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T R Tritton

Publications and source records attributed to T R Tritton.

At least 55 records · Page 3Linked to original sources
PubMed1985

Cell surface effects of adriamycin and carminomycin immobilized on cross-linked polyvinyl alcohol.

Previous reports have claimed Adriamycin to be cytotoxic to cultured tumor cells when the drug is covalently immobilized on a solid support, thus suggesting a cell surface mechanism of action for the drug. Although these previous reports attempted to rule out released drug or endocytosis of drug-support particles as alternative explanations for the observed cytotoxicity, a more thorough analysis is necessary to substantiate fully the cell surface idea. In the present work, the stability of the drug-support linkage was increased by use of cross-linked polyvinyl alcohol as the support and cyanuric chloride or a diazonium salt for attachment of the drug. Different anthracycline orientations were tested by coupling Adriamycin at the amino sugar and carminomycin at the D-ring. The Adriamycin cross-linked polyvinyl alcohol and carminomycin cross-linked polyvinyl alcohol preparations had much lower drug release rates than did the earlier used carbamate-linked Adriamycin cross-linked agarose materials. All three immobilized drug preparations inhibited the growth of L1210 or S180 clones following 2- or 20-h incubation with cells at 37 degrees C. The results strongly support the concept that immobilized anthracyclines can be cytotoxic to cultured cells, for at least two different orientations of the drug on the support.

Animals↗
PubMed1984

Ligand self-association at the surface of liposomes: a complication during equilibrium-binding studies.

Daunomycin and carminomycin, two anthracycline antibiotics known to bind phospholipid bilayers, appear to self-associate at the surface of liposomes at high bound drug/lipid ratios (r). Fluorescence intensity, lifetime, and anisotropy measurements have been used to monitor the equilibrium binding of these drugs to small unilamellar solid-phase dipalmitoylphosphatidylcholine vesicles. Association of an anthracycline with excess liposome (low r) resulted in an increase in both the observed intensity and the fluorescence lifetime. At low vesicle concentrations (high r), a decrease in the total emission intensity was observed which was not paralleled by the excited-state lifetime. The data from these experiments are consistent with the formation of nonfluorescent anthracycline complexes at the surface of liposomes. Such ligand self-association is a potential complication in any studies on the interaction of amphipathic molecules with liposomes conducted at high r values. Because ligand self-association limits the collection of binding data over certain concentration ranges, this consequently results in greater uncertainty in the determination of the maximum value of r (n) in equilibrium binding studies.

Antibiotics, Antineoplastic↗
PubMed1984

Identification of L-ascorbic acid in secretion granules of the rat parotid gland.

We have examined the distribution of L-ascorbic acid in rat parotid acinar cells by analysis of whole tissue, subcellular fractions, and parotid salivary secretion. Acinar cell secretion granules contain reduced ascorbate at a calculated concentration of 3.5 mM. A distinct extragranular pool, comprising as much as 80% of total cellular ascorbate, also exists in these cells. Parotid secretion, collected from the cannulated duct after inducing secretion from acinar cells by isoproterenol administration, contains millimolar reduced ascorbate. Quantitatively, the level measured in parotid secretion, relative to the secreted enzyme alpha-amylase, is nearly identical to that measured in isolated granules, suggesting a common release by exocytosis. Although ascorbate has been extensively studied as a content component of adrenal chromaffin granules and has recently been implicated in secretion granules of other neural and endocrine tissues, its detection in secretion granules of exocrine cells is novel. Thus, ascorbate-dependent processes that occur in exocrine secretion granules, or that may be general to all types of secretion granules, are worthy of consideration.

Animals↗
PubMed1984

Photoaffinity labeling of the Sarcoma 180 cell surface by daunomycin.

We have used photoaffinity labeling to investigate the distribution and function of daunomycin binding sites in Sarcoma 180 cells. When native daunomycin is irradiated at 366 or 488 nm in the presence of cells, the drug is irreversibly incorporated into cellular molecules. The cellular acceptor for the photoincorporation cannot be extracted by chloroform-methanol nor can it be degraded by DNase. However, the drug acceptor is susceptible to trypsin digestion. These results show that the photoincorporation site is composed of protein but not of lipid or DNA. Furthermore, the fact that photoincorporation proceeds equally well at 0 degrees (where drug does not accumulate inside the cells) as compared to 37 degrees (where free drug concentrates in the cells) suggests that the labeling reaction occurs principally at the cell surface. The photolabeling process is not highly specific since it is not saturable at high drug concentrations and cannot be competed for by unlabeled daunomycin. When 2 X 10(5) daunomycin molecules are incorporated per Sarcoma 180 cell, the cells can still accumulate free drug. This result suggests that the photolabeling reaction does not occur at the drug transport locus. Photoincorporation of daunomycin also does not affect the viability of Sarcoma 180 cells, as judged by a cloning assay. Thus, there is probably no surface receptor for the drug which mediates cytotoxicity when occupied. This result is as expected from previous work predicting that the mechanism of daunomycin involves disruption of some generalized membrane property like fluidity. However, in a series of Sarcoma 180 sublines selected for increasing resistance to daunomycin, the photoincorporation increases in direct proportion to drug sensitivity. Consequently, daunomycin appears to be capable of photoaffinity labeling a cell surface protein which, although not directly involved in the mechanism of cytotoxicity is implicated in the expression of drug resistance.

