Bcl-2 overexpression prevents apoptosis induced by ceramidase inhibitors in malignant melanoma and HaCaT keratinocytes

Therapeutic Potential for Sphingolipids in Inflammatory Bowel Disease and Colorectal Cancer

Inflammatory bowel disease (IBD), characterized by chronic inflammation in the intestinal tract, increases the risk for the development of colorectal cancer (CRC). Sphingolipids, which have been implicated in IBD and CRC, are a class of bioactive lipids that regulate cell signaling, differentiation, apoptosis, inflammation, and survival. The balance between ceramide (Cer), the central sphingolipid involved in apoptosis and differentiation, and sphingosine-1-phosphate (S1P), a potent signaling molecule involved in proliferation and inflammation, is vital for the maintenance of normal cellular function. Altered sphingolipid metabolism has been implicated in IBD and CRC, with many studies highlighting the importance of S1P in inflammatory signaling and pro-survival pathways. A myriad of sphingolipid analogues, inhibitors, and modulators have been developed to target the sphingolipid metabolic pathway. In this review, the efficacy and therapeutic potential for modulation of sphingolipid metabolism in IBD and CRC will be discussed.

Mysterious sphingolipids: metabolic interrelationships at the center of pathophysiology

Metabolic pathways are complex and intertwined. Deficiencies in one or more enzymes in a given pathway are directly linked with genetic diseases, most of them having devastating manifestations. The metabolic pathways undertaken by sphingolipids are diverse and elaborate with ceramide species serving as the hubs of sphingolipid intermediary metabolism and function. Sphingolipids are bioactive lipids that serve a multitude of cellular functions. Being pleiotropic in function, deficiency or overproduction of certain sphingolipids is associated with many genetic and chronic diseases. In this up-to-date review article, we strive to gather recent scientific evidence about sphingolipid metabolism, its enzymes, and regulation. We shed light on the importance of sphingolipid metabolism in a variety of genetic diseases and in nervous and immune system ailments. This is a comprehensive review of the state of the field of sphingolipid biochemistry.

Targeting acid ceramidase ameliorates fibrosis in mouse models of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is a common cause of liver disease worldwide, and is characterized by the accumulation of fat in the liver. Non-alcoholic steatohepatitis (NASH), an advanced form of NAFLD, is a leading cause of liver transplantation. Fibrosis is the histologic feature most associated with liver-related morbidity and mortality in patients with NASH, and treatment options remain limited. In previous studies, we discovered that acid ceramidase (aCDase) is a potent antifibrotic target using human hepatic stellate cells (HSCs) and models of hepatic fibrogenesis. Using two dietary mouse models, we demonstrate that depletion of aCDase in HSC reduces fibrosis without worsening metabolic features of NASH, including steatosis, inflammation, and insulin resistance. Consistently, pharmacologic inhibition of aCDase ameliorates fibrosis but does not alter metabolic parameters. The findings suggest that targeting aCDase is a viable therapeutic option to reduce fibrosis in patients with NASH.

Emerging Roles of Ceramides in Breast Cancer Biology and Therapy

One of the classic hallmarks of cancer is the imbalance between elevated cell proliferation and reduced cell death. Ceramide, a bioactive sphingolipid that can regulate this balance, has long been implicated in cancer. While the effects of ceramide on cell death and therapeutic efficacy are well established, emerging evidence indicates that ceramide turnover to downstream sphingolipids, such as sphingomyelin, hexosylceramides, sphingosine-1-phosphate, and ceramide-1-phosphate, is equally important in driving pro-tumorigenic phenotypes, such as proliferation, survival, migration, stemness, and therapy resistance. The complex and dynamic sphingolipid network has been extensively studied in several cancers, including breast cancer, to find key sphingolipidomic alterations that can be exploited to develop new therapeutic strategies to improve patient outcomes. Here, we review how the current literature shapes our understanding of how ceramide synthesis and turnover are altered in breast cancer and how these changes offer potential strategies to improve breast cancer therapy.

Sphingolipids and their role in health and disease in the central nervous system

Sphingolipids (SLs) are lipids derived from sphingosine, and their metabolism involves a broad and complex network of reactions. Although SLs are widely distributed in the body, it is well known that they are present in high concentrations within the central nervous system (CNS). Under physiological conditions, their abundance and distribution in the CNS depend on brain development and cell type. Consequently, SLs metabolism impairment may have a significant impact on the normal CNS function, and has been associated with several disorders, including sphingolipidoses, Parkinson's, and Alzheimer's. This review summarizes the main SLs characteristics and current knowledge about synthesis, catabolism, regulatory pathways, and their role in physiological and pathological scenarios in the CNS.

Ceramide-1-Phosphate Is Involved in Therapy-Induced Senescence

Sphingolipids are key signaling lipids and their dysregulation has been associated with various cellular processes. We have previously shown significant changes in sphingolipids in therapy-induced senescence, a state of cell cycle arrest as a response to chemotherapy, including the accumulation of ceramides, and provided evidence suggesting that ceramide processing is important for this process. Herein, we conducted a focused small molecule inhibitor screen targeting the sphingolipid pathway, which highlighted a new lipid regulator of therapy-induced senescence. Among the inhibitors tested, the inhibition of ceramide kinase by NVP-231 reduced the levels of senescent cells. Ceramide kinase knockdown exhibited similar effects, strongly supporting the involvement of ceramide kinase during this process. We showed that ceramide-1-phosphate was upregulated in therapy-induced senescence and that NVP-231 reduced ceramide-1-phosphate levels in different cell line models of therapy-induced senescence. Finally, ceramide-1-phosphate addition to NVP-231-treated cells reversed the effects of NVP-231 during senescence. Overall, our results identify a previously unknown lipid player in therapy-induced senescence and highlight a potential targetable enzyme to reduce the levels of therapy-induced senescent cells.

Protective Mechanism of Rice-Derived Lipids and Glucosylceramide in an In Vitro Intestinal Tract Model

We previously reported that the ethanol extract from polished rice suppresses inflammation and the formation of aberrant crypt foci in the mouse colon and particularly focused on the plant sphingolipid glucosylceramide (GlcCer). Here, we investigated the effects of rice lipid fractions and GlcCer on differentiated Caco-2 cells treated with lipopolysaccharide (LPS), in particular, we evaluated the mechanism of action of GlcCer using related substances and metabolic enzyme inhibitors. Rice-derived polar lipids suppressed the LPS-induced reduction in the number of cells. The polar lipids with higher GlcCer content exerted a better effect than the other fractions. GlcCer-related substances reversed the LPS-induced reduction in the number of cells, and GlcCer-metabolic inhibitors, including a sphingosine kinase inhibitor, suppressed the beneficial effects of GlcCer-related substances. These results suggest that GlcCer is a rice component with intestinal protection. Secondly, GlcCer is metabolized during inflammation and protects intestinal cells by maintaining the sphingolipid levels in cells and producing sphingoid base-1-phosphate.

