# Anti-Biofilm Agents to Overcome _Pseudomonas aeruginosa Antibiotic Resistance_
## 3 Anti-Biofilm Agents to Tackle _P. aeruginosa_
### Analogs of Native Autoinducers
The development of AI analogs as QSIs seems an interesting way to achieve competitive inhibition of the target. Most of them show very potent anti-biofilm properties. Yet, these compounds are not always specific to only one transcription factor. There seems to be a fine line between the design of an antagonist and that of an agonist. Non-Analogs of Native Autoinducers  
(1)  QSIs targeting LasR or RhlR  
Some natural products possess anti-virulence activity, including anti-biofilm activities. Hence, they constitute a basis for interest in the synthesis of ABAs whose biological and physicochemical properties can easily be optimized. [PERSON] et al. pointed out the ability of (\(S\))-[6]-gingerol, the main component of ginger, to potently decrease _P. aeruginosa_ virulence by competing with odDHL for LasR binding [66]. Based on these results, the team performed SAR studies starting from different derivatives to develop ABAs. Molecular modeling screening indicated the importance of the 3'-hydroxyl-4'-methoxyphenylyl moiety of (\(S\))-[6]-gingerol for LasR binding. The presence of a hydrogen or halogen bond acceptor at the 4-position (-F or -OH) was especially crucial for the activity. Regarding the alkyl chain, the affinity for LasR increased with higher lengths, i.e., 8-gingerol vs. 6-gingerol, which maximize van der Waals interactions with lipophilic amino acid residues (Figure 9). Interestingly, removal of the hydroxyl group on the alkyl tail decreased the anti-biofilm activity, while forming the (\(R\))-enantiomer increased the efficacy. Finally, the introduction of a double bond between the phenyl moiety and the carbonyl group confirmed the importance of restricted rotational flexibility for the affinity to LasR and the anti-biofilm properties. The (\(R\))-[8]-gingerol derivative **ABA-21**, as a LasR competitive antagonist, exhibited 49% anti-biofilm activity at 10 \(\upmu\)M on the PA14 strain. Then, [PERSON] et al. designed new (S)-[6]-gingerol analogs with shorter alkyl chains in an attempt to mimic BHL and bind competitively to RhIR [67]. They developed two series of 3\({}^{\prime}A^{\prime}\)-difluorophenyl derivatives bearing various alkynyl ketones or alcohols. The \(n\)-butyryl compound **ABA-22** displayed the best activity with 32% inhibition of biofilm formation at 10 \(\upmu\)M and even more than 72% in dynamic culture conditions. The exopolysaccharide and protein composition of the matrix are then decreased by 39 and 72%, respectively. Interestingly, the restricted flexibility between the phenyl and carbonyl groups significantly increased the RhIR affinity (IC\({}_{50}\) = 26 \(\upmu\)M) while the removal of the \(\beta\)-hydroxyl group of the natural analog appeared inconsequential. Molecular docking studies revealed a \(\pi\)-stacking between the phenyl ring and Tyr72 as well as an H-bond between the carbonyl and Trp68. Remarkably, longer alkyl chains weaken these interactions, which is correlated with a loss of the antagonist activity towards RhIR. **ABA-22** also reduces rhamnoid production by 42% at 10 \(\upmu\)M, which could slow down bacterial colonization and biofilm formation. This molecule has emerged as one of the only relevant specific inhibitors of RhIR described in the literature. [PERSON] et al. were interested in the development of cajaninstilbene acid derivatives, especially starting from amorfrutin B, which possesses potent anti-biofilm properties. SAR studies led to the compound **ABA-23**, which inactivates LasR and PqsR and diminishes by 50% the biofilm formation at 50 \(\upmu\)M [68; 69]. In 2002, [PERSON] et al. synthetized halogenated furanones inspired by analogs produced by the marine macroa alga _Delisea pulchra_ and which specifically interfere with AHL-regulated bacterial communication processes [70]. Among those new derivatives, **ABA-24** inhibited the biofilm formation of the PAO-JP2 strain by 62% after 7 days of exposure at 29 \(\upmu\)M in dynamic culture conditions. More recently, [PERSON] et al.