin currently in phase 3 clinical development for Clostridium difficile-associated diarrhea (CDAD). We report here the in vitro mechanism of action, spontaneous resistance incidence, resistance by serial passage, time-kill kinetics, postantibiotic effect, and efficacy of CB-183,315 in a hamster model of lethal infection. In vitro data showed that CB-183,315 dissipated the membrane potential of Staphylococcus aureus without inducing changes in membrane permeability to small molecules. The rate of spontaneous resistance to CB-183,315 at 8× the MIC was below the limit of detection in C. difficile. Under selective pressure by serial passage with CB-183,315 against C. difficile, the susceptibility of the bacteria changed no more than 2-fold during 15 days of serial passages. At 16× the MIC, CB-183,315 produced a ≥3-log reduction of C. difficile in the time-kill assay. The postantibiotic effect of CB-183,315 at 8× the MIC was 0.9 h. At 80× the MIC the postantibiotic effect was more than 6 h. In the hamster model of CDAD, CB-183,315 and vancomycin both demonstrated potent efficacy in resolving initial disease onset, even at very low doses. After the conclusion of dosing, CB-183,315 and vancomycin showed a similar dose- and time-dependent pattern with respect to rates of CDAD recurrence.

Daptomycin antibiotic lock therapy in a rat model of staphylococcal central venous catheter biofilm infections.

Antibiotic lock therapy (ALT) is an adjunctive procedure to prevent or treat central venous catheter infections, ensuing catheter-related bacteremia, and catheter-related metastatic infections. Daptomycin is a cyclic lipopeptide that is rapidly bactericidal against methicillin-susceptible and -resistant Staphylococcus aureus. The efficacies of daptomycin against central venous catheter biofilms, catheter-related bacteremia, and catheter-related metastatic infections were evaluated by adapting a previously reported central venous catheter biofilm model in rats. Combined daptomycin ALT and systemic dosing resulted in the clearance of an established in vivo S. aureus central venous catheter biofilm after just two daily ALT treatments (30 min with daptomycin at 5 mg/ml) with concurrent systemic daptomycin dosing (40 mg/kg of body weight/day subcutaneously [s.c.]; equivalent exposure of 6 mg/kg/day in people). Daptomycin ALT solutions formulated in either saline or lactated Ringer's solution were equally fast in eradicating established in vivo methicillin-resistant Staphylococcus epidermidis (MRSE) central venous catheter biofilms. However, the lactated Ringer's formulation was superior to that of saline in sustaining the bacterial clearance of treated central venous catheters (83% versus 50%). In MRSE-infected central venous catheter studies, 3 days of daptomycin or vancomycin ALT (18 h at 5 mg/ml) with systemic s.c. dosing (40 mg/kg/day daptomycin or 100 mg/kg/day vancomycin) was equally effective 1 week posttherapy in maintaining cleared central venous catheters (90% [n = 10] versus 100% [n = 8]). These results suggest that daptomycin ALT, along with systemic dosing, could be an effective treatment option for the prevention or eradication of staphylococcal central venous catheter biofilm infections, thereby reducing the occurrence of catheter-related bacteremia or catheter-related metastatic infections.

Impact of daptomycin resistance on Staphylococcus aureus virulence.

Daptomycin resistance (DAP(R)) in Staphylococcus aureus is associated with mutations in genes that are also implicated in staphylococcal pathogenesis. Using a laboratory-derived series of DAP exposed strains, we showed a relationship between increasing DAP MIC and reduced virulence in a Galleria mellonella infection model. Point mutations in walK and rpoC led to cumulative reductions in virulence and simultaneous increases in DAP MIC. A point mutation to mprF did not impact on S.aureus virulence; however deletion of mprF led to virulence attenuation and hyper-susceptibility to DAP. To validate our findings in G. mellonella, we confirmed the attenuated virulence of select isolates from the laboratory-derived series using a murine septicaemia model. As a corollary, we showed significant virulence reductions for clinically-derived DAP(R) isolates compared to their isogenic, DAP-susceptible progenitors (DAP(S)). Intriguingly, each clinical DAP(R) isolate was persistent in vivo. Taken together, it appears the genetic correlates underlying daptomycin resistance in S. aureus also alter pathogenicity.

Structure-Activity Relationship Studies of a Series of Semisynthetic Lipopeptides Leading to the Discovery of Surotomycin, a Novel Cyclic Lipopeptide Being Developed for the Treatment of Clostridium difficile-Associated Diarrhea.

Novel cyclic lipopeptides with different acyl tails were synthesized via a semisynthetic approach. Structure-activity relationship studies revealed that lipophilicity, chain length, and the location of key aromatic functionalities of the tail modulated activity. The lead compound surotomycin exhibited significantly improved in vitro activity compared with daptomycin (MIC90 0.5 vs 2 µg/mL) against Clostridium difficile including NAP1 epidemic strains. In hamster efficacy studies, surotomycin protected animals at a dose of 0.5 mg/kg, PO.

Rapid bactericidal activity of daptomycin against methicillin-resistant and methicillin-susceptible Staphylococcus aureus peritonitis in mice as measured with bioluminescent bacteria.

The rising rates of antibiotic resistance accentuate the critical need for new antibiotics. Daptomycin is a new antibiotic with a unique mode of action and a rapid in vitro bactericidal effect against gram-positive organisms. This study examined the kinetics of daptomycin's bactericidal action against peritonitis caused by methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in healthy and neutropenic mice and compared this activity with those of other commonly used antibiotics. CD-1 mice were inoculated intraperitoneally with lethal doses of MSSA (Xen-29) or MRSA (Xen-1), laboratory strains transformed with a plasmid containing the lux operon, which confers bioluminescence. One hour later, the animals were given a single dose of daptomycin at 50 mg/kg of body weight subcutaneously (s.c.), nafcillin at 100 mg/kg s.c., vancomycin at 100 mg/kg s.c., linezolid at 100 mg/kg via gavage (orally), or saline (10 ml/kg s.c.). The mice were anesthetized hourly, and photon emissions from living bioluminescent bacteria were imaged and quantified. The luminescence in saline-treated control mice either increased (neutropenic mice) or remained relatively unchanged (healthy mice). In contrast, by 2 to 3 h postdosing, daptomycin effected a 90% reduction of luminescence of MSSA or MRSA in both healthy and neutropenic mice. The activity of daptomycin against both MSSA and MRSA strains was superior to those of nafcillin, vancomycin, and linezolid. Against MSSA peritonitis, daptomycin showed greater and more rapid bactericidal activity than nafcillin or linezolid. Against MRSA peritonitis, daptomycin showed greater and more rapid bactericidal activity than vancomycin or linezolid. The rapid decrease in the luminescent signal in the daptomycin-treated neutropenic mice underscores the potency of this antibiotic against S. aureus in the immune-suppressed host.

Inhibition of daptomycin by pulmonary surfactant: in vitro modeling and clinical impact.

The lipopeptide daptomycin has been approved for use in skin and skin-structure infections but has failed to meet statistical noninferiority criteria in a clinical trial for severe community-acquired pneumonia. Daptomycin exhibited an unusual pattern of activity in pulmonary animal models: efficacy in Staphylococcus aureus hematogenous pneumonia and inhalation anthrax but no activity against Streptococcus pneumoniae in simple bronchial-alveolar pneumonia. Daptomycin was shown to interact in vitro with pulmonary surfactant, resulting in inhibition of antibacterial activity. This effect was specific to daptomycin and consistent with its known mechanism of action. This represents the first example of organ-specific inhibition of an antibiotic.