Preparation of 99mTc-TRODAT-1 with high labeling yield in boiling water bath: a new formulation

68 Ga-Labelled Tropane Analogues for the Visualization of the Dopaminergic System

The development of radiometal-labelled pharmaceuticals for neuroimaging could offer great potential due to easier handling during labelling and availability through radionuclide generator systems. Nonetheless, to date, no such tracers are available for positron emission tomography, primarily owing to the challenge of crossing the blood-brain barrier (BBB) and loss of affinity through chelator attachment. We have prepared a variety of 68 Ga-labelled phenyltropanes showing that, through a simple hydrocarbon-linker, it is possible to introduce a chelator onto the lead structure while maintaining its high affinity for hDAT (human dopamine transporter) and simultaneously achieving adequate lipophilicity. One of the candidates, [68 Ga]Ga-HBED-hexadiyne-tropane, showed an IC50 value of 66 nM, together with a log D7.4 of 0.96. A μPET study in a hemi-parkinsonian rat model showed a fast wash-out of the tracer, and no specific uptake in the brain, thus implying an inability to penetrate the BBB.

In-house Preparation and Quality Control of Tc99m TRODAT 1 for Diagnostic Single-photon Emission Computed Tomography/Computed Tomography Imaging in Parkinson's Disease

Purpose of Study:

Loss of dopamine neurons in the brain is a characteristic feature of Parkinson's disease (PD). TRODAT-1 is a tropane derivative that binds to dopamine transporter (DAT) receptors. It can be used for noninvasive in vivo imaging of DAT receptors leading to the early detection of PD. The present study aims to optimize the in-house radiolabeling of TRODAT-1 with Tc-99 m in hospital radiopharmacy set up along with performing single-photon emission computed tomography/computed tomography imaging in patients with PD.

Materials and Methods:

Radiolabeling was performed through transchelation method. For optimization studies, varied amount of glucoheptonate (GHA) and stannous chloride was incubated with Tc-99 m for 10 min at room temperature. TRODAT-1 was added to the reaction mixture followed by incubation at 95°C for various time intervals. Phosphate buffer saline was added to maintain the pH of the final product. After performing the quality checks, whole-body imaging was performed to check the biodistribution in 4 patients at 1 h postinjection of 20–25 mCi (740–925 MBq) of Tc-99 m-TRODAT-1. Regional brain imaging was performed at 3–4 h. Clinical evaluation was done in control (n = 5) and in patients with PD (n = 5).

Results:

Radiolabeling yield of 100% was achieved by incubating TRODAT-1 with Tc-99 m GHA. All the quality control indicated the suitability of radiopharmaceutical for the intravenous administration. Good uptake of Tc-99 m TRODAT-1 was observed in the striatum of normal patients. However, decreased uptake was seen in patients with PD.

Conclusion:

Tc-99 m TRODAT-1 is a potential radiopharmaceutical for the diagnosis and staging PD which can be radiolabeled in-house with good yield leading to its easy availability.

Production and Clinical Applications of Radiopharmaceuticals and Medical Radioisotopes in Iran

During past 3 decades, nuclear medicine has flourished as vibrant and independent medical specialty in Iran. Since that time, more than 200 nuclear physicians have been trained and now practicing in nearly 158 centers throughout the country. In the same period, Tc-99m generators and variety of cold kits for conventional nuclear medicine were locally produced for the first time. Local production has continued to mature in robust manner while fulfilling international standards. To meet the ever-growing demand at the national level and with international achievements in mind, work for production of other Tc-99m-based peptides such as ubiquicidin, bombesin, octreotide, and more recently a kit formulation for Tc-99m TRODAT-1 for clinical use was introduced. Other than the Tehran Research Reactor, the oldest facility active in production of medical radioisotopes, there is one commercial and three hospital-based cyclotrons currently operational in the country. I-131 has been one of the oldest radioisotope produced in Iran and traditionally used for treatment of thyrotoxicosis and differentiated thyroid carcinoma. Since 2009, (131)I-meta-iodobenzylguanidine has been locally available for diagnostic applications. Gallium-67 citrate, thallium-201 thallous chloride, and Indium-111 in the form of DTPA and Oxine are among the early cyclotron-produced tracers available in Iran for about 2 decades. Rb-81/Kr-81m generator has been available for pulmonary ventilation studies since 1996. Experimental production of PET radiopharmaceuticals began in 1998. This work has culminated with development and optimization of the high-scale production line of (18)F-FDG shortly after installation of PET/CT scanner in 2012. In the field of therapy, other than the use of old timers such as I-131 and different forms of P-32, there has been quite a significant advancement in production and application of therapeutic radiopharmaceuticals in recent years. Application of (131)I-meta-iodobenzylguanidine for treatment of neuroblastoma, pheochromocytoma, and other neuroendocrine tumors has been steadily increasing in major academic university hospitals. Also (153)Sm-EDTMP, (177)Lu-EDTMP, (90)Y-citrate, (90)Y-hydroxyapatite colloid, (188/186)Re-sulfur colloid, and (188/186)Re-HEDP have been locally developed and now routinely available for bone pain palliation and radiosynovectomy. Cu-64 has been available to the nuclear medicine community for some time. With recent reports in diagnostic and therapeutic applications of this agent especially in the field of oncology, we anticipate an expansion in production and availability. The initiation of the production line for gallium-68 generator is one of the latest exciting developments. We are proud that Iran would be joining the club of few nations with production lines for this type of generator. There are also quite a number of SPECT and PET tracers at research and preclinical stage of development preliminarily introduced for possible future clinical applications. Availability of fluorine-18 tracers and gallium-68 generators would no doubt allow rapid dissemination of PET/CT practices in various parts of our large country even far from a cyclotron facility. Also, local production and availability of therapeutic radiopharmaceuticals are going to open exciting horizons in the field of nuclear medicine therapy. Given the available manpower, local infrastructure of SPECT imaging, and rapidly growing population, the production of Tc-99m generators and cold kit would continue to flourish in Iran.

Single vial freeze-dried TRODAT-1 kit: preparation and demonstration of clinical efficacy of [(99m)Tc]TRODAT-1 in Indian scenario

A single vial freeze-dried kit formulation for preparation of three patients' dose of [(99m)Tc]TRODAT-1 has been developed for early diagnosis of Parkinson's disease (PD). Kits were evaluated to ascertain the purity, stability and batch to batch variations. Preclinical evaluation was carried out in laboratory animals and clinical imaging was performed in human patients with PD. The labeling yield and purity of [(99m)Tc]TRODAT-1 was >90%. Swiss mice showed retention of [(99m)Tc]TRODAT-1 in the mid brain region. Clinical studies showed decreased striatal uptake with increasing severity of PD.