Glycosphingolipids and drug resistance

Ceramide synthase-dependent ceramide generation and programmed cell death: involvement of salvage pathway in regulating postmitochondrial events

The sphingolipid ceramide has been widely implicated in the regulation of programmed cell death or apoptosis. The accumulation of ceramide has been demonstrated in a wide variety of experimental models of apoptosis and in response to a myriad of stimuli and cellular stresses. However, the detailed mechanisms of its generation and regulatory role during apoptosis are poorly understood. We sought to determine the regulation and roles of ceramide production in a model of ultraviolet light-C (UV-C)-induced programmed cell death. We found that UV-C irradiation induces the accumulation of multiple sphingolipid species including ceramide, dihydroceramide, sphingomyelin, and hexosylceramide. Late ceramide generation was also found to be regulated by Bcl-xL, Bak, and caspases. Surprisingly, inhibition of de novo synthesis using myriocin or fumonisin B1 resulted in decreased overall cellular ceramide levels basally and in response to UV-C, but only fumonisin B1 inhibited cell death, suggesting the presence of a ceramide synthase (CerS)-dependent, sphingosine-derived pool of ceramide in regulating programmed cell death. We found that this pool did not regulate the mitochondrial pathway, but it did partially regulate activation of caspase-7 and, more importantly, was necessary for late plasma membrane permeabilization. Attempting to identify the CerS responsible for this effect, we found that combined knockdown of CerS5 and CerS6 was able to decrease long-chain ceramide accumulation and plasma membrane permeabilization. These data identify a novel role for CerS and the sphingosine salvage pathway in regulating membrane permeability in the execution phase of programmed cell death.

Inhibition of NADPH oxidase by glucosylceramide confers chemoresistance

The bioactive sphingolipid ceramide induces oxidative stress by disrupting mitochondrial function and stimulating NADPH oxidase (NOX) activity, both implicated in cell death mechanisms. Many anticancer chemotherapeutics (anthracyclines, Vinca alkaloids, paclitaxel, and fenretinide), as well as physiological stimuli such as tumor necrosis factor α (TNFα), stimulate ceramide accumulation and increase oxidative stress in malignant cells. Consequently, ceramide metabolism in malignant cells and, in particular the up-regulation of glucosylceramide synthase (GCS), has gained considerable interest in contributing to chemoresistance. We hypothesized that increases in GCS activity and thus glucosylceramide, the product of GCS activity, represents an important resistance mechanism in glioblastoma. In our study, we determined that increased GCS activity effectively blocked reactive oxygen species formation by NOX. We further showed, in both glioblastoma and neuroblastoma cells that glucosylceramide directly interfered with NOX assembly, hence delineating a direct resistance mechanism. Collectively, our findings indicated that pharmacological or molecular targeting of GCS, using non-toxic nanoliposome delivery systems, successfully augmented NOX activity, and improved the efficacy of known chemotherapeutic agents.

Sphingolipids: the nexus between Gaucher disease and insulin resistance

Sphingolipids constitute a diverse array of lipids in which fatty acids are linked through amide bonds to a long-chain base, and, structurally, they form the building blocks of eukaryotic membranes. Ceramide is the simplest and serves as a precursor for the synthesis of the three main types of complex sphingolipids; sphingomyelins, glycosphingolipids and gangliosides. Sphingolipids are no longer considered mere structural spectators, but bioactive molecules with functions beyond providing a mechanically stable and chemically resistant barrier to a diverse array of cellular processes. Although sphingolipids form a somewhat minor component of the total cellular lipid pool, their accumulation in certain cells forms the basis of many diseases. Human diseases caused by alterations in the metabolism of sphingolipids are conventionally inborn errors of degradation, the most common being Gaucher disease, in which the catabolism of glucosylceramide is defective and accumulates. Insulin resistance has been reported in patients with Gaucher disease and this article presents evidence that this is due to perturbations in the metabolism of sphingolipids. Ceramide and the more complex sphingolipids, the gangliosides, are constituents of specialised membrane microdomains termed lipid rafts. Lipid rafts play a role in facilitating and regulating lipid and protein interactions in cells, and their unique lipid composition enables them to carry out this role. The lipid composition of rafts is altered in cell models of Gaucher disease which may be responsible for impaired lipid and protein sorting observed in this disorder, and consequently pathology. Lipid rafts are also necessary for correct insulin signalling, and a perturbed lipid raft composition may impair insulin signalling. Unravelling common nodes of interaction between insulin resistance and Gaucher disease may lead to a better understanding of the biochemical mechanisms behind pathology.

