PGP and cancer: The obtained data significantly extend our understanding of the anti-P-gp potential of both pentacyclic triterpenoids in general and cyanoenone-bearing triterpenoids in particular, and the identified lead compound 4—soloxolone N-3-(dimethylamino)propylamide [N-(3′-(Dimethylamino)propyl)-2-cyano-3,12-dioxo-18βH-olean-9(11),1(2)-dien-30-amide] can be considered as a drug candidate for controlling the MDR status of tumor cells in cancer.