PubMed Health⌕ Search

Biomedical subjects

J B Hynes

Publications and source records attributed to J B Hynes.

At least 37 records · Page 2Linked to original sources
PubMed1987

Mechanism of action of 5,8-dideazaisofolic acid and other quinazoline antifols in human colon carcinoma cells.

The clonal cytotoxic effects and mechanism of action of a new series of 2-amino-4-hydroxyquinazoline folate analogues (5,8-dideazafolates) have been assessed using the human colon tumor cell line HCT-8. Of these compounds only 5-methyl-5,8-dideazafolate was potentially more effective than a compound previously identified, 5,8-dideazaisofolate (H-338, NSC 289517). HCT-8 sublines resistant to methotrexate, 5-fluorodeoxyuridine, and H-338 were either minimally or not cross-resistant to the other agents. The cytotoxicity of H-338 was strongly dependent on the time of exposure; at exposure times shorter than 8 h it was essentially nontoxic. Thymidine alone, as well as leucovorin or folic acid, protected against the cytotoxic effects of H-338. This is consistent with thymidylate synthase (TS) as its only locus of action. Studies with dihydrofolate reductase and TS isolated from HCT-8 cells indicated that these quinazolines were weaker inhibitors of dihydrofolate reductase than was methotrexate, but they were not particularly potent TS inhibitors. However, synthetic poly-gamma-glutamate derivatives of quinazolines showed dramatically increased TS, but not dihydrofolate reductase, inhibition. TS inhibition increased as the polyglutamate chain length increased. Using isolated HCT-8 folylpolyglutamate synthetase, all the parent quinazolines containing L-glutamate were found to be substrates. With H-338, the results indicated that tetraglutamate or longer derivatives could be synthesized intracellularly. These results are consistent with our hypothesis that cytotoxicity by such quinazolines necessarily involves "lethal synthesis" from a prodrug; i.e., the nontoxic parent drug must be converted to polyglutamates before TS inhibition and subsequent cytotoxicity can occur.

Cell Survival↗
PubMed1987

Purification and characterization of dihydrofolate reductase from soybean seedlings.

Dihydrofolate reductase (DHFR; EC 1.5.1.3) was purified to homogeneity from soybean seedlings by affinity chromatography on methotrexate-aminohexyl Sepharose, gel filtration on Ultrogel AcA-54, and Blue Sepharose chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the enzyme gave a single protein band corresponding to a molecular weight of 22,000. The enzyme is not a 140,000 Da heteropolymer as reported by others. Amino acid sequence-specific antibodies to intact human DHFR and also antibodies to CNBr-generated fragments of human DHFR bound to the plant enzyme on Western blots and cross-reacted significantly in immunoassays, indicating the presence of sequence homology between the two enzymes. The plant and human enzymes migrated similarly on nondenaturing polyacrylamide electrophoretic gels as monitored by activity staining with a tetrazolium dye. The specific activity of the plant enzyme was 15 units/mg protein, with a pH optimum of 7.4. Km values of the enzyme for dihydrofolate and NADPH were 17 and 30 microM, respectively. Unlike other eukaryotic enzymes, the plant enzyme showed no activation with organic mercurials and was inhibited by urea and KCl. The affinity of the enzyme for folate was relatively low (I50 = 130 microM) while methotrexate bound very tightly (KD less than 10(-10) M). Binding of pyrimethamine to the plant enzyme was weaker, while trimethoprim binding was stronger than to vertebrate DHFR. Trimetrexate, a very potent inhibitor of the human and bacterial enzymes showed weak binding to the plant enzyme. However, certain 2,4-diaminoquinazoline derivatives were very potent inhibitors of the plant DHFR. Thus, the plant DHFR, while showing similarity to the vertebrate and bacterial enzymes in terms of molecular weight and immunological cross-reactivity, can be distinguished from them by its kinetic properties and interaction with organic mercurials, urea, KCl and several antifolates.

Amino Acids↗
PubMed1987

Folate analogues as inhibitors of thymidylate synthase.

Recent demonstrations that deazafolate analogues may act as potent inhibitors of thymidylate synthase (TS) provided a firm rationale for the synthesis of N10-propargyl derivatives of 8-deazafolate and 8-deazaaminopterin (4). A complete assignment of the 1H NMR spectra of these compounds was made possible through application of 2D (COSY) techniques at 200 MHz. Data describing the inhibition of TS derived from human leukemia (K562) cells are presented. IC50 values of 2.25 and 1.26 microM were determined for 8-deaza-10-propargylfolate (3) and 8-deaza-10-propargylaminopterin, respectively. Comparison of the data for various folate analogues reveals a striking dependence of TS inhibitory potency upon the number of nitrogens in the folate pyrazine ring.