Targeting acid ceramidase inhibits YAP/TAZ signaling to reduce fibrosis in mice

Hepatic stellate cells (HSCs) drive hepatic fibrosis. Therapies that inactivate HSCs have clinical potential as antifibrotic agents. We previously identified acid ceramidase (aCDase) as an antifibrotic target. We showed that tricyclic antidepressants (TCAs) reduce hepatic fibrosis by inhibiting aCDase and increasing the bioactive sphingolipid ceramide. We now demonstrate that targeting aCDase inhibits YAP/TAZ activity by potentiating its phosphorylation-mediated proteasomal degradation via the ubiquitin ligase adaptor protein β-TrCP. In mouse models of fibrosis, pharmacologic inhibition of aCDase or genetic knockout of aCDase in HSCs reduces fibrosis, stromal stiffness, and YAP/TAZ activity. In patients with advanced fibrosis, aCDase expression in HSCs is increased. Consistently, a signature of the genes most down-regulated by ceramide identifies patients with advanced fibrosis who could benefit from aCDase targeting. The findings implicate ceramide as a critical regulator of YAP/TAZ signaling and HSC activation and highlight aCDase as a therapeutic target for the treatment of fibrosis.

Discovery of deoxyceramide analogs as highly selective ACER3 inhibitors in live cells

Acid (AC), neutral (NC) and alkaline ceramidase 3 (ACER3) are the most ubiquitous ceramidases and their therapeutic interest as targets in cancer diseases has been well sustained. This supports the importance of discovering potent and specific inhibitors for further use in combination therapies. Although several ceramidase inhibitors have been reported, most of them target AC and a few focus on NC. In contrast, well characterized ACER3 inhibitors are lacking. Here we report on the synthesis and screening of two series of 1-deoxy(dihydro)ceramide analogs on the three enzymes. Activity was determined using fluorogenic substrates in recombinant human NC (rhNC) and both lysates and intact cells enriched in each enzyme. None of the molecules elicited a remarkable AC inhibitory activity in either experimental setup, while using rhNC, several compounds of both series were active as non-competitive inhibitors with K_i values between 1 and 5 μM. However, a dramatic loss of potency occurred in NC-enriched cell lysates and no activity was elicited in intact cells. Interestingly, several compounds of Series 2 inhibited ACER3 dose-dependently in both cell lysates and intact cells with IC₅₀'s around 20 μM. In agreement with their activity in live cells, they provoked a significant increase in the amounts of ceramides. Overall, this study identifies highly selective ACER3 activity blockers in intact cells, opening the door to further medicinal chemistry efforts aimed at developing more potent and specific compounds.

Synthesis of erythro- B13 enantiomers and stereospecific action of full set of B13-isomers in MCF7 breast carcinoma cells: Cellular metabolism and effects on sphingolipids

B13 is an acid ceramidase (ACDase) inhibitor. The two chiral centers of this aromatic amido alcohol lead to four stereoisomers, yet we have little knowledge about its erythro- enantiomers, (1R, 2S) and (1S, 2R). In this paper, for the first time, the synthesis of two erythro- enantiomers is described, and the compounds are evaluated along with two threo- enantiomers, (1R, 2R) and (1S, 2S). The key metabolites and sphingolipid (SL) profile of the full set of B13 stereoisomers in MCF7 breast carcinoma cells are presented. The results demonstrated that the erythro- enantiomers were more effective than the threo- enantiomers on growth inhibition in MCF7 cells, although there were no statistically significant differences within the threo- and erythro- series. Measurement of intracellular levels of the compounds indicated that the erythro- seemed a little more cell permeable than the threo- enantiomers; also, the (1R, 2S) isomer with the same stereo structure as natural ceramide (Cer) could be hydrolyzed and phosphorylated in MCF7 cells. Furthermore, we also observed the formation of C16 homologs from the full set of B13 isomers within the cells, indicating the occurrence of de-acylation and re-acylation of the amino group of the aromatic alcohol. Moreover, the decrease in the Cer/Sph ratio suggests that the growth inhibition from (1R, 2S) isomer is not because of the inhibition of ceramidases. Taken together, (1R, 2S) could be developed as a substitute of natural Cer.

Acid ceramidase, a double-edged sword in cancer aggression: A minireview

Acid ceramidase (AC), the key enzyme of the ceramide metabolic pathway hydrolyzes pro-apoptotic ceramide to sphingosine, which by the action of sphingosine-1-kinase is metabolized to mitogenic sphingosine-1-phosphate. The intracellular level of AC determines ceramide/sphingosine-1-phosphate rheostat which in turn decides the cell fate. The upregulated AC expression during cancerous condition acts as a "double-edged sword" by converting pro-apoptotic ceramide to anti-apoptotic sphingosine-1-phosphate, wherein on one end, the level of ceramide is decreased and on the other end, the level of sphingosine-1-phosphate is increased, thus altogether aggravating the cancer progression. In addition, cancer cells with upregulated AC expression exhibited increased cell proliferation, metastasis, chemoresistance, radioresistance and numerous strategies were developed in the past to effectively target the enzyme. Gene silencing and pharmacological inhibition of AC sensitized the resistant cells to chemo/radiotherapy thereby promoting cell death. The core objective of this review is to explore AC mediated tumour progression and the potential role of AC inhibitors in various cancer cell lines/models.

Design, Synthesis, and Biological Evaluation of a Series of Oxazolone Carboxamides as a Novel Class of Acid Ceramidase Inhibitors

Acid ceramidase (AC) is a cysteine hydrolase that plays a crucial role in the metabolism of lysosomal ceramides, important members of the sphingolipid family, a diversified class of bioactive molecules that mediate many biological processes ranging from cell structural integrity, signaling, and cell proliferation to cell death. In the effort to expand the structural diversity of the existing collection of AC inhibitors, a novel class of substituted oxazol-2-one-3-carboxamides were designed and synthesized. Herein, we present the chemical optimization of our initial hits, 2-oxo-4-phenyl-N-(4-phenylbutyl)oxazole-3-carboxamide 8a and 2-oxo-5-phenyl-N-(4-phenylbutyl)oxazole-3-carboxamide 12a, which resulted in the identification of 5-[4-fluoro-2-(1-methyl-4-piperidyl)phenyl]-2-oxo-N-pentyl-oxazole-3-carboxamide 32b as a potent AC inhibitor with optimal physicochemical and metabolic properties, showing target engagement in human neuroblastoma SH-SY5Y cells and a desirable pharmacokinetic profile in mice, following intravenous and oral administration. 32b enriches the arsenal of promising lead compounds that may therefore act as useful pharmacological tools for investigating the potential therapeutic effects of AC inhibition in relevant sphingolipid-mediated disorders.

