Pharicin B presents synergistic effect with RAR-α agonist, while RAR-α antagonist inhibits effect of pharicin B. (A) NB4 and U937 cells were treated with 2μM pharicin B, ATRA (10−8M for NB4 and 10−7M for U937), or AM580 (10−6M), as indicated, for 48 hours, and RAR-α/PML-RAR-α protein was detected by anti–RAR-α antibody. β-actin was used as the internal control. Each experiment was repeated at least 3 times. The number on the bottom indicates signal intensity of RAR-α or PML-RAR-α protein against β-actin. (B) NB4 and U937 cells were treated with pharicin B (2μM), ATRA (10−8M for NB4 and 10−7M for U937), 10−6M Ro 41–5253 alone, or their combination for 3 days. CD11b expression was measured by flow cytometry. All values represent means, with bar as SD of 3 independent experiments, each of which with triplicate samples. *P < .001.
