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Updated: Jun 2, 2026
Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
Published on: May 3, 2018
Assessment of chk1 phosphorylation as a pharmacodynamic biomarker of chk1 inhibition
Leslie A Parsels1, Yushen Qian, Daria M Tanska
1Departments of Radiation Oncology, Pharmacology, and Surgery, University of Michigan Medical School, Ann Arbor, MI 48109-5637, USA.
Purpose:
Chk1 inhibitors, such as AZD7762, are in clinical development in combination with cytotoxic agents for the treatment of solid tumors, including pancreatic cancers. To maximize the likelihood of their clinical success, it is essential to optimize drug scheduling as well as pharmacodynamic biomarkers in preclinical models.
Experimental Design:
We tested multiple schedules of administration of gemcitabine and AZD7762 on the survival of pancreatic cancer cells. Potential pharmacodynamic biomarkers including pChk1, pChk2, pHistone H3, and caspase-3 were evaluated in vitro, followed by assessment of promising candidate biomarkers in vivo. We then went on to determine the contributions of PP2A and DNA damage to the mechanism(s) of induction of the identified biomarker, pS345 Chk1.
Results:
AZD7762 given during and after or after gemcitabine administration produced maximum chemosensitization. In vivo, AZD7762 significantly inhibited the growth of pancreatic tumor xenografts in response to gemcitabine. Of the biomarkers assessed, pS345 Chk1 was most consistently increased in response to gemcitabine and AZD7762 in tumors and normal tissues (hair follicles). pS345 Chk1 induction in response to gemcitabine and AZD7762 occurred in the presence of PP2A inhibition and in association with elevated γH2AX, suggesting that DNA damage is an underlying mechanism.
Conclusions:
AZD7762 sensitizes pancreatic cancer cells and tumors to gemcitabine in association with induction of pS345 Chk1. Together these data support the clinical investigation of AZD7762 with gemcitabine in pancreatic cancer under a dosing schedule in which gemcitabine is administered concurrent with or before AZD7762 and in conjunction with skin biopsies to measure pS345 Chk1.
Insights
Combining gemcitabine with AZD7762 chemotherapy sensitizes pancreatic cancer cells and tumors. The optimal schedule involves administering gemcitabine before or concurrently with AZD7762, with pS345 Chk1 as a biomarker.
Area of Science:
- Oncology
- Pharmacology
- Cancer Biology
Background:
- Checkpoint kinase 1 (Chk1) inhibitors like AZD7762 are being developed for solid tumors, including pancreatic cancer.
- Optimizing drug scheduling and identifying pharmacodynamic biomarkers are crucial for the clinical success of Chk1 inhibitors in combination therapy.
Purpose of the Study:
- To optimize the administration schedule of gemcitabine and AZD7762 for pancreatic cancer treatment.
- To identify and validate pharmacodynamic biomarkers for predicting response to gemcitabine and AZD7762 combination therapy.
Main Methods:
- Evaluated various gemcitabine and AZD7762 administration schedules in pancreatic cancer cells in vitro.
- Assessed potential pharmacodynamic biomarkers (pChk1, pChk2, pHistone H3, caspase-3) in vitro and in vivo.
- Investigated the roles of PP2A and DNA damage in the induction of the pS345 Chk1 biomarker.
Main Results:
- Maximum chemosensitization was achieved when AZD7762 was administered during and after, or after gemcitabine.
- In vivo, AZD7762 significantly inhibited pancreatic tumor xenograft growth when combined with gemcitabine.
- Phosphorylated S345 Chk1 (pS345 Chk1) was the most consistent biomarker, increasing in tumors and normal tissues (hair follicles) in response to the combination therapy, suggesting DNA damage as an underlying mechanism.
Conclusions:
- AZD7762 enhances the sensitivity of pancreatic cancer cells and tumors to gemcitabine, indicated by the induction of pS345 Chk1.
- Clinical investigation of AZD7762 with gemcitabine in pancreatic cancer is supported, using a schedule where gemcitabine precedes or is concurrent with AZD7762.
- Skin biopsies to measure pS345 Chk1 induction can serve as a pharmacodynamic biomarker in clinical trials.
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