Perifosine is a member of the class of synthetic alkylphospholipids (APLs) and is being evaluated as anti-
cancer agent in several clinical trials. These single-chain APLs accumulate in cellular membranes and disturb
lipid-dependent signal transduction, ultimately causing apoptosis in a variety of
tumor cells. The APL prototype
edelfosine was previously found to be endocytosed by S49 mouse
lymphoma cells via
lipid rafts. An
edelfosine-resistant cell variant, S49(AR), was found to be cross-resistant to other APLs, including
perifosine. This resistance was due to defective synthesis of the raft constituent
sphingomyelin, which abrogated APL cellular uptake. Sensitivity of S49 cells to
edelfosine was higher than
perifosine, which correlated with a relatively higher uptake. Human KB epidermal
carcinoma cells were much more sensitive to APLs than S49 cells. Their much higher APL uptake was highly dependent on intracellular
ATP and ambient temperature, and was blocked by
chlorpromazine, independent of canonical endocytic pathways. We found no prominent role of
lipid rafts for APL uptake in these KB cells; contrary to S49(AR) cells,
perifosine-resistant
KBr cells display normal
sphingomyelin synthesis, whereas APL uptake by the responsive KB cells was insensitive to treatment with
methyl-beta-cyclodextrin, a
cholesterol-sequestrator and inhibitor of raft-mediated endocytosis. In conclusion, different mechanisms determine APL uptake and consequent apoptotic toxicity in
lymphoma versus
carcinoma cells. In the latter cells, APL uptake is mainly determined by a raft- and endocytosis-independent process, but metabolic energy-dependent process, possibly by a
lipid transporter.