chondramide-a and Breast-Neoplasms

Targeting the actin cytoskeleton (CSK) of cancer cells offers a valuable strategy in cancer therapy. There are a number of natural compounds that interfere with the actin CSK, but the mode of their cytotoxic action and, moreover, their tumor-specific mechanisms are quite elusive. We used the myxobacterial compound Chondramide as a tool to first elucidate the mechanisms of cytotoxicity of actin targeting in breast cancer cells (MCF7, MDA-MB-231). Chondramide inhibits cellular actin filament dynamics shown by a fluorescence-based analysis (fluorescence recovery after photobleaching (FRAP)) and leads to apoptosis characterized by phosphatidylserine exposure, release of cytochrome C from mitochondria and finally activation of caspases. Chondramide enhances the occurrence of mitochondrial permeability transition (MPT) by affecting known MPT modulators: Hexokinase II bound to the voltage-dependent anion channel (VDAC) translocated from the outer mitochondrial membrane to the cytosol and the proapoptotic protein Bad were recruited to the mitochondria. Importantly, protein kinase C-ɛ (PKCɛ), a prosurvival kinase possessing an actin-binding site and known to regulate the hexokinase/VDAC interaction as well as Bad phosphorylation was identified as the link between actin CSK and apoptosis induction. PKCɛ, which was found overexpressed in breast cancer cells, accumulated in actin bundles induced by Chondramide and lost its activity. Our second goal was to characterize the potential tumor-specific action of actin-binding agents. As the nontumor breast epithelial cell line MCF-10A in fact shows resistance to Chondramide-induced apoptosis and notably express low level of PKCɛ, we suggest that trapping PKCɛ via Chondramide-induced actin hyperpolymerization displays tumor cell specificity. Our work provides a link between targeting the ubiquitously occurring actin CSK and selective inhibition of pro-tumorigenic PKCɛ, thus setting the stage for actin-stabilizing agents as innovative cancer drugs. This is moreover supported by the in vivo efficacy of Chondramide triggered by abrogation of PKCɛ signaling shown in a xenograft breast cancer model.

Topics: Actin Cytoskeleton; Actins; Animals; Antineoplastic Agents; Apoptosis; bcl-Associated Death Protein; Binding Sites; Breast Neoplasms; Cell Line, Tumor; Cell Proliferation; Cytochromes c; Depsipeptides; Female; Fluorescence Recovery After Photobleaching; Hexokinase; Humans; MCF-7 Cells; Membrane Potential, Mitochondrial; Mice; Mice, SCID; Mitochondria; Phosphatidylserines; Protein Kinase C; Signal Transduction; Transplantation, Heterologous; Voltage-Dependent Anion Channels

Inhibiting angiogenesis is a major approach in tumour therapy. To combat angiogenesis, the tubulin cytoskeleton has emerged as an interesting target in many pre- and clinical studies. Contrarily, the actin cytoskeleton has been largely neglected as a potential drug target in angiogenesis. However, due to the development of drug resistances, new therapeutic strategies are always needed in tumour treatment. Therefore, the therapeutic potential of actin-binding small molecules is of particular interest.. We investigate the impact of chondramide (Ch), an actin polymerizing myxobacterial compound, on angiogenesis and underlying signalling. Chondramide treatment not only reduces the migration of endothelial cells but also the maturation of endothelial tube networks on matrigel. These observations can partly be explained by a disintegration of stress fibres due to aggregation and subsequent accumulation of actin in cellular structures known as 'aggresomes'. Chondramide treatment impairs the maturation of focal adhesions and reduces the amount of active β1 integrin at the cell surface. Accordingly, signalling events downstream of focal adhesions are reduced. Thus, we observed that the activity of Src and downstream factors Rho-GTPases Rac1 and Rho is reduced upon Ch treatment. In vivo, Ch was well tolerated in mice and vascularization of a tumour xenograft as well as of the developing retina was significantly reduced.. Chondramide diminishes angiogenesis via two ways: (i) the disintegration of stress fibres and (ii) the reduction of promigratory signals. Our findings highlight Ch as a novel class of therapeutic lead compound with anti-angiogenic potential.

Topics: Actin Cytoskeleton; Angiogenesis Inhibitors; Animals; Bacterial Proteins; Breast Neoplasms; Cell Adhesion; Cell Line, Tumor; Cell Movement; Cell Proliferation; Depsipeptides; Dose-Response Relationship, Drug; Female; Focal Adhesions; Human Umbilical Vein Endothelial Cells; Integrin beta1; Mice, SCID; Neovascularization, Pathologic; Neovascularization, Physiologic; rac1 GTP-Binding Protein; rho GTP-Binding Proteins; Signal Transduction; src-Family Kinases; Stress Fibers; Time Factors; Xenograft Model Antitumor Assays

A major player in the process of metastasis is the actin cytoskeleton as it forms key structures in both invasion mechanisms, mesenchymal and amoeboid migration. We tested the actin binding compound Chondramide as potential anti-metastatic agent.. In vivo, the effect of Chondramide on metastasis was tested employing a 4T1-Luc BALB/c mouse model. In vitro, Chondramide was tested using the highly invasive cancer cell line MDA-MB-231 in Boyden-chamber assays, fluorescent stainings, Western blot and Pull down assays. Finally, the contractility of MDA-MB-231 cells was monitored in 3D environment and analyzed via PIV analysis.. In vivo, Chondramide treatment inhibits metastasis to the lung and the migration and invasion of MDA-MB-231 cells is reduced by Chondramide in vitro. On the signaling level, RhoA activity is decreased by Chondramide accompanied by reduced MLC-2 and the stretch induced guanine nucleotide exchange factor Vav2 activation. At same conditions, EGF-receptor autophosphorylation, Akt and Erk as well as Rac1 are not affected. Finally, Chondramide treatment disrupted the actin cytoskeleton and decreased the ability of cells for contraction.. Chondramide inhibits cellular contractility and thus represents a potential inhibitor of tumor cell invasion.

Topics: Actin Cytoskeleton; Animals; Antineoplastic Agents; Breast Neoplasms; Cardiac Myosins; Cell Line, Tumor; Cell Movement; Contractile Proteins; Depsipeptides; Female; Gene Expression Regulation, Neoplastic; Humans; Injections, Intravenous; Lung; Lung Neoplasms; Mammary Glands, Animal; Mammary Neoplasms, Experimental; Mice; Myosin Light Chains; Peptides, Cyclic; Proto-Oncogene Proteins c-vav; rhoA GTP-Binding Protein; Signal Transduction