COST Action CA19114, Network for Optimized Astatine labelled Radiopharmaceuticals

Cancer is a major health concerns for European citizens. Thus, the main research aim of this Network for Optimized Astatine labeled Radiopharmaceuticals (NOAR) COST Action is to successfully demonstrate that one of the most promising radionuclides for Targeted Alpha Therapy (TAT), namely astatine-211, can become the European standard for treatment of certain cancerous pathologies. To this end, an efficient networking is essential among all European stakeholders interested in promoting astatine-211 for medical applications. NOAR COST Action brings together European and international excellence labs, astatine-211 production centers, hospitals, industry and patient associations from more than 20 countries, thus covering the whole value chain of innovation: production, chemistry, radiochemistry, biology, preclinical and clinical research and delivery of radiopharmaceuticals to patients. A European web portal will be created containing information for patients, practitioners, researchers, Industry and as a contact point for National and European patient associations. The idea is to gather forces at the European level in order to implement actions to leverage hurdles to the development of this powerful radionuclide and to identify pathologies in which it will be particularly relevant. A special emphasis will be given to train a new generation of young researchers and PhD students, promoting interdisciplinary competencies through international and inter-sectoral mobility. The long-term goal of this project is to make Astatine-211 technology available to all European citizen

Evaluation of an Anti-HER2 Nanobody Labeled with 225Ac for Targeted α‑Particle Therapy of Cancer

Human epidermal growth factor receptor type 2 (HER2) is overexpressed in numerous carcinomas. Nanobodies (Nbs) are the smallest antibody-derived fragments with beneficial characteristics for molecular imaging and radionuclide therapy. Therefore, HER2-targeting nanobodies could offer a valuable platform for radioimmunotherapy, especially when labeled with α-particle emitters, which provide highly lethal and localized radiation to targeted cells with minimal exposure to surrounding healthy tissues. In this study, the anti-HER2 2Rs15d-nanobody was conjugated with 2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (p-SCN-Bn-DOTA) and radiolabeled with an α-emitter 225Ac with a high yield (>90%) and a radiochemical purity above 95%. The 225Ac-DOTA-Nb binding affinity was 4.12 ± 0.47 nM with an immunoreactive fraction above 80%. Binding to low HER2-expressing MDA-MB-231 cells was negligible, whereas HER2-overexpressing SKOV-3 cells could be blocked with an excess of unlabeled nanobody, confirming the specificity of binding. Noncompeting binding to HER2 was observed in the presence of an excess of trastuzumab. The cell-associated fraction of 225Ac-DOTA-Nb was 34.72 ± 16.66% over 24 h. In vitro, the radioconjugate was toxic in an HER2-mediated and dose-dependent manner, resulting in IC50 values of 10.2 and 322.1 kBq/mL for 225Ac-DOTA-Nb and the 225Ac-DOTA control, respectively, on SKOV-3 cells, and 282.2 kBq/mL for 225Ac-DOTA-Nb on MDA-MB-231 cells. Ex vivo biodistribution studies, performed in mice bearing subcutaneous HER2-overexpressing and low HER2-expressing tumors, showed a fast uptake in SKOV-3 tumors compared to MDA-MB-231 (4.01 ± 1.58% ID/g vs 0.49 ± 0.20% ID/g after 2 h), resulting also in high tumor-to-normal tissue ratios. In addition, coinjection of 225Ac-DOTA-Nb with Gelofusine reduced kidney retention by 70%. This study shows that 225Ac-DOTA-Nb is a promising new radioconjugate for targeted α-particle therapy and supports its further development.JRC.G.I.5-Advanced Nuclear Knowledg

Bismuth-213 labeled nanobodies as a new treatment approach in Targeted Alpha Therapy

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213Bismuth-labeled nanobodies as a new treatment approach in Targeted Alpha Therapy

status: publishe

The Therapeutic Potential of Anti-HER2 2Rs15d Nanobody Labeled with 225Ac – an In Vitro and In Vivo Evaluation

