Bufalin

Abstract: Bufadienolides bufalin and cinobufagin are cardiotonic steroids isolated from the skin and parotid venom glands of the toad Bufo bufo gargarizans Cantor. They have been shown to induce a wide spectrum of cancer cell apoptosis. However, the detailed molecular mechanisms of inducing apoptosis in hepatocellular carcinoma (HCC) are still unclear. In the present study, the apoptosis-inducing effect of bufalin and cinobufagin on HCC cell line HepG(2) was investigated. We found bufalin and cinobufagin induced marked changes in apoptotic morphology and significantly increased the proportion of apoptotic cells. This apoptotic induction was associated with an increase in Fas, Bax and Bid expression, a decrease in Bcl-2 expression, disruption of the mitochondrial membrane potential, release of cytochrome c, activation of caspase-3, -8, -9 and -10, and the cleavage of poly(ADP-ribose)polymerase (PARP), which indicated that bufalin and cinobufagin induced apoptosis through both Fas- and mitochondria-mediated pathways. In addition, caspase activation during bufalin- and cinobufagin-induced apoptosis was further confirmed by caspase-3 inhibitor Z-DEVD-FMK, caspase-8 inhibitor Z-IETD-FMK, caspase-9 inhibitor Z-LEHD-FMK and caspase-10 inhibitor Z-AEVD-FMK. The results showed that bufalin- and cinobufagin-induced apoptosis was blocked by these inhibitors and particularly by caspase-10 inhibitor. Taken together, bufalin and cinobufagin induce apoptosis of HepG(2) cells via both Fas- and mitochondria-mediated pathways, and a Fas-mediated caspase-10-dependent pathway might play a crucial role.

Abstract: Virtually all transcription factors partner with coactivators that recruit chromatin remodeling factors and interact with the basal transcription machinery. Coactivators have been implicated in cancer cell proliferation, invasion, and metastasis, including the p160 steroid receptor coactivator (SRC) family composed of SRC-1 (NCOA1), SRC-2 (TIF2/GRIP1/NCOA2), and SRC-3 (AIB1/ACTR/NCOA3). Given their broad involvement in many cancers, they represent candidate molecular targets for new chemotherapeutics. Here, we report on the results of a high-throughput screening effort that identified the cardiac glycoside bufalin as a potent small-molecule inhibitor for SRC-3 and SRC-1. Bufalin strongly promoted SRC-3 protein degradation and was able to block cancer cell growth at nanomolar concentrations. When incorporated into a nanoparticle delivery system, bufalin was able to reduce tumor growth in a mouse xenograft model of breast cancer. Our work identifies bufalin as a potentially broad-spectrum small-molecule inhibitor for cancer.