Antimetastatic action of RX-RA 69, a new potent PDE-inhibitor in the Lewis lung carcinoma of the mouse

RX-RA 69, a pyrimido-pyrimidine derivative, is a new potent PDA-inhibitor which inhibits tumor cell induced platelet aggregation in vitro. Also ex vivo an inhibition was found after pretreating mice with 1 mg/kg RX-RA 69 orally one hour before collecting the blood. The same dosage is able to prevent the drop in platelet count induced by injecting a large number of tumor cells into mice. The same dosage schedule in the amputation experiment resulted in a reduction of incidence of matastases in all treated groups; the best results, however, were obtained by starting the treatment two days after the amputation. In the spontaneous model an inhibition of metastases formation by 10-20 mg/kg RX-RA 69 starting from the fourth day after tumor cell implantation was found in four independent experiments. The mechanism of the antimetastatic action of this drug remains to be evaluated.