Ceramide induces a multicomponent intracellular calcium increase triggering the acrosome secretion in human sperm

Exocytosis of spermatozoon's secretory vesicle, named acrosome reaction (AR), is a regulated event that plays a central role in fertilization. It is coupled to a complex calcium signaling. Ceramide is a multitasking lipid involved in exocytosis. Nevertheless, its effect on secretion is controversial and the underlying cellular and molecular mechanisms remain unknown. Human spermatozoa are useful to dissect the role of ceramide in secretion given that the gamete is not capable to undergo any trafficking mechanisms other than exocytosis. We report for the first time, the presence of sphingolipid metabolism enzymes such as neutral-sphingomyelinase and ceramide synthase in sperm. Ceramidases are also present and active. Both the addition of cell-permeable ceramide and the rise of the endogenous one, increase intracellular calcium acting as potent inducers of exocytosis. Ceramide triggers AR in capacitated spermatozoa and enhances the gamete response to progesterone. The lipid induces physiological ultrastructural changes in the acrosome and triggers an exocytosis-signaling cascade involving protein tyrosine phosphatase 1B and VAMP2. Real-time imaging showed an increment of calcium in the cytosol upon ceramide treatment either in the absence or in the presence of extracellular calcium. Pharmacological experiments demonstrate that at early stages the process involves ryanodine receptors, CatSper (calcium channel of sperm), and store-operated calcium channels. We set out the signaling sequence of events that connect ceramide to internal calcium mobilization and external calcium signals during secretion. These results allow the coordination of lipids and proteins in a pathway that accomplishes secretion. Our findings contribute to the understanding of ceramide's role in regulated exocytosis and fertilization.

N-Metallocenoylsphingosines as targeted ceramidase inhibitors: Syntheses and antitumoral effects

Three N-metallocenoylsphingosines with variance in the central metal (Fe, Co, Ru), the charge (neutral or cationic), and the arene ligands (Cp₂, Cp*Ph) were synthesized from serine and metallocene carboxylic acids as substrate-analogous inhibitors of human acid ceramidase (AC). Their inhibitory potential was examined using the recombinant full length ASAH1 enzyme, expressed and secreted from High Five insect cells, and the fluorescent substrate Rbm14-12. All complexes inhibited AC, most strongly so ruthenium(II) complex 13a. Some antitumoral effects of the complexes, such as the interference with the microtubular and F-actin cytoskeleton of cancer cells, were correlated to their AC-inhibition, whereas others, e.g. their cytotoxicity and their induction of caspase-3/-7 activity in cancer cells, were not. All complexes accumulated preferentially in the lysosomes of cancer cells like their target AC, arrested the cells in G1 phase of the cell cycle, and displayed cytotoxicity with mostly single-digit micromolar IC₅₀ values while inducing cancer cell apoptosis.

Validation and Invalidation of Chemical Probes for the Human N-myristoyltransferases

On-target, cell-active chemical probes are of fundamental importance in chemical and cell biology, whereas poorly characterized probes often lead to invalid conclusions. Human N-myristoyltransferase (NMT) has attracted increasing interest as target in cancer and infectious diseases. Here we report an in-depth comparison of five compounds widely applied as human NMT inhibitors, using a combination of quantitative whole-proteome N-myristoylation profiling, biochemical enzyme assays, cytotoxicity, in-cell protein synthesis, and cell-cycle assays. We find that N-myristoylation is unaffected by 2-hydroxymyristic acid (100 μM), D-NMAPPD (30 μM), or Tris-DBA palladium (10 μM), with the latter compounds causing cytotoxicity through mechanisms unrelated to NMT. In contrast, drug-like inhibitors IMP-366 (DDD85646) and IMP-1088 delivered complete and specific inhibition of N-myristoylation in a range of cell lines at 1 μM and 100 nM, respectively. This study enables the selection of appropriate on-target probes for future studies and suggests the need for reassessment of previous studies that used off-target compounds.

Dose dependent actions of LCL521 on acid ceramidase and key sphingolipid metabolites

The function of acid ceramidase (ACDase), whose congenital deficiency leads to Farber disease, has been recognized to be vital to tumor cell biology, and inhibition of its activity may be beneficial in cancer therapy. Therefore, manipulation of the activity of this enzyme may have significant effect, especially on cancer cells. LCL521, Di-DMG-B13, is a lysosomotropic inhibitor of ACDase. Here we define complexities in the actions of LCL521 on ACDase. Systematic studies in MCF7 cells showed dose and time divergent action of LCL521 on ACDase protein expression and sphingolipid levels. Low dose of LCL521 (1 µM) effectively inhibited ACDase in cells, but the effects were transient. A higher dose of LCL521 (10 µM) caused a profound decrease of sphingosine and increase of ceramide, but additionally affected the processing and regeneration of the ACDase protein, with biphasic and reversible effects on the expression of ACDase, which paralleled the long term changes of cellular sphingosine and ceramide. Finally, the higher concentrations of LCL521 also inhibited Dihydroceramide desaturase (DES-1). In summary, LCL521 exhibits significant effects on ACDase in a dose and time dependent manner, but dose range and treatment time need to be paid attention to specify its future exploration on ACDase targeted cancer treatment.

Flupirtine derivatives as potential treatment for the neuronal ceroid lipofuscinoses

Objective

Neuronal Ceroid Lipofuscinoses (NCL) are fatal inherited neurodegenerative diseases with established neuronal cell death and increased ceramide levels in brain, hence, a need for disease‐modifying drug candidates, with potential to enhance growth, reduce apoptosis and lower ceramide in neuronal precursor PC12 cells and human NCL cell lines using enhanced flupirtine aromatic carbamate derivatives in vitro.

Methods

Aromatic carbamate derivatives were tested by establishing growth curves under pro‐apoptotic conditions and activity evaluated by trypan blue and JC‐1 staining, as well as a drop in pro‐apoptotic ceramide in neuronal precursor PC12 cells following siRNA knockdown of the CLN3 gene, and CLN1‐/CLN2‐/CLN3‐/CLN6‐/CLN8 patient‐derived lymphoblasts. Ceramide levels were determined in CLN1‐/CLN2‐/CLN3‐/CLN6‐/CLN8 patient‐derived lymphoblasts before and after treatment. Expression of BCL‐2, ceramide synthesis enzymes (CERS2/CERS6/SMPD1/DEGS2) and Caspases 3/8/9 levels were compared in treated versus untreated CLN3‐deficient PC12 cells by qRT‐PCR.