Aminopterin↗
PubMed1987

Synthesis of 5-chloro-5,8-dideaza analogues of folic acid and aminopterin targeted for colon adenocarcinoma.

Several classical quinazoline analogues of folic acid bearing chloro or methyl substituents at position 5 were evaluated as inhibitors of the growth of four human gastrointestinal adenocarcinoma cell lines in vitro. The preparation of two of these, 5-chloro-5,8-dideazaisofolic acid, 1e, and 5-chloro-5,8-dideazaisoaminopterin, 2a, is reported for the first time. In addition, a new synthetic route to 5-chloro-5,8-dideazaaminopterin, 2b, is described. For compounds having a 2,4-diamino configuration, the presence of chlorine at position 5 afforded superior growth inhibitory potency. However, compound 1e was substantially less effective than its 5-methyl counterpart.

Adenocarcinoma↗
PubMed1986

Micellar high-performance liquid chromatographic determination of folylpolyglutamate hydrolase activity.

A rapid and sensitive method for the quantitative determination of folylpolyglutamate hydrolase activity in crude tissue extracts was developed. The procedure is based on high-performance liquid chromatographic separation of folate analogue mono- and polyglutamates on a reversed-phase column using sodium dodecyl sulfate in water as the mobile phase. Interfering substances in tissue extracts were removed by gel filtration on centrifugally-eluted mini-columns of Sephadex G-25 prior to incubation of polyglutamate substrate with tissue extract hydrolase. Reactions were terminated by denaturation of the enzyme in sodium dodecyl sulfate, which subsequently served as the micellar solvent system for chromatographic separation of substrate from reaction products.

Animals↗
PubMed1986

Further studies on substituted quinazolines and triazines as inhibitors of a methotrexate-insensitive murine dihydrofolate reductase.

Data are presented on the systematic analysis of thirty-five quinazoline and substituted triazine compounds as inhibitors of a methotrexate-insensitive form of dihydrofolate reductase purified from methotrexate-resistant L5178Y murine leukemia cells. Several of the compounds were found to be more potent inhibitors of this enzyme activity than was methotrexate. Two of the triazine compounds had IC50 values approaching 10nM, which is close to that of methotrexate for the normal drug-sensitive dihydrofolate reductase. In addition, some of these compounds, especially the triazines, exhibit a specificity of inhibition for the methotrexate-insensitive enzyme as compared to the normal methotrexate-sensitive dihydrofolate reductase derived from the same cell line. These compounds may, therefore, be potentially useful in the treatment of those methotrexate-resistant tumours which express an altered, methotrexate-insensitive dihydrofolate reductase.

Animals↗
PubMed1986

Effects of 5,8-dideazaisopteroylglutamate (IAHQ) on L1210 leukemia in mice when given alone and in combination with methotrexate, probenecid, or verapamil.

The folate analogue 5,8-dideazaisopteroylglutamate (IAHQ; NSC-289517) inhibits the growth of a variety of human tumor cells in vitro such as colon, breast and osteosarcoma. Since IAHQ has only modest activity against L1210 leukemia in mice, it was tested in combination with methotrexate (MTX), probenecid, or verapamil in an effort to enhance efficacy. Single drug or drug combinations were administered every other day 3 or 5 times beginning on day 1 following the administration of 10(6) L1210 cells per animal. The combination of IAHQ (100 mg/kg) plus MTX (10 mg/kg) produced a decrease in mean survival time compared to that of MTX alone, regardless of whether the drugs were initiated on the same day or whether either one was started 2 days prior to the other. IAHQ (150 mg/kg) plus verapamil (5, 10, or 20 mg/kg) did not alter significantly the results produced by IAHQ alone. However, the combination of IAHQ (150 mg/kg) plus probenecid (250 mg/kg) augmented the increase in mean survival time above that produced by IAHQ alone by 82% (p = less than 0.001). The results suggest that probenecid could be used to enhance the effectiveness of IAHQ against solid tumors such as colon adenocarcinoma.

Animals↗
PubMed1985

Inhibition of dihydrofolate reductase, methotrexate transport, and growth of methotrexate-sensitive and -resistant L1210 leukemia cells in vitro by 5-substituted 2,4-diaminoquinazolines.

