Disruption of lipid domain organization in monolayers of complex yeast lipid extracts induced by the lysophosphatidylcholine analogue edelfosine in vivo

Activation of the cell wall integrity pathway negatively regulates TORC2-Ypk1/2 signaling through blocking eisosome disassembly in Saccharomyces cerevisiae

The target of rapamycin complex 2 (TORC2) signaling is associated with plasma membrane (PM) integrity. In Saccharomyces cerevisiae, TORC2-Ypk1/2 signaling controls sphingolipid biosynthesis, and Ypk1/2 phosphorylation by TORC2 under PM stress conditions is increased in a Slm1/2-dependent manner, under which Slm1 is known to be released from an eisosome, a furrow-like invagination PM structure. However, it remains unsolved how the activation machinery of TORC2-Ypk1/2 signaling is regulated. Here we show that edelfosine, a synthetic lysophospholipid analog, inhibits the activation of TORC2-Ypk1/2 signaling, and the cell wall integrity (CWI) pathway is involved in this inhibitory effect. The activation of CWI pathway blocked the eisosome disassembly promoted by PM stress and the release of Slm1 from eisosomes. Constitutive activation of TORC2-Ypk1/2 signaling exhibited increased sensitivity to cell wall stress. We propose that the CWI pathway negatively regulates the TORC2-Ypk1/2 signaling, which is involved in the regulatory mechanism to ensure the proper stress response to cell wall damage.

Differential impact of synthetic antitumor lipid drugs on the membrane organization of phosphatidic acid and diacylglycerol monolayers

Anti-tumour lipids are synthetic analogues of lysophosphatidylcholine. These drugs are both cytotoxic and cytostatic, and more interestingly, exert these effects preferentially in tumour cells. While the exact mechanism of action isn't fully elucidated, these drugs appear to preferentially partition into rigid lipid domains in cell membranes. Upon insertion, the compounds alter membrane domain organization, disrupt normal signal transduction, and cause cell death. Recently, it has been reported that these drugs induce accumulation of diacylglycerol in yeast cells which in turn sensitizes cells to the drugs. Conversely, phosphatidic acid accumulation appears to protect cells against the drugs. In the current work, the aim was to compare the biophysical effects of the drugs edelfosine, miltefosine and perifosine on monolayers of dimyristoyl phosphatidic acid, dimyristoyl glycerol and an equimolar mixture, to understand how these lipids modulate the mode of action. Surface pressure - area isotherms, compression moduli and Brewster angle microscopy were used to compare drug effects on lipid packing, monolayer compressibility and lateral domain organization of these films. Results suggest that edelfosine and miltefosine have stabilizing effects on all of the monolayers, while perifosine destabilizes dimyristoyl glycerol and the equimolar mixture. Additionally, all three drugs change the morphology of the domains observed. Based on these results the stabilization of diacylgylcerol by edelfosine and miltefosine may contribute to the mode of action as diacylglycerol is a known disruptor of bilayers. Perifosine however does not stabilize diacylglycerol, and therefore cell death may occur through a more direct inhibition of specific signal transduction. These results suggest that perifosine may illicit cytotoxicity through a different mechanism compared to the other antitumor lipid drugs.

A combination drug delivery system employing thermosensitive liposomes for enhanced cell penetration and improved in vitro efficacy

Drug-loaded thermosensitive liposomes are investigated as drug delivery systems in combination with local mild hyperthermia therapy due to their capacity to release their cargo at a specific temperature range (40-42 °C). Additional benefit can be achieved by the development of such systems that combine two different anticancer drugs, have cell penetration properties and, when heated, release their drug payload in a controlled fashion. To this end, liposomes were developed incorporating at low concentration (5 mol%) a number of monoalkylether phosphatidylcholine lipids, encompassing the platelet activating factor, PAF, and its analogues that induce thermoresponsiveness and have anticancer biological activity. These thermoresponsive liposomes were efficiently (>90%) loaded with doxorubicin (DOX), and their thermal properties, stability and drug release were investigated both at 37 ^◦C and at elevated temperatures. In vitro studies of the most advantageous liposomal formulation containing the methylated PAF derivative (methyl-PAF, edelfosine), an established antitumor agent, were performed on human prostate cancer cell lines. This system exhibits controlled release of DOX at 40-42 °C, enhanced cell uptake due to the presence of methyl-PAF, and improved cell viability inhibition due to the combined action of both medications.

