Synthesis of sulfoquinovosylacylglycerols, inhibitors of eukaryotic DNA polymerase alpha and beta

Sulfoquinovosyl acylpropanediol (SQAP): Inhibition of poly(ADP-ribose) metabolism and enhanced cytotoxicity in homologous recombination repair-deficient Chinese hamster-derived cells

Sulfoquinovosyl acylpropanediol (SQAP; a synthetic derivative of the sulfoglycolipid natural product sulfoquinovosyl acylglycerol, SQAG), has anti-tumor and radiosensitizing activities in tumor xenograft mouse models. Here, we have studied the PARP inhibitory activity of SQAP and synthetic lethality in BRCA2-deficient cells. In initial screening studies with DNA repair-deficient Chinese hamster ovary cells, homologous recombination repair-deficient cell lines showed increased sensitivity to SQAP, compared to wild-type cells or other DNA repair-deficient mutants. Chinese hamster lung V79 cells and the derivative cell lines V-C8 (BRCA2-deficient) and V-C8 + BRCA2 gene corrections were used to test the role of BRCA2 in SQAP cytotoxicity. The findings were confirmed in studies of the human colon cancer cell lines DLD-1 and its BRCA2-knockout derivative. SQAP inhibited the enzymes poly(ADP-ribose) polymerase (PARP) and poly(ADP-ribose) glycohydrolase (PARG). SQAP pretreatment decreased H2O2induced poly(ADP-ribose) formation in V79 cells. SQAP caused DNA double-strand breaks and chromosome aberrations in V79 BRCA2-mutated cells but did not affect cells in the G2 phase. We have demonstrated that SQAP induces synthetic lethality in BRCA2-deficient Chinese hamster-derived cells via its effects on poly(ADP-ribose) metabolism, motivating further examination of its therapeutic potential, especially against tumors that are deficient in homologous recombination repair due to mutations in BRCA2 or other genes.

Anticancer agent α-sulfoquinovosyl-acylpropanediol enhances the radiosensitivity of human malignant mesothelioma in nude mouse models

Malignant pleural mesothelioma (MPM) is a highly malignant disease that develops after asbestos exposure. Although the number of MPM cases is predicted to increase, no effective standard therapies have been established. The novel radiosensitizer α-sulfoquinovosyl-acylpropanediol (SQAP) enhances the effects of γ-radiation in human lung and prostate cancer cell lines and in animal models. In this study, we explored the radiosensitizing effect of SQAP and its mechanisms in MPM. The human MPM cell lines MSTO-211H and MESO-4 were implanted subcutaneously into the backs and thoracic cavities of immunodeficient KSN/Slc mice, then 2 mg/kg SQAP was intravenously administered with or without irradiation with a total body dose of 8 Gy. In both the orthotopic and ectopic xenograft murine models, the combination of irradiation plus SQAP delayed the implanted human MSTO-211H tumor growth. The analysis of the changes in the relative tumor volume of the MSTO-211H indicated a statistically significant difference after 8 Gy total body combined with 2 mg/kg SQAP, compared to both the untreated control (P = 0.0127) and the radiation treatment alone (P = 0.0171). After the treatment in each case, immunostaining of the harvested tumors revealed decreased cell proliferation, increased apoptosis and normalization of tumor blood vessels in the SQAP- and irradiation-treated group. Furthermore, hypoxia-inducible factor (HIF) 1 mRNA and protein expression were decreased, indicating reoxygenation in this group. In conclusion, SQAP improved hypoxic conditions in tumor tissue and may elicit a radiosensitizing effect in malignant mesothelioma models.

Structural and Functional Analysis of Bacterial Sulfonosphingolipids and Rosette-Inducing Factor 2 (RIF-2) by Mass Spectrometry-Guided Isolation and Total Synthesis

We have analyzed the abundance of bacterial sulfonosphingolipids, including rosette‐inducing factors (RIFs), in seven bacterial prey strains by using high‐resolution tandem mass spectrometry (HRMS²) and molecular networking (MN) within the Global Natural Product Social Molecular Networking (GNPS) web platform. Six sulfonosphingolipids resembling RIFs were isolated and their structures were elucidated based on comparative MS and NMR studies. Here, we also report the first total synthesis of two RIF‐2 diastereomers and one congener in 15 and eight synthetic steps, respectively. For the total synthesis of RIF‐2 congeners, we employed a decarboxylative cross‐coupling reaction to synthesize the necessary branched α‐hydroxy fatty acids, and the Garner‐aldehyde approach to generate the capnine base carrying three stereogenic centers. Bioactivity studies in the choanoflagellate Salpingoeca rosetta revealed that the rosette inducing activity of RIFs is inhibited dose dependently by the co‐occurring sulfonosphingolipid sulfobacins D and F and that activity of RIFs is specific for isolates obtained from Algoriphagus.

The natural sulfoglycolipid derivative SQAP improves the therapeutic efficacy of tissue factor-targeted radioimmunotherapy in the stroma-rich pancreatic cancer model BxPC-3

•

SQAP enhanced tumor uptake and the therapeutic efficacy of radiolabeled anti-tissue factor antibody 1849.

