I13 overrides resistance mediated by the T315I mutation in chronic myeloid leukemia by direct BCR-ABL inhibition

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by a BCR-ABL fusion gene. Imatinib has significantly improved the treatment of CML as a first-generation tyrosine kinase inhibitor (TKIs). The T315I mutant form of BCR-ABL is the most common mutation that confers resistance to imatinib or the second-generation TKIs, resulting in poor clinical prognosis. In this work, we assessed the effect of a potent histone deacetylase (HDAC) inhibitor, I13, on the differentiation blockade in CML cells harboring T315I-mutated and wild-type BCR-ABL by MTT assay, flow cytometery, cell colony formation assay, mRNA Sequencing, Quantitative real-time PCR and Western blotting analysis. We found that I13 possessed highly potent activity against T315I-mutated BCR-ABL mutant-expressing cells and wild-type BCR-ABL-expressing cells. I13 induced cell differentiation and significantly suppressed the proliferation of these CML cells via the cell cycle G0/G1-phase accumulation. Moreover, it was revealed that I13 triggered the differentiation of BaF3-T315I cells, which was attributed to the block of the chronic myeloid leukemia signaling pathway via the depletion of BCR-ABL that was mediated by the inhibition of HDAC activity presented by the acetylation of histones H3 and H4. Taken together, I13 efficiently depleted BCR-ABL in CML cells expressing the BCR-ABL-T315I mutation, which blocked its function, serving as a scaffold protein that modulated the chronic myeloid leukemia signaling pathway mediating cell differentiation. The present findings demonstrate that I13 is a BCR-ABL modulator for the development of CML therapy that can override resistance caused by T315I-mutated BCR-ABL.