TY - JOUR
T1 - Radiation induced oxidation of [18F]fluorothia fatty acids under cGMP manufacturing conditions
AU - Pandey, Mukesh K.
AU - Jacobson, Mark S.
AU - Groth, Emily K.
AU - Tran, Natalie G.
AU - Lowe, Val J.
AU - DeGrado, Timothy R.
N1 - Funding Information:
The authors wish to thank Ms. Mai Petterson for acquisition of LCMS data. This work was financially supported by Department of Radiology, Mayo Clinic and CTSA Mayo Clinic Rochester. LCMS was performed at Mayo Clinic Metabolomics Core facility, which is financially supported by U24DK100469 and UL1TR000135 grants.
Funding Information:
The authors wish to thank Ms. Mai Petterson for acquisition of LCMS data. This work was financially supported by Department of Radiology, Mayo Clinic and CTSA Mayo Clinic Rochester . LCMS was performed at Mayo Clinic Metabolomics Core facility, which is financially supported by U24DK100469 and UL1TR000135 grants. Appendix A
Publisher Copyright:
© 2019 Elsevier Inc.
PY - 2020/1/1
Y1 - 2020/1/1
N2 - Objective: The objectives of the present work were to optimize and validate the synthesis and stability of 14(R,S)-[18F]fluoro-6-thia-heptadecanoic acid ([18F]FTHA) and 16-[18F]fluoro-4-thia-palmitic acid ([18F]FTP) under cGMP conditions for clinical applications. Methods: Benzyl-14-(R,S)-tosyloxy-6-thiaheptadecanoate and methyl 16-bromo-4-thia-palmitate were used as precursors for the synthesis of [18F]FTHA and [18F]FTP, respectively. For comparison, a fatty acid analog lacking a thia-substitution, 16-[18F]fluoro-palmitic acid ([18F]FP), was synthesized from the precursor methyl 16-bromo-palmitate. A standard nucleophilic reaction using cryptand (Kryptofix/K222, 8.1 mg), potassium carbonate (K2CO3, 4.0 mg) and 18F-fluoride were employed for the 18F-labeling and potassium hydroxide (0.8 M) was used for the post-labeling ester hydrolysis. The final products were purified via reverse phase semi-preparative HPLC and concentrated via trap and release on a C-18 plus solid phase extraction cartridge. The radiochemical purities of the [18F]fluorothia fatty acids and [18F]FP were examined over a period of 4 h post-synthesis using an analytical HPLC. All the syntheses were optimized in an automated TRACERlab FX-N Pro synthesizer. Liquid chromatography mass spectrometry (LCMS) and high resolution mass spectrometry (HRMS) was employed to study the identity and nature of side products formed during radiosynthesis and as a consequence of post-synthesis radiation induced oxidation. Results: Radiosyntheses of [18F]FTHA, [18F]FTP and [18F]FP were achieved in moderate (8–20% uncorrected) yields. However, it was observed that the HPLC-purified [18F]fluorothia fatty acids, [18F]FTHA and [18F]FTP at higher radioactivity concentrations (>1.11 GBq/mL, 30 mCi/mL) underwent formation of 18F-labeled side products over time but [18F]FP (lacking a sulfur heteroatom) remained stable up to 4 h post-synthesis. Various radiation protectors like ethanol and ascorbic acid were examined to minimize the formation of side products formed during [18F]FTHA and [18F]FTP synthesis but showed only limited to no effect. Analysis of the side products by LCMS showed formation of sulfoxides of both [18F]FTHA and [18F]FTP. The identity of the sulfoxide side product was further confirmed by synthesizing a non-radioactive reference standard of the sulfoxide analog of FTP and matching retention times on HPLC and molecular ion peaks on LC/HRMS. Radiation-induced oxidation of the sulfur heteroatom was mitigated by dilution of product with isotonic saline to reduce the radioactivity concentration to <0.518 GBq/mL (14 mCi/mL). Conclusions: Successful automated synthesis of [18F]fluorothia fatty acids were carried out in cGMP facility for their routine production and clinical applications. Instability of [18F]fluorothia fatty acids were observed at radioactivity concentrations exceeding 1.11 GBq/mL (30 mCi/mL) but mitigated through dilution of the product to <0.518 GBq/mL (14 mCi/mL). The identities of the side products formed were established as the sulfoxides of the respective thia fatty acids caused by radiation-induced oxidation of the sulfur heteroatom.