•

SQAP allows for a reduction of the dose of the therapeutic agent ⁹⁰Y-labeled 1849 to half.

•

SQAP did not affect hematologic parameters, or gastrointestinal and respiratory systems in mice.

•

⁹⁰Y-labeled 1849 with SQAP potentially increases exposure of tumors to radiation.

α-Sulfoquinovosylacyl-1,3-propanediol (SQAP) is a semi-synthetic derivative of natural sulfoglycolipid that sensitizes tumors to external-beam radiotherapy. How SQAP affects internal radiotherapy, however, is not known. Here, we investigated the effects of SQAP for radioimmunotherapy (RIT) targeting tissue factor (TF) in a stroma-rich refractory pancreatic cancer mouse model, BxPC-3. A low dose of SQAP (2 mg/kg) increased tumor uptake of the ¹¹¹In-labeled anti-TF antibody 1849, indicating increased tumor perfusion. The addition of SQAP enhanced the growth-inhibitory effect of ⁹⁰Y-labeled 1849 without leading to severe body weight changes, allowing for the dose of ⁹⁰Y-labeled 1849 to be reduced to half that when used alone. Histologic analysis revealed few necrotic and apoptotic cells, but Ki-67–positive proliferating cells and increased vascular formation were detected. These results suggest that the addition of a low dose of SQAP may improve the therapeutic efficacy of TF-targeted RIT by increasing tumor perfusion, even for stroma-rich refractory pancreatic cancer.

Synthesis of 3-octadecanoxypropyl 6-deoxy-6-sulfo-α-d-glucopyranoside (ODSG) as a lipase-resistant SQAP derivative

Sulfoquynovosylacyl propanediol (SQAP; 1) has been developed as a radiosensitizer (anti-cancer agent) for solid tumors, but it was easily cleaved in vivo and had a problem of short residence time. We synthesized a novel compound of a SQAP derivative (3-octadecanoxypropyl 6-deoxy-6-sulfo-α-d-glucopyranoside: ODSG; 2) to solve these problems not easily cleaved by lipase. ODSG (2) cytotoxicity was investigated in vitro, resulting in low toxicity like SQAP (1).

An Alternative Approach for the Synthesis of Sulfoquinovosyldiacylglycerol

Sulfoquinovosyldiacylglycerol (SQDG) is a glycolipid ubiquitously found in photosynthetically active organisms. It has attracted much attention in recent years due to its biological activities. Similarly, the increasing demand for vegan and functional foods has led to a growing interest in micronutrients such as sulfolipids and their physiological influence on human health. To study this influence, reference materials are needed for developing new analytical methods and providing enough material for model studies on the biological activity. However, the availability of these materials is limited by the difficulty to isolate and purify sulfolipids from natural sources and the unavailability of chemical standards on the market. Consequently, an alternative synthetic route for the comprehensive preparation of sulfolipids was established. Here, the synthesis of a sulfolipid with two identical saturated fatty acids is described exemplarily. The method opens possibilities for the preparation of a diverse range of interesting derivatives with different saturated and unsaturated fatty acids.

Standardized Fraction of Turbinaria ornata Alleviates Dextran Sulfate Sodium-Induced Chronic Colitis in C57BL/6 Mice via Upregulation of FOXP3+ Regulatory T Cells

Turbinaria ornata is a tropical brown algae (seaweed) known to have anti-inflammatory properties. In this study, we analyzed T. ornata extract (TOE) using liquid chromatography quadrupole time of flight mass spectrometry (LC-QTOF-MS) and nuclear magnetic resonance (NMR) and evaluated the in vivo efficacy of TOE against dextran sulfate sodium-induced chronic colitis in C57BL/6 mice. The bioactive fraction of TOE was administered orally daily for 6 weeks to mice under different treatments normal, colitis, and colitis + conventional drug (5-aminosalicylic acid, 5-ASA). Regarding clinical manifestation, the disease activity index and colon length of the colitis + TOE group were significantly reduced compared to those of the colitis group. The results of myeloperoxidase activity and histopathological examination showed similar results. Western blot analysis of colon tissues revealed that cyclooxygenase-2, tumor necrosis factor alpha (TNF-α), and phosphorylated signal transducer and activator of transcription-3 (p-STAT3) were significantly decreased in the colitis + 5-ASA group, whereas forkhead box P3 (FOXP3) was increased. qPCR results showed changes in T cell subsets; the administration of TOE upregulated regulatory T cell (Treg) expression, although T helper 17 cell (Th17) expression did not change significantly. Interestingly, the colitis + TOE group showed high levels of both Th1 and Th2 transcription factors, but the secreted cytokine interferon (IFN)-γ and interleukin (IL)-4 remained unchanged and somewhat reduced. Additionally, TNF-α gene expression was significantly reduced in the colitis + TOE group. IL-6 mRNA levels were also decreased, although not significantly. Four compounds were structurally elucidated using 1D- and 2D-NMR spectroscopy, and five compounds were fully identified or tentatively characterized using LC-QTOF-MS. In conclusion, TOE could alleviate chronic colitis via upregulation of Foxp3+ Treg cells and production of the anti-inflammatory cytokine IL-10, which directly inhibits macrophages and pro-inflammatory cytokine synthesis, leading to reduced colitis.

