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 3

I-EPI-002 inhibits full-length AR and constitutively active AR-Vs.

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I-EPI-002 inhibits full-length AR and constitutively active AR-Vs. (A) P...
(A) Probasin luciferase activity in LNCaP cells with endogenous full-length AR (left), with both full-length AR and AR-V567es (middle), or with both full-length AR and V7 (right). Cells were treated with 2 μM I-EPI-002, 25 μM EPI-002, or 5 μM enzalutamide for 1 hour prior to treatment with or without 1 nM R1881 for 24 hours. Data represent mean ± SD from 4 independent experiments, each performed in triplicate. (B) A representative blot showing protein levels of full-length AR, V567es, and V7 from samples in A detected using AR-N20 antibody. (C) LNCaP95 cells treated with enzalutamide (5 μM), EPI-002 (25 μM), or I-EPI-002 (2 μM) for 2 days. n = 4. Data represent mean ± SEM. Proliferation was assessed by BrdU incorporation. (D) LNCaP95 cells treated with different concentrations of I-EPI-002 for 2 days. n = 4. Data represent mean ± SEM. (E) Inhibition of DNA synthesis in LNCaP95 cells by I-EPI-002 (5 μM), EPI-002 (25 μM), or enzalutamide (5 μM) treatment for 48 hours. Bivariate plots show cell cycle distribution of a representative experiment. The stacked graph (below) represents the average results from 3 independent experiments. The percentage of cells in each phase of cell cycle was calculated. (F) Effects of enzalutamide, EPI-002, and I-EPI-002 on cell cycle–regulated proteins in LNCaP95 cells are shown by Western blot analyses. LNCaP95 cells were serum starved for 24 hours and then treated with DMSO, enzalutamide (5 μM), EPI-002 (25 μM), or I-EPI-002 (5 μM) for 48 hours (refer to full and uncut gel images in Supplemental Materials). I-EPI, I-EPI-002; EPI, EPI-002; ENZ, enzalutamide. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. One-way ANOVA Dunnett’s multiple comparison test was utilized.