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Biomedical subjects

E Olah

Publications and source records attributed to E Olah.

At least 37 records · Page 2Linked to original sources
PubMed1998

Haplotype and phenotype analysis of nine recurrent BRCA2 mutations in 111 families: results of an international study.

Several BRCA2 mutations are found to occur in geographically diverse breast and ovarian cancer families. To investigate both mutation origin and mutation-specific phenotypes due to BRCA2, we constructed a haplotype of 10 polymorphic short tandem-repeat (STR) markers flanking the BRCA2 locus, in a set of 111 breast or breast/ovarian cancer families selected for having one of nine recurrent BRCA2 mutations. Six of the individual mutations are estimated to have arisen 400-2,000 years ago. In particular, the 6174delT mutation, found in approximately 1% of individuals of Ashkenazi Jewish ancestry, was estimated to have arisen 29 generations ago (1-LOD support interval 22-38). This is substantially more recent than the estimated age of the BRCA1 185delAG mutation (46 generations), derived from our analogous study of BRCA1 mutations. In general, there was no evidence of multiple origins of identical BRCA2 mutations. Our study data were consistent with the previous report of a higher incidence of ovarian cancer in families with mutations in a 3.3-kb region of exon 11 (the ovarian cancer cluster region [OCCR]) (P=.10); but that higher incidence was not statistically significant. There was significant evidence that age at diagnosis of breast cancer varied by mutation (P<.001), although only 8% of the variance in age at diagnosis could be explained by the specific mutation, and there was no evidence of family-specific effects. When the age at diagnosis of the breast cancer cases was examined by OCCR, cases associated with mutations in the OCCR had a significantly older mean age at diagnosis than was seen in those outside this region (48 years vs. 42 years; P=.0005).

Adult↗
PubMed1997

Molecular mechanisms in the antiproliferative action of quercetin.

A single treatment with quercetin (5.5 microM), a plant flavonoid, activated both apoptosis and differentiation programs in K562 human leukemia cells. K562 cells expressed commitment to apoptosis after 1 h exposure, however, at least 12 h of drug exposure was needed to induce differentiation. Early (1 h) down-regulation of the c-myc and Ki-ras oncogenes and rapid reduction of inositol-1,4,5-trisphosphate (IP3) concentration (IC50 = 9 microM, 1 h incubation) are part of the antiproliferative action of quercetin and appear to relate to induction of differentiation and/or apoptotic program of K562 leukemia cells treated with quercetin.

Apoptosis↗
PubMed1997

Regulation of the signal transduction program by drugs.

