Stability of association of 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine with liposomes is composition dependent

The ether lipid, 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH₃), has anticancer activity, but it has serious side-effects, including hemolysis, which prevent its optimal use. We surmised if ET-18-OCH₃ could be stably associated with liposomes, less free ET-18-OCH₃ would be available for lytic interaction with red cells. Liposome composition variables investigated included acyl chain saturation, phospholipid head group and mole ratio of Chol and ET-18-OCH₃. It was found that attenuation of hemolysis was strongly liposome composition dependent. Some ET-18-OCH₃ liposome compositions were minimally hemolytic. For example, whereas the HI₅ (drug concentration required to cause 5% human red cell lysis) was 5–6 μM for free ET-18-OCH₃, it was approximately 250 μM for DOPC (dioleoylphosphatidylcholine):Chol (cholesterol):DOPE-GA (glutaric acid derivatized DOPE):ET-18-OCH₃, (4:3:1:2) and 640 μM for DOPE (dioleyolphosphatidylethanolamine):Chol:DOPE-GA:ET-18-OCH₃ (4:3:1:2) liposomes. Efflux of carboxyfluorescein (CF) from liposomes and Langmuir trough determinations of mean molecular area of lipids in monolayers (MMAM) were used as indicators of membrane packing and stability. Incorporation of ET-18-OCH₃ in liposomes reduced the MMAM. Reduction in CF permeation was correlated with reduction in hemolysis. The most stable liposomes included components, such as cholesterol, DOPC and DOPE, which have complementary shapes to ET-18-OCH₃.     

Alkyllysophospholipid ET-18-OCH3 acts as an activator of protein kinase C in HL-60 cells

HL-60 cells are very sensitive to the cytotoxic action of ether lipids. Several hypotheses have been proposed to explain this cytotoxicity. We investigated the influence of the alkylphospholipid ET-18-OCH₃ on the activity of protein kinase C. HL-60 cells were incubated with ET-18-OCH₃ at a concentration of 20 μg/ml for 4 h. After the incubation the membrane fraction of the HL-60 cells was isolated and the activity of protein kinase C was determined while it was still associated with the membrane, using the synthetic peptide substrate [Ser²⁵]-protein kinase C (19–31) as a protein kinase C specific substrate. The activity of the membrane-bound protein kinase C was increased in HL-60 cells treated with ET-18-OCH₃ compared to untreated HL-60 cells. The increase in protein kinase C activity was not a consequence of translocation and appeared to be additive to the effect of the phorbol ester 12-myristate 13-acetate. In contrast, solubilized protein kinase C from HL-60 cells could be inhibited or stimulated in vitro by ET-18-OCH₃, dependent on the mode of addition of ET-18-OCH₃ and phospholipids.     

Increased cell-surface receptor expression on U-937 cells induced by 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine

Association of the ether lipid, 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH₃) with liposomes (ELL-12) reduces acute toxicity while maintaining or enhancing anticancer activity in experimental tumor models. ELL-12 has been shown to induce apoptosis by a cytochrome-c-dependent caspase-mediated pathway, which results in proteolytic cleavage of poly(ADP-ribose) polymerase and lamins, but the antitumor effects of ET-18-OCH₃ or ELL-12 could result from tumor cell differentiation or activation. Here we compared the effects of ET-18-OCH₃ and ELL-12 on the expression of cell-surface proteins associated with cell differentiation and/or activation in U-937 cells. Phorbol 12-myristate 13-acetate and all-trans-retinoic acid, which induce differentiation in U-937 cells, up-regulated CD11b (MAC1 α-integrin) and CD82 and down-regulated CD71 (transferrin receptor) in a time- and dose-dependent manner. In contrast, ET-18-OCH₃ and ELL-12 up-regulated both CD71 and CD11b and did not have any effect on expression of CD82 in U-937 cells, suggesting that the ELL-12 may activate these cells rather than induce differentiation. Further evidence of activation was that ET-18-OCH₃ and ELL-12 strongly induced tumor necrosis factor α production by U-937 cells. Received: 25 February 1999 / Accepted: 4 August 1999     

