Chronic Myelogenous Leukemia- Initiating Cells Require Polycomb Group Protein EZH2

Area of Science:

• Oncology
• Molecular Biology
• Hematology

Background:

• Tyrosine kinase inhibitors (TKIs) have transformed chronic myelogenous leukemia (CML) treatment.
• Leukemia-initiating cells (LICs) are resistant to TKIs, leading to disease relapse and resistance.
• EZH2, a component of Polycomb Repressive Complex 2 (PRC2), is implicated in cancer development.

Purpose of the Study:

• To investigate the role of EZH2 in CML, particularly in TKI-resistant cells and LICs.
• To determine if EZH2 represents a therapeutic target for CML management.

Main Methods:

• Overexpression analysis of EZH2 in CML LICs.
• Functional assays assessing colony formation, survival, and cell-cycle progression in CML cell lines.
• Genetic inactivation of Ezh2 in a mouse CML model using conditional knockout and CRISPR/Cas9 gene editing.

Main Results:

• EZH2 is overexpressed in CML LICs and is crucial for their proliferation and survival.
• Inactivation of Ezh2 in mice prevented CML initiation and maintenance, extending survival.
• EZH2 deficiency led to reduced EZH1 expression, mimicking complete PRC2 loss.
• EZH2 dependence was observed irrespective of BCR-ABL1 mutational status.

Conclusions:

• EZH2 is a critical vulnerability in CML cells and LICs, independent of BCR-ABL1 mutations.
• Targeting EZH2 with inhibitors presents a promising therapeutic strategy to enhance TKI therapy and improve CML eradication.
• This provides a rationale for combining EZH2 inhibitors with standard TKI treatment for CML.