Characterization of an HL-60 cell variant resistant to the antineoplastic ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine

Edelfosine lipid nanoparticles overcome multidrug resistance in K-562 leukemia cells by a caspase-independent mechanism

The antitumor ether lipid edelfosine is the prototype of a novel generation of promising anticancer drugs that has been shown to be an effective antitumor agent in numerous malignancies. However, several cancer types display resistance to different antitumoral compounds due to multidrug resistance (MDR). Thus, MDR is a major drawback in anticancer therapy. In that sense, the leukemic cell line K-562 shows resistance to edelfosine. This resistance is overcome by the use of nanotechnology. The present work describes the rate and mechanism of internalization of free and nanoencapsulated edelfosine. The molecular mechanisms underlying cell death are described in the present paper by characterization of several molecules implied in the apoptosic and autophagic pathways (PARP, LC3IIB, caspases-3, -9 and -7), and their pattern of expression is compared with the cell induction in a sensitive cell line HL-60. Results showed different internalization patterns in both cells. Clathrin and lipid raft mediated endocytosis were observable in edelfosine uptake, whereas these mechanism were not visible in the uptake of lipid nanoparticles, which might suffer phagocytosis and macropinocytosis. Both treatments induced caspase-mediated apoptosis in HL-60 cells, whereas this cell death mechanism was unnoticeable in K-562 cells. Moreover, an important increase in autophagic vesicles was visible in K-562 cells. Thus, this mechanism might be implicated in overcoming K-562 resistance with the treatment by lipid nanoparticles.

Anticancer mechanisms and clinical application of alkylphospholipids

Synthetic alkylphospholipids (ALPs), such as edelfosine, miltefosine, perifosine, erucylphosphocholine and erufosine, represent a relatively new class of structurally related antitumor agents that act on cell membranes rather than on DNA. They selectively target proliferating (tumor) cells, inducing growth arrest and apoptosis, and are potent sensitizers of conventional chemo- and radiotherapy. ALPs easily insert in the outer leaflet of the plasma membrane and cross the membrane via an ATP-dependent CDC50a-containing 'flippase' complex (in carcinoma cells), or are internalized by lipid raft-dependent endocytosis (in lymphoma/leukemic cells). ALPs resist catabolic degradation, therefore accumulate in the cell and interfere with lipid-dependent survival signaling pathways, notably PI3K-Akt and Raf-Erk1/2, and de novo phospholipid biosynthesis. At the same time, stress pathways (e.g. stress-activated protein kinase/JNK) are activated to promote apoptosis. In many preclinical and clinical studies, perifosine was the most effective ALP, mainly because it inhibits Akt activity potently and consistently, also in vivo. This property is successfully exploited clinically in highly malignant tumors, such as multiple myeloma and neuroblastoma, in which a tyrosine kinase receptor/Akt pathway is amplified. In such cases, perifosine therapy is most effective in combination with conventional anticancer regimens or with rapamycin-type mTOR inhibitors, and may overcome resistance to these agents. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.

Low plasma membrane expression of the miltefosine transport complex renders Leishmania braziliensis refractory to the drug

Miltefosine (hexadecylphosphocholine, MLF) is the first oral drug with recognized efficacy against both visceral and cutaneous leishmaniasis. However, some clinical studies have suggested that MLF shows significantly less efficiency against the cutaneous leishmaniasis caused by Leishmania braziliensis. In this work, we have determined the cellular and molecular basis for the natural MLF resistance observed in L. braziliensis. Four independent L. braziliensis clinical isolates showed a marked decrease in MLF sensitivity that was due to their inability to internalize the drug. MLF internalization in the highly sensitive L. donovani species requires at least two proteins in the plasma membrane, LdMT, a P-type ATPase involved in phospholipid translocation, and its beta subunit, LdRos3. Strikingly, L. braziliensis parasites showed highly reduced levels of this MLF translocation machinery at the plasma membrane, mainly because of the low expression levels of the beta subunit, LbRos3. Overexpression of LbRos3 induces increased MLF sensitivity not only in L. braziliensis promastigotes but also in intracellular amastigotes. These results further highlight the importance of the MLF translocation machinery in determining MLF potency and point toward the development of protocols to routinely monitor MLF susceptibility in geographic areas where L. braziliensis might be prevalent.