INHIBITION OF CELL DIVISION BUT NOT NUCLEAR DIVISION BY 1- O -OCTADECYL-2- O -METHYL- Sn -GLYCERO-3-PHOSPHOCHOLINE

1- O -Octadecyl-2- O -methyl-glycero-3-phosphocholine (ET-18-OCH₃) selectively inhibits the growth of cancer cells. Here we show that in some cell types ET-18-OCH₃and liposome-associated ET-18-OCH₃inhibit cell division without concurrent inhibition of nuclear division, leading to multinucleate cell formation, and cell death through apoptosis. Cell cycle analysis revealed that ET-18-OCH₃-treated U-937 cells continued to move through the cell cycle, but many cells were not able to divide and instead accumulated as tetraploid cells or octaploid cells in the G0/G1 phase of the cell cycle. Inhibition of cytokinesis has been shown to be paralleled by activation of U-937 cells, including upregulation of some cell-surface markers, acquisition of phagocytic activity, and secretion of tumor necrosis factor (TNF)-α (Pushkareva et al., 2000). Furthermore, treatment of cells with ET-18-OCH₃results in the accumulation of apoptotic cells in time- and dose-dependent manner. It is possible that inhibition of cytokinesis may be related to cytoskeletal effects.     

Platelet-activating factor and its methoxy-analogue et-18-OCH3 stimulate immediate early gene expression in rat astroglial cultures

In the present paper we analyzed c-fos and zif/268 expression in rat primary astroglial cell cultures after treatment with Platelet-activating Factor (PAF) and its 2-O-methyl-analogue, 1-O-octadecyl-2-O-methoxy-glycero-3-phosphocholine (ET-18-OCH₃). Both compounds, at a dose (2 μM) that did not produce toxic effects on astroglial cells, induced a rapid and transient increase of c-fos and zif/268 mRNA level. Pretreatment of astroglial cells with the PAF antagonist BN50730 (5 μM) 10 min prior to the addition of alkyl-phospholipids almost completely prevented the activation of the immediate early genes. On the contrary triazolam, another PAF inhibitor, did not block PAF induced gene expression when added to the medium at 5 μM concentration. ET-18-OCH₃ effect on gene expression is blocked by the same antagonist (BN50730) which is effective in inhibiting PAF effect on astrocytes, suggesting that both substances act through the same binding site.Results obtained support the view that astroglial cells are a cellular target for this lipid mediator, and, like macrophages, respond to its methoxy-analogue.     

2-Benzoylpyridine-N(4)-tolyl thiosemicarbazones and their palladium(II) complexes: Cytotoxicity against leukemia cells

The palladium(II) complexes [Pd(2Bz4oT)Cl], [Pd(2Bz4mT)Cl], and [Pd(2Bz4pT)Cl] were prepared with N(4)-ortho- (H2Bz4oT) N(4)-meta- (H2Bz4mT) and N(4)-para- (H2Bz4pT) tolyl-thiosemicarbazones derived from 2-benzoylpyridine. The free thiosemicarbazones proved to be highly cytotoxic against Jurkat, HL60 and the resistant HL60.Bcl-X_L leukemia cell lines at nanomolar concentrations, but were much less cytotoxic to HepG2 human hepatoma cells. Upon coordination to palladium(II) the cytotoxic activity against all studied cell lines decreases. However, the high cytotoxicity of the free thiosemicarbazones against leukemia, together with their hepatotoxic profile similar to that of cisplatin suggest that N(4)-tolyl thiosemicarbazones have potential as chemotherapeutic drug candidates.     