Concise synthesis of sulfoquinovose and sulfoquinovosyl diacylglycerides, and development of a fluorogenic substrate for sulfoquinovosidases

The sulfolipid sulfoquinovosyl diacylglycerol (SQDG) and its headgroup, the sulfosugar sulfoquinovose (SQ), are estimated to harbour up to half of all organosulfur in the biosphere. SQ is liberated from SQDG and related glycosides by the action of sulfoquinovosidases (SQases). We report a 10-step synthesis of SQDG that we apply to the preparation of saturated and unsaturated lipoforms. We also report an expeditious synthesis of SQ and (¹³C₆)SQ, and X-ray crystal structures of sodium and potassium salts of SQ. Finally, we report the synthesis of a fluorogenic SQase substrate, methylumbelliferyl α-d-sulfoquinovoside, and examination of its cleavage kinetics by two recombinant SQases. These compounds will assist in dissecting the role of sulfoglycolysis in the biogeochemical sulfur cycle and understanding the molecular basis of sulfoglycolysis.

A Multimodal Molecular Imaging Study Evaluates Pharmacological Alteration of the Tumor Microenvironment to Improve Radiation Response

: Hypoxic zones in solid tumors contribute to radioresistance, and pharmacologic agents that increase tumor oxygenation prior to radiation, including antiangiogenic drugs, can enhance treatment response to radiotherapy. Although such strategies have been applied, imaging assessments of tumor oxygenation to identify an optimum time window for radiotherapy have not been fully explored. In this study, we investigated the effects of α-sulfoquinovosylacyl-1,3-propanediol (SQAP or CG-0321; a synthetic derivative of an antiangiogenic agent) on the tumor microenvironment in terms of oxygen partial pressure (pO₂), oxyhemoglobin saturation (sO₂), blood perfusion, and microvessel density using electron paramagnetic resonance imaging, photoacoustic imaging, dynamic contrast-enhanced MRI with Gd-DTPA injection, and T2*-weighted imaging with ultrasmall superparamagnetic iron oxide (USPIO) contrast. SCCVII and A549 tumors were grown by injecting tumor cells into the hind legs of mice. Five days of daily radiation (2 Gy) combined with intravenous injection of SQAP (2 mg/kg) 30 minutes prior to irradiation significantly delayed growth of tumor xenografts. Three days of daily treatment improved tumor oxygenation and decreased tumor microvascular density on T2*-weighted images with USPIO, suggesting vascular normalization. Acute effects of SQAP on tumor oxygenation were examined by pO₂, sO₂, and Gd-DTPA contrast-enhanced imaging. SQAP treatment improved perfusion and tumor pO₂ (ΔpO₂: 3.1 ± 1.0 mmHg) and was accompanied by decreased sO₂ (20%-30% decrease) in SCCVII implants 20-30 minutes after SQAP administration. These results provide evidence that SQAP transiently enhanced tumor oxygenation by facilitating oxygen dissociation from oxyhemoglobin and improving tumor perfusion. Therefore, SQAP-mediated sensitization to radiation in vivo can be attributed to increased tumor oxygenation. SIGNIFICANCE: A multimodal molecular imaging study evaluates pharmacological alteration of the tumor microenvironment to improve radiation response.

Distribution and metabolism of 14C-sulfoquinovosylacylpropanediol (14C-SQAP) after a single intravenous administration in tumor-bearing mice

Sulfoquinovosylacylpropanediol (SQAP) is a novel potent radiosensitizer that inhibits angiogenesis in vivo and results in increased oxigenation and reduced tumor volume. We investigated the distribution, metabolism, and excretion of SQAP in male KSN-nude mice transplanted with a human pulmonary carcinoma, Lu65. For the metabolism analysis, a 2 mg (2.98 MBq)/kg of [glucose-U-¹⁴C]-SQAP (CP-3839) was intravenously injected. The injected SQAP was decomposed into a stearic acid and a sulfoquinovosylpropanediol (SQP) in the body. The degradation was relatively slow in the carcinoma tissue.1,3-propanediol[1-¹⁴C]-SQAP (CP-3635) was administered through intravenous injection of a 1 mg (3.48 MBq)/kg dose followed by whole body autoradiography of the mice. The autoradiography analysis demonstrated that SQAP rapidly distributed throughout the whole body and then quickly decreased within 4 hours except the tumor and excretion organs such as liver, kidney. Retention of SQAP was longer in tumor parts than in other tissues, as indicated by higher levels of radioactivity at 4 hours. The radioactivity around the tumor had also completely disappeared within 72 hours.

