摘要:

The ubiquitin (Ub)-proteasome pathway is the major non-lysosomal pathway of proteolysis in human cells and accounts for the degradation of most short-lived, misfolded or damaged proteins. This pathway is important in the regulation of a number of key biological regulatory mechanisms. Proteins are usually targeted for proteasome-mediated degradation by polyubiquitinylation, the covalent addition of multiple units of the 76 amino acid protein Ub, which are ligated to ε-amino groups of lysine residues in the substrate. Polyubiquitinylated proteins are degraded by the 26S proteasome, a large, ATP-dependent multicatalytic protease complex, which also regenerates monomeric Ub. The targets of this pathway include key regulators of cell proliferation and cell death. An alternative form of the proteasome, termed the immunoproteasome, also has important functions in the generation of peptides for presentation by MHC class I molecules. In recent years there has been a great deal of interest in the possibility that proteasome inhibitors, through elevation of the levels of proteasome targets, might prove useful as a novel class of anti-cancer drugs. Here we review the progress made to date in this area and highlight the potential advantages and weaknesses of this approach.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Abnormalities in the tumor suppressor gene p53 have been identified in over 60% of human cancers. Since it plays such a pivotal role in cell growth regulation and apoptosis, the status of the p53 gene has been proposed as one of the major determinants of a tumor's response to anticancer therapies. In this review we examine the relationship between functional p53 and sensitivity/resistance to both chemotherapy and radiotherapy, and discuss the potential use of some of the current gene therapy approaches to restore functional p53 to tumors as a means of modulating the effects of radiation and chemotherapy.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The Soft Tissue and Bone Sarcoma Group (STBSG) of the EORTC ran a phase II study to assess the therapeutic activity of high-dose ifosfamide in patients with advanced soft tissue sarcomas by means of response rate (RR). Investigators claiming a response submitted the relevant chest radiographs (CXR) or scans to two other members of the STBSG for peer review. The reviewers completed a questionnaire indicating overall response or reasons for rejecting the claimed responses. An independent radiologist also reviewed the cases and he was blinded to the results of the peer review until the study was concluded. Twenty-two patients were reviewed by the radiologist and peer review, and the completed questionnaires were retrospectively reviewed. Two differences were noted, one partial responder (PR) was regarded as stable disease by the radiologist and one PR by peer review was determined a complete response by the radiologist. The radiologist found subsequent evidence of progressive disease in three patients who initially showed a PR, whilst the review group noted only one. This study suggests peer review in this tumor type is a satisfactory method of achieving an accurate, objective RR.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Docetaxel (TaxotereTM) is becoming increasingly important in the treatment of many tumor sites and is unusually active in tumors that are resistant to the structurally similar taxane, paclitaxel. These data suggest that the processes that confer cellular paclitaxel resistance may have a substantially lower impact upon the cytotoxicity induced by docetaxel. We have recently reported that there is a marked Raf-1 kinase dependency of paclitaxel resistance in human cervical and ovarian tumor cell lines. We therefore characterized the impact that inherent and genetically induced variations in Raf-1 kinase activity have on the docetaxel cytotoxicity in human ovarian and cervical cancer cell lines. Our data suggest that docetaxel cytotoxicity is independent of Raf-1 kinase activity in the cell lines studied and that the lack of cross-resistance between these two taxane compounds may be due to the differential impact that Raf-1 kinase activity has on their cytotoxicity. Should these relationships pertain to the clinical situation, these findings could form the basis for a molecular-based triage of patients to receive docetaxel when response to paclitaxel may be unlikely due to high Raf-1 kinase activity.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