The anti-tumor alkylphospholipid perifosine is internalized by an ATP-dependent translocase activity across the plasma membrane of human KB carcinoma cells

Perifosine is a promising anticancer alkylphospholipid (ALP) that induces apoptosis in tumor cells. Here we report evidences against a role of endocytosis in perifosine uptake by human KB carcinoma cells. We have generated a KB cell line resistant to perifosine (KB PER(R) clone10), which shows cross-resistance to the ALPs miltefosine and edelfosine, a marked impairment in the uptake of (14)C-perifosine at both 37 degrees C and 4 degrees C, and no signs for active efflux of the drug. KB PER(R) clone10 cells show a similar rate of raft-dependent endocytosis with respect to the parental cells, and silencing of both clathrin and dynamin in the latter causes only minor changes in the rate of perifosine uptake. Perifosine uptake is a temperature- and ATP-dependent, N-ethylmaleimide- and orthovanadate-sensitive process in parental cells. Accumulation of (14)C-perifosine and the fluorescent phospholipid analogue 6-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)aminocaproyl]-phosphatidylethanolamine (NBD-PE) is inhibited by perifosine in a concentration-dependent manner in parental cells. Moreover, NBD-PE accumulation is slower in PER(R) clone10 cells and correlated with phosphatidylserine exposure in their plasma membrane surface. Together, all these data suggest a role of plasma membrane translocation by a putative phospholipid translocase, rather than endocytosis, as the true mechanism for ALPs uptake in KB carcinoma cells.

Inward Translocation of the Phospholipid Analogue Miltefosine across Caco-2 Cell Membranes Exhibits Characteristics of a Carrier-mediated Process

Miltefosine (hexadecylphosphocholine, HePC) is the first effective oral agent for the treatment of visceral leishmaniasis. The characteristics of HePC incorporation into the human intestinal epithelial cell line Caco-2 were investigated in order to understand its oral absorption mechanism. The results provide evidence for the involvement of a carrier-mediated mechanism, since the association of HePC at the apical pole of Caco-2 cells was (1) saturable as a function of time with a rapid initial incorporation over 5 min followed by a more gradual increase; (2) saturable as a function of concentration over the range studied (2-200 microM) with a saturable component which followed Michaelis-Menten kinetics (apparent K (m) 15.7 micromol/L, V (max) 39.2 nmol/mg protein/h) and a nonspecific diffusion component; (3) partially inhibited by low temperature and ATP depletion, indicating the temperature and energy-dependence of the uptake process. Moreover, we demonstrated, by an albumin back-extraction method, that HePC is internalized via translocation from the outer to the inner leaflet of the plasma membrane and that HePC may preferentially diffuse through intact raft microdomains. In conclusion, our results suggest that incorporation of HePC at the apical membrane of Caco-2 cells may occur through a passive diffusion followed by a translocation in the inner membrane leaflet through an active carrier-mediated mechanism.

Functional cloning of the miltefosine transporter. A novel P-type phospholipid translocase from Leishmania involved in drug resistance

The antitumor drug miltefosine (hexadecylphosphocholine, MIL) has recently been approved as the first oral agent for the treatment of visceral leishmaniasis. Little is known about the mechanisms of action and uptake of MIL in either parasites or tumor cell lines. We have cloned a putative MIL transporter (LdMT) by functional rescue, using a Leishmania donovani-resistant line defective in the inward-directed translocation of both MIL and glycerophospholipids. LdMT is a novel P-type ATPase belonging to the partially characterized aminophospholipid translocase subfamily. Resistant parasites transfected with LdMT regain their sensitivity to MIL and edelfosine and the ability to normally take up [14C]MIL and fluorescent-labeled glycerophospholipids. Moreover, LdMT localizes to the plasma membrane, and its overexpression in Leishmania tarentolae, a species non-sensitive to MIL, significantly increases the uptake of [14C]MIL, strongly suggesting that this protein behaves as a true translocase. Finally, both LdMT-resistant alleles encompass single but distinct point mutations, each of which impairs transport function, explaining the resistant phenotype. These results demonstrate biochemically and genetically the direct involvement of LdMT in MIL and phospholipids translocation in Leishmania and describe for the first time a P-type ATPase involved in MIL uptake and potency in eukaryotic cells.

