RESUMO
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.
Assuntos
Epigênese Genética , Regulação Leucêmica da Expressão Gênica , Rearranjo Gênico , Leucemia Mieloide Aguda/metabolismo , Biossíntese de Proteínas , Linhagem Celular Tumoral , Proteína Potenciadora do Homólogo 2 de Zeste/antagonistas & inibidores , Proteína Potenciadora do Homólogo 2 de Zeste/genética , Proteína Potenciadora do Homólogo 2 de Zeste/metabolismo , Histona-Lisina N-Metiltransferase/antagonistas & inibidores , Histona-Lisina N-Metiltransferase/genética , Histona-Lisina N-Metiltransferase/metabolismo , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Humanos , Leucemia Mieloide Aguda/genética , Leucemia Mieloide Aguda/patologia , Proteína de Leucina Linfoide-Mieloide/antagonistas & inibidores , Proteína de Leucina Linfoide-Mieloide/genética , Complexo Repressor Polycomb 2/genética , Complexo Repressor Polycomb 2/metabolismoRESUMO
Genetic lesions affecting polycomb repressive complex 2 (PRC2) have been found in more than 40% of pediatric cases of early T-cell precursor acute lymphoblastic leukemia. The functional role of these PRC2 alterations has been obscure. Our recent data suggest that compromise of PRC2 blocks differentiation and accentuates growth and survival signaling.
RESUMO
Primitive neuroectodermal tumor (PNET) is most common in the second decade of life. Congenital PNET is very rare. Ocular metastasis of PNET is likewise exceedingly rare; with only 5 previously published cases. We report an unusual congenital PNET of the face, which metastasized to subcutis, eyes, and brain. The primary tumor responded to chemotherapy (vincristine/doxorubicin/cyclophosphamide) with metachronous progression of ocular lesions. A therapeutic trial of intraocular bevacizumab showed no efficacy on intraocular lesions. Eventually the patient developed cerebral metastasis, and second line therapy with topotecan/cyclophosphamide was initiated. The tumor progressed and the patient died after acute herniation.