The cytotoxicity of 4'-leucine-avarone, amino derivative of the sponge Dysidea avara secondary metabolite avarone, was evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay in vitro against seven human solid tumours for the first time. The compound tested induced dose-dependent cytotoxic response in all cancer cells showing better activity towards the lung A-549 and colon HT-29 cell lines (IC50 7.40 μM and 9.62 μM, respectively) than towards the breast adenocarcinoma ER positive MCF-7 and ER negative MDA-MB-231 cells (IC50 11.64 μM and 17.31 μM, respectively), the prostate adenocarcinoma PC-3 and epiteloid cervix carcinoma HeLa cells (IC50 14.24 μM and 15.54 μM, respectively). No toxicity was found towards the foetal lung fibroblast MRC-5 cell line at the concentrations used. According to experimental data obtained, the sesquiterpenoid quinone structure of avarone may inspire development of new drug-like substances with improved cytotoxicity on lung cancer in humans.