Separation of nuclear isomers for cancer therapeutic radionuclides based on nuclear decay after-effects

Removal of 177Lu from radioactive wastewater using Montmorillonite clay

Because radioactive 177Lu has a wide range of possible applications in radiopharmaceuticals, its removal from medical wastewater is particularly important. Montmorillonite clay was employed as an adsorbent in this study. Radioactive solutions were prepared with dilutions of the solution containing 177Lu at various concentrations, in which it was present as Lu3+. ULEGe detector in gamma spectrometer was used to measure 177Lu gamma rays emitted from the radioactive aqueous solutions. The results obtained showed that it is possible to remove 177Lu with a high yield of approximately 90% and it is effective in a period of 90 min under acidic conditions. From the findings, it can be argued that Montmorillonite clay, as an abundant and sustainable adsorbent, may also be suitable for the disposal of different radioactive medical wastes such as 131I and 99mTc, and also the technique based on gamma ray spectroscopy can be used for fast and practical measurements of radioactive material amounts.

Branched-Chain-Induced Host-Guest Assembly in Covalent-Organic Frameworks for Efficient Separation of No-Carrier-Added 177Lu

No-carrier-added (NCA) 177Lu is one of the most interesting nuclides for endoradiotherapy. With the dramatically rapid development of radiopharmaceutical and nuclear medicine, there is a sharp increase in the radionuclide supply of NCA 177Lu, which has formed a great challenge to current radiochemical separation constituted on classical materials. Hence, it is of vital importance to design and prepare new functional materials able of recovering 177Lu from an irradiated target with excellent efficacy. In this work, we proposed to apply noncovalent interactions to regulate the porous properties of covalent organic frameworks (COFs) by tuning the branched chain, rendering related covalent hosts different encapsulation abilities toward a flexible guest, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (P507). More interestingly, we found that the noncovalent interaction has a great effect on the host-guest complexes, which can achieve efficient NCA 177Lu separation with high recovery (95.97%). A systematic mechanism combined with experimental and theoretical investigations has confirmed that the noncovalent interactions between COFs and P507 play a preeminent role in adjusting the macroscopic properties of the host-guest complexes. This work not only uncovers that noncovalent interactions can affect the basic properties of covalent organic bonded materials but also provides a strategy for the design and preparation of other new moieties with specific functionalities.

Separation of 44mSc/44gSc Nuclear Isomers Based on After-Effects

44gSc presents a particular interest for application in nuclear medicine for positron emission tomography (PET) due to its favorable nuclear decay properties (t1/2 = 3.97 h, Emax = 1.47 MeV, branching ratio 94.3% β+). Its nuclear isomer 44mSc (t1/2 = 58.61 h) decays by isomeric transition (IT) into 44gSc, accompanied by ≈12% of conversion electron emission, which can cause a partial release of the daughter 44gSc from the chelate complex. A 13 MeV cyclotron at TRIUMF was used to produce both 44mSc and 44gSc via the natCa(p,n)44m,gSc reaction. A 44mSc/44gSc generator was designed by using a Strata C-18E cartridge. After several tested systems, a successful separation method was developed using DOTATOC as a chelator, a Strata C-18E cartridge as a generator column, and an elution solution of 0.1 M NH4-α-HIB. The yield of the generator with the daughter 44gSc release was equal to 9.8 ± 1.0% (or ≈80% per portion of conversion). This result shows the important role of after-effects in the design of radionuclide generators. Nuclear cross-section calculations were applied using the TALYS code to allow for the determination of the most promising alternative routes for 44mSc production, which will enable the development of a full-scale 44mSc/44gSc radionuclide generator based on after-effects.

Lutetium-177-Labeled Prostate-Specific Membrane Antigen-617 for Molecular Imaging and Targeted Radioligand Therapy of Prostate Cancer

Prostate-specific membrane antigen (PSMA) represents a promising target for PSMA-overexpressing diseases, especially prostate cancer-a common type of cancer among men worldwide. In response to the challenges in tackling prostate cancers, several promising PSMA inhibitors from a variety of molecular scaffolds (e.g., phosphorous-, thiol-, and urea-based molecules) have been developed. In addition, PSMA inhibitors bearing macrocyclic chelators have attracted interest due to their favorable pharmacokinetic properties. Recently, conjugating a small PSMA molecule inhibitor-bearing 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator, as exemplified by [177Lu]Lu-PSMA-617 could serve as a molecular imaging probe and targeted radioligand therapy (TRT) of metastatic castration resistant prostate cancer (mCRPC). Hence, studies related to mCRPC have drawn global attention. In this review, the recent development of PSMA ligand-617-labeled with 177Lu for the management of mCRPC is presented. Its molecular mechanism of action, safety, efficacy, and future direction are also described.

