An imaging agent to detect androgen receptor and its active splice variants in prostate cancer
Yusuke Imamura, … , Raymond J. Andersen, Marianne D. Sadar
Yusuke Imamura, … , Raymond J. Andersen, Marianne D. Sadar
Published July 21, 2016
Citation Information: JCI Insight. 2016;1(11):e87850. https://doi.org/10.1172/jci.insight.87850.
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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.