Overexpression of the ERG oncogene in prostate cancer identifies candidates for PARP inhibitor–based radiosensitization
Sabrina Köcher, Mohamed E. Elsesy, Ayham Moustafa, Wahid Mohammadi, Adriana Perugachi Heinsohn, Yamini Nagaraj, Su Jung Oh-Hohenhorst, Jan Hahn, Bente Siebels, Thomas Mair, Susanne Burdak-Rothkamm, Pierre Tennstedt, Ronald Simon, Tobias Lange, Derya Tilki, Thorsten Frenzel, Tobias Maurer, Cordula Petersen, Hartmut Schlüter, Carsten Bokemeyer, Gunhild von Amsberg, Kai Rothkamm, Wael Y. Mansour
Sabrina Köcher, Mohamed E. Elsesy, Ayham Moustafa, Wahid Mohammadi, Adriana Perugachi Heinsohn, Yamini Nagaraj, Su Jung Oh-Hohenhorst, Jan Hahn, Bente Siebels, Thomas Mair, Susanne Burdak-Rothkamm, Pierre Tennstedt, Ronald Simon, Tobias Lange, Derya Tilki, Thorsten Frenzel, Tobias Maurer, Cordula Petersen, Hartmut Schlüter, Carsten Bokemeyer, Gunhild von Amsberg, Kai Rothkamm, Wael Y. Mansour
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Research Article Clinical Research Oncology

Overexpression of the ERG oncogene in prostate cancer identifies candidates for PARP inhibitor–based radiosensitization

Abstract

Radiotherapy (RT) is a central treatment for prostate cancer (PCa), relying on the induction of DNA double-strand breaks (DSBs). Tumor ability to repair these breaks limits RT efficacy, making DSB repair inhibitors potential radiosensitizers. However, many of these inhibitors lack tumor specificity and harm normal cells. Therefore, tumor-specific radiosensitization strategies are critically needed for PCa. Approximately 50% of PCa cases harbor the TMPRSS2-ERG gene fusion, leading to overexpression of the ERG transcription factor (ERG+). In this study, we demonstrate that ERG+ tumors shift DSB repair toward the poly(ADP-ribose) polymerase 1–dependent end-joining (PARP1-EJ) pathway. Proteomic and Western blot analyses revealed elevated PARP1, XRCC1, and LIG3 levels in ERG+ cells. Notably, PARP inhibition with olaparib increased residual γH2AX/53BP1 foci postirradiation in ERG+ cells, indicating enhanced radiosensitization. In tissue slice cultures (TSCs) from 53 tumors of patients with high-risk PCa, olaparib selectively increased γH2AX/53BP1 foci selectively in ERG+ samples. ERG+ patient–derived organoids also showed significantly delayed growth when treated with olaparib plus RT, compared with either treatment alone. Interestingly, ERG-negative cells within ERG+ TSCs were similarly radiosensitized by olaparib, likely through bystander effect, with residual 53BP1 foci levels comparable to those in ERG+ cells. This was confirmed by medium exchange experiments. These findings suggest that ERG expression promotes dependency on the PARP1-EJ pathway, rendering ERG+ PCa more susceptible to PARP inhibition. This supports combining PARP inhibitors with RT for tumor-selective radiosensitization in ERG+ patients.

Authors

Sabrina Köcher, Mohamed E. Elsesy, Ayham Moustafa, Wahid Mohammadi, Adriana Perugachi Heinsohn, Yamini Nagaraj, Su Jung Oh-Hohenhorst, Jan Hahn, Bente Siebels, Thomas Mair, Susanne Burdak-Rothkamm, Pierre Tennstedt, Ronald Simon, Tobias Lange, Derya Tilki, Thorsten Frenzel, Tobias Maurer, Cordula Petersen, Hartmut Schlüter, Carsten Bokemeyer, Gunhild von Amsberg, Kai Rothkamm, Wael Y. Mansour

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Figure 6

Combined treatment with olaparib and IR delays the tumor growth selectively in ERG-positive PCa PDOs.

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Combined treatment with olaparib and IR delays the tumor growth selectiv...
(A) Representative histopathological images of H&E and AMACR staining in organoids derived from the indicated patients with PCa. Inserts show 4× zoomed selected regions. (B) Representative IF image of ERG staining in PDOs from the indicated patients. Scale bar: 20 µm. (C) Representative heatmap for the ERG scores in the indicated PDOs. (D) Western blot showing the expression of PARP1-EJ–related proteins (PARP1, LIGIII, XRCC1) along with ERG in organoids derived from the indicated patients with PCa. GAPDH was used as a loading control. (E) Schematic of the treatment protocol for the PDOs. Organoids were cultured under optimum conditions for 5 days before undergoing 5 cycles of treatment. Each cycle consisted of 1 μM olaparib for 2 hours, followed by 2 Gy with a 24-hour recovery period between cycles. Images were captured at various time points (0, 4, 7, 10, 16, 23, and 30 days) to track changes in the size and number of organoids. Image analysis was conducted using REBEL Microscopy (ECHO). (F) Representative images of organoid cultures from patient #45 (left) and patient #46 (right) showing the effects of the indicated treatments over the specified time intervals. Shown are mean ± SEM of 3 independent experiments for each PDO. (G) Growth curves showing the effects of combined effect of olaparib and irradiation on organoid area (μm2) over time for 2 independent ERG-negative PCa organoid cultures, #45 and #16, as well as 2 independent ERG-positive PCa organoid cultures, C5 and #46. Organoids were treated with vehicle control (CTR), olaparib (Olap), irradiation (IR), or a combination of olaparib and irradiation (Olap+IR). Differences were analyzed using 2-way ANOVA with Tukey’s multiple comparisons (****P < 0.0001). Data are presented as mean ± SEM of 3 independent experiments.