Ana M. Tari

Silencing of Bcl-2 expression by small interfering RNA induces autophagic cell death in MCF-7 breast cancer cells

Apoptosis (programmed cell death type I) and autophagy (type II) are crucial mechanisms regulating cell death and homeostasis. The Bcl-2 proto-oncogene is overexpressed in 50-70% of breast cancers, potentially leading to resistance to chemotherapy, radiation and hormone therapy induced apoptosis. In this study, we investigated the role of Bcl-2 in autophagy in breast cancer cells. Silencing of Bcl-2 by siRNA in MCF-7 breast cancer cells downregulated Bcl-2 protein levels (>85%) and led to inhibition of cell growth (71%) colony formation (79%), and cell death (up to 55%) by autophagy but not apoptosis. Induction of autophagy was demonstrated by acridine orange staining, electron microscopy and an accumulation of GFP-LC3-II in preautopghagosomal and autophagosomal membranes in MCF-7 cells transfected with GFP-LC-3(GFP-ATG8). Silencing of Bcl-2 by siRNA also led to induction of LC-3-II, a hallmark of autophagy, ATG5 and Beclin-1 autophagy promoting proteins. Knockdown of ATG5 significantly inhibited Bcl-2 siRNA-induced LC3-II expression and the number of GFP-LC3-II-labeled autophagosome (punctuated pattern) positive cells and autophagic cell death (p

Therapeutic Efficacy of a Novel Focal Adhesion Kinase Inhibitor TAE226 in Ovarian Carcinoma

Focal adhesion kinase (FAK) overexpression is frequently found in ovarian and other cancers and is predictive of poor clinical outcome. In the current study, we characterized the biological and therapeutic effects of a novel FAK inhibitor, TAE226. Taxane-sensitive (SKOV3ip1 and HeyA8) and taxane-resistant (HeyA8-MDR) cell lines were used for in vitro and in vivo therapy experiments using TAE226 alone and in combination with docetaxel. Assessment of cytotoxicity, cell proliferation [proliferating cell nuclear antigen (PCNA)], angiogenesis (CD31), and apoptosis (terminal nucleotidyl transferase-mediated nick end labeling) were done by immunohistochemistry and immunofluorescence. In vitro, TAE226 inhibited the phosphorylation of FAK at both Y397 and Y861 sites, inhibited cell growth in a time- and dose-dependent manner, and enhanced docetaxel-mediated growth inhibition by 10- and 20-fold in the taxane-sensitive and taxane-resistant cell lines, respectively. In vivo, FAK inhibition by TAE226 significantly reduced tumor burden in the HeyA8, SKOV3ip1, and HeyA8-MDR models (46-64%) compared with vehicle-treated controls. However, the greatest efficacy was observed with concomitant administration of TAE226 and docetaxel in all three models (85-97% reduction, all P values <0.01). In addition, TAE226 alone and in combination with chemotherapy significantly prolonged survival in tumor-bearing mice. Even in larger tumors, combination therapy with TAE226 and docetaxel resulted in tumor regression. The therapeutic efficacy was related to reduced pericyte coverage, induction of apoptosis of tumor-associated endothelial cells, and reduced microvessel density and tumor cell proliferation. The novel FAK inhibitor, TAE226, offers an attractive therapeutic approach in ovarian carcinoma.

The role of cyclin-dependent kinase inhibitor p27Kip1 in anti-HER2 antibody-induced G1 cell cycle arrest and tumor growth inhibition.

Cyclin-dependent kinase (CDK) inhibitor p27Kip1 binds to the cyclin E·CDK2 complex and plays a major role in controlling cell cycle and cell growth. Our group and others have reported that anti-HER2 monoclonal antibodies exert inhibitory effects on HER2-overexpressing breast cancers through G1 cell cycle arrest associated with induction of p27Kip1 and reduction of CDK2. The role of p27Kip1 in anti-HER2 antibody-induced cell cycle arrest and growth inhibition is, however, still uncertain. Here we have provided several lines of evidence supporting a critical role for p27Kip1 in the anti-HER2 antibody-induced G1 cell cycle arrest and tumor growth inhibition. Induction of p27Kip1 and G1 growth arrest by anti-HER2 antibody, murine 4D5, or humanized trastuzumab (Herceptin®) are concentration-dependent, time-dependent, irreversible, and long-lasting. The magnitude of G1 cell cycle arrest induced by trastuzumab or 4D5 is well correlated with the level of p27Kip1 protein induced. Up-regulation of p27Kip1 and G1 growth arrest could no longer be removed with as little as 14 h of treatment with trastuzumab. Anti-HER2 antibody-induced p27Kip1 protein, G1 arrest, and growth inhibition persist at least 5 days after a single treatment. The magnitude of growth inhibition of breast cancer cells induced by anti-HER2 antibody closely parallels the level of p27Kip1 induced. Induced expression of exogenous p27Kip1 results in a p27Kip1 level-dependent G1 cell cycle arrest and growth inhibition similar to that obtained with anti-HER2 antibodies. Reducing p27Kip1 expression using p27Kip1 small interfering RNA blocks anti-HER2 antibody-induced p27Kip1 up-regulation and G1 arrest. Treatment with anti-HER2 antibody significantly increases the half-life of p27Kip1 protein. Inhibition of ubiquitin-proteasome pathway, but not inhibition of calpain and caspase activities, up-regulates p27Kip1 protein to a degree comparable with that obtained with anti-HER2 antibodies. We have further demonstrated that anti-HER2 antibody significantly decreases threonine phosphorylation of p27Kip1 protein at position 187 (Thr-187) and increases serine phosphorylation of p27Kip1 protein at position 10 (Ser-10). Expression of S10A and T187A mutant p27Kip1 protein increases the fraction of cells in G1 and reduces a further antibody-induced G1 arrest. Consequently, p27Kip1 plays an important role in the anti-HER2 antibody-induced G1 cell cycle arrest and tumor growth inhibition through post-translational regulation. Regulation of the phosphorylation of p27Kip1 protein is one of the post-translational mechanisms by which anti-HER2 antibody upregulates the protein.

