Biochemical characterization of novel tetrahydrofuranyl 1 beta-methylcarbapenems: Stability to hydrolysis by renal dehydropeptidases and bacterial beta-lactamases, binding to penicillin binding proteins, and permeability properties

The biochemical properties of tetrahydrofuranyl (THF) carbapenems, carbapen ems with THF substituents, were evaluated with respect to enzyme stability, binding to penicillin-binding proteins (PBPs), and penetration into gram-n egative organisms. THF carbapenems showed increased stability to hog renal dehydropeptidases (DHPs) compared to that of imipenem or meropenem and were more stable to human DHP than imipenem (<10% hydrolysis compared to that f or imipenem), THF carbapenems were stable to hydrolysis by all serine p-lac tamases tested. CL 191,121, a prototype THF carbapenem, was more stable to hydrolysis by carbapenemhydrolyzing serine beta-lactamases such as IMI-1 an d Sme-l than imipenem,,with a relative k(cat) value of <20% for imipenem. S imilar to imipenem and meropenem, TNF carbapenems were not stable to the me tallo beta-lactamases CcrA and L1, However, CL 191,121 bound to all Staphyl ococcus aurens PBPs at concentrations that were less than or equal to the M ICs. The THF carbapenems bound to PBPs from Escherichia coli and Pseudomona s aeruginosa, with the highest affinities being for PBPs 2 and 4, as noted with imipenem, The affinities for PBPs la and Ib in E. coli were reduced fo r the THF carbapenems compared to that for imipenem, even though the MICs o f the THF carbapenems for E. coli strains were low-er than those of imipene m, The penetrability of the THF carbapenems into Serratia marcescens S6, wh ich produces the Sme-l carbapenemhydrolyzing p-lactamase, was 2.4 to 7.8 ti mes less than that of imipenem, Compounds CL 190,294 and CL 188,624 showed good penetrability, with permeability coefficient values comparable to thos e of the rapidly penetrating agents cephaloridine, imipenem, meropenem, and biapenem. Decreased penetration into wild-type P, aeruginosa was suggested by the high MICs of the THF carbapenems (MICs, 16 to 32 mu g/ml), despite equivalent or better binding to P. aeruginosa PBPs than that of imipenem. H owever, the MICs of the THF carbapenems for wild-type P. aeruginosa compare d to that for an OprD2 mutant generally varied no more than 2-fold, but tho se of imipenem and other carbapenems differed 16-fold. These data indicated that THF carbapenems do not appear to enter through protein OprD2, In conc lusion, the THF carbapenems exhibited stability to hydrolysis by renal DHPs and serine p-lactamases, exhibited strong binding to essential PBPs from E . coli and S. aureus, and penetrated gram-negative enteric bacteria at rate s comparable to those for meropenem and biapenem.