R 59 022 (6-[2-[4-[(4-fluorophenyl)phenylmethylene)-1-piperidinyl]ethyl]-7-methyl-5H-thiazolo[3,2-alpha] pyrimidin-5-one) is is an inhibitor of the enzyme 1,2-diacylglycerol (DAG) kinase, which, by inhibiting the conversion of DAG to phosphatidic acid, causes an increase in endogenous DAG levels and the activity of the DAG-dependent enzyme protein kinase C. R 59 022 was found to inhibit diacylglycerol kinase in human red blood cell membranes at concentrations where poly phosphoinositide phosphodiesterase, phosphatidylinositol kinase, and phosphatidylinositol 4-phosphate kinase activity remained unaffected. In intact platelets, R 59 022 inhibits the phosphorylation of OAG to l-oleoyl-2-acetylglyceryl-3-phosphoric acid (OAPA). R 59 022 2 results in a marked elevation of diacylglycerol levels, a decreased formation of phosphatidic acid and an increased protein kinase C activity in thrombin activated platelets. R59022 induced caspase-mediated apoptosis in glioblastoma, melanoma and in cancer cells, but lacked toxicity in noncancerous cells. Intraperitoneal injections of R59022 at 2 mg/kg significantly increases median survival in mouse xenograft models.