Different modes of internalization of apoptotic alkyl-lysophospholipid and cell-rescuing lysophosphatidylcholine

The synthetic alkyl-lysophospholipid (ALP), Et-18-OCH3 (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine), can induce apoptosis in tumour cells. Unlike conventional chemotherapeutic drugs, ALP acts at the cell-membrane level. We have reported previously that ALP is internalized, and interferes with phosphatidylcholine (PC) biosynthesis de novo, which appeared to be essential for survival in lymphoma cells [Van der Luit, Budde, Ruurs, Verheij and Van Blitterswijk (2002) J. Biol. Chem. 277, 39541-39547]. Here, we report that, in HeLa cells, ALP accumulates in lipid rafts, and that internalization is inhibited by low temperature, monensin, disruption of lipid rafts and expression of a dominant-negative mutant of dynamin bearing a replacement of Lys44 with alanine (K44A). Thus ALP is internalized via raft- and dynamin-mediated endocytosis. Dynamin-K44A alleviated the ALP-induced inhibition of PC synthesis and rescued the cells from apoptosis induction. Additional cell rescue was attained by exogenous lysoPC, which after internalization serves as an alternative substrate for PC synthesis (through acylation). Unlike ALP, and despite the high structural similarity to ALP, lysoPC uptake did not occur via lipid rafts and did not depend on functional dynamin, indicating no involvement of endocytosis. Albumin back-extraction experiments suggested that (radiolabelled) lysoPC undergoes transbilayer movement (flipping). We conclude that ALP is internalized by endocytosis via lipid rafts to cause apoptosis, while exogenous cell-rescuing lysoPC traverses the plasma membrane outside rafts by flipping. Additionally, our data imply the importance of ether bonds in lyso-phospholipids, such as in ALP, for partitioning in lipid rafts.

Leishmania donovani resistance to miltefosine involves a defective inward translocation of the drug

Miltefosine (hexadecylphosphocholine [HePC]) is the first drug approved for the oral treatment of visceral leishmaniasis. As part of a study on the mechanisms of action of this drug and on the rates of resistance to this drug, we have been working in vitro with an Leishmania donovani line that was previously shown to be 15-fold more resistant to HePC. We have studied the accumulation of [(14)C]HePC by L. donovani promastigotes and have found a drastic reduction (>95%) in the ability of the resistant line to internalize the drug. Binding of HePC to the plasma membrane and drug efflux from preloaded cells were similar in both drug-sensitive and -resistant lines, and no [(14)C]HePC metabolism was evident in either line. Resistant parasites were also unable to take up other short-chain phospholipid analogs, independently of their polar head group, even though endocytosis remained unaltered. Finally, HePC uptake was temperature and energy dependent and sensitive to the thiol-reactive agent N-ethylmaleimide. We propose that inward translocation of a short-chain phospholipid across the plasma membrane may exist in Leishmania promastigotes and that such activity is defective in the resistant line.

Alkyl-lysophospholipid accumulates in lipid rafts and induces apoptosis via raft-dependent endocytosis and inhibition of phosphatidylcholine synthesis

The synthetic alkyl-lysophospholipid (ALP), 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine, is an antitumor agent that acts on cell membranes and can induce apoptosis. We investigated how ALP is taken up by cells, how it affects de novo biosynthesis of phosphatidylcholine (PC), and how critical this is to initiate apoptosis. We compared an ALP-sensitive mouse lymphoma cell line, S49, with an ALP-resistant variant, S49(AR). ALP inhibited PC synthesis at the CTP:phosphocholine cytidylyltransferase (CT) step in S49 cells, but not in S49(AR) cells. Exogenous lysophosphatidylcholine, providing cells with an alternative way (acylation) to generate PC, rescued cells from ALP-induced apoptosis, indicating that continuous rapid PC turnover is essential for cell survival. Apoptosis induced by other stimuli that do not target PC synthesis remained unaffected by lysophosphatidylcholine. Using monensin, low temperature and albumin back-extraction, we demonstrated that ALP is internalized by endocytosis, a process defective in S49(AR) cells. This defect neither involved clathrin-coated pit- nor fluid-phase endocytosis, but depended on lipid rafts, because disruption of these microdomains with methyl-beta-cyclodextrin or filipin (sequestering cholesterol) or bacterial sphingomyelinase reduced uptake of ALP. Furthermore, ALP was found accumulated in isolated rafts and disruption of rafts also prevented the inhibition of PC synthesis and apoptosis induction in S49 cells. In summary, ALP is internalized by raft-dependent endocytosis to inhibit PC synthesis, which triggers apoptosis.

