BETP degradation simultaneously targets acute myelogenous leukemic stem cells and the microenvironment
Sujan Piya, … , Michael Andreeff, Gautam Borthakur
Sujan Piya, … , Michael Andreeff, Gautam Borthakur
Published May 1, 2019; First published February 21, 2019
Citation Information: J Clin Invest. 2019;129(5):1878-1894. https://doi.org/10.1172/JCI120654.
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Categories: Research Article Cell biology Oncology

BETP degradation simultaneously targets acute myelogenous leukemic stem cells and the microenvironment

Abstract

The antileukemic effect of inhibiting bromodomain and extra-terminal domain-containing (BET-containing) proteins (BETPs) such as BRD4 has largely been largely attributed to transcriptional downregulation of cellular anabolic and antiapoptotic processes, but its effect on the bone marrow microenvironment, a sanctuary favoring the persistence of leukemic stem/progenitor cells, is unexplored. Sustained degradation of BETP with the small-molecule BET proteolysis-targeting chimera (PROTAC) ARV-825 resulted in a marked downregulation of surface CXCR4 and CD44, key proteins in leukemia-microenvironment interactions, in acute myeloid leukemia (AML) cells. Abrogation of surface CXCR4 expression impaired SDF-1α–directed migration and was mediated through transcriptional downregulation of PIM1 kinase, which in turn phosphorylates CXCR4 and facilitates its surface localization. Downregulation of CD44, including isoforms CD44v8–10 impaired cystine uptake, lowered intracellular reduced glutathione, and increased oxidative stress. More important, BETP degradation markedly decreased the CD34+CD38–CD90–CD45RA+ leukemic stem cell population and, alone or in combination with cytarabine, prolonged survival in a mouse model of human leukemia that included AML patient-derived xenografts (AML-PDX). Gene expression profiling and single-cell proteomics confirmed a downregulation of the gene signatures associated with “stemness” in AML and Wnt/β-catenin and Myc pathways. Hence, BETP degradation by ARV-825 simultaneously targets cell-intrinsic signaling, stromal interactions, and metabolism in AML.

Authors

Sujan Piya, Hong Mu, Seemana Bhattacharya, Philip L. Lorenzi, R. Eric Davis, Teresa McQueen, Vivian Ruvolo, Natalia Baran, Zhiqiang Wang, Yimin Qian, Craig M. Crews, Marina Konopleva, Jo Ishizawa, M. James You, Hagop Kantarjian, Michael Andreeff, Gautam Borthakur

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Figure 8

Simultaneous targeting of leukemia-intrinsic biology and leukemia-microenvironment interaction will be critical for the successful treatment of AML.

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Simultaneous targeting of leukemia-intrinsic biology and leukemia-microe...
ARV-825, a cereblon-based BET-targeting PROTAC, causes sustained BRD4 degradation accompanied by downregulation of targets such as Myc and BCL-2 family molecules, resulting in increased apoptosis and DNA damage. While modulation of chemokine receptor (inhibition of surface expression of CXCR4)/adhesion molecules (transcriptional downregulation of CD44) and Wnt/β-catenin signaling results inactivation of prosurvival signals, modulation of apoptosis regulators, decreased adhesion and impair of self-renewal of leukemic stem cells and persistence residual clones. As a functional correlative of CD44v8–10 downregulation, a reduction in cysteine uptake and cellular GSH levels results in increased ROS generation and mitochondrial metabolic inhibition (OXPHOS). Hence, the antileukemic activity of BET protein degradation by ARV-825 is associated with modulation of chemokine receptors, cell adhesion, and metabolic targets.