Nanobodies show favourable pharmacokinetic characteristics for tumor targeting, including high tumor-to-background-ratios. Labelled with a therapeutic radionuclide, nanobodies could be used as an adjuvant treatment option for HER2-overexpressing minimal residual disease. The therapeutic radionuclide Lutetium-177 is linked to the nanobody using a bifunctional chelator. The choice of the bifunctional chelator could affect the in vivo behaviour of the radiolabeled nanobody. Consequently, we compared four different bifunctional chelators - p-SCN-Bn-DOTA, DOTA-NHS-ester, CHX-A"-DTPA or 1B4M-DTPA - in order to select the optimal chemical link between Lutetium-177 and a HER2 targeting nanobody. MS results revealed different degrees of chelator-conjugation. High stability in time was observed, together with nanomolar affinities on HER2-expressing tumor cells. Ex vivo biodistributions as well as SPECT/micro-CT analyses showed high activities in tumors expressing medium HER2 levels with low background activity except for the kidneys. The 1B4M-DTPA-coupled conjugate was further evaluated in a high HER2-expressing tumor model. Here, tumor uptake values of 5.99 ± 0.63, 5.12 ± 0.17, 2.83 ± 0.36 and 2.47 ± 0.38 %IA/g were obtained at 1, 3, 24 and 48h p.i., which coincided with exceptionally low background values, except for the kidneys, and unprecedented tumor-to-background ratios. No specific binding was observed in a HER2-negative model. In conclusion, the in-house developed anti-HER2 nanobody 2Rs15dHIS can be successfully labeled with (177) Lu using different bifunctional chelators. Both macrocyclic and acyclic chelators show high stability in time. High specific tumor uptake combined with the lowest background uptake was measured using the 1B4M-DTPA-based conjugate.

BackgroundRadiotheragnostics makes use of the same molecular targeting vectors, labeled either with a diagnostic or therapeutic radionuclide, ideally of the same chemical element. The matched pair of scandium radionuclides, 44Sc and 47Sc, satisfies the desired physical aspects for PET imaging and radionuclide therapy, respectively. While the production and application of 44Sc was extensively studied, 47Sc is still in its infancy. The aim of the present study was, therefore, to investigate and compare two different methods of 47Sc production, based on the neutron irradiation of enriched 46Ca and 47Ti targets, respectively.Methods 47Sc was produced by thermal neutron irradiation of enriched 46Ca targets via the 46Ca(n,γ)47Ca → 47Sc nuclear reaction and by fast neutron irradiation of 47Ti targets via the 47Ti(n,p)47Sc nuclear reaction, respectively. The product was compared with regard to yield and radionuclidic purity. The chemical separation of 47Sc was optimized in order to obtain a product of sufficient quality determined by labeling experiments using DOTANOC. Finally, preclinical SPECT/CT experiments were performed in tumor-bearing mice and compared with the PET image of the 44Sc labeled counterpart.ResultsUp to 2 GBq 47Sc was produced by thermal neutron irradiation of enriched 46Ca targets. The optimized chemical isolation of 47Sc from the target material allowed formulation of up to 1.5 GBq 47Sc with high radionuclidic purity (>99.99%) in a small volume (~700 μL) useful for labeling purposes. Three consecutive separations were possible by isolating the in-grown 47Sc from the 46/47Ca-containing fraction. 47Sc produced by fast neutron irradiated 47Ti targets resulted in a reduced radionuclidic purity (99.95–88.5%). The chemical purity of the separated 47Sc was determined by radiolabeling experiments using DOTANOC achievable at specific activities of 10 MBq/nmol. In vivo the 47Sc-DOTANOC performed equal to 44Sc-DOTANOC as determined by nuclear imaging.ConclusionThe production of 47Sc via the 46Ca(n,γ)47Ca nuclear reaction demonstrated significant advantages over the 47Ti production route, as it provided higher quantities of a radionuclidically pure product. The subsequent decay of 47Ca enabled the repeated separation of the 47Sc daughter nuclide from the 47Ca parent nuclide. Based on the results obtained from this work, 47Sc shows potential to be produced in suitable quality for clinical application.Electronic supplementary materialThe online version of this article (doi:10.1186/s41181-017-0024-x) contains supplementary material, which is available to authorized users.