Animals↗
PubMed1983

The role of membranes in the mechanism of action of the antineoplastic agent adriamycin. Spin-labeling studies with chronically hypoxic and drug-resistant tumor cells.

Electron spin resonance spectroscopy has been employed to analyze the changes in membrane order parameter in Sarcoma 180 cells under conditions in which an alteration in cellular susceptibility to the chemotherapeutic agent adriamycin is demonstrable. Changes in relative membrane fluidity using the paramagnetic probe 5-doxyl stearic acid were found to be associated with two phenomena which result in an altered cellular response to adriamycin: (a) the presence of an oxygen-deficient environment and (b) the expression of drug resistance. Under hypoxic conditions, in which the susceptibility to the cytotoxic action of adriamycin is increased, a decrease in bulk membrane order parameter was observed. Upon reoxygenation, the membrane fluidity and enhanced susceptibility to adriamycin reverted to control conditions with the same time course. In the case of drug-resistant cells, a progressive decrease in membrane fluidity was also observed which correlated with the degree of resistance to adriamycin. These data suggest that the physical alterations in the membrane reported by the spin label may be functionally linked to biological alterations in sensitivity to adriamycin.

Aerobiosis↗
PubMed1983

Adriamycin causes up regulation of epidermal growth factor receptors in actively growing cells.

We have demonstrated a drug-dependent increase in the capacity of HeLa and 3T3 cells, grown in the presence of lethal and sublethal concentrations of adriamycin, to bind epidermal growth factor (EGF). Scatchard analysis ascribes this effect to an increase in the number of binding sites, with little change in affinity. The time course of binding of 125I-EGF is unchanged by adriamycin treatment, in both 3T3 and HeLa cells, at both 0 and 37 degrees C. This increase appears gradually over 3 or 4 days' exposure to the drug and is reversible over a similar period. Although in HeLa cells the increase reaches a maximum of about 4-fold, regardless of cell density, the maximum observed in 3T3 cells, over 100-fold, is seen only at low cell densities. This could be related to the density-dependent growth regulation seen in 3T3 cells, but not in HeLa cells. We suggest that the ability of the anticancer agent adriamycin to alter the cellular response to a growth-regulatory substance may be related to the mechanism of its cytotoxic action.

Animals↗
PubMed1983

Comparison of anthracycline concentrations in S180 cell lines of varying sensitivity.

Sublines of sarcoma 180 (S180) of varying sensitivity to adriamycin (ADR) have been selected in culture. The degree of resistance of these sublines ranged from 6- to 125-fold above that of parent S180 cells. ADR-resistant sublines demonstrated comparable degrees of cross-resistance to daunomycin (DNR), marcellomycin and AD 32, but each subline showed a uniform degree of tolerance toward actinomycin D and vincristine. Compared to the anthracycline-sensitive parent tumor, a 40% decrease in the intracellular steady-state level of [3H]-daunomycin was observed in all sublines regardless of the degree of resistance. The level of cell-associated DNR and ADR observed after administration of equipotent concentrations of drug was different for each cell line and increased in proportion to the drug concentration. Thus, altered drug permeability appeared to be of minimal importance in the expression of high levels of resistance. In addition, the extent of DNR metabolism by the anthracycline-resistant sublines was not sufficiently different from that seen in parent S180 cells to account for the observed tolerance to these agents.

Animals↗
PubMed1983

Effects of anthracyclines on oxygenated and hypoxic tumor cells.