Chemical Synthesis of Marine-Derived Sulfoglycolipids, a New Class of Molecular Adjuvants

Vaccines play a primary role in the protection of human health by preventing infectious and chronic diseases. Recently we have reported 1,2-O-distearoyl-3-O-β-d-sulfoquinovosylglycerol (β-SQDG18), here named Sulfavant A (1), which shows promising properties as a new molecular adjuvant in in vitro and in vivo tests. In the present manuscript, we provide full details about a synthetic strategy for the preparation of 1, including a discussion of chemical determinants of the activity and the major technical hurdles we faced during the study. Synthesis of Sulfavant A (1) is achieved by a versatile procedure based on a trichloroacetimidate methodology and peracetate sugar precursors. The final design opens possibilities for the preparation of a series of interesting analogs for further pharmacological optimization and development, including derivatives containing different saturated and polyunsaturated fatty acids (e.g., 17 and 22).

Sulfoquinovose in the biosphere: occurrence, metabolism and functions

The sulfonated carbohydrate sulfoquinovose (SQ) is produced in quantities estimated at some 10 billion tonnes annually and is thus a major participant in the global sulfur biocycle. SQ is produced by most photosynthetic organisms and incorporated into the sulfolipid sulfoquinovosyl diacylglycerol (SQDG), as well as within some archaea for incorporation into glycoprotein N-glycans. SQDG is found mainly within the thylakoid membranes of the chloroplast, where it appears to be important for membrane structure and function and for optimal activity of photosynthetic protein complexes. SQDG metabolism within the sulfur cycle involves complex biosynthetic and catabolic processes. SQDG biosynthesis is largely conserved within plants, algae and bacteria. On the other hand, two major sulfoglycolytic pathways have been discovered for SQDG degradation, the sulfo-Embden–Meyerhof–Parnas (sulfo-EMP) and sulfo-Entner–Doudoroff (sulfo-ED) pathways, which mirror the major steps in the glycolytic EMP and ED pathways. Sulfoglycolysis produces C3-sulfonates, which undergo biomineralization to inorganic sulfur species, completing the sulfur cycle. This review discusses the discovery and structural elucidation of SQDG and archaeal N-glycans, the occurrence, distribution, and speciation of SQDG, and metabolic pathways leading to the biosynthesis of SQDG and its catabolism through sulfoglycolytic and biomineralization pathways to inorganic sulfur.

Natural Products from Microalgae with Potential against Alzheimer's Disease: Sulfolipids Are Potent Glutaminyl Cyclase Inhibitors

In recent years, many new enzymes, like glutaminyl cyclase (QC), could be associated with pathophysiological processes and represent targets for many diseases, so that enzyme-inhibiting properties of natural substances are becoming increasingly important. In different studies, the pathophysiology connection of QC to various diseases including Alzheimer's disease (AD) was described. Algae are known for the ability to synthesize complex and highly-diverse compounds with specific enzyme inhibition properties. Therefore, we screened different algae species for the presence of QC inhibiting metabolites using a new "Reverse Metabolomics" technique including an Activity-correlation Analysis (AcorA), which is based on the correlation of bioactivities to mass spectral data with the aid of mathematic informatics deconvolution. Thus, three QC inhibiting compounds from microalgae belonging to the family of sulfolipids were identified. The compounds showed a QC inhibition of 81% and 76% at concentrations of 0.25 mg/mL and 0.025 mg/mL, respectively. Thus, for the first time, sulfolipids are identified as QC inhibiting compounds and possess substructures with the required pharmacophore qualities. They represent a new lead structure for QC inhibitors.

Total synthesis of a cyclopropane-fatty acid α-glucosyl diglyceride from Lactobacillus plantarum and identification of its ability to signal through Mincle

We report a concise synthesis of glycolipid GL1 from Lactobacillus plantarum commencing from methyl α-d-glucopyroside. A Jacobsen hydrolytic kinetic resolution is used to generate a diastereomerically-pure glycidyl glucoside that was elaborated to the diglyceride by stepwise brominolysis, acylation with oleoyl chloride, and bromide-substitution by the tetrabutylammonium salt of 9S,10R-dihydrosterculic acid. GL1 and analogues were shown to signal through the glycolipid pattern recognition receptor Mincle.

Glycolipids synthesis: improved hydrazinolysis conditions for preparation of 1,2-polyunsaturated fatty acyl-β-monogalactosyl-glycerols

The investigation is related to the development of a general strategy for the synthesis of glycolipids including analogs bearing polyunsaturated fatty acids. In particular, here we report exceptionally mild and selective conditions to remove acetate protecting groups from glyceroglycolipids by hydrazinolysis. Synthetic 1,2-O-di-arachidonoyl-3-O-β-galactosyl-glycerol was used as representative of polyunsaturated β-galactosyl-di-acyl-glycerols due to its reactivity under the conditions usually employed in literature.

Glycolipids from seaweeds and their potential biotechnological applications

Marine macroalgae, or seaweeds, are a formidable source of natural compounds with diverse biological activities. In the last five decades it has been estimated that more than 3000 natural compounds were discovered from these organisms. The great majority of the published works have focused on terpenoids. In comparison, glycolipids are a neglected class of macroalgal secondary metabolites therefore remaining as a largely unknown reservoir of molecular diversity. Nevertheless, the interest regarding these compounds has been growing fast in the last decades as activities of ecological or pharmaceutical interest have been highlighted. This paper will review recent work regarding isolation and structural characterization of glycolipids from seaweeds and their prospective biological activities.