NADPH oxidase is involved in H2O2-induced differentiation of human promyelocytic leukaemia HL-60 cells

The expression and activity of NADPH oxidase increase when HL‐60 cells are induced into terminally differentiated cells. However, the function of NADPH oxidase in differentiation is not well elucidated. With 150–500 μM H₂O₂ inducing differentiation of HL‐60 cells, we measured phagocytosis of latex beads and investigated cell electrophoresis. Two inhibitors of NADPH oxidase, DPI (diphenyleneiodonium) and APO (apocynin), blocked the differentiation potential of cells induced by 200 μM H₂O₂. However, H₂O₂ stimulated the generation of intracellular superoxide (O₂ ^{? ?}), which decreased in the presence of the two inhibitors. DPI also inhibited H₂O₂‐induced ERK (extracellular‐signal‐regulated kinase) activation, as detected by Western blotting. Furthermore, PD98059, the inhibitor of the ERK pathway, inhibited the differentiation of HL‐60 cells induced by H₂O₂. This shows that H₂O₂ can activate NADPH oxidase, leading to O₂ ^{? ?} production, followed by ERK activation and ultimately resulting in the differentiation of HL‐60 cells. The data indicate that NADPH oxidase is an important cell signal regulating cell differentiation.     

Cytotoxic sesquiterpenoids from Winteraceae of Caledonian rainforest

One secobutanolide, two butanolides and six drimane sesquiterpenoids were isolated from the bark and leaves of Zygogynum pancheri and Zygogynum acsmithii (Winteraceae) along with six known drimanes, isodrimanial, 1β-O-p-methoxy-E-cinnamoyl-bemadienolide, 7-ketoisodrimenin, drimenin, polygodial and 1β-E-cinnamoyl-6α-hydroxypolygodial. Their structures were elucidated through analysis of spectroscopic data. Drimane sesquiterpenoids with a dialdehyde function exhibited significant inhibitory activities in the in vitro cytotoxic assays against KB, HL60 and HCT116 cancer cell lines.     

Roles of superoxide and myeloperoxidase in ascorbate oxidation in stimulated neutrophils and H2O2-treated HL60 cells

Ascorbate is present at high concentrations in neutrophils and becomes oxidized when the cells are stimulated. We have investigated the mechanism of oxidation by studying cultured HL60 cells and isolated neutrophils. Addition of H₂O₂ to ascorbate-loaded HL60 cells resulted in substantial oxidation of intracellular ascorbate. Oxidation was myeloperoxidase-dependent, but not attributable to hypochlorous acid, and can be explained by myeloperoxidase (MPO) exhibiting direct ascorbate peroxidase activity. When neutrophils were stimulated with phorbol myristate acetate, about 40% of their intracellular ascorbate was oxidized over 20 min. Ascorbate loss required NADPH oxidase activity but in contrast to the HL60 cells did not involve myeloperoxidase. It did not occur when exogenous H₂O₂ was added, was not inhibited by myeloperoxidase inhibitors, and was the same for normal and myeloperoxidase-deficient cells. Neutrophil ascorbate loss was enhanced when endogenous superoxide dismutase was inhibited by cyanide or diethyldithiocarbamate and appears to be due to oxidation by superoxide. We propose that in HL60 cells, MPO-dependent ascorbate oxidation occurs because cellular ascorbate can access newly synthesized MPO before it becomes packaged in granules: a mechanism not possible in neutrophils. In neutrophils, we estimate that ascorbate is capable of competing with superoxide dismutase for a small fraction of the superoxide they generate and propose that the superoxide responsible is likely to come from previously identified sites of intracellular NADPH oxidase activity. We speculate that ascorbate might protect the neutrophil against intracellular effects of superoxide generated at these sites.     