Human Epidermal Growth Factor Receptor type 2 (HER2) is overexpressed in numerous carcinomas and is often associated with a higher recurrence rate and a shorter time to relapse. Nanobodies (Nbs) are the smallest antibody-derived fragments with beneficial pharmacokinetic properties for molecular imaging and targeted radionuclide therapy (TRT). HER2-targeting nanobodies are very attractive vectors for TRT, especially when labeled with α-particle emitters, which provide highly lethal and localized radiation to targeted cells with minimal exposure to surrounding healthy tissues. The aim of this study was to evaluate the therapeutic potential of the anti-HER2 Nb 2Rs15d labeled with 225Ac.JRC.G.I.5-Advanced Nuclear Knowledg

Pharmacokinetics of radiolabeled dimeric sdAbs constructs targeting human CD20

Single-domain antibody fragments (sdAbs) are the smallest functional antigen-binding fragments, derived from heavy chain-only camelid antibodies. When designed as radiolabeled monomeric probes for imaging and therapy of cancer, their fast and specific targeting results in high tumor-to-background ratios early after injection. However, their moderate absolute uptake into tumors might not always be sufficient to treat cancerous lesions. We have evaluated the pharmacokinetics of seven constructs derived from a CD20-targeting monomeric sdAb (alphaCD20). The constructs differed in affinity or avidity towards CD20 (dimeric alphaCD20-alphaCD20 and alphaCD20 fused to a non-targeting control sdAb, referred to as alphaCD20-ctrl) and blood half-lives (alphaCD20 fused to an albumin-targeting sdAb (alphaAlb)=alphaCD20-alphaAlb). The constructs were radiolabeled with (111)In (imaging) and (177)Lu (therapy) using the bifunctional chelator CHX-A"-DTPA and evaluated in vitro and in vivo. In mice, tumor uptake of (177)Lu-DTPA-alphaCD20 decreased from 4.82+/-1.80 to 0.13+/-0.05% IA/g over 72h. Due to its rapid blood clearance, tumor- to-blood (T/B) ratios of >100 were obtained within 24h. Although in vitro internalization indicated that dimeric (177)Lu-DTPA-alphaCD20-alphaCD20 was superior in terms of total cell-associated radioactivity, this was not confirmed in vivo. Blood clearance was slower and absolute tumor uptake became significantly higher for alphaCD20-alphaAlb. Blood levels of (177)Lu-DTPA-alphaCD20-alphaAlb decreased from 68.30+/-10.53 to 3.58+/-0.66% IA/g over 120h, while tumor uptake increased from 6.21+/-0.94 to 24.90+/-2.83% IA/g, resulting in lower T/B ratios. Taken together, these results indicate that the increased size of dimeric alphaCD20-alphaCD20 or the fusion of monomeric alphaCD20 to an albumin- targeting moiety (alphaAlb) counterbalance their improved tumor targeting capacity compared to monomeric alphaCD20

Gallium-68-labelled NOTA-oligonucleotides: An optimized method for their preparation

One of the most essential aspects to the success of radiopharmaceuticals is an easy and reliable radiolabelling protocol to obtain pure and stable products. In this study, we optimized the bioconjugation and gallium-68 ((68) Ga) radiolabelling conditions for a single-stranded 40-mer DNA oligonucleotide, in order to obtain highly pure and stable radiolabelled oligonucleotides. Quantitative bioconjugation was obtained for a disulfide-functionalized oligonucleotide conjugated to the macrocylic bifunctional chelator MMA-NOTA (maleimido-mono-amide (1,4,7-triazanonane-1,4,7-triyl)triacetic acid). Next, this NOTA-oligonucleotide bioconjugate was radiolabelled at room temperature with purified and pre-concentrated (68) Ga with quantitative levels of radioactive incorporation and high radiochemical and chemical purity. In addition, high chelate stability was observed in physiological-like conditions (37 °C, PBS and serum), in the presence of a transchelator (EDTA) and transferrin. A specific activity of 51.1 MBq/nmol was reached using a 1470-fold molar excess bioconjugate over (68) Ga. This study presents a fast, straightforward and reliable protocol for the preparation of (68) Ga-radiolabelled DNA oligonucleotides under mild reaction conditions and without the use of organic solvents. The methodology herein developed will be applied to the preparation of oligonucleotidic sequences (aptamers) targeting the human epidermal growth factor receptor 2 (HER2) for cancer imaging

