Biomedical subjects

M C Hung

Publications and source records attributed to M C Hung.

At least 55 records · Page 3Linked to original sources

PubMed2000

New taxanes with an opened oxetane ring from the roots of Taxus mairei.

Two novel taxoids, taxumairols N (1) and O (2), have been isolated from extracts of the roots of Taxus mairei. The structures of 1 and 2 were identified as 7beta,9alpha,10beta,13alpha-tetraacetoxy-2alp ha, 4alpha,5alpha,20-tetrahydroxytax-11-ene and 7beta,9alpha,10beta, 13alpha-tetraacetoxy-1beta,2alpha,4alpha,5alp ha, 20-pentahydroxytax-11-ene on the basis of 1D and 2D NMR techniques including COSY, HMQC, HMBC, and NOESY experiments.

Magnetic Resonance Spectroscopy↗

PubMed2000

The ets protein PEA3 suppresses HER-2/neu overexpression and inhibits tumorigenesis.

Because HER-2/neu overexpression is important in cancer development, we looked for a method of suppressing the cell transformation mediated by HER-2/neu overexpression. We have identified that the DNA-binding protein PEA3, which is encoded by a previously isolated gene of the ets family, specifically targeted a DNA sequence on the HER-2/neu promoter and downregulated the promoter activity. Expression of PEA3 resulted in preferential inhibition of cell growth and tumor development of HER-2/neu-overexpressing cancer cells. This is a new approach to targeting HER-2/neu overexpression and also provides a rationale to the design for repressors of diseases caused by overexpression of pathogenic genes.

3T3 Cells↗

PubMed2000

Adenovirus-mediated N5 gene transfer inhibits tumor cell proliferation by induction of apoptosis.

Gene therapy designed to initiate apoptotic cell death provides a potentially effective method to treat cancer. A prerequisite for this approach is the identification of genes that function in distinct apoptotic pathways. Although apoptotic pathways initiated by receptors such as tumor necrosis factor receptor-1 are well characterized, little is known about apoptotic pathways initiated within the nucleus in response to genotoxic stress. We have demonstrated previously that the nuclear, death domain-containing protein p84N5 can induce apoptosis upon transfection into cells, suggesting that it may play a role in an apoptotic pathway initiated within the nucleus. To test the possibility that N5 could be used in the gene therapy of cancer, we have generated a recombinant adenovirus engineered to express N5 and tested the effects of viral infection on the growth and tumorigenicity of tumor cells. N5 adenovirus infection significantly reduced the proliferation and tumorigenicity of breast, ovarian, and osteosarcoma tumor cell lines. Reduced proliferation and tumorigenicity were mediated by an induction of apoptosis as indicated by DNA fragmentation in infected cells. The results suggest that the N5 cDNA is a candidate for the gene therapy of cancer.

Adenoviridae↗

PubMed2000

Use of binomial group testing in tests of hypotheses for classification or quantitative covariables.

In group testing, the test unit consists of a group of individuals. If the group test is positive, then one or more individuals in the group are assumed to be positive. A group observation in binomial group testing can be, say, the test result (positive or negative) for a pool of blood samples that come from several different individuals. It has been shown that, when the proportion (p) of infected individuals is low, group testing is often preferable to individual testing for identifying infected individuals and for estimating proportions of those infected. We extend the potential applications of group testing to hypothesis-testing problems wherein one wants to test for a relationship between p and a classification or quantitative covariable. Asymptotic relative efficiencies (AREs) of tests based on group testing versus the usual individual testing are obtained. The Pitman ARE strongly favors group testing in many cases. Small-sample results from simulation studies are given and are consistent with the large-sample (asymptotic) findings. We illustrate the potential advantages of group testing in hypothesis testing using HIV-1 seroprevalence data.

Adolescent↗

PubMed2000

Cyclin D1 is required for transformation by activated Neu and is induced through an E2F-dependent signaling pathway.