Results

Retigabine, the benzyl‐derivatized carbamate and an allyl carbamate derivative were neuroprotective in CLN3‐defective PC12 cells and rescued CLN1‐/CLN2‐/CLN3‐/CLN6‐/CLN8 patient‐derived lymphoblasts from diminished growth and accelerated apoptosis. All drugs decreased ceramide in CLN1‐/CLN2‐/CLN3‐/CLN6‐/CLN8 patient‐derived lymphoblasts. Increased BCL‐2 and decreased ceramide synthesis enzyme expression were established in CLN3‐derived PC12 cells treated with the benzyl and allyl carbamate derivatives. They down‐regulated Caspase 3/Caspase 8 expression. Caspase 9 expression was reduced by the benzyl‐derivatized carbamate.

Interpretation

These findings establish that compounds analogous to flupirtine demonstrate anti‐apoptotic activity with potential for treatment of NCL disease and use of ceramide as a marker for these diseases.

Novel Sphingolipid-Based Cancer Therapeutics in the Personalized Medicine Era

Sphingolipids are bioactive lipids that participate in a wide variety of biological mechanisms, including cell death and proliferation. The myriad of pro-death and pro-survival cellular pathways involving sphingolipids provide a plethora of opportunities for dysregulation in cancers. In recent years, modulation of these sphingolipid metabolic pathways has been in the forefront of drug discovery for cancer therapeutics. About two decades ago, researchers first showed that standard of care treatments, e.g., chemotherapeutics and radiation, modulate sphingolipid metabolism to increase endogenous ceramides, which kill cancer cells. Strikingly, resistance to these treatments has also been linked to altered sphingolipid metabolism, favoring lipid species that ultimately lead to cell survival. To this end, many inhibitors of sphingolipid metabolism have been developed to further define not only our understanding of these pathways but also to potentially serve as therapeutic interventions. Therefore, understanding how to better use these new drugs that target sphingolipid metabolism, either alone or in combination with current cancer treatments, holds great potential for cancer control. While sphingolipids in cancer have been reviewed previously (Hannun & Obeid, 2018; Lee & Kolesnick, 2017; Morad & Cabot, 2013; Newton, Lima, Maceyka, & Spiegel, 2015; Ogretmen, 2018; Ryland, Fox, Liu, Loughran, & Kester, 2011) in this chapter, we present a comprehensive review on how standard of care therapeutics affects sphingolipid metabolism, the current landscape of sphingolipid inhibitors, and the clinical utility of sphingolipid-based cancer therapeutics.

Translational Aspects of Sphingolipid Metabolism in Renal Disorders

Sphingolipids, long thought to be passive components of biological membranes with merely a structural role, have proved throughout the past decade to be major players in the pathogenesis of many human diseases. The study and characterization of several genetic disorders like Fabry’s and Tay Sachs, where sphingolipid metabolism is disrupted, leading to a systemic array of clinical symptoms, have indeed helped elucidate and appreciate the importance of sphingolipids and their metabolites as active signaling molecules. In addition to being involved in dynamic cellular processes like apoptosis, senescence and differentiation, sphingolipids are implicated in critical physiological functions such as immune responses and pathophysiological conditions like inflammation and insulin resistance. Interestingly, the kidneys are among the most sensitive organ systems to sphingolipid alterations, rendering these molecules and the enzymes involved in their metabolism, promising therapeutic targets for numerous nephropathic complications that stand behind podocyte injury and renal failure.

The antimicrobial peptide nisin Z induces selective toxicity and apoptotic cell death in cultured melanoma cells

Reprogramming of cellular metabolism is now considered one of the hallmarks of cancer. Most malignant cells present with altered energy metabolism which is associated with elevated reactive oxygen species (ROS) generation. This is also evident for melanoma, the leading cause of skin cancer related deaths. Altered mechanisms affecting mitochondrial bioenergetics pose attractive targets for novel anticancer therapies. Antimicrobial peptides have been shown to exhibit selective anticancer activities. In this study, the anti-melanoma potential of the antimicrobial peptide, nisin Z, was evaluated in vitro. Nisin Z was shown to induce selective toxicity in melanoma cells compared to non-malignant keratinocytes. Furthermore, nisin Z was shown to negatively affect the energy metabolism (glycolysis and mitochondrial respiration) of melanoma cells, increase reactive oxygen species generation and cause apoptosis. Results also indicate that nisin Z can decrease the invasion and proliferation of melanoma cells demonstrating its potential use against metastasis associated with melanoma. As nisin Z seems to place a considerable extra burden on the energy metabolism of melanoma cells, combination therapies with known anti-melanoma agents may be effective treatment options.

Anticancer actions of lysosomally targeted inhibitor, LCL521, of acid ceramidase

Acid ceramidase, which catalyzes ceramide hydrolysis to sphingosine and free fatty acid mainly in the lysosome, is being recognized as a potential therapeutic target for cancer. B13 is an effective and selective acid ceramidase inhibitor in vitro, but not as effective in cells due to poor access to the lysosomal compartment. In order to achieve targeting of B13 to the lysosome, we designed lysosomotropic N, N-dimethyl glycine (DMG)-conjugated B13 prodrug LCL521 (1,3-di-DMG-B13). Our previous results indicated the efficient delivery of B13 to the lysosome resulted in augmented effects of LCL521 on cellular acid ceramidase as evaluated by effects on substrate/product levels. Our current studies indicate that functionally, this translated into enhanced inhibition of cell proliferation. Moreover, there were greater synergistic effects of LCL521 with either ionizing radiation or Tamoxifen. Taken together, these results clearly indicate that compartmental targeting for the inhibition of acid ceramidase is an efficient and valuable therapeutic strategy.

The emergence of acid ceramidase as a therapeutic target for acute myeloid leukemia

INTRODUCTION

Acute myeloid leukemia (AML) is the most common adult leukemia. Only a fraction of AML patients will survive with existing chemotherapy regimens. Hence, there is an urgent and unmet need to identify novel targets and develop better therapeutics in AML. In the past decade, the field of sphingolipid metabolism has emerged into the forefront of cancer biology due to its importance in cancer cell proliferation and survival. In particular, acid ceramidase (AC) has emerged as a promising therapeutic target due to its role in neutralizing the pro-death effects of ceramide. Areas covered: This review highlights key information about AML biology as well as current knowledge on dysregulated sphingolipid metabolism in cancer and AML. We describe AC function and dysregulation in cancer, followed by a review of studies that report elevated AC in AML and compounds known to inhibit the enzyme. Expert opinion: AML has a great need for new drug targets and better therapeutic agents. The finding of elevated AC in AML supports the concept that this enzyme represents a novel and realistic therapeutic target for this common leukemia. More effort is needed towards developing better AC inhibitors for clinical use and combination treatment with existing AML therapies.

