Radiolabelling of pharmaceutical dosage forms by neutron activation of samarium-152

Novel Radiolabeled Bisphosphonates for PET Diagnosis and Endoradiotherapy of Bone Metastases

Bone metastases, often a consequence of breast, prostate, and lung carcinomas, are characterized by an increased bone turnover, which can be visualized by positron emission tomography (PET), as well as single-photon emission computed tomography (SPECT). Bisphosphonate complexes of ^99mTc are predominantly used as SPECT tracers. In contrast to SPECT, PET offers a higher spatial resolution and, owing to the ⁶⁸Ge/⁶⁸Ga generator, an analog to the established ^99mTc generator exists. Complexation of Ga(III) requires the use of chelators. Therefore, DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), NOTA (1,4,7-triazacyclododecane-1,4,7-triacetic acid), and their derivatives, are often used. The combination of these macrocyclic chelators and bisphosphonates is currently studied worldwide. The use of DOTA offers the possibility of a therapeutic application by complexing the β-emitter ¹⁷⁷Lu. This overview describes the possibility of diagnosing bone metastases using [⁶⁸Ga]Ga-BPAMD (⁶⁸Ga-labeled (4-{[bis-(phosphonomethyl))carbamoyl]methyl}-7,10-bis(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl)acetic acid) as well as the successful application of [¹⁷⁷Lu]Lu-BPAMD for therapy and the development of new diagnostic and therapeutic tools based on this structure. Improvements concerning both the chelator and the bisphosphonate structure are illustrated providing new ⁶⁸Ga- and ¹⁷⁷Lu-labeled bisphosphonates offering improved pharmacological properties.

Internal radiation dosimetry of orally administered radiotracers for the assessment of gastrointestinal motility

Radionuclide imaging using (111)In, (99m)Tc and (153)Sm is commonly undertaken for the clinical investigation of gastric emptying, intestinal motility and whole gut transit. However the documented evidence concerning internal radiation dosimetry for such studies is not readily available. This communication documents the internal radiation dosimetry for whole gastrointestinal transit studies using (111)In, (99m)Tc and (153)Sm labeled formulations. The findings were compared to the diagnostic reference levels recommended by the United Kingdom Administration of Radioactive Substances Advisory Committee, for gastrointestinal transit studies.

Production and first use of 153SmCl3-ion exchange resin capsule formulation for assessing gastrointestinal motility

We produced an enteric-coated gelatine capsule containing neutron-activated (153)Sm-labelled resin beads for use in gastrointestinal motility studies. In vitro test in simulated gastrointestinal environment and in vivo study on volunteers were performed. Scintigraphic images were acquired from ten volunteers over 24h while blood and urine samples were collected to monitor the presence of (153)Sm. All the capsules remained intact in stomach. This proved to be a safe and practical oral capsule formulation for whole gut transit scintigraphy.

Influence of neutron activation factors on the physico-chemical properties of suppositories and their excipients

The effect of the neutron activation factors, i.e., admixture of samarium oxide (Sm2O3) and irradiation time, on the physico-chemical properties of the raw materials and the in vitro dissolution and disintegration of hydrophilic and lipophilic suppositories was investigated. It was possible to expose the pure bases and the model drugs (5-aminosalicylic acid [5-ASA] and ropivacaine hydrochloride) to 1 min of neutron irradiation in a flux of 1.1.1013 n cm-2s-1. The dissolution and disintegration of the corresponding suppositories showed that the physico-chemical properties and the fraction of incorporated drug together with the lipophilic/hydrophilic nature of the base were important factors. Sm2O3 increased the disintegration time of hydrophilic suppositories containing 5-ASA, while the dissolution of both drugs from these formulations remained unchanged. Sm2O3 did not alter the disintegration time of the lipophilic formulations, but it reduced the dissolution of both drugs from these suppositories. Irradiation induced different behaviour in the different bases.

Effects of thermal neutron irradiation on some potential excipients for colonic delivery systems

Different excipients, which are currently being studied for colon delivery systems, were examined with respect to their stability toward neutron irradiation as a potential method of radiolabeling the formulations for gamma-scintigraphic studies. Three different pectin and four different hydroxypropyl methylcellulose (HPMC) types, in addition to two types of polymethacrylate films, were exposed to 1, 2, and 3 min of thermal neutron irradiation in a flux of 1.1 x 10(13) n cm-2 s-1. The physicochemical characteristics of pectins and HPMCs and the mechanical properties of the polymethacrylate films were examined after the radioactivity of the samples had declined to background levels. Methods included ultraviolet (UV) and Fourier transform infrared (FTIR) spectroscopy, pH measurements, loss on drying, thermogravimetric analysis (TGA), viscosimetry, gas chromatographic (GC) analysis of pectin monosaccharides, and tensile strength testing of the films. The results suggest that pectins and HPMCs undergo degradation, as expressed by a significant reduction in the dynamic and intrinsic viscosities of the samples. Generally, HPMCs were more sensitive than pectins to neutron irradiation. However, calcium pectinate proved to be the most sensitive among all the investigated polymers. Both polymethacrylate films (Eudragit L and S) resisted loss of mechanical properties following 1 and 2 min of neutron irradiation, whereas irradiation for 3 min implied significant changes in the appearance and the mechanical properties of Eudragit L films. As a conclusion, neutron irradiation results in dose-dependent degradation of the investigated polysaccharides and polymethacrylates. The consequences on the in vitro behavior of a formulation containing such polymers are discussed.