Mixed backbone antisense glucosylceramide synthase oligonucleotide (MBO-asGCS) loaded solid lipid nanoparticles: in vitro characterization and reversal of multidrug resistance in NCI/ADR-RES cells

In this study, solid lipid nanoparticles (SLN) loaded with MBO-asGCS oligonucleotide were prepared, characterized and evaluated for cytotoxicity against NCI/ADR-RES human ovary cancer cells. Two types of cetyltrimethyl ammonium bromide (CTAB) stabilized SLN, with or without ceramide VI, were prepared by mixed homogenization/ultrasonication technique. Complexes were characterized for size, zeta-potential, and stability in biorelevant media and against DNaseI activity. Binding and release studies were further confirmed by gel electrophoresis. Cytotoxicity of the SLN against NCI/ADR-RES cells was evaluated by quantizing ATP. SLN with ceramide VI had lower particle size (74.6 nm) with improved stability in RPMI media when compared to reference SLN without ceramide VI (167.16 nm). Both SLN however had similar cytotoxicity profile with an optimum binding at CTAB to MBO-asGCS ratio of 6:1. Blank SLN, and free MBO-asGCS in the presence and absence of free doxorubicin had insignificant effect on the viability of NCI/ADR-RES cells. However, when cells were concurrently treated with MBO-asGCS loaded SLN and free doxorubicin, cell viability significantly decreased to approximately 12%. These results suggested that SLN enhanced internalization and uptake of MBO-asGCS oligonucleotide, which led to the downregulation of GCS and subsequently reversing the resistance of the cells to doxorubicin.

A new approach to comparing anti-CD20 antibodies: importance of the lipid rafts in their lytic efficiency

The view that B lymphocytes are pathogenic in diverse pathological settings is supported by the efficacy of B-cell-ablative therapy in lymphoproliferative disorders, autoimmune diseases and graft rejection. Anti-B-cell antibodies (Abs) directed against CD20 have therefore been generated, and of these, rituximab was the first anti-CD20 monoclonal Ab (mAb) to be applied. Rituximab-mediated apoptosis, complement-dependent cytotoxicity and Ab-dependent cellular cytotoxicity differ from one disease to another, and, for the same disease, from one patient to another. This knowledge has prompted the development of new anti-CD20 mAbs in the hope of improving B-cell depletion. The inclusion of CD20/anti-CD20 complexes in large lipid rafts (LRs) enhances the results of some, but not all, anti-CD20 mAbs, and it may be possible to include smaller LRs. Lipid contents of membrane may be abnormal in malignant B-cells, and could explain resistance to treatment. The function of these mAbs and the importance of LRs warrant further investigation. A detailed understanding of them will increase results for B-cell depletion in lymphoproliferative diseases.

Regulating survival and development in the retina: key roles for simple sphingolipids

Many sphingolipids have key functions in the regulation of crucial cellular processes. Ceramide (Cer) and sphingosine (Sph) induce growth arrest and cell death in multiple situations of cellular stress. On the contrary, sphingosine-1-phosphate (S1P), the product of Sph phosphorylation, promotes proliferation, differentiation, and survival in different cell systems. This review summarizes the roles of these simple sphingolipids in different tissues and then analyzes their possible functions in the retina. Alterations in proliferation, neovascularization, differentiation, and cell death are critical in major retina diseases and collective evidence points to a role for sphingolipids in these processes. Cer induces inflammation and apoptosis in endothelial and retinal pigmented epithelium cells, leading to several retinopathies. S1P can prevent this death but also promotes cell proliferation that might lead to neovascularization and fibrosis. Recent data support Cer and Sph as crucial mediators in the induction of photoreceptor apoptosis in diverse models of oxidative damage and neurodegeneration, and suggest that regulating their metabolism can prevent this death. New evidence proposes a central role for S1P controlling photoreceptor survival and differentiation. Finally, this review discusses the ability of trophic factors to regulate sphingolipid metabolism and transactivate S1P signaling pathways to control survival and development in retina photoreceptors.

