Selective inhibition of phosphatidylinositol 3-kinase by phosphatidic acid and related lipids.

Activation of phosphatidylinositol 3-kinase (PI 3-kinase) is necessary for stimulation of cell division and inhibition of apoptosis in several cell types. We report that a synthetic phosphonolipid, 4-(hexadecyloxy)-3-(S)-methoxybutyl phosphonic acid (PoA), as well as the naturally occurring lipids, phosphatidic acid and lyso-phosphatidic acid, are potent and specific inhibitors of PI 3-kinase. The IC50's for inhibition using phosphatidylinositol as substrate ranged from 10-20 microM. PoA is also the putative primary intracellular metabolite following phospholipase D hydrolysis of the anti-tumour ether lipid, 2'-(trimethylammonio) ethyl-4-(hexadecyloxy)-3-(S)-methoxybutanephosphonate. These results suggests that inhibition of PI 3-kinase following metabolic degradation of ether lipids by phospholipase D may contribute to the cytotoxicity of these compounds. The sensitivity of PI 3-kinase to PA and lyso-PA could imply cross-talk between the phospholipase D and PI 3-kinase signal transduction pathways in vivo.