Triple combination of I-BET762 plus copanlisib and bardoxolone methyl exhibit synergistic activity and downregulate the level of c-MYC. (A) Antiproliferative effects of the triple combination on the ATL43Tβ (-) cell line. Cell viability was measured with a thymidine incorporation assay after 72 hours of treatment with I-BET762 (500 nM), copanlisib (125 nM), and bardoxolone methyl (125 nM). A representative figure of 3 replicate assays is shown. (B) Immunoblot analysis of c-MYC expression of ATL43Tβ (-) cell line treated with 1 μM of a triple combination for 2 hours. (C) Increased expression of active caspase-3⁺ and cleaved-PARP⁺ in ATL43Tβ (-), ST1, and MT1 cell lines after 48 hours of treatment with triple combination measured by flow cytometry. The Jurkat cell line was used as a control. (D) Effects of the triple combination (1 µM each) on HTLV-1 proteins, Tax, and HBZ, for 4 hours. (E-F) p27 and PTEN mRNA expression in the ATL43Tβ (-) cell line after 24 hours of treatment with the triple combination measured by real time-PCR. One-way ANOVA was performed to determine statistical differences. *P < .05, **P < .01, ***P < .001, ****P < .0001.