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 PERR clone10), which shows cross-resistance to the ALPs miltefosine and edelfosine, a marked impairment in the uptake of 14C-perifosine at both 37 °C and 4 °C, and no signs for active efflux of the drug. KB PERR 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 14C-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 PERR 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.