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1167 Olaparib in combination with inhibitors of ATR/CHK1 pathway leads to increased cell death in ovarian cancer cells sensitive and resistant to PARPi
  1. Ł Biegała,
  2. A Gajek,
  3. A Marczak and
  4. A Rogalska
  1. Institute of Biophysics, Department of Medical Biophysics, Lodz, Poland


Introduction/Background*Ovarian cancer (OC) is believed to be one of the most lethal gynaecologic malignancies worldwide. Despite advances in the treatment of OC after the introduction of poly(ADP-ribose) polymerase inhibitors (PARPi) in the frontline setting as maintenance therapy and in the recurrent setting, the 5-year survival rate of high-grade serous ovarian cancer (HGSOC) ranges between 35 and 40%. PARPi exhibit meaningful activity against OC, however resistance to these agents emerges ultimately. Thus, there is a need to develop more effective treatments for OC. Recent reports highlighting increased OC cell reliance on ATR/CHK1 pathway gives hope to overcome PARPi resistance and prolong patient’s survival.

Methodology The aim of this study was to estimate cytotoxic activity of PARPi (olaparib), the ataxia telangiectasia and Rad-3 related protein (ATR) inhibitor (ATRi, ceralasertib), and the checkpoint kinase 1 (CHK1) inhibitor (CHK1i, MK-8776) alone or in combinations in PEO1 (BRCA2MUT) OC cell line, and in PEO1-derived olaparib-resistant (PEO1-OR) cell line developed by continuous incremental long-term treatment with olaparib. Here, we evaluated the effect of tested drugs on cell survival in respect of metabolic activity by MTT assay and colony forming capacity. We also preliminarily elucidated mechanisms conferring resistance to olaparib in OC cells by assessment of expression of key proteins (ATR, CHK1, PARP1, P-glycoprotein) by western blot analysis. Statistical analyses were performed using Student’s t-test and ANOVA followed by the Tukey’s multiple comparisons post-hoc test.

Result(s)*OC cells are more sensitive to combination of the drugs in comparison with monotherapy with each agent alone. What is more, treatment with single-agent PARPi or combination of PARPi/ATRi or PARPi/CHK1i activates ATR/CHK1 pathway through increased phosphorylation of CHK1 on serine 345 in PEO1 olaparib-sensitive cells. Targeting PARP in combination with ATRi or CHK1i is also synergistic in olaparib-resistant OC cells. However, pCHK1 was upregulated after treatment with CHK1i and PARPi/CHK1i in PEO1-OR cells. PARPi-resistance is associated with increased expression of PARP1, but not P-glycoprotein.

Conclusion*Our results show that olaparib in combination with ATRi or CHK1i prompts cell death of OC line sensitive and resistant to olaparib on the path of synthetic lethality.

This research was funded by the Polish National Science Centre, Poland (Project grant number: Sonata Bis 2019/34/E/NZ7/00056).

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