Interaction of acid ceramidase inhibitor LCL521 with tumor response to photodynamic therapy and photodynamic therapy-generated vaccine

Acid ceramidase has been identified as a promising target for cancer therapy. One of its most effective inhibitors, LCL521, was examined as adjuvant to photodynamic therapy (PDT) using mouse squamous cell carcinoma SCCVII model of head and neck cancer. Lethal effects of PDT, assessed by colony forming ability of in vitro treated SCCVII cells, were greatly enhanced when combined with 10 µM LCL521 treatment particularly when preceding PDT. When PDT-treated SCCVII cells are used to vaccinate SCCVII tumor-bearing mice (PDT vaccine protocol), adjuvant LCL521 treatment (75 mg/kg) resulted in a marked retardation of tumor growth. This effect can be attributed to the capacity of LCL521 to effectively restrict the activity of two main immunoregulatory cell populations (Tregs and myeloid-derived suppressor cells, MDSCs) that are known to hinder the efficacy of PDT vaccines. The therapeutic benefit with adjuvant LCL521 was also achieved with SCCVII tumors treated with standard PDT when using immunocompetent mice but not with immunodeficient hosts. The interaction of LCL521 with PDT-based antitumor mechanisms is dominated by immune system contribution that includes overriding the effects of immunoregulatory cells, but could also include a tacit contribution from boosting direct tumor cell kill.

Inhibitors of Ceramidases

The topic of ceramidases has experienced an enormous boost during the last few years. Ceramidases catalyze the degradation of ceramide to sphingosine and fatty acids. Ceramide is not only the central hub of sphingolipid biosynthesis and degradation, it is also a key molecule in sphingolipid signaling, promoting differentiation or apoptosis. Acid ceramidase inhibition sensitizes certain types of cancer to chemo- and radio-therapy and this is suggestive of a role of acid ceramidase inhibitors as chemo-sensitizers which can act synergistically with chemo-therapeutic drugs. In this review, we summarize the development of ceramide analogues as first-generation ceramidase inhibitors together with data on their activity in cells and disease models. Furthermore, we describe the recent developments that have led to highly potent second-generation ceramidase inhibitors that act at nanomolar concentrations. In the third part, various assays of ceramidases are described and their relevance for accurately measuring ceramidase activities and for the development of novel inhibitors is highlighted. Besides potential clinical implications, the recent improvements in ceramidase inhibition and assaying may help to better understand the mechanisms of ceramide biology.

Combined histone deacetylase inhibition and tamoxifen induces apoptosis in tamoxifen-resistant breast cancer models, by reversing Bcl-2 overexpression

INTRODUCTION

The emergence of hormone therapy resistance, despite continued expression of the estrogen receptor (ER), is a major challenge to curing breast cancer. Recent clinical studies suggest that epigenetic modulation by histone deacetylase (HDAC) inhibitors reverses hormone therapy resistance. However, little is known about epigenetic modulation of the ER during acquired hormone resistance. Our recent phase II study demonstrated that HDAC inhibitors re-sensitize hormone therapy-resistant tumors to the anti-estrogen tamoxifen. In this study, we sought to understand the mechanism behind the efficacy of this combination.

METHODS

We generated cell lines resistant to tamoxifen, named TAMRM and TAMRT, by continuous exposure of ER-positive MCF7 and T47D cells, respectively to 4-hydroxy tamoxifen for over 12 months. HDAC inhibition, along with pharmacological and genetic manipulation of key survival pathways, including ER and Bcl-2, were used to characterize these resistant models.

RESULTS

The TAMRM cells displayed decreased sensitivity to tamoxifen, fulvestrant and estrogen deprivation. Consistent with previous models, ER expression was retained and the gene harbored no mutations. Compared to parental MCF7 cells, ER expression in TAMRM was elevated, while progesterone receptor (PGR) was lost. Sensitivity of ER to ligands was greatly reduced and classic ER response genes were suppressed. This model conveyed tamoxifen resistance through transcriptional upregulation of Bcl-2 and c-Myc, and downregulation of the cell cycle checkpoint protein p21, manifesting in accelerated growth and reduced cell death. Similar to TAMRM cells, the TAMRT cell line exhibited substantially decreased tamoxifen sensitivity, increased ER and Bcl-2 expression and significantly reduced PGR expression. Treatment with HDAC inhibitors reversed the altered transcriptional events and reestablished the sensitivity of the ER to tamoxifen resulting in substantial Bcl-2 downregulation, growth arrest and apoptosis. Selective inhibition of Bcl-2 mirrored these effects in presence of an HDAC inhibitor.

CONCLUSIONS

Our model implicates elevated ER and Bcl-2 as key drivers of anti-estrogen resistance, which can be reversed by epigenetic modulation through HDAC inhibition.

Benzoxazolone carboxamides: potent and systemically active inhibitors of intracellular acid ceramidase

The ceramides are a family of bioactive lipid-derived messengers involved in the control of cellular senescence, inflammation, and apoptosis. Ceramide hydrolysis by acid ceramidase (AC) stops the biological activity of these substances and influences survival and function of normal and neoplastic cells. Because of its central role in the ceramide metabolism, AC may offer a novel molecular target in disorders with dysfunctional ceramide-mediated signaling. Here, a class of benzoxazolone carboxamides is identified as the first potent and systemically active inhibitors of AC. Prototype members of this class inhibit AC with low nanomolar potency by covalent binding to the catalytic cysteine. Their metabolic stability and high in vivo efficacy suggest that these compounds may be used as probes to investigate the roles of ceramide in health and disease, and that this scaffold may represent a promising starting point for the development of novel therapeutic agents.

Targeting (cellular) lysosomal acid ceramidase by B13: design, synthesis and evaluation of novel DMG-B13 ester prodrugs

Acid ceramidase (ACDase) is being recognized as a therapeutic target for cancer. B13 represents a moderate inhibitor of ACDase. The present study concentrates on the lysosomal targeting of B13 via its N,N-dimethylglycine (DMG) esters (DMG-B13 prodrugs). Novel analogs, the isomeric mono-DMG-B13, LCL522 (3-O-DMG-B13·HCl) and LCL596 (1-O-DMG-B13·HCl) and di-DMG-B13, LCL521 (1,3-O, O-DMG-B13·2HCl) conjugates, were designed and synthesized through N,N-dimethyl glycine (DMG) esterification of the hydroxyl groups of B13. In MCF7 cells, DMG-B13 prodrugs were efficiently metabolized to B13. The early inhibitory effect of DMG-B13 prodrugs on cellular ceramidases was ACDase specific by their lysosomal targeting. The corresponding dramatic decrease of cellular Sph (80-97% Control/1h) by DMG-B13 prodrugs was mainly from the inhibition of the lysosomal ACDase.

