Biomedical subjects

M R Boyd

Publications and source records attributed to M R Boyd.

At least 127 records · Page 7Linked to original sources

PubMed1996

Role of membrane potential in the accumulation of quaternized ellipticines by human tumor cell lines.

9-Methoxy-N2-methylellipticinium acetate (MMEA) is representative of a series of quaternized ellipticines that exhibited selective cytotoxicity for human brain tumor cell lines of glial origin in the in vitro primary screen of the U.S. National Cancer Institute. The present investigation was initiated to determine whether membrane potential contributes to the cellular accumulation of this lipophilic cation by selected brain tumor and non-brain tumor cell lines. The results indicate that accumulation of MMEA by drug-sensitive cell lines, but not drug-resistant cell lines, is reduced by experimental conditions that depolarize the plasma membrane, e.g., stepped increases in the extracellular potassium concentration. These experimental conditions result in increased cellular fluorescence of cells stained with the voltage-sensitive anionic dye bis(1,3-dibutylbarbituric acid)trimethine oxonol, suggesting that decreased accumulation of MMEA is the result of decreased membrane potential. Membrane potential measurements using the null point method indicated that the mean membrane potential of selected MMEA-sensitive cell lines (-39.4 +/- 6.8 mV) was significantly lower (P < .005) than MMEA-resistant cell lines (-17 +/- 3.8 mV). Ultrastructural studies with the MMEA-sensitive U-251 glioblastoma indicated that the first morphological effects of MMEA occurred in mitochondria, where dissolution of cristae was observed, followed by engulfment of mitochondria in multilamellar phagocytic vesicles. Electron microscopic autoradiographic studies with tritium-labeled MMEA revealed that the drug was localized in mitochondria and nuclei.

Antineoplastic Agents↗

PubMed1996

Comparative antitumor activities of halichondrins and vinblastine against human tumor xenografts.

Halichondrin B and homohalichondrin B are novel tubulin-interacting agents isolated from marine sponges. The in vivo antitumor activities of these compounds were examined in human tumor models in immunodeficient mice and rats. In nude mice, regression or pronounced delay of subcutaneous tumor growth was obtained with both halichondrins, at a maximum tolerable dose of 20 micrograms/kg Q2Dx5, in three of four vinblastine-sensitive tumors, including two melanomas and one osteosarcoma; one small-cell lung cancer line was resistant. The halichondrins as well as vinblastine showed only marginal activity against KM20L colon carcinoma xenografts. In a LOX melanoma lung colony formation assay in groups of six nude mice, all control animals were sacrificed because of respiratory symptoms 38 days after cell injection, and likewise one vinblastine-treated mouse after 53 days. All halichondrin-treated mice in the lung colony assay appeared healthy throughout an observation period of 112 days (p = 0.002). Upon necropsy all vinblastine-treated animals, and two of six mice in the halichondrin group, had macroscopic lung tumor colonies. In a nude rat model for LOX bone marrow metastases, the mean lifespan of untreated control animals was 15 days. Whereas vinblastine had only a marginal effect (17 days) in this model, halichondrin B prolonged the lifespan of the animals to 32 days, representing a significant (p = 0.0016) difference between the two compounds. In conclusion, the halichondrins, which comprise a subtype of tubulin-interactive anti-mitotic agents, showed distinct antitumor activity profiles in human tumor models, thereby encouraging their further preclinical development and possible clinical evaluation.

Animals↗

PubMed1995

4-Ipomeanol and 2-aminoanthracene cytotoxicity in C3H/10T1/2 cells expressing rabbit cytochrome P450 4B1.

