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N Papadopoulos

Publications and source records attributed to N Papadopoulos.

At least 127 records · Page 7Linked to original sources
PubMed1994

Mutations of two PMS homologues in hereditary nonpolyposis colon cancer.

Hereditary nonpolyposis colorectal cancer (HNPCC) is one of man's commonest hereditary diseases. Several studies have implicated a defect in DNA mismatch repair in the pathogenesis of this disease. In particular, hMSH2 and hMLH1 homologues of the bacterial DNA mismatch repair genes mutS and mutL, respectively, were shown to be mutated in a subset of HNPCC cases. Here we report the nucleotide sequence, chromosome localization and mutational analysis of hPMS1 and hPMS2, two additional homologues of the prokaryotic mutL gene. Both hPMS1 and hPMS2 were found to be mutated in the germline of HNPCC patients. This doubles the number of genes implicated in HNPCC and may help explain the relatively high incidence of this disease.

Adenosine Triphosphatases↗
PubMed1994

Paradoxical inhibition of solid tumor cell growth by bcl2.

The BCL2 gene product has been demonstrated to prevent apoptosis and provide a selective growth advantage to many cell types. We report an unexpected effect of bcl2 expression on the in vitro growth of several solid tumor cell lines. Expression of bcl2 in these cell lines resulted in growth inhibition similar to that seen with p53. In contrast, a COOH-terminal deletion mutant of bcl2 was unable to suppress growth. Thus, the bcl2 protein may exert distinct biological effects in different cell types.

Base Sequence↗
PubMed1994

Mutation of a mutL homolog in hereditary colon cancer.

Some cases of hereditary nonpolyposis colorectal cancer (HNPCC) are due to alterations in a mutS-related mismatch repair gene. A search of a large database of expressed sequence tags derived from random complementary DNA clones revealed three additional human mismatch repair genes, all related to the bacterial mutL gene. One of these genes (hMLH1) resides on chromosome 3p21, within 1 centimorgan of markers previously linked to cancer susceptibility in HNPCC kindreds. Mutations of hMLH1 that would disrupt the gene product were identified in such kindreds, demonstrating that this gene is responsible for the disease. These results suggest that defects in any of several mismatch repair genes can cause HNPCC.

Adaptor Proteins, Signal Transducing↗
PubMed1994

APC gene mutations in the mutation cluster region are rare in esophageal cancers.

BACKGROUND/AIMS: The molecular pathogenesis of esophageal cancers is not completely understood. Frequent allelic losses occur on chromosome 5q, suggesting the presence of a tumor-suppressor gene that is important in esophageal tumorigenesis. Because the APC gene is located on chromosome 5q, we sought to determine its involvement as a candidate tumor-suppressor gene in esophageal carcinogenesis. METHODS: Thirty-five esophageal squamous cell carcinomas and 18 adenocarcinomas were collected with corresponding normal gastric mucosae. A region of APC spanning codons 686-1693 and including most reported mutations was screened for truncating mutations using an in vitro synthesized protein assay. Single-strand conformation polymorphism analysis was also used to examine APC codons 764-842 and codons 1032-1310 for missense and nonsense mutations. RESULTS: One squamous cell carcinoma and one adenocarcinoma each contained a truncating mutation within the mutation cluster region of APC. CONCLUSIONS: The discovery of two truncating mutations identifies APC as a gene involved in a subset of esophageal carcinomas. The low rate of APC mutation observed here, coupled with the high reported rate of loss of heterozygosity on chromosome 5q, suggests the possibility that a gene or genes on chromosome 5q distinct from APC may be the target(s) of allelic deletion in most esophageal tumors.

Adenocarcinoma↗
PubMed1994

Migration of cultured vascular smooth muscle cells through a basement membrane barrier requires type IV collagenase activity and is inhibited by cellular differentiation.

