Paving the Way to Personalized Medicine: Production of Some Promising Theragnostic Radionuclides at Brookhaven National Laboratory

SPECT/CT imaging of EGFR-positive head and neck squamous cell carcinoma patient-derived xenografts with 203Pb-PSC-panitumumab in NRG mice

BACKGROUND

The objective of this research was the development and evaluation of 203Pb-labelled panitumumab (203Pb-PSC-panitumumab) as an immuno-SPECT radioligand for the detection of EGFR + head and neck squamous cell carcinoma (HNSCC) in a patient-derived xenograft (PDX) mouse model. The 51.9 h physical half-life and favourable γ-emission (279 keV; 81%) of 203Pb offer an excellent opportunity for developing immuno-SPECT radioligands. Moreover, 203Pb has a complementary therapeutic radionuclide (212Pb), making 203Pb and 212Pb an ideal matched radiotheranostic pair.

RESULTS

Radiolabeling of panitumumab was performed at a pH of 5.0 and room temperature for 5-10 min with [203Pb]Pb(OAc)2, and the incorporation efficiency was determined using radio-TLC. 203Pb-PSC-panitumumab (~ 10 MBq, 140 μl of saline) was injected into the tail vein of NRG mice bearing subcutaneous (s.c.) HNSCC patient-derived xenografts (PDX). SPECT/CT images were acquired at 48 and 120 h post-injection. For biodistribution studies, mice were euthanized five days after 203Pb-panitumumab injection. The tumour and normal tissues were collected and weighed, and uptake of 203Pb was measured in a γ-counter. The uptake was calculated as the percent injected dose per gram of each tissue (ID%/g). Blocking experiments were performed by pretreating a group of mice (n = 5) with 1 mg of panitumumab 1 h before administering 203Pb-PSC-panitumumab. 4-5 chelators of a new lead-specific chelator (PSC) were attached per antibody; radiolabeling efficiency was 99.2 ± 0.7%. The isolated radiochemical yield of 203Pb-PSC-panitumumab was 41.4 ± 8% (n = 5), and the molar activity was 1.2 ± 0.35 GB/mg. SPECT imaging and biodistribution confirmed high accumulation and retention of 203Pb-PSC-panitumumab in the tumour (26% ID/g) at 120 h post-injection (p.i.), which could be reduced to 6.2%ID/g at 120 h p.i. by predosing with panitumumab (1 mg) confirming EGFR specificity of 203Pb-PSC-panitumumab uptake.

CONCLUSIONS

Panitumumab was successfully and reproducibly labelled with 203Pb in high radiochemical purity using the chelator PSC-NCS. 203Pb-PSC-panitumumab was specifically accumulated and retained in EGFR + tumours in NRG mice with s.c. HNSCC PDX. 203Pb-PSC-panitumumab is a suitable immuno-SPECT radioligand for imaging EGFR + tumours and has great potential for combining with 212Pb-PSC-panitumumab in a radiotheranostic strategy for imaging and treating HNSCC.

3D-printed dosage forms for oral administration: a review

Oral administration is the most commonly used form of treatment due to its advantages, including high patient compliance, convenient administration, and minimal preparation required. However, the traditional preparation process of oral solid preparation has many defects. Although continuous manufacturing line that combined all the unit operations has been developed and preliminarily applied in the pharmaceutical industry, most of the currently used manufacturing processes are still complicated and discontinuous. As a result, these complex production steps will lead to low production efficiency and high quality control risk of the final product. Additionally, the large-scale production mode is inappropriate for the personalized medicines, which commonly is customized with small amount. Several attractive techniques, such as hot-melt extrusion, fluidized bed pelletizing and spray drying, could effectively shorten the process flow, but still, they have inherent limitations that are challenging to address. As a novel manufacturing technique, 3D printing could greatly reduce or eliminate these disadvantages mentioned above, and could realize a desirable continuous production for small-scale personalized manufacturing. In recent years, due to the participation of 3D printing, the development of printed drugs has progressed by leaps and bounds, especially in the design of oral drug dosage forms. This review attempts to summarize the new development of 3D printing technology in oral preparation and also discusses their advantages and disadvantages as well as potential applications.

The Role of Molecular Imaging in Personalized Medicine

The concept of personalized medicine refers to the tailoring of medical treatment to each patient's unique characteristics. Scientific advancements have led to a better understanding of how a person's unique molecular and genetic profile makes them susceptible to certain diseases. It provides individualized medical treatments that will be safe and effective for each patient. Molecular imaging modalities play an essential role in this aspect. They are used widely in screening, detection and diagnosis, treatment, assessing disease heterogeneity and progression planning, molecular characteristics, and long-term follow-up. In contrast to conventional imaging approaches, molecular imaging techniques approach images as the knowledge that can be processed, allowing for the collection of relevant knowledge in addition to the evaluation of enormous patient groups. This review presents the fundamental role of molecular imaging modalities in personalized medicine.

Cutting edge rare earth radiometals: prospects for cancer theranostics

Background

With recent advances in novel approaches to cancer therapy and imaging, the application of theranostic techniques in personalised medicine has emerged as a very promising avenue of research inquiry in recent years. Interest has been directed towards the theranostic potential of Rare Earth radiometals due to their closely related chemical properties which allow for their facile and interchangeable incorporation into identical bifunctional chelators or targeting biomolecules for use in a diverse range of cancer imaging and therapeutic applications without additional modification, i.e. a “one-size-fits-all” approach. This review will focus on recent progress and innovations in the area of Rare Earth radionuclides for theranostic applications by providing a detailed snapshot of their current state of production by means of nuclear reactions, subsequent promising theranostic capabilities in the clinic, as well as a discussion of factors that have impacted upon their progress through the theranostic drug development pipeline.

