In Vitro and In Silico Studies of Two 1,4-Naphthoquinones and Their Topical Formulation in Bigels

Background: 1,4-Naphthoquinones (1,4-NQs) are secondary plant metabolites with numerous biological activities. 1,4-NQs display low water solubility and poor bioavailability. Bigels are a new technology with great potential, which are designated as drug delivery systems. Biphasic bigels consisting of solid and liquid components represent suitable formulations improving diffusion and bioavailability of NQs into the skin. Objective: We evaluated the in silico and in vitro activity of 5,8-dihydroxy-1,4-naphthoquinone (M1) and 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone (M2) on elastase and assessed their cytotoxicity towards COLO38 melanoma cells. The 1,4-NQs were loaded into bigels for topical application. Methods: Molecular docking was performed, and cytotoxicity was evaluated on COLO38 cells using the resazurin assay. M1 and M2 were separately incorporated into bigels consisting of hydrogel organogel with sweet almond oil as the non-polar solvent and span 65 as an organogelator. Their rheological behavior and microscopic properties were characterized. The diffusion kinetics and permeation of 1,4-NQs from bigels were studied by a paddle-over-extraction cell and a “Franz cell” in vitro permeation model. Results: Molecular docking data predicted high interactions between elastase and ligands. Hydrogen bonds with LYS233 were observed for M1, M2, and phosphoramidon (positive control). The average binding energies were -8.5 and -9.7 kcal/mol for M1 and M2 and -12.6 kcal/mol for phosphoramidon. M1 and M2 inhibited the elastase activity by 58.9 and 56.6%, respectively. M1 and M2 were cytotoxic towards COLO38 cells (IC50 value: 2.6 and 9.8 μM). The M1 release from bigels was faster and more efficient than that of M2. Conclusion: M1 and M2 are promising for skin disease treatment. Biphasic organogel-hydrogel bigels are efficient and safe formulations to overcome their low bioavailability.