# Anti-Biofilm Agents to Overcome _Pseudomonas aeruginosa Antibiotic Resistance_
## 3 Anti-Biofilm Agents to Tackle _P. aeruginosa_
### Analogs of Native Autoinducers
Accordingly, **ABA-16** exhibited a potent inhibition of biofilm formation in the PAO1 strain by 46% at 50 uM. The authors also described its synergistic activity with ciprofloxacin, without relevant eukaryotic cytotoxicity at anti-virulence concentrations. In combination with 50 uM of **AAB-15**, the MIC of the antibiotic was reduced by half. Then, [PERSON] et al. investigated the effect of quinazolin-4(\(3H\))-one derivatives on the virulence of two clinical strains of _P. aeruginosa_ (BJ5325 and RP73), representative of acute and chronic lung infections, respectively [61]. The compound **ABA-17** bearing two fluor atoms in positions 6 and 7 of the quinazolinone as well as a cinnamic imine in position 3 showed the most interesting efficacy against biofilm formation with a 58% reduction at 50 uM on the BJ3525 strain. It revealed no cytotoxicity on bronchial cells IB3-1 at this concentration. However, **ABA-17** did not decrease the secretion of pyocyanin as much as other compounds of the series, which is why it was not studied further. [PERSON] et al. designed 7-Cl-4-aminoquinolines as isosteres of the 7-Cl-quinazolinone pharmacophore described by [PERSON] et al. They replaced the hydrophobic alkyl chain at the C2 position of the quinazolinone by a succession of aromatic rings at the N4 position of  
Figure 8: Key interactions with the target, anti-QS and anti-biofilm activities of AQ autoinducer analog QSIs bearing a quinazolinone, quinoline or chromone core [47; 60; 61; 62; 63; 64; 65]. the 4-aminoquinoline leading to **AAB-18** (Figure 8) [62]. As well as for its quinazoline analogs, a molecular docking study revealed that the aminoquinoline resides in the planar pocket P1 while the aromatic tail extends in the long pocket P2. The chlorine in position 7 of the core forms, like for **ABA-15**, a halogen bond with Thr265. Accordingly, **ABA-18** displayed very potent biofilm formation inhibitory properties with IC50 of 8 and 34 uM on the PA14 and PAO1 strains, respectively. It also sensitized at these concentrations preformed biofilms from both strains to a tobramycin treatment (100 ug/mL), leading to a significant eradication of the colonies. [PERSON] et al. also described the 7-chloro-4-aminoquinoline analog **ABA-19** for which a benzofurane-substituted aminoalkyl chain was introduced at the N4 position [63; 64]. The presence of the two secondary amines allows the formation of H-bonds with Leu207 and Glu259 while a \(\pi\)-stacking settles between the benzofurane moieties Tyr258 and Glu259. Unlike compounds **ABA-16** and **ABA-18**, the 7-Cl atom forms halogen bonds with Leu197 and Ser196. Thus, **ABA-19** inhibited PAO1 biofilm formation by 50% at 50 uM. However, this result has to be moderated because the compound reduced bacterial growth by 25% at this concentration. It also showed strong cytotoxicity towards pulmonary fibroblasts (MRC5) with a CC50 of 4 uM. In 2022, [PERSON] et al. synthesized PQS analogs by replacing the quinolone with a chromone core, known for its diverse therapeutical applications (anti-inflammatory, anti-tumor, anti-diabetic, vasodilator or antibacterial properties) and which can easily be functionalized [65]. Guided by docking enthalpies of various studied ligands in the autoinduction site of PqsR, the authors replaced the heptyl chain at the C2 position by an amide spacer followed by an aromatic ring (Figure 8). Two series were then developed: a direct-and a retro-chromone carboxamide series, meaning that the chromone could be either linked to the ketone or amine part of the amide. The retro-chromone carboxamide series exhibited the best biofilm formation inhibitors, with no cytotoxicity towards eukaryotic cells. Among those, the 2,4-dinitro-N-(4-oxo-4\(H\)-chromen-2-yl)benzamide **ABA-20** revealed 91% anti-biofilm activity at 50 uM. A molecular docking study pointed out the formation of \(\pi\)-stacking and hydrophobic interactions with key residues such as Leu208, Thr265 or Ile236. **ABA-20** was therefore selected as a hit compound for further optimizations.