Sphingosine kinase mediates resistance to the synthetic retinoid N-(4-hydroxyphenyl)retinamide in human ovarian cancer cells

A2780 human ovarian carcinoma cells respond to treatment with the synthetic retinoid N-(4-hydroxyphenyl)retinamide (HPR) with the production of dihydroceramide and with a concomitant reduction of cell proliferation and induction of apoptosis. The derived HPR-resistant clonal cell line, A2780/HPR, is less responsive to HPR in terms of dihydroceramide generation. In this report, we show that the production of sphingosine 1-phosphate (S1P) is significantly higher in A2780/HPR versus A2780 cells due to an increased sphingosine kinase (SK) activity and SK-1 mRNA and protein levels. Treatment of A2780 and A2780/HPR cells with a potent and highly selective pharmacological SK inhibitor effectively reduced S1P production and resulted in a marked reduction of cell proliferation. Moreover, A2780/HPR cells treated with a SK inhibitor were sensitized to the cytotoxic effect of HPR, due to an increased dihydroceramide production. On the other hand, the ectopic expression of SK-1 in A2780 cells was sufficient to induce HPR resistance in these cells. Challenge of A2780 and A2780/HPR cells with agonists and antagonists of S1P receptors had no effects on their sensitivity to the drug, suggesting that the role of SK in HPR resistance in these cells is not mediated by the S1P receptors. These data clearly demonstrate a role for SK in determining resistance to HPR in ovarian carcinoma cells, due to its effect in the regulation of intracellular ceramide/S1P ratio, which is critical in the control of cell death and proliferation.

The roles of bioactive sphingolipids in resveratrol-induced apoptosis in HL60: acute myeloid leukemia cells

PURPOSE

Acute promyelocytic leukemia results from a translocation between 15 and 17 chromosomes that produce PML/RARα fusion protein. PML/RARα inhibits differentiation of myeloid precursor cells at stem cell level. Resveratrol is a phytoalexin that exerts cytotoxic effects on cancer cells. Ceramides have crucial roles in cell growth, proliferation, differentiation, drug resistance, and apoptosis. In this study, we examined the possible cytotoxic effects of resveratrol on acute myeloid leukemia cells and determined the roles of ceramide-metabolizing genes in resveratrol-induced apoptosis, in addition to investigating the possibility of increasing the sensitivity of HL60 cells to resveratrol by manipulating sphingolipids.

METHODS

Cytotoxic effects of resveratrol, C8:ceramide, PDMP, and SK-1 inhibitor were determined by XTT cell proliferation assay. Changes in caspase-3 enzyme activity and mitochondrial membrane potential (MMP) were measured using caspase-3 colorimetric assay and JC-1 MMP detection kit. Expression levels of ceramide-metabolizing genes were examined by RT-PCR.

RESULTS

The results revealed that manipulations of ceramide metabolism toward generation or accumulation of apoptotic ceramides increased apoptotic effects of resveratrol in HL60 cells, synergistically. More importantly, gene expression analyses revealed that resveratrol-induced apoptosis via increasing expression levels of ceramide-generating genes and decreasing expression levels of antiapoptotic sphingosine kinase-1 and glucosylceramide synthase genes.

CONCLUSION

These results showed for the first time that increasing intracellular levels of ceramides by biochemical approaches has also increased sensitivity of HL60 cells to resveratrol. We also showed that resveratrol induces apoptosis through manipulating ceramide-metabolizing genes that resulted in the accumulation of ceramides in HL60 cells.

Metabolism of short-chain ceramide by human cancer cells--implications for therapeutic approaches

Due to recent use of short-chain ceramides in preclinical studies, we characterized C6-ceramide metabolism in cancer cell lines and assessed metabolic junctures for enhancing efficacy. MDA-MB-231 breast cancer cells decreased the amount of C6-ceramide metabolized to C6-sphingomyelin (C6-SM) and increased the amount metabolized to C6-glucosylceramide (C6-GC) in response to increasing concentrations. A similar trend was seen in DU-145 (prostate cancer), PANC-1 (pancreatic cancer), and LoVo (colorectal cancer) cells. KG-1 leukemia cells favored C6-SM synthesis at low (0.6muM) and high-dose (12muM) C6-ceramide. Partnering C6-ceramide with tamoxifen, a P-glycoprotein antagonist that impedes ceramide glycosylation, was an effective regimen for enhancing cytotoxicity in cells. Experiments to assess the mechanism of cell death using KG-1 cells showed that tamoxifen inhibited synthesis of C6-GC and C6-SM from C6-ceramide by 80% and 50%, respectively, which was accompanied by enhanced apoptosis. Radiolabeling of KG-1 cells with [(3)H]palmitic acid produced a 2-fold increase in (3)H-long-chain ceramides when unlabeled C6-ceramide was added and a 9-fold increase when C6-ceramide and tamoxifen were added. The increase in (3)H-palmitate radiolabeling of long-chain ceramides was blocked by inclusion of a ceramide synthase inhibitor; however, inhibiting synthesis of long-chain ceramide did not rescue cells. These studies show that tamoxifen enhances the apoptotic effects of C6-ceramide. The proposed mechanism involves blocking short-chain ceramide anabolism to favor hydrolysis and generation of sphingosine. We propose that use of tamoxifen and other P-glycoprotein antagonists can be an effective means for enhancing cytotoxic potential of short-chain ceramides in the treatment of cancer.