A novel lysophosphatidylcholine acyl transferase activity is expressed by peroxiredoxin 6

The phospholipase A₂ (PLA₂) activity of peroxiredoxin (Prdx)6 has important physiological roles in the synthesis of lung surfactant and in the repair of peroxidized cell membranes. These functions require the activity of a lysophospholipid acyl transferase as a critical component of the phospholipid remodeling pathway. We now describe a lysophosphatidylcholine acyl transferase (LPCAT) activity for Prdx6 that showed a strong preference for lysophosphatidylcholine (LPC) as the head group and for palmitoyl CoA in the acylation reaction. The calculated kinetic constants for acylation were K_m 18 μM and V_max 30 nmol/min/mg protein; the V_max was increased 25-fold by phosphorylation of the protein while K_m was unchanged. Study of recombinant protein in vitro and in mouse pulmonary microvascular endothelial cells infected with a lentiviral vector construct indicated that amino acid D31 is crucial for LPCAT activity. A linear incorporation of labeled fatty acyl CoA into dipalmitoyl phosphatidylcholine (PC) indicated that LPC generated by Prdx6 PLA₂ activity remained bound to the enzyme for the reacylation reaction. Prdx6 is the first LPCAT enzyme with demonstrated cytoplasmic localization. Thus, Prdx6 is a complete enzyme comprising both PLA₂ and LPCAT activities for the remodeling pathway of PC synthesis or for repair of membrane lipid peroxidation.     

Evidence for NAD(P)H:quinone oxidoreductase 1 (NQO1)-mediated quinone-dependent redox cycling via plasma membrane electron transport: A sensitive cellular assay for NQO1

2,3-Dimethoxy 1,4-naphthoquinone (DMNQ), which redox cycles via two-electron reduction, mediates reduction of the cell-impermeative tetrazolium dye WST-1 in kidney epithelial cells (MDCK), which express high levels of NQO1, but not in HL60 or CHO cells, which are NQO1 deficient. DMNQ-dependent WST-1 reduction by MDCK cells was strongly inhibited by low concentrations of the NQO1 inhibitor dicoumarol and was also inhibited by diphenyleneiodonium, capsaicin, and superoxide dismutase (SOD), but not by the uncoupler FCCP or the complex IV inhibitor cyanide. This suggests that DMNQ-dependent WST-1 reduction by MDCK cells is catalyzed by NQO1 via redox cycling and plasma membrane electron transport (PMET). Interestingly, we observed an association between DMNQ/WST-1 reduction and extracellular H₂O₂ production as determined by Amplex red. Exposure of MDCK cells to DMNQ for 48 h caused cellular toxicity that was extensively reversed by co-incubation with dicoumarol or exogenous SOD, catalase, or N-acetylcysteine. No effects were observed in NQO1-deficient CHO and HL60 cells. In conclusion, we have developed a simple real-time cellular assay for NQO1 and show that PMET plays a significant role in DMNQ redox cycling via NQO1, leading to cellular toxicity in cells with high NQO1 levels.     

Differential Response of Chondrocytes and Chondrogenic-Induced Mesenchymal Stem Cells to C1-OH Tributanoylated N-Acetylhexosamines

Articular cartilage has a limited ability to self-repair because of its avascular nature and the low mitotic activity of the residing chondrocytes. There remains a significant need to develop therapeutic strategies to increase the regenerative capacity of cells that could repair cartilage. Multiple cell types, including chondrocytes and mesenchymal stem cells, have roles in articular cartilage regeneration. In this study, we evaluated a platform technology of multiple functionalized hexosamines, namely 3,4,6-O-tributanoylated-N-acetylgalactosamine (3,4,6-O-Bu₃GalNAc), 3,4,6-O-tributanoylated-N-acetylmannosamine (3,4,6-O-Bu₃ManNAc) and 3,4,6-O-Bu₃GlcNAc, with the potential ability to reduce NFκB activity. Exposure of IL-1β-stimulated chondrocytes to the hexosamine analogs resulted in increased expression of ECM molecules and a corresponding improvement in cartilage-specific ECM accumulation. The greatest ECM accumulation was observed with 3,4,6-O-Bu₃GalNAc. In contrast, mesenchymal stem cells (MSCs) exposed to 3,4,6-O-Bu₃GalNAc exhibited a dose dependent decrease in chondrogenic differentation as indicated by decreased ECM accumulation. These studies established the disease modification potential of a hexosamine analog platform on IL-1β-stimulated chondrocytes. We determined that the modified hexosamine with the greatest potential for disease modification is 3,4,6-O-Bu₃GalNAc. This effect was distinctly different with 3,4,6-O-Bu₃GalNAc exposure to chondrogenic-induced MSCs, where a decrease in ECM accumulation and differentiation was observed. Furthermore, these studies suggest that NFκB pathway plays a complex role cartilage repair.     

