EXTRACELLULAR ADENOSINE-5' TRIPHOSPHATE INVOLVEMENT IN THE DEATH OF LAK-ENGAGED HUMAN TUMOR-CELLS VIA P2X-RECEPTOR ACTIVATION

This study reports that extracellular ATP is a critical factor involve d in LAK cell-mediated cytotoxicity. Human colon carcinoma LoVo cells were resistant to LAK cells as well as to ATP, while their multidrug r esistant (MDR-1(+)) derivative, LoVo-Dx cells, were sensitive to both LAK and ATP. LoVo-Dx cells, became resistant to LAK cells and ATP afte r 48 h pretreatment with Phorbol 12-Myristate-13-Acetate (PMA), while 48 h pretreatment with verapamil in parallel sensitized LoVo cells to LAK cells and to ATP as well. The sensitivity to ATP and LAK cells was not related to the expression of extracellular ecto-ATPase activity o n cell targets membranes. Conversely, apyrase, an enzyme with powerful ecto-ATPas activity, abolished the LAK- and ATP-mediated cytotoxicity . Furthermore, ADP-beta-S, an antagonist of ATP, abolished both LAK an d ATP-mediated cell killing. Purine binding sites have been detected b y radioreceptor assays with ADP-beta[S-35] on the cell surface of ATP and LAK-sensitive LoVo-Dx cells. By contrast, no nucleotide receptor w as found on the ATP and LAK-resistant cells. Such a putative cytotoxic purinoreceptor has been categorized as P2x purinergic receptor by a p anel of synthetic nucleotides, These results demonstrate that extracel lular ATP is needed for an efficient LAK cell-mediated killing of tumo r cells. We propose that ATP acts as a natural amplifier of physical, or immune cytotoxic damages since it may bit released in large amounts from target cells injured by several cytotoxic mediators secreted by LAK effectors. (C) 1997 Elsevier Science B.V.