Production of scandium radionuclides for theranostic applications: towards standardization of quality requirements

In the frame of "precision medicine", the scandium radionuclides have recently received considerable interest, providing personalised adjustment of radiation characteristics to optimize the efficiency of medical care or therapeutic benefit for particular groups of patients. Radionuclides of scandium, namely scandium-43 and scandium-44 (43/44Sc) as positron emitters and scandium-47 (47Sc), beta-radiation emitter, seem to fit ideally into the concept of theranostic pair. This paper aims to review the work on scandium isotopes production, coordination chemistry, radiolabeling, preclinical studies and the very first clinical studies. Finally, standardized procedures for scandium-based radiopharmaceuticals have been proposed as a basis to pave the way for elaboration of the Ph.Eur. monographs for perspective scandium radionuclides.

Synthesis, radiolabeling, and pre-clinical evaluation of [44Sc]Sc-AAZTA conjugate PSMA inhibitor, a new tracer for high-efficiency imaging of prostate cancer

PURPOSE

The aim of this work was to demonstrate the suitability of AAZTA conjugated to PSMA inhibitor (B28110) labeled with scandium-44 as a new PET tracer for diagnostic imaging of prostate cancer.

BACKGROUND

Nowadays, scandium-44 has received significant attention as a potential radionuclide with favorable characteristics for PET applications. A polyaminopolycarboxylate heptadentate ligand based on a 1,4-diazepine scaffold (AAZTA) has been thoroughly studied as chelator for Gd³⁺ ions for MRI applications. The excellent results of the equilibrium, kinetic, and labeling studies led to a preliminary assessment of the in vitro and in vivo behavior of [⁴⁴Sc][Sc-(AAZTA)]^- and two derivatives, i.e., [⁴⁴Sc][Sc (CNAAZTA-BSA)] and [⁴⁴Sc][Sc (CNAAZTA-cRGDfK)].

RESULTS

B28110 was synthesized by hybrid approach, combining solid-phase peptide synthesis (SPPS) and solution chemistry to obtain high purity (97%) product with an overall yield of 9%. Subsequently, the radioactive labeling was performed with scandium-44 produced from natural calcium target in cyclotron, in good radiochemical yields (RCY) under mild condition (pH 4, 298 K). Stability study in human plasma showed good RCP% of [⁴⁴Sc]Sc-B28110 up to 24 h (94.32%). In vivo PET/MRI imaging on LNCaP tumor-bearing mice showed high tracer accumulation in the tumor regions as early as 20 min post-injection. Ex vivo biodistribution studies confirmed that the accumulation of ⁴⁴Sc-PSMA-617 was two-fold lower than that of the radiolabeled B28110 probes.

CONCLUSIONS

This work demonstrated the suitability of B28110 for the complexation with scandium-44 at room temperature and the high performance of the resulting new tracer based on AAZTA chelator for the diagnosis of prostate cancer using PET.

4He+ ion beam irradiation induced modification of poly(dimethylsiloxane). Characterization by infrared spectroscopy and ion beam analytical techniques

In this study we investigated the chemical and surface wettability changes of poly(dimethylsiloxane) (PDMS) induced by a 2.0 MeV He(+) beam irradiation. The chemical changes created in PDMS were characterized by universal attenuated total reflectance infrared (UATR-FTIR) spectroscopy, while the changes of the wettability were determined by contact angle measurements. In a separate analysis, hydrogen depletion was also investigated with a 1.6 MeV He(+) beam by applying the elastic recoil detection analysis (ERDA) and Rutherford backscattering spectrometry techniques simultaneously. The ERDA results showed that the hydrogen content of PDMS decreased irreversibly, which means that volatile products were formed under radiolysis, such as hydrogen or methane. The results were completed with UATR-FTIR measurements. We propose a complete reaction mechanism for the processes taking place in PDMS. These ion beam induced processes, such as chain scissions, cross-linking, and depletion of small molecular weight fragments, lead to the formation of a silica-like final product (SiO(x)). The significant chemical changes at the surface influence the wettability of PDMS, making it considerably more hydrophilic. The penetration depth of the 2.0 MeV He(+) ions is significantly higher compared to that of other surface modification techniques, which makes the modified layer thick and homogeneous; on the other hand, it is easily controllable by the energy of the incident ions.