Comparison of the cytotoxicity and antimicrobial activity of several isohexenylnaphthazarins

Abstract

Shikonins, alkannins and derivatives thereof are natural, lipophilic red pigments and found in many species of the Boraginaceae family. Since many centuries, they are traditionally used for the treatment of wounds and have been shown to possess wound-healing, anti-inflammatory, anti-microbial, anti-thrombotic and anti-cancer activities [1]. The cytotoxicity of several shikonins (shikonin, acetylshikonin, β-hydroxyisovalerylshikonin, isobutyrylshikonin, 2-methyl-n-butyryl-shikonin, deoxyshikonin, dimethylacrylshikonin, epoxyshikonin, and isovalerylshikonin) and alkannins (alkannin, acetylalkannin, β-hydroxyisovalerylalkannin, isobutyrylalkannin, α-methyl-butyryl-alkannin, dimethylacrylalkannin propionylalkannin and teracrylalkannin) was determined using the XTT viability assay and human CCRF-CEM leukemia, MDA-MB-231 breast cancer, U251 glioblastoma and HCT 116 colon cancer cells. Most IC50 values of shikonins were in a range of 0.1 to 10µM, whereby, the highest activity was found for shikonin. IC50 values of alkannins varied from 0.4 to 70µM indicating that shikonin derivatives possess a higher cytotoxic potential than alkannins. Dimethylacrylalkannin exhibited no activity up to 100µg/ml in contrast to dimethylacrylshikonin. Moreover, the anti-microbial activity of the alkannin derivatives and acetylshikonin against nine microorganisms (Staphylococcus aureus, S. epidermidis, Escherichia coli, Enterobacter cloacae, Klebsiella pneumonia, Pseudomonas aeruginosa, Candida albicans, C. tropicalis and C. glabrata) was examined by the disc diffusion method. The most active derivatives were alkannin, acetylshikonin, β-hydroxyisovalerylalkannin and isobutyrylalkannin. Also in this case, acetylshikonin exhibited higher activity than the respective alkannin derivative.