Cilostazol, an inhibitor of platelet phosphodiesterase, was used to inhibit the platelet aggregating potential and metastasis of human adenocarcinoma cell lines. In vitro platelet aggregation potential of HAL8 and HAL33 cell lines was inhibited by cilostazol in a concentration dependent manner. Fatal acute thromboembolism of nude mice induced injection of HAL8 and HAL33 cell was completely inhibited by cilostazol/10 mg/kg p.o. Retention of injected (125)IdUrd-labeled cells in the lungs was also inhibited by cilostazol pretreatment. Cilostazol given 2 h before cell injection inhibited by 87 and 100% respectively, experimental lung metastasis of HAL8 and HAL33. Cilostazol given 72 h after cell injection had no effect on HAL8 and HAL33 metastasis. These results show that platelet aggregation of HAL8 and HAL33 cells play an important role in metastatic systems and that cilostazol inhibits human cancer metastasis.

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