Available online at www.sciencedirect.com ScienceDirect Sphingolipids and membrane targets for therapeutics 1 2 3 Robbie Loewith , Howard Riezman and Nicolas Winssinger Lipids and membranes are often strongly altered in various [1]. Therefore, membrane lipids are likely to play impor- diseases and pathologies, but are not often targeted for tant roles in regulating protein function, including trans- therapeutic advantage. In particular, the sphingolipids are membrane and peripheral membrane proteins, as well as particularly sensitive to altered physiology and have been regulating membrane properties required for membrane implicated as important players in not only several rare deformation and vesicular trafficking. Because of their hereditary diseases, but also other major pathologies, including roles in recruiting proteins to membranes and regulating cancer. This review discusses some potential targets in the important cellular events like transcription and signal sphingolipid pathway and describes how the initial drug transduction, lipids and the proteins they target could compounds have been evolved to create potentially improved be prime targets for therapeutic intervention. The three therapeutics. This reveals how lipids and their interactions with major classes of lipids are the glycerophospholipids, proteins can be used for therapeutic advantage. We also sphingolipids, and sterols. Many studies and drugs have discuss the possibility that modification of the physical targeted the cholesterol synthesis pathway as hypercho- properties of membranes could also affect intracellular lesterolemia has been associated with increased risk of signaling and be of therapeutic interest. cardiovascular disease [2]. Among the glycerophospholi- pids, only phosphoinositides have been extensively Addresses addressed. The inhibition of PI-3 kinases has been devel- 1 Department of Molecular Biology, NCCR Chemical Biology, University oped to treat cancer [3]. Here, we will discuss some of Geneva, 30 quai Ernest Ansermet, CH-1205 Geneva, Switzerland 2 aspects of sphingolipid biosynthesis as targets and their Department of Biochemistry, NCCR Chemical Biology, University of Geneva, 30 quai Ernest Ansermet, CH-1205 Geneva, Switzerland roles in membranes, since they are modulated in a large 3 Department of Organic Chemistry, NCCR Chemical Biology, University number of diseases and mutations affecting their metab- of Geneva, 30 quai Ernest Ansermet, CH-1205 Geneva, Switzerland olism have been shown to cause disease. Sphingolipid analogs are therapeutics because of their bioactive prop- Corresponding authors: erties. However, sphingolipids are also important lipids Loewith, Robbie ([email protected]), Riezman, Howard ([email protected]), that regulate membrane properties such as viscosity and Winssinger, Nicolas ([email protected]) tension, which might also make them suitable as novel targets for therapeutic intervention. Sphingolipid degra- dation also reveals therapeutic targets [4], but this will not Current Opinion in Chemical Biology 2019, 50:19–28 be addressed here. Finally, we will explore the This review comes from a themed issue on Next generation burgeoning idea that membranes per se may serve as therapeutics clinically relevant drug targets. Edited by Yimon Aye and Paul J Hergenrother For a complete overview see the Issue and the Editorial The sphingolipid biosynthesis pathway begins with the Available online 18th March 2019 formation of 3-ketosphinganine from serine and palmi- https://doi.org/10.1016/j.cbpa.2019.02.015 toyl-CoA (Figure 1) by serine palmitoyltransferase (SPT). SPT is composed of two major subunits and several small 1367-5931/ã 2019 Elsevier Ltd. All rights reserved. subunits that are most likely involved in its regulation and specificity. The enzyme is also regulated through the action of ORM proteins, which inhibit SPT activity. Myriocin, a natural product which was originally identi- fied with anti-fungal activity [5], has been shown to inhibit sphingolipid biosynthesis [6], affecting intracellu- Membrane sphingolipids as targets lar transport of glycosylphosphatidylinositol anchored Lipids are essential for life, providing a physical mem- proteins, before SPT was identified as the target [7]. brane barrier between the interior and exterior of cells as As sphingolipids, especially ceramides and glucosylcer- well as between intracellular compartments. Lipids are amides accumulate in a wide variety of diseases, sphin- also used as physiological signaling molecules, called golipid biosynthesis is widely viewed as a therapeutic bioactive lipids, which fulfil functions of intracellular target for many different indications [8] as a large number signaling, as well as intercellular signaling. If the barrier