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D S Duch

Publications and source records attributed to D S Duch.

At least 55 records · Page 3Linked to original sources
PubMed1990

Direct demonstration of the active salvage of preformed purines by murine tumors.

The purine de novo biosynthetic pathway has become a target for chemotherapeutic agents and because of the possible contribution of the salvage of extracellular purines to cellular purine pools an examination of the ability of mouse tumors in vivo to exploit the salvage pathways was undertaken. Our data reveal that circulating radiolabeled preformed purines are rapidly and actively salvaged in both normal liver and in two different types of model tumors. The salvaged purines were found to be distributed between both acid soluble cytoplasmic purines and acid insoluble nucleic acid associated purine species. The ability to salvage adenine, the most abundant circulating purine in C57BL/6 mice, was highest in normal liver with the two different model tumors demonstrating lower specific activities of salvaged acid soluble purines. The amount of radiolabel incorporated into acid insoluble nucleic acid was dependent upon the tumor type. Because of the active salvage observed in these tumors, the mechanism by which de novo purine biosynthesis inhibitors serve as effective chemotherapeutic agents may be more complex than simple biosynthetic inhibition.

Adenocarcinoma↗
PubMed1990

Activity of an NAD-dependent 5,10-methylenetetrahydrofolate dehydrogenase in normal tissue, neoplastic cells, and oncogene-transformed cells.

As an extension of the previously reported observation concerning the existence of NAD-dependent 5,10-methylenetrahydrofolate dehydrogenase in transformed cells a variety of tissues and cell lines have been assayed for this activity. This activity was found in all assayed transformed cells. Results with rat liver derived epithelial (RLE) cells transformed with a series of oncogenes (v-raf, v-raf/v-myc (J2), v-myc (J5), and v-Ha-ras (pRNR16)) indicated that expression of activity correlates with the extent of transformation and was independent of the oncogene used for transformation. Compared to previously reported values for normal tissue, surprisingly high levels of the NAD-dependent 5,10-methylenetetrahydrofolate dehydrogenase were found in the rat adrenal cortex. This activity was not seen in mouse or bovine adrenal. Enzymatic activity was also detected in mouse bone marrow and was strain dependent. The levels of activity in mouse bone marrow were lower than previously reported. The NAD-dependent 5,10-methylenetetrahydrofolate dehydrogenase activity in rat adrenal and RLE cells may represent tools for studying the regulation of expression of this activity.

Animals↗
PubMed1990

Neuraminidase treatment modifies the function of electroplax sodium channels in planar lipid bilayers.

Sodium channels from several sources are covalently modified by unusually large numbers of negatively charged sialic acid residues. In the present studies, purified electroplax sodium channels were treated with neuraminidase to remove sialic acid residues and then examined for functional changes in planar lipid bilayers. Neuraminidase treatment resulted in a large depolarizing shift in the average potential required for channel activation. Additionally, desialidated channels showed a striking increase in the frequency of reversible transitions to subconductance states. Thus it appears that sialic acid residues play a significant role in the function of sodium channels, possibly through their influence on the local electric field and/or conformational stability of the channel molecule.

Animals↗
PubMed1990

Synthesis and biological activity of an acyclic analogue of 5,6,7,8-tetrahydrofolic acid, N-[4-[[3-(2,4-diamino-1,6-dihydro-6-oxo-5- pyrimidinyl)propyl]amino]-benzoyl]-L-glutamic acid.

