The invention provides compositions comprising wilforlide A for overcoming drug resistance in cancer therapy, particularly in the treatment of cancers which have exhibited resistance to treatment by chemotherapeutic drugs. Methods and compositions for treating a cancer are disclosed. The method administers to a patient in need thereof a combination of wilforlide A and a chemotherapeutic drug. Wilforlide A and chemotherapeutic drug are administered in a combined amount effective to treat the cancer. The cancer being treated is at least in part resistant to treatment by the chemotherapeutic drug alone.