posted on 2021-02-12, 16:45authored byJennifer
P. Ditano, Alan Eastman
DNA damage activates the checkpoint
protein CHK1 to arrest cell
cycle progression, providing time for repair and recovery. Consequently,
inhibitors of CHK1 (CHK1i) enhance damage-induced cell death. Additionally,
CHK1i elicits single agent cytotoxicity in some cell lines. We compared
three CHK1i that have undergone clinical trials and exhibited different
toxicities. Each CHK1i inhibits other targets at higher concentrations,
and whether these contribute to the toxicity is unknown. We compared
their sensitivity in a panel of cell lines, their efficacy at inhibiting
CHK1 and CHK2, and their ability to induce DNA damage and abrogate
damage-induced S phase arrest. Published in vitro kinase analyses
were a poor predictor of selectivity and potency in cells. LY2606368
was far more potent at inhibiting CHK1 and inducing growth arrest,
while all three CHK1i inhibited CHK2 at concentrations 10- (MK-8776
and SRA737) to 100- (LY2606368) fold higher. MK-8776 and SRA737 exhibited
similar off-target effects: higher concentrations demonstrated transient
protection from growth inhibition, circumvented DNA damage, and prevented
checkpoint abrogation, possibly due to inhibition of CDK2. Acquired
resistance to LY2606368 resulted in limited cross-resistance to other
CHK1i. LY2606368-resistant cells still abrogated DNA damage-induced
S phase arrest, which requires low CDK2 activity, whereas inappropriately
high CDK2 activity is responsible for sensitivity to CHK1i alone.
All three CHK1i inhibited protein synthesis in a sensitive cell line
correlating with cell death, whereas resistant cells failed to inhibit
protein synthesis and underwent transient cytostasis. LY2606368 appears
to be the most selective CHK1i, suggesting that further clinical development
of this drug is warranted.