The purpose of this paper was to clarify critical aspects of the behavior of signal transduction activity in normal and cancer cells. 1. Signal transduction activity in the conversion of phosphatidylinositol through PI and PIP kinases and PLC to IP3 is regulated at multiple sites. In liver, hepatomas and human carcinomas PIP kinase is the rate limiting enzyme and PLC activity is present in great excess. 2. The steady-state signal transduction activity as measured by the three enzyme activities and IP3 concentration was markedly up-regulated in rat hepatomas of different growth rates. The steady-state specific activities of the three signal transduction enzymes were elevated in ovarian carcinomas as compared to normal ovary. Increased enzyme activities were also observed in human breast carcinoma cells as compared to normal human breast parenchymal cells. In breast, ovarian and rat hepatoma cells as they go through lag, log and plateau phases, IP3 concentration in the early lag phase increased 4.5- to 20-fold and PI and PIP kinase activities peaked in mid-log phase. These events returned to baseline levels in the plateau phase. PLC activity did not change. 3. The bone marrow PI and PIP kinase activities in 3-day starvation were decreased to 13% and IP3 concentration was reduced to 24%; at 1-day refeeding they returned to normal. PLC activity changed little. These alterations are in line with the rapid t1/2 degradation rates (12 min) of PI and PIP kinases observed in studies with cycloheximide. By contrast, PLC has a long half-life. 4. The molecular action of tiazofurin entails inhibition of IMP DH activity, decrease in GTP and IP3 concentrations, reduction of ras and myc oncogene expression, and signal transduction enzyme activities. These events are followed by induced differentiation and apoptosis. There are also decreases in enzyme activities which have rapid turnover, including TdR kinase, dTMP synthase, and GPRT. In vitro studies indicated that these events are abrogated by addition of guanine which restores GTP concentrations. Therefore, most or all these events were brought about by the reduced GTP concentration in the tiazofurin target cells. 5. Quercetin and genistein are able to inhibit PI and PIP kinase activities and reduce IP3 concentration in vivo and in tissue culture systems. These flavonoids are also inhibitors of cell proliferation and clonogenic ability in rat hepatoma 3924A and in human OVCAR-5 and MDA-MB-435 cells. Quercetin down-regulated the expression of c-myc and Ki-ras oncogenes and led to induced differentiation and apoptosis in K562 cells. Genistein reduced IP3 concentration in vivo and in the tissue culture system. Genistein is antiproliferative and has cytototoxicity in human carcinoma cells. All three drugs, tiazofurin, quercetin and genistein, act, in part at least, through depression of cellular IP3 concentration although the mechanisms may not be identical. 6. Quercetin and genistein, which attack different targets and different phases of the cell cycle, proved to be synergistic in OVCAR-5 cells. The impact of tiazofurin, genistein and quercetin is of interest because the drugs crucially inhibit the display of the neoplastic program of cells and lead to induced differentiation and apoptosis.

1-Phosphatidylinositol 4-Kinase↗
PubMed1996

Allele loss from large regions of chromosome 17 is common only in certain histological subtypes of ovarian carcinomas.

Using a panel of ten polymorphic markers, we examined the frequency of loss of heterozygosity (LOH) on chromosome 17 in 55 sporadic ovarian tumours. LOH on 17p and 17q was observed to be 50% and 62% respectively. LOH at D17S5 was detected in 24/36 (67%) of malignant cases and in 19/43 (44%) at TP53; the marker D17S855 intragenic to the BRCA1 gene showed allele loss in 50% (20/40) cases. The data presented here suggest that loss of the whole chromosome 17 is a relatively frequent event (30%) in ovarian carcinomas and this observation is especially frequent for serous, transitional cell and anaplastic histological subtypes. Mucinous and endometrioid ovarian tumours showed only short interstitial deletions (4/11, 36%). The overall frequency of the short deletions was relatively low (7/43, 16%) in our panel of carcinomas. Amplification of c-erbB-2/neu oncogene was detected in 32% (11/34) of the carcinomas tested; the gene was amplified only in those histological subtypes in which high incidence of LOH on chromosome 17 was observed, and was associated with advanced stages of the disease. We conclude that different histological types of tumour may have different aetiological mechanisms, and tumour-suppressor genes on chromosome 17 might be associated specifically with serous and transitional cell ovarian carcinomas.

Alleles↗
PubMed1995

Quercetin down-regulates signal transduction in human breast carcinoma cells.

Signal transduction activity was markedly elevated in cancer cells as shown by the increased activity of enzymes utilizing 1-phosphatidylinositol, PI (PI 4-kinase and PI-4-phosphate 5-kinase) for the production of the second messenger inositol 1,4,5-trisphosphate, IP3, in rat hepatomas (Cancer Res. 54: 2611;5574, 1994) and in human ovarian and breast carcinoma cells (Life Sci. 55:1487, 1994). Quercetin, a flavonoid, in human breast carcinoma MDA-MB-435 cells produced growth inhibition (IC50 = 55 microM) and cytotoxicity (LC50 = 26 microM). Quercetin inhibited PI kinase activity in extracts of breast carcinoma cells (IC50 = 6 microM) and in cultured cells (IC50 = 10 microM) with a minor inhibition of PIP kinase activity. IP3 concentration decreased in parallel with PI kinase activity. In time sequence studies quercetin in breast carcinoma cells brought down PI kinase and IP3 concentration in 60 min to 5 and 6%, respectively; PIP kinase activity was at 63% of controls. The results demonstrate for the first time in proliferating human breast carcinoma cells a reduction by quercetin of the increased capacity for signal transduction, thus providing a novel and sensitive target in cancer cells.