A series of eighteen 2,4-diaminoquinazoline analogues of folic, isofolic, pteroic and isopteroic acids having various substituents at position 5 was studied. Each compound was evaluated as an inhibitor of L1210 dihydrofolate reductase, methotrexate influx into L1210 leukemia cells, and growth of methotrexate-sensitive and -resistant L1210 cells in vitro. Bridge reversal at positions 9 and 10 reduced the effectiveness of the classical analogues only with regard to the inhibition of the drug-sensitive cells as compared to methotrexate (MTX). Absence of the glutamate moiety adversely affected the potency of the compounds, particularly when coupled with reversal of the 9,10-bridge. However, the presence of -Cl at position 5 restored significantly the potency of these compounds. The pteroate and isopteroate analogue ethyl esters were generally more effective inhibitors of cell growth than their non-esterified counterparts. Regarding the effects of substituents at position 5, the data suggest that -Cl greater than -CH3 greater than -H for inhibition of methotrexate transport and growth of methotrexate-sensitive L1210 cells. The 5-Cl pteroate analogue and its corresponding ethyl ester were highly effective as growth inhibitors of methotrexate-resistant, transport-defective, L1210 cells in vitro.

Animals↗
PubMed1985

Chemistry and antitumor evaluation of selected classical 2,4-diaminoquinazoline analogues of folic acid.

A series of six 2,4-diaminoquinazoline analogues of folic acid which bear close structural resemblance to methotrexate, 1a, were synthesized by unequivocal routes. Three of these have not been described previously, while complete structural characterization of the remaining compounds is presented for the first time. Each of the compounds was a potent inhibitor of dihydrofolate reductase (DHFR) from rat liver or L1210 leukemia cells having I50 values in a range similar to that of 1a. However, a wide divergence in inhibitory activity toward the growth of human gastrointestinal adenocarcinoma or L1210 leukemia cells in vitro was observed. Compounds having a normal folate configuration at positions 9 and 10 were more inhibitory than their isomeric reversed-bridge counterparts. The N-formyl modifications were the least active of the compounds studied. Unsubstituted or N-methyl modifications competed effectively with tritiated 1a for uptake into L1210 leukemia cells, while N-formyl modifications did not. Against an L1210 cell line resistant to 1a by virtue of altered transport and overproduction of DHFR, partial but not complete cross-resistance was observed for certain analogues. Of the three compounds selected for in vivo evaluation against L1210 leukemia in mice, two had a similar level of antitumor activity to that of 1a. The compound 5,8-dideazamethopterin, 2b, however, was slightly more active than 1a but at substantially reduced dose levels.

Adenocarcinoma↗
PubMed1984

Improved synthesis and antitumor evaluation of 5,8-dideazaisofolic acid and closely related analogues.

A new synthetic route to 5,8-dideazaisofolic acid (IAHQ) is described which precludes the possibility of contamination due to its 4-amino counterpart 5,8-dideazaisoaminopterin. Substitution of D-glutamic acid in this synthetic scheme gave D-IAHQ. The 9-formyl, 9-methyl, 5-methyl, and 5,9-dimethyl modifications of IAHQ were also prepared. These compounds, together with several structurally related or isomeric analogues, were studied for inhibitory effects upon the growth of four human gastrointestinal adenocarcinoma cell lines in vitro. In general, the compounds having a normal folate configuration at positions 9 and 10 are more active than their reversed bridge isomers. The lack of antitumor activity of D-IAHQ provides indirect evidence concerning the mechanism of action of IAHQ.

Adenocarcinoma↗
PubMed1984

Effects of three new folate antagonists on human breast adenocarcinoma cells in vitro and on immune responses in vivo.

The effects of three selected potential folate antagonists on 3H-leucine incorporation of eight established breast adenocarcinoma cell lines were investigated. The compounds studied were 5,8-dideazaisofolic acid, 5-methyl-5,8-dideazaisofolic acid, and 10-oxa-5,8-dideazafolic acid. All three anti-folates were inhibitory to most of the cells tested. 10-Oxa-5,8-dideazafolic acid was more effective in inhibiting the growth of these tumor cell lines. Both natural killer cell activity and phytohemagglutinin (PHA)-induced lymphocyte proliferation were decreased in hamsters injected with these compounds, with 5,8-dideazaisofolic acid being the most potent in this regard. The natural killer cell activity and lymphocyte proliferation returned to normal levels 12 days post-injection of these compounds. These studies suggest that 10-oxa-5,8-dideazafolic acid may be useful for the treatment of human breast tumors.

Adenocarcinoma↗
PubMed1983

Inhibition of a methotrexate-insensitive dihydrofolate reductase from L5178Y cells by substituted triazines and quinazolines.

Inhibition by a variety of substituted triazines and quinazolines of a methotrexate-insensitive form of dihydrofolate reductase from highly MTX-resistant L5178Y mouse leukemia cells was examined. Some of these compounds were significantly more potent than MTX (up to 100-fold). Two triazenes, terminally substituted with benzenesulfonylfluoride residues, were approximately 30-fold more potent than MTX. Quinazoline analogs of folic acid with alterations in different parts of the molecule varied in their potencies as inhibitors. Although none of the compounds tested was as potent as MTX against MTX-sensitive dihydrofolate reductases, these studies show that some types of folate antagonists have increased specificity against this MTX-insensitive dihydrofolate reductase. This finding increases the likelihood that it may be possible to produce compounds with marked specificity for the insensitive reductase. Such compounds might have utility in antifolate combinations designed to overcome methotrexate resistance.