Main body

In light of this interest, a great deal of research has also been focussed towards certain under-utilised Rare Earth radionuclides with diverse and favourable decay characteristics which span the broad spectrum of most cancer imaging and therapeutic applications, with potential nuclides suitable for α-therapy (¹⁴⁹Tb), β⁻-therapy (⁴⁷Sc, ¹⁶¹Tb, ¹⁶⁶Ho, ¹⁵³Sm, ¹⁶⁹Er, ¹⁴⁹Pm, ¹⁴³Pr, ¹⁷⁰Tm), Auger electron (AE) therapy (¹⁶¹Tb, ¹³⁵La, ¹⁶⁵Er), positron emission tomography (⁴³Sc, ⁴⁴Sc, ¹⁴⁹Tb, ¹⁵²Tb, ¹³²La, ¹³³La), and single photon emission computed tomography (⁴⁷Sc, ¹⁵⁵Tb, ¹⁵²Tb, ¹⁶¹Tb, ¹⁶⁶Ho, ¹⁵³Sm, ¹⁴⁹Pm, ¹⁷⁰Tm). For a number of the aforementioned radionuclides, their progression from ‘bench to bedside’ has been hamstrung by lack of availability due to production and purification methods requiring further optimisation.

Conclusions

In order to exploit the potential of these radionuclides, reliable and economical production and purification methods that provide the desired radionuclides in high yield and purity are required. With more reactors around the world being decommissioned in future, solutions to radionuclide production issues will likely be found in a greater focus on linear accelerator and cyclotron infrastructure and production methods, as well as mass separation methods. Recent progress towards the optimisation of these and other radionuclide production and purification methods has increased the feasibility of utilising Rare Earth radiometals in both preclinical and clinical settings, thereby placing them at the forefront of radiometals research for cancer theranostics.

Mass Spectrometry Imaging Spatial Tissue Analysis toward Personalized Medicine

Novel profiling methodologies are redefining the diagnostic capabilities and therapeutic approaches towards more precise and personalized healthcare. Complementary information can be obtained from different omic approaches in combination with the traditional macro- and microscopic analysis of the tissue, providing a more complete assessment of the disease. Mass spectrometry imaging, as a tissue typing approach, provides information on the molecular level directly measured from the tissue. Lipids, metabolites, glycans, and proteins can be used for better understanding imbalances in the DNA to RNA to protein translation, which leads to aberrant cellular behavior. Several studies have explored the capabilities of this technology to be applied to tumor subtyping, patient prognosis, and tissue profiling for intraoperative tissue evaluation. In the future, intercenter studies may provide the needed confirmation on the reproducibility, robustness, and applicability of the developed classification models for tissue characterization to assist in disease management.

Modulation of Secondary Cancer Risks from Radiation Exposure by Sex, Age and Gonadal Hormone Status: Progress, Opportunities and Challenges

Available data on cancer secondary to ionizing radiation consistently show an excess (2-fold amount) of radiation-attributable solid tumors in women relative to men. This excess risk varies by organ and age, with the largest sex differences (6- to more than 10-fold) found in female thyroid and breasts exposed between birth until menopause (~50 years old) relative to age-matched males. Studies in humans and animals also show large changes in cell proliferation rates, radiotracer accumulation and target density in female reproductive organs, breast, thyroid and brain in conjunction with physiological changes in gonadal hormones during the menstrual cycle, puberty, lactation and menopause. These sex differences and hormonal effects present challenges as well as opportunities to personalize radiation-based treatment and diagnostic paradigms so as to optimize the risk/benefit ratios in radiation-based cancer therapy and diagnosis. Specifically, Targeted Radionuclide Therapy (TRT) is a fast-expanding cancer treatment modality utilizing radiopharmaceuticals with high avidity to specific molecular tumor markers, many of which are influenced by sex and gonadal hormone status. However, past and present dosimetry studies of TRT agents do not stratify results by sex and hormonal environment. We conclude that cancer management using ionizing radiation should be personalized and informed by the patient sex, age and hormonal status.

High purity 47Sc production using high-energy photons and natural vanadium targets

Scandium-47 (⁴⁷Sc) is of high value for targeted radiotherapy and theranostics; we report a novel, cost-effective approach to produce high-purity ⁴⁷Sc via photonuclear reactions with natural vanadium. Irradiation at 20 MeV photon end-point energy produces >99.998% pure ⁴⁷Sc, while irradiation at 38 MeV produces 98.8 ± 1.6% pure ⁴⁷Sc. Experimental data suggest producing greater than 100 mCi (3700 MBq) of ⁴⁷Sc using this approach may be feasible. Future research into refinement and scale-up to support pre-clinical research is recommended.

Radiolabelled Cyclic Bisarylmercury: High Chemical and in vivo Stability for Theranostics

We show the synthesis of an in vivo stable mercury compound with functionality suitable for radiopharmaceuticals. The designed cyclic bisarylmercury was based on the water tolerance of organomercurials, higher bond dissociation energy of Hg-Ph to Hg-S, and the experimental evidence that acyclic structures suffer significant cleavage of one of the Hg-R bonds. The bispidine motif was chosen for its in vivo stability, chemical accessibility, and functionalization properties. Radionuclide production results in 197(m) HgCl2 (aq), so the desired mercury compound was formed via a water-tolerant organotin transmetallation. The Hg-bispidine compound showed high chemical stability in tests with an excess of sulfur-containing competitors and high in vivo stability, without any observable protein interaction by human serum assay, and good organ clearance demonstrated by biodistribution and SPECT studies in rats. In particular, no retention in the kidneys was observed, typical of unstable mercury compounds. The nat Hg analogue allowed full characterization by NMR and HRMS.