1-Phosphatidylinositol 4-Kinase↗
PubMed1995

Linkage of reduction in 1-phosphatidylinositol 4-kinase activity and inositol 1,4,5-trisphosphate concentration in human ovarian carcinoma cells treated with quercetin.

Quercetin inhibited 1-phosphatidylinositol (Pl) 4-kinase, EC 2.7.1.67 (Pl kinase) activity in a concentration-dependent manner (IC50 = 4 microM) in particulate extracts from human ovarian carcinoma. In OVCAR-5 cells quercetin produced growth inhibition (IC50 = 63 microM) and cytotoxicity (LC50 = 17 microM). The growth inhibition by quercetin was accompanied by an 80% decrease in Pl kinase activity and a 65% decrease in the concentration of the second messenger, inositol 1,4,5-trisphosphate (IP3). When human OVCAR-5 cells were plated and expressed their neoplastic proliferative program in the log phase, Pl kinase and Pl 4-phosphate 5-kinase, EC 2.7.1.68 (PIP kinase) activities coordinately increased to a peak of 5.8- and 4.5-fold, respectively. The results demonstrate for the first time inhibition by quercetin of the enhanced capacity for operation of signal transduction in human ovarian carcinoma cells, thus providing a novel target in cancer cells.

1-Phosphatidylinositol 4-Kinase↗
PubMed1994

Synergistic action of taxol with tiazofurin and methotrexate in human breast cancer cells: schedule-dependence.

Taxol (paclitaxel, (NSC 125973)) is an active agent in the treatment of metastatic carcinoma of the breast; however, positive responses were observed in only about 60% of cases. Therefore, drug combinations which might improve the effectiveness are required. Since tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC 286193), methotrexate (MTX) and taxol exert their anticancer action in different phases of the cell cycle and have different biochemical targets, we tested the hypothesis that tiazofurin and methotrexate might by synergistic with taxol. MDA-MB-435 human breast cancer cells were grown in monolayer in flasks. In the growth inhibition assay for tiazofurin, methotrexate and taxol the IC50s were 12.5, 0.5 and 0.016 microM, respectively, and in the clonogenic assay 4.5, 0.065 and 0.004 microM. When taxol was given 6 hr before tiazofurin, antagonism was observed and summation was seen when drugs were given simultaneously. Synergism was obtained in both growth inhibitory and clonogenic assays when tiazofurin was followed 12 hr later by taxol. Methotrexate and taxol had an antagonistic effect when they were added simultaneously or when taxol was given 6 hr before methotrexate; summation was observed when taxol was followed 12 hr later by methotrexate. Synergistic action was obtained in the clonogenic assay when methotrexate was followed 12 hr later by taxol. The protocols yielding synergism should be of value in the design of taxol-based clinical trials for breast cancer.

Cell Division↗
PubMed1992

Inhibition by tiazofurin of inosine 5'-phosphate dehydrogenase (IMP DH) activity in extracts of ovarian carcinomas.