In the present study, retroviral vectors were used to stably transfer and express the cDNA encoding rabbit CYP4B1 in mouse C3H/10T1/2 cells. The replication defective retroviral vector was packaged in the ecotropic packaging cell line, GP+E-86, with infectious titer of approximately 1 x 10(6) cfu/mL. Infection, followed by selection with G418, showed an infection efficiency of approximately 70% for the recipient C3H/10T1/2 cells. Analysis of ten G418 resistant clones showed that the number of vector inserts ranged from 4 to 13 copies per cell genome. Each clone was positive for microsomal CYP4B1 protein as determined by immunoblotting. Cytochrome P450 4B1 activity was assessed by the cytotoxicity of 4-ipomeanol, a known substrate for P450 4B1 and a model compound for chemical-induced injury to the lung. The initial clonigenic assays showed that 100% toxicity occurred in all the clones after a 96-hr exposure to 250 microM 4-ipomeanol. Parental C3H/10T1/2 cells were resistant to 4-ipomeanol at concentrations as high as 1 mM. Two clones, designated No. 2 and No. 19, differing in levels of P450 4B1 protein, were characterized further for 4-ipomeanol and other chemical toxicities. A concentration-response study indicated 50% cytotoxicity at 4-ipomeanol concentrations of 1.5 micrograms/mL for clone No. 2 and 2.5 micrograms/mL for clone No. 19. A panel of agents representing the aromatic amines, some of which are known or suspected P450 4B1 substrates, were tested for cytotoxicity in clone No. 2. These agents included 2-aminoanthracene, 2-aminonaphthalene, 2-aminofluorene, 2-acetylaminofluorene and 4-aminobiphenyl. Only 2-aminoanthracene gave a clear cytotoxic response reducing the survival fraction of clone No. 2 to 50% at 0.2 micrograms/mL while affecting parental cells minimally. In vitro expression of CYP4B1 provides a new experimental system for further elucidating the cytotoxic and mutagenic effects of P450 4B1 substrates.

Amines↗

PubMed1995

Brain mitochondrial cytochromes P450: xenobiotic metabolism, presence of multiple forms and their selective inducibility.

The capability of rat brain mitochondria to metabolize a variety of xenobiotics was examined. The presence of cytochrome P450 (P450) and associated monooxygenase activities were estimated in isolated rat brain mitochondria and compared with the corresponding activities in microsomes. Total P450 content in brain mitochondria from naive rats was twice that of the corresponding microsomal level. The ability of brain mitochondria to metabolize the potent carcinogen N-nitrosodimethylamine was more than twofold that of the corresponding microsomal activity, while the 7-ethoxycoumarin-O-deethylase activity was significantly lower in mitochondria. Immunoblot experiments using antisera to purified rat liver microsomal P450s, namely P450 (2B1/2B2), P4501A1, and P4502E1, and purified phenobarbital-inducible rat brain P450, revealed the presence of immunoreactive bands in isolated brain mitochondria. These various antibodies to P450 inhibited the brain mitochondrial monooxygenase activities to significant, though varying extent. The addition of antiserum to microsomal NADPH cytochrome P450 reductase did not affect the mitochondrial P450 associated monooxygenase activities, although it completely inhibited the corresponding microsomal activities. Chronic ethanol administration resulted in twofold induction of total P450 content and the monooxygenase activities known to be mediated by P4502E1, such as N-nitrosodimethylamine-N-demethylase and p-nitrophenol hydroxylase in brain mitochondria. Pretreatment of animals with phenobarbital resulted in the induction of aminopyrine N-demethylase activity in brain mitochondria. The study demonstrates the presence of multiple forms of P450 in the rat brain mitochondria, their inducibility, and their capability to metabolize xenobiotics.

7-Alkoxycoumarin O-Dealkylase↗

PubMed1995

Antineoplastic agents. 291. Isolation and synthesis of combretastatins A-4, A-5, and A-6(1a)

The antineoplastic constituents of Combretum caffrum (Eckl. and Zeyh) Kuntze (Combretaceae family), a species indigenous to South Africa, have been investigated. Subsequently we isolated a series of closely related bibenzyls, stilbenes, and phenanthrenes from C. caffrum. Some of the stilbenes proved to be potent antimitotic agents which inhibited both tubulin polymerization and the binding of colchicine to tubulin. Combretastatin A-4 has been shown to be the most potent cancer cell growth inhibitor of the series. Presently this cis-stilbene is the most effective inhibitor of colchicine binding to tubulin and the simplest natural product yet described with such potent antitubulin effects. Combretastatin A-4, A-5, and A-6 were also found to inhibit growth of Neisseria gonorrhoeae. Details of the isolation and syntheses of combretastatins A-4 (2a), A-5 (2c), and A-6 (3a) have been described.