The migration of vascular smooth muscle cells (VSMCs) from the tunica media to the neointima is a key event in the development and progression of many vascular diseases and a highly predictable consequence of mechanical injury to the blood vessel. In vivo, VSMCs are surrounded by and embedded in a variety of extracellular matrices (ECMs) that must be traversed during migration. One of the principal barriers to cell movement in the intact vessel is the basement membrane (BM) that surrounds each VSMC and separates the VSMC-containing medial cell layer from the endothelium. We have used a Boyden chamber to monitor the ability of VSMCs to degrade a BM barrier as they migrate toward a chemoattractant and to define the role of extracellular proteases in this process. We show that cultured VSMCs can migrate across a BM barrier and that this ability was dependent on the phenotypic state of the cell. VSMCs maintained in a proliferating or "synthetic" state readily migrated across a BM toward a chemoattractant, whereas the migration of serum-starved/differentiated VSMCs was suppressed by > 80% (P < .001). By use of a number of peptides that inhibit matrix metalloproteinase (MMP) activity, the migration of proliferating VSMCs across the BM barrier was inhibited by > 80% (P < .0001), whereas migration that occurred in the absence of the barrier was unaffected. Northern blotting and zymographic analyses indicated that 72-kD type IV collagenase (MMP2) was the principal MMP expressed and secreted by these cells. Accordingly, antisera capable of selectively neutralizing MMP2 activity also inhibited VSMC migration across the barrier without significantly affecting the migration of VSMCs in the absence of the barrier. Finally, MMP2 activity was also regulated by the phenotypic state of the cells in that MMP2 activity expressed by serum-starved/differentiated VSMCs was < 5% of that measured in proliferating VSMCs. Extrapolating to the in vivo situation in which VSMCs reside in an ECM composed of various BM barriers, these results suggest that VSMC migration in vivo may be dependent on MMP2 activity. That activity, in turn, could be regulated by the phenotypic state of VSMCs and increase as these cells undergo the transition from a quiescent and differentiated state to that of a dedifferentiated, proliferating, and motile phenotype after injury to the vessel.

Animals↗
PubMed1993

Mutations of a mutS homolog in hereditary nonpolyposis colorectal cancer.

Recent studies have shown that a locus responsible for hereditary nonpolyposis colorectal cancer (HNPCC) is on chromosome 2p and that tumors developing in these patients contain alterations in microsatellite sequences (RER+ phenotype). We have used chromosome microdissection to obtain highly polymorphic markers from chromosome 2p16. These and other markers were ordered in a panel of somatic cell hybrids and used to define a 0.8 Mb interval containing the HNPCC locus. Candidate genes were then mapped, and one was found to lie within the 0.8 Mb interval. We identified this candidate by virtue of its homology to mutS mismatch repair genes. cDNA clones were obtained and the sequence used to detect germline mutations, including those producing termination codons, in HNPCC kindreds. Somatic as well as germline mutations of the gene were identified in RER+ tumor cells. This mutS homolog is therefore likely to be responsible for HNPCC.

Amino Acid Sequence↗
PubMed1993

Hypermutability and mismatch repair deficiency in RER+ tumor cells.

A subset of sporadic colorectal tumors and most tumors developing in hereditary nonpolyposis colorectal cancer patients display frequent alterations in microsatellite sequences. Such tumors have been thought to manifest replication errors (RER+), but the basis for the alterations has remained conjectural. We demonstrate that the mutation rate of (CA)n repeats in RER+ tumor cells is at least 100-fold that in RER- tumor cells and show by in vitro assay that increased mutability of RER+ cells is associated with a profound defect in strand-specific mismatch repair. This deficiency was observed with microsatellite heteroduplexes as well as with heteroduplexes containing single base-base mismatches and affected an early step in the repair pathway. Thus, a true mutator phenotype exists in a subset of tumor cells, the responsible defect is likely to cause transitions and transversions in addition to microsatellite alterations, and a biochemical basis for this phenotype has been identified.

Base Sequence↗
PubMed1993

Phase II study of alpha-interferon and 13-cis-retinoic acid in metastatic melanoma.

The combination of alpha-interferon and 13-cis-retinoic acid has shown significant activity against a number of human tumors. We conducted a phase II trial to test whether the combination would have a major response rate of 30% or more in patients with refractory, metastatic melanoma. Eleven patients were treated on the study. Alpha-interferon was administered subcutaneously three times a week at a dose of 10 million U/m2 and 13-cis-retinoic acid was administered orally at a dose of 1 mg/kg/day. No patient achieved a partial or complete remission. The combination of alpha-interferon and 13-cis-retinoic acid is unlikely to have significantly higher therapeutic activity than alpha-interferon alone.

Adult↗
PubMed1993

Nucleolar organizer regions (NORs) staining and proliferating cell nuclear antigen (PCNA) immunostaining in mucosa-associated lymphoid tissue (MALT) gastric lymphomas.

Nucleolar organizer region-associated proteins (AgNOR) and proliferating cell nuclear antigen (PCNA) have been studied by means of a silver staining technique and immunohistochemistry, in paraffin-embedded, gastrectomy specimens of 12 low-grade and 13 high-grade gastric MALT lymphomas respectively. A significant difference was found between the AgNOR count and PCNA index of low-grade lymphomas (mean AgNOR count 2.5 and mean PCNA index 8.33%) and high-grade lymphomas (mean AgNOR count 8.67 and mean PCNA index 49.7%). It is suggested that both methods are useful adjuncts to histopathology for the distinction between low and high grade gastric MALT lymphomas. We also found heterogeneity in AgNOR counts and PCNA index among individual cases of either low or high grade MALT gastric lymphomas. This suggests that the AgNOR count and PCNA index is helpful in the individual approach of the proliferation rate of each tumour, a parameter of potential importance for predicting the biological behaviour of the tumour and the prognosis of the disease.