FR901228, a natural cyclic depsipeptide, shows high cytotoxicity against human cancer cell lines (low nM IC50values). Cells exposed to FR901228 arrest with G1or G2/M DNA content; S phase is depleted. G2/M cells include cells arrested in mitosis. We wished to understand the mitotic arrest by this compound. Mitotic arrest is often due to interference with microtubules and COMPARE testing in the NCI drug screen indicated a possible taxane-like mechanism. Testing of FR901228 for tubulin binding or alteration ofin vitroMT assembly failed to reveal any effect. Likewise, examination of cellular microtubules following exposure to FR901228 did not reveal any change. Similar G2/M accumulation was observed in MCF7, MCF10 and PC3 cells. About 50% of G2/M cells were mitotic and contained microtubule spindles. Mitotic cells peaked at about 14-16 h drug exposure and declined to near 0% by 24-30 h. The block was at prometaphase, with numerous chromosomes unattached to the spindle. We conclude that FR901228 induces formation of aberrant spindles probably by interfering with chromosome attachment, causing mitotic accumulation without affecting mitotic microtubules.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The purpose of this study was to examine the mechanism(s) and differential cell-killing effects of AnvirzelTM, an extract of oleander (Nerium oleander; family-Apocynaceae), and its derivative compound Oleandrin on human, canine and murine tumor cells. Cells received different concentrations of Anvirzel (1.0 ng/ml to 500 μg/ml) or Oleandrin (0.01 ng/ml to 50 μg/ml) in both continuously treated and pulse-treated/recovery cultures. The cytotoxicity of these compounds was then determined. Both Anvirzel and Oleandrin were able to induce cell killing in human cancer cells, but not in murine cancer cells; the cell-killing potency of Oleandrin was greater than that of Anvirzel. Canine oral cancer cells treated with Anvirzel showed intermediate levels of response, with some abnormal metaphases and cell death resulting from the treatment. From these results we conclude that Anvirzel and Oleandrin act in a species-specific manner, and while testing the effectiveness of a new compound for cancer treatment, one must use not only murine but a variety of cancer cells, including those of human origin.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Irinotecan (CPT-11) is a topoisomerase I inhibitor commonly used in the treatment of colorectal tumors. It is a prodrug, converted to an active metabolite, SN-38, by carboxylesterases (CEs). CEs are ubiquitary enzymes that react with numerous substrates. A specific CPT-11 converting enzyme was isolated from rat serum, with different kinetic properties than other CEs. We determined kinetic properties of specific CPT-11 CE activity (CPT-CE) in human normal liver and colon tumors.Kmwere very similar (3.4 μM in liver and 3.8 μM in colon tumors), butVmaxwas higher in liver (2.7 pmol/min/mg protein) than in colon tumor (1.7 pmol/min/mg protein). CPT-CE and total CE (usingp-nitro-phenylacetate as substrate) were weakly correlated in colon tumors. The large interpatient variability observed in liver CPT-CE activity could play a potential role in the pharmacokinetic variability observed with irinotecan.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Topoisomerases I and II unravel DNA during transcription, DNA replication and DNA repair. Inhibitors of both enzymes are important anticancer drugs, but only now are combined inhibitors becoming available for clinical use. In this study we have used an ATP-based chemosensitivity assay to determine the activity of XR5000 and possible combinations against ovarian cancer, a tumor sensitive to current topoisomerase inhibitors, and melanoma, an insensitive tumor. A further six tumors of other types were also tested. The results from 20 ovarian cancer and 18 melanoma biopsies show remarkably little difference between the tumor types in terms of IC50, IC90or two summary indices of chemosensitivity based on all of the concentrations tested. XR5000 on its own shows a steep concentration-response curve in most tumors, only achieving high reduction (above 95%) of ATP levels at 2440 ng/ml (6 μM). The results were often similar to the combination of etoposide and topotecan, particularly at the higher concentrations tested. The combinations with greatest activity in ovarian cancer were with paclitaxel or cisplatin, while melanoma showed greatest improvement with paclitaxel or treosulfan. The results are encouraging for the clinical introduction of this agent, and suggest that it will be effective in combination with currently available drugs for both ovarian cancer and melanoma.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Disseminated neuroblastoma diseases are still indicated by a poor outcome despite treatment regimens including radiation therapy and high-dose chemotherapy with stem cell rescue. Therefore, new substances and treatment regimens are of interest. Aphidicolin (APH), a tetracyclic diterpene antibiotic produced byCephalosporium aphidicola, has a specific toxicity for neuroblastoma cells. Furthermore, it was shown to enhance the effects of X-ray radiation and chemotherapy on malignant cells. To find new substances, 20 APH derivatives were tested for their anti-neuroblastoma efficacyin vitroin UKF-NB-2 cells. Five derivatives had antitumoral activity in neuroblastoma cells. A relationship between the structure and the antitumoral efficacy showed that the hydroxyl groups at C-3 and C-18 are essential for the antitumoral effects. Furthermore, antitumoral effects of APH in combination with doxorubicin and vincristine, both part of commonly used treatment regimens for disseminated neuroblastoma diseases, were tested in the neuroblastoma cell line UKF-NB-2. APH was found to act synergistically with vincristine and synergistically to additive with doxorubicin depending on the molecular ratio of the substances in combination. This may offer the chance to use APH and its derivatives as additional tools in the treatment of neuroblastomas.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The effects of vitamin C on the oxidative stress in blood platelets induced by cisplatin were studied. In the presence of vitamin C we measured in blood platelets the production of thiobarbituric acid reactive substances (TBARS), the generation of superoxide radicals (O2.−), other reactive oxygen species (H2O2, singlet oxygen and organic radicals) and catalase activity. Vitamin C at a low concentration (0.1 mM), like cisplatin (20 μM), induced blood platelet oxidative stress: an increase of TBARS, chemiluminescence and generation of superoxide radicals. After treatment of blood platelets with vitamin C at a high concentration (3 mM), chemiluminescence (p>0.05), the levels of O2.−(p<0.01) and TBARS (p<0.002) were reduced. We have shown that vitamin C at a high concentration (3 mM) had a protective effect against oxidative stress in platelets caused by cisplatin (20 μM). It diminished platelet lipid peroxidation and reactive oxygen species generation induced by cisplatin. In the presence of vitamin C, the catalase activity was suppressed.

ISSN:0959-4973    

出版商:OVID    

年代:2000

数据来源: OVID