Total synthesis and structure-activity relationship of glycoglycerolipids from marine organisms

Glycoglycerolipids occur widely in natural products, especially in the marine species. Glycoglycerolipids have been shown to possess a variety of bioactivities. This paper will review the different methodologies and strategies for the synthesis of biological glycoglycerolipids and their analogs for bioactivity assay. In addition, the bioactivities and structure-activity relationship of the glycoglycerolipids are also briefly outlined.

Telomerase inhibitors from cyanobacteria: isolation and synthesis of sulfoquinovosyl diacylglycerols from Microcystis aeruguinosa PCC 7806

By using the Telospot assay, 27 different extracts of cyanobacteria were evaluated for telomerase inhibition. All extracts showed varying, but significant activity. We selected Microcystis aeruguinosa PCC 7806 to identify the active compound and a bioassay guided fractionation led us to isolate mixtures of sulfoquinovosyl diacylglycerols (SQDGs), which were identified by 2D NMR and MS/MS experiments. Pure SQDG derivatives were then synthesized. The IC(50) values of pure synthetic sulfoquinovosyl dipalmitoylglycerol and the monopalmitoylated derivative against telomerase were determined to be 17 and 40 μM, respectively. A structure-activity relationship study allowed the identification of compounds with modified lipophilic acyl groups that display improved activity.

Evaluation of ion activation strategies and mechanisms for the gas-phase fragmentation of sulfoquinovosyldiacylglycerol lipids from Rhodobacter sphaeroides

Sulfoquinovosyldiacylglycerol (SQDG) lipids, found in plants and photosynthetic bacteria, can substitute for phospholipids under phosphate limiting conditions. Here, various low-energy ion activation strategies have been evaluated for the identification and characterization of deprotonated SQDG lipids from a crude membrane lipid extract of Rhodobacter sphaeroides, using collision- induced dissociation - tandem mass spectrometry (CID-MS/MS) in either a triple quadrupole mass spectrometer or in a hybrid quadrupole ion trap-multipole mass spectrometer coupled with high resolution / accurate mass analysis capabilities. In the triple quadrupole instrument, using energy resolved CID-MS/MS experiments, the SQDG head group specific product ion at m/z 225 (C(6)H(9)O(7)S(-)), rather than m/z 81 (SO(3)H(-)), was determined to provide the greatest sensitivity for SQDG lipid detection, and is therefore the preferred `fingerprint' ion for the identification of this lipid class from within complex lipid mixtures when using precursor ion scan mode MS/MS experiments. A comparison of conventional ion trap CID-MS/MS and -MS(n), with `low Q' CID-MS/MS, pulsed Q dissociation (PQD)-MS/MS and higher energy collision induced dissociation (HCD)-MS/MS performed in an LTQ Orbitrap Velos mass spectrometer, revealed that HCD-MS/MS coupled with high resolution/accurate mass analysis represents the most sensitive, and perhaps most importantly the most specific strategy, for ion trap based identification and characterization of SQDG lipids, due to the ability to readily distinguish the SQDG head group specific product ion at m/z 225.0069 from other products that may be present at the same nominal m/z value. Finally, the mechanisms responsible for formation of each of the major product ions observed by low-energy CID-MS/MS of deprotonated SQDG lipids were elucidated using uniform H/D exchange, HCD-MS/MS and high resolution mass analysis. Formation of the m/z 225 `fingerprint' ion occurs via a charge-remote cis-elimination reaction, likely involving transfer of a hydrogen from the hydroxyl group located on the C2 position of the sugar ring.

Anti-Tumor Effects of the Glycolipids Fraction from Spinach which Inhibited DNA Polymerase Activity

We succeeded in purifying the fraction of monogalactosyl diacylglycerol (MGDG), digalactosyl diacylglycerol (DGDG), and sulfoquinovosyl diacylglycerol (SQDG) containing the major glycolipids from a green vegetable, spinach (Spinacia oleraceaL.). This glycolipids fraction inhibited the activities of replicative DNA polymerases (pols) such as alpha, delta, and epsilon, and mitochondrial pol gamma with IC50 values of 44.0-46.2 microg/ml, but had no influence on the activity of repair-related pol beta. The fraction also inhibited the proliferation of human cervix carcinoma (HeLa) cells with LD50 values of 57.2 microg/ml. In an in vivo anti-tumor assay on nude mice bearing solid tumors of HeLa cells, the fraction was shown to be a promising suppressor of solid tumors. Histopathological examination revealed that tumor necrosis with hemorrhage was significantly enhanced with the glycolipids fraction in vivo. The spinach glycolipids fraction might be a potent anti-tumor compound, and this fraction may be a healthy food substance with anti-tumor activity.

