Silvestrol is a specific eIF4A-targeting translation inhibitor. Silvestrol exhibits significant cytotoxic activity against many human cancer cell lines, such as lung, prostate, and breast cancer with IC50 values ranging from 1 to 7 nM[1]. Silvestrol significantly reduces the number of LNCaP cell colonies. Silvestrol (30 nM, 120 nM) induces apoptosis in LNCaP cells, through the mitochondrial pathway. Apaf-1, Caspase-2, caspase-9, and caspase-10 are involved in Silvestrol-induced apoptosis but caspase-3 and 7 are not[2]. Silvestrol (50 nM) exerts an immediate inhibitory effect and causes near-static cell index compared with the control cells. Silvestrol (6.25 nM) enhances proliferation more than the vehicle control-treated cells, whereas a higher concentration of Silvestrol (50 nM) can inhibit cell proliferation. Silvestrol and episilvestrol display synergistic effects in combination with cisplatin[3]. Silvestrol induces caspase-3 activation and apoptotic cell death in a time- and dose-dependent manner. Silvestrol-mediated cell death is attenuated in ATG7-null mouse embryonic fibroblasts (MEFs) lacking a functional autophagy protein.
Silvestrol (1.5 mg/kg, i.p.) does not adversely affect production of human IgG by xenografted B-lymphocytes in mice. Silvestrol significantly prolongs survival compared to vehicle. There is no such lymphocyte infiltration detected in the spleens of any of the Silvestrol-treated mice, and nor do these animals exhibit any other obvious signs of lymphoma upon necropsy.
The Apo-ONETM homogeneous caspase-3/7 assay kit is used to measure the activities of caspase-3 and -7. Cells (7×104 cells/mL) are treated with Silvestrol (15 nM, 30 nM, 60 nM, 120 nM, and 240 nM) or etoposide for 24 h in a black 96-well plate. Etoposide, which is known to activate caspases-3/7 in LNCaP cells, is used as a positive control for this assay. At the end of the treatment, lysis buffer and the substrate (Z-DEVD-rhodamine 110) are mixed and added to the cells. Upon sequential cleavage and removal of the DEVD peptides by caspase-3 and -7 activity and excitation at 499 nm, the rhodamine 110-leaving group becomes intensely fluorescent. The emission maximum is 521 nm. The amount of fluorescent product generated is proportional to the amount of caspase-3 and -7 cleavage activity present in the sample. The samples are measured in triplicate. Caspase-3 and -7 activity is indicated by net fluorescence[2].
