A novel androgen-independent radiotracer with dual targeting of NTSR1 and PSMA for PET/CT imaging of prostate cancer

A substantial proportion of patients with prostate cancer (PCa) develop treatment resistance or mortality after androgen deprivation therapy (ADT). Current methods for identifying and locating recurrent lesions using prostate-specific membrane antigen (PSMA)-based positron emission tomography (PET) imaging, which relies on androgen levels, often result in diagnostic delays. Therefore, the development of an androgen-independent radiotracer is critical for the early identification of recurrent lesions. The neurotensin receptor 1 (NTSR1) is highly expressed in androgen-independent PCa lesions. Here, we synthesized a bispecific ligand targeting PSMA and NTSR1 by solid-phase peptide synthesis and formulated a ⁶⁸Ga-labelled bispecific radiotracer, ([⁶⁸Ga]Ga-NT-PSMA). This radiotracer exhibited a high radiochemical yield (71.27% ± 1.58%) and demonstrated an affinity for NTSR1 (39.32 ± 2.98 nM) and PSMA (63.47 ± 5.14 nM) in vitro. Small animal PET imaging showed comparable uptake of [⁶⁸Ga]Ga-NT-PSMA and the monomeric radiotracer [⁶⁸Ga]Ga-DOTA-NT20.3 in mice bearing androgen-independent PC3 (3.64 ± 0.49 %ID/g vs. 5.60 ± 1.42 %ID/g, nonsignificant [ns]) and DU145 tumors (2.49 ± 0.20 %ID/g vs. 2.34 ± 0.18 %ID/g, ns) at 90 min post-injection. In androgen-dependent 22Rv1 xenografts, [⁶⁸Ga]Ga-NT-PSMA uptake was lower (1.94 ± 0.29 %ID/g) than [⁶⁸Ga]Ga-PSMA-11 (3.94 ± 0.26 %ID/g, P < 0.001). Nevertheless, [⁶⁸Ga]Ga-NT-PSMA effectively imaged all three xenograft types with high contrast, an achievement not possible with monomeric radiotracers alone. These results indicate that imaging with [⁶⁸Ga]Ga-NT-PSMA is independent of the androgen dependence of the model, highlighting its potential as a promising nuclear medicine diagnostic tool for the early identification and localization of castration-resistant PCa lesions.