Alterations in [3H]thymidine incorporation into DNA and [3H]uridine incorporation into RNA induced by 5-azacytidine in vivo.

Administration in vivo of 5-azacytidine (5-aza-CR) caused suppression of [³H]thymidine ([³H]TdR) incorporation into DNA of bone marrow and gastrointestinal mucosa of mice and a more prolonged suppression of L1210 ascites tumor. Single doses of 5-aza-CR caused a modest and short-lived suppression of incorporation of [³H]uridine ([³H]UR) into nuclear RNA of L1210 ascites tumor cells. No suppression of [³H]UR incorporation into RNA of bone marrow or gastrointestinal mucosa was observed. L1210 tumor cells resistant to the other active cytidine analogue, cytosine arabinoside, demonstrated less disruption of [³H]TdR incorporation after exposure to 5-aza-CR, suggesting some cross resistance in the effects of these two drugs on DNA synthesis. Survival studies carried out in mice bearing both the sensitive and resistant L1210 tumor cell lines confirmed cross resistance of the anti-tumor effects of the two cytidine analogues. Second doses of 5-aza-CR, with the timing og administration based upon the differing patterns of recovery of [³H]TdR incorporation between normal tissues and tumor cells, led to a prolongation of survival in mice bearing the sensitive L1210 ascites tumor.     

A fluorescent analogue of methotrexate as a probe for folate antagonist molecular receptors

A dansyl-l-lysine analogue of methotrexate, $\text{N}{}^{\mathrm{\alpha }}\text{-(}\text{4-amino-4-deoxy-10-methylpteroyl}\text{)-N}{}^{\mathrm{\epsilon }}\text{-(5-[N,N-}\text{dimethylamino]-1-naphthalenesulfonyl]-1-naphthalenesulfonyl)-}\text{l}\text{-lysine}$, is a potent inhibitor of murine L1210 dihydrofolate reductase. The dansyl fluorescence emission was enhanced approximately 3-fold with a 10 nm blue shift upon binding to L1210 dihydrofolate reductase. The fluorescent analogue was only 10-fold less potent than methotrexate in inhibiting the growth of methotrexate-sensitive and -resistant L1210 cells and competes effectively for [³H]methotrexate transport with a K_i of 7.02 μM, a value virtually identical to the K_t for methotrexate in both cell lines. In addition, strong dansyl fluorescence was found to be associated with dihydrofolate reductase from methotrexate-resistant, dihydrofolate reductase-overproducing L1210 cells following incubation of viable cells with the fluorescent methotrexate analogue for 4 hr. The results demonstrate that the dansyl-l-lysine analogue of methotrexate was rapidly transported into L1210 cells where it formed a high-affinity, fluorescent complex with intracellular dihydrofolate reductase.     

Effect of 4-chlorobiphenyl on substrate transport and phospholipid metabolism in mouse L5178Y lymphoma cells

The toxicity of 4-chlorobiphenyl, a constituent of Aroclor 1221, was studied in mouse L5178Y cells, in vitro. 4-Chlorobiphenyl had a varied effect on the uptake of small precursor molecules. Uptake of [³H]l-leucine, [³H]l-serine, [³H]uridine and [³H]thymidine was inhibited, while that of [³H]inositol was stimulated. There was no significant effect on either [¹⁴C]ethanolamine or [¹⁴C]choline uptake. However 4-chlorobiphenyl significantly inhibited incorporation of [¹⁴C]ethanolamine into phosphatidylethanolamine and caused a 2- to 3-fold stimulation in the incorporation of [¹⁴C]choline into phosphatidylcholine. This effect on phosphatidylcholine metabolism depended on the adsorption and continued presence of 4-chlorobiphenyl on the cell plasma membrane. The stimulation of [¹⁴C]choline incorporation was reversed when treated cells were placed in fresh growth medium under conditions where 95 per cent of the 4-chlorobiphenyl was desorbed from the cell surface. The effect of 4-chlorobiphenyl on substrate uptake and phospholipid metabolism appears to depend upon the interaction of the agent with the cell membrane surface.     