Alkyl-lysophospholipid resistance in multidrug-resistant Leishmania tropica and chemosensitization by a novel P-glycoprotein-like transporter modulator

Drug resistance has emerged as a major impediment in the treatment of leishmaniasis. Alkyl-lysophospholipids (ALP), originally developed as anticancer drugs, are considered to be the most promising antileishmanial agents. In order to anticipate probable clinical failure in the near future, we have investigated possible mechanisms of resistance to these drugs in Leishmania spp. The results presented here support the involvement of a member of the ATP-binding cassette (ABC) superfamily, the Leishmania P-glycoprotein-like transporter, in the resistance to ALP. (i) First, a multidrug resistance (MDR) Leishmania tropica line overexpressing a P-glycoprotein-like transporter displays significant cross-resistance to the ALP miltefosine and edelfosine, with resistant indices of 9.2- and 7.1-fold, respectively. (ii) Reduced expression of P-glycoprotein in the MDR line correlates with a significant decrease in ALP resistance. (iii) The ALP were able to modulate the P-glycoprotein-mediated resistance to daunomycin in the MDR line. (iv) We have found a new inhibitor of this transporter, the sesquiterpene C-3, that completely sensitizes MDR parasites to ALP. (v) Finally, the MDR line exhibits a lower accumulation than the wild-type line of bodipy-C(5)-PC, a fluorescent analogue of phosphatidylcholine that has a structure resembling that of edelfosine. Also, C-3 significantly increases the accumulation of the fluorescent analogue to levels similar to those of wild-type parasites. The involvement of the Leishmania P-glycoprotein-like transporter in resistance to drugs used in the treatment of leishmaniasis also supports the importance of developing new specific inhibitors of this ABC transporter.

Similar effects of ether phospholipids, PAF and lyso-PAF on the Ca(2+)-ATPase activity of rat brain synaptosomes and leukocyte membranes

The present study is an extension of our previous work with the antineoplastic ether phospholipid ET-18-OCH3 (edelfosine), which was shown to affect the activity of the Ca(2+)-ATPase of rat brain synaptosomes and peritoneal leukocyte membranes. The effect of ET-18-OCH3 was compared with that of the 16-carbon chain analogue ET-16-OCH3 as well as with the structurally related 16- and 18-carbon PAFs (platelet-activating factors) and lyso-PAFs. In addition, the two alkylphosphocholines D-20166 and D-21266 (perifosine) were included in the investigation. The influence of all of the compounds followed the same pattern, i.e., the Ca(2+)-ATPase activity of the synaptosomes was increased over a relatively narrow concentration range (peak at 20-30 microM) and that of the leukocyte membranes was inhibited in a concentration-dependent manner by 10-50 microM concentrations of the drugs. Ether phospholipids with an 18-carbon chain at C-1 were more potent than those with a 16-carbon chain. All of the compounds increased the activity of the synaptosomal ATPase to the same extend (ca. 50%). With the exception of lyso-PAF, all inhibited the enzyme activity of leukocyte membranes by 60-70%, whereas lyso-PAF was less effective (ca. 50% inhibition). The concentration range of activity for PAF and lyso-PAF indicates that their effect on the enzyme activity was caused by receptor-independent mechanisms. The ether phospholipids and alkylphosphocholines are suggested to act by accumulating in the membranes and thereby altering the character of the lipid environment of the enzyme rather than by a direct interaction with the Ca(2+)-ATPase.