An emulsion of sulfoquinovosylacylglycerol with long-chain alkanes increases its permeability to tumor cells

The alpha-anomer form of sulfoquinovosyl-monoacylglycerol with a saturated C18 fatty acid (alpha-SQMG-C(18:0)) is a natural sulfolipid that is a clinically promising antitumor agent. It forms vesicles, micelles or an emulsion in water, depending on several physicochemical conditions. The type of aggregate formed appears to strongly influence the bioactivity level. Thus, we investigated the nature of the aggregates in relation to their bioactivities. The structure of the alpha-SQMG-C(18:0) assembly was greatly affected by the type of additive used in the preparation. Emulsification with ethanol and n-decane might be more effective at inhibiting tumor cell growth than the micelle or vesicle preparations. alpha-SQMG-C(18:0) formed an "emulsion-like-aggregate" in ethanol containing an n-decane concentration in the range of 1.03-103 mM: . These ethanol/n-alkane/alpha-SQMG-C(18:0) aggregates inhibited cell growth in a dose-dependent manner, under optimum conditions (i.e., ethanol containing 103 mM: of n-decane or n-dodecane dispersed in phosphate-buffered saline or culture medium). Based on these data, we discuss the relationship between the molecular action of and antitumor activity by alpha-SQMG-C(18:0).

New Glycomimetics: Anomeric Sulfonates, Sulfenamides, and Sulfonamides

The synthesis of a variety of new 1-thio-D-glucopyranose derivatives oxidized at the sulfur atom is described, including seven 1-C-sulfonic acids, three sulfonate esters, three sulfinate esters, an S,S'-diglycosyl thiolsulfonate and thiolsulfinate, four S-glycosyl sulfenamides, an S-glycosyl sulfinamide, and two S-glycosyl sulfonamides. These compounds possess unusual anomeric functionality that might be resistant or even inhibitory to normal enzymatic carbohydrate processing, and therefore, they may be of future use in studies of enzyme inhibition, structure, mechanism, and function.

Effective form of sulfoquinovosyldiacyglycerol (SQDG) vesicles for DNA polymerase inhibition

Sulfoquinovosyldiacyglycerol (SQDG) has a wide range of biological activities that make it an attractive compound for the development of new drugs. Chemically synthesized beta-SQDG-C(18:0) (1,2-di-O-stearoyl-3-O-(6-deoxy-6-sulfo-beta-d-glucopyranosyl)-sn-glycerol), for example, has a potent inhibitory effect on DNA polymerases. We investigated the properties of the vesicle form of beta-SQDG-C(18:0) as the monomer has low solubility in water. The structure of the beta-SQDG-C(18:0) vesicles are highly influenced by NaCl concentration in preparation process. At low NaCl concentrations, the beta-SQDG-C(18:0) vesicles have high surface curvature and form small unilamellar vesicles. Increases in NaCl concentration, resulted in decreased surface curvature and a tendency for beta-SQDG-C(18:0) to form large multilamellar vesicles. The small unilamellar vesicles showed a potent inhibitory effect on DNA polymerase beta, whereas the large multilamellar vesicles had no such effect. We investigated further the relationship between vesicle size and activity by preparing smaller vesicles (262, 99 and 43 nm in diameter) using an extrusion technique. These smaller vesicles had a greater inhibitory effect on DNA polymerase beta activity than non-extruded vesicles. beta-SQDG-C(18:0) vesicles, especially those of small size, were effective in DNA polymerase inhibition and are expected to have high applicability in DNA polymerase study.

Inhibitory effects of glycolipids fraction from spinach on mammalian DNA polymerase activity and human cancer cell proliferation

We succeeded in purifying the fraction containing the major glycolipids in monogalactosyl diacylglycerol, digalactosyl diacylglycerol and sulfoquinovosyl diacylglycerol (SQDG) from dried vegetables. This glycolipids fraction was an inhibitor of DNA polymerase alpha (pol alpha) in vitro and also the proliferation of human cancer cells. In this study, eight common vegetables were investigated in terms of the glycolipids fraction, the amounts of major glycolipids, mammalian DNA polymerase inhibitory activity and antiproliferative activity toward human cancer cells. Green tea possessed the largest amount of glycolipids overall. Spinach contained the largest amount of SQDG, followed by parsley, green onion, chive, sweet pepper, green tea, carrot and garlic. Spinach had the strongest inhibitory effect on pol alpha activity and human cancer cell proliferation. A significant correlation was found between SQDG content and inhibition of DNA polymerase. Therefore, the inhibition of pol alpha activity by SQDG may lead to cell growth suppression. Of the six subspecies of spinach (Spinacia oleracea) tested, "Anna" had the largest amount of SQDG, strongest inhibitory activity toward DNA polymerase and greatest effect on human cancer cell proliferation. Based on these results, the glycolipids fraction from spinach is potentially a source of food material for a novel anticancer activity.

