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The use of nanobodies (Nbs) as vehicles in targeted alpha therapy (TAT) has gained great interest because of their excellent properties. They combine high in vivo affinity and specificity of binding with fast kinetics. This research investigates a novel targeted therapy that combines the α-particle emitter astatine-211 (211At) and the anti-HER2 Nb 2Rs15d to selectively target HER2+ cancer cells. Two distinctive radiochemical methodologies are investigated using three different coupling reagents. The first method uses the coupling reagents, N-succinimidyl 4-(1,2-bis-tert-butoxycarbonyl)guanidinomethyl-3-(trimethylstannyl)benzoate (Boc2-SGMTB) and N-succinimidyl-3-(trimethylstannyl)benzoate (m-MeATE), which are both directed to amino groups on the Nb, resulting in random conjugation. The second method aims at obtaining a homogeneous tracer population, via a site-specific conjugation of the N-[2-(maleimido)ethyl]-3-(trimethylstannyl)benzamide (MSB) reagent onto the carboxyl-terminal cysteine of the Nb. The resulting radioconjugates are evaluated in vitro and in vivo. 2Rs15d is labeled with 211At using Boc2-SGMTB, m-MeATE, and MSB. After astatination and purification, the binding specificity of the radioconjugates is validated on HER2+ cells, followed by an in vivo biodistribution assessment in SKOV-3 xenografted mice. α-camera imaging is performed to determine uptake and activity distribution in kidneys/tumors. 2Rs15d astatination resulted in a high radiochemical purity >95% for all radioconjugates. The biodistribution studies of all radioconjugates revealed comparable tumor uptake (higher than 8% ID/g at 1 h). [211At]SAGMB-2Rs15d showed minor uptake in normal tissues. Only in the kidneys, a higher uptake was measured after 1 h, but decreased rapidly after 3 h. Astatinated Nbs consisting of m-MeATE or MSB reagents revealed elevated uptake in lungs and stomach, indicating the presence of released 211At. α-Camera imaging of tumors revealed a homogeneous activity distribution. The radioactivity in the kidneys was initially concentrated in the renal cortex, while after 3 h most radioactivity was measured in the medulla, confirming the fast washout into urine. Changing the reagents for Nb astatination resulted in different in vivo biodistribution profiles, while keeping the targeting moiety identical. Boc2-SGMTB is the preferred reagent for Nb astatination because of its high tumor uptake, its low background signals, and its fast renal excretion. We envision [211At]SAGMB-2Rs15d to be a promising therapeutic agent for TAT and aim toward efficacy evaluation.

Several solvents for Grouped ActiNide EXtraction (GANEX) processes have been investigated at Chalmers University of Technology in recent years. Four different GANEX solvents; cyclo-GANEX (CyMe4--BTBP, 30 vol.% tri-butyl phosphate (TBP) and cyclohexanone), DEHBA-GANEX (CyMe4-BTBP, 20 vol.% N,N-di-2(ethylhexyl) butyramide (DEHBA) and cyclohexanone), hexanol-GANEX (CyMe4-BTBP, 30 vol.% TBP and hexanol) and FS-13-GANEX (CyMe4-BTBP, 30 vol.% TBP and phenyl trifluoromethyl sulfone (FS-13)) have been studied and the results are discussed and compared in this work. The cyclohexanone based solvents show fast and high extraction of the actinides but a somewhat poor diluent stability in contact with the acidic aqueous phase. FS-13-GANEX display high separation factors between the actinides and lanthanides and a good radiolytic and hydrolytic stability. However, the distribution ratios of the actinides are lower, compared to the cyclohexanone based solvents. The hexanol-GANEX is a cheap solvent system using a rather stable diluent but the actinide extraction is, however, comparatively low.

AbstractSpent nuclear fuel contains many highly radioactive species; hence solvents used in reprocessing will be subjected to radiolysis. In this study, solvents containing one of the BTBP molecules intended for the separation of trivalent actinides and lanthanides, the so called C5-BTBP, have been subjected to radiolysis and hydrolysis. We present here that this compound shows a dramatic decrease in both distribution ratios and separation factor when irradiated with higher doses up to 50 kGy; particularly in the presence of an aqueous phase. Furthermore, fast hydrolytic degradation is observed, which significantly contributes to the overall degree of decomposition. This is supported by speciation studies performed by HPLC and LC-MS methods. Proposed structures of the highest-yield degradation products are presented and they seem to confirm previously drawn structures for these products. From these studies it can be concluded that the presence of nitric acid or nitrate during irradiation leads to higher content of species containing keto groups.

Antibodies labeled with alpha-emitter astatine-211 have previously shown effective in intraperitoneal (i.p.) treatments of ovarian cancer. In the present work we explore the use of investigational farletuzumab, aimed at the folate receptor alpha. The aim was to evaluate the biodistribution and therapeutic effect of 211At-farletuzumab in in-vitro and in-vivo experiments and, using models for radiation dosimetry, to translate the findings to expected clinical result. The activity concentration used for therapy in mice (170 kBq/mL) was chosen to be in agreement with an activity concentration that is anticipated to be clinically relevant in patients (200 MBq/L).