Status of the decay data for medical radionuclides: existing and potential diagnostic γ emitters, diagnostic β+ emitters and therapeutic radioisotopes

Recommended half-lives and specific well-defined emission energies and absolute emission probabilities are important input parameters that should be well-defined to assist in ensuring the diagnostic and therapeutic efficacy of individual radionuclides when applied in the field of nuclear medicine. Bearing in mind the nature of these requirements, approximately one hundred radionuclides have been considered and re-assessed as to whether their decay data are either adequately quantified, or require further in-depth measurements to improve their existing status and merit full re-evaluations of their decay schemes. The primary aim of such a review is to provide sufficient information on the existing and future requirements for such atomic and nuclear data.

Diagnostics and Therapeutics in Targeting HER2 Breast Cancer: A Novel Approach

Breast cancer is one of the most commonly occurring cancers in women globally and is the primary cause of cancer mortality in females. BC is highly heterogeneous with various phenotypic expressions. The overexpression of HER2 is responsible for 15-30% of all invasive BC and is strongly associated with malignant behaviours, poor prognosis and decline in overall survival. Molecular imaging offers advantages over conventional imaging modalities, as it provides more sensitive and specific detection of tumours, as these techniques measure the biological and physiological processes at the cellular level to visualise the disease. Early detection and diagnosis of BC is crucial to improving clinical outcomes and prognosis. While HER2-specific antibodies and nanobodies may improve the sensitivity and specificity of molecular imaging, the radioisotope conjugation process may interfere with and may compromise their binding functionalities. Aptamers are single-stranded oligonucleotides capable of targeting biomarkers with remarkable binding specificity and affinity. Aptamers can be functionalised with radioisotopes without compromising target specificity. The attachment of different radioisotopes can determine the aptamer's functionality in the treatment of HER2(+) BC. Several HER2 aptamers and investigations of them have been described and evaluated in this paper. We also provide recommendations for future studies with HER2 aptamers to target HER2(+) BC.

Modelling of the 177mLu/177Lu radionuclide generator

In order to determine the potential of ^177mLu/¹⁷⁷Lu radionuclide generator in ¹⁷⁷Lu production it is important to establish the technical needs that can lead to a clinically acceptable ¹⁷⁷Lu product quality. In this work, a model that includes all the processes and the parameters affecting the performance of the ^177mLu/¹⁷⁷Lu radionuclide generator has been developed. The model has been based on the use of a ligand to complex ^177mLu ions, followed by the separation of the freed ¹⁷⁷Lu ions. The dissociation kinetics of the Lu-ligand complex has been found to be the most crucial aspect governing the specific activity and ^177mLu content of the produced ¹⁷⁷Lu. The dissociation rate constants lower than 1*10^-11 s^-1 would be required to lead to onsite ¹⁷⁷Lu production with specific activity close to theoretical maximum of 4.1 TBq ¹⁷⁷Lu/mg Lu and with ^177mLu content of less than 0.01%. Lastly, the calculations suggest that more than one patient dose per week can be supplied for a period of up to 7 months on starting with the ^177mLu produced using 3 g Lu₂O₃ target with 60% ¹⁷⁶Lu enrichment. The requirements of the starting ^177mLu activity production needs to be adapted depending on the required patient doses, and the technical specifications of the involved ^177mLu-¹⁷⁷Lu separation process.

A Chelate-Free Nano-Platform for Incorporation of Diagnostic and Therapeutic Isotopes

PURPOSE

Using our chelate-free, heat-induced radiolabeling (HIR) method, we show that a wide range of metals, including those with radioactive isotopologues used for diagnostic imaging and radionuclide therapy, bind to the Feraheme (FH) nanoparticle (NP), a drug approved for the treatment of iron anemia.

MATERIAL AND METHODS

FH NPs were heated (120°C) with nonradioactive metals, the resulting metal-FH NPs were characterized by inductively coupled plasma mass spectrometry (ICP-MS), dynamic light scattering (DLS), and r1 and r2 relaxivities obtained by nuclear magnetic relaxation spectrometry (NMRS). In addition, the HIR method was performed with [90Y]Y3+, [177Lu]Lu3+, and [64Cu]Cu2+, the latter with an HIR technique optimized for this isotope. Optimization included modifying reaction time, temperature, and vortex technique. Radiochemical yield (RCY) and purity (RCP) were measured using size exclusion chromatography (SEC) and thin-layer chromatography (TLC).

