Development of DNA polymerase theta inhibitors as tumour specific radiosensitisers
Geoff Higgins,
United Kingdom
OC-0428
Abstract
Development of DNA polymerase theta inhibitors as tumour specific radiosensitisers
Authors: Remko Prevo1, Marco Ranzani2, Rathi Puliyadi3, Gonzalo Rodriguez-Berriguete1, Helen Robinson2, Eeson Rajendra2, Vera Grinkevich2, Marie Boursier2, Alessandro Cicconi2, Desiree Piscitello2, Aurora Cerutti2, Jayesh Majithiya2, Robert Heald2, Martin Stockley2, Graeme Smith2, Geoff Higgins3
1University of Oxford, CRUK RadNet Oxford, Department of Oncology, Oxford, United Kingdom; 2Artios Pharma, Babraham Research Campus, Cambridge, United Kingdom; 3University of Oxford, Department of Oncology, Oxford, United Kingdom
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Purpose or Objective
DNA Polymerase theta (POLQ) is a DNA repair enzyme that has low or absent expression in most normal tissues but is frequently overexpressed in many cancer types, particularly in tumours with homologous recombination (HR) deficiency, which rely on POLQ for repair of replication-associated DNA double strand breaks. As a radiosensitisation target, POLQ inhibition is expected to be effective in a wide range of tumours irrespective of HR status. We previously showed that depleting POLQ through siRNA radiosensitises tumour but not normal cells (Higgins et al., 2010, Cancer Res. 70: 2984).
Recently Artios developed novel and specific POLQ inhibitors (including ART558 and ART812) that showed synthetic lethality against BRCA and also Shieldin deficiency (Zatreaunu et al., 2021 Nat. Commun. 12:3636). The purpose of this work was to test these inhibitors for their ability to induce tumour specific radiosensitisation in vitro and in vivo. We also aimed to define the cellular characteristics that predispose to POLQi-mediated radiosensitisation.
Material and Methods
Cell line panels for head & neck, colorectal and lung cancer were screened for radiosensitisation by POLQ inhibition in colony formation assays. Imaging of DNA damage foci and flow cytometry analysis of G2M arrest and BrdU incorporation were used to study the DNA damage response and cell cycle progression. Colorectal HCT116 subcutaneous xenografts were given daily doses of POLQ inhibitor combined with a fractionated regime of 10 x 2 Gy.
Results
The POLQ inhibitors were effective radiosensitisers in a wide range of tumour cells but did not significantly affect normal cells, which were shown to express only low levels of POLQ. Increasing the number of radiation fractions led to an increase of POLQ inhibitor-mediated radiosensitisation in tumour cells. Radiosensitisation was most effective in cells in the S and G2 phase of the cell cycle and POLQ inhibition appeared to be particularly effective in cells with fast cell cycle progression. POLQ inhibition was associated with an increase in residual DNA damage foci after irradiation and increased G2/M arrest. Combination of POLQ inhibition with radiation in vivo led to a significant reduction in tumour growth and was very well-tolerated.
Conclusion
We showed that Artios’s potent and specific POLQ inhibitors are effective radiosensitisers in a wide range of tumour cells and also elicit tumour radiosensitisation in vivo. Our results will pave the way for testing POLQ inhibitors with radiotherapy in clinical trials.