Identification of novel prolyl oligopeptidase inhibitors from resin of Boswella papyrifera (Del.) Hochst. and their mechanism: Virtual and biochemical studies.

Prolyl endopeptidase or prolyl oligopeptidase (PEP or POP) is highly expressed in brain, and associated with autism spectrum disorders, dementia, aging and various psychological disorders, such as schizophrenia, mania, and neurodegeneration. To design highly potent and novel POP inhibitors, structure-based virtual screening was carried out using pharmacophore modeling and molecular docking studies. The docking based active compounds [incensole (1), incensole acetate (2), incensone (3), incensfuran (4), and epi-incensole acetate (5)] were selected and their dynamic behavior was studied through molecular dynamic simulation. Later, the top-ranked [predicted active, (1-5)] and lower-ranked [predicted in-active, (6-10)] compounds were tested by in-vitro assay. The in-vitro results showed that all top-ranked compounds (1-5) found significantly active against POP enzyme with IC50 values in range of 3.1 ± 0.45 to 24.4 ± 1.16 μM, while lower-ranked (6-10) were inactive, indicated accuracy of docking results. Kinetics studies on all active compounds 1-5 were carried out to investigate their mode of inhibition and dissociation constants Ki. All compounds showed competitive behaviors with Ki values in the range of 0.92-8.12 μM. The study resulted in the identification of five (1-5) diterpene based molecules from natural sources that significantly inhibit the activity of POP by competitive mode of inhibition.