of patents can be found in a simple search. However, function of membrane lipids were their only function, a long-term myriocin treatment does not seem to be a simple lipid composition would most likely be sufficient. feasible therapeutic because of toxic side effects and However, eukaryotic membranes have an enormous lipid because its action on SPT is at least partially irreversible diversity, including thousands of individual lipid species [9]. Nevertheless, myriocin may be used to reduce www.sciencedirect.com Current Opinion in Chemical Biology 2019, 50:19–28 20 Next generation therapeutics Figure 1 serine palmitoyl CoA SPT alanine mycriocin 3-ketosphinganine: R = OH (1-deoxy-3-ketosphinganine: R =H) KSR sphinganine C14-C28 fatty acid CerS fumonisin B1 C14-C28 fatty acid dehydroceramide DH-DES Ceramidase australifunglin sphingosine R = c14-c28 fatty acid SphK ceramide phosphatidylcholine UDP-glucose SMS UGGC sphingosine-1-phosphate sphingomyelin + diacylglycerol (S1P) glucoceramide + UDP miglustat Current Opinion in Chemical Biology Sphingolipid biosynthesis pathway. Only steps up until the formation of the first complex sphingolipids are shown. The sites of action of some inhibitors of the pathway are shown. ischemia-reperfusion injury [10] as a short-term applica- Despite a strong preference for serine, SPT can also tion would be possible. It should be possible to find novel accept alanine or glycine as substrates, which lead to inhibitors of SPT that have less toxicity, especially if the production of 1-deoxysphingolipids [14]. Mutations reversible, and these could be used for a large number of in SPT that decrease the preference for serine and indications where ceramides and sphingolipids are accu- increase the production of 1-deoxysphingolipids are at mulated leading to unwanted side effects. Inhibition of the origin of the rare disease, Hereditary Sensory and SPT can be looked at as similar to inhibition of Autonomic Neuropapthy type 1 [15 ]. The exact mecha- cholesterol production, where statins lower the amounts nism of neurotoxicity of 1-deoxysphingolipids is still of an essential lipid by interfering at a key step early in the unknown, but understanding of the enzymology under- pathway. Both SPT [11] and HMG-CoA reductase [12] lying the disease has led to a strategy to improve the are important regulatory steps in cells. Another similarity quality of life in HSAN type I patients [16] by increasing between SPT inhibition and HMG-CoA reductase inhi- serine in the diet. bition is that downstream products, although essential, can also be obtained through the diet [13], which can After SPT action, 3-ketosphinganine is converted to temper the effect of inhibition of synthesis. sphinganine by 3-ketosphinganine reductase (KSR), Current Opinion in Chemical Biology 2019, 50:19–28 www.sciencedirect.com Sphingolipids and membrane targets for therapeutics Loewith, Riezman and Winssinger 21 which together with acyl CoA is used by multiple inhibitors for fatty hepatocellular carcinoma and per- ceramide synthases (CerS) to form dihydroceramide. haps other lipid-driven cancers. Mammals have 6 CerS which differ in their substrate specificity, best described for their acyl chain length Miglustat (Zavesca, N-butyl-deoxynojirimycin: NB-DNJ, preferences [17]. Fairly general inhibitors of ceramide Figure 2), an alkyl iminosugar which mimics the transi- synthases, fumonisin B1 [18] and australifungin [19], tion state of the cationic intermediate in the glycosylation have been identified, but inhibitors for specific reaction, prevents the accumulation of glucosylceramide. ceramide synthases could be of therapeutic interest. Miglustat is a competitive inhibitor of glucosylceramide Dihydroceramide is then desaturated by dihydrocera- synthase. It has been approved for the treatment of Type mide desaturase (DH-DES) to form ceramide. Many I Gaucher’s disease and Niemann–Pick disease. Interest- biological properties of ceramides, including the ability ingly, iminosugars can also bind glucocerebrosidase and to induce apoptosis are dependent upon this desatura- act as pharmacological chaperones. Specifically, an analog tion [20]. Therefore, DH-DES has been targeted by of miglustat (N-nonyl-deoxynojirimycin, NN-DNJ) was small molecule inhibitors [21]. Both dihydroceramides shown to rescue lysosomal b-glucosidase activity of and ceramides can be transported from their site of N370S, a mutant that is prevalent in Gaucher disease, synthesis in the endoplasmic reticulum to the Golgi by stabilizing the protein and enhancing its trafficking to compartment [1] where they are converted to sphingo- the lysosome [23]. As such, it is a prominent example of a myelin by sphingomyelin synthase (SMS) or glucosyl- corrector for metabolic disease.