Anilino-1,4-naphthoquinones as potent mushroom tyrosinase inhibitors: in vitro and in silico studies

Abstract

Tyrosinase, a pivotal enzyme in melanin synthesis, is a primary target for the development of depigmenting agents. In this work, in vitro and in silico techniques were employed to identify novel tyrosinase inhibitors from a set of 12 anilino-1,4-naphthoquinone derivatives. Results from the mushroom tyrosinase activity assay indicated that, among the 12 derivatives, three compounds (1, 5, and 10) demonstrated the most significant inhibitory activity against mushroom tyrosinase, surpassing the effectiveness of the kojic acid. Molecular docking revealed that all studied derivatives interacted with copper ions and amino acid residues at the enzyme active site. Molecular dynamics simulations provided insights into the stability of enzyme-inhibitor complexes, in which compounds 1, 5, and particularly 10 displayed greater stability, atomic contacts, and structural compactness than kojic acid. Drug likeness prediction further strengthens the potential of anilino-1,4-naphthoquinones as promising candidates for the development of novel tyrosinase inhibitors for the treatment of hyperpigmentation disorders.

Keywords: Tyrosinase inhibition; anilino-14-naphthoquinones; molecular docking; molecular dynamics simulations.

Graphical abstract

Figure 1.

(A) Crystal structure of tyrosinase (PDB ID: 2Y9X²). The catalytic histidine residues and copper ions (CuA and CuB) were labelled in purple and orange, respectively. (B) Melanogenesis pathway produces eumelanin and pheomelanin. (C) Chemical structures of KA, lawsone, plumbagin, and 2-phenyl-1,4-naphthoquinones.

Figure 2.

Chemical structure of 12 anilino-1,4-naphthoquinone derivatives.

Figure 3.

Mushroom tyrosinase inhibitory activity of 12 anilino-1,4-naphthoquinone derivatives at a concentration of 160 μM. Data are shown as the mean ± standard error of the mean (SEM) (n = 3). **p < 0.01, ***p < 0.001, and ****p < 0.0001 vs. control.

Figure 4.

Tyrosinase inhibitory activity of (A) compound 1, (B) compound 5, (C) compound 10, and (D) KA using l-DOPA as a substrate. Data are shown as the mean ± SEM (n = 3). *p < 0.05, **p < 0.01, ***p < 0.001, and ****p < 0.0001 vs. control.

Figure 6.

Time evolution of (A) RMSD and (B) Rg of compounds 1, 5, 10, and KA in complexes with tyrosinase.

Figure 5.

2D interaction profile of (A) compound 1, (B) compound 5, (C) compound 10, and (D) KA in complexes with tyrosinase.

Figure 7.

Time evolution of (A) #Contacts and (B) SASA of compounds 1, 5, 10, and KA in complexes with tyrosinase.

Figure 8.

(Left) ΔG_{bind, res} of compounds 1, 5, 10, and KA in complexes with tyrosinase. (Right) Representative structures showing the ligand orientation in the catalytic site drawn from the last 5 ns MD snapshots. The copper ions were hidden. The residues involved in the ligand binding (energy stabilisation of ≤ −1.0 kcal/mol) were coloured according to their ΔG_{bind, res} values, where the highest to lowest ΔG_{bind, res} values were shaded from yellow to red, respectively.