High-affinity probes for androgen receptor imaging: from cells to whole-body fluorescent applications

The hallmark of castrate-resistant prostate cancer (CRPC) is its continued dependence on androgen receptor (AR) signaling for survival. CRPC is challenging to diagnose, as it often manifests with few to no symptoms. Imaging agents that allow visualization of changes in AR signaling remain a high-priority goal. Here, we report on the development of visible- and near-infrared AR inhibitors for fluorescence imaging (ARi-FL). On the basis of an aryloxycyclohexane AR antagonist, we incorporated a neolinker into the nonsteroidal scaffold, which we could subsequently conjugate to fluorophores via an amide-coupling reaction. Cell assays confirmed that ARi-FL had a high binding affinity to AR (~13 nM). The nondimeric form of AR in individual cells could be visualized in human AR-expressing cells, showing a correlation with AR protein levels, which were blockable (10X). In vivo and ex vivo properties were evaluated in animal models of AR-expressing human prostate cancer using noninvasive imaging systems in the near infrared window. The ARi-FLs and the accompanying experiments demonstrate effective, selective binding to AR with practical synthetic yields and notable metabolic stability, addressing a long-standing challenge in the field of AR-targeted diagnostics. ARi-FL permitted semi-quantitative labeling and noninvasive measurements of AR levels. ARiFL and analogs may prove to be valuable tools for studying and monitoring the mechanisms of AR signaling, progression, and treatment in both preclinical and clinical settings.