Ceramide and ceramide 1-phosphate in health and disease

Sphingolipids are essential components of cell membranes, and many of them regulate vital cell functions. In particular, ceramide plays crucial roles in cell signaling processes. Two major actions of ceramides are the promotion of cell cycle arrest and the induction of apoptosis. Phosphorylation of ceramide produces ceramide 1-phosphate (C1P), which has opposite effects to ceramide. C1P is mitogenic and has prosurvival properties. In addition, C1P is an important mediator of inflammatory responses, an action that takes place through stimulation of cytosolic phospholipase A2, and the subsequent release of arachidonic acid and prostaglandin formation. All of the former actions are thought to be mediated by intracellularly generated C1P. However, the recent observation that C1P stimulates macrophage chemotaxis implicates specific plasma membrane receptors that are coupled to Gi proteins. Hence, it can be concluded that C1P has dual actions in cells, as it can act as an intracellular second messenger to promote cell survival, or as an extracellular receptor agonist to stimulate cell migration.

Glycosphingolipids--nature, function, and pharmacological modulation

The discovery of the glycosphingolipids is generally attributed to Johan L. W. Thudichum, who in 1884 published on the chemical composition of the brain. In his studies he isolated several compounds from ethanolic brain extracts which he coined cerebrosides. He subjected one of these, phrenosin (now known as galactosylceramide), to acid hydrolysis, and this produced three distinct components. One he identified as a fatty acid and another proved to be an isomer of D-glucose, which is now known as D-galactose. The third component, with an "alkaloidal nature", presented "many enigmas" to Thudichum, and therefore he named it sphingosine, after the mythological riddle of the Sphinx. Today, sphingolipids and their glycosidated derivatives are the subjects of intense study aimed at elucidating their role in the structural integrity of the cell membrane, their participation in recognition and signaling events, and in particular their involvement in pathological processes that are at the basis of human disease (for example, sphingolipidoses and diabetes type 2). This Review details some of the recent findings on the biosynthesis, function, and degradation of glycosphingolipids in man, with a focus on the glycosphingolipid glucosylceramide. Special attention is paid to the clinical relevance of compounds directed at interfering with the factors responsible for glycosphingolipid metabolism.

Mechanisms of multidrug resistance in cancer

The development of multidrug resistance (MDR) to chemotherapy remains a major challenge in the treatment of cancer. Resistance exists against every effective anticancer drug and can develop by numerous mechanisms including decreased drug uptake, increased drug efflux, activation of detoxifying systems, activation of DNA repair mechanisms, evasion of drug-induced apoptosis, etc. In the first part of this chapter, we briefly summarize the current knowledge on individual cellular mechanisms responsible for MDR, with a special emphasis on ATP-binding cassette transporters, perhaps the main theme of this textbook. Although extensive work has been done to characterize MDR mechanisms in vitro, the translation of this knowledge to the clinic has not been crowned with success. Therefore, identifying genes and mechanisms critical to the development of MDR in vivo and establishing a reliable method for analyzing clinical samples could help to predict the development of resistance and lead to treatments designed to circumvent it. Our thoughts about translational research needed to achieve significant progress in the understanding of this complex phenomenon are therefore discussed in a third section. The pleotropic response of cancer cells to chemotherapy is summarized in a concluding diagram.

Lipid-based biomarkers for cancer

Lipids play important and diverse roles in cells. Most obvious functions are storage of chemical energy, provision of structural support of biological membranes and signaling. All these cellular processes are of critical relevance to cells which undergo transformation, cancer progression and metastasis. Thus, it is likely that certain classes of lipids are reflective for the cellular physiology in cancer cells and tissue. Here we discuss key roles of lipids involved in cancer as well as challenges for development of novel lipid-based biomarkers. Special emphasis will be given to mass spectrometry based analysis of lipids. Such technology has been successfully used for qualitative and quantitative analysis of lipids with very different chemistries. Comparative analysis, often in case-control regimes, and either in non-targeted (e.g. by liquid chromatography-single stage mass spectrometry) or targeted (i.e. by tandem mass spectrometry) fashion yields vast arrays of information. Uni-variate (such as Student's t-test or Mann-Whitney U-test) and multivariate statistics (principal components analysis, machine learning and regression analysis) are next used to identify variations in individual lipid species and/or to lower dimensions for visualization and grouping of cases and controls. As a result surrogate (single or multi-parameter) markers are identified which form the basis for functional validation as well as potential translation to alternative analytical readouts.

