DNA damage response and double strand break repair in prostate cancer: From mechanisms to clinical application

Abstract

Despite huge improvement in prostate cancer treatment, advanced PCa is still associated with poor outcomes, with CRPC being an incurable disease with limited treatment options. This highlights the urgent need for more tailored therapy that improve the survival of PCa patients. In the current study, we followed two strategies to help improve the treatment of advanced PCa. Strategy 1: Previously published pre-clinical data highlight the role of AR-signaling in fuelling the DNA repair machinery, through regulating the expression of several DNA repair genes. Given that IR kills cells by inducing DSBs, we sought to test the use of ADT to enhance the radiosensitivity of PCa cells. We demonstrate that second generation antiandrogens are potent radiosensitisers that inhibit DSB repair and increase the cytotoxic effect of IR. This conclusion was derived from the following key findings: - Only the second-generation antiandrogens abiraterone acetate, apalutamide or enzalutamide significantly suppressed cell growth and increased the doubling times upon combination with IR compared to IR alone. - The radiosensitising effect was attributed to inhibition of DNA repair capacity as evidenced by significantly increased numbers of residual γH2AX and 53BP1 foci after combined therapy vs. single treatment. - Interestingly, the second-generation antiandrogen-mediated radiosensitising effect was found to be castration-independent, as it was observed in both hormone-responsive LNCaP cells and in sublines resistant to (i) hormone ablation (LNCaP-abl), (ii) abiraterone acetate (LNCaP-abi), (iii) apalutamide (LNCaP-ARN509), (iv) enzalutamide (C4-2B-ENZA). - Further validation of this radiosensitization was performed using tumour slice cultures from 22 PCa patients. Again, regardless of their castration status, a significant increase in the number of residual γH2AX and 53BP1 foci was monitored after combined therapy of IR and abiraterone acetate. Translated into clinical practice, our results may help to find additional strategies to improve the effectiveness of RT in localized PCa, paving the way for a clinical trial. Strategy 2: Currently, there is an urgent need to develop robust pre-clinical models for PCa that are closer to the tumour in-vivo to allow better bench-to bed-side research. In Strategy 2, it was sought to develop pre-clinical models from naive and castration resistant PCa patients that can be used to functionally detect HRR-defects and better stratify PCa patients according to their response to drugs such as PARPi or cisplatin. This individualized drug screening allows immediate translation of treatment sensitivities into tailored clinical therapy recommendations. Key findings can be summarized as follows: - Using ex vivo tumour slice cultures, a substantial benefit was observed for CRPC patients from olaparib and cisplatin, as evidenced by a significantly increased number of residual IR-induced γH2AX/53BP1 foci. - A robust detailed protocol for PDO cultures driven from CRPC-patients was provided. This protocol maintains the morphological structure of the original tumours in the established PDOs. - The methylome profiling analysis revealed that PDOs are clustered with PCa but not with normal prostate or other tumour entities. - Employing these PDOs, patients who would benefit from olaparib or cisplatin were identified, validating the results obtained from ex-vivo tumour slice cultures. - Compared to ex-vivo tumour slice cultures, PDOs present a more robust pre-clinical cancer model for better translational research, as they allow more functional analyses for survival. These pre-clincal models allow individualized functional assessment of HRR deficient disease and provide immediate use to select PCa patients for the treatment with the aforementioned drugs in the clinical settings.