The synthesis and biological evaluation of N-[4-[[3-(2,4-diamino-1,6-dihydro-6-oxo-5-pyrimidinyl)propyl]amino]- benzoyl]-L-glutamic acid (1) (5-DACTHF, 543U76), an acyclic analogue of 5,6,7,8-tetrahydrofolic acid (THFA), are described. The key intermediate, hemiaminal 8, was prepared in four stages from 3-chloropropionaldehyde diethyl acetal. Reaction of 8 with dimethyl N-(4-aminobenzoyl)-L-glutamate gave the 2,4-bis(acetylamino) derivative 11, which was hydrolyzed with 1 N sodium hydroxide to give 1; the glycine analogue 16 was prepared in a similar manner. The N-methyl analogue 2 and N-formyl analogue 3 were prepared from 11 and 1, respectively. Compounds 1-3 inhibited growth of Detroit 98 and L cells in cell culture, with IC50s ranging from 2 to 0.018 microM. Cell culture toxicity reversal studies and enzyme inhibition tests showed that 1 was cytotoxic but not by the mechanism of the dihydrofolate reductase inhibitor aminopterin. Compound 1 and its polyglutamylated homologues inhibited glycinamide ribonucleotide transformylase (GAR-TFase) and aminoimidazole ribonucleotide transformylase (AICAR-TFase), the folate-dependent enzymes in de novo purine biosynthesis; and 1 was an effective substrate for mammalian folyl-polyglutamate synthetase. The compound inhibited (IC50 = 20 nM) the conversion of [14C]formate to [14C]-formylglycinamide ribonucleotide by MOLT-4 cells in culture. These data suggest that the site of action of 1 is inhibition of purine de novo biosynthesis. Moderate activity was observed against P388 leukemia in vivo.

Acyltransferases↗
PubMed1990

Molecular actions of pentobarbital isomers on sodium channels from human brain cortex.

New planar lipid bilayer technology enabled the pharmacologic study of single sodium channels from human brain, overcoming the limitations of tissue availability and the rapid loss of protein function in conventional experimental preparations. Synaptosomal vesicles prepared from human brain cortical tissue were fused with planar lipid bilayers. In the presence of batrachotoxin, sodium channels were incorporated into lipid bilayers and their single-channel properties studied. Pentobarbital was found to depress two major functions of the sodium channel, leading to a voltage-independent reduction of the fractional channel open-time (ED50 0.61-0.75 mM) and an interaction with the voltage-dependent steady-state activation. The steady-state activation curve was shifted to more negative potentials and had a reduced slope, i.e., negative membrane potentials became less effective at closing sodium channels. The results were consistent with a pentobarbital-induced increase in protein flexibility. The actions of the two optical stereoisomers of pentobarbital showed no significant differences, indicating that other ion channels must also be involved in the clinical actions of barbiturates. The pentobarbital effects on sodium channels occurred at concentrations thought to be relevant in general anesthesia and within the clinical range. This suggests that sodium channels could contribute to overall anesthetic depression, supporting our hypothesis that anesthesia results from the superposition and integration of several anesthetic actions at the molecular level.

Cerebral Cortex↗
PubMed1989

Synergistic effects of phorbol ester and INF-gamma on the induction of indoleamine 2,3-dioxygenase in THP-1 monocytic leukemia cells.

Indoleamine 2,3-dioxygenase (IDO) is a flavin-dependent enzyme which uses superoxide anion as a cosubstrate to catalyze the decyclization of the pyrrole ring of L-tryptophan to form formylkynurenine. This enzyme is induced in some tumor cells after treatment with IFN-gamma. The mechanism of induction of IDO in tumor cells by IFN-gamma was studied in THP-1 human monocytic leukemia cells. Before the addition of IFN-gamma, no IDO could be detected in these cells. Treatment of THP-1 cells with IFN-gamma produced an induction of IDO, with peak activity occurring 72 to 96 h after addition of IFN-gamma. Because phorbol esters are known to induce many enzymes in cells, most likely through the activation of protein kinase C, the effects of PMA on the induction of IDO were determined. PMA potentiated the IFN-gamma-induced elevation of IDO, but by itself, was unable to induce enzyme activity. Maximum induction of IDO in the presence of PMA and IFN-gamma was obtained by preexposure of the cells to PMA for 48 h before the addition of IFN-gamma. Maximum induction of IDO after the addition of IFN-gamma occurred 24 to 48 h after addition of the cytokine to the culture medium. However, the induction of IDO does not appear to be potentiated through the activation of protein kinase C, because the addition of the protein kinase C inhibitor H-7 had no effect on the induction of IDO when the cells were exposed to PMA and IFN-gamma. Moreover, diacylglycerol was unable to replace PMA in these studies. Studies with cAMP and cGMP analogs suggest a role for these compounds in the regulation of IDO expression.

Cyclic AMP↗
PubMed1989

Clinical experience with leucovorin and 5-fluorouracil.

Two trials of leucovorin (LV) and 5-fluorouracil (5-FU) in patients with metastatic colorectal cancer were done, both using a 3-day loading dose and then weekly doses to minimize toxicity. The first trial used LV administered by intravenous infusion with a constant dose of 5-FU 400 mg/m2, and the second trail used oral LV with increasing doses of 5-FU. In the first trail, 45 eligible patients (20 with and 25 without previous therapy) were treated. Toxicity usually consisted of diarrhea or weakness and was controlled by delaying or decreasing the 5-FU dose. Subjective responses occurred in 75% of patients but did not correlate with antineoplastic effect. Objective responses were seen in 36% and stabilization of disease in 31% of patients; these correlated with prolonged survival. Median survival was 8 months for patients with previous treatment and 10 for those without. Twelve-month survival was 32% and 40%, respectively. There was no correlation between the development of toxicity and response or survival. The second trial was conducted recently in cooperation with Duke University to determine toxicity and efficacy of oral LV with intravenous 5-FU before a randomized trial of this combination versus placebo with intravenous 5-FU. Eighteen patients were treated, and serum levels of folates were obtained on ten. First toxicity occurred at 5-FU doses ranging from 375 to 850 mg/m2, and consisted of diarrhea in nine, lethargy in seven, nausea/vomiting in four, dermatitis in four, conjunctivitis in two, hypersalivation in two, stomatitis in one, and profound granulocytopenia in one. Response rate was 35%, and stabilization was 35% with median survival of 14 months. Twelve-month survival was 56%.

Adenocarcinoma↗
PubMed1989

Pentobarbital suppresses human brain sodium channels.

Ion channels, key components in neuronal signal transmission and processing, are likely to be important molecular sites of anesthetic action. Sodium channels from human brain tissue were incorporated into planar lipid bilayers in the presence of batrachotoxin and exposed to the anesthetic pentobarbital. This barbiturate, in a dose-dependent manner and at clinically relevant concentrations, reduced fractional channel open time independent of membrane potential, and interfered with the steady-state activation process.

Cerebral Cortex↗
PubMed1989

Folate analogues. 31. Synthesis of the reduced derivatives of 11-deazahomofolic acid, 10-methyl-11-deazahomofolic acid, and their evaluation as inhibitors of glycinamide ribonucleotide formyltransferase.

The Boon-Leigh procedure, involving condensation of a 6-chloro-5-nitropyrimidine (22) with an alpha-amino ketone (20 or 21) followed by reduction of the nitro group, cyclization, and L-glutamylation, led to the formation of 11-deazahomofolate (29) and its 10-methyl derivative (30). The corresponding (6R,S)-5,6,7,8-tetrahydro (4, 5) and 7,8-dihydro (31, 32) derivatives were prepared by catalytic hydrogenation. (6S)-11-Deazatetrahydrohomofolate was prepared from 29 by enzymatic reduction. Compounds 29 and 30 had little effect (IC50 greater than 2 x 10(-5) M) on Lactobacillus casei glycinamide ribonucleotide (GAR) formyltransferase but (6R,S)-11-deazatetrahydrohomofolate (4) is a potent inhibitor of this enzyme (IC50 = 5 x 10(-8) M). It is at least 100 times more inhibitory than 33, the 6S compound, indicating that the 6R component of the mixture having the unnatural configuration at C6 (34) is responsible for the potent inhibition. Compound 4 is a much weaker inhibitor of murine (L1210) and human (MOLT-4) leukemia cell GAR formyltransferases (IC50 greater than 1 x 10(-5) M). (6R,S)-11-Deaza-10-methyltetrahydrohomofolate (5) (IC50 = 1.1 x 10(-5) is 200 times weaker than 4 against L. casei GAR formyltransferase. However, 11-deaza-10-methyldihydrohomofolate (32) is more inhibitory (IC50 = 5.5 x 10(-7) M) than 5 or 30. None of the compounds showed inhibition of L. casei aminoimidazolecarboxamide ribonucleotide (AICAR) formyltransferase, dihydrofolate reductase, or thymidylate synthase. The dihydro derivatives 31 and 32 are 5% as active as dihydrofolate as substrates for L. casei dihydrofolate reductase. Compound 4 showed moderate inhibition of the growth of L. casei, Streptococcus faecium, MOLT-4 cells, and MCF-7 human breast adenocarcinoma cells.

Acyltransferases↗
PubMed1989

Veratridine modification of the purified sodium channel alpha-polypeptide from eel electroplax.

In the interest of continuing structure-function studies, highly purified sodium channel preparations from the eel electroplax were incorporated into planar lipid bilayers in the presence of veratridine. This lipoglycoprotein originates from muscle-derived tissue and consists of a single polypeptide. In this study it is shown to have properties analogous to sodium channels from another muscle tissue (Garber, S. S., and C. Miller. 1987. Journal of General Physiology. 89:459-480), which have an additional protein subunit. However, significant qualitative and quantitative differences were noted. Comparison of veratridine-modified with batrachotoxin-modified eel sodium channels revealed common properties. Tetrodotoxin blocked the channels in a voltage-dependent manner indistinguishable from that found for batrachotoxin-modified channels. Veratridine-modified channels exhibited a range of single-channel conductance and subconductance states. The selectivity of the veratridine-modified sodium channels for sodium vs. potassium ranged from 6-8 in reversal potential measurements, while conductance ratios ranged from 12-15. This is similar to BTX-modified eel channels, though the latter show a predominant single-channel conductance twice as large. In contrast to batrachotoxin-modified channels, the fractional open times of these channels had a shallow voltage dependence which, however, was similar to that of the slow interaction between veratridine and sodium channels in voltage-clamped biological membranes. Implications for sodium channel structure are discussed.

Animals↗
PubMed1988

Clinical experience with CF-FUra.

Two trials of CF-FUra in patients with metastatic colorectal cancer were performed, both using a 3 day loading dose and then weekly maintenance doses to minimize toxicity. The first trial used CF by IV infusion with constant dose of FUra 400 mg/m2, and the second trial used oral CF with escalating doses of FUra. In the first trial, 45 eligible patients (20 with and 25 without prior therapy) were treated. Toxicity usually consisted of diarrhea or weakness and was controlled by delaying or decreasing 5FU dose. Subjective responses occurred in 75% of patients but did not correlate with antineoplastic effect. Objective responses were seen in 36% and stabilization of disease in 31% of patients, and correlated with prolonged survival. Median survival was 8 months for patients with prior treatment and 10 for those without, and 12 month survival was 32% and 40%, respectively. There was no correlation between the development of toxicity and response or survival. The second trial was recently conducted in cooperation with Duke University to determine toxicity and efficacy of oral CP with IV FUra prior to a randomized trial of this combination versus placebo with IV FUra. Eighteen patients were treated and serum levels of folates were obtained on 10. First toxicity occurred at FUra doses ranging from 375 to 850 mg/m2, and consisted of diarrhea in 9, lethargy in 7, nausea/vomiting in 4, dermatitis in 4, conjunctivitis in 2, hypersalivation in 2, stomatitis in 1, and profound granulocytopenia in 1. Response rate was 35% and stabilization was 35% with median survival of 14 months and 12 month survival of 56%.

Adenocarcinoma↗
PubMed1988

In vivo measurement of dihydrofolate reductase and its inhibition by antifolates.

The ability of the enzyme dihydrofolate reductase to catalyze the formation of tetrahydrobiopterin from dihydrobiopterin was used to develop a method for measuring the activity of this enzyme in vivo. This method can be used to determine the activity of the enzyme in tissues as well as the extent and duration of inhibition of the enzyme by antifolates. Sepiapterin, which is converted to dihydrobiopterin by the enzyme sepiapterin reductase, was as effective a precursor as dihydrobiopterin and has been used in these studies because of its greater stability relative to dihydrobiopterin. Assay conditions must be established for each tissue and enzyme activity can be determined either by measuring the rate of disappearance of dihydrobiopterin or the rate of formation of tetrahydrobiopterin.

Animals↗
PubMed1988

Human brain sodium channels in bilayers.

Sodium channels from human cortex were fused into planar lipid bilayers in the presence of batrachotoxin, and their single channel properties examined. Single channel slope conductance averaged 26 ps; tetrodotoxin block of the channels was voltage dependent with a K1/2 at 0 mV of 51 nM. The channel was asymmetrically selective for sodium over potassium. The permeability ratio (PNa/PK) equalled 3.3 when potassium was present only on the intracellular side of the channel, but it was 5.7 with potassium on the extracellular side. The average channel activation gating midpoint was -91 mV. These results indicate that sodium channels from human brain can be successfully studied both electrophysiologically and pharmacologically with the planar bilayer system.

