Individual radiosensitivity reflected by γ-H2AX and 53BP1 foci predicts outcome in PSMA-targeted radioligand therapy

Abstract Purpose γ-H2AX and 53BP1 are fundamental for cellular DNA damage response (DDR) after radiation exposure and are linked to cell repair, arrest, or apoptosis. We aimed to evaluate whether DDR-markers in peripheral blood lymphocytes (PBLs) may have predictive potential for outcome in metastatic castration-resistant prostate cancer (mCRPC) patients receiving [ 177 Lu]Lu-prostate-specific membrane antigen (PSMA) radioligand therapy (RLT). Methods We prospectively enrolled 20 men with advanced mCRPC scheduled for PSMA-targeted RLT. Prior to the first cycle of [ 177 Lu]Lu-PSMA RLT, all patients underwent [ 18 F]F-PSMA-1007 positron emission tomography (PET)/computed tomography (CT) for assessment of tumor PSMA expression (assessing maximum standardized uptake value (SUV max ) of all tumor lesions). Blood samples were collected prior to, + 1 h after, and + 24 h after administration of [ 177 Lu]Lu-PSMA, and DDR-markers γ-H2AX and 53BP1 were determined in PBLs through immunocytofluorescence. We then tested the predictive performance of DDR-markers relative to clinical and PET-based parameters for progressive disease (PSA-PD) after 2 cycles. In addition, the predictive value for progression-free survival (PSA-PFS, provided as median and 95% confidence interval [CI]) was explored. Results Low baseline 53BP1 and γ-H2AX foci ( P = 0.17) tended to predict early PSA-PD, whereas low SUV max was significantly associated with higher risk for PSA-PD ( P = 0.04). In Kaplan–Meier analysis, there was a trend towards prolonged PSA-PFS in patients with higher baseline 53BP1 of 6 months (mo; 95%CI, 4–9 mo) compared to 3 mo in patients with low 53BP1 (95% CI, 2–3 mo; P = 0.12). Comparable results were recorded for higher γ-H2AX expression (6 mo [95% CI, 3–9 mo] relative to 3 mo [95% CI, 2–4 mo] in patients with low γ-H2AX; P = 0.12). SUV max , however, did not demonstrate predictive value ( P = 0.29). Consistently, in univariate Cox-regression analysis, baseline 53BP1 foci demonstrated borderline significance for predicting PSA-PFS under [ 177 Lu]Lu-PSMA RLT ( P = 0.05). Conclusion In this prospective study investigating mCRPC patients undergoing [ 177 Lu]Lu-PSMA RLT, low baseline DDR-markers in PBLs tended to predict poor outcome. Although the study group was small and results need further confirmation, these preliminary findings lay the foundation for exploring additive radiosensitizing or treatment intensification in future studies with high-risk individuals scheduled for RLT.