Comparing beta-carotene, vitamin E and nitric oxide as membrane antioxidants

Singlet oxygen initiates lipid peroxidation via a nonfree radical mechanism by reacting directly with unsaturated lipids to form lipid hydroperoxides (LOOHs). These LOOHs can initiate free radical chain reactions leading to membrane leakage and cell death. Here we compare the ability and mechanism by which three small-molecule membrane antioxidants (beta-carotene, alpha-tocopherol and nitric oxide) inhibit lipid peroxidation in membranes. We demonstrate that beta-carotene provides protection against singlet oxygen-mediated lipid peroxidation, but does not slow free radical-mediated lipid peroxidation. Alpha-Tocopherol does not protect cells from singlet oxygen, but does inhibit free radical formation in cell membranes. Nitric oxide provides no direct protection against singlet oxygen exposure, but is an exceptional chain-breaking antioxidant as evident from its ability to blunt oxygen consumption during free radical-mediated lipid peroxidation. These three small-molecule antioxidants appear to have complementary mechanisms for the protection of cell membranes from detrimental oxidations.

Potent apoptotic effects of saponins from Liliaceae plants in L1210 cells

We isolated eight saponins, a hexacyclic lanosterol tetraglycoside (1), a 27-norlanosterol tetraglycoside (2) and six spirostanol oligoglycosides (3-8), from the plants of the family Liliaceae. In murine leukaemic L1210 cells, saponins 5 and 7 at a concentration of 1 microM showed potent cytotoxic activity and the activities were in the following decreasing order: 5, 7, 1, 3, 2, 8, 4, 6. At a concentration of 10 microM, not only 5 and 7 but also 3 and 8 markedly caused cell death. The flow cytometric analysis indicated that 7 and 8 caused a concentration- and time-dependent apoptosis of L1210 cells (EC50 value = approximately 5 microM). The morphological observation using a light microscope revealed that both 7 and 8 induced shrinkage in cell soma and chromatin condensation, suggesting apoptotic cell death. Moreover, in agarose gel electrophoretic analysis, a typical apoptotic DNA ladder pattern was observed after treatment with both 7 and 8. These results suggest that 7 and 8 caused the death of L1210 cells through the apoptotic process. These compounds may become powerful pharmacological tools for studying the molecular mechanism of apoptosis.

Synthesis, biological evaluation, and quantitative structure-activity relationship analysis of new Schiff bases of hydroxysemicarbazide as potential antitumor agents

Thirty Schiff bases of hydroxysemicarbazide (Ar-CH=NNHCONHOH) have been synthesized and tested against L1210 murine leukemia cells. The IC(50) values were found to be in a range from 2.7 x 10(-6) to 9.4 x 10(-4) M. A total of 17 out of the 30 compounds had higher inhibitory activities than hydroxyurea (an anticancer drug currently used for the treatment of melanoma, leukemia, and ovarian cancer) against L1210 cells. Six compounds with IC(50) values in micromolar range were 11- to 30-fold more potent than hydroxyurea (IC(50) = 8.2 x 10(-5) M). The partition coefficient (log P) and ionization constants (pK(a)) of a model compound [1-(3-trifluoromethylbenzylidene)-4-hydroxysemicarbazide, 1] were measured by the shake-flask method, and the measured log P was used to derive Hansch-Fujita pi constant of -CH=NNHCONHOH. On the basis of the newly derived pi and those of other moieties, the partition coefficients (SlogP) of the other 29 compounds were calculated by the summation of pi values. Quantitative structure-activity relationship (QSAR) analysis showed that, besides the essential pharmacophore (-NHCONHOH), hydrophobicity (SlogP), molecular size/polarizability (calculated molar refractivity), and the presence of an oxygen-containing group at the ortho position (I) were important determinants for the antitumor activities. In conclusion, the results obtained in this study show that several Schiff bases of hydroxysemicarbazide are potent inhibitors of tumor cells and warrant further investigation as cancer chemotherapeutic agents.