Reversal of the cytotoxicity of 3'-amino-3'-deoxythymidine by pyrimidine deoxyribonucleosides.

Mammalian cell replication is strongly inhibited by 3′-amino-3′deoxythymidine (3′-aminothymidine). This cytotoxieity can be specifically prevented or reversed by pyrimidine 2′-deoxyribonucleosides. The addition of 50 μM 2′-deoxycytidine to L1210 cells treated with 10 μM 3′ the population doubling time from about 38 hr to 17 hr. The control cells doubled every 13 hr. Another cytotoxic effect produced by 3′-aminothymidine is a dose- and time-dependent increase in cell volume. 2′-Deoxycytidine can effectively prevent and reverse this increase. 3′-Aminothymidme appears to be a potent selective inhibitor of DNA synthesis in L1210 cells. The incorporation of [³H]thymidine into DNA was inhibited by 50 per cent at 1 μM 3′-aminothymidine, a concentration which reduced L1210 replication by about 65 per cent. The rate of incorporation of [³H] adenine into DNA, another measure of DNA synthesis, was reduced similarly by 3′-aminothymidine. and 2′-deoxycytidine eliminated this inhibition as well. An effect on RNA or protein synthesis was not detected. The incorporation of [³H] uridine or [³H] adenine into RNA, or of tritiated amino acids into protein, was not reduced by 25 μM 3′-aminothymidine. These results suggest that selective disruption of DNA metabolism may account for the cytotoxicity of 3′-aminothymidine.     

4-[4″-(2″,2″,6″,6″-四甲基哌啶氮氧自由基)氨基]-4′-去甲表鬼臼毒对L1210细胞系增殖、克隆形成和DNA合成的影响

新合成的鬼臼毒自旋标记衍生物4-(4″-(2″,2″,6″,6″-四甲基哌啶氮氧自由基)氨基)-4′-去甲表鬼臼毒(GP-7)显著抑制体外培养的L1210细胞生长。抑制作用和浓度及处理时间正相关,作用特点和鬼臼乙叉甙(VP-16)相似,24,48hIC_(50)分别为1.51和0.13μmol/L。GP-7和VP-16对L1210细胞软琼脂克隆形成均有抑制作用,且有浓度依赖性,IC_(50)分别为3.29和2.82μmol/L。GP-70.08～100μmol/L对L1210细胞DNA合成抑制率为18.4～80.7％。本文结果表明GP-7体外抗肿瘤作用与VP-16相似。     

Synergistic effect of 5-fluorouracil and N-(phosphonacetyl)-l-aspartate on cell growth and ribonucleic acid synthesis in a human mammary carcinoma

