Cytotoxicity Assay of Antitumor Compounds

Cytotoxicity was tested by the SRB assay kit. Human melanoma A2058 cells were transferred to 96-well plates at a concentration of 1 × 10⁴ cells per well and treated with lepadin A (1), doxorubicin (2) and cisplatin (2) from 2 nM to 100 µM starting from DMSO stock solutions of each compound at concentration of 5 mg/mL. After 24 h, cells were fixed and stained according to manufacturer’s instructions. The optical density was determined at 565 nm and cytotoxicity was calculated as reported by [16 (link)]. Spectrophotometric measurements were performed using EZ Read 2000 microplate readers (Biochrom, Cambridge, United Kingdom).