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Oncogenic activation of the RET receptor tyrosine kinase is common in different human cancers. We found that the pyrazolo-pyrimidine PP1 inhibited RET-derived oncoproteins with a half maximal inhibitor concentration of 80 nM. Furthermore,RET/PTC3-transformed cells treated with 5 microM of PP1 lost proliferative autonomy and showed morphological reversion. PP1 prevented the growth of two human papillary thyroid carcinoma cell lines that carry spontaneous RET/PTC1 rearrangements and blocked anchorage-independent growth and tumorigenicity in nude mice of NIH3T3 fibroblasts expressing the RET/PTC3 oncogene. These findings suggest targeting RET oncogenes with PP1 or related compounds as a novel treatment strategy for RET-associated neoplasms. View Publication

STI571 is a 2-phenylalaminopyrimidine derivative that inhibits c-abl,Bcr-Abl,and platelet-derived growth factor receptor tyrosine kinases. Recently,inhibition of stem cell factor (SCF)-induced c-kit phosphorylation and cell proliferation by STI571 was reported in the human myeloid cell line MO7e. Because approximately 70% of acute myelogenous leukemia (AML) cases are c-kit positive,we evaluated in vitro effects of STI571 on c-kit-positive cell lines and primary AML blast cells. At concentrations textgreater5 microM,the drug marginally inhibited SCF-independent proliferation of cell lines and most of AML blasts. Treatment of AML cells with cytarabine and STI571 showed synergistic effect at low concentrations. Western blotting analysis documented a distinct band of M(r) 145,000 specific for c-kit in cell lines and in AML samples. There was no correlation between the level of the c-kit expression evaluated by Western blotting and percentage of c-kit-positive blasts as measured by flow cytometry. Neither in cell lines nor in primary AML cells,c-kit autophosphorylation was detectable under standard growth conditions. SCF-induced phosphorylation of c-kit in MO7e cells was inhibited by STI571. In a c-kit-positive AML-4 cell line,as well as in AML samples,c-kit phosphorylation was not induced by SCF exposure,suggesting that in these cases,the receptor could not be functionally activated. In conclusion,with the exception of MO7e,SCF did not induce phosphorylation of c-kit,and cell proliferation was not modulated in the presence of STI571. We did not detect any SCF-independent c-kit phosphorylation in our experimental systems. Consequently,STI571 exerted only a limited inhibitory effect on the cell growth. View Publication

The purpose of the present study was to characterize primitive epithelial progenitor populations present in adult normal human mammary tissue using a combination of flow cytometry and in vitro colony assay procedures. Three types of human breast epithelial cell (HBEC) progenitors were identified: luminal-restricted,myoepithelial-restricted and bipotent progenitors. The first type expressed epithelial cell adhesion molecule (EpCAM),alpha6 integrin and MUC1 and generated colonies composed exclusively of cells positive for the luminal-associated markers keratin 8/18,keratin 19,EpCAM and MUC1. Bipotent progenitors produced colonies containing a central core of cells expressing luminal markers surrounded by keratin 14+ myoepithelial-like cells. Single cell cultures confirmed the bipotentiality of these progenitors. Their high expression of alpha6 integrin and low expression of MUC1 suggests a basal position of these cells in the mammary epithelium in vivo. Serial passage in vitro of an enriched population of bipotent progenitors demonstrated that only myoepithelial-restricted progenitors could be readily generated under the culture conditions used. These results support a hierarchical branching model of HBEC progenitor differentiation from a primitive uncommitted cell to luminal- and myoepithelial-restricted progenitors. View Publication

The transcription factor NF-kappaB has anti-apoptotic properties and may confer chemoresistance to cancer cells. Here,we describe human pancreatic carcinoma cell lines that differ in the responsiveness to the topoisomerase-2 inhibitors VP16 (20 microM) and doxorubicin (0.3 microM): Highly sensitive T3M4 [corrected] and PT45-P1 cells,and Capan-1 and A818-4 cells that were almost resistant to both anti cancer drugs. VP16,but not doxorubicin,transiently induced NF-kappaB activity in all cell lines,whereas basal NF-kappaB binding was nearly undetectable in T3M4 [corrected] and PT45-P1 cells,but rather high in Capan-1 and A818-4 cells,as demonstrated by gel-shift and luciferase assays. Treatment with various NF-kappaB inhibitors (Gliotoxin,MG132 and Sulfasalazine),or transfection with the IkappaBalpha super-repressor,strongly enhanced the apoptotic effects of VP16 or doxorubicin on resistant Capan-1 and 818-4 cells. Our results indicate that under certain conditions the resistance of pancreatic carcinoma cells to chemotherapy is due to their constitutive NF-kappaB activity rather than the transient induction of NF-kappaB by some anti-cancer drugs. Blockade of basal NF-kappaB activity by well established drugs efficiently reduces chemoresistance of pancreatic cancer cells and offers the potential for improved therapeutic strategies. View Publication

