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Radiosensitization by the ATR Inhibitor AZD6738 through Generation of Acentric Micronuclei
Magnus T Dillon1, Holly E Barker1, Malin Pedersen1
1Targeted Therapy Team, Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, UK.
Abstract:
AZD6738 is an orally active ATR inhibitor (ATRi) currently in phase I clinical trials. We found in vitro growth inhibitory activity of this ATRi in a panel of human cancer cell lines. We demonstrated radiosensitization by AZD6738 to single radiation fractions in multiple cancer cell lines independent of both p53 and BRCA2 status by the clonogenic assay. Radiosensitization by AZD6738 to clinically relevant doses of fractionated radiation was demonstrated in vitro using a 3D tumor spheroid model and, in vivo, AZD6738 radiosensitized by abrogating the radiation-induced G2 cell-cycle checkpoint and inhibiting homologous recombination. Mitosis with damaged DNA resulted in mitotic catastrophe as measured by micronucleus formation by live-cell fluorescent-ubiquitination cell-cycle imaging of cell-cycle progression and nuclear morphology. Induction of micronuclei was significantly more prominent for AZD6738 compared with inhibition of the downstream kinase CHK1 alone at isoeffective doses. Micronuclei were characterized as acentric chromosomal fragments, which displayed characteristics of increased DNA damage and cell-cycle dyssynchrony when compared with the primary nucleus. Mol Cancer Ther; 16(1); 25-34. ©2016 AACR.
Insights
AZD6738, an ATR inhibitor, shows promise in cancer therapy by enhancing radiation effectiveness. It sensitizes cancer cells to radiation by disrupting DNA repair mechanisms and causing cell death, independent of p53 or BRCA2 status.
Area of Science:
- Oncology
- Molecular Biology
- Radiation Oncology
Background:
- AZD6738 is an orally active ATR inhibitor (ATRi) investigated in Phase I clinical trials.
- ATR inhibition is a potential strategy for cancer treatment, particularly in combination with DNA-damaging agents like radiation.
Purpose of the Study:
- To evaluate the in vitro and in vivo efficacy of AZD6738 as a radiosensitizer.
- To investigate the mechanisms underlying AZD6738-mediated radiosensitization, including effects on cell cycle checkpoints and DNA repair.
Main Methods:
- In vitro studies using human cancer cell lines and 3D tumor spheroid models.
- Clonogenic assays to assess radiosensitization.
- Live-cell imaging (fluorescent-ubiquitination cell-cycle imaging) to monitor cell cycle progression and nuclear morphology.
- In vivo studies in animal models.
Main Results:
- AZD6738 demonstrated in vitro growth inhibitory activity and radiosensitized multiple cancer cell lines to single and fractionated radiation doses, irrespective of p53 or BRCA2 status.
- In vivo, AZD6738 abrogated the radiation-induced G2 cell-cycle checkpoint and inhibited homologous recombination, leading to radiosensitization.
- AZD6738 treatment resulted in mitotic catastrophe, evidenced by increased micronucleus formation, indicating DNA damage and cell-cycle dyssynchrony.
Conclusions:
- AZD6738 is an effective radiosensitizer in preclinical cancer models.
- The mechanism involves abrogation of the G2 checkpoint and inhibition of homologous recombination, leading to DNA damage and mitotic catastrophe.
- AZD6738 holds potential as a therapeutic agent in combination with radiotherapy for cancer treatment.
