Inhibition of lung carcinoma cell growth by high density lipoprotein-associated α-tocopheryl-succinate

Abstract

α-Tocopheryl-succinate (αTS) is a synthetic, anti-neoplastic derivative of α-tocopherol. Here we studied the effects of free and high-density lipoprotein subclass 3 (HDL₃)-associated αTS on the growth of human (A549) and mouse Lewis (LL2) lung carcinoma cells. Both free and HDL3-associated αTS inhibited A549 growth in a time- and concentration-dependent manner. Treatment of A549 cells with αTS-enriched HDL3 led to DNA fragmentation and a time-dependent decrease in immunoreactivity of poly(ADP-ribose)polymerase. Uptake experiments revealed a high capacity for selective αTS uptake in excess of holoparticle endocytosis. Overexpression of scavenger receptor class B, type I (SR-BI), the prime receptor mediating selective lipid uptake, in A549 cells resulted in significantly increased selective αTS uptake, a finding associated with complete cellular growth arrest. The present in vitro findings were verified in an in vivo model: tumor inoculation in C57BL6 was performed with either wild-type, β-galactosidase- or SR-BI-overexpressing LL2 cells. After tumor inoculation, the animals received six consecutive intravenous injections of αTS. This experimental setup resulted in significantly reduced tumor burden in animals that were inoculated with SR-BI-overexpressing LL2 cells but not in animals inoculated with wild-type or β-galactocidase-transfected cells. Based on our in vitro and in vivo findings, we propose that SR-BI could provide a novel route for HDL₃-mediated drug delivery of anti-neoplastic drugs.