The neu (c-erbB-2) proto-oncogene encodes a tyrosine kinase receptor that is overexpressed in 20 to 30% of human breast tumors. Herein, cyclin D1 protein levels were increased in mammary tumors induced by overexpression of wild-type Neu or activating mutants of Neu in transgenic mice and in MCF7 cells overexpressing transforming Neu. Analyses of 12 Neu mutants in MCF7 cells indicated important roles for specific C-terminal autophosphorylation sites and the extracellular domain in cyclin D1 promoter activation. Induction of cyclin D1 by NeuT involved Ras, Rac, Rho, extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38, but not phosphatidylinositol 3-kinase. NeuT induction of the cyclin D1 promoter required the E2F and Sp1 DNA binding sites and was inhibited by dominant negative E2F-1 or DP-1. Neu-induced transformation was inhibited by a cyclin D1 antisense or dominant negative E2F-1 construct in Rat-1 cells. Growth of NeuT-transformed mammary adenocarcinoma cells in nude mice was blocked by the cyclin D1 antisense construct. These results demonstrate that E2F-1 mediates a Neu-signaling cascade to cyclin D1 and identify cyclin D1 as a critical downstream target of neu-induced transformation.

Animals↗

PubMed2000

Taxane diterpenoids from seeds of Taxus mairei.

A new 2(3-->20) abeotaxane, taxumairone A (1), and a new cis-p-coumaroyl myo-inositol have been isolated from the seeds of Taxus mairei in addition to taxin B (2), taxinine A, taxuspine X, decinnamoyltaxinine E, 5alpha-cinnamoyloxy-9alpha,10beta,13alpha- triacetoxy-taxa-4(20)11-diene and 5alpha-cinnamoyloxy-2alpha,9alpha,10beta,+ ++13alpha-tetraacetoxy-taxa-4(20)11-diene. The structure of 1 was determined by 2D-NMR spectral analysis and chemical correlation with taxin B (2). Compound 1 exhibited potent cytotoxicity against human colon carcinoma cells with an ED50 of 0.1 microg/ml.

Bridged-Ring Compounds↗

PubMed2000

Application of the random arbitrary primed polymerase chain reaction differential display method to isolate genes of cholesterol metabolism-related proteins from rat liver.

The random arbitrary primed (RAP) polymerase chain reaction (PCR) differential display (DD) method was applied to isolate genes related to cholesterol metabolism from exogenously hypercholesterolemic (ExHC) rats and the progenitor, SD rats. Forty-seven trials of RAP-PCR DD resulted in the isolation of 37 clones differing in strain, cholesterol supplementation or their interaction. Among their fingerprints, five clones gave reproducible patterns by a Northern blotting analysis. The sequence of two clones with lower mRNA abundance in ExHC rats than in SD rats was homologous to that of fatty acid synthase and oxalyl-CoA decarboxylase. Two other clones with higher mRNA on the n-cholesterol diet were matrin F/G protein and the NMDA receptor glutamate-binding subunit. The other clone with higher mRNA abundance in ExHC rats on the cholesterol diet was myelodysplasia/myeloid leukemia factor 2. Fifteen trials of reverse transcriptase (RT)-PCR DD yielded 10 clones, but none of the fingerprints were reproduced by the Northern blotting analysis. These results indicate that RAP-PCR DD is an appropriate alternative to RT-PCR DD for isolating the genes involved in hypercholesterolemia.

Animals↗

PubMed2000

Suppressing HER2/neu-mediated cell transformation by transcriptional repressors.

Breast and ovarian cancer are two of the leading causes of death for women in the United States. HER2/neu overexpression is an unfavorable prognosis factor associated with low patient survival rate of multiple cancer types including breast and ovarian cancer. Downregulation of the HER2/neu gene expression in cancer cells has been shown to be a useful strategy to significantly reverse the malignant characteristics induced by HER2/neu overexpression. It is possible that HER2/neu overexpression can be repressed through inhibiting the promoter activity of the gene. We have identified a number of potent transcriptional regulators, including the adenovirus type 5 E1A, the SV40 large T antigen, and the ets family member PEA3, and have tested their activity to repress HER2/neu overexpression. Ectopic expression of these transcriptional regulators resulted in downregulation of the HER2/neu promoter activity and reversed the transformed phenotype of the cancer cells in vitro. These observations were followed by a series of studies to investigate whether these HER2/neu repressors could act therapeutically as tumor suppressor genes for cancers overexpressing HER2/neu. The results of these preclinical studies clearly indicated that transcriptional repressors, which downregulate HER2/neu overexpression, can be an effective regimen for cancer treatment in a gene therapy format combined with an appropriate gene delivery system such as the cationic liposome DC-Chol or replication-deficient adenovirus vector. Our results have demonstrated that these delivery systems can effectively transfer the therapeutic genes into the cancer cells in vivo and lead to significant suppressive effects on tumor growth. Furthermore, tumor-free survival rate of treated animals is increased dramatically using nontoxic doses, compared with animals without the treatment. A great body of evidence has revealed the potential of using transcriptional repressors to suppress HER2/neu overexpression and abolish tumor growth. Thus, suppression of oncogenic gene expression using transcription factors can be a novel field for cancer treatment and prevention.