Coordination chemistry of [Y(pypa)]- and comparison immuno-PET imaging of [44Sc]Sc- and [86Y]Y-pypa-phenyl-TRC105

Both scandium-44 and yttrium-86 are popular PET isotopes with appropriate half-lives for immuno-positron emission tomography (immuno-PET) imaging. Herein, a new bifunctional H4pypa ligand, H4pypa-phenyl-NCS, is synthesized, conjugated to a monoclonal antibody, TRC105, and labeled with both radionuclides to investigate the long-term in vivo stability of each complex. While the 44Sc-labeled radiotracer exhibited promising pharmacokinetics and stability in 4T1-xenograft mice (n = 3) even upon prolonged interactions with blood serum proteins, the progressive bone uptake of the 86Y-counterpart indicated in vivo demetallation, obviating H4pypa as a suitable chelator for Y3+ ion in vivo. The solution chemistry of [natY(pypa)]- was studied in detail and the complex found to be thermodynamically stable in solution with a pM value 22.0, ≥3 units higher than those of the analogous DOTA- and CHX-A''-DTPA-complexes; the 86Y-result in vivo was therefore most unexpected. To explore further this in vivo lability, Density Functional Theory (DFT) calculation was performed to predict the geometry of [Y(pypa)]- and the results were compared with those for the analogous Sc- and Lu-complexes; all three adopted the same coordination geometry (i.e. distorted capped square antiprism), but the metal-ligand bonds were much longer in [Y(pypa)]- than in [Lu(pypa)]- and [Sc(pypa)]-, which could indicate that the size of the binding cavity is too small for the Y3+ ion, but suitable for both the Lu3+ and Sc3+ ions. Considered along with results from [86Y][Y(pypa-phenyl-TRC105)], it is noted that when matching chelators with radionuclides, chemical data such as the thermodynamic stability and in vitro inertness, albeit useful and necessary, do not always translate to in vivo inertness, especially with the prolonged blood circulation of the radiotracer bound to a monoclonal antibody. Although H4pypa is a nonadentate chelator, which theoretically matches the coordination number of the Y3+ ion, we show herein that its binding cavity, in fact, favors smaller metal ions such as Sc3+ and Lu3+ and further exploitation of the Sc-pypa combination is desired.

Harvesting 48V at the National Superconducting Cyclotron Laboratory

As part of an effort to develop aqueous isotope harvesting techniques at radioactive beam facilities, ⁴⁸V and a cocktail of primary- and secondary-beam ions created by the fragmentation reaction of a 160 MeV/nucleon ⁵⁸Ni beam were stopped in an aqueous target cell. After collection, ⁴⁸V was separated from the mixture of beam ions using cation-exchange chromatography. The extraction efficiency from the aqueous solution was (47.0 ± 2.5)%, and the isolated ⁴⁸V had a radiochemical purity of 95.8%. This proof-of-concept work shows that aqueous isotope harvesting could provide significant quantities of rare isotopes which are currently unavailable at conventional facilities.

Radiobromine and radioiodine for medical applications

The halogens bromine and iodine have similar chemical properties and undergo similar reactions due to their closeness in Group 17 of the periodic chart. There are a number of bromine and iodine radionuclides that have properties useful for diagnosis and therapy of human diseases. The emission properties of radiobromine and radioiodine nuclides with half-lives longer than 1 h are summarized along with properties that make radionuclides useful in PET/SPECT imaging and β/Auger therapy, such that the reader can assess which of the radionuclides might be useful for medical applications. An overview of chemical approaches that have been used to radiolabel molecules with radiobromine and radioiodine nuclides is provided with examples. Further, references to a large variety of different organ/cancer-targeting agents utilizing the radiolabeling approaches described are provided.

Photonuclear production, chemistry, and in vitro evaluation of the theranostic radionuclide 47Sc

Background

In molecular imaging and nuclear medicine, theranostic agents that integrate radionuclide pairs are successfully being used for individualized care, which has led to rapidly growing interest in their continued development. These compounds, which are radiolabeled with one radionuclide for imaging and a chemically identical or similar radionuclide for therapy, may improve patient-specific treatment and outcomes by matching the properties of different radionuclides with a targeting vector for a particular tumor type. One proposed theranostic radionuclide is scandium-47 (⁴⁷Sc, T_1/2 = 3.35 days), which can be used for targeted radiotherapy and may be paired with the positron emitting radionuclides, ⁴³Sc (T_1/2 = 3.89 h) and ⁴⁴Sc (T_1/2 = 3.97 h) for imaging. The aim of this study was to investigate the photonuclear production of ⁴⁷Sc via the ⁴⁸Ti(γ,p)⁴⁷Sc reaction using an electron linear accelerator (eLINAC), separation and purification of ⁴⁷Sc, the radiolabeling of somatostatin receptor-targeting peptide DOTATOC with ⁴⁷Sc, and in vitro receptor-mediated binding of [⁴⁷Sc]Sc-DOTATOC in AR42J somatostatin receptor subtype two (SSTR2) expressing rat pancreatic tumor cells.

