PGP and lung carcinoma: 21α-Methylmelianodiol (21α-MMD), an active triterpenoid isolated from Poncirus trifoliate, regulates the PI3K/AKT/AMPK and MAPK pathways, and reverses the MDR activity through the inhibited expressions of P-gp or MDR1, suggesting its anti-lung cancer property through reversal of MDR activity [55].