Alternative chromatographic processes for no-carrier added 177Lu radioisotope separation: Part I. Multi-column chromatographic process for clinically applicable

Preliminary experiments to produce lutetium-177 in the TRR-1/M1 Thai research reactor

Lutetium-177 has emerged as a highly efficient radionuclide for medical applications, particularly in the field of targeted radionuclide therapy. Its production has been increasingly optimized through neutron activation techniques, which offer distinct advantages over alternative methods. Utilizing the TRR-1/M1 research reactor, which has been in operation for nearly six decades, provides a strategic opportunity for advancing domestic radioisotope production, thereby supporting the medical sector in Thailand. The TRR-1/M1 reactor, despite its operational age, continues to exhibit considerable potential for contributing to medical research and radioisotope development in Thailand. Preliminary experimental results, conducted at a flux of 1.42 × 1012 n/cm2/s demonstrated promising outcomes, even under operational constraints such as fuel management limitations. Notably, the direct neutron activation of natural lutetium oxide notably yielded a specific activity of 177Lu at 10.92 GBq/g (295.06 mCi/g) with a production yield of 44.8%, with projections reaching 222 GBq/g (6 Ci/g) after 40 days of neutron irradiation. In comparison, the indirect method, using natural ytterbium oxide as a precursor, achieved a maximum specific activity of 177Lu at 6.6 MBq/g (180.3 μCi/g) with a yield of 37.8% of a theoretical maximum of 17.6 MBq/g (476 μCi/g) after only 10 h of neutron activation. These results highlight the feasibility and promise of 177Lu radioisotope production in Thailand.

Preparation and Biodistribution Assessment of 177Lu-curcumin as a Possible Therapeutic Agent

Purpose

Curcumin as a potent anti-inflammatory and cancer-prevention molecule was labeled with n.c.a 177Lu. The combination of 177Lu as a theranostic agent and curcumin as an anti-cancer can be considered for nuclear medicine.

Methods

First, n.c.a 177Lu (specific activity = 48 Ci/mg) was prepared using the extraction chromatography method. Then, semi-empirical quantum chemical calculations were applied to get a deeper insight into the complexation reaction between Lu+ 3 and curcumin ligand. UV-Vis spectrophotometry was used for the determination of the metal-to-curcumin ratio. Subsequently, a mixture of (111-333 MBq) n.c.a 177Lu, 50 µL curcumin solution in ethanol, and 450 µL acetate buffer at pH = 5 was incubated for 1 h at 95 ºC. The Lu-curcumin complex chemical structure was characterized using IR spectroscopy. Finally, the prepared complex was analyzed by different quality control tests.

Results

Complexometry using UV-Vis studies showed a 1:2 ratio for Lutetium: curcumin complex which is in agreement with theoretical calculations. The IR-spectra analysis also confirmed the complex formation. The radiochemical purity of n.c.a 177Lu -curcumin was more than 95% as determined by radio-TLC. The stability of up to 48 h was observed for the prepared complex in serum. The partition coefficient was calculated for the compound (log P = -0.31). Evaluating biodistribution in tumoral mice exhibited high tumor uptake (%ID/gtissue = 2.03).

Conclusion

The promising results showed that n.c.a 177Lu-curcumin can be considered as a possible radiopharmaceutical agent for therapeutic applications.

Investigation of radiolabeling efficacy by enhancement of the chemical form of no carrier added 177Lu isolated by electro amalgamation process

BACKGROUND

Due to the suitable nuclear decay characteristics, 177Lu is an attractive radionuclide for various therapeutic applications. The non-carrier added form of 177Lu has drawn many attention because of its high specific activity needed in radiolabeling studies. There have been several separation methods for NCA 177Lu production.

OBJECTIVES

Among the various separation methods, the electro-amalgamation separation method has got a large potential for large scale production. Li presence is a significant problem in this separation method, which seriously affects the radiolabeling efficiency.

METHOD

In this study, Li was separated from the final product of electro-amalgamation separation by adding an ion-exchange chromatography column to the separation process.

RESULTS

NCA 177Lu was obtained by 84.09% ELM separation yield, 99.9% radionuclide purity and, 65 Ci/g specific activity. Then, 177Lu (177LuCl3 chemical form) was separated from Li using the ion exchange chromatography method by a separation yield of 94%. The obtained results of the radiolabeling efficacy studies showed that the radiochemical purity and radio-complex stability were significantly increased by separating of NCA 177Lu from Li.

CONCLUSION

This new separation setup consisting of two steps allows using 177Lu of such a favorable quality for labeling studies.

