Mechanisms of Pinometostat (EPZ-5676) Treatment–Emergent Resistance in MLL-Rearranged Leukemia

Abstract

DOT1L is a protein methyltransferase involved in the development and maintenance of MLL-rearranged (MLL-r) leukemia through its ectopic methylation of histones associated with wellcharacterized leukemic genes. Pinometostat (EPZ-5676), a selective inhibitor of DOT1L, is in clinical development in relapsed/ refractory acute leukemia patients harboring rearrangements of the MLL gene. The observation of responses and subsequent relapses in the adult trial treating MLL-r patients motivated preclinical investigations into potential mechanisms of pinometostat treatment-emergent resistance (TER) in cell lines confirmed to have MLL-r. TER was achieved in five MLL-r cell lines, KOPN-8, MOLM-13, MV4-11, NOMO-1, and SEM. Two of the cell lines, KOPN-8 and NOMO-1, were thoroughly characterized to understand the mechanisms involved in pinometostat resistance. Unlike many other targeted therapies, resistance does not appear to be achieved through drug-induced selection of mutations of the target itself. Instead, we identified both drug efflux transporter dependent and independent mechanisms of resistance to pinometostat. In KOPN-8 TER cells, increased expression of the drug efflux transporter ABCB1 (P-glycoprotein, MDR1) was the primary mechanism of drug resistance. In contrast, resistance in NOMO-1 cells occurs through a mechanism other than upregulation of a specific efflux pump. RNA-seq analysis performed on both parental and resistant KOPN-8 and NOMO-1 cell lines supported two unique candidate pathway mechanisms that may explain the pinometostat resistance observed in these cell lines. These results are the first demonstration of TER models of the DOT1L inhibitor pinometostat and may provide useful tools for investigating clinical resistance.

Conserved crosstalk between histone deacetylation and H3K79 methylation generates DOT1L‐dose dependency in HDAC1‐deficient thymic lymphoma

“…These interactions target DOT1L to transcribed chromatin and provide an explanation for the aberrant recruitment of DOT1L by oncogenic MLL fusion proteins (Deshpande et al, 2014;Li et al, 2014;Chen et al, 2015;Kuntimaddi et al, 2015;Wood et al, 2018). Further characterizing the regulatory network of DOT1L could lead to the identification of alternative drug targets for diseases in which DOT1L is critical and provide alternative strategies in case of resistance to treatment with DOT1L inhibitors (Campbell et al, 2017).…”

Epigenetic polypharmacology: A new frontier for epi‐drug discovery

“…Pinometostat 21 (Table ) is a picomolar inhibitor of the H3K79 methyltransferase disruptor of telomeric silencing 1‐like (DOT1L), with more than 30 000‐fold selectivity against other KMTs. When used in rearranged‐MLL (mixed‐lineage‐leukemia) cells and xenograft models, 21 reduced H3K79 methylation level, decreased MLL target gene expression, and induced selective leukemia cell death …”

“…As reported in the literature, HDAC6 and class I HDACs cover an essential role in Alzheimer disease (AD), since their overexpression were detected in the cortex and hippocampus of AD patients . It has been postulated that at the basis of the onset and progression of AD there is the aberrant aggregation of the insoluble hyper‐phosphorylated Tau protein (pTau).…”

“…When used in rearranged-MLL (mixed-lineage-leukemia) cells and xenograft models, 21 reduced H3K79 methylation level, decreased MLL target gene expression, and induced selective leukemia cell death. 25,26 JNJ-64619178 22 27 and GSK3326595 23 28 (Table 1) are two potent and selective PRMT5 inhibitors that induced tumor regression in solid cancers as well as in hematologic malignancies, supporting clinical testing in patients with these kinds of cancer.…”

“…has been conducted with the aim to evaluate the PK and the safety of this combination. [22][23][24][25][26][27][28]. AML makes the affected subjects more susceptible to fungal infections, therefore posaconazole 49 resulted effective to prevent this condition.…”