ESTRO 2024 - Abstract Book

S5354

Radiobiology - Tumour biology

ESTRO 2024

924

Digital Poster

ATM and ATR inhibition increases radiosensitivity and may improve immunogenicity of prostate cancer.

Nina van Campen, Vera E Mekers, Fabian Schuurmans, Esther Fernández Merino, Maaike W Looman, Robert Jan Smeenk, Marcel Verheij, Marleen Ansems, Gosse J Adema

Radboudumc, Radiation Oncology, Nijmegen, Netherlands

Purpose/Objective:

Purpose/objective: Unlike excellent oncologic results of treatments for localized prostate cancer, patients presenting with metastatic disease will eventually develop incurable metastatic castration-resistant prostate cancer (mCRPC). Radiotherapy (RT) is one of the standard treatment options for prostate cancer. It creates DNA breaks resulting in tumor cell death, increased antigenicity and neoantigen release. Such neoantigens can be scavenged by immune cells which can initiate an anti-tumor immune response that can be further boosted by immune checkpoint inhibition (ICI). Prostate cancers are, however, characterized by an immunologically “cold” phenotype and therefore ICI has shown only limited success in non-stratified prostate cancer patients. About 25% of mCRPC patients carry DNA damage repair (DDR) pathway mutations, leading to less effective DNA repair. We hypothesize that these mutations not only increase the radiosensitivity of the tumor cells, but also increase in the immunogenicity by increased neoantigen release and inducing pro-inflammatory pathways such as the cGAS-STING pathway.

Our aim is to investigate the effect of irradiation in combination with DNA damage repair inhibition on the immunogenicity of prostate cancer cells to enhance the potential for RT and ICI combination therapy in the treatment of mCRPC.

Material/Methods:

Material/methods: Three human prostate cancer cell lines LNCaP, PC3, and DU145 were selected for our studies. Dose titration of the DDR inhibitors KU-55933 (ATM inhibitor), AZD-6738 (ATR inhibitor), Olaparib (PARP inhibitor), and SR-4835 (CDK12 inhibitor) was performed to identify the maximal non-toxic dose per cell line. The effect of DDR pathway inhibition on radiosensitivity was investigated by colony forming assays. Western Blots were performed to assess the timing of ATM pathway activation and to confirm ATM pathway blockage induced by the inhibitor. Immunofluorescent staining was done to visualize the effect of DNA repair pathway inhibition on the presence of 53BP1 and yH2AX foci in PC3 cells. The presence and activation of the cGAS-STING pathway was assessed by Western Blot and quantitative PCR (qPCR).

Results:

Results: ATM, ATR, and PARP inhibitors, but not CDK12 inhibitor, increase the radiosensitivity of PC3 and DU145 cells in colony forming assays, whereby ATM inhibition shows the largest effect (Fig. 1). These findings were further