Structure-Activity Relationships of Glucosamine-Derived Glycerolipids: the Role of the Anomeric Linkage, the Cationic Charge and the Glycero Moiety on the Antitumor Activity

Modulating polybasic character of galactose-based glycosylated antitumor ether lipids for enhanced cytotoxic response

We describe the structure-activity relationship studies of galactose-based glycosylated antitumor ether lipids (GAELs) by installing amine groups at different positions of galactose and the glycerol backbone. Different dibasic and tribasic analogues of galacto-GAELs were synthesized and tested against a panel of human epithelial cancer cell lines. A β-anomeric triamino galactose scaffold, was the most active compound of the series and displayed CC50 in the range of 2.6 ± 0.2 μM to 6.5 ± 0.1 μM against various epithelial cancer cell lines. This compound exhibited superior activity to kill cancer cells than cisplatin. The hit GAEL compound did not induce caspase activation and therefore, the cell-killing effect does not occur due to caspase-mediated apoptosis. This observation is in line with the previously reported GAEL prototypes.

Synthesis of ether lipids: natural compounds and analogues

Ether lipids are compounds present in many living organisms including humans that feature an ether bond linkage at the sn-1 position of the glycerol. This class of lipids features singular structural roles and biological functions. Alkyl ether lipids and alkenyl ether lipids (also identified as plasmalogens) correspond to the two sub-classes of naturally occurring ether lipids. In 1979 the discovery of the structure of the platelet-activating factor (PAF) that belongs to the alkyl ether class of lipids increased the interest in these bioactive lipids and further promoted the synthesis of non-natural ether lipids that was initiated in the late 60's with the development of edelfosine (an anticancer drug). More recently, ohmline, a glyco glycero ether lipid that modulates selectively SK3 ion channels and reduces in vivo the occurrence of bone metastases, and other glyco glycero ether also identified as GAEL (glycosylated antitumor ether lipids) that exhibit promising anticancer properties renew the interest in this class of compounds. Indeed, ether lipid represent a new and promising class of compounds featuring the capacity to modulate selectively the activity of some membrane proteins or, for other compounds, feature antiproliferative properties via an original mechanism of action. The increasing interest in studying ether lipids for fundamental and applied researches invited to review the methodologies developed to prepare ether lipids. In this review we focus on the synthetic method used for the preparation of alkyl ether lipids either naturally occurring ether lipids (e.g., PAF) or synthetic derivatives that were developed to study their biological properties. The synthesis of neutral or charged ether lipids are reported with the aim to assemble in this review the most frequently used methodologies to prepare this specific class of compounds.

The Potential of Novel Lipid Agents for the Treatment of Chemotherapy-Resistant Human Epithelial Ovarian Cancer

Simple Summary

Disease recurrence and chemotherapy resistance are the major causes of mortality for the majority of epithelial ovarian cancer (EOC) patients. Standard of care relies on cytotoxic drugs that induce a form of cell death called apoptosis. EOC cells can evolve to resist apoptosis. We developed drugs called glycosylated antitumor ether lipids (GAELs) that kill EOC cells by a mechanism that does not involve apoptosis. GAELs most likely induce cell death through a process called methuosis. Importantly, we showed that GAELs are effective at killing chemotherapy-resistant EOC cells in vitro and in vivo. Our work shows that the EOC community should begin to investigate methuosis-inducing agents as a novel therapeutic platform to treat chemotherapy-resistant EOC.

Abstract

Recurrent epithelial ovarian cancer (EOC) coincident with chemotherapy resistance remains the main contributor to patient mortality. There is an ongoing investigation to enhance patient progression-free and overall survival with novel chemotherapeutic delivery, such as the utilization of antiangiogenic medications, PARP inhibitors, or immune modulators. Our preclinical studies highlight a novel tool to combat chemotherapy-resistant human EOC. Glycosylated antitumor ether lipids (GAELs) are synthetic glycerolipids capable of killing established human epithelial cell lines from a wide variety of human cancers, including EOC cell lines representative of different EOC histotypes. Importantly, GAELs kill high-grade serous ovarian cancer (HGSOC) cells isolated from the ascites of chemotherapy-sensitive and chemotherapy-resistant patients grown as monolayers of spheroid cultures. In addition, GAELs were well tolerated by experimental animals (mice) and were capable of reducing tumor burden and blocking ascites formation in an OVCAR-3 xenograft model. Overall, GAELs show great promise as adjuvant therapy for EOC patients with or without chemotherapy resistance.