Imaging bone metastases in breast cancer: techniques and recommendations for diagnosis

Bone is the most common site of distant metastases from breast carcinoma. The presence of bone metastases affects a patients prognosis, quality of life, and the planning of their treatment. We discuss recent innovations in bone imaging and present algorithms, based on the strengths and weaknesses of each technique, to facilitate the most successful and cost-effective choice of imaging studies for the detection of osseous metastases. Skeletal scintigraphy (bone scan) is very sensitive in the detection of osseous metastases and is recommended as the first imaging study in patients who are asymptomatic. Radiographs are recommended for the assessment of abnormal radionuclide uptake or the risk of pathological fracture and as initial imaging studies in patients with bone pain. MRI or PET-CT can be considered for cases of abnormal radionuclide uptake that are not addressed by radiography. Osseous metastases can lead to emergent situations, such as spinal-cord compression or impending fracture of a weight-bearing bone, and imaging guidelines are essential for early detection and initiation of appropriate therapy. The imaging method used in non-emergent situations, such as assessment of the ribs, sternum, pelvis, hips, and joints, should be guided by the strengths and limitations of each technique.

Programmed Cell Death 4 inhibits breast cancer cell invasion by increasing Tissue Inhibitor of Metalloproteinases-2 expression

High levels of the cyclooxygenase-2 (COX-2) protein have been associated with invasion and metastasis of breast tumors. Both prostaglandin E2 (PGE2) and interleukin-8 (IL-8) have been shown to mediate the invasive activity of COX-2 in breast cancer cells. Here we expand these studies to determine how COX-2 uses PGE2 and IL-8 to induce breast cancer cell invasion. We demonstrated that PGE2 and IL-8 decreased the expression of the tumor suppressor protein Programmed Cell Death 4 (PDCD4). We hypothesized that suppression of PDCD4 expression is vital to the invasive activity of PGE2 and IL-8. In MCF-7 cells overexpressing PDCD4 (MCF-7/PDCD4), PGE2 and IL-8 failed to induce invasion, in contrast to the parental MCF-7 cells, thus indicating that PDCD4 blocks breast cancer cell invasion. MCF-7/PDCD4 cells produced higher levels of the Tissue Inhibitor of Metalloproteinases-2 (TIMP-2) than the parental cells. Silencing TIMP-2 mRNA in MCF-7/PDCD4 cells reversed the anti-invasive effects of PDCD4, allowing PGE2 and IL-8 to induce the invasion of these cells. Here we report the novel findings that suppression of PDCD4 expression is vital for the invasive activity of COX-2 mediated by PGE2 and IL-8, and that PDCD4 increases TIMP-2 expression to inhibit breast cancer cell invasion.

Her2/neu induces all- trans retinoic acid (ATRA) resistance in breast cancer cells

We observed that all-trans retinoic acid (ATRA) inhibited the growth of MCF-7 breast cancer cells, but not those transfected with HER2/NEUor its transactivating ligand HEREGULIN. This suggests that Her2/neu causes breast cancer cells to be resistant to the growth inhibitory effects of ATRA. To confirm this observation, MDA-MB-453 and BT-474 cells, which have high levels of Her2/neu and are resistant to ATRA, were incubated with the trastuzumab (Herceptin™) antibody so that we could determine whether inhibition of the expression and function of Her2/neu would resensitize these cells to ATRA. Indeed, we found that MDA-MB-453 and BT-474 cells treated with trastuzumab were growth inhibitory by ATRA. We then determined whether Her2/neu uses Grb2 and Akt proteins to induce ATRA resistance. Liposome-incorporated Grb2 antisense oligonucleotides (L-Grb2) and a dominant negative (DN) AKTmutant were used to down-regulate Grb2 expression and inhibit Akt activity, respectively. When incubated with L-Grb2 or transfected with the DN AKTmutant, ATRA-resistant, Her2/neu-overexpressing cells became sensitive to ATRA. Our results indicate that Her2/neu utilizes Grb2 and Akt proteins to induce ATRA resistance in breast cancer cells. ATRA sensitivity was also correlated with RARα protein levels since higher RARα protein levels were observed in cells in which the Her2/neu pathway was inhibited.

