An increase in glucosylceramide synthase induces Bcl-xL-mediated cell survival in vinorelbine-resistant lung adenocarcinoma cells

A comprehensive measure of Golgi sphingolipid flux using NBD C6-Ceramide: evaluation of sphingolipid inhibitors

Measurements of sphingolipid metabolism are most accurately performed by liquid chromatography-mass spectrometry. However, this technique is expensive, not widely accessible, and without the use of specific probes, it does not provide insight into metabolic flux through the pathway. Employing the fluorescent ceramide analogue NBD-C6-ceramide as a tracer in intact cells, we developed a comprehensive HPLC-based method that simultaneously measures the main nodes of ceramide metabolism in the Golgi. Hence, by quantifying the conversion of NBD-C6-Ceramide to NBD-C6-sphingomyelin, NBD-C6-Hexosylceramides, and NBD-C6-ceramide-1-phosphate (NBD-C1P), the activities of Golgi resident enzymes sphingomyelin synthase 1, glucosylceramide synthase, and ceramide kinase (CERK) could be measured simultaneously. Importantly, the detection of NBD-C1P allowed us to quantify CERK activity in cells, a usually difficult task. By applying this method, we evaluated the specificity of commonly used sphingolipid inhibitors and discovered that PDMP, which targets glucosylceramide synthase, and fenretinide (4HPR), an inhibitor for dihydroceramide desaturase, also suppress CERK activity. This study demonstrates the benefit of an expanded analysis of ceramide metabolism in the Golgi, and it provides a qualitative and easy-to-implement method.

Targeting glucosylceramide synthase induces antiproliferative and proapoptotic effects in osimertinib-resistant NSCLC cell models

The EGFR tyrosine kinase inhibitor osimertinib has been approved for the first-line treatment of EGFR-mutated Non-Small Cell Lung Cancer (NSCLC) patients. Despite its efficacy, patients develop resistance. Mechanisms of resistance are heterogeneous and not fully understood, and their characterization is essential to find new strategies to overcome resistance. Ceramides are well-known regulators of apoptosis and are converted into glucosylceramides (GlcCer) by glucosylceramide synthase (GCS). A higher content of GlcCers was observed in lung pleural effusions from NSCLC patients and their role in osimertinib-resistance has not been documented. The aim of this study was to determine the therapeutic potential of inhibiting GCS in NSCLC EGFR-mutant models resistant to osimertinib in vitro and in vivo. Lipidomic analysis showed a significant increase in the intracellular levels of glycosylceramides, including GlcCers in osimertinib resistant clones compared to sensitive cells. In resistant cells, the GCS inhibitor PDMP caused cell cycle arrest, inhibition of 2D and 3D cell proliferation, colony formation and migration capability, and apoptosis induction. The intratumoral injection of PDMP completely suppressed the growth of OR xenograft models. This study demonstrated that dysregulation of ceramide metabolism is involved in osimertinib-resistance and targeting GCS may be a promising therapeutic strategy for patients progressed to osimertinib.

Inhibition of Ceramide Glycosylation Enhances Cisplatin Sensitivity in Cholangiocarcinoma by Limiting the Activation of the ERK Signaling Pathway

Cholangiocarcinoma (CCA) is an aggressive tumor of the biliary epithelium with poor survival that shows limited response to conventional chemotherapy. Increased expression of glucosylceramide synthase (GCS) contributes to drug resistance and the progression of various cancers; the expression profiles of GCS (UGCG) and the genes for glucocerebrosidases 1, 2, and 3 (GBA1, GBA2, and GBA3) were therefore studied in CCA. The biological functions of GCS for cell proliferation and cisplatin sensitivity in CCA were explored. GCS expression was higher in CCA tumor tissues than that of GBA1, GBA2, and GBA3. Verification of GCS expression in 29 paired frozen CCA tissues showed that 8 of 29 cases (27.6%) had high GCS expression. The expression of GCS and GBA2 was induced in CCA cell lines following low-dose cisplatin treatment. Suppression of GCS by either palmitoylamino-3-morpholino-1-propanol (PPMP), GCS knockdown or a combination of the two resulted in reduced cell proliferation. These treatments enhanced the effect of cisplatin-induced CCA cell death, increased the expression of apoptotic proteins and reduced phosphorylation of ERK upon cisplatin treatment. Taken together, inhibition of the GCS increased cisplatin-induced CCA apoptosis via the inhibition of the ERK signaling pathway. Thus, targeting GCS might be a strategy for CCA treatment.