Journal Article↗

PubMed2000

E1A-mediated paclitaxel sensitization in HER-2/neu-overexpressing ovarian cancer SKOV3.ip1 through apoptosis involving the caspase-3 pathway.

HER-2/neu-overexpressing breast cancer cells are more resistant to the chemotherapeutic agent paclitaxel (Taxol) than low-HER-2/neu-expressing breast cancer cells, and the adenoviral type 5 EIA can down-regulate HER-2/neu overexpression. Therefore, in this study, we asked (a) whether EIA might sensitize response to paclitaxel in human HER-2/neu-overexpressing ovarian cancer cells, and, if so, what is the mechanism responsible; and (b) whether this enhanced chemosensitivity would translate into a therapeutic effect in an ovarian cancer xenograft model. Consequently, we demonstrated that: (a) adenovirus type 5 E1A could enhance the sensitivity of paclitaxel in paclitaxel-resistant HER-2/neu-overexpressing human ovarian cancer cells in vitro by inducing apoptosis, (b) this induction was heavily dependent on activation of the caspase-3 pathway, and (c) nude mice bearing i.p. HER-2/neu-overexpressing human ovarian cancer cells and treated with both paclitaxel and E1A gene therapy survived significantly longer than did mice treated only with paclitaxel or E1A gene therapy. Thus, we concluded that the E1A gene enhanced both the in vitro and in vivo sensitivity of paclitaxel in paclitaxel-resistant HER-2/ neu-overexpressing ovarian cancer SKOV3.ipl cells. Because a Phase I clinical trial using E1A gene targeted to HER-2/neu down-regulation has recently been completed, the current study also provided a scientific basis to further develop a novel therapy that combines paclitaxel and E1A gene therapy and its testing in a Phase II trial.

Adenovirus E1A Proteins↗

PubMed2000

Adenovirus 5 early region 1A does not induce expression of the ewing sarcoma fusion product EWS-FLI1 in breast and ovarian cancer cell lines.

The adenovirus 5 early region 1A (E1A) can function as a tumor suppressor gene and is being used in clinical trials as a therapeutic agent for advanced breast, ovarian, and head and neck cancer. Recently, there has been a dispute regarding whether transfection with the E1A gene can induce expression of the Ewing sarcoma oncogenic fusion transcript EWS-FLI1 (Sanchez-Prieto et al., Nat. Med., 5: 1076-1079, 1999; Melot and Delattre, Nat. Med., 5: 1331, 1999; Kovar et al., Cancer Res., 60: 1557-1560, 2000). In an effort to settle the controversy, we tested several stable E1A transfectants of cell lines MDA-MB-231, MCF-7, MDA-MB-435 (breast cancer), SKOV3-ipl (ovarian cancer), and PC-3 (prostate cancer), as well as parental and vector-transfected controls, HEK 293 cells, and RD-ES (Ewing sarcoma) cells, for the EWS-FLI1 fusion product. The EWS-FLI1 transcript could not be identified with reverse transcription-PCR in any of the 13 E1A-transfected cell lines analyzed. Furthermore, the EWS-FLI1 fusion protein could not be detected by Western blot analysis in E1A-transfected cell lines. These results suggest that E1A transfection does not necessarily lead to expression of the oncogenic EWS-FLI1 fusion transcript. Thus, the potential induction of this gene rearrangement by E1A gene therapy is unlikely to be clinically significant in the treatment of advanced malignant disease.

Adenovirus E1A Proteins↗

PubMed2000

Transcriptional targeting of the HER-2/neu oncogene.

