An improved one-pot preparation of [18 F]FMISO based on solid phase extraction purification: Pitfalls on the analytical method reported in the Ph.Eur.'s monograph.

By adapting previously reported reaction conditions, [18 F]FMISO was synthesized using a TracerLab FX-FDG module in 31 min from no carrier added [18 F]fluoride in 56% radiochemical yield. A novel and simple purification setup based on disposable cartridges was developed allowing the radiopharmaceutical to be obtained in high radiochemical purity (>99.5%) and with chemical impurities far below the Ph.Eur.'s thresholds. Moreover, the study pinpointed some shortcomings of the high-performance liquid chromatography (HPLC) method reported in the dedicated Ph.Eur's monograph.

Tetrabutylammonium HPLC analysis: shortcomings in the Ph. Eur. method.

Tetrabutylammonium is a phase-transfer agent commonly used in PET radiochemistry. Its toxicity makes its quantification mandatory. However, the official HPLC method for tetrabutylammonium analysis reported in the European Pharmacopoeia (Ph. Eur.) apparently fails to achieve the described separation in most new generation reverse-phase columns. The study highlights the differences in separation achievable by varying some of the chromatographic conditions, such as temperature, eluent composition and ion-pairing agent concentration. In the end, variations to the method within the limits allowed by the Ph. Eur. were not sufficient to overcome the problem, thus forcing to a more radical change of the organic component of the mobile phase.

Practical microscale one-pot radiosynthesis of 18 F-labeled probes.

High specific activity is often a significant requirement for radiopharmaceuticals. To achieve that with fluorine-18 (18 F)-labeled probes, it is mandatory to start from no-carrier-added fluoride and to reduce to a minimum the amount of precursor in order to decrease the presence of any pseudocarrier. In the present study, a feasible and efficient method for microscale one-pot radiosynthesis of 18 F-labeled probes is described. It allows a substantial reduction in precursor, solvent, and reagents, thus reducing also possible side reaction in the case of base-sensitive precursors. The method is based on the use of a small amount of Kryptofix 2.2.2/potassium [18 F]fluoride in MeOH (K.222/K[18 F]F-MeOH) obtained using Oasis MAX and MCX cartridges. Five methods, differing in terms of MeOH evaporation and precursor addition, for the radiosynthesis of [18 F]fallypride and [18 F]FET in ≤50-µL scale, were examined and evaluated. The method using the addition of DMSO to the K.222/K[18 F]F-MeOH solution prior to MeOH evaporation is proposed as a versatile procedure for feasible one-pot 10- to 20-µL scale radiosyntheses. This method was successfully applied also to the radiosynthesis of [18 F]FES, [18 F]FLT, and [18 F]FMISO, with radiochemical yields comparable with those reported in the literature. Purification of a crude product by an analytical HPLC column was also demonstrated.

¹8F-FLT PET/CT as an imaging tool for early prediction of pathological response in patients with locally advanced breast cancer treated with neoadjuvant chemotherapy: a pilot study.

PURPOSE: We evaluated whether (18)F-3'-deoxy-3'-fluorothymidine positron emission tomography (FLT PET) can predict the final postoperative histopathological response in primary breast cancer after the first cycle of neoadjuvant chemotherapy (NCT). METHODS: In this prospective cohort study of 15 patients with locally advanced operable breast cancer, FLT PET evaluations were performed before NCT, after the first cycle of NCT, and at the end of NCT. All patients subsequently underwent surgery. Variables from FLT PET examinations were correlated with postoperative histopathological results. RESULTS: At baseline, median of maximum standardized uptake values (SUVmax) in the groups showing a complete pathological response (pCR) + residual cancer burden (RCB) I, RCB II or RCB III did not differ significantly for the primary tumour (5.0 vs. 2.9 vs. 8.9, p = 0.293) or for axillary nodes (7.9 vs. 1.6 vs. 7.0, p = 0.363), whereas the Spearman correlation between SUVmax and Ki67 proliferation rate index was significant (r = 0.69, p < 0.001). Analysis of the relative percentage change of SUVmaxin the primary tumour (∆SUVTmax(t1)) and axillary nodes (∆SUVNmax(t1)) after the first NCT cycle showed that the power of ∆SUVTmax(t 1) to predict pCR + RCB I responses (AUC = 0.91, p < 0.001) was statistically significant, whereas ∆SUVNmax(t1) had a moderate ability (AUC = 0.77, p = 0.119) to separate subjects with ΔSUVTmax(t1) > -52.9 % into two groups: RCB III patients and a heterogeneous group that included RCB I and RCB II patients. A predictive score µ based on ΔSUVTmax(t1) and ΔSUVNmax(t1) parameters is proposed. CONCLUSION: The preliminary findings of the present study suggest the potential utility of FLT PET scans for early monitoring of response to NCT and to formulate a therapeutic strategy consistent with the estimated efficacy of NCT. However, these results in a small patient population need to be validated in a larger independent cohort.

