Exploring Experimental Hematology: June 2021 (Volume 98)
DNA methylation therapy joins forces in IDH2-mutant AML
Isocitrate
dehydrogenases 1 and 2 (IDH1/2) are frequently mutated in Acute Myeloid Leukemia
(AML), with nearly 20% of patients carrying gain-of-function point mutations in
these genes (Ley et
al., 2013). IDH2 is a metabolic enzyme that catalyzes the conversion
of isocitrate to 2-oxoglutarate during the Krebs cycle. Patients carrying IDH2
gain-of-function mutations produce instead high levels of the oncometabolite 2-hydroxyglutarate
(2-HG), which inhibits oxoglutarate-dependent enzymes such as the TET family of
methylcytosine dioxygenases,
responsible for active DNA demethylation (Xu et al.,
2011). As a consequence, IDH2 mutations in AML patients induce DNA hypermethylation and inhibit hematopoietic
differentiation (Figueroa
et al., 2010).
Azacytidine
(AZA) and enasidenib (ENA) are commonly used AML therapies which induce DNA
hypomethylation, albeit through different mechanisms. AZA is a nucleoside
analog that inhibits DNA methyltransferase enzymes (DNMTs) and ENA impairs IDH2
mutant catalytic activity (Wang et
al., 2013). In a study recently published in Experimental
Hematology (MacBeth
et al., 2021), Macbeth and colleagues hypothesized that combining both
drugs in IDH2-mutant leukemia will produce a synergistic effect to drive
hypomethylation and restore AML differentiation.
To
test this hypothesis, the authors first performed combination or single agent
treatments on a leukemia cell line model overexpressing IDH2 mutation (TF1
IDH2R140Q cells) and evaluated dose-dependent erythroid
differentiation via a hemoglobinization assay. Compared to single agent
treatments, combination treatment with high AZA and ENA doses showed the highest
rate of hemoglobinization.
Their
findings were further strengthen using primary cells from AML patients carrying
IDH2R172 and IDH2R140 mutations. Differentiation
was assessed by flow cytometry using CD34+ (marking stem and
progenitor cells) and CD15+ (marking granulomonocytic cells). Combination
treatment showed a reduction in CD34 and increased CD15 intensity, indicative
of myeloid differentiation, an effect that was not detected in IDH2-WT
AML samples.
Next,
they assessed genome-wide methylation profiles of AZA+ENA treatment on TF1 IDH2R140Q
cells. 5hmC levels were evaluated using hydroxymethylated DNA
immunoprecipitation (hMeDIP) sequencing, showing an increase in 5hmC levels in
ENA treated and ENA+AZA treated cells, with no measurable effects in AZA-only treated
cells. Subsequently, 5mC was measured using EERBS (Enhanced Representation
Bisulfite Sequencing), showing a decrease in both single-agent AZA and
combination treatment, but no difference in single-agent ENA, concordant with
the known mechanism of action of this IDH2 inhibitor. Overall, ENA+AZA combination
showed a greater degree of DNA hypomethylation than both single-agent treatments
alone. These findings support a model in
which restoration of TET activity cooperates with the inhibition of DNMTs to cooperatively
induce DNA hypomethylation in leukemic cells.
Further mechanistic studies would be needed to elucidate the precise molecular mechanisms of AZA+ENA synergistic effect, such the identification of methylation patterns at specific genomic regions and functional regulatory elements responsible for the increased myeloid differentiation. DNA hypomethylation agents are widely used in AML therapy, although only a modest proportion of patients respond. Therefore, resolving the underlying mechanism of action of DNA methylation therapies and designing new rational combinations to enhance response rates continues to be a promising avenue for AML treatment.
Figueroa, M. E., Abdel-Wahab, O., Lu, C., Ward, P. S.,
Patel, J., Shih, A., Li, Y., Bhagwat, N., Vasanthakumar, A., Fernandez, H. F.,
Tallman, M. S., Sun, Z., Wolniak, K., Peeters, J. K., Liu, W., Choe, S. E.,
Fantin, V. R., Paietta, E., Löwenberg, B., . . . Melnick, A. (2010). Leukemic
IDH1 and IDH2 mutations result in a hypermethylation phenotype, disrupt TET2
function, and impair hematopoietic differentiation. Cancer Cell, 18(6),
553-567. https://doi.org/10.1016/j.ccr.2010.11.015
Ley, T. J., Miller, C.,
Ding, L., Raphael, B. J., Mungall, A. J., Robertson, A., Hoadley, K., Triche,
T. J., Jr., Laird, P. W., Baty, J. D., Fulton, L. L., Fulton, R., Heath, S. E.,
Kalicki-Veizer, J., Kandoth, C., Klco, J. M., Koboldt, D. C., Kanchi, K. L.,
Kulkarni, S., . . . Eley, G. (2013). Genomic and epigenomic landscapes of adult
de novo acute myeloid leukemia. N Engl J
Med, 368(22), 2059-2074. https://doi.org/10.1056/NEJMoa1301689
MacBeth, K. J., Chopra,
V. S., Tang, L., Zheng, B., Avanzino, B., See, W. L., Schwickart, M., Figueroa,
M. E., Quek, L., & DiMartino, J. F. (2021). Combination of azacitidine and
enasidenib enhances leukemic cell differentiation and cooperatively
hypomethylates DNA. Exp Hematol, 98, 47-52.e46. https://doi.org/10.1016/j.exphem.2021.03.003
Wang, F., Travins, J.,
DeLaBarre, B., Penard-Lacronique, V., Schalm, S., Hansen, E., Straley, K.,
Kernytsky, A., Liu, W., Gliser, C., Yang, H., Gross, S., Artin, E., Saada, V.,
Mylonas, E., Quivoron, C., Popovici-Muller, J., Saunders, J. O., Salituro, F.
G., . . . Yen, K. E. (2013). Targeted Inhibition of Mutant IDH2 in Leukemia
Cells Induces Cellular Differentiation. Science, 340(6132), 622-626. https://doi.org/doi:10.1126/science.1234769
Xu, W., Yang, H., Liu,
Y., Yang, Y., Wang, P., Kim, S. H., Ito, S., Yang, C., Wang, P., Xiao, M. T.,
Liu, L. X., Jiang, W. Q., Liu, J., Zhang, J. Y., Wang, B., Frye, S., Zhang, Y.,
Xu, Y. H., Lei, Q. Y., . . . Xiong, Y. (2011). Oncometabolite
2-hydroxyglutarate is a competitive inhibitor of alpha-ketoglutarate-dependent
dioxygenases. Cancer Cell, 19(1), 17-30. https://doi.org/10.1016/j.ccr.2010.12.014
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