Analysis of residual solvents in 2-[(18)F]FDG by GC

A generic gas chromatography method for determination of residual solvents in PET radiopharmaceuticals

A novel gas chromatography (GC) method for quantitation of volatile organic compounds (VOCs) in ¹⁸F- and ¹¹C-radiopharmaceuticals listed in the European Pharmacopoeia (Ph. Eur.) was proposed. Optimized chromatographic parameters were used for separation of ethanol, acetone, acetonitrile, tetrahydrofuran (THF), dibromomethane (DBM), 2-dimethylaminoethanol (deanol), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) which could be detected in radioactive drug samples. The calculated peak resolutions (R_S) were higher than 2.0 at ethanol concentration of up to 11 m/m%. Reproducible results could be obtained using base deactivated fused silica wool as packing material of inlet liner. Validation parameters showed excellent linearity (r² ≥0.9998) in the range from 10 to at least 120% of concentration limit of solvents. The accuracy was determined as recovery of concentrations which ranged from 99.3% to 103.8%. Additionally, the relative standard deviation (RSD) of each solvent for inter-day and intra-day precision were in the range of 0.5-4.2% and 0.4-4.4%, respectively. The limit of quantitation (LOQ) for ethanol, acetone, acetonitrile, THF, DBM, deanol, DMF and DMSO was 0.48, 0.42, 0.43, 0.46, 4.35, 0.73, 0.68 and 0.50 mg/L, respectively. The developed procedure was successively applied for quantitation of ethanol, acetone, acetonitrile and deanol in radioactive drug samples of [¹¹C]methionine, [¹¹C]choline, 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) and O-(2-[¹⁸F]fluoroethyl)-L-tyrosine ([¹⁸F]FET). The proposed GC method applying flame ionization detection (FID) could be adapted in routine quality control of most frequently used positron emission tomography (PET) radiopharmaceuticals to perform the determination of residual solvents with analysis time of 12 min.

The quest for improving the management of breast cancer by functional imaging: The discovery and development of 16α-[18F]fluoroestradiol (FES), a PET radiotracer for the estrogen receptor, a historical review

INTRODUCTION

16α-[18F]Fluoroestradiol (FES), a PET radiotracer for the estrogen receptor (ER) in breast cancer, was the first receptor-targeted PET radiotracer for oncology and is continuing to prove its value in clinical research, antiestrogen development, and breast cancer care. The story of its conception, design, evaluation and use in clinical studies parallels the evolution of the whole field of receptor-targeted radiotracers, one greatly influenced by the research and intellectual contributions of William C. Eckelman.

METHODS AND RESULTS

The development of methods for efficient production of fluorine-18, for conversion of [18F]fluoride ion into chemically reactive form, and for its rapid and efficient incorporation into suitable estrogen precursor molecules at high molar activity, were all methodological underpinnings required for the preparation of FES. FES binds to ER with very high affinity, and its in vivo uptake by ER-dependent target tissues in animal models was efficient and selective, findings that preceded its use for PET imaging in patients with breast cancer.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Comparisons between ER levels measured by FES-PET imaging of breast tumors with tissue-specimen ER quantification by IHC and other methods show that imaging provided improved prediction of benefit from endocrine therapies. Serial imaging of ER by FES-PET, before and after dosing patients with antiestrogens, is used to determine the efficacious dose for established antiestrogens and to facilitate clinical development of new ER antagonists. Beyond FES imaging, PET-based hormone challenge tests, which evaluate the functional status of ER by monitoring rapid changes in tumor metabolic or transcriptional activity after a brief estrogen challenge, provide highly sensitive and selective predictions of whether or not there will be a favorable response to endocrine therapies. There is sufficient interest in the clinical applications of FES that FDA approval is being sought for its wider use in breast cancer.

CONCLUSIONS

FES was the first PET probe for a receptor in cancer, and its development and clinical applications in breast cancer parallel the conceptual evolution of the whole field of receptor-binding radiotracers.

Analytical GC-FID Method for the Determination of Organic Solvents in Radiopharmaceuticals

BACKGROUND

Organic solvents play an indispensable role in most of the radiopharmaceutical production stages. It is almost impossible to remove them entirely in the final formulation of the product.