Cycloartane triterpenoids from the aerial parts of Cimicifuga foetida Linnaeus

Cycloartane triterpenoids, 2′,24-O-diacetylisodahurinol-3-O-α-l-arabinopyranoside, 24-O-acetylisodahurinol-3-O-α-l-arabinopyranoside, 12β-hydroxy-25-anhydrocimigenol, cimigenol-12-one, 12β-hydroxy-15-deoxycimigenol, 2′-O-acetyl-24-epi-cimigenol-3-O-α-l-arabinopyranoside, 2′-O-acetylcimigenol-3-O-β-d-xylopyranoside, 25-anhydrocimigenol-3-O-α-l-arabinopyranoside, 2′,23-O-diacetylshengmanol-3-O-α-l-arabinopyranoside, and 2′,24-O-diacetyl-25-anhydrohydroshengmanol-3-O-α-l-arabinopyranoside, together with eight known compounds, were isolated from aerial parts of Cimicifuga foetida. Their structures were determined by application of spectroscopic analyses and chemical methods. Biological evaluation of the compounds against human HL-60, SMMC-7721, A549, SK-BR-3, and PANC-1 cell lines indicated that three of these compounds exhibited broad-spectrum and moderate cytotoxic activities, with IC₅₀ values ranging from 6.20 to 22.74 μM. By comparing previous cytotoxic testing data and bioassay results from this study, preliminary structure–activity relationships of compounds with a cimigenol-skeleton can be proposed.     

Endothelins Inhibit Osmotic Swelling of Rat Retinal Glial and Bipolar Cells by Activation of Growth Factor Signaling

Water accumulation in retinal glial (Müller) and neuronal cells resulting in cellular swelling contributes to the development of retinal edema and neurodegeneration. Here, we show that endothelin-1 (ET-1) dose-dependently inhibits the hypoosmotic swelling of Müller cells in freshly isolated retinal slices of control and diabetic rats, with a maximal inhibition at 100 nM. Osmotic Müller cell swelling was also inhibited by ET-2. The effect of ET-1 was mediated by activation of ET_A and ET_B receptors resulting in transactivation of metabotropic glutamate receptors, purinergic P2Y₁, and adenosine A₁ receptors. ET-1 (but not ET-2) also inhibited the osmotic swelling of bipolar cells in retinal slices, but failed to inhibit the swelling of freshly isolated bipolar cells. The inhibitory effect of ET-1 on the bipolar cell swelling in retinal slices was abrogated by inhibitors of the FGF receptor kinase (PD173074) and of TGF-β1 superfamily activin receptor-like kinase receptors (SB431542), respectively. Both Müller and bipolar cells displayed immunoreactivities of ET_A and ET_B receptor proteins. The data may suggest that neuroprotective effects of ETs in the retina are in part mediated by prevention of the cytotoxic swelling of retinal glial and bipolar cells. ET-1 acts directly on Müller cells, while the inhibitory effect of ET-1 on bipolar cell swelling is indirectly mediated, via stimulation of the release of growth factors like bFGF and TGF-β1 from Müller cells.     