Arachidonic acid and lysophosphatidylcholine inhibit multiple late steps of regulated exocytosis

The canonical Phospholipase A₂ (PLA₂) metabolites lysophosphatidylcholine (LPC) and arachidonic acid (ARA) affect regulated exocytosis in a wide variety of cells and are proposed to directly influence membrane merger owing to their respective spontaneous curvatures. According to the Stalk-pore hypothesis, negative curvature ARA inhibits and promotes bilayer merger upon introduction into the distal or proximal monolayers, respectively; in contrast, with positive curvature, LPC has the opposite effects. Using fully primed, release-ready native cortical secretory vesicles (CV), well-established fusion assays and standardized lipid analyses, we show that exogenous ARA and LPC, as well as their non-metabolizable analogous, ETYA and ET-18-OCH3, inhibit the docking/priming and membrane merger steps, respectively, of regulated exocytosis.

Primary Metabolism and Medium-Chain Fatty Acid Alterations Precede Long-Chain Fatty Acid Changes Impacting Neutral Lipid Metabolism in Response to an Anticancer Lysophosphatidylcholine Analogue in Yeast

The nonmetabolizable lysophosphatidylcholine (LysoPC) analogue edelfosine is the prototype of a class of compounds being investigated for their potential as selective chemotherapeutic agents. Edelfosine targets membranes, disturbing cellular homeostasis. Is not clear at this point how membrane alterations are communicated between intracellular compartments leading to growth inhibition and eventual cell death. In the present study, a combined metabolomics/lipidomics approach for the unbiased identification of metabolic pathways altered in yeast treated with sublethal concentrations of the LysoPC analogue was employed. Mass spectrometry of polar metabolites, fatty acids, and lipidomic profiling was used to study the effects of edelfosine on yeast metabolism. Amino acid and sugar metabolism, the Krebs cycle, and fatty acid profiles were most disrupted, with polar metabolites and short-medium chain fatty acid changes preceding long and very long-chain fatty acid variations. Initial increases in metabolites such as trehalose, proline, and γ-amino butyric acid with a concomitant decrease in metabolites of the Krebs cycle, citrate and fumarate, are interpreted as a cellular attempt to offset oxidative stress in response to mitochondrial dysfunction induced by the treatment. Notably, alanine, inositol, and myristoleic acid showed a steady increase during the period analyzed (2, 4, and 6 h after treatment). Of importance was the finding that edelfosine induced significant alterations in neutral glycerolipid metabolism resulting in a significant increase in the signaling lipid diacylglycerol.

Applications of Brewster angle microscopy from biological materials to biological systems

Brewster angle microscopy (BAM) is a powerful technique that allows for real-time visualization of Langmuir monolayers. The lateral organization of these films can be investigated, including phase separation and the formation of domains, which may be of different sizes and shapes depending on the properties of the monolayer. Different molecules or small changes within a molecule such as the molecule's length or presence of a double bond can alter the monolayer's lateral organization that is usually undetected using surface pressure-area isotherms. The effect of such changes can be clearly observed using BAM in real-time, under full hydration, which is an experimental advantage in many cases. While previous BAM reviews focused more on selected compounds or compared the impact of structural variations on the lateral domain formation, this review provided a broader overview of BAM application using biological materials and systems including the visualization of amphiphilic molecules, proteins, drugs, extracts, DNA, and nanoparticles at the air-water interface.

Comparative chemical genomics reveal that the spiroindolone antimalarial KAE609 (Cipargamin) is a P-type ATPase inhibitor

The spiroindolones, a new class of antimalarial medicines discovered in a cellular screen, are rendered less active by mutations in a parasite P-type ATPase, PfATP4. We show here that S. cerevisiae also acquires mutations in a gene encoding a P-type ATPase (ScPMA1) after exposure to spiroindolones and that these mutations are sufficient for resistance. KAE609 resistance mutations in ScPMA1 do not confer resistance to unrelated antimicrobials, but do confer cross sensitivity to the alkyl-lysophospholipid edelfosine, which is known to displace ScPma1p from the plasma membrane. Using an in vitro cell-free assay, we demonstrate that KAE609 directly inhibits ScPma1p ATPase activity. KAE609 also increases cytoplasmic hydrogen ion concentrations in yeast cells. Computer docking into a ScPma1p homology model identifies a binding mode that supports genetic resistance determinants and in vitro experimental structure-activity relationships in both P. falciparum and S. cerevisiae. This model also suggests a shared binding site with the dihydroisoquinolones antimalarials. Our data support a model in which KAE609 exerts its antimalarial activity by directly interfering with P-type ATPase activity.