The biological effects of $\text{N-(}\text{phosphonacetyl}\text{)-}\text{l}\text{-}\text{aspartate}$ (PALA) and 5-fluorouracil (5-FU) were examined singly, and in combination, on the growth of a human mammary carcinoma (MDA) cell line in culture. All combinations of 5-FU (2.5 × 10^?7 to 1.5 × 10^?5M) and PALA (6.0 × 10^?5 to 3.6 × 10^?3 M) resulted in synergistic inhibition of cell growth as revealed by a 50 per cent isobologram.To examine the biochemical basis for the synergism, measurements of the incorporation of [³H]-5-FU into total non-poly(A)- and poly(A)-RNA, and of the simultaneous incorporation of [¹⁴C]deoxyguanosine and [³H]deoxyuridine into DNA, were determined. The combination of 3.7 × 10^?5M PALA and 1 × 10^?6 M 5-FU produced 65–85 per cent inhibition of cell growth after continuous treatment for 13 days. Treatment of the cells for 3 or 24 hr with the same drug regimen produced approximately a 170 per cent increase in the incorporation of 1 × 10^?6M [³H]-5-FU into poly(A)RNA in comparison to [³H]-5-FU treatment alone; exposure for 24 hr to 3.7 × 10^?5 M PALA and 1 × 10^?6 M [³H]-5-FU resulted in a 285 per cent increase in the incorporation of [³H]-5-FU into non-poly(A)RNA. The incorporation of either [¹⁴C]deoxyguanosine or [³H]deoxyuridine into DNA was not inhibited by this drug regimen; however, the incorporation of [³H]deoxyuridine into DNA was elevated significantly upon 12 or 24 hr of exposure to PALA alone. PALA and 5-FU treatment resulted in a 75 per cent reduction in the concentration of UTP and no change in the concentration of 5-fluorouridine-5′triphosphate 5-FUTP) versus 5-FU treatment alone. Thus, the proportion of 5-FUTP in the total 5FUTP + UTP pool was enhanced more than 3-fold by the combination regimen. These results indicate that the synergistic effect of the combination of PALA and 5-FU on the growth of MDA cells correlates with an increased proportion of 5-FUTP in the pyrimidine nucleotide pool and, consequently, with an enhanced incorporation of 5-FU into RNA, but not with inhibition of DNA synthesis.     

Histamine synthesis in intact and disrupted rat mast cells

Histamine production by purified intact rat peritoneal mast cells, as measured by formation of [β-³H]histamine from [β-³H]l-histidine or by release of ¹⁴CO₂ from ¹⁴C-carboxyl-labeled histidine, was ten to thirty times greater than that of disrupted cells or soluble extracts of these cells. Loss of activity was evident whether cells were disrupted by sonification, freezing and thawing, or lysis, both in the absence and presence of inhibitors of proteolytic enzymes and agents known to preserve enzyme activity. Studies with decarboxylase inhibitors indicated that a specific histidine decarboxylase was responsible for histamine formation in both the intact cells and cell extracts. In the presence of subsaturating concentrations of histidine, various histidine analogs and glutamine inhibited histidine uptake and histamine formation in intact mast cells but did not inhibit synthesis in cell extracts. These data indicate that, at physiological concentrations of histidine, blockade of histidine transport (through system N) may limit histamine synthesis in the intact cell and that measurement of histidine decarboxylase activity in tissue homogenates or cell extracts may not reflect actual histidine decarboxylase activity in vivo.     

Purine salvage pathways for the biosynthesis in vitro of adenine nucleotides in the guinea pig vas deferens

The guinea pig vas deferens has been found to possess at least two active anabolic pathways for adenine nucleotide biosynthesis. Our studies in vitro show that [³H]adenosine and [³H]adenine may be important precursors in purine salvage. Both precursors are eventually converted to [³H]AMP prior to final incorporation into [³H]ATP. [³H]adenosine is transported across the cell membrane and then phosphorylated intracellularly to [³H]AMP with the subsequent formation of [³H]ADP and [³H]ATP. [³H]adenine, on the other hand, is probably converted to [³H]AMP by a mechanism that does not involve [³H]adenosine transport, since 6-nitrobenzylthioguanosine (6-NBTG), a nucleoside transport inhibitor, does not inhibit [³H]adenine utilization. Conversion of [³H]adenosine to [³H]inosine or [³H]hypoxanthine prior to incorporation into [³H]ATP is probably only of minor importance since: (1) 6-NBTG reduces [³H]adenosine conversion to phosphorylated adenine compounds by 90 per cent; and (2) the adenosine deaminase inhibitor, 6-thioguanosine, even at high concentrations could only slightly reduce the amount of [³H]ATP formed from [³H]adenosine. Incubation of vas deferens with either [³H]inosine or [³H]hypoxanthine also failed to result in appreciable labeling of adenine nucleotide pools. The relative contributions of tritium labeled nucleosides and bases to [³H]ATP synthesis in vitro in the guinea pig vas deferens are; [³H]adenosine > [³H]adenine ? [³H]inosine > [³H]hypoxanthme.     

