A new cytotoxic sesquiterpene lactone from Euphorbia microsphaera Boiss against human breast cancer (MCF-7) and human fibrosarcoma (HT1080) cells

A new guaianolide sesquiterpene lactone with cytotoxic properties was isolated from Euphorbia microsphaera Boiss. To determine the highest active fraction and isolate bioactive compounds, a bioassay guided fractionation approach was used. The general toxicity properties of the plant's extracts and fractions (fr_1-10) were assessed against Artemia salina, Oryzeaphilus mercator, and Tribolium castaneum. Cytotoxic activities were investigated against normal human foreskin fibroblasts and two malignant cell lines, including human breast cancer (MCF-7) and human fibrosarcoma cells (HT1080) using the MTT assay at different time points of 24, 48, and 72 h. Single crystal X-ray diffraction (SC-XRD) and mass spectrometry data were used to determine the structure of the active guaianolide sesquiterpene lactone (3aR,4S,4aS,5R,7aS,9aS)-5-hydroxy-5,8-dimethyl-3-methylene-2-oxo-2,3,3a,4,4a,5,6,7,7a, 9a decahydroazuleno [6,5-b] furan-4-yl acetate (named aryanin). Chloroformic fraction 7 (fr₇, LC₅₀ = 93.50 μg/mL for general toxicity) had the highest toxicity result, with a mortality rate of more than 50% for both insect species after 12 h at 15 mg/mL. The highest cytotoxicity of aryanin was observed on 24 h treated MCF-7 with an IC₅₀ of 13.81 μg/mL. After 24 h, the inhibition of MCF-7 cell proliferation was 92%-94% at concentrations of 25-50 μg/mL, respectively. On MCF-7, the IC₅₀ was found to be 49.35 μg/mL after 72 h. This compound had a considerable cytotoxicity (IC₅₀ ≤ 12.5 μg/mL, 24 h) on human foreskin fibroblasts. In contrast to the MCF-7 cell line, the proliferation of human foreskin fibroblasts was increased after 72 h.