Symplostatin 3, a new dolastatin 10 analogue from the marine cyanobacterium Symploca sp. VP452

Symplostatin 3 (1), a new analogue of dolastatin 10 (2), has been isolated from a tumor selective extract of a Hawaiian variety of the marine cyanobacterium Symploca sp. VP452. Compound 1 differs from 2 only in the C-terminal unit; the dolaphenine unit is substituted by a 3-phenyllactic acid residue. Symplostatin 3 (1) possesses IC(50) values for in vitro cytotoxicity toward human tumor cell lines ranging from 3.9 to 10.3 nM. It disrupts microtubules, but at a higher concentration than 2, correlating with the weaker in vitro cytotoxicity.

Synthesis, characterization and antitumor activity of quinolone-platinum(II) conjugates

A new series of quinolone-platinum(II) conjugates, [Pt(Q'-NH2)(dmso)X2] and cis-[Pt(Q"-en)X2], where Q' and Q" are quinolones (flumequine, nalidixic acid or oxolinic acid) linked to monodentate and bidentate amine ligands, respectively, and X2 is Cl2 or 1,1-cyclobutanedicarboxylate, have been synthesized with the aim of examining the synergetic antitumor activity of quinolone intercalation and platinum(II) chelation. The complexes were characterized by elemental analyses and IR and multinuclear (1H and 195Pt) NMR spectroscopies, and then subjected to in vitro and in vivo bioassays using the leukemia L1210 cell line.

Four new bioactive pyrrole-derived alkaloids from the marine sponge Axinella brevistyla

Four new alkaloids (1-4) were isolated from the marine sponge Axinella brevistyla, and their structures were determined on the basis of spectroscopic analysis. The alkaloids 1-4 were antifungal against the yeast Saccharomyces cerevisiae at <1.0, <1.0, 30, and 100 microg/disk, respectively. Compounds 1-3 also exhibited cytotoxicity against L1210 cells with IC(50) values of 1.1, 0.66, and 2.5 microg/mL, respectively.

Synthesis of halogen-substituted 3-deazaadenosine and 3-deazaguanosine analogues as potential antitumor/antiviral agents

Various 2-halogen-substituted analogues (38, 39, 43 and 44), 3-halogen-substituted analogues (51 and 52), and 2',3'-dihalogen-substituted analogues (57-60) of 3-deazaadenosine and 3-halogen-substituted analogues (61 and 62) of 3-deazaguanosine have been synthesized as potential anticancer and/or antiviral agents. Among these compounds, 3-deaza-3-bromoguanosine (62) showed significant cytotoxicity against L1210, P388, CCRF-CEM and B16F10 cell lines in vitro, producing IC50 values of 3, 7, 9 and 7 microM, respectively. Several 3-deazaadenosine analogues (38, 51, 57 and 59) showed moderate to weak activity against hepatitis B virus.

Reversal effect of specific inhibitors of extracellular-signal regulated protein kinase pathway on P-glycoprotein mediated vincristine resistance of L1210 cells

Effect of specific inhibitors of extracellular-signal regulated protein kinase (ERK) pathway, PD98059 and U0126, on P-glycoprotein (Pgp)-mediated vincristine resistance of L1210/VCR cells was investigated. Both test inhibitors significantly reduced the survival of L1210/VCR cells in the presence of vincristine and this was associated with a decrease of LC50 values to vincristine from 2.65+/-0.43 to 0.67+/-0.28 micromol/l and to 0.69+/-0.09 micromol/l after treatment with 50 micromol/l PD98059 and 25 micromol/l UO126, respectively. Moreover, the effects of PD98059 are connected also with an increased intracellular accumulation of radiolabeled vincristine in resistant L1210/VCR cells in concentration dependent manner. The results of this study demonstrate that inhibitors of ERK signaling pathway are reversal agents of vincristine resistance in L1210/VCR cells. The precise mechanism of PD98059 and U0126 action in modulation of MDR is not resolved yet, but the role of ERK-mediated phosphorylation cascade could be considered.

