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Biomedical subjects

G R Pettit

Publications and source records attributed to G R Pettit.

At least 109 records · Page 6Linked to original sources
PubMed1996

Isolation and structure of hemibastadinols 1-3 from the Papua New Guinea marine sponge Ianthella basta.

Further investigation of the Bismarck Archipelago (Papua New Guinea) marine sponge Ianthella basta for biologically active constituents has led to the isolation of hemibastadins 1 (2), 2 (3), and 3 (4) and the new brominated tyrosine derivatives hemibastadinols 1-3 (9, 13, and 14). Isolation and structure elucidation of the monomethyl ether derivatives (7 and 8) of hemibastadins 1 and 2 and the 3-bromotyramine amide of oxalic acid amide (1a) concluded our chemical investigation of I. basta. The hemibastadins and hemibastadinols represent important biosynthetic links to a series of bromotyrosine tetramers collectively known as the bastadins. The antimicrobial activity of the bastadins, hemibastadins, and hemibastadinols is summarized.

Animals↗
PubMed1996

Effect of dolastatin 10 on human non-Hodgkin's lymphoma cell lines.

It is crucial to incorporate new and more potent antineoplastic agents in treating non-Hodgkin's lymphoma since standard chemotherapy fails to cause a significant increase in the survival rate. A potential chemotherapeutic agent is dolastatin 10; hence, the objective of our study is to investigate the effect of the antiproliferative agent dolastatin 10 on different grades of non-Hodgkin's lymphoma cell lines. All cell lines exposed to dolastatin 10 initiated an apoptosis process. Alteration of oncogenes and their product may direct the entry of the cells into apoptosis, among these oncogenes are bcl-2 and c-myc. All cell lines tested expressed c-myc and bcl-2 proteins. However, 24 h after exposing the cell lines to 1 ng/ml dolastatin 10, bcl-2 expression was abolished but there was no significant change in c-myc protein expression. The contradictory roles of c-myc in cell proliferation and death require that other gene(s) products regiment the outcomes of c-myc activity on a cell. A possible candidate for such a modifying gene is bcl-2, whose product prolongs cell survival and blocks apoptosis. Given the above, dolastatin 10 induction of cell arrest is the initiating signal to downregulate the antiapoptotic bcl-2 and reactivate the apoptotic pathway. The reductions in bcl-2 may stabilize the c-myc proliferative action and induce apoptosis.

Antineoplastic Agents↗
PubMed1996

Dephosphorylation of activated protein kinase C contributes to downregulation by bryostatin.

We show that bryostatin 1 (Bryo) rapidly produces an inactive, incompetent 76-kDa form of protein kinase C-alpha (PKC-alpha) in the LLC-MK2 line of renal epithelial cells. Bryo, like phorbol 12-myristate 13-acetate (PMA), acutely activated PKC, as indicated by autophosphorylation and translocation of PKC-alpha, the predominant PMA-sensitive isoform expressed by the cells. Bryo concomitantly increased the 32P labeling of 80-kDa PKC-alpha by autophosphorylation and produced a 76-kDa form of PKC-alpha that lacked detectable 32P. The 76-kDa form was in the particulate rather than the cytosolic fraction, which suggests that it was produced from activated kinase. Alkaline phosphatase treatment of immunoprecipitated PKC-alpha converted the 80-kDa form to 76 kDa, but it had no effect on the mobility of the 76-kDa form, suggesting that it was not phosphorylated. Pulse-chase labeling of PKC-alpha with [35S]Met/Cys indicated that there is a precursor-product relationship between the 80- and 76-kDa forms, respectively. Inhibition of protein synthesis had no effect on the production of 76-kDa PKC-alpha by Bryo. PMA also produced 76-kDa PKC-alpha but was less potent and efficacious than Bryo. Bryo produced a more rapid loss of 80-kDa PKC-alpha protein and total Ca(2+)- and phospholipid-dependent PKC activity than PMA. The 76-kDa form is inactive and incompetent because it lacked detectable 32P under conditions that strongly autophosphorylated the 80-kDa form. We suggest that dephosphorylation predisposes PKC to proteolysis, and greater production of the 76-kDa form explains the more efficient downregulation of the kinase by Bryo vs. PMA.

Alkaline Phosphatase↗
PubMed1996

Bryostatin 1 induces ubiquitin COOH-terminal hydrolase in acute lymphoblastic leukemia cells.

