Objective: The development of natural and new P-gp modulators to reverse tumor multidrug resistance (MDR).
Methods: Test compounds were prepared from the plant
Metaplexis japonica, and their ability to reverse P-glycoprotein (P-gp)-mediated MDR was investigated in HepG2/Dox cells. Their effects on P-gp expression and function and their interaction modes with P-gp were also investigated.
Results: Natural product 3β,12β,14β, 17β,20(
S)-pentahydroxy-5α-pregnan-12β-
O-(
E)-cinnamate (
1) and its new semisynthetic derivative 3β12β,14β,17β,20(
S)-pentahydroxy-5α-pregnan-3β-
O-nicotinate-12β-
O-(E)-cinnamate (
1a) were obtained. At non-cytotoxic concentrations of 5 or 10 μM, they significantly reversed the resistance of HepG2/Dox cells to P-gp substrate drugs doxorubicin, paclitaxel, and vinblastine, with reversal folds of 7.1, 118.5, and 198.3 (
1), and 18.8, 335.8, and 140.0 (
1a), respectively, at 10 μM. Cell apoptosis and expression of caspase 9 were both triggered by the combination of 10 μM of compound
1 or
1a and 500 nM of paclitaxel (
p < 0.001). Compound
1 or
1a did not affect P-gp expression, but it did significantly suppress the efflux of Rhodamine 123 out of HepG2/Dox cells (
p < 0.001). On the Caco-2 cell monolayer,
1 and
1a were shown to be non-substrates of P-gp, with efflux ratios of 0.83 and 0.89. Molecular docking revealed their strong binding energies (−8.2 and −8.4 kcal/mol) with P-gp, and their direct binding to P-gp was confirmed by their dissociation constants (5.53 µM for
1 and 3.72 µM for
1a), determined using surface plasmon resonance.
Conclusions: Compounds
1 and
1a are potential P-gp modulators; they may reverse P-gp-MDR through interacting with P-gp to interfere with substrate binding and transporting, and have the potential to improve the efficacy of paclitaxel or vinblastine drugs for combating P-gp-mediated MDR in tumor cells.
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