Glycolipid acquisition by human glycolipid transfer protein dramatically alters intrinsic tryptophan fluorescence: insights into glycolipid binding affinity

Glycolipid transfer proteins (GLTPs) are small, soluble proteins that selectively accelerate the intermembrane transfer of glycolipids. The GLTP fold is conformationally unique among lipid binding/transfer proteins and serves as the prototype and founding member of the new GLTP superfamily. In the present study, changes in human GLTP tryptophan fluorescence, induced by membrane vesicles containing glycolipid, are shown to reflect glycolipid binding when vesicle concentrations are low. Characterization of the glycolipid-induced "signature response," i.e. approximately 40% decrease in Trp intensity and approximately 12-nm blue shift in emission wavelength maximum, involved various modes of glycolipid presentation, i.e. microinjection/dilution of lipid-ethanol solutions or phosphatidylcholine vesicles, prepared by sonication or extrusion and containing embedded glycolipids. High resolution x-ray structures of apo- and holo-GLTP indicate that major conformational alterations are not responsible for the glycolipid-induced GLTP signature response. Instead, glycolipid binding alters the local environment of Trp-96, which accounts for approximately 70% of total emission intensity of three Trp residues in GLTP and provides a stacking platform that aids formation of a hydrogen bond network with the ceramide-linked sugar of the glycolipid headgroup. The changes in Trp signal were used to quantitatively assess human GLTP binding affinity for various lipids including glycolipids containing different sugar headgroups and homogenous acyl chains. The presence of the glycolipid acyl chain and at least one sugar were essential for achieving a low-to-submicromolar dissociation constant that was only slightly altered by increased sugar headgroup complexity.

Glucosylceramide synthase inhibitors sensitise CLL cells to cytotoxic agents without reversing P-gp functional activity

Malignant B-cells from most chronic lymphocytic leukaemia (CLL) patients over-express MDR1 encoded P-glycoprotein (P-gp) multidrug efflux pump. Inhibition of glucosylceramide (GC) synthesis has been shown in cell lines to correlate with the expression and function of P-gp and sensitise cancer cells to cytotoxic agents. We investigated the hypothesis that reducing intracellular GC levels will reduce P-gp expression in malignant cells from CLL patients. We studied the ability of glucosylceramide synthase (GCS) inhibitors N-butyl-deoxygalactonojirimycin (OGB-1) and N-nonyl-deoxygalactonojirimycin (OGB-2) to sensitise CLL cells to conventional cytotoxic drug 2-chlorodeoxyadenosine (CdA) and the cytostatic drugs chlorambucil and fludarabine. The effect on P-gp activity was analysed using the calcein-AM accumulation assay where a multidrug activity factor (MAF) of >10 in the presence of a P-gp inhibitor denotes P-gp functional activity. The P-gp over-expressing cell line CEM-VLB showed a MAF value of 96.4 with the P-gp inhibitor Z.3HCL, which fell to 15.7 after co-incubation with OGB-1 and 45.9 with OGB-2. The IC(50) for vincristine fell from >10 microg/ml to 55.5 ng/ml in the presence of OGB-2. In P-gp(+ve) peripheral blood mononuclear cells from three normal volunteers, the mean MAF values for Z.3HCL, OGB-1 and OGB-2 were 23.86, 1.83 and 16.2 respectively. In 9/13 CLL samples the mean P-gp functional activity was 22.15 and P-gp was over-expressed in 12/13 samples. However, the MAF value with OGB-1 and OGB-2 was <10. Nevertheless, sensitisation in CLL cells was observed by a reduction in the IC(50) in the presence of OGB-1 and OGB-2 with the conventional drugs. We conclude that although GCS inhibitors sensitize CLL cells to cytotoxic and cytostatic drugs, they do not appear to have any effect on P-gp functional activity.

Gene expression of ceramide kinase, galactosyl ceramide synthase and ganglioside GD3 synthase is associated with prognosis in breast cancer

PURPOSE

Sphingolipids are bioactive lipids implicated in apoptosis, cell survival and proliferation. We analyzed the prognostic value of enzymes from sphingolipid metabolism in breast cancer.

METHODS

Differences in expression of ceramide galactosyl transferase (UGT8), ceramide kinase (CERK), and Ganglioside GD3-Synthase (ST8SIA1) in breast cancer cells were investigated by using microarray data of 1,581 tumor samples.