Breast and ovarian cancers are the leading cause of death for women in many areas in the world including the United States. Overexpression of the HER-2/neu gene (also known as c-erbB2) is a frequent event in about 30% of breast as well as ovarian cancers. The overall survival rates of breast and ovarian cancer patients whose tumors overexpress HER-2/neu are significantly lower than those of patients whose tumors do not overexpress HER-2/neu. Overexpression of HER-2/neu leads to elevated tumorigenicity, enhanced metastatic potential, increased resistance to TNF-alpha-induced apoptosis and resistance to treatments such as paclitaxel and tamoxifen. Down-regulation of the HER-2/neu oncogene causes suppression of the cell-transforming phenotype induced by the oncogene. For example, downregulation of the HER-2/neu gene expression by E1A significantly mitigated tumorigenic activity of human breast and ovarian cancer cells in nude mice. These results strongly imply that HER-2/neu mediated cell transformation may be inhibited by transcriptional repressors that target the promoter of the oncogene. In addition to E1A, we recently identified the ets transcription factor PEA3 as a potential HER-2/neu gene inhibitor. PEA3 binds directly to this consensus binding motif and suppresses the HER-2/neu gene promoter activity. Downregulation of HER-2/neu expression led to inhibition of cell transformation and proliferation in vitro. In a preclinical gene therapy setting, in which the PEA3 gene tumor delivery was facilitated by a cationic liposome DC-Chol, blocked HER-2/neu overexpression by PEA3 resulted in prolonged survival of treated animals. These studies demonstrate a promising approach to cancer gene therapy using transcriptional repressors to target expression of oncogenes such as HER-2/neu.

Journal Article↗

PubMed1999

The PTEN/MMAC1/TEP tumor suppressor gene decreases cell growth and induces apoptosis and anoikis in breast cancer cells.

The PTEN/MMAC1/TEP (PTEN) tumor suppressor gene at 10q23.3 is mutated in multiple types of sporadic tumors including breast cancers and also in the germline of patients with the Cowden's breast cancer predisposition syndrome. The PTEN gene encodes a multifunctional phosphatase capable of dephosphorylating the same sites in membrane phosphatidylinositols phosphorylated by phosphatidylinositol 3'-kinase (PI3K). We demonstrate herein that loss of PTEN function in breast cancer cells results in an increase in basal levels of phosphorylation of multiple components of the P13K signaling cascade as well as an increase in duration of ligand-induced signaling through the P13K cascade. These alterations are reversed by wild-type but not phosphatase inactive PTEN. In the presence of high concentrations of serum, enforced expression of PTEN induces a predominant G1 arrest consistent with the capacity of PTEN to evoke increases in the expression of the p27Kip1 cyclin dependent kinase inhibitor. In the presence of low concentrations of serum, enforced PTEN expression results in a marked increase in cellular apoptosis, a finding which is consistent with the capacity of PTEN to alter the phosphorylation, and presumably function, of the AKT, BAD, p70S6 kinase and GSK3 alpha apoptosis regulators. Under anchorage-independent conditions, PTEN also induces anoikis, a form of apoptosis that occurs when cells are dissociated from the extracellular matrix, which is enhanced in conjunction with low serum culture conditions. Together, these data suggest that PTEN effects on the PI3K signaling cascade are influenced by the cell stimulatory context, and that depending on the exposure to growth factors and other exogenous stimuli such as integrin ligation, PTEN can induce cell cycle arrest, apoptosis or anoikis in breast cancer cells.

Apoptosis↗

PubMed1999

E1A sensitizes cells to tumor necrosis factor-induced apoptosis through inhibition of IkappaB kinases and nuclear factor kappaB activities.

The adenovirus E1A protein has been implicated in increasing cellular susceptibility to apoptosis induced by tumor necrosis factor (TNF); however, its mechanism of action is still unknown. Since activation of nuclear factor kappaB (NF-kappaB) has been shown to play an anti-apoptotic role in TNF-induced apoptosis, we examined apoptotic susceptibility and NF-kappaB activation induced by TNF in the E1A transfectants and their parental cells. Here, we reported that E1A inhibited activation of NF-kappaB and rendered cells more sensitive to TNF-induced apoptosis. We further showed that this inhibition was through suppression of IkappaB kinase (IKK) activity and IkappaB phosphorylation. Moreover, deletion of the p300 and Rb binding domains of E1A abolished its function in blocking IKK activity and IkappaB phosphorylation, suggesting that these domains are essential for the E1A function in down-regulating IKK activity and NF-kappaB signaling. However, the role of E1A in inhibiting IKK activity might be indirect. Nevertheless, our results suggest that inhibition of IKK activity by E1A is an important mechanism for the E1A-mediated sensitization of TNF-induced apoptosis.

Adenovirus E1A Proteins↗

PubMed1999

Collagen-homology domain 1 deletion mutant of Shc suppresses transformation mediated by neu through a MAPK-independent pathway.