Studies with a 2,4-diamino-5-(3',4'-dichlorophenyl)-6-methylpyrimidine (DDMP)-resistant L1210 leukemia cell line without cross-resistance to methotrexate

An L1210 leukemia cell line resistant to 2,4-diamino-5-(3',4'-dichlorophenyl)-6-methylpyrimidine (DDMP) (L1210/DDMP) was developed in vivo by treatment of tumor-bearing mice. Resistance to DDMP was confirmed by subsequent in vivo survival experiments and by in vitro dose-response curves. The L1210/DDMP line demonstrated little cross-resistance to another folate analog, methotrexate (MTX). This was confirmed both in vivo, with survival experiments, and in vitro, using dose-response curves. A statistical analysis of the in vivo data confirmed DDMP resistance with lack of MTX cross-resistance. Dihydrofolate reductase (DHFR) activity in the L1210/DDMP/R₅ line was no greater than in the parent cell line (L1210/S). and the K_m of DHFR for dihydrofolate was the same in the L1210/DDMP/R₅ and L1210/S lines. The K_i for DHFR of the L1210/DDMP/R₅ cell line versus the L1210/S cell line was increased 3.0-fold for MTX and 3.5-fold for DDMP. Total accumulation of [¹⁴C]DDMP was identical in the two cell lines. The explanation for the lack of MTX cross-resistance in the L1210/DDMP/R₅ line is unknown.     

Potentiation by 2'-deoxycoformycin of the inhibitory effect of xylosyladenine on nuclear RNA synthesis in L1210 cells in vitro

The effect of the adenosine deaminase inhibitor, 2'-deoxycoformycin (dCF), on the inhibitory effect of 9-β-d-xylofuranosyladenine (XA) on nuclear RNA synthesis was examined in L1210 cells in vitro. Pretreatment of cells for 15 min with a 100 per cent inhibitory dose (1 × 10^?6 M) of dCF resulted in approximately a 3- to 8-fold reduction in the 50 per cent inhibitory dose (id₅₀) of XA for [³H]uridine and [³H]thymidine incorporation into RNA and DNA respectively. The id₅₀ for XA for RNA synthesis vs DNA synthesis was 5-fold lower in the absence of dCF and 20-fold lower in the presence of dCF, indicating the greater sensitivity of RNA synthesis to this inhibitor. Fractionation of nuclear RNA into rRNA, non-poly(A) heterogeneous RNA and poly(A)heterogeneous RNA revealed the latter species of RNA to be less sensitive to XA in the absence of dCF; however, in the presence of dCF, all three species of nuclear RNA showed similar sensitivities. Nuclear polyadenylic acid synthesis was among the most sensitive RNA fractions to XA, and was also inhibited to a greater degree by pretreatment of cells with dCF. These results indicate that XA is potentiated markedly by inhibition of adenosine deaminase, and that deamination serves as a major catabolic route for this drug.     

Cytotoxicity of Cinnamic Aldehyde on Leukemia L1210 Cells

ABSTRACT

Cytotoxic effect of cinnamic aldehyde (CA) on L1210 mouse leukemia cells was tested. Addition of CA in Fischer's medium at 4.8 μg/ml could inhibit the growth of L1210 by 50 per cent. The terminal aldehyde-group of CA molecule was found to be responsible to the inhibition.Experiments of incorporating [³H]-uridine, [³H] -thymidine, and [³H]-leucine by the cells revealed that the syntheses of protein, DNA, and RNA were suppressed by the presence of CA in the culture solution with potency appeared in that order. The inhibitory effect of CA on glycolysis was insignificant. Direct reaction between aldehyde-groups of CA molecules and sulf-hydryl-groups of cell components was proved. The results suggested that CA inhibited L1210 cells by blocking protein synthesis through trapping sulfhydryl-containing amino acids in the cell.     

Some effects of hydrocortisone on the early development of the rat cotton pellet granuloma.