Amphiphilic glycoconjugates as potential anti-cancer chemotherapeutics

Amphiphilicity is one of the desirable features in the process of drug development which improves the biological as well as the pharmacokinetics profile of bioactive molecule. Carbohydrate moieties present in anti-cancer natural products and synthetic molecules influence the amphiphilicity and hence their bioactivity. This review focuses on natural and synthetic amphiphilic anti-cancer glycoconjugates. Different classes of molecules with varying degree of amphiphilicity are covered with discussions on their structure-activity relationship and mechanism of action.

Ultrashort cationic lipopeptides and lipopeptoids: Evaluation and mechanistic insights against epithelial cancer cells

Peptides present an attractive scaffold for the development of new anticancer lead agents due to their accessibility and ease of modification. Synthetic ultrashort cationic lipopeptides, with four amino acids or less conjugated to a fatty acid, were developed to retain the biological activity of longer peptides in a smaller molecular size. Herein, we report the activity of amphiphilic lipotripeptides, lipotripeptoids and lipotetrapeptides against breast (MDA-MB-231, JIMT-1), prostate (DU145) and pancreas (MiaPaCa2) epithelial cancer cell lines. The lipotripeptide C16-KKK-NH2 and lipotetrapeptide C16-PCatPHexPHexPCat-NH2 were identified to possess anticancer activity. The latter lipotetrapeptide possess a short polyproline scaffold consisting of only two L-4R-aminoproline (PCat) and two L-4R-hexyloxyproline (PHex). However, all the prepared lipotripeptoids lack anticancer activity. The amphiphilic C16-PCatPHexPHexPCat-NH2 exhibited similar anticancer potency to the surfactant benzethonium chloride while superior activity was observed in comparison to myristylamine. Mechanistic studies revealed that the peptides do not lyse ovine erythrocytes nor epithelial cancer cells, thus ruling out necrosis as the mechanism of cell death. Surprisingly, the two lipopeptides exhibit different mechanisms of action that result in cancer cell death. The lipotripeptide C16-KKK-NH2 was found to induce caspase-mediated apoptosis while C16-PCatPHexPHexPCat-NH2 kills tumor cells independent of caspases.

Design, synthesis and evaluation of cytotoxic properties of bisamino glucosylated antitumor ether lipids against cancer cells and cancer stem cells

Glycosylated antitumor ether lipids (GAELs) are a class of amphiphilic antitumor agents that kill cancer cells by a non-apoptotic pathway.

Synthetic Glycosylated Ether Glycerolipids as Anticancer Agents

Glycosylated antitumor ether lipids (GAELs) are a class of synthetic antitumor ether lipids (AELs) with a sugar moiety in place of the phosphocholine found in the prototypical AEL, edelfosine. This chapter reviews the development of GAELs as antitumor agents. Studies on structure–activity relationships, mechanism of induction of cell death, metabolism, selectivity against cancer cells, toxicity, hemolysis and thrombogenic effects are discussed. The requirements for significant cytotoxic activity include a glycerol moiety, a cationic sugar other than mannose and an O- or C-glycosidic bond with either α- or β-configuration. Compounds with S- and N-glycosidic linkages are not very active. The most active GAEL to date, 1-O-hexadecyl-2-O-methyl-3-O-(2′-amino-2′-deoxy-α-d-galactopyranosyl)-sn-glycerol, displays greater in vitro activity than edelfosine, the AEL “gold standard”. The unique properties of GAELs as antitumor agents include their apoptotic-independent mechanism of inducing cell death and the ability to kill cancer stem cells. These characteristics of GAELs offer the potential for their development into chemotherapeutic agents to prevent the recurrence of tumors as well as for treatment against drug-resistant cancers.