Shc proteins are implicated in coupling receptor tyrosine kinase to the mitogen-activated protein kinase (MAPK) pathway by recruiting Grb2/SOS to the plasma membrane. To better understand the role of Shc in the oncogenesis by point-mutation activated neu (p185*), we transfected a Shc mutant (ShcdeltaCHI), which lacks the Grb2 binding site Y317 by deletion of collagen-homology domain 1, into p185*-transformed NIH3T3 cells. The cellular transformation phenotypes were found to be largely suppressed by expression of ShcdeltaCH1. Although ShcdeltaCH1 still retained another Grb2 binding site (Y239/240), we did not detect its physical association with Grb2. We also found that ShcdeltaCH1 could associate with p185*; however, this association did not interfere with the endogenous Shc-p185* interaction or the Shc-Grb2 interaction. In addition, p185*-mediated MAPK and Elk activation likewise were not inhibited by ShcdeltaCH1 expression. Taken together, these data demonstrate that ShcdeltaCH1 suppresses the transformation induced by activated neu through a MAPK-independent pathway, indicating that Shc may be involved in other signal pathway(s) critical for cellular transformation in addition to the MAPK pathway.

Adaptor Proteins, Signal Transducing↗

PubMed1999

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.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Reduced growth rate and transformation phenotype of the prostate cancer cells by an interferon-inducible protein, p202.

Interferons (IFNs) can exert cytostatic and immunomodulatory effects on carcinoma cells. In particular, growth inhibition of human prostate carcinoma by IFNs has been demonstrated both in vitro and in vivo. p202 is a 52 kd nuclear phosphoprotein known to be induced by IFNs. In this report, we showed that the expression of p202 was associated with an anti-proliferative effect on human prostate cancer cells. More importantly, cells that expressed p202 showed reduced ability to grow in soft-agar, indicating a loss of transformation phenotype. Our data suggest that p202 is a growth inhibitor gene in prostate cancer cells and its expression may also suppress transformation phenotype of prostate cancer cells.

Carrier Proteins↗

PubMed1999

Chemo-signal therapy, an emerging new approach to modify drug resistance in breast cancer.

Recent advances in understanding how response or resistance to cytotoxic drugs develops at the cellular level resulted in the development of novel, non-cytotoxic agents that modulate response the chemotherapy. 'Chemo-signal therapy', the combination of chemotherapy with cellular response modifiers, is a very promising new treatment modality that has entered the arena of clinical trials. Clinical experience with the anti-HER-2 antibody, trastuzumab, in breast cancer has demonstrated that manipulation of growth factor signalling can enhance sensitivity to cytotoxic drugs in a clinically meaningful way. Several other agents that were designed to modulate response to chemotherapy are currently in early phases of clinical drug development. It is likely that some of these new molecules will have a major impact on how chemotherapy will be given in the next decade. This paper will review current clinical research with a select group of chemotherapy response modifiers. We will focus on agents that modulate signal transduction, oncogene expression and apoptosis with an emphasis on breast cancer.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1999

Chronic low-dose gamma-radiation exposure and the alteration of the distribution of lymphocyte subpopulations in residents of radioactive buildings.

PURPOSE: To elucidate the immunological change incurred in a human population by protracted gamma-radiation exposure at home environment. MATERIALS AND METHODS: An examination on the CD3+, CD4+, CD8+ and HLA-DR+ lymphocyte subsets was arranged for 196 exposed subjects with mean excess cumulative dose of 169 mSv during 2-13 years of exposure. Another 55 close relatives of the exposed subjects were recruited as the non-exposed reference population. RESULTS: The mean percentages of CD4+ T-lymphocytes, HLA-DR+ lymphocytes and the CD4+ /CD8+ ratios in the exposed subjects (35.5, 19.9 and 1.51 respectively) were significantly lower than those of reference individuals (38.0, 22.6 and 1.72; p= 0.02, 0.003, and 0.03 respectively), while the CD8+ in total counts of the exposed was moderately increased above that of the reference populations (p=0.1). By ANOVA analysis, the percentages of CD4+ and HLA-DR+ subsets were significantly associated with radiation dose (p=0.0046, 0.003), while CD4+/CD8+ ratios were moderately associated with dose (p=0.073). HLA-DR+ counts were significantly and positively associated with duration of relocation from radioactive apartments (p = 0.029). CONCLUSIONS: Significant immunological effects were observed in those who had received chronic low-dose radiation exposure.

Adolescent↗