The alkylphospholipid analog miltefosine (hexadecylphosphocholine) is a membrane-directed antitumoral and antileishmanial drug belonging to the alkylphosphocholines, a group of synthetic antiproliferative agents that are promising candidates in anticancer therapy. A variety of mechanisms have been suggested to explain the actions of these compounds, which can induce apoptosis and/or cell growth arrest. In this review, we focus on recent advances in our understanding of the actions of miltefosine and other alkylphospholipids on the human hepatoma HepG2 cell line, with a special emphasis on lipid metabolism. Results obtained in our laboratory indicate that miltefosine displays cytostatic activity and causes apoptosis in HepG2 cells. Likewise, treatment with miltefosine produces an interference with the biosynthesis of phosphatidylcholine via both CDP-choline and phosphatidylethanolamine methylation. With regard to sphingolipid metabolism, miltefosine hinders the formation of sphingomyelin, which promotes intracellular accumulation of ceramide. We have demonstrated for the first time that treatment with miltefosine strongly impedes the esterification of cholesterol and that this effect is accompanied by a considerable increase in the synthesis of cholesterol, which leads to higher levels of cholesterol in the cells. Indeed, miltefosine early impairs cholesterol transport from the plasma membrane to the endoplasmic reticulum, causing a deregulation of cholesterol homeostasis. Similar to miltefosine, other clinically-relevant synthetic alkylphospholipids such as edelfosine, erucylphosphocholine and perifosine show growth inhibitory effects on HepG2 cells. All the tested alkylphospholipids also inhibit the arrival of plasma-membrane cholesterol to the endoplasmic reticulum, which induces a significant cholesterogenic response in these cells, involving an increased gene expression and higher levels of several proteins related to the pathway of biosynthesis as well as the receptor-mediated uptake of cholesterol. Thus, membrane-targeted alkylphospholipids exhibit a common mechanism of action through disruption of cholesterol homeostasis. The accumulation of cholesterol within the cell and the reduction in phosphatidylcholine and sphingomyelin biosyntheses certainly alter the ratio of choline-bearing phospholipids to cholesterol, which is critical for the integrity and functionality of specific membrane microdomains such as lipid rafts. Alkylphospholipid-induced alterations in lipid homeostasis with probable disturbance of the native membrane structure could well affect signaling processes vital to cell survival and growth.

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Hexadecylphosphocholine (HePC) is a synthetic lipid representative of a new group of antiproliferative agents, alkylphosphocholines (APC), which are promising candidates in anticancer therapy. Thus we have studied the action of HePC on the human hepatoblastoma cell line HepG2, which is frequently used as a model for studies into hepatic lipid metabolism. Non‐toxic, micromolar concentrations of HePC exerted an antiproliferative effect on this hepatoma cell line. The incorporation into phosphatidylcholine (PC) of the exogenous precursor [methyl‐14C]choline was substantially reduced by HePC. This effect was not due to any alteration in choline uptake by the cells, the degradation rate of PC or the release of PC into the culture medium. As anaccumulation of soluble choline derivatives points to CTP:phosphocholine cytidylyltransferase (CT) as the target of HePC activity we examined its effects on the different enzymes involved in the biosynthesis of PC via CDP–choline. Treatment with HePC altered neither the activity of choline kinase (CK) nor that of diacylglycerol cholinephosphotransferase (CPT), but it did inhibit CT activity in HepG2 cells. In vitro HePC also inhibited the activity of cytosolic but not membrane‐bound CT. Taken together our results suggest that HePC interferes specifically with the biosynthesis of PC in HepG2 cells by depressing CT translocation to the membrane, which may well impair their proliferation.

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We isolated hepatocytes from rats chronically fed with ethanol and pair-fed control rats and incubated them both in the presence and absence of 100 mM ethanol in order to analyze the uptake into their lipids of several radiolabeled exogenous substrates. The hepatocytes treated chronically with ethanol showed higher lipogenic activity both in neutral lipids and phospholipids from serine, ethanolamine, glycerol and oleate. The only exception found was in the incorporation of choline into phosphatidylcholine (PC), which was lower in the hepatocytes from ethanol-fed rats than in the controls and was concomitant with a decrease in the PC levels of the ethanol-fed hepatocytes. The results obtained after exposing the cells to 100 mM ethanol in vitro indicate that in general the hepatocytes from ethanol-fed rats exhibit a higher lipogenic activity than the control cells. The only difference in the response to ethanol in vitro was found in the biosynthesis of phosphatidylserine (PS) from serine, which rose significantly in control cells but was unaffected in alcoholic hepatocytes. We put this difference in response down to specific adaptation to ethanol feeding.