Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Uridine phosphorylase activity was detected in sonic extracts of six different mammalian cell lines and, in conjunction with uridine kinase, provides a route for the conversion of uracil to UMP via uridine. Uracil phosphoribosyl transferase activity was not detected in any of eight different mammalian cell lines. Uridine phosphorylase was purified 5,330-fold from Novikoff rat hepatoma cells by ammonium sulfate precipitation, DEAE-Sephadex chromatography, hydroxyapatite chromatography, and Sephadex G-200 fractionation. The molecular weight of the enzyme by gel filtration was approximately 45,000. The kinetics of the purified enzyme were analyzed with respect to all four substrates at saturating cosubstrate concentration, yielding the parameters KmUra = 360 microM, KmRib-1-P = 88 microM, KmUrd = 16 micron, and KmPi = 130 microM. However, in intact cells the phosphorolysis of uridine proceeded with an apparent Km of 231 microM. Novikoff cells treated with 0.5 mM inosine exhibited an increase in uracil uptake rate which was proportional to an observed increase in intracellular ribose-1-phosphate. Nevertheless, in cells whose de novo synthesis of pyrimidines was blocked by pyrazofurin or N-(phosphonacetyl)-L-aspartate ("PALA"), the uptake of uracil was insufficient to support proliferation, even when enhanced by inosine. These observations are consistent with the kinetic characteristics of the enzyme and provide evidence that the intracellular level of ribose-1-phosphate plays a rate-limiting role in the uptake of uracil mediated by uridine phosphorylase.
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PMID:Uridine phosphorylase from Novikoff rat hepatoma cells: purification, kinetic properties, and its role in uracil anabolism. 298 97

The inhibitory effects of nicotinamide analogs on the activity of poly(ADP-ribose)) synthetase were compared to effects on precursor incorporation into macromolecules in three lines of hepatoma cells (Morris hepatomas 5123C, 7777 and HTC). N'-methylnicotinamide was a less effective inhibitor of poly (ADP-ribose) synthetase than was 1-methylnicotinamide while both these compounds had smaller inhibitory effects on the enzyme than were seen with nicotinamide or 3-aminobenzamide. On the other hand, the incorporation of [3H]thymidine into DNA and of [3H]uridine into RNA were inhibited by N'-methylnicotinamide in the concentration range 2-20 mM but not by 1-methylnicotinamide. Under the conditions examined there were no significant effects on the incorporation of [14C]lysine and [3H]leucine in hepatoma cells. The data indicated that the inhibitory effect of N'-methylnicotinamide on nucleic acid synthesis may be unrelated to action on poly (ADP-ribose) synthetase.
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PMID:Disparity in the effects of two N-methyl nicotinamides on poly(ADP-ribose) synthetase and macromolecular synthesis in hepatomas. 299 58

Inhibition of colony formation in cultured hepatocellular carcinoma cells of the rat was used to test the efficacy of inhibitors of de novo pyrimidine biosynthesis as potential anticancer drugs. N-(phosphonacetyl)-L-aspartic acid (PALA) (10 and 100 micrograms/ml) and 5-aza-5,6-dihydroorotic acid (DHOX) (100 micrograms/ml) inhibited the formation of colonies and these inhibitions were completely reversed by inclusion of 0.1 mM uridine, the end product of de novo pyrimidine biosynthesis, in the culture medium. With some lots of fetal bovine serum where PALA and DHOX had little effect on inhibiting colony formation, addition of 0.1 mM cytidine restored the inhibitory characteristics of PALA and, to some extent, DHOX. The results demonstrate that cytidine levels modulate the inhibitions of hepatoma colony formation by both PALA and DHOX and that co-administration of these drugs together with cytidine provides a simple expedient to increase drug efficacy.
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PMID:Pyrimidine nucleosides enhance the efficacy of inhibitors of pyrimidine biosynthesis in cultured hepatocellular carcinoma cells. 334 91