ET-18-OCH(3)-induced cytotoxicity and DNA damage in rat astrocytes

The ether lipid 1-octadecyl-2-methyl-rac-glicero-3-phosphocholine (ET-18-OCH(3)) is known to be selectively cytotoxic toward several types of tumor cells, in which it seems to activate a process of apoptotic cell death. Moreover, the drug has been demonstrated to be active in normal cells too, particularly in rat astrocytes. In these cells at low dosage (from 1 to 6 microg/ml of medium) ET-18-OCH(3) stimulates maturation and protective responses, whereas at increasing dosages (from 8 to 20 microg/ml) it shows cytotoxic effects. The present study demonstrates that when ET-18-OCH(3) is added to astrocytes, it activates, in a time- and concentration-dependent manner, an oxidative process by increasing both the generation of reactive oxygen species (ROS), including nitric oxide, and lipid peroxidation. When there is a high ET-18-OCH(3) concentration or the time of treatment is prolonged, the increased oxidative condition seems to trigger DNA fragmentation (monitored by COMET assay) as well as loss in cell viability. These cytotoxic effects indicate that ROS may be considered, in our experimental model, as executioners of a program of cell death. In addition, ET-18-OCH(3) being a promising molecule in antitumor therapy, our data, while reinforcing the importance of monitoring the therapeutic drug dosage employed, also suggest that it may be useful to associate some antioxidants with antitumor treatments.

Bcl-2 plays a key role instead of mdr1 in the resistance to hexadecylphosphocholine in human epidermoid tumor cell line KB

We induced tolerance to hexadecylphosphocholine (HePC) in the human epidermoid tumor cell line, KB. After 70 weeks of adaptation, the IC50 of HePC in the resistant cells KBr was 32-fold higher than in parental KB cells, and they were 30-fold more resistant to another ether lipid analogue, ET-18-OCH3. The KBr cells also showed cross-resistance to vincristine and colchicine while remaining sensitive to other chemotherapy agents. RT-PCR assays showed that expression of the multidrug resistance gene (MDR1) was positive in KBr cells, whereas the expression of GST-pi (glutathione S-transferase pi) and MRP (multidrug resistance protein) was undetectable in KBr cells. Both an immunocytochemistry test and Western blot analysis indicated that the expression of bcl-2 in KBr cells was strongly positive, while it was only mildly expressed in KB cells. Verapamil could not reverse the resistance of KBr to HePC although it is a well-known reversing agent against MDR1. Our results suggest that bcl-2 instead of MDR1 plays a major role in the resistance of KBr cells.

Synergistic effects of heat and ET-18-OCH3 on membrane expression of hsp70 and lysis of leukemic K562 cells

We previously reported that cell surface expression of hsp70, the major stress inducible member of the 70-kDa heat shock protein family, is inducible by nonlethal heat as well as by treatment with the membrane-interactive compound alkyl-lysophospholipid 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) selectively on human tumor cell lines. Plasma membrane expression of hsp70 increases selectively the sensitivity of tumor cells to lysis and, therefore, might play an important role in the antitumor immune response. Here, we demonstrate that a combined treatment consisting of sublethal heat (41.8 degrees C) and a noncytotoxic concentration of ET-18-OCH3 (25 micrograms/mL) results in a synergistic increase in the amount of cell membrane-bound hsp70 on leukemic K562 cells and on freshly isolated bone marrow of a chronic myelogeneous leukemia (CML) patient, but not on peripheral blood lymphocytes or CD34+ hematopoietic progenitor cells of healthy human individuals. Under these conditions the repopulating capacity of progenitor cells was not influenced. The increased hsp70 membrane expression on leukemic K562 cells results in a significantly increased sensitivity to lysis mediated by natural killer cells. In contrast to leukemic cells, the lysis of peripheral blood lymphocytes and CD34+ progenitor cells that lack expression of hsp70 on their plasma membrane was not negatively influenced by this treatment. A nonspecific disruption of the plasma membrane could be excluded, because treatment with a nontoxic concentration of the detergent Tween20 did not have an influence on hsp70 cell surface expression or on the sensitivity to lysis. Our findings might have further clinical implications with respect to purging of bone marrow from patients suffering from leukemia at sublethal conditions to induce a tumor-selective immune response.