Characterisation of the tumour microenvironment in homologous recombination-deficient prostate cancer

Thesis

Alterations in homologous recombination (HR) genes drive genomic instability and chronic inflammation. Approximately 2-14% of prostate cancer patients harbour mutations in BRCA2 and PALB2, which are associated with early onset of disease and poor prognosis. There are currently no in vivo immunocompetent models of prostate cancer that explore how deficiencies in homology-directed repair impact the tumour microenvironment (TME). Here, two novel mouse models of HR-deficient (HRD) prostate cancer were developed by abrogating expression of Palb2 in MyC-CaP (Hi-Myc) and DVL3 (Pten^-/-, Trp53^-/-) cells. Functional validation of CRISPR Palb2 (crPalb2) cells demonstrated greater sensitivity to PARP inhibition in vitro, consistent with a HRD phenotype. crPalb2 cells accumulated in S phase with increased numbers of γH2AX foci and demonstrated heightened cGAS-STING and inflammasome pathway activation. MyC-CaP crPalb2 flank tumours in immunocompetent mice propagated more slowly than wild type tumours. Treatment with fractionated radiotherapy induced a significant growth delay in MyC-CaP crPalb2 tumours, consistent with retention of HRD status in vivo. Bulk transcriptomic profiling of MyC-CaP and DVL3 crPalb2 tumours demonstrated enrichment in genes indicative of pro-inflammatory cytokine secretion and an augmented immune response. Flow cytometry analysis of MyC-CaP crPalb2 tumours revealed global changes in immune populations in the TME, with increased PMN-MDSC and dendritic cell infiltration alongside reduced CD8⁺ T cell and Malt macrophage influx. CD8⁺ T cells isolated from crPalb2 tumours had elevated PD-1 positivity, which was not affected by olaparib treatment. Dendritic cells and antigen-experienced macrophages from crPalb2 tumours had increased MHC class II expression. These observations suggest a dual role for HRD in prostate cancer, where it can potentiate anti-tumour immunity through enhanced antigen presentation and promote therapy resistance via sustained immunosuppression in the TME.

Authors: Kwon, J

• DOI: 10.5287/ora-ozaqwzya0
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: DNA repair; tumour microenvironment; prostate cancer; inflammation
• Subjects: Oncology; Immunology