We present evidence that normal hepatocytes can be specifically protected from galactosamine toxicity in vitro by targeting an antagonist to these cells via receptor-mediated endocytosis. The strategy is based upon the following principles: 1) galactosamine is a highly selective hepatotoxin that causes a dose-dependent depletion of uridine intermediates; 2) galactosamine toxicity can be antagonized by supplemental administration of uridine; 3) normal hepatocytes possess unique cell-surface receptors that can internalize galactose terminal (asialo-)glycoproteins with subsequent degradation of the glycoprotein ligand. Based on these facts, we hypothesized that chemical coupling of a galactosamine antagonist to an asialoglycoprotein could result in cell-specific delivery and protection of normal hepatocytes by targeting the antagonist via asialoglycoprotein receptors. Using a model system consisting of freshly isolated rat hepatocytes (receptor (+)) and Morris 7777 rat hepatoma (receptor (-)) cells, sensitivity to galactosamine in vitro was determined and found to be similar for both types of cells. A targetable antagonist was synthesized by coupling uridine monophosphate to asialoorosomucoid in a molar ratio of 5 to 1. Exposure of Morris 7777 cells to the targetable antagonist in the presence of a toxic concentration of galactosamine did not protect these cells as evidenced by a steady decline in the number of viable cells in a fashion identical to cells treated with galactosamine alone. However, normal hepatocytes that received the conjugate in the presence of galactosamine were protected as their viable cell number remained the same as control (untreated) cells. Competition by an excess of asialoglycoprotein inhibited the protective effect of the conjugate, supporting the concept that the asialoglycoprotein component of the conjugate was responsible for the specific delivery of the antagonist to the target cells.
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PMID:Targeted antagonism of galactosamine toxicity in normal rat hepatocytes in vitro. 335 Aug 10

It is shown that during 10 days after transplantation of syngenic 22a hepatoma cells to C3HA mice, wave-like fluctuations of the natural killer cell (NK) activity of splenocytes take place. Xenogenic (K-562) and allogenic (AC-1) cells are used as target cells in the 18th hour 3H-uridine cytotoxic test. A significant increase in the NK-activity on the 2nd-3rd and 7-9th days after tumour cells transplantation is observed. Elimination of adherent cells from suspension of splenocytes lead to an increase in the NK-activity especially on the 7th-9th days.
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PMID:[Natural killer activity of splenocytes of C3HA mice in the early period after transplantation of hepatoma 22a cells]. 343 91

The natural cytotoxicity of Percoll fractions of CBA mice splenocytes was tested against cells of human erythroblastosis suspension culture K-562 and murine C3HA hepatoma solid culture MGXXIIa. The 1.076 g/ml dense fraction was shown to have the highest activity in 3H-uridine cytotoxic test against the cell targets. Immunosera prepared by the Golub method against CBA mouse brains and exhausted supplementary by syngeneic thymocytes decreased the natural cytotoxicity of CBA mouse splenocytes against MGXXIIa tumor cells and, on the contrary, increased it against K-562 tumor cells.
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PMID:[Heterogeneity of the effectors of natural killer activity in CBA mice]. 346 11

Lidoflazine strongly inhibited the equilibrium exchange of uridine in human erythrocytes (Ki approximately 16 nM). Uridine zero-trans influx was similarly inhibited by lidoflazine in cultured HeLa cells (IC50 approximately to 80 nM), whereas P388 mouse leukemia and Novikoff rat hepatoma cells were three orders of magnitude more resistant (IC50 greater than 50 microM). Uridine transport was also inhibited by nifedipine, verapamil, diltiazem, prenylamine and trifluoperazine, but only at similarly high concentrations in both human erythrocytes and the cell lines. IC50 values ranged from about 10 microM for nifedipine and about 20 microM for verapamil to more than 100 microM for diltiazem, prenylamine and trifluoperazine. The concentrations required for inhibition of nucleoside transport are several orders higher than those blocking Ca2+ channels. Lidoflazine competitively inhibited the binding of nitrobenzylthioinosine to high-affinity sites in human erythrocytes, but did not inhibit the dissociation of nitrobenzylthioinosine from these sites on the transporter as is observed with dipyridamole and dilazep.
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PMID:Effects of Ca2+-channel antagonists on nucleoside and nucleobase transport in human erythrocytes and cultured mammalian cells. 356 29

A high-pressure liquid chromatographic method was developed which achieved a separation and quantitation of 20 biologically important nucleosides and bases. The concentrations of pyrimidine nucleosides and bases, namely deoxycytidine, cytosine, cytidine, uracil, and uridine (22.6, 10.1, 5.2, 2.9, and 2.4 nmol/ml, respectively) were high in plasma, whereas purine nucleosides and bases were present in concentrations less than 2.5 nmol/ml. In erythrocytes, the pools of xanthine, hypoxanthine, and xanthosine were 32-, 27-, and 22-fold larger, respectively, whereas cytidine, uridine, and deoxycytidine were only 21, 12, and 5% of plasma concentrations. The results suggest a compartmental system for transport of some of the purine and pyrimidine nucleosides and bases in the whole blood. Studies on the effect of ischemia on nucleoside and base pools in rat liver indicated marked increases within 30 s in the concentrations of adenine, adenosine, inosine, hypoxanthine, uridine, and xanthine, whereas in hepatoma the effects were less pronounced. By 2 and 5 min ischemia these perturbations were most marked in both liver and hepatoma. These results indicate a need for rapid freeze-clamp preparation of tissue samples to obtain precise and repeatable results in the determination of tissue nucleoside and nucleobase concentrations.
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PMID:Effect of ischemia on nucleosides and bases in rat liver and hepatoma 3924A. 358 Oct 61