Cytotoxic properties of D-gluco-, D-galacto- and D-manno-configured 2-amino-2-deoxy-glycerolipids against epithelial cancer cell lines and BT-474 breast cancer stem cells

Glycosylated antitumor ether lipids (GAELs) 6 and 7 containing a α- or β-D-gluco-configured 2-amino-2-deoxy (2-NH2-Glc) sugar moiety linked to a glycerolipid aglycone kill cancer cell lines via a non-apoptotic mechanism that could be exploited to kill cancer stem cells. To test this hypothesis and develop novel potent GAEL analogs, we synthesized GAELS which contain D-galacto- and D-manno-configured 2-amino-2-deoxy sugar moieties (2-NH2-Gal or 2-NH2-Man) and investigated their cytotoxicity against human epithelial cancer cell lines and cancer stem cells derived from BT-474 breast cancer cells. Within the class of D-galacto-configured GAELs, we prepared both O- and S-glycosidic linkages as well as their corresponding α- and β-anomers and screened against breast (BT-474, JIMT-1 and BT-549), pancreas (MiaPaCa2) and prostate cancer (DU145, PC3) cancer cell lines. The α-anomeric 2-NH2-Gal-based lipid 1 was the most active of all the compounds tested with CC50 values of 4.4-8 μM and is the most active GAEL synthesized to date. The β-anomer 2 was 4->5-fold less active than 1. Replacement of the α-O-glycosidic by an α-S-glycosidic linkage resulted in a 2-4-fold reduction in activity, while the β-S-glycolipid 4 was inactive. In comparison, α-configured 2-NH2-Man-based glycerolipid 5 displayed very little activity with CC50 > 30 μM. The effect of the most active GAELs, 1, 6, or 7, on cancer stem cell viability revealed that all three inhibited the formation of tumorspheres from BT-474 cancer stem cell lines, caused the disintegration of preformed tumorspheres and resulted in total loss of cell viability of the cancer stem cells at concentrations of 20 μM. In contrast, the related antitumor ether lipid gold standard, edelfosine that is in clinical development was much less effective in preventing tumorsphere formation and affecting the viability of the cancer stem cells. Taken together our study demonstrates that α-GAEL anomers are more potent than their corresponding β-anomers and that the nature of the CHO moiety as well as the glycosidic bond significantly affects activity. The study also showed that GAELs are effective in killing CSCs while the apoptosis-inducing edelfosine is not.

Structure activity relationships of N-linked and diglycosylated glucosamine-based antitumor glycerolipids

1-O-Hexadecyl-2-O-methyl-3-O-(2'-amino-2'-deoxy-β-d-glucopyranosyl)-sn-glycerol (1) was previously reported to show potent in vitro antitumor activity on a range of cancer cell lines derived from breast, pancreas and prostate cancer. This compound was not toxic to mice and was inactive against breast tumor xenografts in mice. This inactivity was attributed to hydrolysis of the glycosidic linkage by glycosidases. Here three N-linked (glycosylamide) analogs 2–4, one triazole-linked analog 5 of 1 as well as two diglycosylated analogs 6 and 7 with different stereochemistry at the C2-position of the glycerol moiety were synthesized and their antitumor activity against breast (JIMT-1, BT-474, MDA-MB-231), pancreas (MiaPaCa2) and prostrate (DU145, PC3) cancer cell lines was determined. The diglycosylated analogs 1-O-hexadecyl-2(R)-, 3-O-di-(2'-amino-2'-deoxy-β-d-glucopyranosyl)-sn-glycerol (7) and the 1:1 diastereomeric mixture of 1-O-hexadecyl-2(R/S), 3-O-di-(2'-amino-2'-deoxy-β-d-glucopyranosyl)-sn-glycerol (6) showed the most potent cytotoxic activity at CC₅₀ values of 17.5 µM against PC3 cell lines. The replacement of the O-glycosidic linkage by a glycosylamide or a glycosyltriazole linkage showed little or no activity at highest concentration tested (30 µM), whereas the replacement of the glycerol moiety by triazole resulted in CC₅₀ values in the range of 20 to 30 µM. In conclusion, the replacement of the O-glycosidic linkage by an N-glycosidic linkage or triazole-linkage resulted in about a two to three fold loss in activity, whereas the replacement of the methoxy group on the glycerol backbone by a second glucosamine moiety did not improve the activity. The stereochemistry at the C2-position of the glycero backbone has minimal effect on the anticancer activities of these diglycosylated analogs.