Kopetdaghinanes, pro-apoptotic hemiacetialic cyclomyrsinanes from Euphorbia kopetdaghi.

Euphorbia kopetdaghi grows wild in the Northeast parts of Iran. Phytochemical study of its aerial parts led to the isolation of two undescribed cyclomyrsinol macrocyclic diterpenes with a new tetrahydrofuran oxidation pattern containing a hemiacetal group named: kopetdaghinane A and B. The structure of the isolated compounds was elucidated by extensive spectroscopic methods. Cytotoxic activity of kopetdaghinane A was evaluated using standard MTT assay against MCF-7 breast cancer and OVCAR-3 ovary cells. HUVEC cells were used as a normal cell line for calculation of the selectivity index. The MTT showed cyclomyrsinol diterpene has a significant cytotoxic effect with good selectivity indexes against both cell lines but with more selectivity against MCF-7 cells. Apoptosis induction by cyclomyrsinol treatment was confirmed by annexin V-FITC/PI staining, and caspase-6 activation. Western blot analysis showed that the expression of Bcl-2 was noticeably decreased in response to kopetdaghinane A treatment, while the expression of Bax protein was increased. Moreover, the apoptotic effect of cyclomyrsinol was shown to be related to ROS production, and loss of mitochondrial membrane potential (ΔΨm). Taken together, these results showed that kopetdaghinane A inhibits the growth of MCF-7 breast cancer cells through the activation of the mitochondrial apoptotic pathway and may be considered as an investigational compound in breast cancer preclinical study.