Preparation and evaluation of a single vial AMBA kit for 68Ga labeling with potential for imaging of GRP receptor-positive cancers

[113mIn]In-AMBA: A Novel Diagnostic Agent for SPECT Imaging of GRPR-Expressing Tumors

Purpose

Gastrin-releasing peptide receptor (GRPR), a member of the bombesin G-protein-coupled receptor family, is introduced as the promising target for the diagnosis and therapy of various tumors. This study aimed to develop a novel diagnostic agent of [113mIn]In-AMBA for single photon emission computed tomography (SPECT) imaging of GRPR expressing tumors.

Methods

113mIn was provided from an in-house made 113Sn/113mIn generator in the chloride form. [113mIn]In-AMBA was prepared in the optimal conditions and the stability was checked in PBS buffer and human serum, Then the binding affinity and internalization of the radiolabeled compound were investigated in PC3 cell lines at 120 min. the biodistribution of the radiolabeled peptide was studied in normal rats.

Results

[113mIn]In-AMBA was prepared with radiochemical purity (RCP) > 98% under the optimal labeling conditions. The compound indicated significant stability in PBS buffer and human serum (> 95% at 180 min post preparation). High binding affinity (51% at 60 min) and internalization (64% at 120 min) of the radiolabeled compound towards PC3 cell lines were also observed. The major accumulation of the compound was seen in kidneys, and other GRPR-expressing tissues.

Conclusion

The biodistribution of the labeled compound in normal rats indicated rapid elimination of the complex from the blood, and considerable accumulation in the GRPR-expressing organ of pancreas, in complete agreement with similar labeled compounds. [113mIn]In-AMBA can be a suitable candidate for SPECT imaging of GRPR-expressed tumors.

Cold Kit Labeling: The Future of 68Ga Radiopharmaceuticals?

Over the last couple of decades, gallium-68 (68Ga) has gained a formidable interest for PET molecular imaging of various conditions, from cancer to infection, through cardiac pathologies or neuropathies. It has gained routine use, with successful radiopharmaceuticals such as somatostatin analogs ([68Ga]Ga-DOTATOC and [68Ga]GaDOTATATE) for neuroendocrine tumors, and PSMA ligands for prostate cancer. It represents a major clinical impact, particularly in the context of theranostics, coupled with their 177Lu-labeled counterparts. Beside those, a bunch of new 68Ga-labeled molecules are in the preclinical and clinical pipelines, with some of them showing great promise for patient care. Increasing clinical demand and regulatory issues have led to the development of automated procedures for the production of 68Ga radiopharmaceuticals. However, the widespread use of these radiopharmaceuticals may rely on simple and efficient radiolabeling methods, undemanding in terms of equipment and infrastructure. To make them technically and economically accessible to the medical community and its patients, it appears mandatory to develop a procedure similar to the well-established kit-based 99mTc chemistry. Already available commercial kits for the production of 68Ga radiopharmaceuticals have demonstrated the feasibility of using such an approach, thus paving the way for more kit-based 68Ga radiopharmaceuticals to be developed. This article discusses the development of 68Ga cold kit radiopharmacy, including technical issues, and regulatory aspects.

Recent Breakthrough in 68Ga-Radiopharmaceuticals Cold Kits for Convenient PET Radiopharmacy

⁶⁸Ga-PET has emerged as an important diagnostic tool for precise detection and monitoring of oncological situations. Availability, cost, and radiosynthesis procedure are determining steps for success of a radioisotope/radiopharmaceutical in nuclear medicine. Availability of ⁶⁸Ga from a ⁶⁸Ge/⁶⁸Ga generator containing a long-lived parent radioisotope (⁶⁸Ge: t_1/2 = 271 days) and an inexpensive, simplified production of ⁶⁸Ga-radiopharmaceuticals through kit methodology has allowed smooth accommodation of ⁶⁸Ga-PET in clinics. The uncomplicated formulation of ⁶⁸Ga-radiopharmaceuticals from a lyophilized, cold kit is an impending breakthrough in clinical PET. The huge success of ⁶⁸Ga in neuroendocrine tumor and prostate cancer imaging along with the regulatory approval of respective cold kits has opened a pathway for development of kits for other evolving radiotracers. There is a definite scope for increased participation of commercial manufacturers and distributors of cold kits to spread the potential of ⁶⁸Ga worldwide across all the geographical locations and satellite centers.