Diversification of 99Mo/99mTc separation: non–fission reactor production of 99Mo as a strategy for enhancing 99mTc availability

Production scheme for diagnostic-therapeutic radioisotopes by accelerator neutrons

Interest has been growing in the development of medical radioisotopes used for noninvasive nuclear medicine imaging of disease and cancer therapy. Especially the development of an alternative production scheme of ⁹⁹Mo, the mother radioisotope of ^99mTc used for imaging, is required, because the current supply chain of the reactor product ⁹⁹Mo is fragile worldwide. We have proposed a new production scheme of ⁹⁹Mo as well as therapeutic radioisotopes, such as ⁶⁴Cu and ⁶⁷Cu, using accelerator neutrons provided by the ^natC(d,n) reaction. Based on this scheme we have obtained high-quality ^99mTc, ⁶⁴Cu, and ⁶⁷Cu suitable for clinical use by developing both production and separation methods of the radioisotopes. We proposed a new facility to constantly and reliably produce a wide variety of high-quality, carrier-free radioisotopes, including ⁹⁹Mo, with accelerator neutrons. We report on the development of the proposed scheme and future prospects of the facility toward the domestic production of medical radioisotopes.

Altered [99mTc]Tc-MDP biodistribution from neutron activation sourced 99Mo

Given potential worldwide shortages of fission sourced ⁹⁹Mo/^99mTc medical isotopes there is increasing interest in alternate production strategies. A neutron activated ⁹⁹Mo source was utilized in a single center phase III open label study comparing ^99mTc, as ^99mTc Methylene Diphosphonate ([^99mTc]Tc-MDP), obtained from solvent generator separation of neutron activation produced ⁹⁹Mo, versus nuclear reactor produced ⁹⁹Mo (e.g., fission sourced) in oncology patients for which an [^99mTc]Tc-MDP bone scan would normally have been indicated. Despite the investigational [^99mTc]Tc-MDP passing all standard, and above standard of care, quality assurance tests, which would normally be sufficient to allow human administration, there was altered biodistribution which could lead to erroneous clinical interpretation. The cause of the altered biodistribution remains unknown and requires further research.

New Gastrin Releasing Peptide Receptor-Directed [99mTc]Demobesin 1 Mimics: Synthesis and Comparative Evaluation

We have previously reported on the gastrin releasing peptide receptor (GRPR) antagonist [^99mTc]1, ([^99mTc]demobesin 1, ^99mTc-[N₄'-diglycolate-dPhe⁶,Leu-NHEt¹³]BBN(6-13)). [^99mTc]1 has shown superior biological profile compared to analogous agonist-based ^99mTc-radioligands. We herein present a small library of [^99mTc]1 mimics generated after structural modifications in (a) the linker ([^99mTc]2, [^99mTc]3, [^99mTc]4), (b) the peptide chain ([^99mTc]5, [^99mTc]6), and (c) the C-terminus ([^99mTc]7 or [^99mTc]8). The effects of above modifications on the biological properties of analogs were studied in PC-3 cells and tumor-bearing SCID mice. All analogs showed subnanomolar affinity for the human GRPR, while most receptor-affine 4 and 8 behaved as potent GRPR antagonists in a functional internalization assay. In mice bearing PC-3 tumors, [^99mTc]1-[^99mTc]6 exhibited GRPR-specific tumor uptake, rapidly clearing from normal tissues. [^99mTc]4 displayed the highest tumor uptake (28.8 ± 4.1%ID/g at 1 h pi), which remained high even after 24 h pi (16.3 ± 1.8%ID/g), well surpassing that of [^99mTc]1 (5.4 ± 0.7%ID/g at 24 h pi).