Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Antineoplastic activity of tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide) is mediated by an anabolite of the drug thiazole-4-carboxamide adenine dinucleotide (TAD), an analog of NAD which inhibits IMP dehydrogenase activity resulting in the depletion of guanylate pools and cell death. Human chronic myelogenous leukemia K 562 cells were found to be sensitive to tiazofurin with an IC50 of 19.2 microM. TAD content in K 562 cells (1.3 nmol/10(9)/h) was in the range found in susceptible murine and human tumor cells. Studies were conducted to relate tiazofurin toxicity with biochemical effects by examining nucleotide pools. Among the nucleotides, only guanylate pools were significantly depleted by the drug. To further study the effect of the drug on the purine nucleotide de novo and salvage biosynthetic pathways, flux of radiolabelled formate and guanine was employed. The results showed that de novo synthesis of guanylates was curtailed primarily by the drug's action without influencing adenylate biosynthesis or salvage of guanine to guanylates. These studies show that K 562 cells are sensitive to selective inhibition of de novo guanylate pathway indicating that human chronic myelogenous leukemia in blast crisis might be a good candidate for Phase II clinical trials with tiazofurin.
 ...
PMID:Studies of purine and tiazofurin metabolism in drug sensitive human chronic myelogenous leukemia K 562 cells. 316 81

The diminution of NAD level in mouse thymus lymphocytes precedes their death under the effect of various genotoxic agents and manifests itself by the time of the onset of chromatin degradation. At the same time, in vitro, NAD does not influence the activity of micrococcus nuclease of Ca2+,Mg2+-dependent endonuclease from human spleen. Stimulation of protein poly(ADP-ribosylation) by exogenous NAD does not change the sensitivity of chromatin to micrococcus nuclease. In contrast to hepatocytes, in the thymus, no inhibition of Ca2+,Mg2+-endonuclease, resulting from ADP-ribosylation, occurs which may be due to low activity of ADP-ribosyl transferase in thymocytes. Incubation of thymus lymphocytes with benzamide prior to irradiation does not inhibit chromatin degradation. It is suggested that the decrease in the NAD level is one of the indications of the injury to thymocytes which is not related to the induction of their death. In contrast to thymocytes, the pretreatment of Ehrlich ascites tumor cells with benzamide produces a radiosensitizing effect.
 ...
PMID:[Participation of the NAD-poly(ADP ribose) system in the degradation of chromatin in irradiated thymocytes]. 325 28

The bifunctional NAD-dependent methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase from ascites tumor cells has very different kinetic properties from the larger NADP-dependent methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase-formyltetrahydrofolate synthetase present in all mammalian cells. The NAD-dependent dehydrogenase is unique in that it requires formation of a magnesium.enzyme complex to allow addition of the first substrate, NAD+. It catalyzes an equilibrium ordered kinetic mechanism that has methylenetetrahydrofolate as the last reactant to add and NADH as the last product released. The NADP-dependent dehydrogenase has the same order of addition of substrates, but NADPH is released prior to methenyltetrahydrofolate. The dehydrogenase-cyclohydrolase activities of both enzymes channel methenyltetrahydropteroylglutamate intermediates with the same efficiency which is unaffected by the number of glutamyl residues in the methylenetetrahydrofolate substrate. However, the cyclohydrolase activity of the bifunctional protein is kinetically independent of its dehydrogenase activity, as supported by its lack of inhibition by NAD+, whereas NADP+ strongly inhibits that of the NADP-dependent enzyme. This difference is further demonstrated by the observation that conversion of formyltetrahydrofolate to methylenetetrahydrofolate in the presence of reduced pyridine nucleotide is catalyzed readily only by the bifunctional enzyme.
 ...
PMID:The activities of the NAD-dependent methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase from ascites tumor cells are kinetically independent. 325 7

The substrate preference of an aldehyde dehydrogenase induced in rat liver cytosol by 3-methylcholanthrene was examined. This enzyme, T-ALDH, is identical to the aldehyde dehydrogenase inducible in rat liver by 2,3,7,8-tetrachloro-dibenzo-p-dioxin and the tumor-associated aldehyde dehydrogenase found in rat hepatocellular neoplasms. With either NAD or NADP as coenzyme, the preferred substrates were the aliphatic aldehydes n-hexanal, n-nonanal, and isobutyraldehyde and the aromatic aldehydes 2,5-dihydroxybenzaldehyde, benzaldehyde, and 3-hydroxybenzaldehyde. The results indicate that T-ALDH may play a role in oxidizing a variety of aldehydes produced in physiological lipid metabolism. On the contrary, this isozyme does not seem to participate in the oxidation of small aliphatic aldehydes generated during lipid peroxidation. Similarly, no significant activity could be detected when the enzyme was tested with aldehydes produced in carbohydrate, amino acid, polyamine, steroid, and vitamin metabolism.
 ...
PMID:Substrate preference of a cytosolic aldehyde dehydrogenase inducible in rat liver by treatment with 3-methylcholanthrene. 342 Jun 20