The functional characteristics were compared for acute myelogenous leukemia (AML) cells (native blasts and AML cell lines) cultured in three serum-free media (X-vivo 10,X-vivo 15,[Bio-Whitacker,Walkersville,MD] and StemSpan [Stem Cell Technologies,Vancouver,BC,Canada]) and in medium containing 10% inactivated fetal calf serum (FCS). For native AML blasts the following functions were compared: (1) autonomous and cytokine-dependent proliferation; (2) frequency of clonogenic cell; and (3) constitutive cytokine secretion. AML blast proliferation differed between patients independent of the culture medium used,and clonogenic cells were maintained after in vitro culture in all media. In contrast,constitutive cytokine secretion was higher for cells cultured in StemSpan and FCS-containing medium than for cells cultured in the X-vivo media. Native AML blasts incubated in StemSpan also showed a low frequency of apoptotic cells. The three serum-free media could also be used for long-term expansion of well-characterized AML cell lines,but the optimal medium for cell expansion and cytokine secretion differed between cell lines. We conclude that standardized serum-free culture conditions can be used for in vitro studies of native AML blasts and AML cell lines. View Publication

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BACKGROUND: Compelling evidence indicates that paclitaxel kills cancer cells through the induction of apoptosis. Paclitaxel binds microtubules and causes kinetic suppression (stabilization) of microtubule dynamics. The consequent arrest of the cell cycle at mitotic phase has been considered to be the cause of paclitaxel-induced cytotoxicity. However,the biochemical events,downstream from paclitaxel's binding to microtubules,that lead to apoptosis are not well understood. METHODS: The authors examined recent scientific literature about the mechanisms by which paclitaxel exerts cytotoxicity. RESULTS: In addition to an arrest of the cell cycle at the mitotic phase in paclitaxel-treated cells,recent discoveries of activation of signaling molecules by paclitaxel and paclitaxel-induced transcriptional activation of various genes indicate that paclitaxel initiates apoptosis through multiple mechanisms. The checkpoint of mitotic spindle assembly,aberrant activation of cyclin-dependent kinases,and the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) are shown to be involved in paclitaxel-induced apoptosis. Consistent with observations that microtubules of different status (e.g.,cytoskeletal microtubules vs. mitotic spindles) have different sensitivity to paclitaxel,the concentration of paclitaxel appears to be the major determinant of its apoptogenic mechanisms. CONCLUSIONS: Advances in research of the cell cycle and apoptosis have extended our understanding of the mechanisms of paclitaxel-induced cell death. Further elucidation of resistance and enhancement of paclitaxel-induced apoptosis should expedite the development of better paclitaxel-based regimens for cancer therapy. View Publication

The molecular mechanisms by which tumor cells metastasize to bone are likely to involve invasion,cell adhesion to bone,and the release of soluble mediators from tumor cells that stimulate osteoclast-mediated bone resorption. Bisphosphonates (BPs) are powerful inhibitors of the osteoclast activity and are,therefore,used in the treatment of patients with osteolytic metastases. However,an added beneficial effect of BPs may be direct antitumor activity. We previously reported that BPs inhibit breast and prostate carcinoma cell adhesion to bone (Boissier et al.,Cancer Res.,57: 3890-3894,1997). Here,we provided evidence that BP pretreatment of breast and prostate carcinoma cells inhibited tumor cell invasion in a dose-dependent manner. The order of potency for four BPs in inhibiting tumor cell invasion was: zoledronate textgreater ibandronate textgreater NE-10244 (active pyridinium analogue of risedronate) textgreater clodronate. In addition,NE-58051 (the inactive pyridylpropylidene analogue of risedronate) had no inhibitory effect,whereas NE-10790 (a phosphonocarboxylate analogue of risedronate in which one of the phosphonate groups is substituted by a carboxyl group) inhibited tumor cell invasion to an extent similar to that observed with NE-10244,indicating that the inhibitory activity of BPs on tumor cells involved the R2 chain of the molecule. BPs did not induce apoptosis in tumor cells,nor did they inhibit tumor cell migration at concentrations that did inhibit tumor cell invasion. However,although BPs did not interfere with the production of matrix metalloproteinases (MMPs) by tumor cells,they inhibited their proteolytic activity. The inhibitory effect of BPs on MMP activity was completely reversed in the presence of an excess of zinc. In addition,NE-10790 did not inhibit MMP activity,suggesting that phosphonate groups of BPs are responsible for the chelation of zinc and the subsequent inhibition of MMP activity. In conclusion,our results provide evidence for a direct cellular effect of BPs in preventing tumor cell invasion and an inhibitory effect of BPs on the proteolytic activity of MMPs through zinc chelation. These results suggest,therefore,that BPs may be useful agents for the prophylactic treatment of patients with cancers that are known to preferentially metastasize to bone. View Publication