RESULTS

UGT8, CERK, and ST8SIA1 were associated with poor pathohistological grading (P < 0.001). High CERK expression was correlated with ErbB2 status (P = 0.006). Among ER positive breast cancers a significant worse prognosis for patients with tumors showing low ST8SIA1 and UGT8 expression was observed. In the ER negative subgroup those samples with high CERK expression displayed a worse prognosis. In a multivariate analysis only ST8SIA1 and tumor size remained significant.

CONCLUSIONS

Our experiments reveal that expression of enzymes from the sphingolipid metabolism has prognostic implications in breast cancer.

Coordinate control of lipid composition and drug transport activities is required for normal multidrug resistance in fungi

Pathogenic fungi present a special problem in the clinic as the range of drugs that can be used to treat these types of infections is limited. This situation is further complicated by the presence of robust inducible gene networks encoding different proteins that confer tolerance to many available antifungal drugs. The transcriptional control of these multidrug resistance systems in several key fungi will be discussed. Experiments in the non-pathogenic Saccharomyces cerevisiae have provided much of our current understanding of the molecular framework on which fungal multidrug resistance is built. More recent studies on the important pathogenic Candida species, Candida albicans and Candida glabrata, have provided new insights into the organization of the multidrug resistance systems in these organisms. We will compare the circuitry of multidrug resistance networks in these three organisms and suggest that, in addition to the well-accepted drug efflux activities, the regulation of membrane composition by multidrug resistance proteins provides an important contribution to the resistant phenotypes observed.

Roles of bioactive sphingolipids in cancer biology and therapeutics

In this chapter, roles of bioactive sphingolipids in the regulation of cancer pathogenesis and therapy will be reviewed. Sphingolipids have emerged as bioeffector molecules, which control various aspects of cell growth, proliferation, and anti-cancer therapeutics. Ceramide, the central molecule of sphingolipid metabolism, generally mediates anti-proliferative responses such as inhibition of cell growth, induction of apoptosis, and/or modulation of senescence. On the other hand, sphingosine 1-phosphate (S1P) plays opposing roles, and induces transformation, cancer cell growth, or angiogenesis. A network of metabolic enzymes regulates the generation of ceramide and S1P, and these enzymes serve as transducers of sphingolipid-mediated responses that are coupled to various exogenous or endogenous cellular signals. Consistent with their key roles in the regulation of cancer growth and therapy, attenuation of ceramide generation and/or increased S1P levels are implicated in the development of resistance to drug-induced apoptosis, and escape from cell death. These data strongly suggest that advances in the molecular and biochemical understanding of sphingolipid metabolism and function will lead to the development of novel therapeutic strategies against human cancers, which may also help overcome drug resistance.

Calcium phosphate nanocomposite particles for in vitro imaging and encapsulated chemotherapeutic drug delivery to cancer cells

Paradigm-shifting modalities to more efficiently deliver drugs to cancerous lesions require the following attributes: nanoscale-size, targetability, and stability under physiological conditions. Often, these nanoscale drug delivery vehicles are limited due to agglomeration, poor solubility, or cytotoxicity. Thus, we have designed a methodology to encapsulate hydrophobic antineoplastic chemotherapeutics within a 20-30 nm diameter, pH-responsive, nonagglomerating, nontoxic calcium phosphate nanoparticle matrix. In the present study, we report on calcium phosphate nanocomposite particles (CPNPs) that encapsulate both fluorophores and chemotherapeutics, are colloidally stable in physiological solution for an extended time at 37 degrees C and can efficaciously deliver hydrophobic antineoplastic agents, such as ceramide, in several cell model systems.

N-(4-Hydroxyphenyl)retinamide increases dihydroceramide and synergizes with dimethylsphingosine to enhance cancer cell killing

Fenretinide [N-(4-hydroxyphenyl)retinamide (4-HPR)] is cytotoxic in many cancer cell types. Studies have shown that elevation of ceramide species plays a role in 4-HPR cytotoxicity. To determine 4-HPR activity in a multidrug-resistant cancer cell line as well as to study ceramide metabolism, MCF-7/AdrR cells (redesignated NCI/ADR-RES) were treated with 4-HPR and sphingolipids were analyzed. TLC analysis of cells radiolabeled with [3H]palmitic acid showed that 4-HPR elicited a dose-responsive increase in radioactivity migrating in the ceramide region of the chromatogram and a decrease in cell viability. Results from liquid chromatography/electrospray tandem mass spectrometry revealed large elevations in dihydroceramides (N-acylsphinganines), but not desaturated ceramides, and large increases in complex dihydrosphingolipids (dihydrosphingomyelins, monohexosyldihydroceramides), sphinganine, and sphinganine 1-phosphate. To test the hypothesis that elevation of sphinganine participates in the cytotoxicity of 4-HPR, cells were treated with the sphingosine kinase inhibitor d-erythro-N,N-dimethylsphingosine (DMS), with and without 4-HPR. After 24 h, the 4-HPR/DMS combination caused a 9-fold increase in sphinganine that was sustained through +48 hours, decreased sphinganine 1-phosphate, and increased cytotoxicity. Increased dihydrosphingolipids and sphinganine were also found in HL-60 leukemia cells and HT-29 colon cancer cells treated with 4-HPR. The 4-HPR/DMS combination elicited increased apoptosis in all three cell lines. We propose that a mechanism of 4-HPR-induced cytotoxicity involves increases in dihydrosphingolipids, and that the synergy between 4-HPR and DMS is associated with large increases in cellular sphinganine. These studies suggest that enhanced clinical efficacy of 4-HPR may be realized through regimens containing agents that modulate sphingoid base metabolism.