NAD-dependent methylenetetrahydrofolate dehydrogenase is expressed in transformed or established mammalian cell lines in vitro but only in the developmental tissues of normal adult animals (Mejia, N. R. and MacKenzie, R. E. (1985) J. Biol. Chem. 260, 14616-14620). The enzyme, which contains methenyltetrahydrofolate cyclohydrolase activity as well, has been purified 6000-fold from Ehrlich ascites tumor cells. The preparation is homogeneous by sodium dodecyl sulfate gel electrophoresis (Mr = 34,000), and results from cross-linking with bis(sulfosuccinimidyl)suberate are consistent with a dimeric structure (Mr = 68,000) for the native bifunctional enzyme. The dehydrogenase is specific for NAD and requires both a divalent cation, Mg2+ or Mn2+, for activity and as well is stimulated by inorganic phosphate. When compared to the usual NADP-dependent methylenetetrahydrofolate dehydrogenase from mouse liver, the NAD-dependent dehydrogenase activity of the murine tumor enzyme shows a greater affinity for the polyglutamate forms of folate.
 ...
PMID:NAD-dependent methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase from ascites tumor cells. Purification and properties. 348 46

Pertussis toxin catalyzes the ADP-ribosylation of the inhibitory subunit (Ni) of adenylate cyclase. Despite several studies which demonstrate that pertussis toxin influences cyclic AMP accumulation and hormone secretion in normal anterior pituitary cells, the target protein(s) for this toxin in these cells has not been identified. We have examined pertussis toxin mediated ADP-ribosylation in membrane preparations of tumor-derived (235-1, GH4C1, GH3) and normal anterior pituitary cells. Autoradiograms of SDS gels reveal that in the presence of [32P]NAD and pertussis toxin, a 40 kilodalton protein band was labeled in membrane preparations from cells cultured with vehicle. Such labeling was diminished when the cells were exposed to pertussis toxin (35 ng/ml) for 18 hours. Similar results were found in both tumor-derived and normal (monkey and rat) anterior pituitary cells. The pertussis toxin specific band was further resolved into two bands of approximately 39 and 41 kilodaltons. Autoradiograms of two dimensional gels revealed two ADP-ribosylated spots with isoelectric points of 5.7 and 6.2, although the molecular weights appeared identical (approx. 40 kilodaltons). Cholera toxin, which catalyzes the ADP-ribosylation of a 45 kilodalton protein did not prevent labeling of the pertussis toxin-specific band(s) in cells pretreated with cholera toxin. These results suggest that pertussis toxin specifically mediates ADP-ribosylation of the Ni protein in normal anterior pituitary cells.
 ...
PMID:Pertussis toxin mediates ADP-ribosylation of pituitary membrane proteins. 373 93

The purpose of this investigation was to examine factors which regulate the reprogramming of gene expression in tumors responsible for resistance to tiazofurin. To study the resistance phenomenon drug-induced tumor lines were selected and examined for the mechanism of resistance. A comparison of the biochemical expression of resistance to tiazofurin in drug-induced resistant lines of hepatoma 3924A, leukemias L1210 and P388 revealed that the 3 lines expressed similar genetic alterations related to reduced TAD content, decreased NAD pyrophosphorylase activity and increased synthesis of guanylates from salvaging preformed guanine indicating that these 3 factors play an important role in the resistance to tiazofurin. Resistance was stable in the leukemia lines and did not require drug to maintain resistance. Hepatoma 3924A resistant line reverted to sensitive state in the absence of drug selection pressure. NAD pyrophosphorylase activity was substantially deleted in the tiazofurin resistant leukemia lines, but was only significantly decreased in the hepatoma resistant line. Extensive biochemical alterations including enhanced activity of IMP dehydrogenase, increased inosinate and guanylate pools, and reduced uptake of tiazofurin were found in the hepatoma line resistant to tiazofurin. To examine the applicability of these results to naturally sensitive and spontaneously resistant tumors, murine tumors were examined. In murine tumors, TAD accumulation, ratios of enzyme activities responsible for the synthesis and degradation of TAD, and the ratios of perturbation of inosinate and guanylate pools following tiazofurin challenge demonstrated significant correlation with the sensitive or resistant nature of the tumors. To extrapolate these observations to human tumor systems, cytotoxicity of tiazofurin and its metabolic effects were compared in 6 human lung cancer cell lines derived from cancer patients with small cell lung cancer (4 lines) and lung adenocarcinoma (2 lines). Cell lines exhibiting greater sensitivity to tiazofurin accumulated significantly larger amounts of TAD and showed significant reduction of guanylate pools following tiazofurin incubation. The activity of the enzyme responsible for the formation of TAD, NAD pyrophosphorylase, did not correlate with responsiveness to tiazofurin but the enzyme which hydrolyzes TAD, TADase, correlated positively with the status of resistance.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Biochemical mechanisms of resistance to tiazofurin. 383 25