Biological carrier molecules of radiopharmaceuticals for molecular cancer imaging and targeted cancer therapy

Many tumors express one or more proteins that are either absent or hardly present in normal tissues, and which can be targeted by radiopharmaceuticals for either visualization of tumor cells or for targeted therapy. Radiopharmaceuticals can consist of a radionuclide and a carrier molecule that interacts with the tumor target and as such guides the attached radionuclide to the right spot. Radiopharmaceuticals hold great promise for the future of oncology by providing early, precise diagnosis and better, personalized treatment. Most advanced developments with marketed products are based on whole antibodies or antibody fragments as carrier molecules. However, a substantial number of (pre)clinical studies indicate that radiopharmaceuticals based on other carrier molecules, such as peptides, nonimmunoglobulin scaffolds, or nucleic acids may be valuable alternatives. In this review, we discuss the biological molecules that can deliver radionuclide payloads to tumor cells in terms of their structure, the selection procedure, their (pre)clinical status, and advantages or obstacles to their use in a radiopharmaceutical design. We also consider the plethora of molecular targets existing on cancer cells that can be targeted by radiopharmaceuticals, as well as how to select a radionuclide for a given diagnostic or therapeutic product

Combining Bismuth-213 with Nanobodies: finding the perfect match for Targeted Alpha Therapy

This study investigates a novel targeted therapy which combines the α-emitter Bismuth-213 (213Bi) and HER2-targeting nanobodies (Nbs) to selectively kill HER2+ metastases in breast- and ovarian cancer. The use of nanobodies as vehicles in TAT is promising due to their excellent in vivo properties, high affinity and specificity, fast diffusion and clearance kinetics. Moreover, Nbs show good tumor penetration due to their small size. The aim of this study is to develop and evaluate the in vitro binding characteristics on HER+ SKOV-3 cells, the in vitro stability using radio-ITLC and HPLC and the in vivo biodistribution of 213Bi-DTPA HER2 targeting Nb.JRC.G.I.5-Advanced Nuclear Knowledg

Theranostic radiolabeled anti-CD20 sdAb for targeted radionuclide therapy of non-Hodgkin lymphoma

Anti-CD20 radioimmunotherapy is an effective approach for therapy of relapsed or refractory CD20(pos) lymphomas, but faces limitations due to poor tumor penetration and undesirable pharmacokinetics of full antibodies. Camelid single-domain Ab fragments (sdAb) might circumvent some of the limitations of radiolabeled full antibodies. In this study, a set of hCD20-targeting sdAbs was generated, and their capacity to bind hCD20 was evaluated in vitro and in vivo A lead sdAb, sdAb 9079, was selected on the basis of its specific tumor targeting and significant lower kidney accumulation compared with other sdAbs. SdAb 9079 was then radiolabeled with (68)Ga and (177)Lu for PET imaging and targeted therapy. The therapeutic potential of (177)Lu-DTPA-sdAb was compared with that of (177)Lu-DTPA-rituximab and unlabeled rituximab in mice bearing hCD20(pos) tumors. Radiolabeled with (68)Ga, sdAb 9079 showed specific tumor uptake, with very low accumulation in nontarget organs, except kidneys. The tumor uptake of (177)Lu-DTPA-sdAb 9079 after 1.5 h was 3.4 +/- 1.3% ID/g, with T/B and T/M ratios of 13.3 +/- 4.6 and 32.9 +/- 15.6. Peak tumor accumulation of (177)Lu-DTPA-rituximab was about 9 times higher, but concomitantly with high accumulation in nontarget organs and very low T/B and T/M ratios (0.8 +/- 0.1 and 7.1 +/- 2.4). Treatment of mice with (177)Lu-DTPA-sdAb 9079 significantly prolonged median survival compared with control groups and was as effective as treatment with rituximab or its (177)Lu-labeled variant. Taken together, sdAb 9079 displays promising features as a theranostic drug to treat CD20(pos) lymphomas. Mol Cancer Ther; 16(12); 2828-39. (c)2017 AACR