Antigens, Neoplasm↗
PubMed1993

Phase II study of vindesine and dacarbazine with or without non-specific stimulation of the immune system in patients with metastatic melanoma.

A single dose of dacarbazine (DTIC), followed by a 5-day intravenous infusion of vindesine (VDS) was administered every 3 weeks to 103 patients with metastatic melanoma. One half of the patients were randomised to receive intravenous methanol extraction residue (MER) of bacillus Calmette-Guerin (BCG) in addition to chemotherapy, on days 7 and 14 of each course. 98 patients were evaluable. The response rates in treatment groups were 16 and 17%, respectively (confidence interval 9-24%). Neither the response rate nor the survival improved when MER was added to chemotherapy. Toxicity was moderate except for a significant granulocytopenia. The combination of DTIC and VDS is not more effective than DTIC alone and has added neurotoxicity.

Adolescent↗
PubMed1993

Transcriptional control of the chicken cardiac myosin light-chain gene is mediated by two AT-rich cis-acting DNA elements and binding of serum response factor.

Transcriptional control of the cardiac/slow skeletal alkali myosin light-chain (MLC1c/1s) gene is mediated, in part, by two highly conserved AT-rich cis-acting elements present in the immediate 5' flanking region. These elements cooperate to form an enhancer that can impart tissue specificity to heterologous promoters that are themselves not tissue specific in their pattern of expression. In the chicken, one of these elements matches the binding site for myocyte-specific enhancer-binding factor 2, while the other is a cis-acting element present in the transcriptional control regions of all striated alkali MLC genes (except MLC3f) and is referred to as the MLC box. The central decanucleotide core region of the MLC box closely resembles the CArG (CC[A/T]6GG) box of the serum response element, and the binding of muscle nuclear protein complexes to this element can be competed for with a synthetic serum response element. On the basis of their competition profiles and requirements for nonspecific competitor, two nuclear protein complexes, which compete for binding to the CArG-like region of the MLC box, have been identified. One of the complexes binds to a mutation of the CArG-like region that inactivates transcription of a linked reporter gene, while binding of the other complex is inhibited by this mutation. This latter complex reacts with an antibody to serum response factor (SRF) and exhibits the same binding characteristics as purified SRF. These results demonstrate that transcriptional control of the chicken MLC1c/1s gene resides in an upstream enhancer that is composed of two separate AT-rich elements, both of which are required to drive expression of a linked reporter gene. The binding of a nuclear protein complex containing SRF to one of these elements, the MLC box, is required for gene activation and apparently inhibited by other nuclear factors whose binding overlaps that of the SRF complex.

Animals↗
PubMed1992

Experimental models that mimic the differentiation and dedifferentiation of vascular cells.

Endothelial and smooth muscle cells normally exist in a quiescent differentiated state. After injury to the vessel, these cells dedifferentiate, migrate, and proliferate as needed for repair. In culture on plastic, both endothelial and smooth muscle cells exhibit the dedifferentiated phenotype. We have found that laminin and reconstituted basement membrane proteins (Matrigel) induce a very rapid cessation of endothelial cell proliferation followed by alignment and subsequent reorganization into tubelike structures. We have also found that smooth muscle cells in culture exhibit a differentiated phenotype when exposed to Matrigel. The molecular mechanisms involved in smooth muscle differentiation resemble those of skeletal muscle, in which proliferation and differentiation appear to be mutually exclusive states controlled by both positive and negative transcriptional regulators. The dedifferentiated smooth muscle cells produce proteases and exhibit a migratory and invasive phenotype capable of destroying normal tissue architecture. These studies suggest that the modulation of endothelial and smooth muscle cells between a differentiated and dedifferentiated phenotype is regulated by extracellular matrix components as well as by cytokines. Model systems such as those described here should allow the identification of molecular events controlling the differentiation of vascular cells and facilitate the development of therapeutic agents that maintain healthy vessels.

Basement Membrane↗
PubMed1991

Comparison of two schedules of cefoperazone plus aztreonam in the treatment of neutropenic patients with fever.

