Structurally diverse MDM2–p53 antagonists act as modulators of MDR-1 function in neuroblastoma

BACKGROUND: A frequent mechanism of acquired multidrug resistance in human cancers is overexpression of ATP-binding cassette transporters such as the Multi-Drug Resistance Protein 1 (MDR-1). Nutlin-3, an MDM2–p53 antagonist, has previously been reported to be a competitive MDR-1 inhibitor. METHODS: This study assessed whether the structurally diverse MDM2–p53 antagonists, MI-63, NDD0005, and RG7388 are also able to modulate MDR-1 function, particularly in p53 mutant neuroblastoma cells, using XTT-based cell viability assays, western blotting, and liquid chromatography–mass spectrometry analysis. RESULTS: Verapamil and the MDM2–p53 antagonists potentiated vincristine-mediated growth inhibition in a concentration-dependent manner when used in combination with high MDR-1-expressing p53 mutant neuroblastoma cell lines at concentrations that did not affect the viability of cells when given alone. Liquid chromatography–mass spectrometry analyses showed that verapamil, Nutlin-3, MI-63 and NDD0005, but not RG7388, led to increased intracellular levels of vincristine in high MDR-1-expressing cell lines. CONCLUSIONS: These results show that in addition to Nutlin-3, other structurally unrelated MDM2–p53 antagonists can also act as MDR-1 inhibitors and reverse MDR-1-mediated multidrug resistance in neuroblastoma cell lines in a p53-independent manner. These findings are important for future clinical trial design with MDM2–p53 antagonists when used in combination with agents that are MDR-1 substrates.