Cancer cells have an increased ability to synthesize GTP (guanosine triphosphate) because of increased activity of IMP DH (inosine 5'-phosphate dehydrogenase, EC 1.1.1.205). Because IMP DH activity is rate limiting for de novo biosynthesis of GTP, this enzyme was suggested as a sensitive target for chemotherapy. Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide) is converted in the cells into the active metabolite, TAD, (thiazole-4-carboxamide adenine dinucleotide) which potently inhibits IMP DH activity. By adding TAD to tissue extracts one can determine the extent of inhibition of IMP DH. We applied the IMP DH assay method to extracts of normal ovaries (N = 11) and epithelial ovarian carcinomas (N = 10). The IMP DH activity (mean +/- SE) in ovarian carcinoma was 21.1 +/- 5.8 which was markedly higher than that observed in normal ovaries (2.9 +/- 0.7 nmol/hr/mg protein) (P < 0.05%). The inhibition by TAD of IMP DH activity in ovarian carcinomas (N = 4) was 81%. The results indicate that IMP DH activity is elevated sevenfold in ovarian carcinomas as compared to normal ovary and can be inhibited by exposure to tiazofurin (TAD). Similar high IMP DH activity and inhibition of the activity by TAD was observed in patients with chronic granulocytic leukemia in blast crisis among whom 70 to 80% remissions were reported. Since there is increased IMP DH activity in human ovarian carcinomas and in OVCAR-5 cells and tiazofurin and TAD inhibit IMP DH activity of these cells and the proliferation of human ovarian carcinoma xenografts in the mouse, tiazofurin may merit serious consideration for a Phase II trial for patients with recurrent/refractory epithelial ovarian carcinoma.

Adenocarcinoma↗
PubMed1991

AZT: a biochemical response modifier of methotrexate and 5-fluorouracil cytotoxicity in human ovarian and pancreatic carcinoma cells.

In ovarian and pancreatic carcinoma cell lines, the activity of the salvage enzyme, thymidine kinase (EC 2.7.1.21), was 2- to 13-fold higher than that of the key enzyme of thymidylate de novo biosynthesis, thymidylate synthase (dTMP synthase, EC 2.1.1.45). AZT (3'-azido-3'-deoxythymidine, zidovudine) competitively inhibited thymidine kinase activity in extracts of human ovarian and pancreatic carcinoma cells, with Dixon plots yielding Ki = 1.1 microM in both cell lines. AZT (20 microM) yielded synergistic cytotoxicity with methotrexate (0.4 microM) in human pancreatic carcinoma cells in clonogenic assay and also with methotrexate (0.02 microM) in human ovarian carcinoma cells, as measured by cell counts. Thymidine (10 microM) and hypoxanthine (100 microM) reversed these inhibitions. AZT (20 or 40 microM) also provided synergistic cytotoxicity with 5-fluorouracil (0.5 and 1.0 microM) in human pancreatic carcinoma cells in clonogenic assay. These studies suggest a new role for AZT, which, as an inhibitor of thymidine salvage, should be useful as a biochemical response modifier to provide a synergistic clinical anticancer impact on de novo biosynthesis of thymidylates in conjunction with methotrexate or 5-fluorouracil.

Animals↗
PubMed1990

Cytogenetic analyses of three papillary carcinomas and a follicular adenoma of the thyroid.

Cytogenetic data of three papillary carcinomas and a follicular adenoma using direct preparations or cell cultures or both after 7 to 60 days in vitro are presented. Although karyotype of the follicular adenoma proved completely normal, in each of the three papillary carcinomas a modal chromosome number in the diploid range and a deleted 11q were observed. In case 1 the del(11)(q23) was associated with rearrangement of chromosome 1 and other marker chromosomes. Our results suggest that 11q deletion may be specific for papillary carcinoma of the thyroid.

Adenoma↗
PubMed1990

Down-regulation of c-myc and c-Ha-ras gene expression by tiazofurin in rat hepatoma cells.