Anti-Bacterial Agents↗

PubMed1995

Flavin-containing monooxygenase mediated metabolism of psychoactive drugs by human brain microsomes.

Flavin-containing monooxygenases (FMO) catalyze the oxidation of certain xenobiotics and drugs which contain a nucleophilic heteroatom. Here we report the first assessment of human brain flavin-containing monooxygenase from tissues obtained at autopsy from seven traffic accident victims. Human brain microsomes catalyzed the S-oxidation or N-oxidation of model substrates methimazole and N,N-dimethylaniline, respectively. The psychoactive drugs chlorpromazine, imipramine and fluoxetine, were also metabolized by human brain FMO. 'Western' immunoblot analyses revealed immunological cross-reactivity of the human brain FMO with rabbit pulmonary FMO. Immunocytochemistry further revealed the localization of the FMO predominantly in the neuronal cell bodies in the magnocellular reticular nuclei, colliculi and substantia nigra. Human brain clearly contains an active FMO system, and it is conceivable that such enzyme(s) are significantly involved in the local metabolism and modulation of pharmacological effects of psychoactive drugs.

Adult↗

PubMed1995

Uptake and cytotoxicity of 9-methoxy-N2-methylellipticinium acetate in human brain and non-brain tumor cell lines.

9-Methoxy-N2-methylellipticinium acetate (MMEA) was preferentially cytotoxic to human brain tumor cell lines in the in vitro primary screen of the U.S. National Cancer Institute. In the present study, the average intracellular accumulation of radioactivity derived from [14C]MMEA concentrations that were selectively cytotoxic to sensitive brain tumor cell lines was nearly 4-fold greater than in human tumor cell lines derived from the lung, kidney, ovary and colon. The extent of peak cellular accumulation of [14C]MMEA-derived radioactivity, achieved after 10-15 hr of drug exposure, was correlated positively with relative MMEA cytotoxicity in brain tumor cell lines (r2 = 0.963). A similar correlation (r2 = 0.967) was observed in selected non-brain tumor cell lines but required substantially higher (18-fold) concentrations of MMEA. [14C]MMEA radioactivity accumulation by a selected glioblastoma cell line occurred via an energy-requiring system that was predominantly sodium and pH independent.

Antineoplastic Agents↗

PubMed1995

Comparative anti-HIV evaluation of diverse HIV-1-specific reverse transcriptase inhibitor-resistant virus isolates demonstrates the existence of distinct phenotypic subgroups.

We have biologically and biochemically evaluated a structurally diverse group of HIV-1-specific reverse transcriptase (RT) inhibitors and determined that the members of this class share many common properties. These include reproducible and selective antiviral activity against a panel of biologically distinct laboratory and clinical strains of HIV-1, activity against HIV-1 in a wide variety of cultured and fresh human cells, and potent inhibition of HIV-1 RT when evaluated using a heteropolymeric ribosomal RNA template assay. Each of the HIV-1-specific compounds was capable of inhibiting HIV replication when challenged at high m.o.i., further distinguishing them from the nucleoside analogs 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxycytidine (ddC). When tested in combination with AZT, each of the HIV-1-specific compounds synergistically inhibited the replication of HIV-1. HIV-1 isolates resistant to different HIV-1-specific inhibitors exhibited heterogeneous patterns of cross-resistance to other members of this pharmacologic class. Four distinct phenotypic classes have been defined through the use of drug-resistant virus isolates which derive from distinct mutations in the RT. These results indicate that the various subgroups of HIV-1-specific inhibitors interact differently with HIV-1 RT, suggesting important potential implications for drug combination therapeutic strategies.

Antiviral Agents↗

PubMed1995

Cytochrome P450 and associated monooxygenase activities in the rat and human spinal cord: induction, immunological characterization and immunocytochemical localization.