The Enhanced Efficacy of Intracellular Delivery of Doxorubicin/C6-Ceramide Combination Mediated by the F3 Peptide/Nucleolin System Is Supported by the Downregulation of the PI3K/Akt Pathway

Simple Summary

Targeted nanomedicine-based approaches that aim at the simultaneous delivery of synergistic drug combinations to multiple cellular populations are of high relevance for tackling heterogeneity on solid tumors. Considering that cancer stem cells (CSC) may originate from non-stem cancer cells, single-drug regimens targeting only one of these cell populations could enable tumors to evade treatments. As such, the identification of a common marker, such as nucleolin, might result in a therapeutic advantage. The results herein generated suggested a transversal role of nucleolin in the internalization of F3 peptide-targeted pegylated pH-sensitive liposomes into bulk ovarian cancer cells, including putative CSC-enriched ovarian cells. The intracellular delivery of a drug combination such as the one tested herein was relevant in the context of cell lines with higher intrinsic resistances to doxorubicin. The enhanced efficacy of the F3 peptide-targeted liposomal combination of doxorubicin/C6-ceramide was supported by the downregulation of the Akt pathway, within a specific range of basal level of expression.

Abstract

Targeting multiple cellular populations is of high therapeutic relevance for the tackling of solid tumors heterogeneity. Herein, the ability of pegylated and pH-sensitive liposomes, functionalized with the nucleolin-binding F3 peptide and containing doxorubicin (DXR)/C6-ceramide synergistic combination, to target, in vitro, ovarian cancer, including ovarian cancer stem cells (CSC), was assessed. The underlying molecular mechanism of action of the nucleolin-mediated intracellular delivery of C6-ceramide to cancer cells was also explored. The assessment of overexpression of surface nucleolin expression by flow cytometry was critical to dissipate differences identified by Western blot in membrane/cytoplasm of SKOV-3, OVCAR-3 and TOV-112D ovarian cancer cell lines. The former was in line with the significant extent of uptake into (bulk) ovarian cancer cells, relative to non-targeted and non-specific counterparts. This pattern of uptake was recapitulated with putative CSC-enriched ovarian SKOV-3 and OVCAR-3 sub-population (EpCAM^high/CD44^high). Co-encapsulation of DXR:C6-ceramide into F3 peptide-targeted liposomes improved cytotoxic activity relative to liposomes containing DXR alone, in an extent that depended on the intrinsic resistance to DXR and on the incubation time. The enhanced cytotoxicity of the targeted combination was mechanistically supported by the downregulation of PI3K/Akt pathway by C6-ceramide, only among the nucleolin-overexpressing cancer cells presenting a basal p-Akt/total Akt ratio lower than 1.

The Phenoxyphenol Compound diTFPP Mediates Exogenous C2-Ceramide Metabolism, Inducing Cell Apoptosis Accompanied by ROS Formation and Autophagy in Hepatocellular Carcinoma Cells

Hepatocellular carcinoma (HCC) is a severe disease that accounts for 80% of liver cancers. Chemotherapy is the primary therapeutic strategy for patients who cannot be treated with surgery or who have late-stage HCC. C₂-ceramide is an effective reagent that has been found to inhibit the growth of many cancer types. The metabolism of C₂-ceramide plays a vital role in the regulation of cell death/cell survival. The phenoxyphenol compound 4-{2,3,5,6-tetrafluoro-4-[2,3,5,6-tetrafluoro-4-(4-hydroxyphenoxy)phenyl]phenoxy}phenol (diTFPP) was found to have a synergistic effect with C₂-ceramide, resulting in considerable cell death in the HA22T HCC cell line. diTFPP/C₂-ceramide cotreatment induced a two- to threefold increase in cell death compared to that with C2-ceramide alone and induced pyknosis. Annexin V/7-aminoactinomycin D (7AAD) double staining and Western blotting indicated that apoptosis was involved in diTFPP/C₂-ceramide cotreatment-mediated cell death. We next analyzed transcriptome alterations in diTFPP/C₂-ceramide-cotreated HA22T cells with next-generation sequencing (NGS). The data indicated that diTFPP treatment disrupted sphingolipid metabolism, inhibited cell cycle-associated gene expression, and induced autophagy and reactive oxygen species (ROS)-responsive changes in gene expression. Additionally, we assessed the activation of autophagy with acridine orange (AO) staining and observed alterations in the expression of the autophagic proteins LC3B-II and Beclin-1, which indicated autophagy activation after diTFPP/C₂-ceramide cotreatment. Elevated levels of ROS were also reported in diTFPP/C₂-ceramide-treated cells, and the expression of the ROS-associated proteins SOD1, SOD2, and catalase was upregulated after diTFPP/C₂-ceramide treatment. This study revealed the potential regulatory mechanism of the novel compound diTFPP in sphingolipid metabolism by showing that it disrupts ceramide metabolism and apoptotic sphingolipid accumulation.