Differential cell counts, DNA levels, cellular proliferation (studied by in vitro [³H]thymidine incorporation) and hydrolytic enzyme release into inflammatory exudates were investigated in sterile cotton wool pellets at various times after subcutaneous implantation in rats. At 2 days (the earliest time studied) the predominant cell type was the polymorphonuclear leucocyte (PMNL), but by 5 and 7 days increasing numbers of mononuclear cells (macrophages and lymphocytes) were present. Total DNA levels were almost constant, usually increasing slightly with time. DNA synthesis did not occur before day 3 and was still increasing at day 7. The two lysosomal hydrolases measured (N-acetyl-glucosaminidase) and β-glucuronidase) were present in the cell-free pellet exudate in high concentrations, suggesting that they had been released during phagocytosis. Treatment with hydrocortisone (10 mg/kg/day p.o.) during the earlier phase of the response reduced dry granuloma weight, total DNA levels and release of hydrolytic enzymes, and delayed the onset of cellular proliferation. Steroid treatment during the later proliferative phase only (days 3 to 6), reduced dry granuloma weight, total DNA level and hydrolytic enzyme release but did not affect [³H]thymidine incorporation.     

A new synthesis of 2-deoxy-2-[18f]fluoro-D-galactose using [18f]fluoride ion

A nucleophilic radiofluorination of methyl 3,4-0-isopropylidene-2-0-(trifluoromethanesulfonyl)-6-0-trityl-β-D- talopyranoside ( 1 ) with aminopolyether (Kryptofix 2.2.2.) supported potassium [¹⁸F]fluoride in acetonitrile gave methyl 2-deoxy-2-(¹⁸F) fluoro-3,4-o-isopropylidene-6-0-trityl-β-D-galactopyranoside ( 2 ). Hydrolysis of 2 with 6N HCl followed by passage through an ion retardation resin column and a neutral alumina column gave 2-deoxy-2-[¹⁸F]fluoro-D-galactose (2-¹⁸FDGal) in 36–39% overall radiochemical yield without correction for decay. The total preparation time was about 90 min from start of the radiofluorination.     

Plasma membrane inhibition of macromolecular precursor transport by THC.

10^?6to 10^?4 M of delta-9-tetrahydrocannabinol (THC) or of other cannabinoids, which all have in common the C ring of olivetol, inhibit in cultured lymphocytes incorporation of [³H]thymidine. The inhibitory effect of olivetol derivatives is related to their octanol-water partition coefficient (liposolubility). Within 15 min of incubation, THC inhibits precursor pool formation and macromolecular incorporation of thymidine, uridine and leucine. THC inhibits also [¹⁴C] aminoisobutyric acid uptake into the cell, but does not alter the cellular “leakage” of this amino acid analogue. Using the isotopic dilution technique with L 1210 murine lymphoma cells and human lymphocytes, it was observed that THC decreases [³H]thymidine uptake within fifteen seconds after addition of the drug to the culture. Experiments performed at 0° indicate that THC has no action on thymidine binding to the carrier. All of these observations suggest that THC in micromolar concentration inhibits DNA synthesis through a “non-specific” alteration of membrane configuration. This effect, due to the liposolubility of the drug, could induce eonfonnational changes of membrane-bound transport systems which would inhibit their function.     

2,4-diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)methyl]quinazoline (tmq), a potent non-classical folate antagonist inhibitor--I effect on dihydrofolate reductase and growth of rodent tumors in vitro and in vivo.

