Resistance of acute
myeloid leukemia (AML) cells to
DNA damaging therapeutic agents is dependent on CHK1
protein levels. Here, the inventors demonstrate that in AML, CHK1
protein stability relies on the expression and activity of
Ubiquitin Specific
Protease 7 (USP7). CHK1 and USP7 levels are positively correlated in AML
cell lines and primary patient specimens with high CHK1
protein levels. USP7 associates with CHK1, leading to its stabilization by deubiquitinylation, and this association is enhanced in response to
cytarabine treatment. Pharmacological or
RNA interference-mediated inhibition of USP7 significantly reduced AML proliferation
in vitro and
in vivo, and increased AML
cell death. It is important to note that USP7 inhibition synergized with
cytarabine to kill AML
cell lines. This is also the case in primary patient specimens with high CHK1 levels. Transcriptomic dataset analyses revealed that a USP7
gene signature is highly enriched in cells from AML patients at relapse, as well as in residual blasts from Patient Derived Xenograft (PDX) models treated with clinically relevant doses of
cytarabine, strongly suggesting a relationship between USP7 expression and resistance to therapy. Finally,
single cell analysis from AML patient at relapse versus diagnosis showed that a
gene signature of the pre-existing subpopulation responsible for relapse is enriched in transcriptomes of patients with high USP7 level. Altogether, these data demonstrate that USP7 is a master
regulator of CHK1 protein
kinase in AML cells, and represents both a marker of resistance to chemotherapeutic treatments, as well as a potential therapeutic target to overcome
treatment resistance.