In Vitro Activity of Tebipenem (SPR859) against Penicillin-Binding Proteins of Gram-Negative and Gram-Positive Bacteria

Abstract

Tebipenem (SPR859) is the microbiologically active form of SPR994 (tebipenem-pivoxil), an orally available carbapenem with activity against extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae Measurement of the relative binding of SPR859 to the bacterial cell targets revealed that it is a potent inhibitor of multiple penicillin-binding proteins (PBPs) but primarily a Gram-negative PBP 2 inhibitor, similar to other compounds in this class. These data support further clinical development of SPR994.

Keywords: PBP; carbapenems; penicillin-binding proteins; tebipenem.

FIG 1

PBP binding competition assay between Bocillin FL and SPR859 (a) or meropenem (b) using E. coli K-12 cell membranes. The fluorescent Bocillin FL signal decreases with increasing antibiotic concentrations. The calculated IC₅₀ values are reported in Table 1. The controls (CTRL) are the unlabeled membranes (no Bocillin FL and antibiotic), showing nonspecific (ns) autofluorescent bands that are not PBPs.

FIG 2

Microscopy of E. coli K-12 (a) and P. aeruginosa ATCC 27853 (b) incubated with 1 × MIC of the indicated antibiotics for 4 h. Paraformaldehyde 1% was used to fix the cells before phase-contrast microscopy. CAZ mainly targets PBP 3 (Table 1), leading to cell filamentation. AMD, MEM, and SPR859 target PBP 2 causing the rounding of the cells for E. coli K-12. AMD caused a similar morphological change in P. aeruginosa ATCC 27853, but conical shaped cells and filament bulging are observed with MEM and SPR859.