Peptidomimetic blockade of MYB in acute myeloid leukemia

Abstract

Aberrant gene expression is a hallmark of acute leukemias. MYB-driven transcriptional coactivation with CREB-binding protein (CBP)/P300 is required for acute lymphoblastic and myeloid leukemias, including refractory MLL-rearranged leukemias. Using structure-guided molecular design, we developed a peptidomimetic inhibitor MYBMIM that interferes with the assembly of the molecular MYB:CBP/P300 complex and rapidly accumulates in the nuclei of AML cells. Treatment of AML cells with MYBMIM led to the dissociation of the MYB:CBP/P300 complex in cells, its displacement from oncogenic enhancers enriched for MYB binding sites, and downregulation of MYB-dependent gene expression, including of MYC and BCL2 oncogenes. AML cells underwent mitochondrial apoptosis in response to MYBMIM, which was partially rescued by ectopic expression of BCL2. MYBMIM impeded leukemia growth and extended survival of immunodeficient mice engrafted with primary patient-derived MLL-rearranged leukemia cells. These findings elucidate the dependence of human AML on aberrant transcriptional coactivation, and establish a pharmacologic approach for its therapeutic blockade.

Convergent organization of aberrant MYB complex controls oncogenic gene expression in acute myeloid leukemia

“…Importantly, CRYBMIM achieved significantly improved, logarithmic suppression of growth and survival of most AML cell lines tested, as compared to MYBMIM and CREBMIM ( Figure 2F). For example, whereas MYBMIM induced nearly 100-fold suppression of growth of MV411 cells after six days of treatment in agreement with prior studies (Ramaswamy et al, 2018), CRYBMIM achieved more than 1,000-fold suppression compared to control (p = 8.6e-3; Figure 2F), consistent with its improved biochemical affinity ( Figure 1D). This improved activity of CRYBMIM spanned diverse MLL-rearranged and non-MLL-rearranged AML subtypes, AML1-ETO translocated, PML-RARA-translocated, DNMT3A-mutant, NPM1c-mutant, TP53-mutant, MYCamplified, and WT1-mutant cell lines, with the exception of erythroblastic BCR-ABL1-translocated K562 cells (10 of 11 cell lines tested; Figure 2F and Table S2).…”

“…Previously, we observed that MYBMIM blocks the binding of MYB to the CBP/P300 in AML cells, requiring relatively high 20 µM concentrations for 3 hours to achieve this effect (Ramaswamy et al, 2018). To ascertain whether CRYBMIM can achieve more potent interference with the binding of MYB to the CBP/P300 complex in cells due to its improved affinity as compared to MYBMIM ( Figure 1D), we treated MV411 cells with 10 µM peptides for one hour and immunoprecipitated CBP/P300 using specific antibodies ( Figure 2B).…”

“…The helical MYB transactivation domain comprising residues 293-310 binds to the KIX domain of CBP/P300 (Zor et al, 2004). Using molecular mechanics simulations, we previously developed a peptidomimetic inhibitor of this interaction, termed MYBMIM (Ramaswamy et al, 2018). MYBMIM uses stereoselective substitution of D-amino acids to confer proteolytic stability, and the cationic TAT domain for cell penetration.…”

“…As a result, MYBMIM can specifically inhibit MYB:CBP/P300 binding in cells, but its activity less pronounced in non-MLL-rearranged AML cells. Given that MYBMIM bound to recombinant CBP KIX domain with the dissociation constant of 21.3 ± 2.9 µM, as compared to the native MYB peptide of 4.2 ± 0.5 µM (Ramaswamy et al, 2018), we reasoned that a peptidomimetic inhibitor with higher affinity to CBP/P300 would be more effective.…”

“…Recently, we developed a peptidomimetic inhibitor of MYB:CBP/P300 (Ramaswamy et al, 2018). Here, we report its second-generation version that has significantly increased potency, and consequently suppresses leukemic MYB functions in most AML subtypes tested, while sparing normal hematopoietic progenitor cells.…”