AB - Objective: The objectives of the present work were to optimize and validate the synthesis and stability of 14(R,S)-[18F]fluoro-6-thia-heptadecanoic acid ([18F]FTHA) and 16-[18F]fluoro-4-thia-palmitic acid ([18F]FTP) under cGMP conditions for clinical applications. Methods: Benzyl-14-(R,S)-tosyloxy-6-thiaheptadecanoate and methyl 16-bromo-4-thia-palmitate were used as precursors for the synthesis of [18F]FTHA and [18F]FTP, respectively. For comparison, a fatty acid analog lacking a thia-substitution, 16-[18F]fluoro-palmitic acid ([18F]FP), was synthesized from the precursor methyl 16-bromo-palmitate. A standard nucleophilic reaction using cryptand (Kryptofix/K222, 8.1 mg), potassium carbonate (K2CO3, 4.0 mg) and 18F-fluoride were employed for the 18F-labeling and potassium hydroxide (0.8 M) was used for the post-labeling ester hydrolysis. The final products were purified via reverse phase semi-preparative HPLC and concentrated via trap and release on a C-18 plus solid phase extraction cartridge. The radiochemical purities of the [18F]fluorothia fatty acids and [18F]FP were examined over a period of 4 h post-synthesis using an analytical HPLC. All the syntheses were optimized in an automated TRACERlab FX-N Pro synthesizer. Liquid chromatography mass spectrometry (LCMS) and high resolution mass spectrometry (HRMS) was employed to study the identity and nature of side products formed during radiosynthesis and as a consequence of post-synthesis radiation induced oxidation. Results: Radiosyntheses of [18F]FTHA, [18F]FTP and [18F]FP were achieved in moderate (8–20% uncorrected) yields. However, it was observed that the HPLC-purified [18F]fluorothia fatty acids, [18F]FTHA and [18F]FTP at higher radioactivity concentrations (>1.11 GBq/mL, 30 mCi/mL) underwent formation of 18F-labeled side products over time but [18F]FP (lacking a sulfur heteroatom) remained stable up to 4 h post-synthesis. Various radiation protectors like ethanol and ascorbic acid were examined to minimize the formation of side products formed during [18F]FTHA and [18F]FTP synthesis but showed only limited to no effect. Analysis of the side products by LCMS showed formation of sulfoxides of both [18F]FTHA and [18F]FTP. The identity of the sulfoxide side product was further confirmed by synthesizing a non-radioactive reference standard of the sulfoxide analog of FTP and matching retention times on HPLC and molecular ion peaks on LC/HRMS. Radiation-induced oxidation of the sulfur heteroatom was mitigated by dilution of product with isotonic saline to reduce the radioactivity concentration to <0.518 GBq/mL (14 mCi/mL). Conclusions: Successful automated synthesis of [18F]fluorothia fatty acids were carried out in cGMP facility for their routine production and clinical applications. Instability of [18F]fluorothia fatty acids were observed at radioactivity concentrations exceeding 1.11 GBq/mL (30 mCi/mL) but mitigated through dilution of the product to <0.518 GBq/mL (14 mCi/mL). The identities of the side products formed were established as the sulfoxides of the respective thia fatty acids caused by radiation-induced oxidation of the sulfur heteroatom.
KW - [F]FP and radiation induced oxidation
KW - [F]FTHA
KW - [F]FTP
KW - [F]fluorothia fatty acid
UR - http://www.scopus.com/inward/record.url?scp=85076511642&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85076511642&partnerID=8YFLogxK
U2 - 10.1016/j.nucmedbio.2019.11.004
DO - 10.1016/j.nucmedbio.2019.11.004
M3 - Article
C2 - 31759313
AN - SCOPUS:85076511642
VL - 80-81
SP - 13
EP - 23
JO - International journal of radiation applications and instrumentation. Part B, Nuclear medicine and biology
JF - International journal of radiation applications and instrumentation. Part B, Nuclear medicine and biology
SN - 0969-8051
ER -