The joint roadmap for radiation protection research: outreach and future.

During the last decade there has been remarkable integration of radiation protection research in Europe, driven by six research platforms. The platforms are associations of research centres, university research groups and funding bodies in Member States that are dedicated to specialised areas of research in radiation protection, such as health risks (MELODI), radioecology (ALLIANCE), radiological emergencies (NERIS), dosimetry (EURADOS), medical use of radiation (EURAMED) and societal aspects (SHARE). Recently these platforms established an umbrella organisation MEENAS, to endorse further integration and joint activities in research, education and training, and infrastructures. A milestone in this process of integration and priority setting was achieved in 2020 when the first edition of the joint roadmap for radiation protection research was finalised. In this paper we describe the various roles for research and development in the radiation protection context, ranging from basic scientific knowledge underpinning the system of protection to research supporting the development and application of international standards and research and development activities needed to ensure safety in radiation practices and in potential exposure scenarios. We describe the process of how the joint roadmap has been developed and how it could be implemented. Finally, we address the need to anticipate potential future exposure scenarios and to systematically consider the impact of emerging technologies and global challenges in the context of radiation protection. The joint roadmap is a living document that needs to be regularly updated to cover both current and potential exposures of humans and the environment.

Ionizing radiation-induced circulatory and metabolic diseases.

Risks to health are the prime consideration in all human situations of ionizing radiation exposure and therefore of relevance to radiation protection in all occupational, medical, and public exposure situations. Over the past few decades, advances in therapeutic strategies have led to significant improvements in cancer survival rates. However, a wide range of long-term complications have been reported in cancer survivors, in particular circulatory diseases and their major risk factors, metabolic diseases. However, at lower levels of exposure, the evidence is less clear. Under real-life exposure scenarios, including radiotherapy, radiation effects in the whole organism will be determined mainly by the response of normal tissues receiving relatively low doses, and will be mediated and moderated by systemic effects. Therefore, there is an urgent need for further research on the impact of low-dose radiation. In this article, we review radiation-associated risks of circulatory and metabolic diseases in clinical, occupational or environmental exposure situations, addressing epidemiological, biological, risk modelling, and systems biology aspects, highlight the gaps in knowledge and discuss future directions to address these gaps.

Low dose ionizing radiation effects on the immune system.

Ionizing radiation interacts with the immune system in many ways with a multiplicity that mirrors the complexity of the immune system itself: namely the need to maintain a delicate balance between different compartments, cells and soluble factors that work collectively to protect, maintain, and restore tissue function in the face of severe challenges including radiation damage. The cytotoxic effects of high dose radiation are less relevant after low dose exposure, where subtle quantitative and functional effects predominate that may go unnoticed until late after exposure or after a second challenge reveals or exacerbates the effects. For example, low doses may permanently alter immune fitness and therefore accelerate immune senescence and pave the way for a wide spectrum of possible pathophysiological events, including early-onset of age-related degenerative disorders and cancer. By contrast, the so called low dose radiation therapy displays beneficial, anti-inflammatory and pain relieving properties in chronic inflammatory and degenerative diseases. In this review, epidemiological, clinical and experimental data regarding the effects of low-dose radiation on the homeostasis and functional integrity of immune cells will be discussed, as will be the role of immune-mediated mechanisms in the systemic manifestation of localized exposures such as inflammatory reactions. The central conclusion is that ionizing radiation fundamentally and durably reshapes the immune system. Further, the importance of discovery of immunological pathways for modifying radiation resilience amongst other research directions in this field is implied.

When a duck is not a duck; a new interdisciplinary synthesis for environmental radiation protection.

This consensus paper presents the results of a workshop held in Essen, Germany in September 2017, called to examine critically the current approach to radiological environmental protection. The meeting brought together participants from the field of low dose radiobiology and those working in radioecology. Both groups have a common aim of identifying radiation exposures and protecting populations and individuals from harmful effects of ionising radiation exposure, but rarely work closely together. A key question in radiobiology is to understand mechanisms triggered by low doses or dose rates, leading to adverse outcomes of individuals while in radioecology a key objective is to recognise when harm is occurring at the level of the ecosystem. The discussion provided a total of six strategic recommendations which would help to address these questions.