Results

The rate of ⁴⁷Sc production in a stack of natural titanium foils (n = 39) was 8 × 10⁷ Bq/mA·h (n = 3). Irradiated target foils were dissolved in 2.0 M H₂SO₄ under reflux. After dissolution, trivalent ⁴⁷Sc ions were separated from natural Ti using AG MP-50 cation exchange resin. The recovered ⁴⁷Sc was then purified using CHELEX 100 ion exchange resin. The average decay-corrected two-step ⁴⁷Sc recovery (n = 9) was (77 ± 7)%. A radiolabeling yield of > 99.9% of [⁴⁷Sc]Sc-DOTATOC (0.384 mg in 0.3 mL) was achieved using 1.7 MBq of ⁴⁷Sc. Blocking studies using Octreotide illustrated receptor-mediated uptake of [⁴⁷Sc]Sc-DOTATOC in AR42J cells.

Conclusions

⁴⁷Sc can be produced via the ⁴⁸Ti(γ,p)⁴⁷Sc reaction and separated from natural Ti targets with a yield and radiochemical purity suitable for radiolabeling of peptides for in vitro studies. The data in this work supports the potential use of eLINACs for studies of photonuclear production of medical radionuclides and the future development of high-intensity eLINAC facilities capable of producing relevant quantities of carrier-free radionuclides currently inaccessible via routine production pathways or limited due to costly enriched targets.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0515-8) contains supplementary material, which is available to authorized users.

Radioactive Main Group and Rare Earth Metals for Imaging and Therapy

Radiometals possess an exceptional breadth of decay properties and have been applied to medicine with great success for several decades. The majority of current clinical use involves diagnostic procedures, which use either positron-emission tomography (PET) or single-photon imaging to detect anatomic abnormalities that are difficult to visualize using conventional imaging techniques (e.g., MRI and X-ray). The potential of therapeutic radiometals has more recently been realized and relies on ionizing radiation to induce irreversible DNA damage, resulting in cell death. In both cases, radiopharmaceutical development has been largely geared toward the field of oncology; thus, selective tumor targeting is often essential for efficacious drug use. To this end, the rational design of four-component radiopharmaceuticals has become popularized. This Review introduces fundamental concepts of drug design and applications, with particular emphasis on bifunctional chelators (BFCs), which ensure secure consolidation of the radiometal and targeting vector and are integral for optimal drug performance. Also presented are detailed accounts of production, chelation chemistry, and biological use of selected main group and rare earth radiometals.

Studies towards elucidating the potential of 5,10,15,20-tetrakis(p-carboxy-methyleneoxyphenyl)porphyrin as a theranostic agent for applications in PET and PDT

Porphyrins, owing to their inherent tendency to accumulate in tumorous lesions, are considered suitable for developing agents for theranostic applications involving tumor diagnosis and targeted tumor therapy. The aim of the present work is to study the potential of a porphyrin derivative namely, 5,10,15,20-tetrakis(p-carboxymethyleneoxyphenyl)porphyrin (SPTA) as a theranostic agent for applications in positron emission tomography (PET) and photodynamic therapy (PDT). SPTA was synthesized in-house following a three-step reaction process and characterized by using spectroscopic techniques, viz. UV-vis, FT-IR, ¹H-NMR and ¹³C-NMR spectroscopy, as well as by mass spectrometry. SPTA was labeled with ⁶⁸Ga, a generator produced PET radioisotope, and the radiolabeled product was characterized by HPLC. The ⁶⁸Ga-SPTA complex was prepared with a radiochemical purity of >95% under optimized conditions. The diagnostic potential of ⁶⁸Ga-SPTA was evaluated by cell uptake studies in two different tumor cell lines (HT1080 and A549) which revealed the affinity of ⁶⁸Ga-SPTA towards the cancer cells. Biodistribution studies carried out in Swiss mice bearing fibrosarcoma tumors exhibited the accumulation of the radiotracer in the tumor. The therapeutic potential of SPTA was evaluated by determining its photo-cytotoxicity employing the MTT assay in HT1080 and A549 cell lines using three different light doses, which indicated the significant cytotoxicity of SPTA in the presence of light. The present study indicates the possible potential of SPTA in radionuclide imaging as well as in photodynamic therapy (PDT) thus confirming the promising theranostic nature of this porphyrin derivative.

Targeted α Therapies for the Treatment of Bone Metastases

The skeleton is the target tissue for many types of tumors, and, recently, the survival of patients with prostate cancer metastasis has been increased using α-emitting drugs known as targeted α therapies. The use of α-radiopharmaceuticals in medicine was hypothesized at the beginning of the nineteenth century after the observation that α-radionuclides were associated with high cell-killing energy and low tissue penetration in healthy tissues. In the prostate cancer (PC) scenario, current research suggests that this class of radiopharmaceuticals has limited toxicity, and that the mechanism of action does not overlap with pre-existing drugs, allowing us to extend therapeutic armaments and address medical oncology towards personalized and precision medicine. Ongoing studies may extend these benefits also to bone metastases deriving from other neoplasms. The aim of this review is to summarize the current research on targeted α therapies and try to identify the right patient to be treated in the right time in order to integrate in these medications in the every-day clinical practice.

