20S-protopanaxadiol inhibits P-glycoprotein in multidrug resistant cancer cells

Area of Science:

• Pharmacology
• Cancer Biology
• Drug Resistance

Background:

• Multidrug resistance (MDR) in cancer is often mediated by P-glycoprotein (P-gp) over-expression, limiting chemotherapy effectiveness.
• Ginsenosides Rg3 and Rh2, derived from protopanaxadiols (PPDs), exhibit anticancer properties and synergize with chemotherapy, potentially by inhibiting P-gp.
• 20S-protopanaxadiol (aglycone PPD, aPPD), an in vivo metabolite of PPDs, also possesses anticancer activity.

Purpose of the Study:

• To investigate whether aPPD inhibits P-gp activity in P-gp over-expressing cancer cells.
• To determine if aPPD is a substrate of P-gp and to characterize its mechanism of P-gp inhibition.

Main Methods:

• Cytotoxicity assays were performed on P388adr (P-gp over-expressing) and parental non-MDR cells.
• Calcein AM efflux assay was used to assess P-gp inhibition by aPPD and verapamil.
• ATPase activity assay was conducted to investigate the mechanism of P-gp inhibition.

Main Results:

• aPPD exhibited similar cytotoxicity in P-gp over-expressing cells and parental cells, suggesting it is not a P-gp substrate.
• aPPD potently inhibited P-gp activity, comparable to verapamil, as demonstrated by the calcein AM efflux assay.
• P-gp inhibition by aPPD was reversible upon washout, and aPPD did not affect P-gp ATPase activity, indicating a distinct mechanism from verapamil.

Conclusions:

• aPPD is not a substrate of P-gp and demonstrates potent, reversible inhibition of P-gp activity.
• The mechanism of P-gp inhibition by aPPD differs from that of verapamil.
• aPPD represents a potential novel P-gp inhibitor for cancer treatment, possibly enhancing chemotherapy efficacy due to its pro-apoptotic and P-gp inhibitory properties.