Profiling thein vitroandin vivoactivity of streptothricin-F against carbapenem-resistant Enterobacterales: a historic scaffold with a novel mechanism of action

Abstract

Streptothricins are components of the natural product, nourseothricin; each containing identical streptolidine and gulosamine aminosugar moieties attached to varying numbers of linked b-lysines. Nourseothricin was discovered by Waksman and colleagues in the early 1940's, generating intense interest because of excellent Gram-negative activity. However, the natural product mixture was associated with toxicity, and subsequent exploration was limited. Here, we establish the activity spectrum of nourseothricin and its main components, streptothricin-F (S-F, one lysine) and streptothricin D (S-D, three lysines), purified to homogeneity, against highly drug-resistant, carbapenem-resistant Enterobacterales (CRE). The MIC50 and MIC90 for S-F and S-D were 2 and 4 µM, and 0.25 and 0.5 µM, respectively. S-F and nourseothricin showed rapid, bactericidal activity. S-F and S-D both showed approximately 40-fold greater selectivity for prokaryotic than eukaryotic ribosomes in in vitro translation assays. There was >10-fold in vitro selectivity of S-F compared with S-D on LLC-PK1 and J774 cell lines. In vivo, delayed renal toxicity occurred at >10-fold higher doses of S-F compared with S-D. Substantial treatment effect of S-F in the murine thigh model was observed against the otherwise pandrug-resistant, NDM-1-expressing Klebsiella pneumoniae Nevada strain at dosing levels without observable or minimal toxicity. Resistance mutations obtained in single ribosomal operon E. coli identify novel interactions with 16S rRNA helix 34, i.e., C1504A and A1196G/C conferred high level resistance to nourseothricin. Based on promising, unique activity, we suggest that the streptothricin scaffold deserves further pre-clinical exploration as a potential therapeutic for the treatment of CRE and potentially other multidrug-resistant, Gram-negative pathogens

Innovative Strategies to Overcome Antimicrobial Resistance and Tolerance

“…The aminoglycoside antibiotic, nourseothricin, a natural product of the streptothricin class, is composed of a streptolidine, carbamyolated gulosamine, and variable number of β-lysine moieties. This antibiotic causes miscoding by a potentially unique binding mechanism to the ribosome [ 177 , 178 ]. Nourseothricin is effective not only against bacteria, but also against other microorganisms, such as archaea, fungi, protozoa, and microalgae.…”

The convergent total synthesis and antibacterial profile of the natural product streptothricin F

“…Streptothricin F, ( n = 1, LD 50 : 300 mg kg −1 ) shows remarkably less toxicity than streptothricin E ( n = 2, LD 50 : 26 mg kg −1 ), streptothricin D ( n = 3, LD 50 : ∼10 mg kg −1 ), and streptothricin C ( n = 4, LD 50 : ∼10 mg kg −1 ). 6,15,34 Conversely, antimicrobial activity favors longer β-lysine homopolymer chains, with nourseothricin ( K. pneumoniae Nevada strain AR-0636 MIC: 0.15 μg mL −1 ) and streptothricin D (MIC: 0.19 μg mL −1 ) exhibiting approximately 4-fold more activity (per mol) than streptothricin F (MIC: 1 μM). 34…”

“…32,33 Our main attraction to this natural product class derives from previous reports that have demonstrated streptothricin F (1) to be less toxic than other ). 6,15,34 Conversely, antimicrobial activity favors longer blysine homopolymer chains, with nourseothricin (K. pneumoniae Nevada strain AR-0636 MIC: 0.15 mg mL À1 ) and streptothricin D (MIC: 0.19 mg mL À1 ) exhibiting approximately 4-fold more activity (per mol) than streptothricin F (MIC: 1 mM). 34…”

“…6,15,34 Conversely, antimicrobial activity favors longer blysine homopolymer chains, with nourseothricin (K. pneumoniae Nevada strain AR-0636 MIC: 0.15 mg mL À1 ) and streptothricin D (MIC: 0.19 mg mL À1 ) exhibiting approximately 4-fold more activity (per mol) than streptothricin F (MIC: 1 mM). 34…”

The Activity of Nourseothricin Against Drug-Resistant Bacteria

“…Nourseothricin differs from the majority of conventional antibiotics due to its distinct mechanism of action, which prevents the development of single-target resistance. [10] Nourseothricin has a lot of intriguing properties, but more research is needed to understand its pharmacokinetics and toxicity before it can be used effectively and safely in clinical settings. A drug's pharmacokinetics investigates how it is metabolized and eliminated from the body.…”