Cancer patients were randomized to receive an every 4 hour or every 8 hour schedule of cefoperazone plus aztreonam during 617 febrile episodes. The overall response rate for the 478 evaluable episodes was 76% and there was no difference in response rate between the two schedules. The response rate was 79% for cases of pneumonia and 63% for cases of bacteremia. Only 50% of the microbiologically documented infections caused by gram-positive organisms responded whereas 95% of gram-negative infections, including all of those caused by Pseudomonas aeruginosa, responded. Response rates were lower among patients whose neutrophil counts decreased during therapy than among those whose neutrophil counts increased (64% vs. 85%, p = 0.008). Side-effects that were possibly or probably related to antibiotic therapy were observed during 11% of the episodes. The most common side-effects were diarrhea and rashes including one case of Stevens-Johnson syndrome. Three patients developed a coagulopathy during therapy. Cefoperazone plus aztreonam proved to be an effective combination for treatment of gram-negative infections and fever of unknown origin in cancer patients and an every 8-hour schedule of administration was as effective as an every 4-hour schedule. Approximately half of the patients with gram-positive infections required additional antibiotics for successful therapy.

Aztreonam↗
PubMed1990

A phase II trial of taxol in metastatic melanoma.

Taxol is an investigational new drug which is currently undergoing Phase II evaluation in various tumors. It is a plant alkaloid extracted from the western Yew, Taxus brevifolia. In this study, patients with metastatic melanoma who were previously untreated, received Taxol at a starting dose of 250 mg/m2 delivered as a continuous intravenous (IV) infusion over 24 hours, at 3-week intervals. All patients were premedicated with oral dexamethasone and IV diphenhydramine hydrochloride as prophylaxis against allergic reactions. Three of 25 patients had a partial response (PR) for a response rate of 12% (CI, 3%-31%). In addition four patients had objective regression of tumor that failed to qualify for a PR but these responses were as durable, lasting 6 to 17 months. No patient experienced acute allergic reactions. The major toxicity of Taxol was neutropenia requiring dose reduction to 200 mg/m2 in a majority of the patients. Our data confirm that Taxol has definite although limited activity against metastatic melanoma.

Adult↗
PubMed1990

Intracarotid cisplatin-based chemotherapy in patients with malignant melanoma and central nervous system (CNS) metastases.

Twenty-three patients with malignant melanoma metastatic to the central nervous system (CNS) were treated with intracarotid cisplatin-based chemotherapy. Twenty-two had failed prior cranial radiation therapy (one patient refused radiation therapy) and had progressive brain metastases documented by computerized tomography (CT). Intracarotid cisplatin 40-75 mg/m2 was administered alone (seven patients) with 1,3-bis(2-Chloroethyl)-1-nitrosourea (BCNU) (13 patients) or bleomycin (three patients). Courses were repeated monthly with CT scan. Seven patients (30%) had objective improvement in CT scans and three patients (13%) had stabilization of disease. The median time to tumor progression for responding patients was 20 weeks (range 8-34 weeks) while stable disease ranged from 9-12 weeks. In three patients the extracranial disease progressed while the brain metastases responded. Neurological and retinal toxicity were potential complications of therapy. Intracarotid cisplatin-based chemotherapy may be useful for palliation in selected patients with malignant melanoma and CNS metastases.

Adult↗
PubMed1989

A prospective evaluation of a triple-drug regimen containing cisplatin, vinblastine, and dacarbazine (CVD) for metastatic melanoma.

Based on the independent activity of cisplatin, vinblastine, and dimethyl-triazeno-imidazole-carboxamide (DTIC) (CVD), a combination of these agents was used in the treatment of patients with advanced melanoma. Vinblastine was used in a dose of 1.6 mg/m2/d for 5 days, DTIC was used in a dose of 800 mg/m2 intravenously (IV) on day 1, and cisplatin was used in a dose of 20 mg/m2/d for 4 days starting on day 2 of chemotherapy. The courses of chemotherapy were repeated at 3-week intervals. All patients were premedicated with antiemetics, and IV hydration was used before cisplatin. Fifty-two consecutive patients were registered and 50 were evaluable for response. Two patients achieved a complete response (CR) and 18 patients had a partial response (PR) for an overall response rate of 40% (95% confidence interval, 27% to 55%). The median duration of response was 9 months and the median survival time of the responders was 12 months. The overall median survival time of patients treated on this protocol was 9 months. The treatment was associated with significant toxicity consisting of nausea, vomiting, diarrhea, and partial hair loss. Additionally, neutropenia with a median nadir granulocyte count of 500/microliters was observed, and significant anemia required blood transfusions in a majority of the patients after three to four courses of chemotherapy. The dose-limiting toxicity was peripheral neuropathy which required discontinuation of cisplatin after six to eight courses of chemotherapy. We believe that this triple-drug regimen has significant activity that appears to be superior to the single-agent activity of these drugs, both in terms of increased response rate and duration of response.

Adult↗