Exposure of target cells to a bolus of H2O2 induced cell lysis after a latent period of several hours, which was prevented only when the H2O2 was removed within the first 30 min of injury by addition of catalase. This indicated that early metabolic events take place that are important in the fate of the cell exposed to oxidants. In this study, we described two early and independent events of H2O2-induced injury in P388D1 macrophagelike tumor cells: activation of the glutathione cycle and depletion of cellular NAD. Glutathione cycle and hexose monophosphate shunt (HMPS) were activated within seconds after the addition of H2O2. High HMPS activity maintained glutathione that was largely reduced. However, when HMPS activity was inhibited--by glucose depletion or by incubation at 4 degrees C--glutathione remained in the oxidized state. Total pyridine nucleotide levels were diminished when cells were exposed to H2O2, and the breakdown product, nicotinamide, was recovered in the extracellular medium. Intracellular NAD levels fell by 80% within 20 min of exposure of cells to H2O2. The loss of NADP(H) and stimulation of the HMPS could be prevented when the glutathione cycle was inhibited by either blocking glutathione synthesis with buthionine sulfoximine (BSO) or by inhibiting glutathione reductase with (1,3-bis) 2 chlorethyl-1-nitrosourea. The loss of NAD developed independently of glutathione cycle and HMPS activity, as it also occurred in BSO-treated cells.
 ...
PMID:Glutathione cycle activity and pyridine nucleotide levels in oxidant-induced injury of cells. 384 Jan 76

Microcirculation is a very sensitive process. Under hyperthermia and/or artificial tissue acidification bloodflow ceased regularly and reproducibly. This bloodflow inhibition imposes seemingly as a consequence of a progressing decrease of blood fluidity. However, blood flowing through irritated vessels is subjected to local heat and acidic milieu only for few seconds, whereas the vessels of the respective area are exposed to these conditions as long as they continue. Hence, it is important to look for lesions of the vessels, particularly for enhanced porosity.--Using light-conducting electrodes we have studied the perivascular glucose concentrations and the influence of oxygen deficiency on microvessels in vivo. In contrast to our expectation, we have failed to detect endothelial cell swelling. On the other hand, we could observe diminished blood fluidity under anaerobic conditions by use of a simple method with filterpaper strips.--In our tumor studies we achieved reproducibly microcirculation inhibition of about 95% in DS carcinosarcomas as compared to muscle by combining hyperglycemia with hyperthermia (100 min at 43 C degrees). Each of these measures applied alone resulted only exceptionally in an approximately comparable effect. For therapeutic purposes the combination of both seems to us the method of choice.--Controlled hypotension, which can be adjusted extremely well by NAD, caused blood flow inhibition selectively in the tumors.--The remarkable bloodflow inhibition in tumors is achievable in principle also in human tumors.
 ...
PMID:Some experimental and methodological experiences on the selective inhibition of blood microcirculation in tumor tissues as the central mechanism of the cancer multistep therapy (CMT). 389 89

Lonidamine is a potent inhibitor of spermatogenesis and a hyperthermic sensitizer. The principal established locus of biochemical action of lonidamine is a selective inhibitory effect of the energy metabolism either in NAD-linked reactions in germ cell mitochondria, as well as the glycolytic metabolism of a variety of tumor cell lines by means of inhibition of mitochondrially bound hexokinase. We carried out in vivo tumor experiments to determine whether lonidamine when combined with radiation could potentiate the cytotoxic effects of radiation on two murine tumors. The combined effects of single acute lonidamine (100 mg/kg) and single dose X-irradiation were evaluated on the transplanted methylcholanthrene-induced fibrosarcoma in BALB/c mice and on the radiation-induced fibrosarcoma in C3H/He mice. The radiosensitizing effect by lonidamine was maximal when lonidamine was administered immediately prior to or after X-irradiation. The dose modifying factor of lonidamine is estimated to be 1.36 for methylcholanthrene-induced fibrosarcoma tumors and 1.25 for radiation-induced fibrosarcoma tumors. There was no disproportionately enhanced skin reaction following the combined treatments. The present results of the potentiating effects of radiation may be attributed, in part, to the findings of cell culture studies that lonidamine is a potent inhibitor of repair of potentially lethal damage.
 ...
PMID:Potentiation of radiation effects on two murine tumors by lonidamine. 394 89


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>