Rabbit Anti-Human CDC25A (Phospho-Ser75) polyclonal antibody

To elucidate the molecular mechanisms of tamoxifen resistance in breast cancer, we performed gene array analyses and identified 366 genes with altered expression in four unique tamoxifen-resistant (TamR) cell lines vs the parental tamoxifen-sensitive MCF-7/S0.5 cell line. Most of these genes were functionally linked to cell proliferation, death and control of gene expression, and include FYN, PRKCA, ITPR1, DPYD, DACH1, LYN, GBP1 and PRLR. Treatment with FYN-specific small interfering RNA or a SRC family kinase inhibitor reduced cell growth of TamR cell lines while exerting no significant effect on MCF-7/S0.5 cells. Moreover, overexpression of FYN in parental tamoxifen-sensitive MCF-7/S0.5 cells resulted in reduced sensitivity to tamoxifen treatment, whereas knockdown of FYN in the FYN-overexpressing MCF-7/S0.5 cells restored sensitivity to tamoxifen, demonstrating growth-and survival-promoting function of FYN in MCF-7 cells. FYN knockdown in TamR cells led to reduced phosphorylation of 14-3-3 and Cdc25A, suggesting that FYN, by activation of important cell cycle-associated proteins, may overcome the anti-proliferative effects of tamoxifen. Evaluation of the subcellular localization of FYN in primary breast tumors from two cohorts of endocrine-treated ER+ breast cancer patients, one with advanced disease (N = 47) and the other with early disease (N = 76), showed that in the former, plasma membrane-associated FYN expression strongly correlated with longer progression-free survival (P < 0.0002). Similarly, in early breast cancer patients, membrane-associated expression of FYN in the primary breast tumor was significantly associated with increased metastasis-free (P < 0.04) and overall (P < 0.004) survival independent of tumor size, grade or lymph node status. Our results indicate that FYN has an important role in tamoxifen resistance, and its subcellular localization in breast tumor cells may be an important novel biomarker of response to endocrine therapy in breast cancer.

Multiple myeloma is still uncurable. Myeloma cells become resistant to common drugs and patients eventually die of tumour progression. Therefore, new targets and drugs are urgently needed. NVP-BGT226 is a novel, orally bioavailable small-molecule inhibitor of phosphoinositol-3-kinase and mammalian target of rapamycin. Here, we show that NVP-BGT226 inhibits growth in common myeloma cell lines and primary myeloma cells at nanomolar concentrations in a time-dependent and dose-dependent manner. Western blots for the detection of caspase 3 cleavage and annexin-V-fluorescein isothiocyanate/propidium iodide assays revealed induction of apoptosis in common myeloma cells lines. Induction of apoptosis was accompanied by upregulation of proapoptotic Bim and a moderate upregulation of Mcl-1 and Bad and a downregulation of Bcl-2, Bax and Bcl-Xl. Inhibition of cell growth was mainly due to inhibition of myeloma cell proliferation, as shown by the 5-bromo-2'-deoxyuridine assay. Cell cycle analysis revealed induction of cell cycle arrest in the G1 phase, which was due to downregulation of cyclin D1, cyclin D2, pRb and cdc25a. NVP-BGT226 inhibited phosphorylation of protein kinase B (Akt), P70S6k and 4E-BP-1 in a time-dependent and dose-dependent manner. Furthermore, we show that the stimulatory effect of insulin-like growth factor 1, interleukin-6 and conditioned medium of HS-5 stromal cells on myeloma cell growth is completely abrogated by NVP-BGT226. Overall, inhibition of phosphoinositol-3-kinase/mammalian target of rapamycin by NVP-BGT226 is highly effective, and NVP-BGT226 represents a potential new candidate for targeted therapy in multiple myeloma. Anti-Cancer Drugs 23:131-138 (C) 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins.