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Biomedical subjects

K D Tew

Publications and source records attributed to K D Tew.

142 records · Page 8Linked to original sources
PubMed1979

Effect of 1-methyl-1-nitrosourea on poly(adenosine diphosphate-ribose) polymerase activity at the nucleosomal level.

The stimulation of poly(adenosine diphosphate ribose) [poly(ADP-ribose)] polymerase activity at the nuclear level after damage of HeLa cells by 1-methyl-1-nitrosourea has been previously reported. We have observed a similar activation of the enzyme after treatment of cells with MNU at the nucleosomal level of chromatin (greater than 1N). This stimulation of enzyme activity did not occur through an inhibition of the glycohydrolase enzyme which cleaves poly(ADP-ribose), or elongation of poly(ADP-ribose) chains, or an increased biosynthesis of enzyme protein. The increased activity appears to be a consequence of the generation of more acceptor sites on nuclear proteins for initiation of poly(ADP-ribose) synthesis. The data indicate that MNU increased the accessibility of nucleosome core histones for modification by poly(ADP) ribosylation.

Chromatin↗
PubMed1979

Nitrosourea interaction with chromatin and effect on poly(adenosine diphosphate ribose) polymerase activity.

Poly(adenosine diphosphate ribose) polymerase, a chromatin-bound enzyme, was stimulated 150 to 200% after treatment of HeLa cells with methylnitrosourea (MNU). In contrast, a slight inhibitory effect on enzyme activity was observed after treatment of cells with various concentrations of chloroethylnitrosoureas. To define precisely the differential effects of nitrosoureas on the enzyme activity, their interactions with chromatin substructure were studied. A nonrandom, in vivo alkylation of chromatin DNA by equimolar concentrations of MNU and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) was revealed by digestion of nuclei from drug-treated cells with micrococcal nuclease and DNase I. [methyl-14C]MNU interacted preferentially with the more accessible regions of chromatin, the internucleosome linkers, whereas, the [chloroethyl-14C]CCNU alkylated the nucleosomal core DNA to a greater extent. These two drugs also differed in their extent of covalent modification of histone and nonhistone chromosomal protein. The binding of MNU to histones was greater than of CCNU. CCNU mainly affected nonhistone proteins. This difference in the reactivity of methyl and chloroethyl nitrosoureas with chromatin may relate to their differential effect on poly(adenosine diphosphate ribose) polymerase activity, as well as to their carcinogenic and antitumor properties.

Alkylation↗
PubMed1977

Studies with cyclophosphamide labeled with phosphorus-32: nucleic acid alkylation and its effect on DNA synthesis in rat tumor and normal tissues.

The gross distribution of levels of [32P]cyclophosphamide ([32P]CY) in August female rats was similar in tumor, intestinal mucosa, spleen, bone marrow, and striated muscle tissue, with slightly higher levels in liver and kidney tissue. A triphasic association with nucleic acids was found and actual alkylation of DNA and RNA reached a maximum of 48 hours post treatment. There was no evidence of 32P-label reutilization that could have accounted for prolonged alkylation. We found that 100 mg CY/kg suppressed the incorporation of [3H]thymidine, [3H]deoxyuridine, and [14C]sodium formate into the DNA of the BICR-A15 carcinoma for at least 10 days. This correlated well with the observed regression of tumor volume. Bone marrow and intestinal mucosa, two tissues which limit chemotherapuetic treatment of the tumor, were less affected by 100 mg CY/kg. Bone marrow had regained normal levels of DNA precursor incorporation by 5 days, and intestinal mucosa had regained normal levels by 3 days. Results indicated that this differential in recovery time may assist in the successful scheduling of vital tissue-sparing drug regimens.

Alkylation↗
PubMed1976

Some studies on the distribution and effects of cyclophosphamide (NSC-26271) in normal and neoplastic tissue.

The gross uptake and intracellula distribution of 32P-cyclophosphamide has been studied in normal and neoplastic rat and mouse tissues. Prolonged alkylation of DNA and RNA occurs over periods of 24 hours in the mouse and 48 hours in the rat, and it is suggested that this may involve slow release of active metabolites from a drug-macromolecule complex. The survival of cells in pulmonary and sc tumors after cyclophosphamide treatment has been studied in situ using a biochemical assay, and the influence of environmental factors at the tumor site has been assessed. The pattern of drug distribution has been studied in large sc tumors, and in one tumor line the drug concentration achieved has been related to estimated cell survival.

Alkylation↗
PubMedDate not supplied

The antioxidant role of selenium and seleno-compounds.

Selenium (Se) is an essential trace element for animals and humans that is obtained from dietary sources including cereals, grains and vegetables. The Se content of plants varies considerably according to its concentration in soil. Plants convert Se mainly into Se-methionine (Se-Met) and incorporate it into protein in place of methionine (Met). Selenocystine (Se-Cys), methyl-Se-Cys and gamma-glutamyl-Se-methyl-Cys are not significantly incorporated into plant protein and are at relatively low levels irrespective of soil Se content. Higher animals are unable to synthesize Se-Met and only Se-Cys was detected in rats supplemented with Se as selenite. Renal regulation is the mode by which whole body Se is controlled. Se is concentrated in hair and nail and it occurs almost exclusively in organic compounds. The potentiating effect of Se deficiency on lipid peroxidation is enhanced in some tissues by concurrent deficiency of copper or manganese. In the in vitro system, the chemical form of Se is an important factor in eliciting cellular responses. Although the cytotoxic mechanisms of selenite and other redoxing Se compounds are still unclear, it has been suggested that they derive from their ability to catalyze the oxidation of thiols and to produce superoxide simultaneously. Selenite-induced cytotoxicity and apoptosis in human carcinoma cells can be inhibited with copper (CuSO(4)) as an antioxidant. High doses of selenite result in induction of 8-hydroxydeoxyguanosine (8-OHdG) in mouse skin cell DNA and in primary human keratinocytes. It may cause DNA fragmentation and decreased DNA synthesis, cell growth inhibition, DNA synthesis, blockade of the cell cycle at the S/G(2)-M phase and cell death by necrosis. In contrast, in cells treated with methylselenocyanate or Se methylselenocysteine, the cell cycle progression was blocked at the G(1) phase and cell death was predominantly induced by apoptosis.

Aging↗
PubMedDate not supplied

Cytotoxicity and DNA damaging effects of a new nitrosourea, fotemustine, diethyl- 1-(3-(2-chloroethyl)-3-nitrosoureido) ethylphosphonate-S10036.

Fotemustine is a new chloroethylnitrosourea which has recently entered a Phase II clinical trial. Using standard cytotoxicity analyses, Fotemustine was shown to be preferentially active in two Mer- cell lines, human colon BE and human lung A427. Comparative cell kill in the Mer+ counterparts HT29 and A549 (respectively) was significantly lower. In a mouse cell line, P388, alkaline elution studies showed that Fotemustine caused fewer DNA strand breaks and total crosslinks (including DNA-protein) than either BCNU or MeCCNU at equivalent cytotoxic concentrations. In addition, the removal of DNA damage caused by Fotemustine was more rapid than of damage, three times as much Fotemustine was required. These data suggest that the cytotoxic mechanism of Fotemustine, although subject to the same repair mechanisms as other nitrosoureas, may not be entirely dependent upon DNA as the sole drug target. The previously reported reduced mutagenicity of this agent may also be a function of the less extensive nucleic acid damage. The encouraging early clinical trial results with this drug may reflect its improved pharmacokinetics and bioavailability, rather than any significant modification in its cellular pharmacology when compared to other nitrosoureas.

Antineoplastic Agents↗
PubMedDate not supplied

Immunofluorescent studies of the anti-microtubule effects of the anti-cancer drug estramustine.

Immunofluorescent studies in human prostatic carcinoma cells (DU 145) and cultured squirrel fish epithelial cells (a non-cancer cell) revealed that estramustine, a conjugate of estradiol and nor-nitrogen mustard, possessed microtubule disassembly properties. Sixty microM estramustine produced disassembly at both the proximal and distal ends of microtubules, producing short pieces of less than 2 microM which were "wavy" and oriented in a random manner. With increased time of drug exposure these short microtubules disappeared, to be accompanied by a gradual disassembly of a small population of longer microtubules (greater than 7-8 microM). In dividing DU 145 cells it was possible to show a different degree of sensitivity of specific microtubule-containing cellular structures. In mitotic figures the asters were most sensitive and disappeared completely following exposure to estramustine. These were followed by the "pole-to-pole" and "chromosomal" fibers. In cytokinesis, the intercellular fibers between daughter cells were comparatively resistant to the drug. Estramustine did not induce disassembly of the vimentin filaments in non-dividing or dividing cells but did cause their collapse around the nucleus or the mitotic apparatus. These data suggest that specific microtubules have differing sensitivity to estramustine.

Cells, Cultured↗
PubMedDate not supplied

C-banding of two Walker 256 rat carcinoma cell lines sensitive and resistant to bifunctional mustards.

Walker 256 rat carcinosarcoma cell lines sensitive (WS) or resistant (WR) to bifunctional nitrogen mustards have modal chromosome numbers of 60 and 55 respectively. Karyotype analysis revealed that these cell lines have retained the major marker chromosomes present in the original in vivo Walker tumours. One new marker chromosome, a metacentric, was found in the WR cell line. C-banding revealed that in the WS cell line the secondary constriction of the marker chromosome was stained, whereas no staining was found on this chromosome in the WR cell line. Three autosomes containing very prominent non-centromeric C-bands were present in WS but not in the WR cell line which has 2 other chromosomes with minor C-bands. As non-centromeric C-bands do not occur in the normal rat karyotype, these are easily identifiable specific tumour markers for these two cell lines.

Alkylating Agents↗
PubMedDate not supplied

Impact of dietary supplement of Crassostrea gigas extract (JCOE) on glutathione levels and glutathione S-transferase activity in rat tissues.

Male Sprague Dawley rats received various amounts of extract of Crassostrea gigas by gavage every day for 2 weeks or one month. At these times, groups of animals were sacrificed and samples of major organs analyzed for levels of glutathione (GSH) and glutathione S-transferase (GST) activities. Following the two week protocol, GSH levels were significantly increased in the mucosa of the large intestine; at one month the small intestine and spleen were elevated. GST activity increased in liver under both schedules and at one month, activity was also elevated in kidney and small intestine. Since the Crassostrea gigas extract contains high levels of a variety of important amino acids, it is concluded that biologically available peptides are taken up in target organs and stimulate GSH metabolism. Enhanced levels of GSH and associated enzymes may contribute to a more effective detoxification phenotype, thus providing enhanced chemoprotective capacity.

Animals↗
PubMedDate not supplied

The antioxidant effects of Crassostrea gigas extract (JCOE) in human volunteers.

Since several in vitro and animal studies of an extract from Crassostrea gigas (JCOE) have demonstrated its antioxidant properties and other interesting effects, a preliminary human trial was carried out. Seven healthy male volunteers aged 23-37 received orally 3 x 2 capsules of JCOE per day for 8 days. On days 0, 1, 4, 8 and 15 (7 days after completion of the schedule) blood samples were drawn and the antioxidant potential of serum was tested. A statistically significant increase in the buffering effects of serum against hemoglobin (Hb) and lactate dehydrogenase (LDH) release from red blood cells treated with the free radical generator azobis amidino propane (AAPH) was found following JCOE treatment. At 8 days, the oxidative effects were reduced by > 90% of the pretreatment values. In these same individuals, serum levels of reduced glutathione were increased by an average of 1.5-fold over the time course of treatment. It is concluded that in normal human volunteers, JCOE capsules provide an orally available formula for enhancing the antioxidant capacity of blood serum. While the extract is known to contain some direct acting antioxidant components, at least a portion of the protective effect is facilitated by enhancement of GSH biosynthesis.

Adult↗