A concentration-based microscale method for 18F-nucleophilic substitutions and its testing on the one-pot radiosynthesis of [18F]FET and [18F]fallypride.

When applied to a radiosynthesis, a microscale approach can help to save precursor and improve yields. Thus, a 5-10 µL microscale method based on a concentration procedure was developed and applied to the radiosynthesis of [18F]FET and [18F]fallypride. In spite of using an amount of precursor ca. 100 times smaller, radiochemical yields were comparable or even higher than those reported in literature. Because of the very low reaction volumes, the possible effects of concentrated dose of activity and carrier fluoride were also investigated.

[18F]FDG and [18F]FLT PET for the evaluation of response to neo-adjuvant chemotherapy in a model of triple negative breast cancer.

RATIONALE: Pathological response to neo-adjuvant chemotherapy (NAC) represents a commonly used predictor of survival in triple negative breast cancer (TNBC) and the need to identify markers that predict response to NAC is constantly increasing. Aim of this study was to evaluate the potential usefulness of PET imaging with [18F]FDG and [18F]FLT for the discrimination of TNBC responders to Paclitaxel (PTX) therapy compared to the response assessed by an adapted Response Evaluation Criteria In Solid Tumors (RECIST) criteria based on tumor volume (Tumor Volume Response). METHODS: Nu/nu mice bearing TNBC lesions of different size were evaluated with [18F]FDG and [18F]FLT PET before and after PTX treatment. SUVmax, Metabolic Tumor Volume (MTV) and Total Lesion Glycolysis (TLG) and Proliferation (TLP) were assessed using a graph-based random walk algorithm. RESULTS: We found that in our TNBC model the variation of [18F]FDG and [18F]FLT SUVmax similarly defined tumor response to therapy and that SUVmax variation represented the most accurate parameter. Response evaluation using Tumor Volume Response (TVR) showed that the effectiveness of NAC with PTX was completely independent from lesions size at baseline. CONCLUSIONS: Our study provided interesting results in terms of sensitivity and specificity of PET in TNBC, revealing the similar performances of [18F]FDG and [18F]FLT in the identification of responders to Paclitaxel.

Minimization of the amount of Kryptofix 222 - KHCO3 for applications to microscale 18F-radiolabeling.

Conversion of aqueous [18F]fluoride to reactive [18F]fluoride is an important first step in the radiosynthesis of 18F-labeled compounds by nucleophilic substitution. A versatile method for the rapid preparation of reactive [18F]fluoride by the combined use of an Oasis MAX cartridge and a methanolic solution of the Kryptofix 222-KHCO3 complex (K.222/KHCO3) was developed. The latter amount was optimized with the aim to keep it as low as possible while achieving recovery yields of [18F]fluoride comparable to those attained with the commonly used QMA cartridge. Thus, a 97% recovery yield was obtained with just 2µmol of K.222/KHCO3 methanolic solution (10mM, 200µL) within 7min. This result allowed in turn to optimize the microscale radiosynthesis of [18F]FDG. Moreover, the method was successfully applied to the 100µL-scale 18F-substitution reactions of several precursors.

Simple automated preparation of O-[11C]methyl-l-tyrosine for routine clinical use.

The previously reported preparation of O-[(11)C]methyl-l-tyrosine ([(11)C]MT), a promising tumor imaging agent, has been now considerably simplified and automated. Main changes were the use of [(11)C]methyl iodide ([(11)C]MeI) in the reaction with l-tyrosine disodium and the use of solid phase extraction on commercially available cartridges instead of HPLC for the final purification. An injectable saline solution of [(11)C]MT was obtained within 30 min after EOB with radiochemical yield of ca. 60% (decay-corrected, based on [(11)C]MeI). Radiochemical purity was over 97%. The automated preparation was carried out using a miniature module employing manifold valves.

Effect of radiochemical modification on biodistribution of scFvD2B antibody fragment recognising prostate specific membrane antigen.

Antibody-based reagents represent a promising strategy as clinical diagnostic tools. Prostate cancer (PCa) is the second-leading cause of death in males in the Western population. There is a presently unmet need for accurate diagnostic tool to localize and define the extent of both primary PCa and occult recurrent disease. One of the most suitable targets for PCa is the prostate-specific membrane antigen (PSMA) recognised by the monoclonal antibody D2B that we re-shaped into the single chain Fv (scFv format). Aim of this study was to evaluate in preclinical in vivo models the target specificity of scFvD2B after labelling with different radionuclides. (111)In radiolabelling was performed via the chelator Bz-NOTA, and (131)I radioiodination was performed using iodogen. The potential for molecular imaging and the biological behaviour of the radiolabelled scFvD2B were evaluated in mice bearing two subcutaneous PCa isogenic cell lines that differed only in PSMA expression. Biodistribution studies were performed at 3, 9, 15 and 24h after injection to determine the optimal imaging time point. A significant kidney accumulation, as percentage of injected dose of tissue (%ID/g), was observed for (111)In-scFvD2B at 3h after injection (45%ID/g) and it was maintained up to 24h (26%ID/g). By contrast, kidney accumulation of (131)I-scFvD2B was only marginally (0.3%ID/g at 24h). At the optimal time point defined between 15h and 24h, regardless of the radionuclide used, the scFvD2B was able to localize significantly better in the PSMA expressing tumours compared to the negative control; with (131)I-scFvD2B yielding a significantly better target/background ratio compared to (111)In-scFvD2B. These data suggest that, besides antigen specificity, chemical modification may affect antibody fragment biodistribution.