Sulfoquinovosylmonoacylglycerol inhibitory mode analysis of rat DNA polymerase beta

We have previously reported that sulfoquinovosylmonoacylglycerol (SQMG) is a potent inhibitor of mammalian DNA polymerases. DNA polymerase beta (pol beta) is one of the most important enzymes protecting the cell against DNA damage by base excision repair. In this study, we characterized the inhibitory action of SQMG against rat pol beta. SQMG competed with both the substrate and the template-primer for binding to pol beta. A gel mobility shift assay and a polymerase activity assay showed that SQMG competed with DNA for a binding site on the N-terminal 8-kDa domain of pol beta, subsequently inhibiting its catalytic activity. Fragments of SQMG such as sulfoquinovosylglycerol (SQG) and fatty acid (myristoleic acid, MA) weakly inhibited pol beta activity and the inhibitory effect of a mixture of SQG and MA was stronger than that of SQG or MA. To characterize this inhibition more precisely, we attempted to identify the interaction interface between SQMG and the 8-kDa domain by NMR chemical shift mapping. Firstly, we determined the binding site on a fragment of SQMG, the SQG moiety. We observed chemical shift changes primarily at two sites, the residues comprising the C-terminus of helix-1 and the N-terminus of helix-2, and residues in helix-4. Finally, based on our present results and our previously reported study of the interaction interface of fatty acids, we constructed two three-dimensional models of a complex between the 8-kDa domain and SQMG and evaluated them by the mutational analysis. The models show a SQMG interaction interface that is consistent with the data.

Structural analysis of catechin derivatives as mammalian DNA polymerase inhibitors

The inhibitory activities against DNA polymerases (pols) of catechin derivatives (i.e., flavan-3-ols) such as (+)-catechin, (-)-epicatechin, (-)-gallocatechin, (-)-epigallocatechin, (+)-catechin gallate, (-)-epicatechin gallate, (-)-gallocatechin gallate, and (-)-epigallocatechin gallate (EGCg) were investigated. Among the eight catechins, some catechins inhibited mammalian pols, with EGCg being the strongest inhibitor of pol alpha and lambda with IC(50) values of 5.1 and 3.8 microM, respectively. EGCg did not influence the activities of plant (cauliflower) pol alpha and beta or prokaryotic pols, and further had no effect on the activities of DNA metabolic enzymes such as calf terminal deoxynucleotidyl transferase, T7 RNA polymerase, and bovine deoxyribonuclease I. EGCg-induced inhibition of pol alpha and lambda was competitive with respect to the DNA template-primer and non-competitive with respect to the dNTP (2'-deoxyribonucleotide 5'-triphosphate) substrate. Tea catechins also suppressed TPA (12-O-tetradecanoylphorbol-13-acetate)-induced inflammation, and the tendency of the pol inhibitory activity was the same as that of anti-inflammation. EGCg at 250 microg was the strongest suppressor of inflammation (65.6% inhibition) among the compounds tested. The relationship between the structure of tea catechins and the inhibition of mammalian pols and inflammation was discussed.

Effects of DNA polymerase inhibitory and antitumor activities of lipase-hydrolyzed glycolipid fractions from spinach

We succeeded in purifying the major glycolipid fraction in the class of sulfoquinovosyl diacylglycerol, monogalactosyl diacylglycerol and digalactosyl diacylglycerol (DGDG) from a green vegetable, spinach (Spinacia oleracea L.). This glycolipid fraction was an inhibitor of DNA polymerases and a growth inhibitor of NUGC-3 human gastric cancer cells, and, interestingly, the activities were much stronger when the fraction was hydrolyzed by lipase. Glycolipids in the hydrolyzed fraction consisted of sulfoquinovosyl monoacylglycerol (SQMG), monogalactosyl monoacylglycerol (MGMG) and DGDG. In the in vivo antitumor assay using Greene's melanoma, the fraction containing SQMG, MGMG and DGDG showed to be a promising suppressor of solid tumors. Spinach glycolipid fraction might be a potent antitumor compound if directly injected into a tumor-carrying body, and this fraction may be a healthy food material that has antitumor activity.

Dipeptide alcohol-based inhibitors of eukaryotic DNA polymerase α

We reported previously that a novel dipeptide alcohol, l-homoserylaminoethanol (Hse-Gly-ol), is a selective inhibitor of eukaryotic DNA polymerase epsilon (pol epsilon) [Bioorg. Med. Chem.2004, 12, 957-962]. The discovery suggests that the dipeptide structure could be a chemical frame for a DNA polymerase inhibitor. Therefore, we chemically synthesized 27 different species of dipeptide alcohols, and tested this inhibitory capability. Compound 6 (l-aspartylaminoethanol, Asp-Gly-ol) was found to be the strongest pol alpha inhibitor. Compound 6 did not influence the activities of other replicative DNA polymerases such as delta and epsilon, and had no effect on the activities of prokaryotic DNA polymerases, nor DNA metabolic enzymes such as human immunodeficiency virus type 1 reverse transcriptase, T7 RNA polymerase and bovine deoxyribonuclease I. The inhibitory effect of compound 6 on pol alpha was dose-dependent, and 50% inhibition was observed at a concentration of 33.5 microM. Compound 6-induced inhibition of pol alpha activity was non-competitive with both the DNA template-primer and the dNTP substrate. This is the first report on a water-soluble pol alpha-specific inhibitor, sought for precise biochemical studies of pol alpha. The relationships between the structures of dipeptide alcohols and the inhibition of eukaryotic DNA polymerases are discussed.

