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 2

I-EPI-002 has better potency than EPI-002 for AR and maintains specificity.

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I-EPI-002 has better potency than EPI-002 for AR and maintains specifici...
(A) Dose-dependent inhibition of androgen induced transcriptional activity of endogenous full-length AR in LNCaP cells by I-EPI-002. n ≥ 3. Representative data are shown. (B) Effects of I-EPI-002 on androgen-dependent proliferation of LNCaP cells treated with R1881 compared with PC3 and DU145 cell viability. n ≥ 3. Data represent mean ± SD. (C) Effect of I-EPI-002 (2 μM) vs. EPI-002 (25 μM) on AR transcriptional activity in LNCaP cells that were transiently transfected with PSA(6.1 kb) luciferase reporter and induced with R1881 (1 nM). n = 5. Data represent mean ± SEM. (D) Effect of I-EPI-002 (2 μM) vs. EPI-002 (25 μM) on 4-pregnene-3,20-dione (Progesterone, 10 nM) induced PR transcriptional activity in LNCaP cells that were transiently transfected with PRE luciferase reporter and expression vector for PRβ. n = 5. Data represent mean ± SEM. (E) A representative competition binding curve showing displacement of 1 nM fluorescently labeled ligand from recombinant AR LBD (25 nM) by enzalutamide and R1881 but not with I-EPI-002 or EPI-002. The experiment was repeated 3 times. (F) Androgen-induced AR-transcriptional activity measured in LNCaP cells transfected with PSA(6.1 kb) luciferase reporter and treated with vehicle (DMSO), enzalutamide (ENZ, 5 μM), I-EPI-002 (5 μM), or EPI-002 (25 μM) and increasing concentrations of R1881. n = 4. Values shown are the mean ± SD. I-EPI, I-EPI-002; EPI, EPI-002; ENZ, enzalutamide. (A–F) Each independent experiment was performed in triplicate. **P < 0.01. One-way ANOVA Dunnett’s multiple comparison test was utilized.