Homodimeric Tobramycin Adjuvant Repurposes Novobiocin as an Effective Antibacterial Agent against Gram-Negative Bacteria

Abstract

Low permeability across the outer membrane is a major reason why most antibiotics are ineffective against Gram-negative bacteria. Agents that permeabilize the outer membrane are typically toxic at their effective concentrations. Here, we report the development of a broad-spectrum homodimeric tobramycin adjuvant that is nontoxic and more potent than the gold standard permeabilizing agent, polymyxin B nonapeptide. In pilot studies, the adjuvant confers potent bactericidal activity on novobiocin against Gram-negative bacteria, including carbapenem-resistant and colistin-resistant strains bearing plasmid-borne mcr-1 genes. Resistance development to the combination was significantly reduced, relative to novobiocin alone, and there was no induction of cross-resistance to other antibiotics, including the gyrase-acting fluoroquinolones. Tobramycin homodimer may allow the use of lower doses of novobiocin, overcoming its twin problem of efficacy and toxicity.

A Dimer, but Not Monomer, of Tobramycin Potentiates Ceftolozane against Multidrug-Resistant and Extensively Drug-Resistant Pseudomonas aeruginosa and Delays Resistance Development

“…We found that the MICs of tobramycin across these isolates were identical ( Table 5), suggesting that compound 1 does not trigger resistance development to aminoglycosides. This observation is consistent with a previous report on studies with A. baumannii (34).…”

“…To investigate whether ceftolozane suffers from either of the intrinsic resistance mechanisms of outer membrane permeability and efflux, we assessed its potency, alone and in combination with compound 1, against efflux-competent MDR and efflux-deficient P. aeruginosa isolates. Compound 1, a molecule derived by dimerization of short-chain amphiphilic tobramycins, has been previously reported as a nontoxic and more potent outer membrane permeabilizer than polymyxin B nonapeptide (PMBN) (34). A checkerboard assay was therefore used to assess the interactions between ceftolozane and compound 1, and the results were interpreted as a function of the fractional inhibitory concentration index (FICI) (42).…”

“…Antibiotic adjuvants without overt antibacterial activity as standalone agents are less likely to select for resistance (28,29). A number of nonribosomal tobramycin molecules that potentiate different antibiotics (including ␤-lactams) against P. aeruginosa have been documented in literature but none has been reported to synergize with ceftolozane (28,(30)(31)(32)(33)(34). Recently, we identified a tobramycin homodimer scaffold that is: (i) more potent than the gold standard OM permeabilizer, polymyxin B nonapeptide (PMBN); (ii) nonhemolytic against red blood cells; (iii) noncytotoxic against human embryonic kidney (HEK293) and liver (HepG2) cells; and (iv) nontoxic in vivo against Galleria mellonella wax moths where colistin was toxic (34).…”

“…A number of nonribosomal tobramycin molecules that potentiate different antibiotics (including ␤-lactams) against P. aeruginosa have been documented in literature but none has been reported to synergize with ceftolozane (28,(30)(31)(32)(33)(34). Recently, we identified a tobramycin homodimer scaffold that is: (i) more potent than the gold standard OM permeabilizer, polymyxin B nonapeptide (PMBN); (ii) nonhemolytic against red blood cells; (iii) noncytotoxic against human embryonic kidney (HEK293) and liver (HepG2) cells; and (iv) nontoxic in vivo against Galleria mellonella wax moths where colistin was toxic (34). In the current study, we investigated a combination of tobramycin homodimer in combination with ceftolozane and compared its activity with standard ␤-lactam/␤-lactamase inhibitor combinations against Gram-negative bacteria in vitro, using the current CLSI broth microdilution methodology.…”

Aminoglycoside Conjugation for RNA Targeting: Antimicrobials and Beyond

“…Other conjugates were prepared in as imilar way by using polymyxin B, which is am embrane-targeting decalipopeptide antibiotic used to treat MDR/XDR Gram-negative bacterial infections. [118] Rifampicin-5 conjugates werea lso prepared to break the intrinsic resistance and sensitize multidrug and extensively drug-resistant P. aeruginosa to doxycycline and chloramphenicol in vitro and in vivo. [119] Conjugation of 5 to cyclam abrogated the ribosomale ffects of 5,b ut conferredapotent adjuvant property that restored full antibiotic activity of meropenem and aztreonam against carbapenem-resistant P. aeruginosa.…”