Table_1.doc

Abstract

Farnesol, a self- secreted quorum sensing molecule (QSM) of Candida albicans has been known to limit yeast to hyphal transition by blocking RAS1-cAMP-PKA pathway. In a similar fashion, certain bacterial QSMs have also been reported to be successful in attenuating C. albicans’ biofilm and hyphal formation at relatively high cell density. This prompted us to investigate the antihyphal efficacy of certain bacterial QSMs through virtual docking against seminal drug targets viz., CYCc and RAS1 that have been reported to be the hallmark players in C. albicans dimorphic virulence cascade. In this backdrop, 64 QSMs belonging to 5 different bacterial QS signaling systems were subjected to initial virtual screening with farnesol as reference. Data of the virtual screening unveiled that QSMs belonging to diketopiperazines (DKPs) i.e., 3-benzyl-6-isobutylidene-2, 5-piperazinedione (QSSM 1157) and cyclo(L-Pro-L-Leu) (QSSM 1112) as potential inhibitors of CYCc and RAS1 with binding energy of -8.2 and -7.3 kcal mol-1, respectively. Further, the molecular dynamics simulations (for 50ns) of CYCc - QSSM 1157 and RAS1- QSSM 1112 complexes revealed the mean ligand RMSD values of 0.35 and 0.27 Å, respectively which endorsed the rigid nature, less fluctuation in binding stiffness and conformation of binding complexes. Furthermore, the identified two QSMs were found to be good in solubility, absorption and permeation, and less-toxic in nature, as revealed by pharmacokinetics and toxicity analyses. In addition, the in vitro antihyphal assays using liquid and solid media, germ-tube experiment as well as microscopic analysis strongly validated DKP - QSSM 1112 as a promising inhibitor of hyphal transition. Taken together, the present study unequivocally proves that diketopiperazines can be used as potent inhibitors of C. albicans’ virulence dimorphism.