BackgroundRecently, 44Sc (T1/2 = 3.97 h, Eβ+ av = 632 keV, I = 94.3 %) has emerged as an attractive radiometal candidate for PET imaging using DOTA-functionalized biomolecules. The aim of this study was to investigate the potential of using NODAGA for the coordination of 44Sc. Two pairs of DOTA/NODAGA-derivatized peptides were investigated in vitro and in vivo and the results obtained with 44Sc compared with its 68Ga-labeled counterparts.DOTA-RGD and NODAGA-RGD, as well as DOTA-NOC and NODAGA-NOC, were labeled with 44Sc and 68Ga, respectively. The radiopeptides were investigated with regard to their stability in buffer solution and under metal challenge conditions using Fe3+ and Cu2+. Time-dependent biodistribution studies and PET/CT imaging were performed in U87MG and AR42J tumor-bearing mice.ResultsBoth RGD- and NOC-based peptides with a DOTA chelator were readily labeled with 44Sc and 68Ga, respectively, and remained stable over at least 4 half-lives of the corresponding radionuclide. In contrast, the labeling of NODAGA-functionalized peptides with 44Sc was more challenging and the resulting radiopeptides were clearly less stable than the DOTA-derivatized matches. 44Sc-NODAGA peptides were clearly more susceptible to metal challenge than 44Sc-DOTA peptides under the same conditions. Instability of 68Ga-labeled peptides was only observed if they were coordinated with a DOTA in the presence of excess Cu2+. Biodistribution data of the 44Sc-labeled peptides were largely comparable with the data obtained with the 68Ga-labeled counterparts. It was only in the liver tissue that the uptake of 68Ga-labeled DOTA compounds was markedly higher than for the 44Sc-labeled version and this was also visible on PET/CT images. The 44Sc-labeled NODAGA-peptides showed a similar tissue distribution to those of the DOTA peptides without any obvious signs of in vivo instability.ConclusionsAlthough DOTA revealed to be the preferred chelator for stable coordination of 44Sc, the data presented in this work indicate the possibility of using NODAGA in combination with 44Sc. In view of a clinical study, thorough investigations will be necessary regarding the labeling conditions and storage solutions in order to guarantee sufficient stability of 44Sc-labeled NODAGA compounds.Electronic supplementary materialThe online version of this article (doi:10.1186/s41181-016-0013-5) contains supplementary material, which is available to authorized users.

Targeted radionuclide therapy with 177Lu- and 90Y-labeled radioconjugates is a clinically-established treatment modality for metastasized cancer. 47Sc is a therapeutic radionuclide that decays with a half-life of 3.35 days and emits medium-energy β−-particles. In this study, 47Sc was investigated, in combination with a DOTA-folate conjugate, and compared to the therapeutic properties of 177Lu-folate and 90Y-folate, respectively. In vitro, 47Sc-folate demonstrated effective reduction of folate receptor-positive ovarian tumor cell viability similar to 177Lu-folate, but 90Y-folate was more potent at equal activities due to the higher energy of emitted β−-particles. Comparable tumor growth inhibition was observed in mice that obtained the same estimated absorbed tumor dose (~21 Gy) when treated with 47Sc-folate (12.5 MBq), 177Lu-folate (10 MBq), and 90Y-folate (5 MBq), respectively. The treatment resulted in increased median survival of 39, 43, and 41 days, respectively, as compared to 26 days in untreated controls. There were no statistically significant differences among the therapeutic effects observed in treated groups. Histological assessment revealed no severe side effects two weeks after application of the radiofolates, even at double the activity used for therapy. Based on the decay properties and our results, 47Sc is likely to be comparable to 177Lu when employed for targeted radionuclide therapy. It may, therefore, have potential for clinical translation and be of particular interest in tandem with 44Sc or 43Sc as a diagnostic match, enabling the realization of radiotheragnostics in future.

Fast progressing immuno-PET asks to explore new radionuclides. One of the promising candidates is 90 Nb. It has a half-life of 14.6 h that allows visualizing and quantifying biological processes with medium and slow kinetics, such as tumor accumulation of antibodies and antibodies fragments or drug delivery systems and nanoparticles. 90 Nb exhibits a positron branching of 53% and an average kinetic energy of emitted positrons of mean = 0.35 MeV. Currently, radionuclide production routes and Nb V labeling techniques are explored to turn this radionuclide into a useful imaging probe. However, efficient separation of 90 Nb from irradiated targets remains in challenge.Ion exchange based separation of 90 Nb from zirconium targets was investigated in systems AG 1 × 8 -HCl/H 2 O 2 and UTEVA-HCl. 95 Nb ( 1/2 = 35.0 d), 95 Zr ( 1/2 = 64.0 d) and 92m Nb ( 1/2 = 10.15 d) were chosen for studies on distribution coefficients. Separation after AG 1 × 8 anion exchange yields 99% of 90/95 Nb. Subsequent use of a solidphase extraction step on UTEVA resin further decontaminates 90/95 Nb from traces of zirconium with yields 95% of 90/95 Nb.A semi-automated separation takes one hour to obtain an overall recovery of 90/95 Nb of 90%. The amount of Zr was reduced by factor of 10 8 . The selected separation provides rapid preparation (< 1 h) of high purity 90 Nb appropriate for the synthesis of 90 Nb-radiopharmaceuticals, relevant for purposes of immuno-PET. Applying the radioniobium obtained, 90/95 Nb-labeling of a monoclonal antibody (rituximab) modified with desferrioxamine achieved labeling yields of > 90% after 1 h incubation at room temperature.