1. Introduction
Assumed its half-life and decay scheme, 64Cu (T1/2 = 12.7 h, 17.4% b+, 39% b−, 43.6% EC) has the potential to serve a dual role in the development of molecular agents for PET imaging and radioimmunotherapy drugs in oncology [1] . In this study, small irradiations were performed, demonstrating the feasibility of 64Cu production by this method [2] [3] . 64Cu of a high specific activity in the form of copper chloride (CuCl2) was produced at the Radiopharmacy Cyclotron Unit of the Faculty of Medicine, UNAM by the 64Ni(p,n)64Cu reaction with 11 MeV protons as previously reported [1] . After radiochemical purification, the copper fraction was evaporated to dryness, and the metal was recovered with a physiological saline solution for injection [3] . The use of 64Cu has dramatically increased in the past decade and its production has now been reported by academic sources in the United States, Europe, and Japan [4] [5] [6] [7] .
Developing countries have been performing Emission Tomography (PET) scans, first animals and then with patients. Nearest PET of Mexico, it was at Los Angeles California University (UCLA). In Mexico the application of diagnostic technique began in an academic environment at UNAM in 2002. The institution few years later, began to research on animals, as well as provides studies to localize cancer at public [8] .
The first reported system for small animal imagining was developed by Pichler et al. [8] [9] and used the combination of lutetium oxyorthosilicate (LSO) and Avalanche Photon Diodes (APDs) which was the state of the art technology at this time. The system had an outer diameter of 120 mm and was placed inside the gradient of a 7-T magnetic resonance (MR) imagine scanner, while the radiofrequency coil had an outer diameter of 60 mm and was fitted inside the PET ring. Each detector had 19 × 19 mm2 crystal block and each block consisted of a 12 × 12 array of 1.5 × 1.5 × 4.5 mm3 LSO crystals, each crystal block was placed on a monolithic 3 × 3 APD. The system showed very good performance with no interference from the magnetic field and reported energy resolution of ~15%. All crystal pixels were clearly resolved, and success simultaneous mouse imagine was performed [9] [10] [11] .
A series of new hexadentate and pentadentate chelators were designed and synthetized as chelators 64Cu. The new chelators contain different types of donor groups and are expected to form neutral complexes with copper (II). This was aimed to detect and treat at the same time the cancer. Ewen Bodio et al. [12] . propose different compounds tetradentates, where the ligands are joint easily to 64Cu [13] .
The aim of this research was to evaluate the radiolabeling and biodistribution of a new nanocompound 64Cu-(acac)2/F-TiO2 [14] . The radioactive material was administered in three male Wistar rats to visualize biodistribution of this new nanoradio compound in the organs. This compound will be tested after biodistribution, in rats with specific tumors of cancer.
Across the world, it was tried chelating 64Cu-CuCl2 with molecules containing “d” metals of the periodic table through covalent bonds. In addition, porphyrin compounds, among others.
2. Methodology
Copper production was carried out in a cyclotron (Siemens Eclipse HP) via the reaction 64Ni (p, n) 64Cu 11 MeV proton using 64Ni and electrodeposited on a gold disc as a white solid. Three male Wistar rats (195 ± 18 g) were used to visualize the in vivo whole-body (WB) distribution of the radionuclide by microPET imaging with a Focus 120 instrument (Concorde Microsystems). A series of microPET images were acquired with the rats under gaseous anesthesia ((2 - 3)% isoflurane) 30 min after injections (p.i.) of 20 - 37 MBq of 64CuCl2. The procedure for labeled nanoparticles was performed using 20 μg of the nanocatalysts, which were dissolved in absolute ethanol placing them under constant stirring during 10 minutes at 600 rpm. Then the 64CuCl2 (20 - 37 MBq) was added to the final solution, at pH ~3. Finally, it were placed in incubation at 85˚C and 450 rpm, during 30 minutes. After the incubation 200 μL of saline solution (17%) was added at pH~5. Healthy rats were intravenously injected with the radio-nanoparticle solution. The studied rats were treated under protocol of The Universidad Nacional Autónoma Metropolitana accepted by COFEPRIS (Mexican FDA)
3. Results
The results obtained in this research shown the caption of the radionanoparticle this radionanoparticle linked to 64CuCl2 trough of the groups OH (Figure 1), that are formed during the functionalization of the Cu(acac)2/F-TiO2. Previous works have reported that the marked radionanoparticles have been used linked to chelate agent (68Ga, 64Cu and 89Zr) [15] . Then the Cu(acac)2/F-TiO2 acts at the same way behavior as chelate agent mixed with 64CuCl2.
The Cu(acac)2/F-TiO2, acetylacetonate in the copper may have different arrangements. The ligand acetylacetonate in nanomaterial may take different structures, depending where is bonding (Figure 2).
The aqueous-solution coordination chemistry of copper is limited to three oxidation states (I, II, III). Due to the lability of most Cu(I) complexes, they typically lack sufficient kinetic stability for radiopharmaceutical applications, while
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Figure 2. Copper acetylacetonate with different arrangements.
Cu(III) is very rare and difficult to attain without the use of strong p-donating ligands. Therefore, it is easy to incorporate copper acetylacetonate in a matrix of Titania sol-gel.
4. Discussion
One of the main tests in developing radiopharmaceuticals labeled with 64Cu is their in vivo stability important for averting transchelation of copper with the many copper chelating proteins present in the blood.
The most important of this research is: a) verify if the 64CuCl2 linked to the new nanoparticle proposed having incorporated copper; b) Achieved the goal a), healthy rats are injected with the radioactive solution, it is important verify if exist any signal.
The “in vivo” evaluation after realize the images study in micro PET equipment, uptake of the radio-nanoparticle was observed in the digestive system in the healthy Wistar rats, as shows the Figure 3.
The nanoparticle Cu(acac)2/F-TiO2 is functionalized with
,
and GABA (aminobutyric acid), the final result is a nanomaterial OH saturated [12] [14] [15] ; it is the ligand which 64CuCl2 is labeled.
In previous studies, have been proved that elimination of radionuclide is trough liver and intestines with little accumulation in the kidneys [11] [16] [17] .
5. Conclusions
In this research healthy Wistar rats were used as a control, for the biodistribution study of 30 min [5] . An uptake of the radio-nanoparticle is observed in the digestive system. Nevertheless, the nanoparticle linked to 64CuCl2 is useful for purposes.
Now, it is well known that this system is useful for detecting damaged zones while treating those areas. In the references given in the discussion part clearly, it illustrates how the nanomaterial of just 10 nm cross-cell barriers.
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Figure 3. Representative whole body maximum intensity projections of micro PET images showing the biodistribution of 64Cu(AcAc)2.
Therefore the radioactive properties of 64Cu (T1/2 = 12.7 h, 17.4% b+, 39% b−, 43.6% EC) make them ideal candidates for use in theragnostic applications.
Acknowledgements
The author Paola Ramírez would like to thank the CONACYT for her scholarships.