An imaging agent to detect androgen receptor and its active splice variants in prostate cancer
Yusuke Imamura, Amy H. Tien, Jinhe Pan, Jacky K. Leung, Carmen A. Banuelos, Kunzhong Jian, Jun Wang, Nasrin R. Mawji, Javier Garcia Fernandez, Kuo-Shyan Lin, Raymond J. Andersen, Marianne D. Sadar
Yusuke Imamura, Amy H. Tien, Jinhe Pan, Jacky K. Leung, Carmen A. Banuelos, Kunzhong Jian, Jun Wang, Nasrin R. Mawji, Javier Garcia Fernandez, Kuo-Shyan Lin, Raymond J. Andersen, Marianne D. Sadar
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Resource and Technical Advance Oncology

An imaging agent to detect androgen receptor and its active splice variants in prostate cancer

Abstract

Constitutively active splice variants of androgen receptor (AR-Vs) lacking ligand-binding domain (LBD) are a mechanism of resistance to androgen receptor LBD–targeted (AR LBD–targeted) therapies for metastatic castration-resistant prostate cancer (CRPC). There is a strong unmet clinical need to identify prostate cancer patients with AR-V–positive lesions to determine whether they will benefit from further AR LBD–targeting therapies or should receive taxanes or investigational drugs like EPI-506 or galeterone. Both EPI-506 (NCT02606123) and galeterone (NCT02438007) are in clinical trials and are proposed to have efficacy against lesions that are positive for AR-Vs. AR activation function-1 (AF-1) is common to the N-terminal domains of full-length AR and AR-Vs. Here, we provide proof of concept for developing imaging compounds that directly bind AR AF-1 to detect both AR-Vs and full-length AR. 123I-EPI-002 had specific binding to AR AF-1, which enabled direct visualization of CRPC xenografts that express full-length AR and AR-Vs. Our findings highlight the potential of 123I-EPI-002 as an imaging agent for the detection of full-length AR and AR-Vs in CRPC.

Authors

Yusuke Imamura, Amy H. Tien, Jinhe Pan, Jacky K. Leung, Carmen A. Banuelos, Kunzhong Jian, Jun Wang, Nasrin R. Mawji, Javier Garcia Fernandez, Kuo-Shyan Lin, Raymond J. Andersen, Marianne D. Sadar

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Figure 4

Synthesis of 123I-EPI-002 and its binding to AR AF-1.

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Synthesis of 123I-EPI-002 and its binding to AR AF-1. (A) Synthetic rout...
(A) Synthetic route to [123I]15-iodoEPI-002 starting from (R)-tosylglycerolacetonide[1] and bisphenol A[1] and using Na123I as a source of radiolabeled iodine. (B) Recombinant full-length AR protein was incubated with 123I-EPI-002 for 16 hours at room temperature. Binding of 123I-EPI-002 to AR was detected by SDS-PAGE followed by phosphorimaging. Coomassie blue staining was used to provide an indication of equal loading. (C) Recombinant AF-1 protein was incubated with vehicle (DMSO) or EPI-002 (60 μM) for 6 hours at room temperature prior to addition of 123I-EPI-002 (200 μCi) and then incubated for 16 hours more prior to SDS-PAGE and phosphorimaging. Less binding of 123I-EPI-002 was observed when AF-1 was preincubated with excess cold EPI-002. Coomassie blue staining was used to provide an indication of equal loading (refer to full and uncut gel images in Supplemental Materials). (D) Binding of 123I-EPI-002 to endogenous AR in LNCaP95 cells that were incubated with or without 25 μM EPI-002 overnight at 37°C prior to harvesting cells. Whole cell lysates were used for SDS-PAGE to reveal 123I-EPI-002 covalently bound to full-length AR in the LNCaP95 cells, as detected by phosphorimage. Western blot analysis detection of bands corresponding to AR for radiolabeled phosphorimaged bands. n ≥ 3 for B, C, and D binding experiments.