Plazomicin Retains Antibiotic Activity against Most Aminoglycoside Modifying Enzymes

Abstract

Plazomicin is a next-generation, semisynthetic aminoglycoside antibiotic currently under development for the treatment of infections due to multidrug-resistant Enterobacteriaceae. The compound was designed by chemical modification of the natural product sisomicin to provide protection from common aminoglycoside modifying enzymes that chemically alter these drugs via N-acetylation, O-adenylylation, or O-phosphorylation. In this study, plazomicin was profiled against a panel of isogenic strains of Escherichia coli individually expressing twenty-one aminoglycoside resistance enzymes. Plazomicin retained antibacterial activity against 15 of the 17 modifying enzyme-expressing strains tested. Expression of only two of the modifying enzymes, aac(2')-Ia and aph(2″)-IVa, decreased plazomicin potency. On the other hand, expression of 16S rRNA ribosomal methyltransferases results in a complete lack of plazomicin potency. In vitro enzymatic assessment confirmed that AAC(2')-Ia and APH(2'')-IVa (aminoglycoside acetyltransferase, AAC; aminoglycoside phosphotransferase, APH) were able to utilize plazomicin as a substrate. AAC(2')-Ia and APH(2'')-IVa are limited in their distribution to Providencia stuartii and Enterococci, respectively. These data demonstrate that plazomicin is not modified by a broad spectrum of common aminoglycoside modifying enzymes including those commonly found in Enterobacteriaceae. However, plazomicin is inactive in the presence of 16S rRNA ribosomal methyltransferases, which should be monitored in future surveillance programs.

Keywords: Enterobacteriaceae; aminoglycoside-modifying enzymes; antibiotic resistance; plazomicin.

Figure 1.

Chemical structures of sisomicin and plazomicin. The next-generation aminoglycoside plazomicin is derived from the naturally produced sisomicin scaffold by the addition of a N1 2(S)-hydroxy aminobutyryl and a hydroxyethyl substituent at the 6′ position (shown in blue).

Figure 2.

Crystal structure of APH(2′′)-IVa bound to plazomicin. (A) APH(2′′)-IVa, in gray; plazomicin (plazo), in green. Interacting residue side chains are highlighted and shown as sticks. The site of modification on plazomicin (2′′-OH group) is labeled. The electron density F_o–F_c map for plazomicin is contoured at 2.0 σ after refinement. (B) Overlay of APH(2′′)-IVa bound to plazo (colored green) and kanamycin A (kanA, colored black). The 2′′-OH of each molecule is labeled.

Figure 3.

Crystal structure of AAC(2′)-Ia bound to acetylated gentamicin. AAC(2′)-Ia dimer, in gray; 2′-N-acetylgentamicin, in blue; coenzyme A (CoA), in black. The active site of one of the AAC(2′)-Ia molecules is highlighted, and plazomicin (plazo, colored green) has been modeled into the gentamicin binding site. Plazomicin interacting residue side chains are highlighted and shown as sticks.