Blockade of lysosomal acid ceramidase induces GluN2B-dependent Tau phosphorylation in rat hippocampal slices

The lysosomal acid ceramidase, an enzyme known to limit intracellular ceramide accumulation, has been reported to be defective in neurodegenerative disorders. We show here that rat hippocampal slices, preincubated with the acid ceramidase inhibitor (ACI) d-NMAPPD, exhibit increased N-methyl-D-aspartate (NMDA) receptor-mediated field excitatory postsynaptic potentials (fEPSPs) in CA1 synapses. The ACI by itself did not interfere with either paired pulse facilitation or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-mediated fEPSPs, indicating that its influence on synaptic transmission is postsynaptic in origin and specific to the NMDA subtype of glutamate receptors. From a biochemical perspective, we observed that Tau phosphorylation at the Ser262 epitope was highly increased in hippocampal slices preincubated with the ACI, an effect totally prevented by the global NMDA receptor antagonist D/L(−)-2-amino-5-phosphonovaleric acid (AP-5), the calcium chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA), and the GluN2B (but not the GluN2A) receptor antagonist RO25-6981. On the other hand, preincubation of hippocampal slices with the compound KN-62, an inhibitor known to interfere with calcium/calmodulin-dependent protein kinase II (CaMKII), totally abolished the effect of ACI on Tau phosphorylation at Ser262 epitopes. Collectively, these results provide experimental evidence that ceramides play an important role in regulating Tau phosphorylation in the hippocampus via a mechanism dependent on GluN2B receptor subunits and CaMKII activation.

A review of ceramide analogs as potential anticancer agents

Ceramide serves as a central mediator in sphingolipid metabolism and signaling pathways, regulating many fundamental cellular responses. It is referred to as a 'tumor suppressor lipid', since it powerfully potentiates signaling events that drive apoptosis, cell cycle arrest, and autophagic responses. In the typical cancer cell, ceramide levels and signaling are usually suppressed by overexpression of ceramide-metabolizing enzymes or downregulation of ceramide-generating enzymes. However, chemotherapeutic drugs as well as radiotherapy increase intracellular ceramide levels, while exogenously treating cancer cells with short-chain ceramides leads to anticancer effects. All evidence currently points to the fact that the upregulation of ceramide levels is a promising anticancer strategy. In this review, we exhibit many anticancer ceramide analogs as downstream receptor agonists and ceramide-metabolizing enzyme inhibitors.

Cytotoxic activity and quantitative structure activity relationships of arylpropyl sulfonamides

B13 is a ceramide analogue and apoptosis inducer with potent cytotoxic activity. A series of arylpropyl sulfonamide analogues of B13 were evaluated for their cytotoxicity using MTT assays in prostate cancer PC-3 and leukemia HL-60 cell lines. Some compounds (4, 9, 13, 14, 15, and 20) showed stronger activities than B13 in both tumor cell lines, and compound (15) gave the most potent activity with IC₅₀ values of 29.2 and 20.7 µM, for PC-3and HL-60 cells, respectively. Three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis was performed to build highly reliable and predictive CoMSIA models with cross-validated q² values of 0.816 and 0.702, respectively. Our results suggest that long alkyl chains and a 1R, 2R configuration of the propyl group are important for the cytotoxic activities of arylpropyl sulfonamides. Moreover, the introduction of small hydrophobic groups in the phenyl ring and sulfonamide group could increase biological activity.

Discovery of highly potent acid ceramidase inhibitors with in vitro tumor chemosensitizing activity

The expression of acid ceramidase (AC) - a cysteine amidase that hydrolyses the proapoptotic lipid ceramide - is abnormally high in several human tumors, which is suggestive of a role in chemoresistance. Available AC inhibitors lack, however, the potency and drug-likeness necessary to test this idea. Here we show that the antineoplastic drug carmofur, which is used in the clinic to treat colorectal cancers, is a potent AC inhibitor and that this property is essential to its anti-proliferative effects. Modifications in the chemical scaffold of carmofur yield new AC inhibitors that act synergistically with standard antitumoral drugs to prevent cancer cell proliferation. These findings identify AC as an unexpected target for carmofur, and suggest that this molecule can be used as starting point for the design of novel chemosensitizing agents.

Novel drugs targeting sphingolipid metabolism

While the evidence for an involvement of sphingolipids (SLs) in a variety of diseases is rapidly increasing, the development of sphingolipid-related drugs is still in its infancy. In fact, the recently FDA-approved fingolimod or FTY-720 (see chapter by J. Pfeilschifter for more information) is the first drug on the market to interfere with sphingolipid signaling. The reasons for this lagging are manifold and within this chapter we try to name some of them. Ceramide is in the center of sphingolipid metabolism. We describe the most important and most recent inhibitors for enzymes controlling cellular ceramide levels.

Ceramide biosynthesis and metabolism in trophoblast syncytialization

Sphingolipid mediators such as ceramide are pleiotropic regulators of cellular growth, differentiation and apoptosis. We investigated the role of ceramide biosynthesis, metabolism and actions in term human cytotrophoblasts syncytialized over 7 days in culture. Intracellular C16 ceramide levels increased modestly after 3 days in culture, then declined. Ceramidase was present at particularly high levels in syncytialized trophoblasts; inhibition of ceramidase reduced the degree of cell fusion. Exposure to short chain C8 ceramide or aSMase enhanced secretion of the differentiation marker hCG without affecting fusion or cell viability. In contrast, pharmacological inhibition of ceramidase reduced the extent of fusion. Inhibition of the ceramide-responsive JNK and PP2A pathways did not abolish the effects of ceramide, and JNK phosphorylation was unresponsive to ceramide; however, ceramide significantly inhibited phosphorylation of Akt. This study suggests that changes in ceramide biosynthesis and metabolism play a differential role in the biochemical and morphological features of trophoblast differentiation.

Novel amide- and sulfonamide-based aromatic ethanolamines: effects of various substituents on the inhibition of acid and neutral ceramidases

In the present study we describe the design and synthesis of a series of amide- and sulfonamide-based compounds as inhibitor of recombinant acid and neutral ceramidases. Inhibition of ceramidases has been shown to induce apoptosis and to increase the efficacy of conventional chemotherapy in several cancer models. B-13, lead in vitro inhibitor of acid ceramidase has been recently shown to be virtually inactive towards lysosomal acid ceramidase in living cells at lower concentrations and for a shorter time of treatment, suggesting the development of more potent inhibitors. In this study, a detailed SAR investigation has been performed to understand the effect of different substituents on the phenyl ring of amide- and sulfonamide-based compounds that partially resemble the structure of well-known inhibitors such as B-13, D-e-MAPP as well as NOE. Our results suggest that the electronic effects of the substituents on phenyl ring in B-13 and D-e-MAPP analogues have negligible effects either in enhancing the inhibition potencies or for selectivity towards aCDase over nCDase. However, the hydrophobicity and the steric effects of longer alkyl chains (n-Pr, n-Bu or t-Bu groups) at the phenyl ring were found to be important for an enhanced selectivity towards aCDase over nCDase.