It has been previously reported that Bryostatin 1 (Bryo1) induces differentiation of the human acute lymphoblastic leukemia (ALL) cell line, Reh, to a monocytoid B-cell stage. In this study we demonstrate that a novel protein, ubiquitin COOH-terminal hydrolase (UCH-L1), is associated with this differentiation. Reh cells were treated with 200 nmol/l of Bryo1 for 72 h and analyzed for changes in morphology, surface immunophenotype, acid phosphatase and terminal deoxynucleotidyl transferase. Protein patterns of the parent and differentiated cells, by two-dimensional polyacrylamide gel electrophoresis (2D PAGE), were studied. Bryo1-treated cells expressed morphologic, phenotypic and enzymatic features of the monocytoid B-cell stage. The UCH-L1 enzyme (MW-pl 34-5.3) was detected by 2 D PAGE in the differentiated, but not in parent cells. The presence of UCH-L1 in the Bryo1-treated cells was further confirmed by immunoblotting of 2 D PAGE using UCH-L1 polyclonal antibody. Ubiquitin expression was studied in parent and Bryo1-treated cells and was compared with 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated cells. Both agents, TPA and Bryo1, increased the level of ubiquitin expression as detected by flow cytometry. Sodium borohydride, an inhibitor of UCH-L1, inhibited the Bryo1-induced differentiating effect on Reh cells. To date, the mechanism by which Bryo1, exerts its B-cell differentiating effect is not fully understood. This study shows that UCH-L1 expression may play a major role in Bryo1-induced differentiation in pre-B-ALL.

Adolescent↗
PubMed1996

Antivascular approaches to solid tumour therapy: evaluation of tubulin binding agents.

We have assessed the vascular effects of vinblastine and four other tubulin binding agents (dolastatin 10, dolastatin 15, combretastatin A1 and combretastatin A4), which are awaiting clinical evaluation. All five agents induce a reduction in tumour blood flow as measured by uptake of RbCI 24 h post drug administration. The degree of reduction ranged from 50% with combretastatin A1 to 90% with dolastatin 10. These reductions were similar to that seen with flavone acetic acid (FAA) and indicate that antivascular effects are a common feature of tubulin binding agents. We subsequently evaluated whether the blood flow reductions, induced by FAA and vinblastine, could be used to enhance the activity of the bioreductive drug tirapazamine. Since the kinetics and extent of blood flow reductions induced by the agents is comparable, similar therapeutic response was expected. Potentiation was only evident with FAA, indicating that this effect is not directly related to killing of hypoxic tumour cells induced as a consequence of blood flow reduction.

Animals↗
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

The spongistatins, potently cytotoxic inhibitors of tubulin polymerization, bind in a distinct region of the vinca domain.

The highly cytotoxic, sponge-derived, antimitotic macrolide polyether spongistatin 1 has been previously shown to inhibit microtubule assembly, the binding of vinblastine and GTP to tubulin, and displacement of GDP bound in the exchangeable site of tubulin. We have now examined in detail inhibition by spongistatin 1 of both [3H]vinblastine and [3H]dolastatin 10 binding to tubulin. We found spongistatin 1 to be a noncompetitive inhibitor of the binding of both radiolabeled drugs to tubulin, in contrast to competitive patterns obtained with vincristine versus [3H]vinblastine and with a chiral isomer of dolastatin 10 versus [3H]dolastatin 10. Since dolastatin 10 is itself a noncompetitive inhibitor of vinca alkaloid binding to tubulin, this implies at least three distinct binding sites for the structurally complex and diverse natural products that interfere with each others binding to tubulin and with nucleotide exchange. Spongistatin 1, in contrast to both vinca alkaloids and peptide antimitotic agents like dolastatin 10, does not induce formation of a GTP-independent, morphologically distinctive polymer ("aggregate"). We also examined eight compounds closely related structurally to spongistatin 1 (spongistatins 2-9). The most distinctive in their properties were spongistatins 6 and 8. These two compounds, despite activity comparable to spongistatin 1 as inhibitors of tubulin polymerization and [3H]vinblastine binding, had much reduced activity as inhibitors of nucleotide exchange and [3H]dolastatin 10 binding. Spongistatins 1 and 6 were compared for effects on dolastatin 10-induced aggregate formation in conjunction with effects on [3H]dolastatin 10 binding. Spongistatin 6 was about 4-fold less active than spongistatin 1 as an inhibitor of aggregation and over 20-fold less active as an inhibitor of dolastatin 10 binding.

Animals↗
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

The antineoplastic bryostatins affect human basophils and mast cells differently.

