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A.K. Abdel-Aziz et al.
LSD1 on ACC and mTOR enrich the evidences linking LSD1 to the regulation of lipid metabolism.
Upstream regulator IPA predicted ERK1/2 to be activat- ed in resistant but not sensitive AML following LSD1i. Of note, ERK1/2 is known to positively regulate the activity of mTOR signaling via acting both upstream and down- stream of mTOR.23,45 Inhibiting ERK1/2 inhibited mTOR and counteracted AML resistance to LSD1i. Moreover, transcriptomic studies showed that IRS1 was upregulated following LSD1i in resistant but not responsive AML cells. We found LSD1 to be associated with the IRS1 promoter only in AML cells resistant to LSD1i, suggesting that AML cells display different modes of regulation of this gene (negative regulation by LSD1 in resistant cells, other mechanisms in sensitive cells). Consistently, LSD1i led to remodeling of the IRS1 promoter in resistant AML cells, with a prominent accumulation of H3K4me3, H3K9Ac and H3K27Ac histone marks. Our findings are consistent with the previously reported studies which demonstrated that the transcriptional consequences of LSD1 inhibition are preceded by the preferential enrichment of H3K9Ac and H3K27Ac marks at LSD1-bound regulatory regions.14,46
Notably, a selective IRS1/2 inhibitor, NT157,31 reversed LSD1i-induced ERK1/2 and mTOR activation and thereby sensitized resistant AML cells to LSD1i. Our data are in accordance with Machado-Neto and colleagues who reported that silencing IRS1 inactivates ERK1/2 and mTOR signaling in K562 CML cells.30 In line with previous studies which reported that ATRA downregulates IRS1,32,33 we have further demonstrated that ATRA reduced H3K4me2 and H3K27Ac accumulation on IRS1 promoter. Indeed, ATRA dramatically abolished LSD1i-mediated IRS1 induction and rendered resistant AML vulnerable to LSD1i. Within this context, we speculate that LSD1i and ATRA cooperate by acting via distinct mechanisms. LSD1i unlocks ATRA-differentiation pathway4 whereas ATRA counteracts LSD1i-mediated upregulation of IRS1. These complementary activities might contribute to the syner- gistic antileukemic activity of their combination.4 Altogether, our findings imply that LSD1i-mediated mod- ulation of IRS1 and ERK1/2 might contribute –at least
Table 1. Targeting mammalian target of rapamycin (mTOR) sensitizes primary patient-derived acute myeloid leukemia (AML) blasts (AML-IEO20) to LSD1 inhibition. Degree of leukemic cells infiltration of the spleen, bone marrow and surrounding muscular tissues harvested from NSG mice transplanted with human primary AML-IEO20 cells, sacrificed 15 days after initiation of treat- ment.
Treated Group
(#designated labeled mouse number)
Non-transplanted
Vehicle-treated group (#A2)
Vehicle-treated group (#A3) DDP38003-treated group (#B11) DDP38003-treated group (#B12) Rapamycin-treated group (#D33) Rapamycin-treated group (#D36) DDP38003/Rapamycin co-treated group (#C21) DDP38003/Rapamycin co-treated group (#C25)
Extent of infiltration
Spleen Bone marrow
- -
+++ Necrotic +++ +++ ++ +++ ++ +++ ++ +++ ++ +++
+ ++
+ ++
Muscle
-
++ ++ + + + + - -
References
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14. Maes T, Mascaro C, Tirapu I, et al. ORY- 1001, a potent and selective covalent
Degree/extent of leukemia infiltration; null (-), mild (+), moderate (++), severe (+++).
partly–to mTOR regulation by LSD1 (Figure 7K).
In conclusion, our data underscore a pro-survival role of mTOR in mediating both intrinsic and acquired resistance of AML cells to LSD1i and provide an objective rationale for considering epigenetic (LSD1i)/metabolic (mTORi)
combinatorial regimens for irresponsive AML patients.
Acknowledgments
We would like to thank Dr. Fabio Santoro, Dr. Roberto Ravasio and Prof. Pier Giuseppe Pelicci for their support and constructive discussions. We are also thankful to Dr. Federica Pisati who performed the histopathological and immunohisto- chemical analyses. AKA has been awarded a fellowship by AIRC (Italian Association for Cancer Research). Work in SM's lab is supported by AIRC, CNR (Epigen Flahsgip Project), Regione Lombardia (Progetto Neon) and Horizon 2020 (TRAN- SCAN DRAMA) grants. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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