There was an overexpression of the c-myc gene (11-fold) and of the c-Ha-ras gene (2-fold) in rat hepatoma 3924A cells compared to normal rat liver as measured by dot-blot analysis of total cytoplasmic RNA. The overexpression of c-myc was attributed to a 10- to 14-fold amplification and rearrangement of the c-myc sequences as determined by Southern blot analysis. The expression of the c-myc also was dependent upon the proliferative state of the hepatoma cells. Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide; NSC 286193), an inhibitor of the activity of IMP dehydrogenase (EC 1.1.1.205), the rate-limiting enzyme of GTP biosynthesis, resulted in a rapid drop (less than 1 h) to 50% of control in the target enzyme activity in the hepatoma cells and in a subsequent marked decrease to 55% in GTP concentration. These events were followed at 12 h of tiazofurin treatment by a 3-fold reduction in the expression of the c-myc gene and a 9-fold decline in that of the c-Ha-ras gene. These results in the hepatoma cells provide evidence in support of the earlier demonstrated correlation in K562 cells between GTP concentration and expression of c-myc and c-ras genes (Olah et al., 1989). These genes might depend on GTP for their expression in hepatoma cells and they might cooperate in a signal pathway that controls cell proliferation.

Animals↗
PubMed1989

Significance of purine salvage in circumventing the action of antimetabolites in rat hepatoma cells.

The flux activities of de novo and salvage purine synthesis were compared in rat hepatoma 3924A cells in various growth phases. The initial rate assays of [14C]adenine, [14C]hypoxanthine, and [14C]guanine incorporation yielded Michaelis-Menten kinetics with Kms of 5, 7, and 7 microM, respectively. After replating plateau phase cells in lag and log phases the activity of purine de novo pathway increased 4.5- to 8-fold with a preferential rise in guanylate synthesis, whereas purine salvage activities increased only 1.6- to 2.1-fold. However, for the syntheses of IMP, AMP, and GMP, the activities of purine salvage pathways were 2- to 7-fold, 5- to 28-fold, and 2- to 32-fold higher than those of the de novo purine pathway. Treatment of cells with acivicin, an inhibitor of the activity of amidophosphoribosyltransferase, phosphoribosylformylglycinamidine synthase, and GMP synthase, inhibited the flux activities of de novo purine, adenylate, and guanylate syntheses to 37, 73, and 3% of the controls and decreased the concentration of GTP to 42%; the concentration of ATP did not change and that of 5-phosphoribosyl 1-pyrophosphate increased 3.1-fold. Under these conditions the activities of salvage synthesis from hypoxanthine and guanine were enhanced 2.5-fold. Treatment of hepatoma cells with IMP dehydrogenase inhibitors, tiazofurin, ribavirin, and 4-carbamoylimidazolium 5-olate, to block de novo guanylate synthesis accelerated the flux activity of guanine salvage pathway. The higher capacity of purine salvage pathway than that of the de novo one and the further rise of the activity in response to the drugs targeted against the de novo pathway highlight the important role salvage synthesis might play in circumventing the impact of antimetabolites of de novo purine synthesis in cancer chemotherapy.

Animals↗
PubMed1989

Clinical and molecular impact of inhibition of IMP dehydrogenase activity by tiazofurin.

The impact of tiazofurin on inhibition of IMP dehydrogenase was discussed at the clinical and molecular levels. 1. Evidence was provided for the role of IMP dehydrogenase and guanylates in the expression of the neoplastic program in cancer cells with particular relevance to human leukemic cells. 2. The argument for expecting an impact of tiazofurin in human myelocytic cells was provided. 3. Similarity of the kinetics of human leukemic cell IMP dehydrogenase to the rat hepatoma enzyme was documented. 4. New evidence was provided for the role of salvage in chemotherapy and the function of hypoxanthine in inhibiting guanine salvage. 5. The action of tiazofurin and retinoic acid was reported in HL-60 leukemic cells. 6. The effect of tiazofurin and retinoic acid on proliferation and cytotoxicity was outlined for hepatoma 3924A cells. 7. The effect of guanine on induced differentiation by tiazofurin and retinoic acid was examined. 8. Biochemical basis was provided for the lack of development of resistance in patients treated with tiazofurin. 9. Presumptive evidence was provided that tiazofurin treatment induced differentiation of leukemic cells in the patients. 10. The molecular biology of tiazofurin-induced differentiation in K-562 cells was reviewed with the possible relevance to clinical treatment that tiazofurin might also act through down-regulation of ras oncogene.

