Metronomic dosing of ovarian cancer cells with the ATR inhibitor AZD6738 leads to loss of CDC25A expression and resistance to ATRi treatment

Wei Ao, Hong Im Kim, Domenic Tommarello, Kelly A. Conrads, Brian L. Hood, Tracy Litzi, Tamara Abulez, Pang Ning Teng, Clifton L. Dalgard, Xijun Zhang, Matthew D. Wilkerson, Kathleen M. Darcy, Christopher M. Tarney, Neil T. Phippen, Christopher J. Bakkenist, G. Larry Maxwell, Thomas P. Conrads, John I. Risinger, Nicholas W. Bateman*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Objective: ATR kinase inhibitors promote cell killing by inducing replication stress and through potentiation of genotoxic agents in gynecologic cancer cells. To explore mechanisms of acquired resistance to ATRi in ovarian cancer, we characterized ATRi-resistant ovarian cancer cells generated by metronomic dosing with the clinical ATR inhibitor AZD6738. Methods: ATRi-resistant ovarian cancer cells (OVCAR3 and OV90) were generated by dosing with AZD6738 and assessed for sensitivity to Chk1i (LY2603618), PARPi (Olaparib) and combination with cisplatin or a CDK4/6 inhibitor (Palbociclib). Models were characterized by diverse methods including silencing CDC25A in OV90 cells and assessing impact on ATRi response. Serum proteomic analysis of ATRi-resistant OV90 xenografts was performed to identify circulating biomarker candidates of ATRi-resistance. Results: AZD6738-resistant cell lines are refractory to LY2603618, but not to Olaparib or combinations with cisplatin. Cell cycle analyses showed ATRi-resistant cells exhibit G1/S arrest following AZD6738 treatment. Accordingly, combination with Palbociclib confers resistance to AZD6738. AZD6738-resistant cells exhibit altered abundances of G1/S phase regulatory proteins, including loss of CDC25A in AZD6738-resistant OV90 cells. Silencing of CDC25A in OV90 cells confers resistance to AZD6738. Serum proteomics from AZD6738-resistant OV90 xenografts identified Vitamin D-Binding Protein (GC), Apolipoprotein E (APOE) and A1 (APOA1) as significantly elevated in AZD6738-resistant backgrounds. Conclusions: We show that metronomic dosing of ovarian cancer cells with AZD6738 results in resistance to ATR/ Chk1 inhibitors, that loss of CDC25A expression represents a mechanism of resistance to ATRi treatment in ovarian cancer cells and identify several circulating biomarker candidates of CDC25A low, AZD6738-resistant ovarian cancer cells.

Original languageEnglish
Pages (from-to)60-71
Number of pages12
JournalGynecologic Oncology
StatePublished - Oct 2023
Externally publishedYes


  • (CDC25A)
  • ATR
  • Ataxia telangiectasia and Rad3-related
  • Cell division cycle 25A
  • Checkpoint kinase 1
  • Chk1
  • Drug resistance
  • Ovarian cancer


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