In the present study, the authors evaluated the anticancer mechanism of vanadium, a dietary micronutrient and an important pharmacological agent, on a defined model of chemically induced rat mammary carcinogenesis in vivo and on human breast cancer cell line MCF7 in vitro. Female Sprague-Dawley rats were treated with 7,12-dimethylbenz(a)anthracene (0.5 mg/100 g body weight) by a single tail vein injection in an oil emulsion to induce mammary preneoplasia. Vanadium (ammonium monovanadate) at a concentration of 0.5 ppm (4.27 lmol/l) was supplemented in drinking water and given ad libitum to the experimental groups for 24 weeks. Histological finding showed substantial repair of hyperplastic lesions. There was a significant reduction in incidence, multiplicity (34%, p < 0.01), size of palpable mammary tumors and delay in mean latency period of tumor appearance. Immunohistochemical analysis in vivo indicated a decrease in cell proliferation (24.68% p < 0.05) and an increase among the TUNEL-positive apoptotic cells along with strong expressions of p53 and Bax, and downregulation of Bcl2 proteins in the mammary tissue of vanadium-treated animals. Further, MCF7 cells were cultured in minimal essential medium and were treated with 100, 175 and 250 lM of vanadium (ammonium monovanadate) for 36 hr. Exposure of MCF7 cells to vanadium led to induction of apoptosis in a dose-dependent manner. It was found further that vanadium treatment brought about a prominent cell cycle arrest and chromosomal condensation, leading to apoptosis (42.62%, p < 0.05). Results of both the in vivo and in vitro study demonstrate that vanadium has the potential to be developed into an anti-breast cancer drug in the near future. ' 2006 Wiley-Liss, Inc.

With the completion of the human genome project, analysis of enriched phosphotyrosyl proteins from epidermal growth factor (EGF)-induced phosphotyrosine proteome permits the identification of novel downstream substrates of the EGF receptor (EGFR). Using cICAT-based LC-MS/MS method, we identified and relatively quantified the tyrosine phosphorylation levels of 21 proteins between control and EGF-treated A431 human cervical cancer cells. Of these, Endofin, DCBLD2, and KIAA0582 were validated to be novel tyrosine-phosphorylation targets of EGF signaling and Iressa, a highly selective inhibitor of EGFR. In addition, EGFR activity was shown to be necessary for EGF-induced localization of Endofin, an FYVE domain-containing protein regulated by phosphoinositol lipid and engaged in endosome-mediated receptor modulation. Although several groups have conducted phosphoproteomics of EGF signaling in recent years, our study is the first to identify and validate Endofin, DCBLD2, and KIAA0582 as part of a complex EGF phosphotyrosine signaling network. These novel data will provide new insights into the complex EGF signaling and may have implications on target-directed cancer therapeutics.

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Little knowledge exists about the mechanisms by which estrogen can impede chemotherapy-induced cell death of breast cancer cells. 17β-Estradiol (E 2 ) hinders cytotoxic drug-induced cell death in estrogen receptor-positive (ER + ) breast cancer cells. We noted that the activity of the proapoptotic mixed lineage kinase 3 (MLK3) kinase was relatively higher in estrogen receptor-negative (ER − ) breast tumors, suggesting that E 2 might inhibit MLK3 activity. The kinase activities of MLK3 and its downstream target, c-Jun NH 2 -terminal kinase, were rapidly inhibited by E 2 in ER + but not in ER − cells. Specific knockdown of AKT1/2 prevented MLK3 inhibition by E 2 , indicating that AKT mediated this event. Furthermore, MLK3 inhibition by E 2 involved phosphorylation of MLK3 Ser 674 by AKT, attenuating the proapoptotic function of MLK3. We found that a pan-MLK inhibitor (CEP-11004) limited Taxol-induced cell death and that E 2 accentuated this limitation. Taken together, our findings indicate that E 2 inhibits the proapoptotic function of MLK3 as a mechanism to limit cytotoxic drug-induced death of ER + breast cancer cells.