OBJECTIVE

In this presented work, an analytical method by gas chromatography coupled with flame ionization detection (GC-FID) has been developed to determine organic solvents in radiopharmaceutical samples. The effect of injection holding time, temperature variation in the injection port, and the column temperature on the analysis time and resolution (R ≥ 1.5) of ethanol and acetonitrile was studied extensively.

METHODS

The experimental conditions were optimized with the aid of further statistical analysis; thence, the proposed method was validated following the International Council for Harmonisation (ICH) Q2 (R1) guideline.

RESULTS

The proposed analytical method surpassed the acceptance criteria including the linearity > 0.990 (correlation coefficient of R²), precision < 2%, LOD, and LOQ, accuracy > 90% for all solvents. The separation between ethanol and acetonitrile was acceptable with a resolution R > 1.5. Further statistical analysis of Oneway ANOVA revealed that the increment in injection holding time and variation of temperature at the injection port did not significantly affect the analysis time. Nevertheless, the variation in injection port temperature substantially influenced the resolution of ethanol and acetonitrile peaks (p < 0.05).

CONCLUSION

The proposed analytical method has been successfully implemented to determine the organic solvent in the [¹⁸F]fluoro-ethyl-tyrosine ([¹⁸F]FET), [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO), and [¹⁸F]fluorothymidine ([¹⁸F]FLT).

Mechanochemical removal of carbamazepine

Carbamazepine (CBZ) is a drug used for treating epilepsy, neuropathic pain, schizophrenia and bipolar disorder. Its widespread use is indicated by its listing in the WHO's Model List of Essential Medicines. The accumulation of CBZ in various environmental compartments, specifically in crops irrigated with treated effluent or grown on soils containing biosolids, is often reported. Being a persistent PPCP (a pharmaceutical and personal care product), developing procedures to remove CBZ is of great importance. In the present study, the breakdown of CBZ by surface reactions in contact with various minerals was attempted. While Al-montmorillonite enhanced CBZ disappearance without the need to apply mechanical force, the efficiency of magnetite in enhancing the disappearance increased considerably upon applying such force. Ball milling with magnetite generated a virtually complete disappearance of CBZ (∼94% of the applied CBZ disappeared after milling for 30 min). HPLC, LC/MS and FTIR were employed in an attempt to elucidate the rate of disappearance and degradation mechanisms of CBZ. A small amount of the hydrolysis product iminostilbene was identified by LC/MS and the breaking off of carbamic acid from the fused rings skeleton of CBZ was indicated by FTIR spectroscopy, confirming the formation of iminostilbene.

Radiosynthesis, photoisomerization, biodistribution, and metabolite analysis of 11C-PBB3 as a clinically useful PET probe for imaging of tau pathology

2-((1E,3E)-4-(6-((11)C-methylamino)pyridin-3-yl)buta-1,3-dienyl)benzo[d]thiazol-6-ol ((11)C-PBB3) is a clinically useful PET probe that we developed for in vivo imaging of tau pathology in the human brain. To ensure the availability of this probe among multiple PET facilities, in the present study we established protocols for the radiosynthesis and quality control of (11)C-PBB3 and for the characterization of its photoisomerization, biodistribution, and metabolism.

METHODS

(11)C-PBB3 was synthesized by reaction of the tert-butyldimethylsilyl desmethyl precursor ( 1: ) with (11)C-methyl iodide using potassium hydroxide as a base, followed by deprotection. Photoisomerization of (11)C-PBB3 under fluorescent light was determined. The biodistribution and metabolite analysis of (11)C-PBB3 was determined in mice using the dissection method.

RESULTS

(11)C-PBB3 was synthesized with 15.4% ± 2.8% radiochemical yield (decay-corrected, n = 50) based on the cyclotron-produced (11)C-CO2 and showed an averaged synthesis time of 35 min from the end of bombardment. The radiochemical purity and specific activity of (11)C-PBB3 were 98.0% ± 2.3% and 180.2 ± 44.3 GBq/μmol, respectively, at the end of synthesis (n = 50). (11)C-PBB3 showed rapid photoisomerization, and its radiochemical purity decreased to approximately 50% at 10 min after exposure to fluorescent light. After the fluorescent light was switched off, (11)C-PBB3 retained more than 95% radiochemical purity over 60 min. A suitable brain uptake (1.92% injected dose/g tissue) of radioactivity was observed at 1 min after the probe injection, which was followed by rapid washout from the brain tissue. More than 70% of total radioactivity in the mouse brain homogenate at 5 min after injection represented the unchanged (11)C-PBB3, despite its rapid metabolism in the plasma.