Evaluation of O-[11C]methyl-L-tyrosine and O-[18F]fluoromethyl-L-tyrosine as tumor imaging tracers by PET.

We investigated the potential of O-[(11)C]methyl-L-tyrosine and O-[(18) F]fluoromethyl-L-tyrosine as positron-emitting tracers for tumor imaging. The two tracers had similar distribution patterns in rats bearing AH109A hepatoma, with pancreas and, on a lesser extent, AH109A showing the highest uptake. Uptake of both tracers in the AH109A and uptake ratios of AH109A-to-tissues (with the exception of AH109A-to-bone) gradually increased for 60 min. O-[(11)C]methyl-L-tyrosine was metabolically stable, whereas a negligible low amount of metabolites was observed for O-[(18)F]fluoromethyl-L-tyrosine. Both tracers showed the potential for tumor imaging.

[18F]fluoromethyl triflate, a novel and reactive [18F]fluoromethylating agent: preparation and application to the on-column preparation of [18F]fluorocholine.

The production and use of [18F]fluoromethyl triflate ([18F]CH2FOTf), a more reactive [18F]fluoromethylating agent than [18F]fluoromethyl bromide ([18F]CH2BrF), is described. [18F]CH2FOTf was prepared from [18F]CH2BrF. The latter was synthesized by nucleophilic substitution of CH2Br2 with no-carrier-added [18F]fluoride and purified by four Sep-Pak Plus silica cartridges connected in series. It was then quantitatively converted on-line to [18F]CH2FOTf by passing through a heated AgOTf column. Decay-corrected radiochemical yields of [18F]CH2FOTf based on [18F]fluoride were 47 +/- 8% (n = 20). Both [18F]CH2BrF and [18F]CH2FOTf were applied to solid-supported [18F]fluoromethylation of N,N-dimethylaminoethanol on a Sep-Pak Plus C18 cartridge to produce the 18F-labeled choline analogue, (beta-hydroxyethyl)dimethyl-[18F]fluoromethylammonium ([18F]fluorocholine). Depending on flow rate and amount of precursor used, decay corrected radiochemical yields of [18F]fluorocholine from [18F]CH2BrF ranged from 6% to 63%, while [18F]CH2FOTf afforded yields of more than 80%. Thus, by using the latter reagent and a subsequent purification on a Sep-Pak Accell CM cartridge, [18F]fluorocholine was produced from [18F]fluoride in overall radiochemical yields of 40% (decay corrected) in less than 30 min.

Simple preparation and purification of ethanol-free solutions of 3'-deoxy-3'-[18F]fluorothymidine by means of disposable solid-phase extraction cartridges.

INTRODUCTION: 3'-Deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) shows great potential as a tracer for proliferative studies with PET. However, its regular application is often limited by low radiochemical yields and the use of a troublesome HPLC separation. Moreover, a high content of ethanol, at least one-fold higher than the European Pharmacopoeia and US Pharmacopoeia's established limit, is always present in the final product. The present study reports an optimization of the reaction conditions and a simple and straightforward purification step which affords a solution of [(18)F]FLT suitable for human use. METHODS: Several conditions and materials were tested for both the nucleophilic substitution and purification step. The latter was achieved by means of a series of commercial solid-phase extraction cartridges. Very conveniently, the whole one-pot synthesis was carried out on commercial automated modules using basically the same setup employed for the synthesis of [(18)F]FDG. RESULTS: Under routine conditions, radiochemical yields of 37% [decay-corrected to start of synthesis (SOS)] were achieved in ca. 39 min from SOS, with radiochemical purities >98% (usually >99%). The negligible radiolysis observed could be easily suppressed by adding 0.5% of EtOH. Typical unlabelled chemical impurities detected were thymidine (0.15 ppm), thymine (0.28 ppm) and stavudine (0.05 ppm). CONCLUSIONS: A reliable, simple and efficient preparation of [(18)F]FLT has been developed, able to afford an ethanol-free solution of the tracer with no need for any HPLC purification. Because of its similarity to the [(18)F]FDG synthesis, the method can be readily implemented on basically all the commercial modules developed for this common radiotracer.