Design, Synthesis, and Biological Evaluation of Indole Derivatives Targeting LsrK as AI-2 Quorum Sensing Inhibitors

A series of novel indole derivatives targeting LsrK as AI-2 quorum sensing (QS) inhibitors against antimicrobial resistance (AMR) were designed, synthesized, and evaluated in vitro and in vivo. 3-Cyano-indol derivative <b>A19</b> showed more potent activity than that of all reported LsrK inhibitors, with an IC₅₀ value of 340 nM and a <i>K</i>_D value of 485 nM. The in-depth biological evaluation indicated that the potent compounds <b>A19</b>, <b>A40</b>, and <b>A49</b> inhibited biofilm formation and bacterial motility and changed biofilm morphology through AI-2 QS inhibition rather than direct antibacterial effects. Surprisingly, they showed the synergistic eradication effect for preformed biofilms combined with antibiotics and no obvious in vitro hemolysis and cellular toxicity. Moreover, the best-performing compound <b>A40</b> showed favorable oral PK properties. In summary, this work identified that <b>A40</b> was a promising lead with a novel scaffold for the further development of LsrK inhibitors as AI-2 QS inhibitors against AMR.