We have discovered cytochrome P450 and associated monooxygenase activities in microsomes prepared from spinal cord tissues from rats and a human. Cytochrome P450 levels and nicotinamide adenine dinucleotide phosphate cytochrome c reductase activities in microsomes from rat spinal cord were similar to those observed from the whole brain. However, certain monooxygenase activities were significantly lower in the rat spinal cord microsomes as compared to the corresponding activities observed in the whole brain. Cytochrome P450-mediated monooxygenase activities were also detectable in microsomes prepared from human spinal cord. Immunoblot analyses of rat and human spinal cord microsomes using antisera to various forms of hepatic cytochrome P450 namely (2B1 + 2B2), 1A1, 1A2 and 2E1 revealed the presence of immunologically similar forms. The spinal cord microsomes also cross-reacted with the antiserum to the phenobarbital-inducible form of rat brain cytochrome P450. Immunocytochemical stain was predominant in the gray horns of the rat spinal cord. At the cervical level, lamina 1 and 2 representing the substantia gelatinosa were intensely stained. In the ventral horns, lamina 7, 8 and 9 containing the large motor neurons were strongly labelled, while small neurons revealed variable staining. In the white matter, the glial cells were stained but the axons remained non-reactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Patellamide F, A new cytotoxic cyclic peptide from the colonial ascidian Lissoclinum patella.

Cytotoxicity-directed fractionation of an organic extract of the tunicate Lissoclinum patella afforded a new cyclic octapeptide, patellamide F [1]. The structure and absolute stereochemistry of 1 were established by a combination of spectroscopic and chemical methods. Three known cyclic peptides, patellamide B [2], ulithiacyclamide, and lissoclinamide 3, were also isolated and identified.

Animals↗

PubMed1995

A novel phorbol ester from Excoecaria agallocha.

The novel phorbol ester 12-deoxyphorbol 13-(3E,5E-decadienoate) [1] was isolated as the anti-HIV principle of Excoecaria agallocha leaves and stems collected in northwest Australia. The structure was determined by spectral means. Compound 1 was also a potent displacer of [3H]-phorbol dibutyrate from rat brain membranes.

Animals↗

PubMed1995

The pseudocalanolides: structure revision of calanolides C and D.

Nmr spectra of synthetic structures corresponding to those initially reported for natural compounds calanolide C [1] and calanolide D [2] showed some subtle differences from those of the natural products. Further analysis has resulted in revision of the structures of the natural compounds, now renamed pseudocalanolides C [3] and D [4]. The absolute stereochemistry of pseudocalanolide C was established as [6S, 7S, 8R] using the modified Mosher's method.

Coumarins↗

PubMed1995

Antineoplastic agents, 325. Isolation and structure of the human cancer cell growth inhibitory cyclic octapeptides phakellistatin 10 and 11 from Phakellia sp.

The two new marine sponge (Phakellia sp., western Pacific Ocean) constituents, phakellistatin 10 [1] and 11 [2], were found to be cyclic octapeptides that significantly inhibited growth of the murine P-388 lymphocytic leukemia (ED50 values of 2.1 and 0.20 micrograms/ml, respectively) and human cancer cell lines. The structures were established based on results of extensive tandem ms/ms and high-field (500-MHz) 2D 1H- and 13C-nmr analyses. All of the amino acid units (except Trp, not determined) were found to correspond to the (S)-configuration.

Amino Acid Sequence↗

PubMed1995

A reinvestigation of Maprounea triterpenes.

Anti-HIV activity and the inhibition of phorbol ester receptor binding activity in two species of Maprounea were traced to small amounts of highly potent phorbol esters of the daphnane type. The triterpenes previously isolated from this genus were found to be devoid of biological activity when scrupulously purified. Four new triterpene esters were elucidated; two [3,4] were found in M. africana, while three [4,6,7] were found in M. membranacea. Nmr assignments have also been made for two previously known compounds [2,5] in this group.

Acetylation↗

PubMed1995

Mycalolides D and E, new cytotoxic macrolides from a collection of the stony coral Tubastrea faulkneri.