Monolayer membranes and bilayer vesicles characterized by α- and β-anomer of sulfoquinovosyldiacyglycerol (SQDG)

Physicochemical properties of 1,2-di-O-stearoyl-3-O-(6-deoxy-6-sulfo-alpha-D-glucopyranosyl)-sn-glycerol (alpha-SQDG-C(18:0)) and 1,2-di-O-stearoyl-3-O-(6-deoxy-6-sulfo-beta-D-glucopyranosyl)-sn-glycerol (beta-SQDG-C(18:0)) in monolayer and bilayer membranes were examined. Surface pressure measurements in monolayer membranes indicated the molecular area of beta-SQDG-C(18:0) to be slightly smaller than that of alpha-SQDG-C(18:0). In bilayer membranes, the phase transition temperature and the enthalpy of beta-SQDG-C(18:0) were higher than those of alpha-SQDG-C(18:0), while the trapping efficiency of beta-SQDG-C(18:0) vesicles was lower. The results suggested tighter packing with beta-SQDG-C(18:0) than alpha-SQDG-C(18:0), due to differences in the head group stereochemistry. High-performance liquid chromatography-electrospray ionization ion trap mass spectrometry (HPLC-ESI-MS) data and computational modeling studies provided supporting evidence for morphological differences. In both monolayer and bilayer membranes, the affinity of beta-SQDG-C(18:0) with cholesterol was greater than that of alpha-SQDG-C(18:0), again due to the differences in head group properties. Turbidity measurement and microscopic examination of alpha- and beta-SQDG-C(18:0)/cholesterol mixtures confirmed formation of large vesicles. The addition of cholesterol to SQDG-C(18:0) optimized membrane formation and stabilized its structure.

Design of vesicles of 1,2-di-O-acyl-3-O-(β-d-sulfoquinovosyl)-glyceride bearing two stearic acids (β-SQDG-C18), a novel immunosuppressive drug

The immunosuppressive effects of synthetic sulfo-glycolipids in the class of sulfoquinovosyl-diacylglycerols (SQDG), including stereoisomers, were interesting in development of a promising clinical drug. Especially, 1,2-di-O-stearoyl-3-O-(6-deoxy-6-sulfo-beta-D-glucopyranosyl)-sn-glycerol (beta-SQDG-C18) was thought to be a valuable candidate because of the preliminary observations of its high inhibitory activities in spite of low toxicities. The problem of using this material is to find an applicable way avoiding its low solubility in water. The vesicle formation of beta-SQDG-C18 is advantageous to i.v. administration in its chemico-structural character. With preparation in water, beta-SQDG-C18 was hard to form vesicles, because its hydrophilicity was strong. We examined the suitable parameter of the vesicle forming condition. It was possible to take a balance between the hydrophilicity and the hydrophobicity of the beta-SQDG-C18 molecule to be optimized to form vesicles in 150 mM PBS. In addition, we demonstrated the strong immunosuppressive activity of beta-SQDG-C18 vesicles. This is the first report of the preparation method of beta-SQDG-C18 vesicles, which should facilitate in vitro and in vivo application.

Synthesis of an immunosuppressant SQAG9 and determination of the binding peptide by T7 phage display

SQAG9, a new class of immunosuppressive sulfoquinovosylacylglycerol, and its biotinylated derivatives have been synthesized. A T7 Phage library, composed of random cDNA fragments from Drosophila melanogaster, displayed a possible binding peptide of 14 amino acids. The immobilized synthetic peptide on a sensor chip showed a dissociation constant of K(D)=1.5 x 10(-6) against SQAG9 in a surface plasmon resonance experiment.

L-Homoserylaminoethanol, a novel dipeptide alcohol inhibitor of eukaryotic DNA polymerase from a plant cultured cells, Nicotina tabacum L

We found a novel inhibitor specific to eukaryotic DNA polymerase epsilon(pol epsilon) from plant cultured cells, Nicotina tabacum L. The compound (compound 1) was a dipeptide alcohol, L-homoserylaminoethanol. The 50% inhibition of pol epsilon activity by the compound was 43.6 microg/mL, and it had almost no effect on the activities of the other eukaryotic DNA polymerases such as alpha, beta, gamma and delta, prokaryotic DNA polymerases, nor DNA metabolic enzymes such as human telomerase, human immunodeficiency virus type 1 reverse transcriptase, T7 RNA polymerase, human DNA topoisomerase I and II, T4 polynucleotide kinase and bovine deoxyribonuclease I. Kinetic studies showed that inhibition of pol epsilon by the compound was non-competitive with respect to both template-primer DNA and nucleotide substrate. We succeeded in chemically synthesizing the stereoisomers, L-homoserylaminoethanol and D-homoserylaminoethanol, and found both were effective to the same extent. The IC(50) values of L- and D-homoserylaminoethanols for pol epsilon were 42.0 and 41.5 microg/mL, respectively. This represents the second discovery of a pol epsilon-specific inhibitor, and the first report on a water-soluble peptide-like compound as the inhibitor, which is required in biochemical studies of pol epsilon.