Pseudomonas aeruginosa, is among the bacteria for which antibiotics are urgently needed. At present, the old antibiotic colistin, is used as the last-resort treatment. In Cystic Fibrosis (CF), colistin has been used for decades suggesting that resistance to this antibiotic might become soon critical for CF patients. Indeed, an increase of colistin-resistant P. aeruginosa isolates in CF has been recently reported.
The antibacterial activity of colistin relies on its interaction with LPS. Aminoarabinosylation of the lipid A moiety of LPS is strictly required for the development of colistin resistance in P. aeruginosa. Therefore, the main objective of this project is to develop small molecules that revert colistin resistance by targeting lipid A aminoarabinosylation.
Taking advantage of the resolved structure of the aminoarabinose transferase, which catalyzes the last step of lipid A aminoarabinosylation, and using a structure-guided in silico approach, we have identified a short list of candidate hits from the screening of a library of natural compounds. Growth-inhibition assays of a colistin-resistant tester strain led to the identification of one lead compound, which was active at relatively low concentration.
The proposed project comprises the following aims: optimization of potency and specificity of the lead compound; analysis of the efficacy of lead inhibitors on different model systems. Each aim is accomplished through the execution of different tasks, carried out by a multidisciplinary team.
Modification of the lead compound through combined computational and medicinal chemistry followed by activity testing will allow the development of small molecule/s that meet the criteria for clinical use, such as potent IC50, water solubility and low off-target effects.
As few treatment options exist for colistin-resistant Gram-negative bacteria, development of new drugs is of critical value to postpone the advancement of the post-antibiotic era.
The absolute requirement of Arn-mediated lipid A aminoarabinosylation for acquired colistin resistance in P. aeruginosa was definitely demonstrated by showing that Ara4N defective mutants are unable to develop colistin resistance (8). Additionally, it was demonstrated that that PEtN modification of lipid A, by either endogenous (EptA) or plasmid-mediated PEtN transferases, has marginal effects on colistin resistance in P. aeruginosa. These findings strongly support the notion that pharmacological inhibition of Ara4N biosynthetic enzymes inactivate the colistin-resistance in P. aeruginosa and in other gram-neg bacteria such as K. peneumoniae and B. cenocepacia. Based on this we expect to identify druggable compounds that, by inhibiting Arn-mediated lipid A aminoarabinosylation, restore sensitivity to colistin.
Our ability to treat common infection diseases is heavily compromised by the appearance of multi-resistant pathogens, which restrict the therapeutic options for the treatment of common infectious diseases. Based on the identification of a target of colistin resistance, ArnT, and the availability of a library of natural compounds at CTD, we have identified BBN149 as a lead compounds to inhibit colistin resistance in gram-neg bacteria.
By combining computational and medicinal approaches, BBN149 optimization up to drug-like compounds is undergoing at CTD. The resulting compounds will be tested as reported above up to the identification of the most efficient compounds that act in synergy with colistin.
The results of this project is expected to enlarge the therapeutic options for infectious diseases and positively impact the outcome of gram-negative infections.