Radiotherapy often fails to kill oesophageal cancer cells, and a new study will test whether blocking a specific DNA repair enzyme can make those cells more vulnerable to radiation. Oesophageal adenocarcinoma kills most patients within five years, and radiotherapy alone frequently delivers inadequate responses. The cancer cells become resistant by using an error-prone DNA repair pathway called microhomology-mediated end joining (MMEJ), which relies on an enzyme called polymerase theta (Polθ). This project will first analyse genetic data from 377 patients to see how levels of the gene encoding Polθ vary across tumours and correlate with clinical outcomes. The researcher will then test 30 patient-derived tumour organoids to determine whether high Polθ expression predicts resistance to radiation. Finally, a small molecule Polθ inhibitor will be added to irradiated organoids to see whether it restores radiosensitivity and changes the mutation patterns left behind by treatment. If Polθ inhibition proves effective, it could provide a targeted radiosensitisation strategy for the subset of oesophageal cancers that are already deficient in homologous repair—a group that may be especially dependent on MMEJ to survive. This would offer a new drug-radiotherapy combination for a cancer with few good treatment options.
View original technical description
Background Oesophageal adenocarcinoma (OAC) is a cancer of significant unmet need with high rates of morbidity and mortality. Radiotherapy is an important treatment option for OAC but delivers inadequate responses. Improving the biological effect achieved by radiotherapy, such as through the identification of effective radiosensitisers, holds the potential to improve outcomes. However, the development of novel drug-radiotherapy combinations requires an understanding of the processes mediating radioresistance. We have recently demonstrated an increase in mutational signatures with a microhomology signal in radioresistant OAC cells, suggesting involvement of error-prone microhomology-mediated end joining (MMEJ) in the development of resistance. MMEJ activity is contingent on DNA polymerase θ (Polθ), which is encoded by the POLQ gene. Deficiency of Polθ has been shown to increase cellular radiosensitivity across a variety of tumour cells. This effect is particularly profound in models of homologous repair (HR) deficiency, in which Polθ inhibition results in synthetic lethality due to their otherwise increased reliance on MMEJ. This is of pertinence given that our work has also shown that a subset of OAC cases is defined by a relative HR deficiency. Aims I will use an existing RNA sequencing dataset to characterise the heterogeneity of expression of POLQ in 377 patients diagnosed with OAC, and to derive clinicopathological correlates for this. I will subsequently evaluate whether POLQ/Polθ expression correlates with radiosensitivity in a panel of 30 OAC patient-derived organoids (PDOs). Finally, I will analyse the impact of a small molecule Polθ inhibitor on OAC PDO radiosensitivity and changes in radiotherapy-induced mutational burden following radiation treatment. Methods The heterogeneity of POLQ RNA expression will be explored using data from the Oesophageal Cancer Clinical & Molecular Stratification (OCCAMS) consortium. Existing radiation sensitivity data for a panel of 30 OAC PDOs will be correlated against POLQ expression determined from existing PDO RNA sequencing datasets. I will then irradiate a subset of PDOs with varying radiation sensitivities in the presence and absence of Polθ inhibition to assess their impact on radiation sensitivity. Finally, I will extract and sequence using whole genome sequencing DNA from irradiated PDOs to evaluate the relative change in mutational burden with and without the use of a Polθ inhibitor. How the results of this research will be used This research will provide insight into the role of MMEJ in OAC response to radiotherapy. Positive results may lead to the identification of Polθ inhibition as a viable radiosensitisation target of HR-deficient OACs.
Research Careers Committee - Training Intervention
Plain English summaries and category classifications on this site are generated by AI and may not perfectly reflect the original research.
Is something wrong? Let us know