Preparation, characterization, and radiolabeling of [68Ga]Nodaga-pamidronic acid: a potential PET bone imaging agent

Early diagnosis of bone metastases is crucial to prevent skeletal-related events, and for that, the non-invasive techniques to diagnose bone metastases that make use of image-guided radiopharmaceuticals are being employed as an alternative to traditional biopsies. Hence, in the present work, we tested the efficacy of a gallium-68 (68Ga)-based compound as a radiopharmaceutical agent towards the bone imaging in positron emitting tomography (PET). For that, we prepared, thoroughly characterized, and radiolabeled [68Ga]Ga-NODAGA-pamidronic acid radiopharmaceutical, a 68Ga precursor for PET bone cancer imaging applications. The preparation of NODAGA-pamidronic acid was performed via the N-Hydroxysuccinimide (NHS) ester strategy and was characterized using liquid chromatography-mass spectrometry (LC-MS) and tandem mass spectrometry (MSn). The unreacted NODAGA chelator was separated using the ion-suppression reverse phase-high performance liquid chromatography (RP-HPLC) method, and the freeze-dried NODAGA-pamidronic acid was radiolabeled with 68Ga. The radiolabeling condition was found to be most optimum at a pH ranging from 4 to 4.5 and a temperature of above 60 °C. From previous work, we found that the pamidronic acid itself has a good bone binding affinity. Moreover, from the analysis of the results, the ionic structure of radiolabeled [68Ga]Ga-NODAGA-pamidronic acid has the ability to improve the blood clearance and may exert good renal excretion, enhance the bone-to-background ratio, and consequently the final image quality. This was reflected by both the in vitro bone binding assay and in vivo animal biodistribution presented in this research

Preparation and characterization of [68Ga]NODAGA-Pamidronic acid for pet bone cancer imaging

Early detection of bone metastases is essential to prevent skeletal-related events. Unlike biopsies, a non-invasive technique to diagnose bone metastases is by utilizing radiopharmaceuticals and detected using a nuclear imaging modality. Hence, this research deems to determine the role of gallium-68 radiolabeled bisphosphonates ([68Ga]NODAGA-Pamidronic acid) for PET bone cancer imaging. This study aims to ascertain the preparation, characterization, and radiolabeling of [68Ga]NODAGA-Pamidronic acid. Lastly, to determine its potential application, the in vitro bone binding assay and in vivo bone-to-blood ratio is examined. Firstly, NODAGA-Pamidronic acid (NODPAM) was prepared via the NHS ester conjugation method and characterized using tandem mass spectrometry (MS/MS). The RP-HPLC method was then developed to remove the free NODAGA using 0.1% trifluoroacetic acid and water as the mobile phase at a flow rate of 0.5 ml/ min. Based on the MS/MS analysis of NODPAM, the precursor ion and product ion observed were according to the theoretical value (theoretical [M-H]-m/z: 591.14, obtained [M-H]-m/z: 591.14, [M-H-H3PO3]-m/z: 509.17). The isotopic abundance M+1 (calculated m/z: 22.02, obtained m/z: 20.99±0.94) confirms the molecular formula C18H34N4O14P2. The HPLC method developed shows a good separation between peaks with a resolution of 1.613. The freeze-dried NODPAM produces a solid white powder. Next, the radiolabeling of [68Ga]NODPAM was optimized by looking into three parameters; pH, temperature, and amount NODPAM. Finally, the in vitro bone binding assay and in vivo bone-to-blood ratio was determined using synthetic hydroxyapatite and Sprague Dawley rats, respectively. From the results obtained, the %RCP of radiolabeled [68Ga]NODPAM was above 90% within 15 minutes at pH 4-4.5 and a temperature of above 60ºC. The in vitro hydroxyapatite (HA) bone binding assay displayed a significant difference between the [68Ga]NODPAM 82.25%±1.72 and [99mTc]MDP of 53.21%±0.28 (p<0.05). The bone-to-blood ratio of [68Ga]NODPAM 2-hour post-injection was significantly higher (P<0.05) compared to 68Ga(III); 27.53 and 0.74, respectively. In conclusion, [68Ga]NODPAM was prepared and characterized accordingly, and the in vitro bone binding assay and in vivo bone-to-blood ratio were assessed. The preliminary data suggests that there is a need for a complete pre-clinical study of [68Ga]NODPAM before translating it into clinical research