Seventeen non-classical 2,4-diamino-6-[(anilino)methyl]quinazoline antifolates were tested as inhibitors of dihydrofolate reductase from L1210 leukemia cells and from human leukemia cells (acute lymphocytic leukemia). Several potent inhibitors of this enzyme were found, some with I₅₀ values of 10^?9 M, thus displaying activity comparable to that of methotrexate. In general, the potency of dihydrofolate reductase inhibition correlated with the inhibition of cell growth in vitro against L1210 cells. Two of these compounds, compound 14 (2,4-diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)methyl]quinazoline; TMQ, JB-11, NSC 249008) and compound 3 (2,4-diamino-5-chloro-6-[(3,4-dichloroanilino)methyl]quinazoline; NSC 208652), were further evaluated against murine tumors in vivo and both showed a broad spectrum of antitumor effects. The results of these studies encourage further evaluation of these compounds, in particular compound 14, as possible anti-neoplastic agents in the treatment of human disease.     

Stereospecificity at carbon 6 of fomyltetrahydrofolate as a competitive inhibitor of transport and cytotoxicity of methotrexate in vitro

The unnatural diastereoisomer of l-5-formyltetrahydrofolate was 20-fold less effective as a competitive inhibitor of [³H] methotrexate influx than the natural diastereoisomer during carrier-mediated membrane transport in L1210, S180 and Ehrlich cells. Values derived for K_i, were 1.84 to 2.29 μM for the natural derivative and 35.2 to 53.8 μM for the unnatural derivative. Values for K_i derived with a chemically synthesized mixture containing equal amounts of both natural and unnatural diastereoisomers were 2-fold greater than values obtained for the natural diastereoisomer. The unnatural diastereoisomer was 100-fold less effective and the chemically synthesized mixture was 2-fold less effective than the natural diastereoisomer in preventing inhibition by methotrexate of L1210 cell growth in culture. These results indicate that the unnatural diastereoisomer competes relatively ineffectively with the natural diastereoisomer or methotrexate for transport in these murine tumor cells.     

Effects of 8-azaadenosine and formycin on cell lethality and the synthesis and methylation of nucleic acids in human colon carcinoma cells in culture

The cytocidal and biochemical effects of formycin and 8-azaadenosine in the presence and absence of the adenosine deaminase inhibitor, 2′-deoxycoformycin, were studied in human colon carcinoma (HT-29) cells in culture. Logarithmically growing cells were unaffected by 24-hr exposure to either 10^?6M formycin or 8-azaadenosine, but 1 to 1.4 log reductions in colony formation were produced by 10^?5M of each analog. In the presence of 10^?6M 2′-deoxycoformycin, a 3- and 30-fold potentiation of the cytocidal activity of 8-azaadenosine and formycin, respectively, was produced. Inhibition of DNA synthesis but not RNA synthesis by 8-azaadenosine paralleled its cytocidal activity; however, neither variable correlated closely with the cytotoxic effects of formycin. In addition, the methylation of nuclear RNA was unaffected by both drugs while the methylation of 5-methyl-deoxycytidine in DNA was inhibited to a lesser extent than DNA synthesis. Measurements of the incorporation of [³H]formycin and [³H]8-azaadenosine into nuclear RNA and DNA in the presence and absence of 2′-deoxycorformycin indicated that formycin substitution in RNA and DNA was enhanced 10- and 20-fold, respectively, while [³H]8-azaadenosine incorporation into both nucleic acids was increased 6- to 7-fold. These results suggest that the incorporation of formycin into nucleic acids, particularly DNA, correlates closely with its lethal effect on cell viability. On the other hand, the cytocidal activity of 8-azaadenosine more clearly parallels its inhibitory effect on DNA synthesis rather than its substitution into nucleic acids.     

Isothiazole dioxide derivative 6n inhibits vascular smooth muscle cell proliferation and protein farnesylation

