Anti-proliferative activity and suppression of P-glycoprotein by (−)-antofine, a natural phenanthroindolizidine alkaloid, in paclitaxel-resistant human lung cancer cells

Multidrug resistance (MDR) is a major obstacle in effective chemotherapy for cancer patients. The expression of P-glycoprotein (P-gp) in cancer cells is highly correlated with resistance to chemotherapeutic drugs. (−)-Antofine, a phenanthroindolizidine alkaloid derived from Cynanchum paniculatum, inhibits the growth of various human cancer cells. In this study, we further explored the potential of (−)-antofine to overcome the resistance induced by anti-cancer drugs. To this end, we established the paclitaxel-resistant human lung cancer cell line A549-PA by gradually exposing A549 cells to increasing concentrations of paclitaxel. As a result, the A549-PA cells acquired resistance against paclitaxel treatment and had an IC50 that was more than 200 times that of the parental A549 cells. (−)-Antofine, however, effectively suppressed the growth of both the parental and drug-resistant cells. Additional studies revealed that the anti-proliferative activity of (−)-antofine in A549-PA cells is accompanied by a down-regulation of P-gp mRNA and protein expression. The effect of reversing the multidrug resistance of A549-PA cells via (−)-antofine treatment was demonstrated an increase in intracellular rhodamine-123 accumulation, measured using FACS analysis. These findings suggest an additional chemotherapeutic value of (−)-antofine, that is, regulation of cancer cell drug resistance, in addition to its antitumor effect.