PBA2, a novel inhibitor of the β-catenin/CBP pathway, eradicates chronic myeloid leukemia including BCR-ABL T315I mutation

BCR-ABL is a constitutively active tyrosine kinase that stimulates multiple downstream signaling pathways to promote the survival and proliferation of chronic myeloid leukemia (CML) cells. The clinical application of specific BCR-ABL tyrosine kinase inhibitors (TKIs) has led to significantly improved prognosis and overall survival in CML patients compared to previous treatment regimens. However, direct targeting of BCR-ABL does not eradicate CML cells expressing T315I-mutated BCR-ABL. Our previous study revealed that inhibiting CREB binding protein (CBP) is efficacious in activating β-catenin/p300 signaling, promoting cell differentiation and inducing p53/p21-dependent senescence regardless of BCR-ABL mutation status. We hypothesize that the specific inhibition of CBP may represent a novel strategy to promote β-catenin/p300-mediated differentiation and suppress cancer cell proliferation for treating CML patients. The anticancer efficacy of PBA2, a novel CBP inhibitor, in CML cells expressing wild-type or T315I-mutated BCR-ABL was investigated in vitro and in vivo. Cell differentiation was determined by the nitroblue tetrazolium (NBT) reduction assay. The extent of cellular senescence was assessed by senescence-associated β-galactosidase (SA-β-Gal) activity. Cytotoxicity was measured by MTS assay. RNA interference was performed to evaluate the cell proliferation effects of CBP knockdown. The interaction of β-catenin and CBP/p300 was examined by co-immunoprecipitation assay. PBA2 exhibited significantly higher anticancer effects than imatinib in CML cells harboring either wild-type or T315I-mutated BCR-ABL both in vitro and in vivo. Mechanistically, PBA2 reduced CBP expression and promoted β-catenin-p300 interaction to induce cell differentiation and senescence. Our data supported the rational treatment of CML by inhibiting the β-catenin/CBP pathway regardless of BCR-ABL mutation status.