tetrocarcin-a and Breast-Neoplasms

Overexpression of the tight junction protein Junctional Adhesion Molecule-A (JAM-A) has been linked to aggressive disease in breast and other cancers, but JAM-targeting drugs remain elusive. Screening of a natural compound library identified the antibiotic Tetrocarcin-A as a novel downregulator of JAM-A and human epidermal growth factor receptor-2 (HER2) protein expression in breast cancer cells. Lysosomal inhibition partially rescued the downregulation of JAM-A and HER2 caused by Tetrocarcin-A, and attenuated its cytotoxic activity. Tetrocarcin-A treatment or JAM-A silencing reduced AKT and ERK phosphorylation, inhibited c-FOS phosphorylation at Threonine-232 (its transcriptional regulation site), inhibited nuclear localization of c-FOS, and downregulated expression of the inhibitor of apoptosis proteins (IAP). This was accompanied by Tetrocarcin-A-induced caspase-dependent apoptosis. To begin evaluating the potential clinical relevance of our findings, we extended our studies to other models. Encouragingly, Tetrocarcin-A downregulated JAM-A expression and caused cytotoxicity in primary breast cells and lung cancer stem cells, and inhibited the growth of xenografts in a semi-in vivo model involving invasion across the chicken egg chorioallantoic membrane. Taken together, our data suggest that Tetrocarcin-A warrants future evaluation as a novel cancer therapeutic by virtue of its ability to downregulate JAM-A expression, reduce tumorigenic signaling and induce apoptosis.

Topics: Aminoglycosides; Animals; Apoptosis; Breast Neoplasms; Cell Adhesion Molecules; Cell Growth Processes; Cell Line, Tumor; Chick Embryo; Down-Regulation; Humans; Immunohistochemistry; Inhibitor of Apoptosis Proteins; Lung Neoplasms; Lysosomes; MCF-7 Cells; Neoplastic Stem Cells; Receptor, ErbB-2; Receptors, Cell Surface; Xenograft Model Antitumor Assays

A survival kinase, Akt, is a downstream factor in the phosphatidylinositide-3'-kinase-dependent pathway, which mediates many biological responses including glucose uptake, protein synthesis and the regulation of proliferation and apoptosis, which is assumed to contribute to acquisition of malignant properties of human cancers. Here we find that an anti-tumor antibiotic, tetrocarcin A, directly induces apoptosis of human breast cancer cells. The apoptosis is accompanied by the activation of a proteolytic cascade of caspases including caspase-3 and -9, and concomitantly decreases phosphorylation of Akt, PDK1, and PTEN, a tumor suppressor that regulates the activity of Akt through the dephosphorylation of polyphosphoinositides. Tetrocarcin A affected neither expression of Akt, PDK1, or PTEN, nor did it affect the expression of Bcl family members including Bcl-2, Bcl-X(L), and Bax. These results suggest that tetrocarcin A could be a potent chemotherapeutic agent for human breast cancer targeting the phosphatidylinositide-3'-kinase/Akt signaling pathway.

Topics: 3-Phosphoinositide-Dependent Protein Kinases; Aminoglycosides; Antibiotics, Antineoplastic; Apoptosis; bcl-2-Associated X Protein; bcl-X Protein; Blotting, Western; Breast Neoplasms; Caspase 3; Caspase 9; Cell Line, Tumor; Cell Survival; Dose-Response Relationship, Drug; Enzyme Activation; Humans; Phosphatidylinositol 3-Kinases; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; PTEN Phosphohydrolase; Signal Transduction