A functional ex vivo assay to detect PARP1-EJ repair and radiosensitization by PARP-inhibitor in prostate cancer

TY - JOUR

T1 - A functional ex vivo assay to detect PARP1-EJ repair and radiosensitization by PARP-inhibitor in prostate cancer

AU - Köcher, S

AU - Beyer, B

AU - Lange, T

AU - Nordquist, L

AU - Volquardsen, J

AU - Burdak-Rothkamm, S

AU - Schlomm, T

AU - Petersen, C

AU - Rothkamm, K

AU - Mansour, W Y

N1 - © 2018 UICC.

PY - 2019/4/1

Y1 - 2019/4/1

N2 - Here, we present a functional assay to detect the repair switch to the alternative PARP1-dependent end joining (PARP1-EJ) pathway and the associated susceptibility to PARPi-mediated radiosensitization in freshly collected tumor samples from prostate cancer (PCa) patients, thereby facilitating the selection of patients who should benefit from combined PARPi plus radiotherapy (RT) treatment. Our optimized ex-vivo approach sustains tumor slices for up to 15 days under culture conditions that maintain proliferation and oxygenation rates, as measured by EdU incorporation and pimonidazole staining, respectively. We present a robust system to analyze DSB repair using, for the first time in an ex vivo tumor slice setting, two DSB-markers simultaneously i.e. γH2AX and 53BP1. A computer-based processing method (i) controls variations in DNA content and slicing on the number of repair foci and (ii) measures the PARPi-mediated enhancement ratio on DSB foci numbers to ensure inter-patient-comparability. We validated this approach using a PC3 xenograft model with its previously described repair switch to PARP1-EJ. More importantly, we show that approximately 30% of the analyzed tumor tissue samples collected from PCa patients display a switch to PARP1-EJ, as indicated by the enhanced number of residual γH2AX/53BP1 foci exclusively after PARPi+RT. Furthermore, normal prostatic tissues show no repair switch to PARP1-EJ, indicating that this repair switch and its associated radiosensitizing effect is tumor-specific. Collectively, we present here a predictive assay for the switch to PARP1-EJ that enables individualization of anti-cancer treatment using a combination of RT and radiosensitizing anticancer agents such as PARPi in PCa.

AB - Here, we present a functional assay to detect the repair switch to the alternative PARP1-dependent end joining (PARP1-EJ) pathway and the associated susceptibility to PARPi-mediated radiosensitization in freshly collected tumor samples from prostate cancer (PCa) patients, thereby facilitating the selection of patients who should benefit from combined PARPi plus radiotherapy (RT) treatment. Our optimized ex-vivo approach sustains tumor slices for up to 15 days under culture conditions that maintain proliferation and oxygenation rates, as measured by EdU incorporation and pimonidazole staining, respectively. We present a robust system to analyze DSB repair using, for the first time in an ex vivo tumor slice setting, two DSB-markers simultaneously i.e. γH2AX and 53BP1. A computer-based processing method (i) controls variations in DNA content and slicing on the number of repair foci and (ii) measures the PARPi-mediated enhancement ratio on DSB foci numbers to ensure inter-patient-comparability. We validated this approach using a PC3 xenograft model with its previously described repair switch to PARP1-EJ. More importantly, we show that approximately 30% of the analyzed tumor tissue samples collected from PCa patients display a switch to PARP1-EJ, as indicated by the enhanced number of residual γH2AX/53BP1 foci exclusively after PARPi+RT. Furthermore, normal prostatic tissues show no repair switch to PARP1-EJ, indicating that this repair switch and its associated radiosensitizing effect is tumor-specific. Collectively, we present here a predictive assay for the switch to PARP1-EJ that enables individualization of anti-cancer treatment using a combination of RT and radiosensitizing anticancer agents such as PARPi in PCa.

KW - Journal Article

KW - Prostatic Neoplasms/genetics

KW - Tissue Culture Techniques

KW - Humans

KW - Male

KW - DNA Breaks, Double-Stranded

KW - Histones/metabolism

KW - Poly(ADP-ribose) Polymerase Inhibitors/administration & dosage

KW - Poly (ADP-Ribose) Polymerase-1/antagonists & inhibitors

KW - Animals

KW - Neoplasm Grading

KW - Radiation-Sensitizing Agents/administration & dosage

KW - Tumor Suppressor p53-Binding Protein 1/metabolism

KW - Cell Line, Tumor

KW - Mice

KW - Cell Proliferation/drug effects

KW - DNA End-Joining Repair/drug effects

U2 - 10.1002/ijc.32018

DO - 10.1002/ijc.32018

M3 - SCORING: Journal article

C2 - 30478958

VL - 144

SP - 1685

EP - 1696

JO - INT J CANCER

JF - INT J CANCER

SN - 0020-7136

IS - 7

ER -