GRB2: a pivotal protein in signal transduction.

The growth factor receptor-bound protein-2 (GRB2) is essential for multiple cellular functions. Inhibition of GRB2 function impairs developmental processes in various organisms and blocks transformation and proliferation of various cell types. GRB2 is most well known for its ability to link the epidermal growth factor receptor tyrosine kinase to the activation of RAS and its downstream kinases, ERK1,2. We recently reported that GRB2 does not link the HER2 tyrosine kinase to the activation of ERK1,2 but to another kinase, AKT. So, different tyrosine kinases may converge on GRB2 for signaling; however, they may not always use GRB2 to effect the same downstream kinases for cellular functions. It is likely that GRB2 will be found to regulate many more kinases because it plays such a pivotal role in signal transduction.

Growth inhibition of breast cancer cells by Grb2 downregulation is correlated with inactivation of mitogen-activated protein kinase in EGFR, but not in ErbB2, cells

Increased breast cancer growth has been associated with increased expression of epidermal growth factor receptor (EGFR) and ErbB2 receptor tyrosine kinases (RTKs). Upon activation, RTKs may transmit their oncogenic signals by binding to the growth factor receptor bound protein-2 (Grb2), which in turn binds to SOS and activates the Ras/Raf/MEK/mitogen-activated protein (MAP) kinase pathway. Grb2 is important for the transformation of fibroblasts by EGFR and ErbB2; however, whether Grb2 is also important for the proliferation of breast cancer cells expressing these RTKs is unclear. We have used liposomes to deliver nuclease-resistant antisense oligodeoxynucleotides (oligos) specific for the GRB2 mRNA to breast cancer cells. Grb2 protein downregulation could inhibit breast cancer cell growth; the degree of growth inhibition was dependent upon the activation and/or endogenous levels of the RTKs. Grb2 inhibition led to MAP kinase inactivation in EGFR, but not in ErbB2, breast cancer cells, suggesting that different pathways might be used by EGFR and ErbB2 to regulate breast cancer growth.

Cyclooxygenase-2 is essential for HER2/neu to suppress N- (4-hydroxyphenyl)retinamide apoptotic effects in breast cancer cells.

We reported that HER2/neu reduces the sensitivity of breast cancer cells to N-(4-hydroxyphenyl)retinamide (4-HPR) by suppressing nitric oxide production. We show that HER2/neu uses Akt to induce cyclooxygenase-2 (COX-2) expression and that inhibition of Akt or COX-2 increases 4-HPR-induced apoptosis and nitric oxide production. Apoptosis induced by the 4-HPR and COX-2 inhibitor combination, although unaffected by an anti-HER2/neu antibody, was reversed by the COX-2 product prostaglandin E2, indicating that COX-2 is a major mechanism by which HER2/neu suppresses 4-HPR apoptosis in breast cancer cells. Combining 4-HPR with COX-2 inhibitors may be a novel chemopreventive strategy against HER2/neu-overexpressing breast tumors.

TIMP-2 mediates the anti-invasive effects of the nitric oxide-releasing prodrug JS-K in breast cancer cells.

IntroductionTumor invasion and metastasis remain a major cause of mortality in breast cancer patients. High concentrations of nitric oxide (NO) suppress tumor invasion and metastasis in vivo. NO prodrugs generate large amounts of NO upon metabolism by appropriate intracellular enzymes, and therefore could have potential in the prevention and therapy of metastatic breast cancer.MethodsThe present study was designed to determine the effects of the NO-releasing prodrug O2-(2,4-dinitrophenyl) 1- [(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) on breast cancer invasion and the mechanisms involved. MDA-MB-231, MDA-MB-231/F10, and MCF-7/COX-2 were the three breast cancer cell lines tested. NO levels were determined spectrophotometrically using a NO assay kit. Invasion and the expression of matrix metalloproteinases (MMPs) and tissue inhibitor of MMPs were determined using Matrigel invasion assays, an MMP array kit and ELISAs. The activity and expression of extracellular signal-regulated kinase 1/2, p38, and c-Jun N-terminal kinase mitogen-activated protein kinases were determined using western blot analyses.ResultsUnder conditions by which JS-K was not cytotoxic, JS-K significantly decreased (P < 0.05) the invasiveness of breast cancer cells across the Matrigel basement membrane, which was directly correlated with NO production. JS-43-126, a non-NO-releasing analog of JS-K, had no effect on NO levels or invasion. JS-K increased (P < 0.05) TIMP-2 production, and blocking TIMP-2 activity with a neutralizing antibody significantly increased (P < 0.05) the invasive activity of JS-K-treated cells across Matrigel. JS-K decreased p38 activity, whereas the activity and the expression of extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinase were unaffected.ConclusionWe report the novel findings that JS-K inhibits breast cancer invasion across the Matrigel basement membrane, and NO production is vital for this activity. Upregulation of TIMP-2 production is one mechanism by which JS-K mediates its anti-invasive effects. JS-K and other NO prodrugs may represent an innovative biological approach in the prevention and treatment of metastatic breast cancer.