Cytotoxic and Apoptosis‐Inducing Activities of Steviol and Isosteviol Derivatives against Human Cancer Cell Lines

Seventeen steviol derivatives, i.e., 2 – 18 , and 19 isosteviol derivatives, i.e., 19 – 37 , were prepared from a diterpenoid glycoside, stevioside ( 1 ). Upon evaluation of the cytotoxic activities of these compounds against leukemia (HL60), lung (A549), stomach (AZ521), and breast (SK‐BR‐3) cancer cell lines, nine steviol derivatives, i.e., 5 – 9 and 11 – 14 , and five isosteviol derivatives, i.e., 28 – 32 , exhibited activities with single‐digit micromolar IC₅₀ values against one or more cell lines. All of these active compounds possess C(19)‐O‐acyl group, and among which, ent‐kaur‐16‐ene‐13,19‐diol 19‐O‐4′,4′,4′‐trifluorocrotonate ( 14 ) exhibited potent cytotoxicities against four cell lines with IC₅₀ values in the range of 1.2–4.1 μM . Compound 14 induced typical apoptotic cell death in HL60 cells upon evaluation of the apoptosis‐inducing activity by flow‐cytometric analysis. These results suggested that acylation of the 19‐OH group of kaurane‐ and beyerane‐type diterpenoids might be useful for enhancement of their cytotoxicities with apoptosis‐inducing activity.     

Hybrid molecules based on fullerene C60 and 5Z,9Z-dienoic acids: Synthesis and cytotoxic activity

The present research project details synthesis of new hybrid methanofullerenes based on acetylene and triazole esters of malonic acid containing 5Z,9Z-dienoic acids and fullerene C₆₀ under Bingel-Hirsch conditions, including study of the cytotoxic activity with respect to Jurkat, K562, U937 and HL60 tumor cell lines. Hybrid methanofullerenes containing acetylenic fragments, unlike triazole substituents, were found to exhibit higher cytotoxicity, but are characterized by lower selectivity of action in relation to healthy cells.     

A dimeric pyrrocidine from Neonectria ramulariae is an inhibitor of prolyl oligopeptidase

Four novel alkaloids, bispyrrocidine (5), the epoxy derivative of pyrrocidine B (6), 19-O-methyl-pyrrrocidine B (7) and 19-O-ethyl-pyrrrocidine B (8) were isolated from the endophytic fungus Neonectria ramulariae Wollenw KS-246. Their structures were elucidated using 1D- and 2D-NMR spectroscopy. Compound 6 exhibited cytotoxicity against HL60 cells (IC₅₀ 4.6 μM), whereas 5 showed specific inhibitory activity against prolyl oligopeptidase (IC₅₀ 2.6 μM) in a non-competitive manner.     

4-O-methylhonokiol inhibits colon tumor growth via p21-mediated suppression of NF-κB activity

Biphenolic components in the Magnolia family have shown several pharmacological activities such as antitumor effects. This study investigated the effects of 4-O-methylhonokiol (MH), a constituent of Magnolia officinalis, on human colon cancer cell growth and its action mechanism. 4-O-methylhonokiol (0–30 μM) decreased constitutive activated nuclear factor (NF)-κB DNA binding activity and inhibited growth of human colon (SW620 and HCT116) cancer cells. It also caused G₀–G₁ phase cell cycle arrest followed by an induction of apoptotic cell death. However, knockdown with small interfering RNA (siRNA) of p21 or transfection with cyclin D1/Cdk4 binding site-mutated p21 abrogated MH-induced cell growth inhibition, inhibition of NF-κB activity as well as expression of cyclin D1 and Cdk4. Conversely, inhibition of NF-κB with specific inhibitor or siRNA augmented MH-induced apoptotic cell death. 4-O-methylhonokiol inhibited tumor growth, NF-κB activity and expression of antiapoptotic proteins; however, it increased the expression of apoptotic proteins as well as p21 in xenograft nude mice bearing SW620 cancer cells. The present study reveals that MH causes p21-mediated human colon cancer cell growth inhibition through suppression of NF-κB and indicates that this compound by itself or in combination with other anticancer agents could be useful for the treatment of cancer.