Improved Aptamers for the Diagnosis and Potential Treatment of HER2-Positive Cancer.

Aptamers provide a potential source of alternative targeting molecules for existing antibody diagnostics and therapeutics. In this work, we selected novel DNA aptamers targeting the HER2 receptor by an adherent whole-cell SELEX approach. Individual aptamers were identified by next generation sequencing and bioinformatics analysis. Two aptamers, HeA2_1 and HeA2_3, were shown to bind the HER2 protein with affinities in the nanomolar range. In addition, both aptamers were able to bind with high specificity to HER2-overexpressing cells and HER2-positive tumor tissue samples. Furthermore, we demonstrated that aptamer HeA2_3 is being internalized into cancer cells and has an inhibitory effect on cancer cell growth and viability. In the end, we selected novel DNA aptamers with great potential for the diagnosis and possible treatment of HER2-positive cancer.

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.

Targeted radionuclide therapy with A 177Lu-labeled anti-HER2 nanobody.

RIT has become an attractive strategy in cancer treatment, but still faces important drawbacks due to poor tumor penetration and undesirable pharmacokinetics of the targeting vehicles. Smaller radiolabeled antibody fragments and peptides feature highly specific target accumulation, resulting in low accumulation in healthy tissue, except for the kidneys. Nanobodies are the smallest (MW<15 kDa) functional antigen-binding fragments that are derived from heavy chain-only camelid antibodies. Here, we show that the extend of kidney retention of nanobodies is predominantly dictated by the number of polar residues in the C-terminal amino acid tag. Three nanobodies were produced with different C-terminal amino-acid tag sequences (Myc-His-tagged, His-tagged, and untagged). Dynamic planar imaging of Wistar rats with 111In-DTPA-nanobodies revealed that untagged nanobodies showed a 70% drop in kidney accumulation compared to Myc-His-tagged nanobodies at 50 min p.i.. In addition, coinfusion of untagged nanobodies with the plasma expander Gelofusin led to a final reduction of 90%. Similar findings were obtained with different 177Lu-DTPA-2Rs15d nanobody constructs in HER2pos tumor xenografted mice at 1 h p.i.. Kidney accumulation decreased 88% when comparing Myc-His-tagged to untagged 2Rs15d nanobody, and 95% with a coinfusion of Gelofusin, without affecting the tumor targeting capacity. Consequently, we identified a generic method to reduce kidney retention of radiolabeled nanobodies. Dosimetry calculations of Gelofusin-coinfused, untagged 177Lu-DTPA-2Rs15d revealed a dose of 0.90 Gy/MBq that was delivered to both tumor and kidneys and extremely low doses to healthy tissues. In a comparative study, 177Lu-DTPA-Trastuzumab supplied 6 times more radiation to the tumor than untagged 177Lu-DTPA-2Rs15d, but concomitantly also a 155, 34, 80, 26 and 4180 fold higher radioactivity burden to lung, liver, spleen, bone and blood. Most importantly, nanobody-based targeted radionuclide therapy in mice bearing small estiblashed HER2pos tumors led to an almost complete blockade of tumor growth and a significant difference in event-free survival between the treated and the control groups (P<0.0001). Based on histology analyses, no evidence of renal inflammation, apoptosis or necrosis was obtained. In conclusion, these data highlight the importance of the amino acid composition of the nanobody's C-terminus, as it has a predominant effect on kidney retention. Moreover, we show successful nanobody-based targeted radionuclide therapy in a xenograft model and highlight the potential of radiolabeled nanobodies as a valuable adjuvant therapy candidate for treatment of minimal residual and metastatic disease.

Development of 177Lu-nanobodies for radioimmunotherapy of HER2-positive breast cancer: evaluation of different bifunctional chelators.

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.