Fractionation of a cytotoxic extract of the stony coral Tubastrea faulkneri yielded a series of cytotoxic polyoxazole macrolides and several noncytotoxic indole derivatives. Two new macrolides, mycalolides D [1] and E [2], were isolated and identified, in addition to the known compound mycalolide C [3]. The macrolide structures were elucidated by detailed analysis of their spectroscopic data and by comparison with related compounds.

Animals↗

PubMed1995

Antitumor activity and stereochemistry of acetylenic alcohols from the sponge Cribrochalina vasculum.

Antitumor bioassay-guided fractionation of the organic extract of the marine sponge Cribrochalina vasculum resulted in the isolation of several closely related cytotoxic acetylenic alcohols [1-8], the structures of which were assigned on the basis of chemical and spectral studies. 3-Hydroxyeicos-(4E)-en-1-yne[1], 3-hydroxydocosa-(4E,15Z)-dien-1-yne[2], 3-hydroxy-16-methyleicos-(4E)-en-1-yne[3], 3-hydroxy-19-methyleicos-(4E)-en-1-yne[4], 3-hydroxy-21-methyldocosa-(4E,15Z)-dien-1-yne [5], and 3-hydroxy-14-methyldocosa-(4E)-en-1-yne [6] are enantiomers of known compounds, while 3-hydroxyheneeicos-(4E)-en-1-yne [7] and 5-hydroxy-16-methyleicos-(3Z)-en-1-yne [8] are new metabolites isolated as minor components. The absolute configuration of C-3 in 1-7 and C-5 in 8 has been assigned as S using the modified Mosher's method. Compounds selected from this series showed selective in vitro antitumor activity against the H-522 non-small cell lung line and the IGROV-1 ovarian line. Synthetic racemic 1 demonstrated a modest dose-related therapeutic activity in a preliminary in vivo xenograft assay based on the latter cell line.

Alkynes↗

PubMed1995

Majapolene A, a cytotoxic peroxide, and related sesquiterpenes from the red alga Laurencia majuscula.

Seven new sesquiterpenes, majapolenes A [1] and B [2], majapolone [3], and majapols A [4], B [5], C [6], and D [7], were isolated from a Philippine collection of Laurencia majuscula. With the exception of majapolene B [2], all compounds were isolated as inseparable diastereomeric mixtures. Structure elucidation was achieved by spectroscopic methods. Majapolene A [1], a dioxabicyclo[2.2.2]-alkene, displayed modest activity in the NCI 60-cell line cytotoxicity screen. Majapolene A was also found as a major component of a Philippine collection of Laurencia caraibica.

Antineoplastic Agents↗

PubMed1995

Michellamine B, a novel plant alkaloid, inhibits human immunodeficiency virus-induced cell killing by at least two distinct mechanisms.

Studies of the mechanism of action of michellamine B, a novel anti-human immunodeficiency virus (HIV) alkaloid from the tropical plant Ancistrocladus korupensis, have revealed that the compound acts at two distinct stages of the HIV life cycle. The compound had no direct effect on HIV virions and did not block the initial binding of HIV to target cells. Postinfection time course studies revealed that the agent partially inhibited HIV-induced cell killing and syncytium formation when added up to 48 h following acute infection; however, viral reproduction was fully inhibited only when the compound was added immediately after infection. Time-limited treatments of HIV-infected cells revealed that michellamine B had to be present continuously to provide maximum antiviral protection. HIV replication in cells in which infection was already fully established or in chronically infected cells was unaffected by michellamine B. Biochemical studies showed that michellamine B inhibited the enzymatic activities of reverse transcriptases (RTs) from both HIV type 1 and HIV type 2 as well as two different nonnucleoside drug-resistant RTs with specific amino acid substitutions. In addition, human DNA polymerases alpha and beta were inhibited by the alkaloid. Michellamine B exerted a potent dose-dependent inhibition of cell fusion in two independent cell-based fusion assays. Thus, michellamine B acts both at an early stage of the HIV life cycle by inhibiting RT as well as at later stages by inhibiting cellular fusion and syncytium formation.

Antiviral Agents↗