Scale-up of high specific activity 186gRe production using graphite-encased thick 186W targets and demonstration of an efficient target recycling process

Production of high specific activity 186gRe is of interest for development of theranostic radiopharmaceuticals. Previous studies have shown that high specific activity 186gRe can be obtained by cyclotron irradiation of enriched 186W via the 186W(d,2n)186gRe reaction, but most irradiations were conducted at low beam currents and for short durations. In this investigation, enriched 186W metal targets were irradiated at high incident deuteron beam currents to demonstrate production rates and contaminants produced when using thick targets. Full-stopping thick targets, as determined using SRIM, were prepared by uniaxial pressing of powdered natural abundance W metal or 96.86% enriched 186W metal encased between two layers of graphite flakes for target material stabilization. An assessment of structural integrity was made on each target preparation. To assess the performance of graphite-encased thick 186W metal targets, along with the impact of encasing on the separation chemistry, targets were first irradiated using a 22 MeV deuteron beam for 10 min at 10, 20, and 27 μA, with an estimated nominal deuteron energy of 18.7 MeV on the 186W target material (after energy degradation correction from top graphite layer). Gamma-ray spectrometry was performed post EOB on all targets to assess production yields and radionuclidic byproducts. The investigation also evaluated a method to recover and recycle enriched target material from a column isolation procedure. Material composition analyses of target materials, pass-through/wash solutions and recycling process isolates were conducted with SEM, FTIR, XRD, EDS and ICP-MS spectrometry. To demonstrate scaled-up production, a graphite-encased 186W target made from recycled 186W was irradiated for ~2 h with 18.7 MeV deuterons at a beam current of 27 μA to provide 0.90 GBq (24.3 mCi) of 186gRe, decay-corrected to the end of bombardment. ICP-MS analysis of the isolated 186gRe solution provided data that indicated the specific activity of 186gRe in this scaled-up production run was 2.6±0.5 GBq/μg (70±10 Ci/mg).

Drug Discovery by Molecular Imaging and Monitoring Therapy Response in Lymphoma

Molecular imaging allows a noninvasive assessment of biochemical and biological processes in living subjects. Treatment strategies for malignant lymphoma depend on histology and tumor stage. For the last two decades, molecular imaging has been the mainstay diagnostic test for the staging of malignant lymphoma and the assessment of response to treatment. This technology enhances our understanding of disease and drug activity during preclinical and clinical drug development. Here, we review molecular imaging applications in drug development, with an emphasis on oncology. Monitoring and assessing the efficacy of anti-cancer therapies in preclinical or clinical models are essential and the multimodal molecular imaging approach may represent a new stage for pharmacologic development in cancer. Monitoring the progress of lymphoma therapy with imaging modalities will help patients. Identifying and addressing key challenges is essential for successful integration of molecular imaging into the drug development process. In this review, we highlight the general usefulness of molecular imaging in drug development and radionuclide-based reporter genes. Further, we discuss the different molecular imaging modalities for lymphoma therapy and their preclinical and clinical applications.

The Beginning and Development of the Theranostic Approach in Nuclear Medicine, as Exemplified by the Radionuclide Pair 86Y and 90Y

In the context of radiopharmacy and molecular imaging, the concept of theranostics entails a therapy-accompanying diagnosis with the aim of a patient-specific treatment. Using the adequate diagnostic radiopharmaceutical, the disease and the state of the disease are verified for an individual patient. The other way around, it verifies that the radiopharmaceutical in hand represents a target-specific and selective molecule: the "best one" for that individual patient. Transforming diagnostic imaging into quantitative dosimetric information, the optimum radioactivity (expressed in maximum radiation dose to the target tissue and tolerable dose to healthy organs) of the adequate radiotherapeutical is applied to that individual patient. This theranostic approach in nuclear medicine is traced back to the first use of the radionuclide pair 86Y/90Y, which allowed a combination of PET and internal radiotherapy. Whereas the β-emitting therapeutic radionuclide 90Y (t½ = 2.7 d) had been available for a long time via the 90Sr/90Y generator system, the β⁺ emitter 86Y (t½ = 14.7 h) had to be developed for medical application. A brief outline of the various aspects of radiochemical and nuclear development work (nuclear data, cyclotron irradiation, chemical processing, quality control, etc.) is given. In parallel, the paper discusses the methodology introduced to quantify molecular imaging of 86Y-labelled compounds in terms of multiple and long-term PET recordings. It highlights the ultimate goal of radiotheranostics, namely to extract the radiation dose of the analogue 90Y-labelled compound in terms of mGy or mSv per MBq 90Y injected. Finally, the current and possible future development of theranostic approaches based on different PET and therapy nuclides is discussed.

47Sc production development by cyclotron irradiation of 48Ca

The therapeutic radionuclide ⁴⁷Sc was produced through the ⁴⁸Ca(p,2n) channel on a proton beam accelerator. The obtained results show that the optimum proton energies are in the range of 24-17 MeV, giving the possibility to produce ⁴⁷Sc radionuclide containing 7.4% of ⁴⁸Sc. After activation, the powdery CaCO₃ target material was dissolved in HCl and scandium isotopes were isolated from the targets. The performed separation experiments indicate that, due to the simplicity of the operations and the chemical purity of the obtained ⁴⁷Sc the best separation process is when scandium radioisotopes are separated on the 0.2 µm filter.

47Sc as useful β--emitter for the radiotheragnostic paradigm: a comparative study of feasible production routes

Background

Radiotheragnostics 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.

Results

Up 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.

Conclusion

The 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 material

The online version of this article (doi:10.1186/s41181-017-0024-x) contains supplementary material, which is available to authorized users.

