RWJ-54428 (MC-02,479), a New Cephalosporin with High Affinity for Penicillin-Binding Proteins, Including PBP 2a, and Stability to Staphylococcal Beta-Lactamases

Abstract

RWJ-54428 (MC-02,479) is a new cephalosporin active against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). The potency of this new cephalosporin against MRSA is related to a high affinity for penicillin-binding protein 2a (PBP 2a), as assessed in a competition assay using biotinylated ampicillin as the reporter molecule. RWJ-54428 had high activity against MRSA strains COL and 67-0 (MIC of 1 μg/ml) and also showed affinity for PBP 2a, with a 50% inhibitory concentration (IC ₅₀ ) of 0.7 μg/ml. RWJ-54428 also displayed excellent affinity for PBP 5 from Enterococcus hirae R40, with an IC ₅₀ of 0.8 μg/ml and a MIC of 0.5 μg/ml. The affinity of RWJ-54428 for PBPs of β-lactam-susceptible S. aureus (MSSA), enterococci ( E. hirae ), and Streptococcus pneumoniae showed that the good affinity of RWJ-54428 for MRSA PBP 2a and E. hirae PBP 5 does not compromise its binding to susceptible PBPs. RWJ-54428 showed stability to hydrolysis by purified type A β-lactamase isolated from S. aureus PC1. In addition, RWJ-54428 displayed low MICs against strains of S. aureus bearing the four classes of staphylococcal β-lactamases, including β-lactamase hyperproducers. The frequency of isolation of resistant mutants to RWJ-54428 from MRSA strains was very low. In summary, RWJ-54428 has high affinity to multiple PBPs and is stable to β-lactamase, properties that may explain our inability to find resistance by standard methods. These data are consistent with its excellent activity against β-lactam-resistant gram-positive bacteria.