Fluorescence HPLC Analysis of the in-vivo Activity of Glucosylceramide Synthase

Almost all functions of cells or organs rely on the activities of cellular enzymes. Indeed, the in-vivo activities that directly represent the cellular effects of enzymes in live organs are critical importance to appreciate the roles enzymes play in modulating physiological or pathological processes, although assessments of such in-vivo enzyme activity are more difficult than typical test-tube assays. Recently, we, for the first time, developed a direct and easy-handling method for HPLC analyzing the in-vivo activity of glucosylceramide synthase (GCS). GCS that converts ceramide into glucosylceramide is a limiting-enzyme in the syntheses of glycosphingolipids and is one cause of cancer drug resistance. In our method developed, rubusoside nanomicelles delivers fluorescence N-[6-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]hexanoyl]-d-erythro-sphingosine (NBD C₆-ceramide) into mice, tissues uptake the cell-permeable substrate, and GCS converts it into NBD C₆-glucosylceramide in all organs simultaneously. Further, HPLC analyzes the extracted NBD C₆-glucosylceramide to assess alterations of the in-vivo GCS activities in tissues. This method can be broadly used to assess the in-vivo GCS activities in any kind of animal models to appreciate either the role GCS plays in diseases or the therapeutic efficacies of GCS inhibitors.

Autophagy regulates vinorelbine sensitivity due to continued Keap1-mediated ROS generation in lung adenocarcinoma cells

Autophagy is one of the induced mechanisms in metastatic cancer to escape death due to starvation, hypoxia, metabolic stresses, chemotherapy, and radiation. Some publications have revealed that chemotherapy combined with autophagy inhibitor will overcome drug resistance. We modified AS2 cells with PTEN overexpression, mTOR knockdown, or Keap1 knockdown, and made modification of A549 cells with PTEN knockdown, Atg5 knockdown, and Keap1 overexpression. Our study was aimed toward an exploration of how autophagy modulates Keap1, ROS generation, and vinorelbine-induced apoptosis in these cell lines. We found that lung cancer PC14PE6/AS2 (AS2) had higher mTOR and Akt and also lower PTEN expression than A549 cells. Descended autophagy was demonstrated with more decreased p62 accumulation and LC3 II conversion in AS2 cells as compared to A549 cells. The A549 cells had lower Keap1/Nrf2 and more active anti-oxidant response element (ARE) activity than the AS2 cells. We modified AS2 cells with PTEN overexpression, mTOR knockdown, Keap1 knockdown, and revealed amplified p62 and LC3 expression accompanied with decreased Akt, Keap1, ROS, and vinorelbine-induced apoptosis. Declined p62, LC3 expression were accompanied with increased Akt, Keap1, ROS, and vinorelbine-induced apoptosis after modification of A549 cells with PTEN knockdown, Atg5 knockdown, and Keap1 overexpression. Keap1 overexpression lowered ARE levels in A549 cells, and ARE level exhibited up-growth in Keap1 knockdown AS2 cells. The autophagy inhibitor caused more ROS generation and vinorelbine-induced apoptosis in the A549 and CL1-5 cells. According to these findings, autophagy regulates vinorelbine sensitivity by continuing Keap1-mediated ROS generation in lung adenocarcinoma cells.

It needs more evidence to prove that chemotherapy combined with autophagy inhibitor will overcome drug resistance. The pilot study demonstrated a VNR-sensitive strategy in lung adenocarcinoma cells, by which regulators of autophagy modulated Keap1-mediated ROS generation and VNR-induced apoptosis.

The UDP-glucose ceramide glycosyltransferase (UGCG) and the link to multidrug resistance protein 1 (MDR1)

The UDP-glucose ceramide glycosyltransferase (UGCG) is a key enzyme in the sphingolipid metabolism by generating glucosylceramide (GlcCer), the precursor for all glycosphingolipids (GSL), which are essential for proper cell function. Interestingly, the UGCG is also overexpressed in several cancer types and correlates with multidrug resistance protein 1 (MDR1) gene expression. This membrane protein is responsible for efflux of toxic substances and protects cancer cells from cell damage through chemotherapeutic agents. Studies showed a connection between UGCG and MDR1 overexpression and multidrug resistance development, but the precise underlying mechanisms are unknown. Here, we give an overview about the UGCG and its connection to MDR1 in multidrug resistant cells. Furthermore, we focus on UGCG transcriptional regulation, the impact of UGCG on cellular signaling pathways and the effect of UGCG and MDR1 on the lipid composition of membranes and how this could influence multidrug resistance development. To our knowledge, this is the first review presenting an overview about UGCG with focus on the relationship to MDR1 in the process of multidrug resistance development.

