# Anti-Biofilm Agents to Overcome _Pseudomonas aeruginosa Antibiotic Resistance_
## 3 Anti-Biofilm Agents to Tackle _P. aeruginosa_
### Analogs of Native Autoinducers
#### 3.1.4 Antimicrobial Peptides  
The antimicrobial peptides (AMPs) are small amphiphilic, cationic molecules usually composed of 10-50 residues. They are naturally produced by mammals, amphibians andfishes, micro-organisms and insects and act as a first line of defense for the innate immune system. These peptides are known to induce bacterial death by membranolytic and/or intracellular mechanisms quenching the cell cycle progression. They have triggered the interest of medicinal chemists due to their fast bactericidal mode of action and the absence of resistance appearance after repeated exposition [88]. Interestingly, some AMPs also possess anti-biofilm activities. This can either be due to (i) the eradication of sessile bacteria inside the biofilms, associated with an increased ability to penetrate through the matrix in comparison with the conventional antibiotics, or to (ii) anti-biofilm activity at a sub-MIC concentration like an AVA, hindering the biofilm cycle without any effect on bacterial growth. In this review, we are interested in those AMPs able to inhibit biofilm formation or to stimulate its dispersal. Figure 12: Key interactions with the target, anti-lectin and anti-biofilm activities of lectin A and B inhibitors (the peptide backbone appears in purple) [82; 83; 84; 85; 86]. Most synthetic AMPs of interest are derived from natural AMPs. The human cathelicidin **LL-37 (ABA-41)** has originated several analogs due to its potent anti-biofilm activity towards _P. aeruginosa_, with an 80% reduction in biofilm formation at 3.5 \(\upmu\)M (Figure 13). [PERSON] et al. [89] highlighted the deleterious effect of the peptide towards initial attachment of the cells to a surface and its ability to inactivate the _las_ and _rhl_ QS systems, as well as its promoting effect on twitching motility, which helps dispersing the biofilm (60% dispersal at 1 \(\upmu\)M). The design of synthetic derivatives aims at diminishing the peptide's length, its sensitivity to proteases and saline media as well as its moderate cytotoxicity towards eukaryotic cells (45% permeabilization of HUVEC epithelial cell line at 50 \(\upmu\)M). [PERSON] et al. thus developed a library of truncated fragments derived from **LL-37**, conserving the active part of the peptide only [90]. A screening brought out the AMP **LL-31 (ABA-42)**, which is less cytotoxic (15% permeabilization of HUVEC cells at 50 \(\upmu\)M) and slightly less efficient than **LL-37** (60% inhibition of biofilm formation at 10 \(\upmu\)M). The facilitated synthesis of smaller peptides seems to favor better metabolic stability and lower eukaryotic cytotoxicity. Similarly, from the peptide esculent-1a (**Esc-(1-21)**), unstable and toxic in vivo (LD50 = 12 \(\upmu\)M in a zebrafish model), [PERSON] et al. constructed the diastereoisomer **Esc(1-21)-1c (ABA-43)** by replacing Leu14 and Ser17 with their D-enantiomers ((\(R\)) configuration) [91; 92]. This modification destabilizes the helical folding and thus increases the peptide's stability towards proteases. The anti-biofilm activity was conserved with 75% inhibition of biofilm formation at 4 \(\upmu\)M, with a diminished toxicity (LD50 = 124 \(\upmu\)M in a zebrafish model). The peptide also reduces pyoverdine and rhamnid secretion (by 60 and 20%, respectively, at 1 \(\upmu\)M), as well as bacterial swimming motility (55% inhibition at 1 \(\upmu\)M). Figure 13: Rational design and anti-biofilm activities of AMPs derived from natural AMPs [87; 88; 89; 90; 91]. The synthesis of AMPs based on natural peptides has led to some highly interesting compounds, with more efficacy and less toxicity. However, new knowledge now enables a de novo rational design, with or without the use of informatic tools. This approach favors the optimization of the helical and amphipathic structure, charge and hydrophobic densities of the new AMPs. [PERSON] et al. have studied several small anti-biofilm peptides that are efficient against _P. aeruginosa_[93].