Pre- and Intraoperative Visualization of GRPR-Expressing Solid Tumors: Preclinical Profiling of Novel Dual-Modality Probes for Nuclear and Fluorescence Imaging

SIMPLE SUMMARY: Image-guided surgery is a technique that can help the surgeon detect and remove tumors more precisely. Using a tumor-targeting agent with both a radioactive and a fluorescent label allows us to combine the benefits of two imaging modalities; preoperative nuclear imaging for tumor localization and intraoperative fluorescence imaging for precise and real-time visualization of tumor tissue during surgery. The gastrin-releasing peptide receptor (GRPR) is a promising target for this application because of its overexpression in several solid tumors, e.g., prostate and breast cancers. In this study, a full preclinical characterization of four previously developed GRPR-targeting dual-modality probes is presented, including the characterization of the biodistribution profile, selection of the optimal probe and a proof-of-concept for image-guided surgery. This project is the first comprehensive investigation of the effect of linker modifications and administered dose on the in vivo behavior of GRPR-targeting dual-modality probes, and provides a basis for clinical translation. ABSTRACT: Image-guided surgery using a gastrin-releasing peptide receptor (GRPR)-targeting dual-modality probe could improve the accuracy of the resection of various solid tumors. The aim of this study was to further characterize our four previously developed GRPR-targeting dual-modality probes that vary in linker structures and were labeled with indium-111 and sulfo-cyanine 5. Cell uptake studies with GRPR-positive PC-3 cells and GRPR-negative NCI-H69 cells confirmed receptor specificity. Imaging and biodistribution studies at 4 and 24 h with 20 MBq/1 nmol [(111)In]In-12-15 were performed in nude mice bearing a PC-3 and NCI-H69 xenograft, and showed that the probe with only a pADA linker in the backbone had the highest tumor-to-organ ratios (T/O) at 24 h after injection (T/O > 5 for, e.g., prostate, muscle and blood). For this probe, a dose optimization study with three doses (0.75, 1.25 and 1.75 nmol; 20 MBq) revealed that the maximum image contrast was achieved with the lowest dose. Subsequently, the probe was successfully used for tumor excision in a simulated image-guided surgery setting. Moreover, it demonstrated binding to tissue sections of human prostate, breast and gastro-intestinal stromal tumors. In summary, our findings demonstrate that the developed dual-modality probe has the potential to aid in the complete surgical removal of GRPR-positive tumors.