In doxorubicin-resistant human T-cell lymphoma cells (CEM/ADR5000), ATRA outperformed verapamil in suppressing ABCB1 activity at non-cytotoxic concentrations of 20, 50, and 100 μM in the Rh-123 assay, and at 10, 20, 50, and 100 μM in the calcein-AM assay [79]. The gene discussed is ABCB1; the disease is T-cell non-Hodgkin lymphoma.