Cytotoxicity of Grewia tenax on A375 human melanoma cells, and its antimelanogenesis and antioxidant activities

As part of our continuous efforts in screening the bioactivities of Saudi Arabian plants, we here characterize the in vitro cytotoxicity of Grewia tenax (Forssk.) Fiori on the human melanoma A375 cell line with the SRB [1] and Alamar Blue [2] methods, its inhibition of melanogenesis by mushroom tyrosinase enzyme [3] and its free radical scavenging activity against the synthetic stable radical DPPH [4]. The active secondary metabolites were dereplicated by means of HPTLC analyses. Only the chloroform extract of G. tenax had significant inhibitory effects on the cytotoxicity assays (IC₅₀= 45 – 83 µg/ml). Cell cycle analyses showed that this extract arrested the cell cycle at S phase as well as inducing the activity of caspases 3/7. The inhibitory activity upon tyrosinase enzyme was restricted to one of the fractions of the hexane extract (IC₅₀ = 59 µg/ml). HPTLC analyses confirmed that it contained lupeol (main component) and beta-sitosterol (minor amounts). Lupeol is here described in this plant species for the first time and is already a known inhibitor of this enzyme⁵. Based on the results of the DPPH assay the hexane and chloroform fractions were devoid of any radical scavenging activity and only one of the fractions of the methanol extract demonstrated a significant activity (EC₅₀ = 10 µg/ml). Further studies are carried out to identify further active principles and opportunities for the use of this popular herbal medicinal plant in the context of this research.

Acknowledgements: AA and AY were sponsored by The Ministry of Higher Education and are thankful to the Arabian Cultural Bureau.

Keywords: Cytotoxicity, tyrosinase, melanoma, antioxidant activity, natural product.

References:

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No conflict of interest has been declared by the author(s).