Animals↗
PubMed1983

Improved synthetic routes to 5,8-dideazapteroylglutamates amenable to the formation of poly-gamma-L-glutamyl derivatives.

A variety of quinazoline analogues of folic acid (5,8-dideazafolates) are of interest as potential antineoplastic agents, biochemical probes, and/or affinity ligands for the purification of folate requiring enzymes. Chief among these are 5,8-dideazaisopteroylglutamate, 5,8-dideazaisoPteGlu, (IAHQ), a compound with proven activity against the growth of human colon adenocarcinoma cells in vitro, and 10-formyl-5,8-dideazapteroylglutamic acid, which serves as a substrate for glycinamide ribonucleotide transformylase and is also an effective inhibitor of mammalian thymidylate synthase. New methods for preparing these compounds in excellent purity as determined by high performance liquid chromatography (HPLC) have been developed. In each case the carboxyl groups of L-glutamic acid are protected with t-butyl ester groups, since these can subsequently be removed readily using trifluoroacetic acid without decomposition or racemization of the final product. This approach has proven to be of particular value in the formation of gamma-L-glutamyl derivatives of IAHQ containing 1-3 additional glutamyl residues.

Cell Line↗
PubMed1983

Effects of 5,8-dideazaisopteroylglutamate and its possible tri-gamma-glutamyl metabolite (5,8-dideazaisoPteGlu3) on colon adenocarcinoma, and the folate dependent enzymes thymidylate synthase and dihydrofolate reductase.

A series of 2-amino-4-hydroxy-quinazolines was synthesized and evaluated as inhibitors of colon adenocarcinoma and the folate-dependent enzymes, thymidylate synthase and dihydrofolate reductase. Of the quinazolines tested, 5,8-dideazaisopteroylglutamate, (IAHQ), when administered at 85 mg/kg on days 2 and 10 after tumor implantation delayed the growth of colon tumor No. 38, and resulted in 6 of 20 tumor-free animals at 90 days. In contrast, methotrexate had no effect on the growth of colon tumor No. 38 at maximally tolerated doses. IAHQ was also active against human colon adenocarcinoma cells (HCT-8) in tissue culture, requiring a concentration of 5 X 10(-7) M to inhibit cell growth 50% after 72 hours continuous exposure. Since IAHQ was an effective substrate for folylpolyglutamate synthetase, we examined the effects of IAHQ and its possible tri-gamma-glutamyl metabolite, 5,8-dideazaisoPteGLu3, on thymidylate synthase and dihydrofolate reductase. Neither IAHQ nor 5,8-dideazaisoPteGlu3 stimulated significant binding of 5-fluorodeoxyuridylate to thymidylate synthase. This was consistent with the observation that IAHQ antagonized the killing of HCT-8 cells by 5-fluorouracil. 5,8 DideazaisoPteGlu3 bound more tightly to thymidylate synthase than dihydrofolate reductase as indicated by Kis of 0.09 and 0.7 microM when deoxyuridylate and dihydropteroylglutamate, respectively, were the variable substrates. Inhibition studies also revealed that binding of IAHQ and 5,8-dideazaisoPteGlu3 to thymidylate synthase is promoted and not antagonized by deoxyuridylate. The data suggests that the biochemical basis for the antitumor effects of IAHQ is the intracellular conversion of IAHQ to poly-gamma-glutamyl metabolites, which inhibit thymidylate synthase via formation of an inhibitor-deoxyuridylate-enzyme complex.

Adenocarcinoma↗
PubMed1982

Effects of 5,8-dideazaisofolic acid (IAHQ) on human tumor cells in culture and on normal and tumor-bearing hamsters.

The quinazoline analog of folic acid, 5,8-dideazaisofolic acid (IAHQ), was tested for its effects on the growth of human tumor cells in vitro and in vivo. Of 23 human tumor cell lines tested in vitro, 7 were inhibited by IAHQ (ED50, 5 X 10(-6) to 5 X 10(-7) M). For in vivo studies, human osteosarcoma (OS) cells from the IAHQ-sensitive line TE-85 were implanted intraperitoneally in newborn hamsters: in the group treated with IAHQ, only 30% of the animals developed OS, compared with 100% of those not treated with IAHQ. The effects of IAHQ injections on mitogenic responses and natural killer activity of lymphocytes from normal 3-month-old hamsters were also examined.

Animals↗