A new class of anticancer alkylphospholipids uses lipid rafts as membrane gateways to induce apoptosis in lymphoma cells

Abstract

Single-chain alkylphospholipids, unlike conventional chemotherapeutic drugs, act on cell membranes to induce apoptosis in tumor cells. We tested four different alkylphospholipids, i.e., edelfosine, perifosine, erucylphosphocholine, and compound D-21805, as inducers of apoptosis in the mouse lymphoma cell line S49. We compared their mechanism of cellular entry and their potency to induce apoptosis through inhibition of de novo biosynthesis of phosphatidylcholine at the endoplasmic reticulum. Alkylphospholipid potency closely correlated with the degree of phosphatidylcholine synthesis inhibition in the order edelfosine > D-21805 > erucylphosphocholine > perifosine. In all cases, exogenous lysophosphatidylcholine, an alternative source for cellular phosphatidylcholine production, could partly rescue cells from alkylphospholipid-induced apoptosis, suggesting that phosphatidylcholine biosynthesis is a direct target for apoptosis induction. Cellular uptake of each alkylphospholipid was dependent on lipid rafts because pretreatment of cells with the raft-disrupting agents, methyl-B-cyclodextrin, filipin, or bacterial sphingomyelinase, reduced alkylphospholipid uptake and/or apoptosis induction and alleviated the inhibition of phosphatidylcholine synthesis. Uptake of all alkylphospholipids was inhibited by small interfering RNA (siRNA) -mediated blockage of sphingomyelin synthase (SMS1), which was previously shown to block raft-dependent endocytosis. Similar to edelfosine, perifosine accumulated in (isolated) lipid rafts independent on raft sphingomyelin content per se. However, perifosine was more susceptible than edelfosine to back-extraction by fatty acid-free serum albumin, suggesting a more peripheral location in the cell due to less effective internalization. Overall, our results suggest that lipid rafts are critical membrane portals for cellular entry of alkylphospholipids depending on SMS1 activity and, therefore, are potential targets for alkylphospholipid anticancer therapy. [Mol Cancer Ther 2007;6(8):2337 -45]

CDC50A plays a key role in the uptake of the anticancer drug perifosine in human carcinoma cells

“…Thus, we have found a positive correlation between perifosine uptake and NBD-aminophospholipid translocation (a wellestablished marker for aminophospholipid translocase activity) in several KB clones obtained in our laboratory. Furthermore, we found no correlation whatsoever between perifosine uptake and endocytosis rates in a subset of fourteen cell lines, which is in stark contrast with previous works where the role of raft-dependent endocytosis in perifosine uptake has been proposed [13,32,33]. This discrepancy 18 may, however, only be apparent if we consider that only adherent cell lines, but no leukemia or lymphoma cells, were used in the present study, whereas the authors who proposed the raft-dependent hypothesis for perifosine uptake have recently published a further study [15] where they discriminate between lymphoma and carcinoma cells on the basis of their prevalent perifosine-uptake mechanism (raftdependent endocytosis in the former, and a plasma membrane translocator in the latter).…”

“…However, some discrepancies have arisen concerning how perifosine enters cancer cells, and what previous steps are required for the drug to reach its intracellular targets and trigger cell death. Thus, it has been proposed that ALP enters cells either by raft-dependent endocytosis [13,32,33] or by transporter-mediated translocation of perifosine through the plasma membrane [14,15,16].…”

“…Two pathways for the entry of ALP into cancer cells, namely raft-mediated endocytosis in lymphoma cells [13] and translocator-mediated uptake in carcinoma 4 cells [14][15][16], have been described. A clearer insight into the molecular determinants of perifosine entry into cancer cells would therefore be of enormous importance for the identification of additional biomarkers for the efficacy of perifosine as an anticancer drug.…”

Induction of death receptor 5 expression in tumor vasculature by perifosine restores the vascular disruption activity of TRAIL-expressing CD34+ cells

“…In addition to targeting Akt and modulating JNK activation and DR5 expression, perifosine possesses other biologic activities (reviewed in [59]) that may contribute to the effects observed in this work. These include, accumulation into lipid rafts of the plasma membrane [60] and downregulation of ERK 1/2 phosphorylation [48]. Analysis of tumor xenografts revealed a strong reduction in ERK phosphorylation levels following perifosine treatment (data not shown), indicating that inhibition of MAPK signaling by perifosine toghether with Akt inhibition might also be involved in inducing tumor cells apoptosis and tumor growth delay.…”

Silencing of anti-apoptotic transmembrane protein lifeguard sensitizes solid tumor cell lines MCF-7 and SW872 to perifosine-induced cell death activation

“…Various studies have shown that perifosine accumulates in lipid rafts in a manner sensitive to raft disruption by cholesterol depletion (9)(10)(11). Subsequently, it was suggested that LFG, an anti-apoptotic protein with subcellular localization in lipid rafts, may interfere with perifosine-induced apoptosis.…”