A-54556A (Synonyms: ADEP 1,A-54556 Factor A)

IC50: 0.2 μg/ml for Bacillus subtilis 168

A-54556A is a natural acyldepsipeptide (ADEP) antibiotic.

Acyldepsipeptides (ADEP), a new class of antibiotics, has antibacterial activity against Gram-positive bacteria. The acyldepsipeptides are active against isolates that are resistant to antibiotics, implying a new target identify as ClpP.

In vitro: Previous study found that the treatment of B. subtilis with 1.6 mg/ml of A-54556A reduced the number of viable cells by 2 log units. In addition, the biosynthesis of DNA, RNA, protein, cell wall and fatty acid proceeded unhindered for 1 h at 2 mg/ml A-54556A, whereas classical antibiotics were clearly distinguished by preferential inhibition of their target pathway. Microscopic examination showed that after addition of A-54556A at concentrations as low as 0.4 mg/ml, B. subtilis started to form filaments [1].

In vivo: Two A-54556A analogs, ADEP 2 and ADEP 4, were proven to be active in the treatment of bacterial infections in rodents. When mice were challenged with a lethal systemic infection of E. faecalis, 1 mg/kg ADEP 2 or 0.5 mg/kg ADEP 4 were sufficient for 100% survival. In lethal sepsis caused by S. aureus, 12.5 mg/kg ADEP 4 rescued 80% of the mice and reduced the bacterial loads in liver, spleen and lung by 2–3 log units compared to an untreated control [1].

Clinical trial: Up to now, A-54556A is still in the preclinical development stage.

Reference:
[1] H.  Brtz-Oesterhelt, D. Beyer, H. P. Kroll, et al. Dysregulation of bacterial proteolytic machinery by a new class of antibiotics. Nature Medicine 11(10), 1082-1087 (2005).