Equilibrium binding of [3H]dipyridamole identified high-affinity (Kd approximately 10 nM) binding sites on human erythrocytes (approximately 5 X 10(5) sites/cell) and on HeLa cells (approximately 5 X 10(6) sites/cell). The equilibration of dipyridamole with these sites on human erythrocytes was compatible with a second-order process which proceeded at 22 degrees C with a rate constant of about 6 X 10(6) M-1 sec-1. Binding of dipyridamole to these sites correlated kinetically with the inhibition of the equilibrium exchange of 500 microM uridine in these cells and was inhibited in a concentration-dependent manner by nucleosides and other inhibitors of nucleoside transport, such as nitrobenzylthioinosine, dilazep and lidoflazine, but not by hypoxanthine, which is not a substrate for the nucleoside transporter of human erythrocytes. The results indicate that the substrate binding site of the transporter is part of the high-affinity dipyridamole binding site. Bound [3H]dipyridamole became displaced from these sites on human erythrocytes by incubation with an excess of unlabeled dipyridamole or high concentrations of nucleosides and inhibitors of nucleoside transport, but neither by hypoxanthine nor sugars. Dissociation of [3H]dipyridamole behaved as a simple first-order process, but the rate constant was about one order of magnitude lower (about 3 X 10(-3) sec-1) than anticipated for typical ligand-protein binding on the basis of the measured association rate and equilibrium constants. The reason for this discrepancy has not been resolved. No high-affinity dipyridamole binding sites were detected on Novikoff rat hepatoma cells, P388, L1210 and S49 mouse leukemia cells or Chinese hamster ovary cells, and their absence correlated with a greater resistance of nucleoside transport in these cells to inhibition by dipyridamole. All cells expressed considerable low affinity (Kd greater than 0.5 microM) and nonspecific binding of dipyridamole.
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PMID:Interaction of [3H]dipyridamole with the nucleoside transporters of human erythrocytes and cultured animal cells. 366 65

The transport of 500 microM uridine by human erythrocytes and S49, P388 and L1210 mouse leukemia cells, Chinese hamster ovary (CHO) cells and Novikoff rat hepatoma cells was inhibited strongly by dilazep and hexobendine with similar concentration dependence, but the sensitivity of transport in the various cell types varied greatly; IC50 values ranged from 5-30 nM for human erythrocytes and S49 and P388 cells to greater than 1 microM for CHO and Novikoff cells. The binding of nitrobenzylthioinosine (NBTI) to high-affinity sites on these cells (Kd approximately equal to 0.5 nM) was inhibited by hexobendine and dilazep in a similar pattern. Furthermore, these drugs, just as dipyridamole and papaverine, inhibited the dissociation of NBTI from high-affinity binding sites but only at concentrations 10-100 times higher than those inhibiting uridine transport. In contrast, high uridine concentrations (greater than 2 mM) accelerated the dissociation of NBTI. Dilazep also inhibited the transport of hypoxanthine, but only in those cell lines whose transporter is sensitive to inhibition by uridine and dipyridamole. Adenine transport was not inhibited significantly by dilazep in any of the cell lines tested, except for a slight inhibition in Novikoff cells. [14C]Hexobendine equilibrated across the plasma membrane in human erythrocytes within 2 sec of incubation at 25 degrees, but accumulated to 6-10 times the extracellular concentration in cells of the various cultured lines. Uptake was not affected by high concentrations of uridine, NBTI or dipyridamole. Hexobendine inhibited the growth of various cell lines to a lesser extent (IC50 = greater than or equal to 100 microM) than dipyridamole (IC50 = 15-40 microM). At 40 microM, however, it completely inhibited the growth of S49 cells that had been made nucleoside dependent by treatment with methotrexate or pyrazofurin.
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PMID:Inhibition of nucleoside and nucleobase transport and nitrobenzylthioinosine binding by dilazep and hexobendine. 374 59


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