Contributions
Abstract: EP418
Type: E-Poster Presentation
Session title: Acute myeloid leukemia - Biology & Translational Research
Background
Checkpoint kinase 1 (CHK1), encoded by CHEK1, supports tumor cell survival by restraining replication stress (RS), either induced, endogenously, by oncogenic transformation or, exogenously, by chemotherapy. CHK1 upregulation in cancer cells has been associated with decreased proteasomal degradation, challenging a direct correlation between CHK1 transcript and protein levels. CHK1 inhibition appears to be an attractive strategy for acute myeloid leukemia (AML) treatment (NCT02649764; NCT03735446). However, CHK1 protein expression in AML patients (pts) remains uncharacterized, precluding the identification of AML subgroups that may benefit the most from CHK1 targeted therapy.
Aims
We sought to measure CHK1 expression and activity in AML and assess whether it associates with specific clinical or biological AML features.
Methods
Bone marrow aspirate and peripheral blood cells from de novo diagnosed AML pts (n=29) were processed for RNA and protein extraction. Normal bone marrow (NBM) aspirates (n=8) were used as controls. CHEK1 transcript was quantified by qRT-PCR. CHK1 protein was quantified by total CHK1 immunoblot and its kinase activity was detected by immunoblotting Serine 296-phosphorylated CHK1. AML pts were then divided according to low or high CHEK1 mRNA levels, low or high protein expression, or detectable versus undetectable CHK1 activity and the various subgroups were tested for differences in the frequency of clinically relevant characteristics.
Results
We found no correlation between CHEK1 mRNA and CHK1 protein levels or activity in our AML cohort. Furthermore, AML pts expressed similar CHEK1 transcript levels to those observed in healthy controls. In contrast, CHK1 protein was significantly upregulated in AML when compared to NBM. This led us to hypothesize that CHK1 protein may be biologically and clinically more relevant than the transcript levels in AML. Indeed, there were no significant differences between CHEK1 mRNA-low and -high pts in any of the features analysed (age, sex, WBC, morphologic classification and ELN genetic risk). In contrast, AML pts with high CHK1 protein were significantly enriched in monocytic/monoblastic morphology (90% of all monocytic AML, n=10), and also included all immature AML cases (n=5). Notably, CHK1-high pts were significantly enriched in ELN intermediate-risk cases. Finally, we observed that constitutive CHK1 activation was associated with hyperleukocytosis, with a 10-fold higher median of WBC at presentation.
Conclusion
Our data show that CHK1 upregulation takes place during AML development in a post-transcriptional manner. We propose that highly proliferative AML activate CHK1, affording protection against proliferation-associated RS. CHK1 upregulation occurs preferentially in immature and monocytic lineage committed AML, suggesting these subgroups may be optimal candidates for therapeutic intervention with CHK1 inhibitors.
Keyword(s): AML, DNA damage, Therapy
Abstract: EP418
Type: E-Poster Presentation
Session title: Acute myeloid leukemia - Biology & Translational Research
Background
Checkpoint kinase 1 (CHK1), encoded by CHEK1, supports tumor cell survival by restraining replication stress (RS), either induced, endogenously, by oncogenic transformation or, exogenously, by chemotherapy. CHK1 upregulation in cancer cells has been associated with decreased proteasomal degradation, challenging a direct correlation between CHK1 transcript and protein levels. CHK1 inhibition appears to be an attractive strategy for acute myeloid leukemia (AML) treatment (NCT02649764; NCT03735446). However, CHK1 protein expression in AML patients (pts) remains uncharacterized, precluding the identification of AML subgroups that may benefit the most from CHK1 targeted therapy.
Aims
We sought to measure CHK1 expression and activity in AML and assess whether it associates with specific clinical or biological AML features.
Methods
Bone marrow aspirate and peripheral blood cells from de novo diagnosed AML pts (n=29) were processed for RNA and protein extraction. Normal bone marrow (NBM) aspirates (n=8) were used as controls. CHEK1 transcript was quantified by qRT-PCR. CHK1 protein was quantified by total CHK1 immunoblot and its kinase activity was detected by immunoblotting Serine 296-phosphorylated CHK1. AML pts were then divided according to low or high CHEK1 mRNA levels, low or high protein expression, or detectable versus undetectable CHK1 activity and the various subgroups were tested for differences in the frequency of clinically relevant characteristics.
Results
We found no correlation between CHEK1 mRNA and CHK1 protein levels or activity in our AML cohort. Furthermore, AML pts expressed similar CHEK1 transcript levels to those observed in healthy controls. In contrast, CHK1 protein was significantly upregulated in AML when compared to NBM. This led us to hypothesize that CHK1 protein may be biologically and clinically more relevant than the transcript levels in AML. Indeed, there were no significant differences between CHEK1 mRNA-low and -high pts in any of the features analysed (age, sex, WBC, morphologic classification and ELN genetic risk). In contrast, AML pts with high CHK1 protein were significantly enriched in monocytic/monoblastic morphology (90% of all monocytic AML, n=10), and also included all immature AML cases (n=5). Notably, CHK1-high pts were significantly enriched in ELN intermediate-risk cases. Finally, we observed that constitutive CHK1 activation was associated with hyperleukocytosis, with a 10-fold higher median of WBC at presentation.
Conclusion
Our data show that CHK1 upregulation takes place during AML development in a post-transcriptional manner. We propose that highly proliferative AML activate CHK1, affording protection against proliferation-associated RS. CHK1 upregulation occurs preferentially in immature and monocytic lineage committed AML, suggesting these subgroups may be optimal candidates for therapeutic intervention with CHK1 inhibitors.
Keyword(s): AML, DNA damage, Therapy