RESUMO
Understanding mechanisms of cooperation between oncogenes is critical for the development of novel therapies and rational combinations. Acute myeloid leukemia (AML) cells with KMT2A-fusions and KMT2A partial tandem duplications (KMT2APTD) are known to depend on the histone methyltransferase DOT1L, which methylates histone 3 lysine 79 (H3K79). About 30% of KMT2APTD AMLs carry mutations in IDH1/2 (mIDH1/2). Previous studies showed that 2-hydroxyglutarate produced by mIDH1/2 increases H3K79 methylation, and mIDH1/2 patient samples are sensitive to DOT1L inhibition. Together, these findings suggested that stabilization or increases in H3K79 methylation associated with IDH mutations support the proliferation of leukemias dependent on this mark. However, we found that mIDH1/2 and KMT2A alterations failed to cooperate in an experimental model. Instead, mIDH1/2 and 2-hydroxyglutarate exert toxic effects, specifically on KMT2A-rearranged AML cells (fusions/partial tandem duplications). Mechanistically, we uncover an epigenetic barrier to efficient cooperation; mIDH1/2 expression is associated with high global histone 3 lysine 79 dimethylation (H3K79me2) levels, whereas global H3K79me2 is obligate low in KMT2A-rearranged AML. Increasing H3K79me2 levels, specifically in KMT2A-rearrangement leukemias, resulted in transcriptional downregulation of KMT2A target genes and impaired leukemia cell growth. Our study details a complex genetic and epigenetic interaction of 2 classes of oncogenes, IDH1/2 mutations and KMT2A rearrangements, that is unexpected based on the high percentage of IDH mutations in KMT2APTD AML. KMT2A rearrangements are associated with a trend toward lower response rates to mIDH1/2 inhibitors. The substantial adaptation that has to occur for 2 initially counteracting mutations to be tolerated within the same leukemic cell may provide at least a partial explanation for this observation.
Assuntos
Rearranjo Gênico , Leucemia Mieloide Aguda , Histonas/metabolismo , Humanos , Leucemia Mieloide Aguda/genética , Metilação , OncogenesRESUMO
Inhibition of the H3K79 histone methyltransferase DOT1L has exhibited encouraging preclinical and early clinical activity in KMT2A (MLL)-rearranged leukemia, supporting the development of combinatorial therapies. Here, we investigated two novel combinations: dual inhibition of the histone methyltransferases DOT1L and EZH2, and the combination with a protein synthesis inhibitor. EZH2 is the catalytic subunit in the polycomb repressive complex 2 (PRC2), and inhibition of EZH2 has been reported to have preclinical activity in KMT2A-r leukemia. When combined with DOT1L inhibition, however, we observed both synergistic and antagonistic effects. Interestingly, antagonistic effects were not due to PRC2-mediated de-repression of HOXA9. HOXA cluster genes are key canonical targets of both KMT2A and the PRC2 complex. The independence of the HOXA cluster from PRC2 repression in KMT2A-r leukemia thus affords important insights into leukemia biology. Further studies revealed that EZH2 inhibition counteracted the effect of DOT1L inhibition on ribosomal gene expression. We thus identified a previously unrecognized role of DOT1L in regulating protein production. Decreased translation was one of the earliest effects measurable after DOT1L inhibition and specific to KMT2A-rearranged cell lines. H3K79me2 chromatin immunoprecipitation sequencing patterns over ribosomal genes were similar to those of the canonical KMT2A-fusion target genes in primary AML patient samples. The effects of DOT1L inhibition on ribosomal gene expression prompted us to evaluate the combination of EPZ5676 with a protein translation inhibitor. EPZ5676 was synergistic with the protein translation inhibitor homoharringtonine (omacetaxine), supporting further preclinical/clinical development of this combination. In summary, we discovered a novel epigenetic regulation of a metabolic process-protein synthesis-that plays a role in leukemogenesis and affords a combinatorial therapeutic opportunity.