Investigating the role of poly (ADP-ribose ) polymerase inhibitors in the treatment of endometrial cancer

Abstract

Introduction: Endometrial cancer is the most common gynaecological malignancy in the UK. Whilst most women have low grade indolent cancers, 20% have high grade tumours which result in a disproportionate number of deaths. Following first line treatment, there is no standard of care and response rates are poor. In line with ovarian cancer treatment, where PARP inhibitors have resulted in better survival, it is anticipated that a proportion of endometrial cancers are homologous recombination DNA repair deficient (HRD), providing opportunity to exploit this with PARP inhibitors. The work in this thesis included pre-clinical and translational studies to assess the effect of cisplatin, ionising radiation and PARP inhibitor (Niraparib) on endometrial cancer cell lines and ex-vivo patient derived cultures, as well as assessing HRR status and other pathology markers as biomarkers to stratify the use of PARP inhibitor therapy. Methodology: Cytotoxicity, growth inhibition, PARP assays and immunohistochemistry studies were undertaken in 6 endometrial cancer cell lines, along with functional HRR assay measuring RAD51 foci formation by immunofluorescence. Direct endometrial tumour biopsies were taken from 54 patients (REC: 12/NE/0395) and the method optimised for ex-vivo culture. Where feasible, the RAD51 foci HRR assay alongside growth inhibition with Niraparib was undertaken. A tissue microarray was constructed from available FFPE patient samples and cell line thrombin clots. Common IHC markers (p53, ER, PR, p53, MMR proteins) and PTEN were quantified and analysed stratified by HRR function and clinicopathological data. Results: The diverse panel of endometrial cell lines were all HRR competent using the RAD51 foci functional assay, with similar growth and PARP activity levels. No significant differences in sensitivity to single agent IR, cisplatin were detected but trends in sensitivity were consistent (AN3CA most sensitive and HEC1A least sensitive). PARP activity was inhibited by 90% with Niraparib 1 µM, with no significant differences in cytotoxicity or growth inhibition across the cell lines. Radiopotentiation with Niraparib at the lethal concentration 50 (PF50) ranged from 1.00 to 1.84 in the Ishikawa cell line. Higher doses of IR (4 Gy) yielded greater potentiation in the endometrial cancer cell lines (PF up to 2.41). Minimal potentiation was ii seen when increasing concentrations of cisplatin was combined with Niraparib 1 µM (PF50 ranging from 0.77- 1.44). 54 endometrial cancer biopsies were obtained with consent. 30 samples were successful in culture of which 18 completed RAD51 foci HRR assay. 3/18 were HRD and 15/18 were HRR competent (HRC). Niraparib growth inhibition studies were completed on 10 samples. The 2/10 samples that were HRD had lower mean GI50 when compared to 8/10 HRC samples (1.5 µM vs 20 µM, p=0.047). There were no clinicopathological or IHC markers which accurately correlated with HRR status in this small cohort. Conclusion: Endometrial cancer cell lines are a limited resource with a lack of DNA repair dysfunction. There was modest potentiation when Niraparib 1 µM was combined with IR, and no potentiation in combination with cisplatin. It is possible to develop ex-vivo endometrial cancer cultures, but the lifespan of cultures is short. 3/18 patients were HRD with corresponding sensitivity to Niraparib. This study justifies further exploration to determine the incidence of HRD in endometrial cancer, with initial studies suggesting a potential role in radiosensitisation and as a single agent treatment. Further optimisation of primary cell culture is needed along with better models to test biomarkers for appropriate stratification of therapy. The results support taking forward PARPi into xenograft models and early phase clinical trials to determine exact role of PARPi in endometrial cancer.