Theoretical estimation of 64Cu production with neutrons emitted during 18F production with a 30MeV medical cyclotron

PURPOSE

This work presents the theoretical estimation of a combined production of ¹⁸F and ⁶⁴Cu isotopes for PET applications. ⁶⁴Cu production is induced in a secondary target by neutrons emitted during a routine ¹⁸F production with a 30MeV cyclotron: protons are used to produce ¹⁸F by means of the ¹⁸O(p,n)¹⁸F reaction on a [¹⁸O]-H₂O target (primary target) and the emitted neutrons are used to produce ⁶⁴Cu by means of the ⁶⁴Zn(n,p)⁶⁴Cu reaction on enriched zinc target (secondary target).

METHODS

Monte Carlo simulations were carried out using Monte Carlo N Particle eXtended (MCNPX) code to evaluate flux and energy spectra of neutrons produced in the primary (Be+[¹⁸O]-H₂O) target by protons and the attenuation of neutron flux in the secondary target. ⁶⁴Cu yield was estimated using an analytical approach based on both TENDL-2015 data library and experimental data selected from EXFOR database.

RESULTS

Theoretical evaluations indicate that about 3.8 MBq/μA of ⁶⁴Cu can be obtained as a secondary, 'side' production with a 30MeV cyclotron, for 2h of irradiation of a proper designed zinc target. Irradiating for 2h with a proton current of 120 μA, a yield of about 457 MBq is expected. Moreover, the most relevant contaminants result to be ^63,65Zn, which can be chemically separated from ⁶⁴Cu contrarily to what happens with proton irradiation of an enriched ⁶⁴Ni target, which provides ⁶⁴Cu mixed to other copper isotopes as contaminants.

CONCLUSIONS

The theoretical study discussed in this paper evaluates the potential of the combined production of ¹⁸F and ⁶⁴Cu for medical purposes, irradiating a properly designed target with 30MeV protons. Interesting yields of ⁶⁴Cu are obtainable and the estimation of contaminants in the irradiated zinc target is discussed.

Characterization of the distribution, retention, and efficacy of internal radiation of 188Re-lipid nanocapsules in an immunocompromised human glioblastoma model

Internal radiation strategies hold great promise for glioblastoma (GB) therapy. We previously developed a nanovectorized radiotherapy that consists of lipid nanocapsules loaded with a lipophilic complex of Rhenium-188 (LNC188Re-SSS). This approach resulted in an 83 % cure rate in the 9L rat glioma model, showing great promise. The efficacy of LNC188Re-SSS treatment was optimized through the induction of a T-cell immune response in this model, as it is highly immunogenic. However, this is not representative of the human situation where T-cell suppression is usually encountered in GB patients. Thus, in this study, we investigated the efficacy of LNC188Re-SSS in a human GB model implanted in T-cell deficient nude mice. We also analyzed the distribution and tissue retention of LNC188Re-SSS. We observed that intratumoral infusion of LNCs by CED led to their complete distribution throughout the tumor and peritumoral space without leakage into the contralateral hemisphere except when large volumes were used. Seventy percent of the 188Re-SSS activity was present in the tumor region 24 h after LNC188Re-SSS injection and no toxicity was observed in the healthy brain. Double fractionated internal radiotherapy with LNC188Re-SSS triggered survival responses in the immunocompromised human GB model with a cure rate of 50 %, which was not observed with external radiotherapy. In conclusion, LNC188Re-SSS can induce long-term survival in an immunosuppressive environment, highlighting its potential for GB therapy.

Therapeutic radionuclides in nuclear medicine: current and future prospects

The potential use of radionuclides in therapy has been recognized for many decades. A number of radionuclides, such as iodine-131 ((131)I), phosphorous-32 ((32)P), strontium-90 ((90)Sr), and yttrium-90 ((90)Y), have been used successfully for the treatment of many benign and malignant disorders. Recently, the rapid growth of this branch of nuclear medicine has been stimulated by the introduction of a number of new radionuclides and radiopharmaceuticals for the treatment of metastatic bone pain and neuroendocrine and other malignant or non-malignant tumours. Today, the field of radionuclide therapy is enjoying an exciting phase and is poised for greater growth and development in the coming years. For example, in Asia, the high prevalence of thyroid and liver diseases has prompted many novel developments and clinical trials using targeted radionuclide therapy. This paper reviews the characteristics and clinical applications of the commonly available therapeutic radionuclides, as well as the problems and issues involved in translating novel radionuclides into clinical therapies.

Monte Carlo Evaluation of Auger Electron-Emitting Theranostic Radionuclides

Several radionuclides used in medical imaging emit Auger electrons, which, depending on the targeting strategy, either may be exploited for therapeutic purposes or may contribute to an unintentional mean absorbed dose burden. In this study, the virtues of 12 Auger electron-emitting radionuclides were evaluated in terms of cellular S values in concentric and eccentric cell-nucleus arrangements and by comparing their dose-point kernels.

METHODS

The Monte Carlo code PENELOPE was used to transport the full particulate spectrum of (67)Ga, (80m)Br, (89)Zr, (90)Nb, (99m)Tc, (111)In, (117m)Sn, (119)Sb, (123)I, (125)I, (195m)Pt, and (201)Tl by means of event-by-event simulations. Cellular S values were calculated for varying cell and nucleus radii, and the effects of cell eccentricity on S values were evaluated. Dose-point kernels were determined up to 30 μm. Energy deposition at DNA scales was also compared with an α emitter, (223)Ra.