A Step-by-Step Guide for the Novel Radiometal Production for Medical Applications: Case Studies with 68Ga, 44Sc, 177Lu and 161Tb

The production of novel radionuclides is the first step towards the development of new effective radiopharmaceuticals, and the quality thereof directly affects the preclinical and clinical phases. In this review, novel radiometal production for medical applications is briefly elucidated. The production status of the imaging nuclide 44Sc and the therapeutic β--emitter nuclide 161Tb are compared to their more established counterparts, 68Ga and 177Lu according to their targetry, irradiation process, radiochemistry, and quality control aspects. The detailed discussion of these significant issues will help towards the future introduction of these promising radionuclides into drug manufacture for clinical application under Good Manufacturing Practice (GMP).

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.

Feasibility study for production and quality control of Yb-175 as a byproduct of no carrier added Lu-177 preparation for radiolabeling of DOTMP

Skeletal uptake of β^- emitters of DOTMP complexes is used for the bone pain palliation. In this study, two moderate energy β^- emitters, ¹⁷⁷Lu (T_1/2 = 6.7 days, E_βmax = 497 keV) and ¹⁷⁵Yb (T_1/2 = 4.2 days, E_βmax = 480 keV), are considered as potential agents for the development of the bone-seeking radiopharmaceuticals. Since the specific activity of the radiolabelled carrier molecules should be high, the non-carrier-added (NCA) radionuclides have an effective role in nuclear medicine. Many researchers have presented the synthesis of NCA ¹⁷⁷Lu. Among these separation techniques, extraction chromatography has been considered more capable than other methods. In this study, a new approach, in addition to production of NCA ¹⁷⁷Lu by EXC procedure is using pure ¹⁷⁵Yb that was usually considered as a waste material in this method but because of high radionuclidic purity of ¹⁷⁵Yb produced by this method we used it for radiolabeling as well as NCA ¹⁷⁷Lu. To obtain optimum conditions, some effective factors on separation of Lu/Yb by EXC were investigated. The NCA ¹⁷⁷Lu and pure ¹⁷⁵Yb were produced with radionuclidic purity of 99.99 and 99.97% respectively by irradiation of enriched ¹⁷⁶Yb target in thermal neutron flux of 5 × 10¹³ n/cm² s for 14 days. ¹⁷⁷Lu-DOTMP and ¹⁷⁵Yb-DOTMP were obtained with high radiochemical purities (> 95%) under optimized reaction conditions. Two radiolabeled complexes exhibited excellent stability at room temperature. Biodistribution studies in rats showed favorable selective skeletal uptake with rapid clearance from blood along with insignificant accumulation of activity in other non-target organs for two radiolabelled complexes.

Separation of radioisotopes of terbium from a europium target irradiated by 27 MeV α-particles

A method for obtaining 156, 155, 154m2, 154, 153Tb radiotracers by the irradiation of a europium oxide target of natural isotopic composition by 27 MeV α-particles is proposed. Terbium can be efficiently separated from bulk of europium by the reduction of the latter by zinc in an acidic solution and precipitation as EuSO4. The optimum Zn/Eu3+ and (NH4)2SO4/Eu3+ molar ratios are 20 and 3, respectively. Terbium is additionally purified from europium and gadolinium by extraction chromatography using LN Resin. It is demonstrated that optimum separation is attained in 0.6 M HNO3. The Tb/Eu separation coefficient was ~5·105. The yield of terbium was about 90%. Time of all steps was 1.5–2 h. The proposed procedure makes it possible to obtain no carrier added terbium radiotracers.

Production and quality control 177Lu (NCA)-DOTMP as a potential agent for bone pain palliation