C(6)-Ceramide-Coated Catheters Promote Re-Endothelialization of Stretch-Injured Arteries

OBJECTIVE: Drug eluting stents have recently been associated with the increased risk of adverse thrombogenic events and/or late luminal loss, which is highly associated with incomplete re-endothelialization. The increased risks behoove the design of alternative delivery modalities and/or drugs that do not compromise the re-endotheliaization process. The objective of the present study is to elucidate the biological mechanism(s) by which non-stent-based delivery modalities for the anti-proliferative lipid metabolite, C(6)-ceramide, could lead to a reduction in arterial injury after angioplasty. RESULTS: Immunohistochemical studies in rabbit and porcine models suggest that C(6)-ceramide-coated balloon catheters limit arterial stenosis without inhibiting endothelial wound healing responses. Specifically, C(6)-ceramide-coated balloon catheters reduce internal elastica injury with a corresponding reduction in medial fracture length in a 28-day porcine coronary artery stretch model. In addition, C(6)-ceramide decreases the formation of the fibrin matrix to possibly augment the subsequent wound healing response. We hypothesized that differential metabolism of exogenous ceramide by coronary endothelial and smooth muscle cells could explain the apparent discrepancy between the anti-proliferative actions of ceramide and the pro-wound healing responses of ceramide. Human coronary artery endothelial cells (HCAEC), in contrast to human coronary artery smooth muscle cells (HCASMC), preferentially express ceramide kinase and form ceramide-1-phosphate, which promotes endothelial cell survival. CONCLUSION: Differential metabolism of ceramide between HCASMC and HCAEC offers a mechanism by which ceramide preferentially limits smooth muscle cell growth, in the presence of active wound healing. The combinatorial ability of ceramide to limit vascular smooth muscle proliferation and promote re-endothelialization, offers the potential for C(6)-ceramide-coated catheters to serve as adjuncts to stent-based modalities or as a stand-alone treatment.

Prognostic relevance of glucosylceramide synthase (GCS) expression in breast cancer

PURPOSE

Multidrug resistance (MDR) has been linked to sphingolipid metabolism and preclinical data ascribe glucosylceramide synthase (GCS) a major role for MDR especially in breast cancer cells but no profound data are available on the expression of this potential therapeutic target in clinical breast cancer specimens.

METHODS

We analyzed microarray data of GCS expression in a large cohort of 1,681 breast tumors.

RESULTS

Expression of GCS was associated with a positive estrogen receptor (ER) status, lower histological grading, low Ki67 levels and ErbB2 negativity (P < 0.001 for all). In univariate analysis there was a benefit for disease free survival for patients with tumors displaying low levels of GCS expression but this significance was lost in multivariate Cox regression.

CONCLUSIONS

Our results suggest ER positive tumors may be the most promising candidates for a potential therapeutic application of GCS inhibitors.

Gaucher disease: unmet treatment needs

Gaucher disease is a multisystemic metabolic disorder arising from a deficiency of lysosomal glucocerebrosidase. The predominant clinical manifestations of the disease are hepatosplenomegaly, peripheral blood cytopenias and skeletal disease. Treatment with enzyme replacement therapy (ERT) and substrate reduction therapy (SRT) has been shown to be effective in improving organ volume, anaemia, thrombocytopenia, bone markers and biomarkers in patients with Gaucher disease. However, some patient needs remain unmet because of the limited availability of treatment, the inaccessibility of certain disease sites and emerging disease manifestations. An increase in haematological, lymphoreticular and immune system malignancies has been observed in patients with Gaucher disease, but mechanisms underlying the development of these are not fully understood. Mild neurological manifestations may also affect patients with type 1 Gaucher disease, but treatment with ERT or SRT does not improve neurological function. Potential new treatments for Gaucher disease include small molecules, which may penetrate tissues that are not accessible by ERT.