RESULTS

PENELOPE-determined S values were generally within 10% of MIRD values when the source and target regions strongly overlapped, that is, S(nucleus←nucleus) configurations, but greater differences were noted for S(nucleus←cytoplasm) and S(nucleus←cell surface) configurations. Cell eccentricity had the greatest effect when the nucleus was small, compared with the cell size, and when the radiation sources were on the cell surface. Dose-point kernels taken together with the energy spectra of the radionuclides can account for some of the differences in energy deposition patterns between the radionuclides. The energy deposition of most Auger electron emitters at DNA scales of 2 nm or less exceeded that of a monoenergetic 5.77-MeV α particle, but not for (223)Ra.

CONCLUSION

A single-cell dosimetric approach is required to evaluate the efficacy of individual radionuclides for theranostic purposes, taking cell geometry into account, with internalizing and noninternalizing targeting strategies.

Peptide receptor radionuclide therapy: an overview

Peptide receptor radionuclide therapy (PRRT) is a site-directed targeted therapeutic strategy that specifically uses radiolabeled peptides as biological targeting vectors designed to deliver cytotoxic levels of radiation dose to cancer cells, which overexpress specific receptors. Interest in PRRT has steadily grown because of the advantages of targeting cellular receptors in vivo with high sensitivity as well as specificity and treatment at the molecular level. Recent advances in molecular biology have not only stimulated advances in PRRT in a sustainable manner but have also pushed the field significantly forward to several unexplored possibilities. Recent decades have witnessed unprecedented endeavors for developing radiolabeled receptor-binding somatostatin analogs for the treatment of neuroendocrine tumors, which have played an important role in the evolution of PRRT and paved the way for the development of other receptor-targeting peptides. Several peptides targeting a variety of receptors have been identified, demonstrating their potential to catalyze breakthroughs in PRRT. In this review, the authors discuss several of these peptides and their analogs with regard to their applications and potential in radionuclide therapy. The advancement in the availability of combinatorial peptide libraries for peptide designing and screening provides the capability of regulating immunogenicity and chemical manipulability. Moreover, the availability of a wide range of bifunctional chelating agents opens up the scope of convenient radiolabeling. For these reasons, it would be possible to envision a future where the scope of PRRT can be tailored for patient-specific application. While PRRT lies at the interface between many disciplines, this technology is inextricably linked to the availability of the therapeutic radionuclides of required quality and activity levels and hence their production is also reviewed.

The copper radioisotopes: a systematic review with special interest to 64Cu

Copper (Cu) is an important trace element in humans; it plays a role as a cofactor for numerous enzymes and other proteins crucial for respiration, iron transport, metabolism, cell growth, and hemostasis. Natural copper comprises two stable isotopes, (63)Cu and (65)Cu, and 5 principal radioisotopes for molecular imaging applications ((60)Cu, (61)Cu, (62)Cu, and (64)Cu) and in vivo targeted radiation therapy ((64)Cu and (67)Cu). The two potential ways to produce Cu radioisotopes concern the use of the cyclotron or the reactor. A noncopper target is used to produce noncarrier-added Cu thanks to a chemical separation from the target material using ion exchange chromatography achieving a high amount of radioactivity with the lowest possible amount of nonradioactive isotopes. In recent years, Cu isotopes have been linked to antibodies, proteins, peptides, and nanoparticles for preclinical and clinical research; pathological conditions that influence Cu metabolism such as Menkes syndrome, Wilson disease, inflammation, tumor growth, metastasis, angiogenesis, and drug resistance have been studied. We aim to discuss all Cu radioisotopes application focusing on (64)Cu and in particular its form (64)CuCl2 that seems to be the most promising for its half-life, radiation emissions, and stability with chelators, allowing several applications in oncological and nononcological fields.

Future prospects for SPECT imaging using the radiolanthanide terbium-155 - production and preclinical evaluation in tumor-bearing mice

INTRODUCTION

We assessed the suitability of the radiolanthanide (155)Tb (t1/2=5.32 days, Eγ=87 keV (32%), 105keV (25%)) in combination with variable tumor targeted biomolecules using preclinical SPECT imaging.

METHODS

(155)Tb was produced at ISOLDE (CERN, Geneva, Switzerland) by high-energy (~1.4 GeV) proton irradiation of a tantalum target followed by ionization and on-line mass separation. (155)Tb was separated from isobar and pseudo-isobar impurities by cation exchange chromatography. Four tumor targeting molecules - a somatostatin analog (DOTATATE), a minigastrin analog (MD), a folate derivative (cm09) and an anti-L1-CAM antibody (chCE7) - were radiolabeled with (155)Tb. Imaging studies were performed in nude mice bearing AR42J, cholecystokinin-2 receptor expressing A431, KB, IGROV-1 and SKOV-3ip tumor xenografts using a dedicated small-animal SPECT/CT scanner.

RESULTS

The total yield of the two-step separation process of (155)Tb was 86%. (155)Tb was obtained in a physiological l-lactate solution suitable for direct labeling processes. The (155)Tb-labeled tumor targeted biomolecules were obtained at a reasonable specific activity and high purity (>95%). (155)Tb gave high quality, high resolution tomographic images. SPECT/CT experiments allowed excellent visualization of AR42J and CCK-2 receptor-expressing A431 tumors xenografts in mice after injection of (155)Tb-DOTATATE and (155)Tb-MD, respectively. The relatively long physical half-life of (155)Tb matched in particular the biological half-lives of (155)Tb-cm09 and (155)Tb-DTPA-chCE7 allowing SPECT imaging of KB tumors, IGROV-1 and SKOV-3ip tumors even several days after administration.