Cyclotron Production of Gallium-68 Radiopharmaceuticals Using the ⁶⁸Zn(p,n)⁶⁸Ga Reaction and Their Regulatory Aspects

Designing and implementing various radionuclide production methods guarantees a sustainable supply, which is important for medical use. The use of medical cyclotrons for radiometal production can increase the availability of gallium-68 (68Ga) radiopharmaceuticals. Although generators have greatly influenced the demand for 68Ga radiopharmaceuticals, the use of medical cyclotrons is currently being explored. The resulting 68Ga production is several times higher than obtained from a generator. Moreover, the use of solid targets yields end of purification and end of synthesis (EOS) of up to 194 GBq and 72 GBq, respectively. Furthermore, experiments employing liquid targets have provided promising results, with an EOS of 3 GBq for [68Ga]Ga-PSMA-11. However, some processes can be further optimized, specifically purification, to achieve high 68Ga recovery and apparent molar activity. In the future, 68Ga will probably remain one of the most in-demand radionuclides; however, careful consideration is needed regarding how to reduce the production costs. Thus, this review aimed to discuss the production of 68Ga radiopharmaceuticals using Advanced Cyclotron Systems, Inc. (ACSI, Richmond, BC, Canada) Richmond, Canada and GE Healthcare, Wisconsin, USA cyclotrons, its related factors, and regulatory concerns

Preparation, Optimisation, and In Vitro Evaluation of [18F]AlF-NOTA-Pamidronic Acid for Bone Imaging PET

[18F]sodium fluoride ([18F]NaF) is recognised to be superior to [99mTc]-methyl diphosphate ([99mTc]Tc-MDP) and 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) in bone imaging. However, there is concern that [18F]NaF uptake is not cancer-specific, leading to a higher number of false-positive interpretations. Therefore, in this work, [18F]AlF-NOTA-pamidronic acid was prepared, optimised, and tested for its in vitro uptake. NOTA-pamidronic acid was prepared by an N-Hydroxysuccinimide (NHS) ester strategy and validated by liquid chromatography-mass spectrometry analysis (LC-MS/MS). Radiolabeling of [18F]AlF-NOTA-pamidronic acid was optimised, and it was ensured that all quality control analysis requirements for the radiopharmaceuticals were met prior to the in vitro cell uptake studies. NOTA-pamidronic acid was successfully prepared and radiolabeled with 18F. The radiolabel was prepared in a 1:1 molar ratio of aluminium chloride (AlCl3) to NOTA-pamidronic acid and heated at 100 &deg;C for 15 min in the presence of 50% ethanol (v/v), which proved to be optimal. The preliminary in vitro results of the binding of the hydroxyapatite showed that [18F]AlF-NOTA-pamidronic acid was as sensitive as [18F]sodium fluoride ([18F]NaF). Normal human osteoblast cell lines (hFOB 1.19) and human osteosarcoma cell lines (Saos-2) were used for the in vitro cellular uptake studies. It was found that [18F]NaF was higher in both cell lines, but [18F]AlF-NOTA-pamidronic acid showed promising cellular uptake in Saos-2. The preliminary results suggest that further preclinical studies of [18F]AlF-NOTA-pamidronic acid are needed before it is transferred to clinical research

Performance evaluation of Gallium-68 radiopharmaceuticals production using liquid target PETtrace 800 cyclotron

Due to increased demand, cyclotron has an expanding role in producing Gallium-68 (68Ga) radiopharmaceuticals using solid and liquid targets. Though the liquid target produces lower end-of-bombardment activity compared to the solid target, our study presents the performance of 68Ga radiopharmaceuticals production using the liquid target by evaluating the end-of-bombardment activity and the end-of-purification activity of 68GaGaCl3. We also present the effect of increasing irradiation time, which significantly improves the end-of-synthesis yield. From the result obtained, the end-of-bombardment activity produced was 4.48 GBq, and the 68GaGaCl3 end-of-purification activity produced was 2.51 GBq with below-limit metallic impurities. Increasing the irradiation time showed a significant increase in the end-of-synthesis activity from 1.33 GBq to 1.95 GBq for 68GaGa-PSMA-11 and from 1.13 GBq to 1.74 GBq for 68GaGa-DOTA-TATE. Based on the improvements made, the liquid target production of 68Ga radiopharmaceuticals is feasible and reproducible to accommodate up to 5 patients per production. In addition, this work also discusses the issues encountered, together with the possible corrective and preventative measures. © 2023 Elsevier Lt