Isothiazole dioxides have been shown to inhibit Trypanosoma brucei protein farnesyltransferase (PFTase) in isolated enzyme, but elicited only a minor effect on mammalian PFTase. In the present study we have evaluated the effect of 3-diethylamino-4-(4-methoxyphenyl)-isothiazole 1,1-dioxides with different substituents at C5, on rat PFTase and protein geranylgeranyltransferase-I (PGGTase-I) with the final aims to improve the potency against mammalian PFTase and to identify new compounds with antiproliferative properties. For these purposes, in vitro and cell culture models have been utilized. The results showed that isothiazole dioxides with C4–C5 double bond and sulfaryl substituted at the C5 position but none of the dihydro-derivatives, were able to inhibit in vitro PFTase in a concentration dependent manner (IC₅₀ ranging from 8.56 to 1015 μM). Among those, compound 6n (C5; methyl-S) displayed 500-fold higher inhibitory potency on PFTase than PGGTase-I. Compound 6n was shown to affect rat smooth muscle cell (SMC) proliferation at concentrations similar (IC₅₀ = 61.4 μM) to those required to inhibit [³H]-farnesol incorporation into cellular proteins (−44.1% at 100 μM). Finally, compound 6n interferes with rat SMC proliferation by blocking the progression of G0/G1 phase without inducing apoptosis, as assessed by [³H]-thymidine incorporation assay and flow cytometry analysis. Taken together, we described a new PFTase inhibitor containing the isothiazole dioxide moiety that affects mammalian protein farnesylation and SMC proliferation by inhibiting G0/G1 phase of the cell cycle.     

Probes of eukaryotic DNA-dependent RNA polymerase II-II: Covalent binding of two purine nucleoside dialdehydes to the initiation subsite

The catalytic center of wheat germ DNA-dependent RNA polymerase RNA polymerase II (nucleosidetriphosphate: RNA nucleotidyltransferase, EC 2.7.7.6) as a model eukaryotic enzyme system was probed with two purine nucleoside dialdehydes, 6-methylthioinosinedicarboxaldehyde (MMPR-OP) and a derivative 6-[(acetylaminoethyl)-1-naphthylamine-5-sulfonyl]thioinosinedicarboxaldehyde (AMPR-OP). Both drugs gave noncompetitive inhibition with respect to [³H]UMP incorporations into RNA, and inhibitor bindings were reversed with initiation substrates. The K_i values for MMPR-OP and AMPR-OP were determined to be 0.64 mM and 1.0 μM respectively. The drugs were covalently bound to the catalytic center by NaBH₄ reduction. Both were found bound to the largest enzyme subunit, IIa. It is essential lysine in the initiation subsite of the catalytic center located on the IIa subunit.     

The effects of aspirin and other non-steroid anti-inflammatory/analgesic drugs on gastro-intestinal mucus glycoprotein biosynthesis in vivo: relationship to ulcerogenic actions.

Aspirin and certain other ulcerogenic non-steroid antiinflammatory (NSAI) drugs inhibit the incorporation in vivo of [³⁵S]sulphate into the mucus glycoproteins isolated from the gastric mucosa of rats. Some NSAI drugs, which are shown to be relatively non-ulcerogenic in a sensitive gastric ulcer assay and the analgesic drugs paracetamol and dextropropoxyphene (which are non-ulcerogenic) did not inhibit the biosynthesis of sulphated mucus glycoproteins in vivo. A relationship is therefore shown between the ulcerogenicity of NSAI drugs and the inhibitory effects on gastric mucus biosynthesis. Some potent intestinal ulcerogens (e.g. indomethacin) also inhibit the incorporation of [³⁵S]sulphate into the glycoproteins from the upper intestinal mucosa. Aspirin in contrast stimulates the incorporation of [³⁵S]sulphate into intestinal mucus glycoproteins. The inhibition of the biosynthesis of sulphated gastric mucus glycoproteins by aspirin is shown to (1) depend on the presence of high concentrations of salicylates in the mucosal tissue, (2) be as a consequence of combined inhibitory capacity of aspirin, salicylate and possibly traces of metabolites in the mucosa and (3) be due to an inhibition of the sulphotransferase activity in vitro. Aspirin also inhibits the incorporation into gastric glycoproteins of [¹⁴C]acetate, but not [¹⁴C]threonine, but the effect on [¹⁴C]acetate incorporation may be due to the redistribution of the isotope in vivo.