CONCLUSIONS

The radiolanthanide (155)Tb may be of particular interest for low-dose SPECT prior to therapy with a therapeutic match such as the β(-)-emitting radiolanthanides (177)Lu, (161)Tb, (166)Ho, and the pseudo-radiolanthanide (90)Y.

Promises of cyclotron-produced 44Sc as a diagnostic match for trivalent β--emitters: in vitro and in vivo study of a 44Sc-DOTA-folate conjugate

In recent years, implementation of (68)Ga-radiometalated peptides for PET imaging of cancer has attracted the attention of clinicians. Herein, we propose the use of (44)Sc (half-life = 3.97 h, average β(+) energy [Eβ(+)av] = 632 keV) as a valuable alternative to (68)Ga (half-life = 68 min, Eβ(+)av = 830 keV) for imaging and dosimetry before (177)Lu-based radionuclide therapy. The aim of the study was the preclinical evaluation of a folate conjugate labeled with cyclotron-produced (44)Sc and its in vitro and in vivo comparison with the (177)Lu-labeled pendant.

METHODS

(44)Sc was produced via the (44)Ca(p,n)(44)Sc nuclear reaction at a cyclotron (17.6 ± 1.8 MeV, 50 μA, 30 min) using an enriched (44)Ca target (10 mg (44)CaCO3, 97.00%). Separation from the target material was performed by a semiautomated process using extraction chromatography and cation exchange chromatography. Radiolabeling of a DOTA-folate conjugate (cm09) was performed at 95°C within 10 min. The stability of (44)Sc-cm09 was tested in human plasma. (44)Sc-cm09 was investigated in vitro using folate receptor-positive KB tumor cells and in vivo by PET/CT imaging of tumor-bearing mice

RESULTS

Under the given irradiation conditions, (44)Sc was obtained in a maximum yield of 350 MBq at high radionuclide purity (>99%). Semiautomated isolation of (44)Sc from (44)Ca targets allowed formulation of up to 300 MBq of (44)Sc in a volume of 200-400 μL of ammonium acetate/HCl solution (1 M, pH 3.5-4.0) within 10 min. Radiolabeling of cm09 was achieved with a radiochemical yield of greater than 96% at a specific activity of 5.2 MBq/nmol. In vitro, (44)Sc-cm09 was stable in human plasma over the whole time of investigation and showed folate receptor-specific binding to KB tumor cells. PET/CT images of mice injected with (44)Sc-cm09 allowed excellent visualization of tumor xenografts. Comparison of cm09 labeled with (44)Sc and (177)Lu revealed almost identical pharmacokinetics.

CONCLUSION

This study presents a high-yield production and efficient separation method of (44)Sc at a quality suitable for radiolabeling of DOTA-functionalized biomolecules. An in vivo proof-of-concept study using a DOTA-folate conjugate demonstrated the excellent features of (44)Sc for PET imaging. Thus, (44)Sc is a valid alternative to (68)Ga for imaging and dosimetry before (177)Lu-radionuclide tumor therapy.

The necessity of nuclear reactors for targeted radionuclide therapies

Nuclear medicine has been contributing towards personalized therapies. Nuclear reactors are required for the working horses of both diagnosis and treatment, i.e., Tc-99m and I-131. In fact, reactors will remain necessary to fulfill the demand for a variety of radionuclides and are essential in the expanding field of targeted radionuclide therapies for cancer. However, the main reactors involved in the global supply are ageing and expected to shut down before 2025. Therefore, the fields of (nuclear) medicine, nuclear industry and politics share a global responsibility, faced with the task to secure future access to suitable nuclear reactors. At the same time, alternative production routes should be industrialized. For this, a coordinating entity should be put into place.

A Bridge not too Far: Personalized Medicine with the use of Theragnostic Radiopharmaceuticals

This article deals primarily with the selection criteria, production, and the nuclear, physical, and chemical properties of certain dual-purpose radionuclides, including those that are currently being used, or studied and evaluated, and those that warrant future investigations. Various scientific and practical issues related to the production and availability of these radionuclides is briefly addressed. At brookhaven national laboratory (BNL), we have developed a paradigm that involves specific individual ‘dual-purpose’ radionuclides or radionuclide pairs with emissions suitable for both imaging and therapy, and which when molecularly (selectively) targeted using appropriate carriers, would allow pre-therapy low-dose imaging plus higher-dose therapy in the same patient. We have made an attempt to sort out and organize a number of such theragnostic radionuclides and radionuclide pairs that may thus potentially bring us closer to the age-long dream of personalized medicine for performing tailored low-dose molecular imaging (SPECT/CT or PET/CT) to provide the necessary pretherapy information on biodistribution, dosimetry, the limiting or critical organ or tissue, and the maximum tolerated dose (MTD), etc., followed by performing higher-dose targeted molecular therapy in the same patient with the same radiopharmaceutical. As an example, our preclinical and clinical studies with the theragnostic radionuclide Sn-117m are covered in somewhat greater detail.

A troublesome problem that remains yet to be fully resolved is the lack of availability, in sufficient quantities and at reasonable cost, of a majority of the best candidate theragnostic radionuclides in a no-carrier-added (NCA) form. In this regard, a summary description of recently developed new or modified methods at BNL for the production of five theragnostic radionuclide/radionuclide pair items, whose nuclear, physical, and chemical characteristics seem to show promise for therapeutic oncology and for treating other disorders that respond to radionuclide therapy, is provided.

How to cite this article

Srivastava SC. A Bridge not too Far: Personalized Medicine with the use of Theragnostic Radiopharmaceuticals. J Postgrad Med Edu Res 2013;47(1):31-46.