Cellular proliferation and prevalence of micrometastatic cells in the bone marrow of patients with clinically localized prostate cancer.
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The presence of prostate cancer cells in the bone marrow (BM) of patients with clinically localized disease is associated with an increased chance of disease recurrence; however, not all patients develop recurrence. We therefore sought to determine the phenotype of individual micrometastatic cells as a potential method to better predict disease outcome. Immunostaining was performed on BM cells from 46 patients whose BM RNA fraction had been identified to contain prostate-specific antigen mRNA. The prevalence of micrometastatic cells among BM mononuclear cells was determined using an anticytokeratin antibody. Mib-1 antibody was used to determine the percentage of micrometastatic cells that were proliferating. Micrometastatic cells were found in 96% of patient samples, with a 30-fold variation in prevalence ranging from 0.1-3.26/10(5) BM cells. Prior androgen ablation was associated with a reduced prevalence of micrometastatic cells (P = 0.010). In 68% of patients, some micrometastatic cells were judged to be proliferating at proportions ranging from 1 of 11 (9%) to 4 of 4 (100%). Higher Gleason score of the primary tumor was associated with a higher proliferative proportion of micrometastatic cells (P = 0.038). We conclude that, in patients with clinically localized disease, there is wide variability in the prevalence of micrometastatic cells and the proportion which are proliferating. Long-term follow-up will determine whether the development of clinically obvious metastatic disease is related to higher prevalence of micrometastatic cells in the marrow or the proportion that are proliferating. (+info)
Phenylarsine oxide blocks interleukin-1beta-induced activation of the nuclear transcription factor NF-kappaB, inhibits proliferation, and induces apoptosis of acute myelogenous leukemia cells.
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Arsenic compounds have recently been shown to induce high rates of complete remission in patients with acute promyelocytic leukemia (APL). One of these compounds, As(2)O(3), induces apoptosis in APL cells via a mechanism independent of the retinoic acid pathway. To test the hypothesis that arsenic compounds may be effective against other forms of acute myelogenous leukemia (AML), we studied the membrane-permeable arsenic compound phenylarsine oxide (PAO). Because interleukin-1beta (IL-1beta) plays a key role in AML cell proliferation, we first tested the effect of PAO on OCIM2 and OCI/AML3 AML cell lines, both of which produce IL-1beta and proliferate in response to it. We found that PAO inhibited the proliferation of both OCIM2 and OCI/AML3 cells in a dose-dependent fashion (0.01 to 0.1 micromol/L) and that IL-1beta partially reversed this inhibitory effect. We then measured IL-1beta levels in these cells by using an enzyme-linked immunosorbent assay and Western immunoblotting and found that PAO almost completely abolished the production of IL-1beta in these AML cells, whereas it did not affect the production of IL-1 receptor antagonist. Because PAO inhibits activation of the transcription factor NF-kappaB and because NF-kappaB modulates an array of signals controlling cellular survival, proliferation, and cytokine production, we also studied the effect of PAO on NF-kappaB activation in AML cells and found that PAO suppressed the IL-1beta-induced activation of NF-kappaB. Because inhibition of NF-kappaB may result in cellular apoptosis, we also tested whether PAO may induce apoptotic cell death in AML cells. We found that PAO induced apoptosis in OCIM2 cells through activation of the cystein protease caspase 3 and subsequent cleavage of its substrate, the DNA repair enzyme poly (ADP-ribose) polymerase. The PAO-induced apoptosis was caspase dependent, because it was completely blocked by the caspase inhibitor Z-DEVD-FMK. Finally, we tested the effect of PAO on fresh AML marrow cells from 7 patients with newly diagnosed AML and found that PAO suppressed AML colony-forming cell proliferation in a dose-dependent fashion. Taken together, our data showing that PAO is an effective in vitro inhibitor of AML cells suggest that this compound may have a role in future therapies for AML. (+info)
Shiga-like toxin-1 receptor on human breast cancer, lymphoma, and myeloma and absence from CD34(+) hematopoietic stem cells: implications for ex vivo tumor purging and autologous stem cell transplantation.
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The ribosome-inactivating protein, Shiga-like toxin-1 (SLT-1), targets cells that express the glycolipid globotriaosylceramide (CD77) on their surface. CD77 and/or SLT-1 binding was detected by flow cytometry and immunocytochemistry on lymphoma and breast cancer cells recovered from biopsies of primary human cancers as well as on B cells or plasma cells present in blood/bone marrow samples of multiple myeloma patients. Breast cancer cell lines also expressed receptors for the toxin and were sensitive to SLT-1. Treatment of primary B lymphoma, B-cell chronic lymphocytic leukemia, and myeloma B or plasma cells with SLT-1-depleted malignant B cells by 3- to 28-fold, as measured by flow cytometry. Depletion of myeloma plasma cells was confirmed using a cellular limiting dilution assay followed by reverse transcriptase-polymerase chain reaction analysis of clonotypic IgH transcripts, which showed a greater than 3 log reduction in clonotypic myeloma cells after SLT-1 treatment. Receptors for the toxin were not detected on human CD34(+) hematopoietic progenitor cells (HPC). HPC were pretreated with a concentration of SLT-1 known to purge primary malignant B cells and cultured for 6 days. The number of HPC was comparable in toxin-treated and untreated cultures. HPC were functionally intact as well. Colony-forming units (CFU) were present at an identical frequency in untreated and SLT-1 pretreated cultures, confirming that CFU escape SLT-1 toxicity. The results suggest the ex vivo use of SLT-1 in purging SLT-1 receptor-expressing malignant cells from autologous stem cell grafts of breast cancer, lymphoma, and myeloma patients. (+info)
Isoforms of c-KIT differ in activation of signalling pathways and transformation of NIH3T3 fibroblasts.
