lignans and Hemangiosarcoma

The Shb adapter protein is an Src homology 2-domain containing signaling intermediate operating downstream of several tyrosine kinase receptors, including vascular endothelial growth factor receptor-2. Shb is multifunctional and apoptosis is one response that Shb regulates. Inhibition of angiogenesis can be used in cancer therapy, and one way to achieve this is by inducing endothelial cell apoptosis. The angiosarcoma cell line SVR is of endothelial origin and can be used as a tool for studying in vivo inhibition of angiogenesis, and we thus employed an Shb-knockdown strategy using an inducible lentiviral system to reduce Shb levels in SVR cells and to study their responses. Shb knockdown increases the susceptibility of SVR cells to the apoptotic agents, cisplatin and staurosporine. Simultaneously, Shb knockdown causes reduced focal adhesion kinase (FAK) activation, monitored as phosphorylation of the regulatory residues tyrosines 576/577. No detectable effects on Akt or extracellular signal-regulated kinase activity were noted. The altered FAK activity coincided with an elongated cell phenotype that was particularly noticeable in the presence of staurosporine. In order to relate the effects of Shb knockdown to in vivo tumorigenicity, cells were exposed to the angiogenesis inhibitor honokiol, and again the cells with reduced Shb content exhibited increased apoptosis. Tumor growth in vivo was strongly reduced in the Shb-knockdown cells upon honokiol treatment. It is concluded that Shb regulates apoptosis and cell shape in tumor endothelial cells via FAK, and that Shb is a potential target for inhibition of angiogenesis.

Topics: Animals; Antineoplastic Agents; Antineoplastic Agents, Phytogenic; Apoptosis; Biphenyl Compounds; Cell Line, Tumor; Cisplatin; Endothelial Cells; Enzyme Inhibitors; Extracellular Signal-Regulated MAP Kinases; Focal Adhesion Protein-Tyrosine Kinases; Hemangiosarcoma; In Vitro Techniques; Lignans; Mice; Mice, Nude; Mutagenesis; Neoplasm Transplantation; Neovascularization, Pathologic; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Staurosporine

Natural products comprise a major source of small molecular weight angiogenesis inhibitors. We have used the transformed endothelial cell line SVR as an effective screen of natural product extracts to isolate anti-angiogenesis and anti-tumor compounds. Aqueous extracts of Magnolia grandiflora exhibit potent activity in our SVR proliferation assays. We found that the small molecular weight compound honokiol is the active principle of magnolia extract. Honokiol exhibited potent anti-proliferative activity against SVR cells in vitro. In addition, honokiol demonstrated preferential inhibition of primary human endothelial cells compared with fibroblasts and this inhibition was antagonized by antibodies against TNF alpha-related apoptosis-inducing ligand. In vivo, honokiol was highly effective against angiosarcoma in nude mice. Our preclinical data suggests that honokiol is a systemically available and non-toxic inhibitor of angiogenesis and should be further evaluated as a potential chemotherapeutic agent.

Topics: Angiogenesis Inhibitors; Animals; Apoptosis; Biphenyl Compounds; Cell Division; Cell Line; Cell Line, Transformed; Endothelium, Vascular; Hemangiosarcoma; Humans; Lignans; Magnolia; MAP Kinase Signaling System; Mice; Mice, Nude; Phytotherapy; Plant Extracts; Transplantation, Heterologous