Pre-clinical efficacy of combined therapy with novel β-catenin antagonist BC2059 and histone deacetylase inhibitor against AML cells

The canonical WNT-β-catenin pathway is essential for self-renewal, growth and survival of AML stem/blast progenitor cells (BPCs). Deregulated WNT signaling inhibits degradation of β-catenin, causing increased nuclear translocation and co-factor activity of β-catenin with the transcriptional regulator TCF4/LEF1 in AML BPCs. Here, we determined the pre-clinical anti-AML activity of the anthraquinone oxime-analog BC2059 (BC), known to attenuate β-catenin levels. BC treatment disrupted the binding of β-catenin with the scaffold protein TBL1 (transducin β-like 1) and proteasomal degradation and decline in the nuclear levels of β-catenin. This was associated with reduced transcriptional activity of TCF4 and expression of its target genes, cyclin D1, c-MYC and survivin. BC treatment dose-dependently induced apoptosis of cultured and primary AML BPCs. Treatment with BC also significantly improved the median survival of immune-depleted mice engrafted with either cultured or primary AML BPCs exhibiting nuclear expression of β-catenin. Co-treatment with the pan-histone deacetylase inhibitor panobinostat and BC synergistically induced apoptosis of cultured and primary AML BPCs, including those expressing FLT3-ITD, as well as further significantly improved the survival of immune-depleted mice engrafted with primary AML BPCs. These findings underscore the promising pre-clinical activity and warrant further testing of BC against human AML, especially those expressing FLT3-ITD.

Highly effective combination of LSD1 (KDM1A) antagonist and pan-histone deacetylase inhibitor against human AML cells

The histone demethylase LSD1 (KDM1A) demethylates mono- and di-methylated (Me2) lysine (K) 4 on histone H3. High LSD1 expression blocks differentiation and confers a poor prognosis in AML. Here, treatment with the novel LSD1 antagonist SP2509 attenuated the binding of LSD1 with the co-repressor CoREST, increased the permissive H3K4Me3 mark on the target gene promoters, and increased the levels of p21, p27 and C/EBPα in cultured AML cells. Additionally, SP2509 treatment or LSD1 shRNA inhibited the colony growth of AML cells. SP2509 also induced morphologic features of differentiation in the cultured and primary AML blasts. SP2509 induced more apoptosis of AML cells expressing mutant NPM1 than MLL fusion oncoproteins. Treatment with SP2509 alone significantly improved the survival of immune-depleted mice following tail-vein infusion and engraftment of cultured or primary human AML cells. Co-treatment with pan-HDAC inhibitor (HDI) panobinostat (PS) and SP2509 was synergistically lethal against cultured and primary AML blasts. Compared to each agent alone, co-treatment with SP2509 and PS significantly improved the survival of the mice engrafted with the human AML cells, without exhibiting any toxicity. Collectively, these findings show that the combination of LSD1 antagonist and pan-HDI is a promising therapy warranting further testing against AML.