RESULTS

With ICP-MS, metals incorporated into FH at high efficiency were bismuth, indium, yttrium, lutetium, samarium, terbium and europium (>75% @ 120 oC). Incorporation occurred with a small (less than 20%) but statistically significant increases in size and the r2 relaxivity. An improved HIR technique (faster heating rate and improved vortexing) was developed specifically for copper and used with the HIR technique and [64Cu]Cu2+. Using SEC and TLC analyses with [90Y]Y3+, [177Lu]Lu3+ and [64Cu]Cu2+, RCYs were greater than 85% and RCPs were greater than 95% in all cases.

CONCLUSION

The chelate-free HIR technique for binding metals to FH NPs has been extended to a range of metals with radioisotopes used in therapeutic and diagnostic applications. Cations with f-orbital electrons, more empty d-orbitals, larger radii, and higher positive charges achieved higher values of RCY and RCP in the HIR reaction. The ability to use a simple heating step to bind a wide range of metals to the FH NP, a widely available approved drug, may allow this NP to become a platform for obtaining radiolabeled nanoparticles in many settings.

Large-scale production of lutetium-177m for the 177mLu/177Lu radionuclide generator

In this work, ^177mLu has been produced by irradiation of natural Lu₂O₃ targets at the BR2 reactor (Mol, Belgium) and the obtained data together with literature values have been used to theoretically investigate the production of ^177mLu at different neutron fluxes, irradiation times and enrichment of ¹⁷⁶Lu. The irradiation time (t_max) needed to reach the maximum ^177mLu production has been found to change from 42, 12, 4 days with the increase in the thermal neutron flux from 2*10¹⁴, 8*10¹⁴, 2.5*10¹⁵ n cm^-2 s^-1, respectively while keeping the maximum ^177mLu activity unaffected. The results of our calculations suggest that 0.11 TBq ^177mLu with a specific activity of 0.3 TBq g^-1 Lu can be produced in a short irradiation time of 4 days using 1g of 84.44% ¹⁷⁶Lu enriched Lu₂O₃ and a thermal neutron flux of 2.5*10¹⁵ n cm^-2 s^-1.

Radionuclide generator-based production of therapeutic 177Lu from its long-lived isomer 177mLu

Background

In this work, a lutetium-177 (¹⁷⁷Lu) production method based on the separation of nuclear isomers, ^177mLu & ¹⁷⁷Lu, is reported. The ^177mLu-¹⁷⁷Lu separation is performed by combining the use of DOTA & DOTA-labelled peptide (DOTATATE) and liquid-liquid extraction.

Methods

The ^177mLu cations were complexed with DOTA & DOTATATE and kept at 77 K for periods of time to allow ¹⁷⁷Lu production. The freed ¹⁷⁷Lu ions produced via internal conversion of ^177mLu were then extracted in dihexyl ether using 0.01 M di-(2-ethylhexyl) phosphoric acid (DEHPA) at room temperature. The liquid-liquid extractions were performed periodically for a period up to 35 days.

Results

A maximum ¹⁷⁷Lu/^177mLu activity ratio of 3500 ± 500 was achieved with [^177mLu]Lu-DOTA complex, in comparison to ¹⁷⁷Lu/^177mLu activity ratios of 1086 ± 40 realized using [^177mLu]Lu-DOTATATE complex. The ¹⁷⁷Lu-^177mLu separation was found to be affected by the molar ratio of lutetium and DOTA. A ¹⁷⁷Lu/^177mLu activity ratio up to 3500 ± 500 was achieved with excess DOTA in comparison to ¹⁷⁷Lu/^177mLu activity ratio 1500 ± 600 obtained when lutetium and DOTA were present in molar ratio of 1:1. Further, the ¹⁷⁷Lu ion extraction efficiency, decreases from 95 ± 4% to 58 ± 2% in the presence of excess DOTA.

Conclusion

The reported method resulted in a ¹⁷⁷Lu/ ^177mLu activity ratio up to 3500 after the separation. This ratio is close to the lower end of ¹⁷⁷Lu/^177mLu activity ratios, attained currently during the direct route ¹⁷⁷Lu production for clinical applications (i.e. 4000–10,000). This study forms the basis for further extending the liquid-liquid extraction based ^177mLu-¹⁷⁷Lu separation in order to lead to a commercial ^177mLu/¹⁷⁷Lu radionuclide generator.

Electronic supplementary material

The online version of this article (10.1186/s41181-019-0064-5) contains supplementary material, which is available to authorized users.