LYSOLECITHIN AND THE ACTION OF COMPLEMENT

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.

Glyceryl-ether monooxygenase [EC 1.14.16.5]. A microsomal enzyme of ether lipid metabolism

The history, biological, and medical aspects of glyceryl ethers, as well as their chemical syntheses, biosynthesis, and their chemical and physical properties are briefly reviewed as background information for appreciating the importance of the enzyme glyceryl-ether monooxygenase, and for embarking on new studies of this enzyme. The occurrence, isolation and general properties of the microsomal, membrane-bound, glyceryl-ether monooxygenase from rat liver are described. Radiometric, nonradiometric, and coupled and direct spectrophotometric assays for this enzyme are detailed. The effects of detergents on the kinetics of this enzyme are described together with the stoichiometry and the effects of inhibitors. The structure-activity relationships of pterin cofactors and of ether lipid substrates, including their stereospecificities, have been summarized from enzyme kinetic data which are also tabulated. The mechanism of enzymic hydroxylation of glyceryl ethers and a model for the active site of glyceryl-ether monooxygenase are proposed from these apparent kinetic data. Notes on useful future studies of this monooxygenase have been made.

The membrane attack complex of complement and its precursor proteins lack phospholipase activity

The membrane attack complex of human complement and its highly purified precursor proteins have been analyzed for phospholipase activity. Using three different sensitive assays, phospholipase A1, A2, C or D activity could not be detected. Based on the sensitivity of the assays employed, these results indicate the complement-mediated membrane damage is not enhanced by covalent breakdown of membrane phospholipids, but is entirely caused by physical action of the membrane attack complex. The results also imply that the putative serine esterase sites of C6 and C7 are not acting on phospholipids.

Changes in lipid pattern of HeLa cells exposed to immunoglobulin G and complement

1. Immunoglobulin G was isolated from sera of non-immunized rabbits or rabbits immunized with whole HeLa cell homogenate. The anti-HeLa immunoglobulin G and its Fab fragment precipitated the particulate 400000g-min. fraction of HeLa cell homogenate. 2. Immunoglobulin G from immunized or non-immunized rabbits and fresh or inactivated complement were added to HeLa cell cultures. Changes in the cell count and cellular contents of DNA, RNA, protein, total and individual phospholipids, cholesterol (and esters) and ganglioside were followed. 3. Addition of immunoglobulin G from non-immunized rabbits and guinea-pig serum (complement) caused a transient increase in DNA followed by a permanent increase in RNA, protein, dry weight and number of cells per culture. 4. Addition of anti-HeLa immunoglobulin G and active complement caused an increase in the cellular content of cholesterol, total phospholipids, lysophosphatidylcholine and lysophosphatidylethanolamine greater than the increase of the controls and a decrease in the molar percentages of phosphatidylcholine and phosphatidylethanolamine as compared with the controls. 5. The cholesterol/phospholipid ratio remained constant. 6. The appearance of lysophosphoglycerides was transient, reaching a maximum 3hr. after addition of anti-HeLa immunoglobulin G. 7. The content of lysophosphoglycerides in HeLa cultures exposed to immunoglobulin G from non-immunized rabbits ranged from 50% to 30% of the values obtained from cultures exposed to the anti-HeLa immunoglobulin G and complement. 8. The changes in the lipid pattern of the HeLa cells were associated with the appearance of juxta-nuclear vacuoles in cells, but were apparently not specifically related to the presence of active complement.

Inflammatory changes in tumour vessels after systemic 5-hydroxytryptamine, bradykinin, kallikrein, or lysolecithin

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