Abstract
We have studied the effects of a novel derivative of apovincaminic acid ester, VA-033, on the resistance of tumors to chemotherapeutic agents. VA-033 increased the sensitivity of drug-resistant cell lines (P388/VCR, P388/ADM, AD10, and K562/ADM) to adriamycin or vincristine. The potency of VA-033 was stronger than verapamil. The drug lengthened the survival time of the P388/VCR-implanted mice treated with vincristine. VA-033 increased the intracellular accumulation of vincristine in the tumor cells, and the photolabeling of P-glycoprotein by [ 3H]azidopine was inhibited by VA-033. VA-033 showed a slight inhibitory effect on the L-type Ca 2+ current in the ventricular myocytes, and had less effect on the cardiovascular parameters such as blood pressure, contractile force and atrio-ventricular conduction time than verapamil when administered systemically in the dog. These results suggest that VA-033 may become a beneficial compound as a modifier to the neoplastic cell resistant to multidrugs.
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