Novel approaches to polynuclear platinum pro-drugs. Selective release of cytotoxic platinum-spermidine species through hydrolytic cleavage of carbamates

BBR3464 is a novel trinuclear platinum drug currently in Phase II clinical trials. Polyamine-bridged dinuclear platinum compounds as represented by [[trans-Pt(NH(3))(2)Cl](2)-mu-spermidine-N(1),N(8)]Cl(3) (1) are highly interesting second-generation analogues of BBR3464 because the hydrogen-bonding and electrostatic contributions of the central platinum-amine group in BBR3464 are replicated by the free, noncoordinated "central" quaternary nitrogens of the linear polyamine linker while the presence of two separate Pt-Cl bonds maintains the bifunctional binding mode on the DNA adducts. Preclinical investigations confirm the potency of these species with cytotoxicity in the nanomolar range. This remarkable potency results in a relatively narrow therapeutic index. To enhance the therapeutic index of these drugs, we investigated the potential for "pro-drug" delivery of less toxic and better tolerated derivatives such as the compounds [[trans-Pt(NH(3))(2)Cl](2)-mu-N(4)-R-spermidine-N(1),N(8)]Cl(2) where N(4)-R represents BOC (tert-butyl), CBz (benzyl), and Fmoc (fluorenylmethyl) carbamate blocking groups, 2-4, respectively. The bulky Fmoc derivative showed evidence for conformational isomers by (1)H NMR spectroscopy due to the inequivalence of the two n-propyl and n-butyl side chains of the spermidine moiety. The rate constants for hydrolysis and release of 1 were calculated. Release of cytotoxic 1 at physiologically relevant pH followed the order 4 > 2 > 3. The calculated values for 4 (pH 5, 6.0(+/-3.9) x 10(-10) s(-1); pH 6, 6.5(+/-0.2) x 10(-9) s(-1); pH 7, 6.0(+/-0.2) x 10(-8) s(-1); pH 8, 1.6(+/-0.1) x 10(-7) s(-1)) show a more pronounced pH dependence compared to 2 (pH 5, 4.6(+/-0.1) x 10(-8) s(-1); pH 6, 4.2(+/-0.1) x 10(-8) s(-1); pH 7, 3.2(+/-0.1) x 10(-8) s(-1)). Preliminary biological assays of cellular uptake and cytotoxicity confirm the utility of the pro-drug concept. While blocked-polyamine compounds such as 2-4 are, in general, 2-3 orders of magnitude less cytotoxic than 1, there is significant cell type variability. Specifically, the Fmoc derivative 4 showed significantly enhanced cytotoxicity warranting further study of the pro-drug concept for greater selectivity and/or oral delivery.

Two steroidal saponins from Camassia cusickii induce L1210 cell death through the apoptotic mechanism

Two steroidal saponins, tigogenin hexasaccharide-1 (TGHS-1, (25R)-5alpha-spirostan-3beta-yl 4-O-[2-0-[3-O-(alpha-L-rhamnopyranosyl)-beta-D-glucopyranosyl]-3-0-[4-0- (alpha-L-rhamnopyranosyl)-beta-D-glucopyranosyl]-beta-D-glucopyranosyl]-3-D- galactopyranoside) and tigogenin hexasaccharide-2 (TGHS-2, (25R)-5alpha-spirostan-3beta-yl 4-O-[2-0-[3-0-(beta-D-glucopyranosyl)-beta-D-glucopyranosyl]-3-0-[4-0- (alpha-L-rhamnopyranosyl)-beta-D-glucopyranosyl]-beta-D-glucopyranosyl]beta-D-galactopyranoside), were isolated from the fresh bulbs of Camassia cusickii. In murine leukemic L1210 cells, both compounds showed cytotoxicity with an EC50 value of 0.06 microM. The morphological observation revealed that TGHS-1 and TGHS-2 induced shrinkage in cell soma and chromatin condensation, suggesting apoptotic cell death. The cell death was confirmed to be apoptosis by Annexin V binding to phosphatidylserine in the cell membrane and excluding propidium iodide. A typical apoptotic DNA ladder and the cleavage of caspase-3 were observed after treatment with TGHS-1 and TGHS-2. In the presence of both the compounds, cells with sub-G1 DNA content were detected by flow cytometric analysis, indicating that TGHS-1 and TGHS-2 (each EC50 value of 0.1 microM) are the most powerful apoptotic saponins known. These results suggest that TGHS-1 and TGHS-2 induce apoptotic cell death through caspase-3 activation.