Effects of berberine, curcumin, resveratrol alone and in combination with chemotherapeutic drugs and signal transduction inhibitors on cancer cells-Power of nutraceuticals

Over the past fifty years, society has become aware of the importance of a healthy diet in terms of human fitness and longevity. More recently, the concept of the beneficial effects of certain components of our diet and other compounds, that are consumed often by different cultures in various parts of the world, has become apparent. These "healthy" components of our diet are often referred to as nutraceuticals and they can prevent/suppress: aging, bacterial, fungal and viral infections, diabetes, inflammation, metabolic disorders and cardiovascular diseases and have other health-enhancing effects. Moreover, they are now often being investigated because of their anti-cancer properties/potentials. Understanding the effects of various natural products on cancer cells may enhance their usage as anti-proliferative agents which may be beneficial for many health problems. In this manuscript, we discuss and demonstrate how certain nutraceuticals may enhance other anti-cancer drugs to suppress proliferation of cancer cells.

Incorporation of Fluorescence Ceramide-Based HPLC Assay for Rapidly and Efficiently Assessing Glucosylceramide Synthase In Vivo

Glucosylceramide synthase (GCS) is a rate-limiting enzyme catalyzing ceramide glycosylation, thereby regulating cellular ceramide levels and the synthesis of glycosphingolipids (GSLs) in cellular membranes. Alterations of GCS not only affect membrane integrity, but also closely correlate with stem cell pluripotency, cancer drug resistance, GSL storage disorders and other diseases. Enzyme activities measured conventionally with currently available ex-vivo methods do not enable reliable assessment of the roles played by GCS in vivo. We report herein a substrate-incorporation method enabling rapid and efficient assessment of GCS in-vivo activity. Upon nanoparticle-based delivery, fluorescent NBD C6-ceramide was efficiently converted to NBD C6-glucosylceramide in live cells or in mouse tissues, whereupon an HPLC assay enabled detection and quantification of NBD C6-glucosylceramide in the low-femtomolar range. The enzyme kinetics of GCS in live cells and mouse liver were well-described by the Michaelis-Menten model. GCS activities were significantly higher in drug-resistant cancer cells and in tumors overexpressing GCS, but reduced after silencing GCS expression or inhibiting this enzyme. Our studies indicate that this rapid and efficient method provides a valuable means for accurately assessing the roles played by GCS in normal vs. pathological states, including ones involving cancer drug resistance.

Targeting glucosylceramide synthase upregulation reverts sorafenib resistance in experimental hepatocellular carcinoma

Evasive mechanisms triggered by the tyrosine kinase inhibitor sorafenib reduce its efficacy in hepatocellular carcinoma (HCC) treatment. Drug-resistant cancer cells frequently exhibit sphingolipid dysregulation, reducing chemotherapeutic cytotoxicity via the induction of ceramide-degrading enzymes. However, the role of ceramide in sorafenib therapy and resistance in HCC has not been clearly established. Our data reveals that ceramide-modifying enzymes, particularly glucosylceramide synthase (GCS), are upregulated during sorafenib treatment in hepatoma cells (HepG2 and Hep3B), and more importantly, in sorafenib-resistant cell lines. GCS silencing or pharmacological GCS inhibition sensitized hepatoma cells to sorafenib exposure. GCS inhibition, combined with sorafenib, triggered cytochrome c release and ATP depletion in sorafenib-treated hepatoma cells, leading to mitochondrial cell death after energetic collapse. Conversely, genetic GCS overexpression increased sorafenib resistance. Of interest, GCS inhibition improved sorafenib effectiveness in a xenograft mouse model, recovering drug sensitivity of sorafenib-resistant tumors in mice. In conclusion, our results reveal GCS induction as a mechanism of sorafenib resistance, suggesting that GCS targeting may be a novel strategy to increase sorafenib efficacy in HCC management, and point to target the mitochondria as the subcellular location where sorafenib therapy could be potentiated.

YM155, a small molecule inhibitor of survivin expression, sensitizes cancer cells to hypericin-mediated photodynamic therapy

Here we show for the first time that the repression of survivin expression by YM155 is effective in sensitizing cancer cells to HY-PDT, as measured by the decrease in cell viability and induction of apoptosis.