CONCLUSION

(11)C-PBB3 was produced with sufficient radioactivity and high quality, demonstrating its clinical utility. The present results of radiosynthesis, photoisomerization, biodistribution, and metabolite analysis could be helpful for the reliable production and application of (11)C-PBB3 in diverse PET facilities.

Synthesis, quality control and determination of metallic impurities in 18F-fludeoxyglucose production process

AIM

The aim of this study was to synthesize ¹⁸FDG in some consecutive runs and check the quality of manufactured radiopharmaceuticals and to determine the distribution of metallic impurities in the synthesis process.

BACKGROUND

For radiopharmaceuticals the general requirements are listed in European Pharmacopeia and these parameters have to be checked before application for human use.

MATERIALS AND METHODS

Standard methods for the determination of basic characteristics of radiopharmaceuticals were used. Additionally, high resolution γ spectrometry was used for the assessment of nuclidic purity and inductively coupled plasma with mass spectrometry to evaluate metallic content.

RESULTS

Results showed sources and distribution of metallic and radiometallic impurities in the production process. Main part is trapped in the initial separation column of the synthesis unit and is not distributed to the final product in significant amounts.

CONCLUSIONS

Produced ¹⁸FDG filled requirements of Ph.Eur. and the content of radionuclidic and metallic impurities was in the acceptable range.

Synthesis of Clinical-Grade [(18)F]-Fluoroestradiol as a Surrogate PET Biomarker for the Evaluation of Estrogen Receptor-Targeting Therapeutic Drug

16α-[¹⁸F]-fluoroestradiol ([¹⁸F]FES), a steroid-based positron emission tomography (PET) tracer, has emerged as a dependable tracer for the evaluation and management of estrogen receptor-positive (ER+) breast cancer patients. We have developed a fully automatic, one-pot procedure for the synthesis of [¹⁸F]FES using the Eckert & Ziegler (E & Z) radiomodular system. After [¹⁸F]fluorination, the intermediate was hydrolyzed with 2.0 M HCl twice and neutralized with sodium bicarbonate. After high-performance liquid chromatography (HPLC) purification, the decay-corrected radiochemical yield and purity of [¹⁸F]FES were 40 ± 5.0% (n = 12) and >97%, respectively. The product was stable up to 10 h. Total synthesis time including HPLC purification was 80 min. This new, fully automated rapid synthetic procedure provided high and reproducible yields of [¹⁸F]FES. Quality control (QC) tests showed that the [¹⁸F]FES produced by this method met all specifications for human injection.

The possibility of a fully automated procedure for radiosynthesis of fluorine-18-labeled fluoromisonidazole using a simplified single, neutral alumina column purification procedure

A novel fully automated radiosynthesis procedure for [(18)F]Fluoromisonidazole using a simple alumina cartridge-column for purification instead of conventionally used semi-preparative HPLC was developed. [(18)F]FMISO was prepared via a one-pot, two-step synthesis procedure using a modified nuclear interface synthesis module. Nucleophilic fluorination of the precursor molecule 1-(2'-nitro-1'-imidazolyl)-2-O-tetrahydropyranyl-3-O-toluenesulphonylpropanediol (NITTP) with no-carrier added [(18)F]fluoride followed by hydrolysis of the protecting group with 1M HCl. Purification was carried out using a single neutral alumina cartridge-column instead of semi-preparative HPLC. The maximum overall radiochemical yield obtained was 37.49+/-1.68% with 10mg NITTP (n=3, without any decay correction) and the total synthesis time was 40+/-1 min. The radiochemical purity was greater than 95% and the product was devoid of other chemical impurities including residual aluminum and acetonitrile. The biodistribution study in fibrosarcoma tumor model showed maximum uptake in tumor, 2h post injection. Finally, PET/CT imaging studies in normal healthy rabbit, showed clear uptake in the organs involved in the metabolic process of MISO. No bone uptake was observed excluding the presence of free [(18)F]fluoride. The reported method can be easily adapted in any commercial FDG synthesis module.

