Novel multifunctional 18F-labelled PET tracer with prostate-specific membrane antigen-targeting and hypoxia-sensitive moieties

Abstract

Prostate cancer is one of the most frequently found cancers in men worldwide. Prostate-specific membrane antigen (PSMA) is typically highly expressed in prostate cancer, and the Glu-Urea-Lys (GUL) structure has recently received considerable attention as a key unit of PSMA-targeting agents. Additionally, one of the common characteristics of many solid tumors, such as prostate cancer, is hypoxia. In this study, novel multifunctional PSMA inhibitors containing a PSMA-targeting moiety either with or without a hypoxia-sensitive moiety (¹⁸F-PEG₃-ADIBOT-2NI-GUL and ¹⁸F-PEG₃-ADIBOT-GUL, respectively; ADIBOT: azadibenzocyclooctatriazole, 2NI: 2-nitroimidazole) were designed and synthesized, and their feasibility as PET tracers for prostate cancer imaging studies was examined. The compounds labelled with ¹⁸F via the copper-free click reaction were stable in human serum and showed nanomolar binding affinities in in vitro PSMA binding assays. Micro-PET and biodistribution studies indicate that both ¹⁸F-labelled inhibitors successfully accumulated in prostate cancer regions, and ¹⁸F-PEG₃-ADIBOT-2NI-GUL showed a 2-fold higher tumor-to-total non-target organ ratio than that of ¹⁸F-PEG₃-ADIBOT-GUL, suggesting that the synergistic effects of the PSMA-targeting GUL moiety and the hypoxia-sensitive 2-nitroimidazole moiety can increase tumor uptake of the novel PET tracers in prostate cancer. These findings suggest that this novel multifunctional PET tracer with an ¹⁸F-labelled PSMA inhibitor and a 2-nitroimidazole moiety is a potent candidate to provide better diagnosis of prostate cancer via PET imaging studies.

Keywords: Cupper-free click reaction; Fluorine-18; Positron-emission tomography; Prostate cancer; Prostate-specific membrane antigen.