CONCLUSION

ERT currently remains the most effective treatment for Gaucher disease. New treatments are emerging, but deficiencies in understanding basic pathophysiological mechanisms hinder progress.

Principles of bioactive lipid signalling: lessons from sphingolipids

It has become increasingly difficult to find an area of cell biology in which lipids do not have important, if not key, roles as signalling and regulatory molecules. The rapidly expanding field of bioactive lipids is exemplified by many sphingolipids, such as ceramide, sphingosine, sphingosine-1-phosphate (S1P), ceramide-1-phosphate and lyso-sphingomyelin, which have roles in the regulation of cell growth, death, senescence, adhesion, migration, inflammation, angiogenesis and intracellular trafficking. Deciphering the mechanisms of these varied cell functions necessitates an understanding of the complex pathways of sphingolipid metabolism and the mechanisms that regulate lipid generation and lipid action.

Human glycolipid transfer protein (GLTP) genes: organization, transcriptional status and evolution

BACKGROUND

Glycolipid transfer protein is the prototypical and founding member of the new GLTP superfamily distinguished by a novel conformational fold and glycolipid binding motif. The present investigation provides the first insights into the organization, transcriptional status, phylogenetic/evolutionary relationships of GLTP genes.

RESULTS

In human cells, single-copy GLTP genes were found in chromosomes 11 and 12. The gene at locus 11p15.1 exhibited several features of a potentially active retrogene, including a highly homologous (approximately 94%), full-length coding sequence containing all key amino acid residues involved in glycolipid liganding. To establish the transcriptional activity of each human GLTP gene, in silico EST evaluations, RT-PCR amplifications of GLTP transcript(s), and methylation analyses of regulator CpG islands were performed using various human cells. Active transcription was found for 12q24.11 GLTP but 11p15.1 GLTP was transcriptionally silent. Heterologous expression and purification of the GLTP paralogs showed glycolipid intermembrane transfer activity only for 12q24.11 GLTP. Phylogenetic/evolutionary analyses indicated that the 5-exon/4-intron organizational pattern and encoded sequence of 12q24.11 GLTP were highly conserved in therian mammals and other vertebrates. Orthologs of the intronless GLTP gene were observed in primates but not in rodentiates, carnivorates, cetartiodactylates, or didelphimorphiates, consistent with recent evolutionary development.

CONCLUSION

The results identify and characterize the gene responsible for GLTP expression in humans and provide the first evidence for the existence of a GLTP pseudogene, while demonstrating the rigorous approach needed to unequivocally distinguish transcriptionally-active retrogenes from silent pseudogenes. The results also rectify errors in the Ensembl database regarding the organizational structure of the actively transcribed GLTP gene in Pan troglodytes and establish the intronless GLTP as a primate-specific, processed pseudogene marker. A solid foundation has been established for future identification of hereditary defects in human GLTP genes.

Recent advances on the molecular mechanisms involved in the drug resistance of cancer cells and novel targeting therapies

This review summarizes the recent knowledge obtained on the molecular mechanisms involved in the intrinsic and acquired resistance of cancer cells to current cancer therapies. We describe the cascades that are often altered in cancer cells during cancer progression that may contribute in a crucial manner to drug resistance and disease relapse. The emphasis is on the implication of ATP-binding cassette (ABC) multidrug efflux transporters in drug disposition and antiapoptotic factors, including epidermal growth factor receptor cascades and deregulated enzymes in ceramide metabolic pathways. The altered expression and activity of these signaling elements may have a critical role in the resistance of cancer cells to cytotoxic effects induced by diverse chemotherapeutic drugs and cancer recurrence. Of therapeutic interest, new strategies for reversing the multidrug resistance and developing more effective clinical treatments against the highly aggressive, metastatic, and recurrent cancers, based on the molecular targeting of the cancer progenitor cells and their further differentiated progeny, are also described.

Translational aspects of sphingolipid metabolism

Sphingolipids, a major class of lipids in cell membranes, play diverse roles in biological processes. As bioactive and structural molecules, they have signaling activities and biophysical properties that are essential for regulating various cellular, tissue and systemic functions. Moreover, sphingolipids are receiving increasing attention as contributors to the pathogenesis of several human disorders, including, cancer, inflammation and neurological, immune and metabolic disorders. Small-molecule inhibitors and monoclonal antibodies that target sphingolipid metabolism recently enabled giant strides toward treatment of malignant and autoimmune disorders. Here, we review the emerging roles of sphingolipids in disease pathogenesis and the attendant possibilities for sphingolipid-based therapeutics.