Protein kinase CK2 (formerly casein kinase II) is a serine/threonine kinase overexpressed in many human tumors,transformed cell lines,and rapidly proliferating tissues. Recent data have shown that many cancers involve inappropriate reactivation of Wnt signaling through ectopic expression of Wnts themselves,as has been seen in a number of human breast cancers,or through mutation of intermediates in the Wnt pathway,such as adenomatous polyposis coli or beta-catenin,as described in colon and other cancers. Wnts are secreted factors that are important in embryonic development,but overexpression of certain Wnts,such as Wnt-1,leads to proliferation and transformation of cells. We report that upon stable transfection of Wnt-1 into the mouse mammary epithelial cell line C57MG,morphological changes and increased proliferation are accompanied by increased levels of CK2,as well as of beta-catenin. CK2 and beta-catenin co-precipitate with the Dvl proteins,which are Wnt signaling intermediates. A major phosphoprotein of the size of beta-catenin appears in in vitro kinase reactions performed on the Dvl immunoprecipitates. In vitro translated beta-catenin,Dvl-2,and Dvl-3 are phosphorylated by CK2. The selective CK2 inhibitor apigenin blocks proliferation of Wnt-1-transfected cells,abrogates phosphorylation of beta-catenin,and reduces beta-catenin and Dvl protein levels. These results demonstrate that endogenous CK2 is a positive regulator of Wnt signaling and growth of mammary epithelial cells. View Publication

Hematologic malignancies such as acute and chronic myeloid leukemia are characterized by the malignant transformation of immature CD34(+) progenitor cells. Transformation is associated with elevated expression of the Wilm's tumor gene encoded transcription factor (WT1). Here we demonstrate that WT1 can serve as a target for cytotoxic T lymphocytes (CTL) with exquisite specificity for leukemic progenitor cells. HLA-A0201- restricted CTL specific for WT1 kill leukemia cell lines and inhibit colony formation by transformed CD34(+) progenitor cells isolated from patients with chronic myeloid leukemia (CML),whereas colony formation by normal CD34(+) progenitor cells is unaffected. Thus,the tissue-specific transcription factor WT1 is an ideal target for CTL-mediated purging of leukemic progenitor cells in vitro and for antigen-specific therapy of leukemia and other WT1-expressing malignancies in vivo. View Publication

Bispecific antibodies directed against tumor-associated target antigens and to surface receptors mediating T-cell activation,such as the TCR/CD3 complex and the costimulatory receptor CD28,are capable of mediating T-cell activation resulting in tumor cell killing. In this study,we used the B-cell-associated antigens CD19 and CD20 as target structures on human leukemic cells. We found that a combination of bispecific antibody fragments (bsFab2) with target x CD3 and target x CD28 specificity induces vigorous autologous T-cell activation and killing of malignant cells in peripheral blood and bone marrow cultures from patients with chronic lymphocytic leukemia and follicular lymphoma. The bsFab2 targeting CD20 were considerably more effective than those binding to CD19. The colony-forming capacity of treated bone marrow was impaired due to large amounts of tumor necrosis factor alpha produced during bsFab2-induced T-cell activation. Neutralizing tumor necrosis factor alpha antibodies were found to reverse this negative effect without affecting T-cell activation and tumor cell killing. CD20 x CD28 bsFab2,when used alone rather than in combination,markedly improved the recognition of leukemic cells by allogeneic T cells. Therefore,these reagents may be capable of enhancing the immunogenicity of leukemic cells in general and,in particular,of increasing the antileukemic activity of allogeneic donor buffy coat cells in relapsed bone marrow transplanted patients. View Publication