Novel fluorescent ceramide derivatives for probing ceramidase substrate specificity

Ceramidases are key regulators of cell fate. The biochemistry of different ceramidases and of their substrate ceramide appears to be complex, mainly due to specific biophysical characteristics at the water-membrane interface. In the present study, we describe the design and synthesis of a set of fluorescently labeled ceramides as substrates for acid and neutral ceramidases. For the first time we have replaced the commonly used polar NBD-dye with the lipophilic Nile Red (NR) dye. Analysis of kinetic data reveal that although both the dyes do not have any noticeable preference for the substitution at acyl or sphingosine (Sph) part in ceramide towards hydrolysis by acid ceramidase, the ceramides with acyl-substituted NBD and Sph-substituted NR dyes have been found to be a better substrate for neutral ceramidase.

Cytotoxicities and Quantitative Structure Activity Relationships of B13 Sulfonamides in HT-29 and A549 Cells

B13 analogues are being considered as therapeutic agents for cancer cells, since B13 is a ceramide analogue and inhibits ceramidase to promote apoptosis in cancer cells. B13 sulfonamides are assumed to have biological activity similar to B13, since they are made by bioisosterically substituting the carboxyl moiety of B13 with sulfone group. Twenty B13 sulfonamides were evaluated for their in vitro cytotoxicities against human colon cancer HT-29 and lung cancer A549 cell lines using MTT assays. Replacement of the amide group with a sulfonamide group increased cytotoxicity in both cancer cell lines. The sulfonamides with long alkyl chains exhibited activities two to three times more potent than that of B13 and compound (15) had the most potent activity with IC₅₀ values of 27 and 28.7µM for HT-29 and A549, respectively. The comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were used to carry out QSAR molecular modeling of these compounds. The predictive CoMSIA models for HT-29 and A549 gave cross-validated q2 values of 0.703 and 0.830, respectively. From graphical analysis of these models, we suppose that the stereochemistry of 1,3-propandiol is not important for activity and that introduction of a sulfonamide group and long alkyl chains into B13 can increase cytotoxicity.

Withaferin A induces apoptosis in human melanoma cells through generation of reactive oxygen species and down-regulation of Bcl-2

A high resistance and heterogeneous response to conventional anti-cancer chemotherapies characterize malignant cutaneous melanoma, the most aggressive and deadly form of skin cancer. Withaferin A (WFA), a withanolide derived from the medicinal plant Withania somnifera, has been reported for its anti-tumorigenic activity against various cancer cells. For the first time, we examined the death-inducing potential of WFA against a panel of four different human melanoma cells and investigated the cellular mechanisms involved. WFA induces apoptotic cell death with various IC50 ranging from 1.8 to 6.1 μM. The susceptibility of cells toward WFA-induced apoptosis correlated with low Bcl-2/Bax and Bcl-2/Bim ratios. In all cell lines, the apoptotic process triggered by WFA involves the mitochondrial pathway and was associated with Bcl-2 down regulation, Bax mitochondrial translocation, cytochrome c release into the cytosol, transmembrane potential (ΔΨm) dissipation, caspase 9 and caspase 3 activation and DNA fragmentation. WFA cytotoxicity requires early reactive oxygen species (ROS) production and glutathione depletion, the inhibition of ROS increase by the antioxidant N-acetylcysteine resulting in complete suppression of mitochondrial and nuclear events. Altogether, these results support the therapeutic potential of WFA against human melanoma.

Drug targeting of sphingolipid metabolism: sphingomyelinases and ceramidases

Sphingolipids represent a class of diverse bioactive lipid molecules that are increasingly appreciated as key modulators of diverse physiologic and pathophysiologic processes that include cell growth, cell death, autophagy, angiogenesis, and stress and inflammatory responses. Sphingomyelinases and ceramidases are key enzymes of sphingolipid metabolism that regulate the formation and degradation of ceramide, one of the most intensely studied classes of sphingolipids. Improved understanding of these enzymes that control not only the levels of ceramide but also the complex interconversion of sphingolipid metabolites has provided the foundation for the functional analysis of the roles of sphingolipids. Our current understanding of the roles of various sphingolipids in the regulation of different cellular processes has come from loss-of-function/gain-of-function studies utilizing genetic deletion/downregulation/overexpression of enzymes of sphingolipid metabolism (e.g. knockout animals, RNA interference) and from the use of pharmacologic inhibitors of these same enzymes. While genetic approaches to evaluate the functional roles of sphingolipid enzymes have been instrumental in advancing the field, the use of pharmacologic inhibitors has been equally important in identifying new roles for sphingolipids in important cellular processes.The latter also promises the development of novel therapeutic targets with implications for cancer therapy, inflammation, diabetes, and neurodegeneration. In this review, we focus on the status and use of pharmacologic compounds that inhibit sphingomyelinases and ceramidases, and we will review the history, current uses and future directions for various small molecule inhibitors, and will highlight studies in which inhibitors of sphingolipid metabolizing enzymes have been used to effectively treat models of human disease.

Discovery and evaluation of inhibitors of human ceramidase

The ceramide/sphingosine-1-phosphate (S1P) rheostat has been hypothesized to play a critical role in regulating tumor cell fate, with elevated levels of ceramide inducing death and elevated levels of S1P leading to survival and proliferation. Ceramidases are key enzymes that control this rheostat by hydrolyzing ceramide to produce sphingosine and may also confer resistance to drugs and radiation. Therefore, ceramidase inhibitors have excellent potential for development as new anticancer drugs. In this study, we identify a novel ceramidase inhibitor (Ceranib-1) by screening a small molecule library and describe the synthesis of a more potent analogue (Ceranib-2). In a cell-based assay, both compounds were found to inhibit cellular ceramidase activity toward an exogenous ceramide analogue, induce the accumulation of multiple ceramide species, decrease levels of sphingosine and S1P, inhibit the proliferation of cells alone and in combination with paclitaxel, and induce cell-cycle arrest and cell death. In vivo, Ceranib-2 was found to delay tumor growth in a syngeneic tumor model without hematologic suppression or overt signs of toxicity. These data support the selection of ceramidases as suitable targets for anticancer drug development and provide the first nonlipid inhibitors of human ceramidase activity.

