Eliana S. Armstrong

Synthesis and spectrum of the neoglycoside ACHN-490.

ABSTRACT ACHN-490 is a neoglycoside, or “next-generation” aminoglycoside (AG), that has been identified as a potentially useful agent to combat drug-resistant bacteria emerging in hospitals and health care facilities around the world. A focused medicinal chemistry campaign produced a collection of over 400 sisomicin analogs from which ACHN-490 was selected. We tested ACHN-490 against two panels of Gram-negative and Gram-positive pathogens, many of which harbored AG resistance mechanisms. Unlike legacy AGs, ACHN-490 was active against strains expressing known AG-modifying enzymes, including the three most common such enzymes found in Enterobacteriaceae. ACHN-490 inhibited the growth of AG-resistant Enterobacteriaceae (MIC90, ≤4 μg/ml), with the exception of Proteus mirabilis and indole-positive Proteae (MIC90, 8 μg/ml and 16 μg/ml, respectively). ACHN-490 was more active alone in vitro against Pseudomonas aeruginosa and Acinetobacter baumannii isolates with AG-modifying enzymes than against those with altered permeability/efflux. The MIC90 of ACHN-490 against AG-resistant staphylococci was 2 μg/ml. Due to its promising in vitro and in vivo profiles, ACHN-490 has been advanced into clinical development as a new antibacterial agent.

ACHN-490, a Neoglycoside with Potent In Vitro Activity against Multidrug-Resistant Klebsiella pneumoniae Isolates

ABSTRACT The in vitro activity of ACHN-490, a novel aminoglycoside (“neoglycoside”), was evaluated against 102 multidrug-resistant (MDR) Klebsiella pneumoniae strains, including a subset of 25 strains producing the KPC carbapenemase. MIC50 values for gentamicin, tobramycin, and amikacin were 8 μg/ml, 32 μg/ml, and 2 μg/ml, respectively; MIC90 values for the same antimicrobials were ≥64 μg/ml, ≥64 μg/ml, and 32 μg/ml, respectively. ACHN-490 showed an MIC50 of 0.5 μg/ml and an MIC90 of 1 μg/ml, which are significantly lower than those of comparator aminoglycosides. ACHN-490 represents a promising aminoglycoside for the treatment of MDR K. pneumoniae isolates, including those producing KPC β-lactamase.

Detection of Methyltransferases Conferring High-Level Resistance to Aminoglycosides in Enterobacteriaceae from Europe, North America, and Latin America

ABSTRACT The alteration of ribosomal targets by recently described 16S rRNA methyltransferases confers resistance to most aminoglycosides, including arbekacin. Enterobacteriaceae and nonfermentative bacilli acquired through global surveillance programs were screened for the presence of these enzymes on the basis of phenotypes that were resistant to nine tested aminoglycosides. Subsequent molecular studies determined that 20 of 21 (95.2%) methyltransferase-positive isolates consisted of novel species records or geographic occurrences (North America [armA and rmtB], Latin America [rmtD], and Europe [armA]; rmtA, rmtC, and npmA were not detected). The global emergence of high-level aminoglycoside resistance has become a rapidly changing event requiring careful monitoring.

Combating evolution with intelligent design: the neoglycoside ACHN-490.

The challenge posed by increasing levels of drug-resistant bacteria world-wide is manifest, and must be dealt with both by new approaches to the use of existing antibiotics and by the introduction of novel drugs. ACHN-490 is the first neoglycoside, or next-generation aminoglycoside, to begin clinical development. ACHN-490 was designed to target key pathogens, particularly gram-negative organisms and those resistant to older antibiotics. ACHN-490 demonstrates promising in vitro activity against wild-type and resistant bacteria while retaining the favorable bactericidal and synergistic properties of the aminoglycoside class. These attributes, along with the results of Phase 1 studies of ACHN-490 injection, suggest that ACHN-490 may help to fill the growing unmet need for new antibacterial agents.

Toxicity modulation, resistance enzyme evasion, and A-site X-ray structure of broad-spectrum antibacterial neomycin analogs.

Aminoglycoside antibiotics are pseudosaccharides decorated with ammonium groups that are critical for their potent broad-spectrum antibacterial activity. Despite over three decades of speculation whether or not modulation of pKa is a viable strategy to curtail aminoglycoside kidney toxicity, there is a lack of methods to systematically probe amine-RNA interactions and resultant cytotoxicity trends. This study reports the first series of potent aminoglycoside antibiotics harboring fluorinated N1-hydroxyaminobutyryl acyl (HABA) appendages for which fluorine-RNA contacts are revealed through an X-ray cocrystal structure within the RNA A-site. Cytotoxicity in kidney-derived cells was significantly reduced for the derivative featuring our novel β,β-difluoro-HABA group, which masks one net charge by lowering the pKa without compromising antibacterial potency. This novel side-chain assists in evasion of aminoglycoside-modifying enzymes, and it can be easily transferred to impart these properties onto any number of novel analogs.

Activity of ACHN-490 Tested Alone and in Combination with Other Agents against Pseudomonas aeruginosa

ABSTRACT ACHN-490 was tested alone and in combination with cefepime, doripenem, imipenem, or piperacillin-tazobactam in a synergy time-kill analysis against 25 Pseudomonas aeruginosa strains with different resistance phenotypes. Each combination was synergistic against most isolates at 24 h, and antagonism was not observed. Combinations of ACHN-490 with cefepime, doripenem, imipenem, or piperacillin-tazobactam yielded synergies in ≥70% and ≥80% of strains at 6 and 12 h, respectively, and in ≥68% at 24 h.

Toward Overcoming Staphylococcus aureus Aminoglycoside Resistance Mechanisms with a Functionally Designed Neomycin Analogue.

Deoxygenation of the diol groups in rings A and D of neomycin in combination with the introduction of an N1-(l)-HABA group in the 2-deoxystreptamine subunit (ring B) leads to a novel and potent antibiotic (1) with activity against strains of S. aureus carrying known aminoglycoside resistance determinants, as well as against an extended panel of Methicillin-resistant S. aureus isolates (n = 50). Antibiotic 1 displayed >64 fold improvement in MIC50 and MIC90 against this MRSA collection when compared to the clinically relevant aminoglycosides amikacin and gentamicin. The synthesis was achieved in six steps and 15% overall yield.