Skeletal uptake of radiolabeled-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetramethylene phosphoric acid (e.g., 177Lu-DOTMP) complex, is used for bone pain palliation. The moderate energy of β-emitting 177Lu (T½ = 6.7 d, Eβmax = 497keV) has been considered as a potential radionuclide for development of the bone-seeking radiopharmaceutical. Since the specific activity of the radiolabeled carrier molecules should be high, the "no-carrier-added radionuclides" have sig-nificant roles in nuclear medicine. Many researchers illustrated no-carrier-added 177Lu production; among these separation techniques such as ion exchange chromatography, reversed phase ion-pair, and electrochemical method, extraction chromatography has been considered more capable than other methods. In order to optimize the conditions, some effective factors on separation of Lu/Yb were investigated by EXC. The NCA 177Lu, produced by this method, was mixed with 300 μl of DOTMP solution (20 mg in 1 mL of 0.5 M NaHCO3, pH = 8) and incu-bated under stirring at room temperature for 45 min. Radiochemical purity of the 177Lu-DOTMP complex was determined using radio-thin-layer chromatography (RTLC) method. The complex was injected to wild-type rats and biodistribution was then studied for seven days. The NCA 177Lu was produced with specific activ-ity of 48 Ci/mg and with a radinuclidic purity of 99.99% through irradiation of enriched 176Yb target (1 mg) in a thermal neutron flux of 4 × 1013 n.cm-2.s-1 for 14 days. 177Lu-DOTMP was obtained with high radiochemical purities (> 98%) under optimized reaction conditions. The radiolabeled complex exhibited excellent stability at room temperature. Biodistribution of the radiolabeled complex studies in rats showed favorable selective skeletal uptake with rapid clearance from blood along with insignificant accumulation within the other nontargeted organs.

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.

Production of (177)Lu for Targeted Radionuclide Therapy: Available Options

BACKGROUND

This review provides a comprehensive summary of the production of (177)Lu to meet expected future research and clinical demands. Availability of options represents the cornerstone for sustainable growth for the routine production of adequate activity levels of (177)Lu having the required quality for preparation of a variety of (177)Lu-labeled radiopharmaceuticals. The tremendous prospects associated with production of (177)Lu for use in targeted radionuclide therapy (TRT) dictate that a holistic consideration should evaluate all governing factors that determine its success.

METHODS

While both "direct" and "indirect" reactor production routes offer the possibility for sustainable (177)Lu availability, there are several issues and challenges that must be considered to realize the full potential of these production strategies.

RESULTS

This article presents a mini review on the latest developments, current status, key challenges and possibilities for the near future.

CONCLUSION

A broad understanding and discussion of the issues associated with (177)Lu production and processing approaches would not only ensure sustained growth and future expansion for the availability and use of (177)Lu-labeled radiopharmaceuticals, but also help future developments.

An electro-amalgamation approach to produce 175Yb suitable for radiopharmaceutical applications

175Yb is a prospective reactor produced radionuclide suitable for preparation of therapeutic radiopharmaceuticals. However, a major restraint in the use of 175Yb produced via the (n, γ) reaction, for therapeutic applications, is the presence of longer-lived 177Lu impurity which is co-produced along with 175Yb on irradiation of natural Yb2O3 target. A radiochemical separation procedure adopting electro-amalgamation approach for the removal of 177Lu impurity from 175Yb has been critically evaluated. The experimental parameters such as applied potential, electrolysis time and the pH of the electrolyte, affecting the electrochemical separation process, were studied and optimized. The developed radiochemical procedure was extensively tested for purification of up to 15 GBq of 175Yb. The purified 175Yb could be obtained in HCl medium with ∼95% yield. The 177Lu impurity could not be detected in the purified product and 175Yb was found suitable for the preparation of potential radiotherapeutic agents.

Specific radioactivity of neutron induced radioisotopes: assessment methods and application for medically useful 177Lu production as a case

The conventional reaction yield evaluation for radioisotope production is not sufficient to set up the optimal conditions for producing radionuclide products of the desired radiochemical quality. Alternatively, the specific radioactivity (SA) assessment, dealing with the relationship between the affecting factors and the inherent properties of the target and impurities, offers a way to optimally perform the irradiation for production of the best quality radioisotopes for various applications, especially for targeting radiopharmaceutical preparation. Neutron-capture characteristics, target impurity, side nuclear reactions, target burn-up and post-irradiation processing/cooling time are the main parameters affecting the SA of the radioisotope product. These parameters have been incorporated into the format of mathematical equations for the reaction yield and SA assessment. As a method demonstration, the SA assessment of ¹⁷⁷Lu produced based on two different reactions, ¹⁷⁶Lu (n,γ)¹⁷⁷Lu and ¹⁷⁶Yb (n,γ) ¹⁷⁷Yb (β^- decay) ¹⁷⁷Lu, were performed. The irradiation time required for achieving a maximum yield and maximum SA value was evaluated for production based on the ¹⁷⁶Lu (n,γ)¹⁷⁷Lu reaction. The effect of several factors (such as elemental Lu and isotopic impurities) on the ¹⁷⁷Lu SA degradation was evaluated for production based on the ¹⁷⁶Yb (n,γ) ¹⁷⁷Yb (β^- decay) ¹⁷⁷Lu reaction. The method of SA assessment of a mixture of several radioactive sources was developed for the radioisotope produced in a reactor from different targets.