Production and radioassay of Tc-94m for PET studies

The radionuclide Tc-94m with its positron branching ratio of 72, positron end-point energy of 2.47MeV, and relatively short half-life of 52 minutes is suitable for quantitative measurements using PET. Tc-94m can be produced by proton bombardment of isotopically enriched [Mo-94]MoO3. We prepare Tc-94m as pertechnetate in saline solution using a wet-chemical separation procedure employing a semi-automated apparatus. Tc-94m sestamibi and other radiopharmaceuticals are routinely produced from this reagent.

Simple purification of recovered [18O]H2O by UV, ozone, and solid-phase extraction methods

We have developed three methods for removing organic impurities as well as a solid-phase extraction (SPE) method for removing metallic and ionic impurities from recovered [18O]H2O. Preliminary experiments with [16O]H2O were used to determine the optimal purification conditions. These showed that UV irradiation rapidly (<4 h) eliminated low boiling point impurities such as acetonitrile and acetone with only a slight loss of mass. A combination of UV irradiation and purging with ozone removed high boiling point impurities such as ethanol and methanol more quickly than UV irradiation alone. UV irradiation followed by a SPE with [18O]H2O removed all organic and inorganic impurities. The purified [18O]H2O gave a saturation yield of 128.62+/-15.6 mCi/microA for [18F]fluoride and a 49.8+/-12.7% radiochemical yield for [18F]fluorodeoxyglucose.

Residual solvent analysis by gas chromatography in radiopharmaceutical formulations containing up to 12% ethanol

For the detection and quantification of residual solvents in solutions of radiopharmaceuticals for human applications, a new analysis method was set up. With a simple direct gas chromatography injection, no special sample treatments or special injection techniques (such as head-space or solid-phase microextraction) are necessary. This method is especially suited for the fast and quantitative analysis of residual solvents in radiopharmaceutical formulations where 5-12% ethanol is present. The method proved to be both accurate and linear. The quantification limit is in the lower parts-per-million range, which is sufficient given the need for a fast analysis and the maximally allowed concentration for these residual solvents.

Determination of residual solvents and investigation of their effect on ampicillin trihydrate crystal structure

In the present work, the relationship between residual solvents concentration and ampicillin trihydrate crystals stability has been investigated. The amounts of residual solvents determined by GC, X-ray powder diffraction (XRPD) and Fourier transform infrared spectroscopy (FT-IR) were used for characterization of solid state. The obtained results have shown good relationship between concentration of methylene chloride (as a critical residue solvent) and degree of ampicillin trihydrate crystallinity. As with the increasing methylene chloride concentration in the sample the degree of crystallinity decreased after stability test. From this relationship, critical concentration of methylene chloride into the ampicillin trihydrate is obtained and the results can be used for improving the large-scale production of ampicillin trihydrate.

Routine quality control of recycled target [18O]water by capillary electrophoresis and gas chromatography

Recycling of [(18)O]water for [(18)F]fluoride production can be accomplished with reliable results. We have developed sensitive, robust, and rapid analyses of impurities in [(18)O]water. Anions were quantitated by capillary electrophoresis and organic residuals were quantitated by gas chromatography using methods with excellent reproducibility and linearity. Kryptofix 222 (K-222) was quantitated by a sensitive LC-MS-MS technique. Isotopic composition was determined by GC-MS with satisfactory accuracy and precision. These methods were employed to evaluate recovered [(18)O]water purified by a novel electrolysis method. 2-[(18)F]FDG yields using purified [(18)O]water with very low levels of impurities are indistinguishable from newly purchased [(18)O]water. High (> 300 ppm) carbonate concentration reduces the fluoride trapping efficiency of QMA. The analyses of anions, organics, and isotopic enrichment were applied routinely for quality control of [(18)O]water to predict a satisfactory outcome of 2-[(18)F]FDG production.