Abstract 924: The androgen receptor antagonist darolutamide shows strong antitumor efficacy in patient- and cell line-derived xenograft prostate cancer models

Abstract

Darolutamide is a structurally unique androgen receptor (AR) antagonist which has recently completed a pivotal clinical phase 3 trial. Here we explored the efficacy of darolutamide in different prostate cancer models and in combination with the ATR inhibitor BAY 1895344. Darolutamide was tested in the patient-derived xenografts LuCaP35 and LuCaP96. The studies were performed with SCID male mice implanted subcutaneously. Oral, twice daily treatment with 100 mg/kg darolutamide started at a mean tumor size of about 150 mm 3 ; the study was stopped 3.5 weeks later. In addition the cell line-derived xenograft LAPC-4 was tested after subcutaneous inoculation of SCID male mice. Oral, daily treatment with 100 mg/kg darolutamide started at a mean tumor size of about 50 mm 2 . The ATR inhibitor BAY 1895344 was applied at 20 mg/kg, twice daily for 3 days followed by 4 days without treatment. X-ray radiation was performed at 5 Gy, once weekly on days 26 and 33 after start of compound treatment. Efficacy was evaluated by calculating the ΔT/ΔC values. Gene expression analysis was performed on RNA extracted from prostate cancer cells treated with darolutamide and/or BAY 1895344, and analyzed using RT 2 Profiler PCR arrays (Qiagen). RNA-seq and AR ChIP-seq (06-680, Millipore) datasets of darolutamide-treated cell lines were used for genome-wide studies. γH2AX (ab2893, abcam) levels were evaluated by Western blot analysis. Darolutamide showed strong anti-tumor activity in the LuCaP96 model (6% ΔT/ΔC). Significant anti-tumor efficacy was also observed in the LAPC-4 model following treatment with darolutamide (36% ΔT/ΔC) or with radiation (19% ΔT/ΔC). Stronger efficacy was observed when combining darolutamide with the ATR inhibitor BAY 1895344 (17% ΔT/ΔC) or with BAY 1895344 plus radiation (1% ΔT/ΔC). RNAseq analysis of LAPC-4 and VCaP cells showed that expression of DNA repair genes was regulated by androgen and efficiently blocked by darolutamide. In line with this, we observed androgen-dependent AR binding close to DNA repair genes, which supports a regulatory role of the AR signalling pathway in the regulation of these genes. We also found that γH2AX levels were increased after treatment with BAY 1895344 alone or in combination with darolutamide. Expression of H2AX was also increased following combination treatment. Notably, darolutamide treatment alone did not have comparable effects on H2AX but strongly reduced androgen-driven expression of several DNA damage response genes. In conclusion, darolutamide demonstrated strong in vivo efficacy in xenograft models as single agent, and enhanced activity in combination with radiation and an ATR inhibitor, with the latter involving down-regulation of DNA repair genes. Together these results suggest broad anti-tumor activity of darolutamide in prostate cancer as a single agent or in combination with other anti-tumor modalities. Citation Format: Pascale Lejeune, Antje Wengner, Simon J. Baumgart, Ekaterina Nevedomskaya, Eva Corey, Dominik Mumberg, Bernard Haendler. The androgen receptor antagonist darolutamide shows strong antitumor efficacy in patient- and cell line-derived xenograft prostate cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 924.