Batrachotoxins↗
PubMed1988

Induction of indoleamine 2,3-dioxygenase: a mechanism of the antitumor activity of interferon gamma.

The antiproliferative effects of interferon alpha (IFN-alpha) and interferon gamma (IFN-gamma) were found to be cell-dependent. Among the human cell lines examined, IFN-gamma had a greater antiproliferative effect against cell lines that exhibited induction of indoleamine 2,3-dioxygenase, such as the KB oral carcinoma or WiDr colon adenocarcinoma, than against those that lacked the enzyme activity, such as the SW480 colon adenocarcinoma or NCI-H128 small-cell lung carcinoma. Induction of this dioxygenase showed a clear temporal relationship with increased metabolism of L-tryptophan and the depletion of this amino acid in the culture medium. While 70-80% of L-tryptophan remained in the medium of IFN-alpha- or vehicle-treated cells, virtually all of this amino acid was depleted in the medium of the IFN-gamma-treated group following 2-3 days of culture. Supplementing the growth medium with additional L-tryptophan reversed the antiproliferative effect of IFN-gamma against KB cells in a dose- and time-dependent manner. The antiproliferative effects of IFN-alpha and IFN-gamma on SW480 and NCI-H128 cells, which are independent of the dioxygenase activity, and the inability of added L-tryptophan to reverse the effects of IFN-gamma in WiDr cells suggest multiple mechanisms of action of the IFNs. The data show that the antiproliferative effect of IFN-gamma through induction of indoleamine 2,3-dioxygenase, with a consequent L-tryptophan deprivation, is an effective means of regulating cell growth.

Cell Division↗
PubMed1987

Utilization of dihydroflavin mononucleotide and superoxide anion for the decyclization of L-tryptophan by murine epididymal indoleamine 2,3-dioxygenase.

Dihydroflavin mononucleotide (FMNH2) together with a regenerating enzyme system effectively supported L-tryptophan decyclization by indoleamine 2,3-dioxygenase isolated from murine epididymis. The native murine dioxygenase was a monomeric protein with Mr 40,000 +/- 1000, an apparent pI of 4.9 +/- 0.1, and an optimum pH within the range of 7 to 8. Using FMNH2 with FMN oxidoreductase, the enzyme attained significantly higher activity than the apparent maximal activity obtained by using the other electron donor systems examined (e.g., riboflavin, FAD, tetrahydrobiopterin, methylene blue). A kinetic study with the FMNH2 cofactor suggested the occurrence of a complex reaction (L-tryptophan-FMNH2 interdependency) and a theoretical K'm of 14 microM or a Km of 13 microM was estimated for the substrate. L-Tryptophan 2,3-dioxygenation was competitively inhibited by L-5-hydroxytryptophan with a Ki of 1 microM. The reaction rate was reduced to less than 50% of that of the control in the presence of superoxide dismutase and was decreased to 3% of the control in the absence of catalase. Thus, superoxide anion does not appear to be the only form of O2 participating in the reaction. However, these data indicate that the activation of molecular oxygen is an essential factor for an optimum catalysis and a mechanism of FMNH2-dependent oxygenation of L-tryptophan by murine indoleamine 2,3-dioxygenase.

5-Hydroxytryptophan↗
PubMed1987

The actions of interferon and antiinflammatory agents of induction of indoleamine 2,3-dioxygenase in human peripheral blood monocytes.

Interferon substantially induced indoleamine 2,3-dioxygenase and increased L-tryptophan metabolism in human peripheral blood monocytes. The induction of dioxygenase by gamma-interferon was significantly higher than that observed with alpha-interferon. This cytokine-dependent induction of the enzyme was markedly and differentially altered by antiinflammatory drugs (i.e., acetaminophen, 3-deazaadenosine, indomethacin and dexamethasone). Dexamethasone potentiated the effect of gamma-interferon and resulted in "super-induction" of the enzyme. This is the first demonstration of the interferon-elicited induction of the dioxygenase in the cells of the immune system and of a novel mechanism for regulating tryptophan metabolism in the cells.

Anti-Inflammatory Agents, Non-Steroidal↗