The cytotoxic effects of anthracyclines and other chemotherapeutic agents were examined in normally aerated and hypoxic Sarcoma 180 and EMT6 tumor cells in vitro. Adriamycin, daunomycin, and mitomycin C were selectively toxic to hypoxic Sarcoma 180 cells. The augmented sensitivity was not the result of an increase in susceptibility of oxygen-deprived cells toward antitumor agents in general. 1,3-Bis(2-chloroethyl)-1-nitrosourea, for example, exhibited equal cytotoxicity toward normally aerated and hypoxic cells, while streptonigrin was selectively toxic toward normally aerated cells. The cellular levels of [3H]daunomycin in both Sarcoma 180 and EMT6 cells were not different under the two conditions of oxygenation, and no greater production of either the alcohol or aglycone metabolites of daunomycin occurred in hypoxic cells, compared with their normally aerated counterparts. In addition, analysis of cellular pellets for residual drug remaining after exhaustive extraction showed no significant difference between normally aerated and hypoxic cells. The effects of reoxygenation of hypoxic cells on their sensitivity to mitomycin C and to Adriamycin were studied in both Sarcoma 180 and EMT6 cells. The enhanced efficacy of mitomycin C as a cytotoxic agent observed under hypoxia was reversed after a 2-hr reoxygenation. In contrast, the augmented toxicity of Adriamycin toward hypoxic cells was not reversible in either cell line after 2 or 4 hr of reoxygenation. The results suggest that neither the formation of a reactive oxygen species nor direct involvement of an alkylating agent generated by drug metabolism is an obligatory step in the cytotoxic action of these anthracyclines.

Animals↗
PubMed1983

Immobilized adriamycin: a tool for separating cell surface from intracellular mechanisms.

Pharmacologic agents may exert their biological activity at the level of the cell membrane. Of particular interest is the anticancer agent adriamycin. This drug has previously been considered to act by intercalation with nuclear DNA, but recent evidence suggests the possibility that the cell surface membrane may represent an alternative target. To test this hypothesis, adriamycin was attached to insoluble supports, and conditions suggesting that the drug was actively cytotoxic without entering cells were demonstrated.

Animals↗
PubMed1983

Evidence for the lack of relationship between inhibition of nucleic acid synthesis and cytotoxicity of adriamycin.

The ability of adriamycin-sensitive and -resistant Sarcoma 180 cells to incorporate thymidine and uridine into macromolecular material following exposure to this antibiotic was directly compared to the degree of cell survival by measuring in the same population precursor incorporation and cloning efficiency in soft agar after different intensities of drug exposure. The concentration and time dependence of inhibition of these processes by adriamycin wer compared. No correlation between the ability to incorporate radioactive precursors into DNA and RNA and the extent of cell survival was observed except ay very toxic drug concentrations. The results indicate that the extent of inhibition of precursor incorporation into DNA and RNA following drug exposure is not predictive of cell survival. This finding implies that the effect of adriamycin on nucleic acid synthesis is not directly coupled to cytotoxicity.

Animals↗
PubMed1982

Inhibition of herpes simplex virus replication by methyl daunosamine.

Methyl daunosamine inhibited the replication of herpes simplex virus type 1 in a dose-dependent manner. The growth of the host Vero cells was not affected by daunosamine levels that had significant antiviral activity (2.5 mM) but was inhibited by concentrations of 5 mM or greater. Methyl daunosamine appears to be unique among the sugars with antiviral activity because at antiviral concentrations it did not inhibit the glycosylation of macromolecules.

Aminoglycosides↗
PubMed1982

Dissociation of the inhibitory effects of 2-deoxy-D-glucose on Vero cell growth and the replication of herpes simplex virus.

Vero cells treated for 24 h with a concentration of 2-deoxy-D-glucose (2dGlc) that inhibited the production of infectious herpes simplex virus type 1 grew at the same rate as untreated cells. Longer exposures to 2dGlc inhibited the growth of Vero cells in a dose-dependent manner, but without any loss of viability, and could be reversed by replating the cells in the absence of drug. To exhibit antiviral activity, 2dGlc had to be present during the replication cycle of herpes simplex virus type 1. Treatment of Vero cells, even with a cytotoxic dose of 2dGlc, was without effect on the yield of infectious virus, provided the drug was removed before infection. Thus the antiviral effects of 2dGlc were not the result of, and appeared to be independent of, persistent host cell toxicity.

Cell Division↗
PubMed1981

Adriamycin-induced changes in the surface membrane of sarcoma 180 ascites cells.

Adriamycin increases (a) the rate of agglutination of Sarcoma 180 cells by concanavalin A after brief exposure of 2-3 h and (b) membrane fluidity as measured by ESR within 30 min of exposure at concentrations of the anthracycline of 10(-7)-10(-5) M. The effect of adriamycin on agglutination is not due to an increase in the number of surface receptors for concanavalin A, since the extent of binding of the lectin is not altered by adriamycin and no change occurs in the rate of occupancy of the concanavalin A binding sites by the lectin in cells treated with the antibiotic. The order parameter, a measurement of membrane fluidity, decreases in cells exposed to adriamycin and is dose-related. The results indicate that adriamycin can induce changes in the surface membrane of Sarcoma 180 cells within a brief period of exposure to a low but cytotoxic level of this agent.

Agglutination↗