Animals↗
PubMed1988

Induction of erythroid differentiation and modulation of gene expression by tiazofurin in K-562 leukemia cells.

Tiazofurin (2-beta-D-ribofuranosyl-4-thiazole-carboxamide; NSC 286193), an antitumor carbon-linked nucleoside that inhibits IMP dehydrogenase (IMP:NAD+ oxidoreductase; EC 1.1.1.205) and depletes guanylate levels, can activate the erythroid differentiation program of K-562 human leukemia cells. Tiazofurin-mediated cell differentiation is a multistep process. The inducer initiates early (less than 6 hr) metabolic changes that precede commitment to differentiation; among these early changes are decreases in IMP dehydrogenase activity and in GTP concentration, as well as alterations in the expression of certain protooncogenes (c-Ki-ras). K-562 cells do express commitment-i.e., cells exhibit differentiation without tiazofurin. Guanosine was effective in preventing the action of tiazofurin, thus providing evidence that the guanine nucleotides are critically involved in tiazofurin-initiated differentiation. Activation of transcription of the erythroid-specific gene that encodes A gamma-globin is a late (48 hr) but striking effect of tiazofurin. Down-regulation of the c-ras gene appears to be part of the complex process associated with tiazofurin-induced erythroid differentiation and relates to the perturbations of GTP metabolism.

Antimetabolites, Antineoplastic↗
PubMed1986

Aggressive infantile myofibromatosis: report of a case of a clinically progressive congenital multiple fibromatosis.

We report a case of congenital multiple fibromatosis (infantile myofibromatosis) showing the typical spindle-cellular proliferation with prominent vascularity on light microscopical observations. Electron microscopy showed the abundance of fibroblasts with conspicuous collagen and reticulin fibers together with numerous cells sharing the characteristics of both fibroblasts and smooth muscle cells (myofibroblasts). Neither visceral involvement nor ossification has been detected during the 4-year-long follow-up period. However, the clinical course has shown a slow, continuous, protracted though destructive proliferation of subcutaneous myofibroblastic nodules. These findings are contrasted with previous reports that claimed that the presence of myofibroblasts indicates benign behavior and results in the regression of fibromatous lesions.

Extremities↗
PubMed1984

Modulation of IMP dehydrogenase activity and guanylate metabolism by tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide).

Tiazofurin, a C-nucleoside, was cytotoxic in hepatoma 3924A cells grown in culture with an LC50 = 7.5 microM. In the culture, a closely linked dose-related response of tumor cell-kill and depletion of GTP pools was observed after tiazofurin treatment. In rats carrying subcutaneously transplanted hepatoma 3924A solid tumors, a single intraperitoneal injection of tiazofurin (200 mg/kg) caused a rapid inhibition of IMP dehydrogenase (EC 1.2.1.14) activity and depleted GDP, GTP, and dGTP pools in the tumor; concurrently, the 5-phosphoribosyl 1-pyrophosphate (PRPP) and IMP pools expanded 8- and 15-fold, respectively. Tiazofurin decreased tumoral IMP dehydrogenase activity and dGTP pools in a dose-dependent manner over a range of 50-200 mg/kg; by contrast, the depletion of GTP and the accumulation of IMP and PRPP pools were near maximum at 50 mg/kg. The increase in PRPP pools may be attributed to an inhibition by IMP of the activity of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8). The IMP dehydrogenase activity and the pools of ribonucleotides returned to the normal range by 24-48 h after the single injection of tiazofurin. However, the markedly depleted dGTP pools remained low for 72 h. Tiazofurin treatment resulted in significant anti-tumor activity in rats inoculated with hepatoma 3924A. The decrease in GTP levels and particularly the sustained depletion in the dGTP pools may explain, in part at least, the chemo-therapeutic action of tiazofurin on hepatoma 3924A. This is the first report showing that a marked therapeutic response was achieved against rapidly growing hepatoma 3924A by treatment with a single anti-metabolite.

Animals↗