Inhibition of acid ceramidase by a 2-substituted aminoethanol amide synergistically sensitizes prostate cancer cells to N-(4-hydroxyphenyl) retinamide

BACKGROUND

The purpose of this study was to determine whether the therapeutic efficacy of fenretinide (4-HPR), a ceramide-generating anticancer agent, could be enhanced in prostate cancer cells by inclusion of a novel synthetic acid ceramidase (AC) inhibitor, DM102, a pivaloylamide of a 2-substituted aminoethanol. In prostate cancer, AC plays a role in progression and resistance to chemotherapy.

METHODS

PC-3 and DU 145 hormone-refractory human prostate cancer cell lines were used. Cells were exposed to 4-HPR, DM102, and combinations; viability, apoptosis, cell migration, ceramide metabolism, and levels of reactive oxygen species (ROS) were assessed.

RESULTS

Single agent 4-HPR and DM102 (2.5-10 µM) were weakly cytotoxic; however, combinations synergistically decreased cell viably to as low as 1.5% of control. N-oleoylethanolamine (NOE), a frequently employed AC inhibitor, was not effective in producing synergy. The 4-HPR/DM102 regimen enhanced caspase activity and increased [(3) H](dihydro)ceramide and ROS levels 6- and 30-fold over control, respectively. The antioxidant vitamin E, but not the de novo ceramide synthesis inhibitor myriocin, partially rescued cells from 4-HPR/DM102 cytotoxicity. The 4-HPR/DM102 combination also elicited synergistic cytotoxicity in DU 145 cells, another human hormone-refractory prostate cancer cell line.

CONCLUSION

This study shows that 4-HPR cytotoxicity is enhanced in a synergistic fashion by inclusion of the AC inhibitor DM102, by a mechanism that enlists generation of ROS, and thus provides a system to raise 4-HPR therapeutic potential. The role of ceramide however in the cytotoxic response is not clear, as blocking ceramide generation failed to rescue PC-3 cells from 4-HPR/DM102 cytotoxicity.

Acid ceramidase expression modulates the sensitivity of A375 melanoma cells to dacarbazine

Dacarbazine (DTIC) is the treatment of choice for metastatic melanoma, but its response in patients remains very poor. Ceramide has been shown to be a death effector and to play an important role in regulating cancer cell growth upon chemotherapy. Among ceramidases, the enzymes that catabolize ceramide, acid ceramidase (aCDase) has been implicated in cancer progression. Here we show that DTIC elicits a time- and dose-dependent decrease of aCDase activity and an increase of intracellular ceramide levels in human A375 melanoma cells. The loss of enzyme activity occurred as a consequence of reactive oxygen species-dependent activation of cathepsin B-mediated degradation of aCDase. These events preceded autophagic features and loss of cell viability. Down-regulation of acid but not neutral or alkaline ceramidase 2 resulted in elevated levels of ceramide and sensitization to the toxic effects of DTIC. Conversely, inducible overexpression of acid but not neutral ceramidase reduced ceramide levels and conferred resistance to DTIC. In conclusion, we report that increased levels of ceramide, due to enhanced degradation of aCDase, are in part responsible for the cell death effects of DTIC. These results suggest that down-regulation of aCDase alone or in combination with DTIC may represent a useful tool in the treatment of metastatic melanoma.

Cytotoxic Activity and Structure Activity Relationship of Ceramide Analogues in Caki-2 and HL-60 Cells

B13, a ceramide analogue, is a ceramidase inhibitor and induces apoptosis to give potent anticancer activity. A series of thiourea B13 analogues was evaluated for their in vitro cytotoxic activities against human renal cancer Caki-2 and leukemic cancer HL-60 in the MTT assay. Some compounds (12, 15, and 16) showed stronger cytotoxicity than B13 and C6-ceramide against both tumor cell lines, and compound (12) gave the most potent activity with IC(50) values of 36 and 9 µM, respectively. Molecular modeling of thiourea B13 analogues was carried out by comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). We obtained highly reliable and predictive CoMSIA models with cross-validated q(2) values of 0.707 and 0.753 and CoMSIA contour maps to show the structural requirements for potent activity. These data suggest that the amide group of B13 could be replaced by thiourea, that the stereochemistry of 1,3-propandiol may not be essential for activity and that long alkyl chains increase cytotoxicity.

Potent inhibition of Acid ceramidase by novel B-13 analogues

The lipid-signalling molecule ceramide is known to induce apoptosis in a variety of cell types. Inhibition of the lysosomal acid ceramidase can increase cellular ceramide levels and thus induce apoptosis. Indeed, inhibitors of acid ceramidase have been reported to induce cell death and to display potentiating effects to classical radio- or chemo therapy in a number of in vitro and in vivo cancer models. The most potent in vitro inhibitor of acid ceramidase, B-13, recently revealed to be virtually inactive towards lysosomal acid ceramidase in living cells. In contrast, a number of weakly basic B-13 analogues have been shown to accumulate in the acidic compartments of living cells and to efficiently inhibit lysosomal acid ceramidase. However, introduction of weakly basic groups at the ω-position of the fatty acid moiety of B-13 led to a significant reduction of potency towards acid ceramidase from cellular extracts. Herein, we report a novel B-13-derived scaffold for more effective inhibitors of acid ceramidase. Furthermore, we provide hints for an introduction of basic functional groups at an alternative site of the B-13 scaffold that do not interfere with acid ceramidase inhibition in vitro.

Serum autoantibody profiling using a natural glycoprotein microarray for the prognosis of early melanoma

The poor prognosis of melanoma and the high cost of lymph node biopsy for melanoma patients have led to an urgent need for the discovery of convenient and accurate prognostic indicators. Here, we have developed a natural glycoprotein microarray to discover serum autoantibodies to distinguish between patients with node negative melanoma and node positive melanoma. Dual-lectin affinity chromatography was used to extract glycoproteins from a melanoma cell line. Liquid-based reverse phase separation and microarray platforms were then applied to separate and spot these natural proteins on nitrocellulose slides. The serum autoantibodies were investigated by exposing these proteins to sera from 43 patients that have already been diagnosed to have different stages of early melanoma. The combination of 9 fractions provides a 55% sensitivity with 100% specificity for the detection of node positive against node negative and a 62% sensitivity with 100% specificity for the detection of node negative against node positive. Recombinant proteins were used to confirm the results using a sample set with 79 patients with diagnosed melanoma. The response of sera against recombinant 94 kD glucose-regulated protein (GRP94), acid ceramidase (ASAH1), cathepsin D (CTSD), and lactate dehydrogenase B (LDHB) shared a similar pattern to the fractions where they were identified. The glycoarray platform provides a convenient and highly reproducible method to profile autoantibodies that could be used as serum biomarkers for prognosis of melanoma.