Compound 2 was reported as a better P-gp inhibitor than 1 in KB-3-1 and KB-C2 cell lines [49], while 3 and 4 also showed a reversal of MDR in the same tumor cells, but did not reveal the effect on cells lacking P-gp expression or expressing MRP1, MRP7, or BCRP transporters [36,45,49]. The gene discussed is PGP; the disease is neoplasm.