Re-emergence of the important role of radionuclide generators to provide diagnostic and therapeutic radionuclides to meet future research and clinical demands

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.

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

¹⁷⁷Lu has sprung as a promising radionuclide for targeted therapy. The low soft tissue penetration of its β^- emission results in very efficient energy deposition in small-size tumours. Because of this, ¹⁷⁷Lu is used in the treatment of neuroendocrine tumours and is also clinically approved for prostate cancer therapy. In this work, we report a separation method that achieves the challenging separation of the physically and chemically identical nuclear isomers, ^177mLu and ¹⁷⁷Lu. The separation method combines the nuclear after-effects of the nuclear decay, the use of a very stable chemical complex and a chromatographic separation. Based on this separation concept, a new type of radionuclide generator has been devised, in which the parent and the daughter radionuclides are the same elements. The ^177mLu/¹⁷⁷Lu radionuclide generator provides a new production route for the therapeutic radionuclide ¹⁷⁷Lu and can bring significant growth in the research and development of ¹⁷⁷Lu based pharmaceuticals.

Radiolabeled enzyme inhibitors and binding agents targeting PSMA: Effective theranostic tools for imaging and therapy of prostate cancer

Because of the broad incidence, morbidity and mortality associated with prostate-derived cancer, the development of more effective new technologies continues to be an important goal for the accurate detection and treatment of localized prostate cancer, lymphatic involvement and metastases. Prostate-specific membrane antigen (PSMA; Glycoprotein II) is expressed in high levels on prostate-derived cells and is an important target for visualization and treatment of prostate cancer. Radiolabeled peptide targeting technologies have rapidly evolved over the last decade and have focused on the successful development of radiolabeled small molecules that act as inhibitors to the binding of the N-acetyl-l-aspartyl-l-glutamate (NAAG) substrate to the PSMA molecule. A number of radiolabeled PSMA inhibitors have been described in the literature and labeled with SPECT, PET and therapeutic radionuclides. Clinical studies with these agents have demonstrated the improved potential of PSMA-targeted PET imaging agents to detect metastatic prostate cancer in comparison with conventional imaging technologies. Although many of these agents have been evaluated in humans, by far the most extensive clinical literature has described use of the ⁶⁸Ga and ¹⁷⁷Lu agents. This review describes the design and development of these agents, with a focus on the broad clinical introduction of PSMA targeting motifs labeled with ⁶⁸Ga for PET-CT imaging and ¹⁷⁷Lu for therapy. In particular, because of availability from the long-lived ⁶⁸Ge (T_1/2=270days)/⁶⁸Ga (T_1/2=68min) generator system and increasing availability of PET-CT, the ⁶⁸Ga-labeled PSMA targeted agent is receiving widespread interest and is one of the fastest growing radiopharmaceuticals for PET-CT imaging.

Preparation of [(68)Ga]PSMA-11 for PET-CT imaging using a manual synthesis module and organic matrix based (68)Ge/(68)Ga generator

INTRODUCTION

[(68)Ga]PSMA-11 is a relatively recently introduced radiopharmaceutical for PET-CT imaging of prostate cancer patients. The availability of (68)Ge/(68)Ga generator and PSMA-11 ligand from commercial sources is facilitating the production of the radiopharmaceutical in-house. This paper describes our experience on the preparation of ~200 batches of [(68)Ga]PSMA-11 for conducting PET-CT imaging in patients suspected/suffering from prostate cancer.

METHODS

The radiosynthesis of [(68)Ga]PSMA-11 was done in a hospital based nuclear medicine department using (68)Ge/(68)Ga generator and a manual synthesis module, both supplied by Isotope Technologies Garching (ITG), Germany. The production involved the reaction of 5μg (5.3nmol) of PSMA-11 ligand in 1 ml of 0.25M sodium acetate buffer with 4ml of (68)GaCl3 in 0.05M HCl for 5min at 105°C; followed by purification in a C18 cartridge and collection through a 0.22μm pore size filter.

RESULTS

The radiochemical yields obtained were consistently high, 93.19%±3.76%, and there was hardly any batch failure. The radiochemical purity of the product was >99% and the product was stable for over 2h; however it was used in patients immediately after preparation. About 200 batches of [(68)Ga]PSMA-11 were prepared during the period and more than 300 patients received the tracer during the 14months of study. No adverse reaction was observed in any of the patients and the image qualities were consistent with literature reports.

CONCLUSION

[(68)Ga]PSMA-11 with high radiochemical and radionuclidic purity is conveniently prepared by using a (68)Ge/(68)Ga generator and manual synthesis module. The radiochemical yields are very high; and activity sufficient for 3-4 patients can be prepared in a single batch; multiple batches can be done on the same day and when needed after a gap of 1.5-2h.

Diversification of 99Mo/99mTc separation: non–fission reactor production of 99Mo as a strategy for enhancing 99mTc availability

This paper discusses the benefits of obtaining (99m)Tc from non-fission reactor-produced low-specific-activity (99)Mo. This scenario is based on establishing a diversified chain of facilities for the distribution of (99m)Tc separated from reactor-produced (99)Mo by (n,γ) activation of natural or enriched Mo. Such facilities have expected lower investments than required for the proposed chain of cyclotrons for the production of (99m)Tc. Facilities can receive and process reactor-irradiated Mo targets then used for extraction of (99m)Tc over a period of 2 wk, with 3 extractions on the same day. Estimates suggest that a center receiving 1.85 TBq (50 Ci) of (99)Mo once every 4 d can provide 1.48-3.33 TBq (40-90 Ci) of (99m)Tc daily. This model can use research reactors operating in the United States to supply current (99)Mo needs by applying natural (nat)Mo targets. (99)Mo production capacity can be enhanced by using (98)Mo-enriched targets. The proposed model reduces the loss of (99)Mo by decay and avoids proliferation as well as waste management issues associated with fission-produced (99)Mo.

An overview of radioisotope separation technologies for development of 188W/188Re radionuclide generators providing 188Re to meet future research and clinical demands

Separation technologies for ¹⁸⁸W/¹⁸⁸Re radionuclide generators.