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Alternate splicing of mRNA encoding c-KIT results in isoforms which differ in the presence or absence of four amino acids (GNNK) in the juxtamembrane region of the extracellular domain of the receptor. In this study we show that these isoforms of human c-KIT, expressed at similar levels in NIH3T3 cells, display differential effects on various attributes of transformation. The GNNK- isoform strongly promoted anchorage independent growth (colony formation in semi-solid medium), loss of contact inhibition (focus formation), and led to tumorigenicity in nude mice. In contrast, the GNNK+ isoform elicited colony formation but relatively poor focus formation and no tumorigenicity. Saturation binding analysis indicated that the isoforms do not differ significantly in their affinity for the KIT ligand, Steel Factor (SLF). Negligible ligand-independent receptor phosphorylation was observed in either case but, after ligand stimulation, the GNNK- isoform displayed more rapid and extensive tyrosine autophosphorylation and faster internalization. Both isoforms recruited the p85 subunit of phosphatidylinositol 3-kinase and led to similar phosphorylation of its downstream effector c-Akt, but the GNNK- isoform gave rise to more MAP kinase phosphorylation. Thus the c-KIT isoforms display different signalling characteristics and have different transforming activity in NIH3T3 cells. (+info)
Transforming activity of EWS/FLI is not strictly dependent upon DNA-binding activity.
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In approximately 85% of Ewing sarcomas, chromosomal translocations give rise to the chimeric gene EWS/FLI, encoding the N-terminus of the RNA binding protein EWS fused to the DNA-binding domain of the ETS protein FLI-1. EWS/FLI is a stronger transcriptional activator than wild-type FLI-1, although both proteins bind to the same DNA sequences in vitro. In addition, EWS/FLI, but not FLI-1, is a transforming oncogene in NIH3T3 fibroblasts. EWS/FLI is thought to transform through its ability to deregulate the expression of target genes. We introduced several point mutations into the ETS domain of EWS/FLI that abolished DNA-binding activity. Although two of these mutations disrupted the transforming activity of EWS/FLI, one mutated protein containing a substitution of isoleucine 347 with glutamic acid (I347E) retained diminished transforming activity. In addition, EWS/FLI I347E did not activate expression of the endogenous EWS/FLI target gene manic fringe (MFNG). These studies demonstrate that a portion of the oncogenic activity of EWS/FLI is independent of FLI DNA-binding activity. (+info)
Inhibition of SV40 large T antigen induced apoptosis by small T antigen.
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It is well established that the expression of simian virus 40 (SV40) early gene products causes oncogenic transformation of rodent cells. An important aspect of this process is the inactivation of the p53 and retinoblastoma (pRb) tumour suppressor proteins through interaction with the SV40 large tumour antigen (LT). In addition, the SV40 small tumour antigen (ST) may enhance LT induced transformation. Here we show that LT induces apoptotic cell death in rat embryo fibroblast (REF) cells and that ST functions to inhibit this effect by a mechanism which is different from other known anti-apoptotic proteins. Mutational analysis of LT indicates that mutants defective in the pRb-binding domain are unable to induce apoptosis whereas LT mutants defective in the p53-binding domain are still competent to induce apoptosis. Thus, interaction between LT and one or more pRb family members must occur for induction of apoptosis and that binding of p53 by LT is insufficient to inhibit LT induced apoptosis in REFs. The data presented herein suggest that the anti-apoptotic function of ST may explain, at least in part, how ST contributes to SV40 early region induced transformation of REF cells. (+info)
Function for p300 and not CBP in the apoptotic response to DNA damage.
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The cellular response to ionizing radiation (IR) includes the induction of apoptosis. The p300/CBP proteins possess histone acetyltransferase activity and function as transcriptional coactivators of p53. We have prepared cells deficient in p300 or CBP to define the roles of these proteins in the cellular response to DNA damage. The present results demonstrate that p300, but not CBP, contributes to IR sensitivity of cells. The results also demonstrate that IR-induced apoptosis is impaired in the p300-, but not CBP-, deficient cells. These findings indicate that p300 functions in the apoptotic response to DNA damage. (+info)
Enzyme prodrug gene therapy: synergistic use of the herpes simplex virus-cellular thymidine kinase/ganciclovir system and thymidylate synthase inhibitors for the treatment of colon cancer.
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The goal of this study was to improve the therapeutic index of the herpes simplex virus-thymidine kinase/ganciclovir (HSV-tk/GCV) system by the addition of thymidylate synthase (TS) inhibitors. For this, we assessed the potential of GCV to synergistically interact with 5-fluorouracil (5-FU), ZD1694 (Tomudex), and (E)-5-(2-bromovinyl)-2'-deoxyuridine in HSV-tk-expressing murine MC38 STK and human HT-29 STK colon carcinoma cell lines. Synergistic cell killing was observed in a clonogenic assay over most of the cytotoxic dose range by the median-effect principle of Chou and Talalay (T. C. Chou and P. Talalay, Adv. Enzyme Regul., 22: 27-55, 1984). In a s.c. HT-29 STK xenograft tumor model, we demonstrated that the combination of GCV and 5-FU resulted in statistically significant enhanced animal survival over single-agent treatment. Furthermore, we showed that the combination of GCV and ZD1694 in association with the HSV-tk/GCV system was at least as effective as GCV/5-FU in vitro and in vivo. The mechanism for the observed synergy is most likely attributable to the increased GCV phosphorylation in the presence of the tested TS inhibitors. Our data suggest that the HSV-tk/GCV metabolic suicide gene transfer system could serve as an adjuvant of the presently used TS inhibitors, thus potentially improving the efficacy of present cancer gene therapy approaches. (+info)