Bryostatins, macrocyclic lactones from the marine bryozoan Bugula neritina, are potent antineoplastic agents and multi-potential stimulators of immune cells. We have examined the effects of bryostatins on mediator release from human basophilic leukocytes and human tissue mast cells. Bryostatins 1, 2, and 5 (10 to 3,000 nmol/L) induced histamine secretion from purified and unpurified peripheral blood basophils, whereas they caused no release of peptide-leukotriene C4 from these cells. The rate of histamine release caused by bryostatin 1 was slower than that caused by anti-IgE (t1/2 +/- SEM = 38.2 +/- 4.7 minutes v 8.9 +/- 0.2 minutes; P < .01), whereas the temperature dependence was similar (optimum release at 37 degrees C, approximately 30% less at 30 degrees C, and no release at 22 degrees C or 4 degrees C). The addition of increasing concentrations of extracellular Ca2+ to the medium caused histamine release in the presence of bryostatins. Subeffective concentrations of bryostatins and anti-IgE produced a synergistic effect on histamine release from basophils. Staurosporine, chelerythrine, and calphostin C (0.1 to 10 nmol/L), which are protein kinase C inhibitors, inhibited the histamine secretion activated by bryostatin 1 and tetradecanoylphorbol-acetate (TPA). Preincubation with granulocyte-monocyte colony-stimulating factor (GM-CSF; 1 and 5 nmol/L) and interleukin-3 (IL-3; 10 ng/mL) potentiated the activation of human basophils induced by bryostatin 1. Neither bryostatin 1 nor bryostatin 2 induced the release of histamine from mast cells isolated from human lung or skin tissues. However, brief (10 minutes) preincubation with bryostatin 1 (3 to 300 nmol/L) potently inhibited the histamine secretion induced by anti-IgE from skin or lung mast cells. Bryostatin 1 was a more potent (by approximately 30 times) inhibitor of IgE-mediated histamine release than was TPA. The heterogeneous effects exerted by bryostatins on human basophils and mast cells can be of interest for those designing therapeutic trials using these agents.

Antibodies, Anti-Idiotypic↗
PubMed1995

Bryostatin 1 induces apoptosis and augments inhibitory effects of vincristine in human diffuse large cell lymphoma.

Bryostatin 1 (Bryo1), a macrocyclic lactone and a protein kinase C activator, is isolated from the marine bryozoan Bugula neritina. In this study we describe its effect, alone or after sequential use with vincristine (VCR), on the human diffuse large cell lymphoma cell line WSU-DLCL2. Our results show that both Bryo1 and VCR induced apoptosis as demonstrated by morphological examination, DNA flow cytometry (FCM), and DNA fragmentation on agarose gel electrophoresis. Cells pretreated for 24 h with Bryo1 and then exposed to VCR showed an increase in apoptosis compared to cells that were exposed to Bryo1 or VCR alone. We also studied the effects of Bryo1, VCR and their combination on cell growth, bcl-2 and p53 expression, and inhibition of cell proliferation as measured by [3H]-thymidine incorporation. Cell analysis showed significant growth inhibition of WSU-DLCL2 cells by the Bryo1/VCR combination as compared to either agent alone. Immunocytochemistry (ICC) revealed that relative bcl-2 oncoprotein expression was decreased in cells treated with Bryo1, or VCR separately and was abolished by combining both drugs. When examined by ICC, WSU-DLCL2 cells were initially negative for the p53 protein. However, upon treatment with the above agents, the relative expression of p53 was moderate on Bryo1-or VCR-treated cells and strong on cells treated with the Bryo1/VCR combination. Cell proliferation as measured by [3H]-thymidine incorporation revealed significant inhibition of tumor growth by exposure to the agents when compared to the control. In contrast, Bryo1, VCR and their combination did not show any inhibition of normal bone marrow growth. These findings taken together, suggest that the exposure of WSU-DLCL2 cells to Bryo1 prior to treatment with VCR enhances apoptosis, a phenomenon which might be exploited for future therapies.

Antineoplastic Agents↗
PubMed1995

Antineoplastic agents, 294. Variations in the formation of pancratistatin and related isocarbostyrils in Hymenocallis littoralis.

By cloning Hymenocallis littoralis, a practical biosynthetic procedure was developed for producing pancratistatin [1]. The plant tissue culture-->greenhouse-->field production sequence was successively utilized for increasing an original 1.5 kg of wild H. littoralis bulbs to some 60,000 bulbs at present. In the central Arizona Sonoran Desert, the tropical H. littoralis was found to reach a maximum pancratistatin content in October and a minimum in May. Generally pancratistatin [1] was accompanied by lesser yields of narciclasine [2], 7-deoxynarciclasine [3], and 7-deoxy-trans-dihydronarcicasine [4]. Improved laboratory and pilot-plant scale techniques were also developed for the isolation of pancratistatin [1] from difficult-to-separate mixtures of narciclasine [2] and 7-deoxynarciclasine [3]occurring in H. littoralis.

Amaryllidaceae Alkaloids↗
PubMed1995

Antineoplastic agents, 326. The stereochemistry of bastadins 8, 10, and 12 from the Bismarck archipelago marine sponge Ianthella basta.

An investigation of cancer cell-growth inhibitory constituents of the Papua New Guinea marine sponge Ianthella basta led to isolation of the C-6 hydroxybastadins 8 [1] 10 [2], and 12 [3]. The absolute stereochemistry (6S) of each bastadin (or its tetramethyl ester derivative) was determined by means of the Mosher-Trost method. Bastadins 10 [2] and 12 [3] were found to significantly inhibit the growth of a selection of human cancer cell lines. Bastadins 8, 10, and 12 inhibited growth of the Gram-positive opportunists Staphylococcus aureus and Enterococcus faecalis.

Animals↗
PubMed1995

Antineoplastic agents, 301. An investigation of the Amaryllidaceae genus Hymenocallis.

Seven species (and one cultivated variety) of Hymenocallis (Amaryllidaceae) and the related Pancratium maritima, representing a broad geographical selection, were investigated as sources of pancratistatin [1] now undergoing preclinical development as an anticancer agent. Pancratistatin [1] was found to be a constituent of H. speciosa (Singapore), H. variegated (Singapore), H. pedalis (Seychelles), H. expansa (Bermuda), H. sonoranensis (Mexico), and P. maritimum (Israel). Only two species of Hymenocallis failed to yield one or more of the related cell-growth inhibitory isocarbostyrils such as narciclasine [3a], 7-deoxynarciclasine [3b], and 7-deoxy-trans-dihydronarciclasine [2].

Amaryllidaceae Alkaloids↗
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

An improved source of bryostatin 10, Bugula neritina from the Gulf of Aomori, Japan.

Bryostatins have been isolated from diverse Japanese coastal specimens of Bugula neritina guided by inhibitory activity against fertilized sea urchin egg cell division. B. neritina from the Gulf of Aomori, Japan, has been found to contain bryostatin 10 [1b] in high yield (10(-3)%) for this class of compounds. The 1H- and 13C-nmr signals of bryostatin 10 [1b] were reassigned by 2D nmr techniques. The conformation of bryostatin 10 [1b] in solution was revealed by nmr studies. This compound also exhibited activity in a steroidogenesis assay by increasing the production of adrenocortical hormones nearly twofold.

Animals↗
PubMed1995

The interaction with tubulin of a series of stilbenes based on combretastatin A-4.

A series of stilbenes, based on combretastatin A-4, were synthesised. A structure-activity study was carried out to characterise the interaction of these agents with tubulin. The substitution of small alkyl substituents for the 4'-methoxy group of combretastatin A-4 and the loss of the 3'-hydroxyl group does not have a major effect on the interaction with tubulin. trans-Stilbenes were shown to bind tubulin, but do not inhibit microtubule assembly. This work, together with previous studies, has been used to propose an idealised structure for a tubulin-binding agent of this type.

Animals↗
PubMed1995

The bcl-2 and p53 oncoproteins can be modulated by bryostatin 1 and dolastatins in human diffuse large cell lymphoma.

The effects of dolastatin 10 (Dol10) and dolastatin 15 (Dol15) alone, and after treatment with bryostatin 1 (Bryo1), on human diffuse large cell lymphoma cell line (WSU-DLCL2) were studied. At a concentration of 1.0 ng/ml Dol10 and Dol15 showed significant growth inhibition (p < 0.05). This inhibition was intensified when the cells were pretreated for 24 h with 200 nM Bryo1. Bryo1, Dol10 and Dol15 induced apoptosis which was seen on morphological examination, by flow cytometry and DNA fragmentation on agarose gel electrophoresis. Cells pretreated with Bryo1 and then exposed to Dol10 showed an increase in apoptosis compared with cells that were treated with the Dol10, Dol15 alone. Immunocytochemistry revealed that WSU-DLCL2 cells express the bcl-2 oncoprotein constitutively. bcl-2 expression was decreased when cells were treated with Bryo1, Dol10 or Dol15 and abolished with the Bryo1/Dol10 combination. WSU-DLCL2 cells were negative for p53 protein expression, upon treatment with Bryo1 or Dol10, the expression of p53 was weak and moderate with the Bryo1/Dol10 combination. The inverse correlation between bcl-2 and p53 oncoprotein expression seems to be related to induction of apoptosis in this lymphoma cell line.

Antineoplastic Agents↗