Synthesis and Evaluation of 11C-Labeled Triazolones as Probes for Imaging Fatty Acid Synthase Expression by Positron Emission Tomography.

Cancer cells require lipids to fulfill energetic, proliferative, and signaling requirements. Even though these cells can take up exogenous fatty acids, the majority exhibit a dependency on de novo fatty acid synthesis. Fatty acid synthase (FASN) is the rate-limiting enzyme in this process. Expression and activity of FASN is elevated in multiple cancers, where it correlates with disease progression and poor prognosis. These observations have sparked interest in developing methods of detecting FASN expression in vivo. One promising approach is the imaging of radiolabeled molecular probes targeting FASN by positron emission tomography (PET). However, although [11C]acetate uptake by prostate cancer cells correlates with FASN expression, no FASN-specific PET probes currently exist. Our aim was to synthesize and evaluate a series of small molecule triazolones based on GSK2194069, an FASN inhibitor with IC50 = 7.7 ± 4.1 nM, for PET imaging of FASN expression. These triazolones were labeled with carbon-11 in good yield and excellent radiochemical purity, and binding to FASN-positive LNCaP cells was significantly higher than FASN-negative PC3 cells. Despite these promising characteristics, however, these molecules exhibited poor in vivo pharmacokinetics and were predominantly retained in lymph nodes and the hepatobiliary system. Future studies will seek to identify structural modifications that improve tumor targeting while maintaining the excretion profile of these first-generation 11C-methyltriazolones.

A general 11C-labeling approach enabled by fluoride-mediated desilylation of organosilanes.

Carbon-11 (11C) is one of the most ideal positron emitters for labeling bioactive molecules for molecular imaging studies. The lack of convenient and fast incorporation methods to introduce 11C into organic molecules often hampers the use of this radioisotope. Here, a fluoride-mediated desilylation (FMDS) 11C-labeling approach is reported. This method relies on thermodynamically favored Si-F bond formation to generate a carbanion, therefore enabling the highly efficient and speedy incorporation of [11C]CO2 and [11C]CH3I into molecules with diversified structures. It provides facile and rapid access to 11C-labeled compounds with carbon-11 attached at various hybridized carbons as well as oxygen, sulfur and nitrogen atoms with broad functional group tolerance. The exemplified syntheses of several biologically and clinically important radiotracers illustrates the potentials of this methodology.

Synthesis of [1-11C]Butanol via a facile solid phase extraction protocol.

A facile synthesis method for the preparation of [1-11C]butanol, a regional cerebral blood flow imaging agent, was developed. Using a solid phase extraction method, the highly polar and volatile molecule [1-11C]butanol was quickly concentrated, purified, and released as final product; boasting high radiochemical and chemical purities as well as high radiochemical yields. The final drug product was obtained as a sterile, pyrogen-free solution that conforms United States Pharmacopeia (USP) <823> requirements.

Otto: a 4.04 GBq (109 mCi) 68Ge/68Ga generator, first of its kind - extended quality control and performance evaluation in the clinical production of [68Ga]Ga-PSMA-11.

BACKGROUND: Here we report on the comprehensive quality control of a 4.04 GBq (109 mCi) generator supplied by itG (Munich, Germany), and used for routine production of [68Ga]Ga-PSMA-11 for clinical imaging. The performance of the 4.04 GBq itG 68Ge/68Ga generator was studied for a year and parameters including elution yield, elution profile, radioactive and stable contaminants were collected. The production yields of a series of 175 [68Ga]Ga-PSMA-11 clinical batches are also reported herein. RESULTS: This first-of-its-kind GMP grade 68Ge/68Ga generator from itG with a nominal activity of 4.04 GBq (109 mCi) showed a stable 68Ga elution profile with elution efficiency averaging 58.3 ± 3.7%. 68Ge contaminant in the eluent slightly increased over time but remained 100x lower than those reported for comparable 1.85 GBq (50 mCi) itG generators. Metal impurities were found in concentrations lower than 100 ng/ml (ppb) throughout the study. [68Ga]Ga-PSMA-11 was obtained in 89 ± 4% radiochemical yields and > 99% radiochemical and chemical purities. CONCLUSION: 4.04 GBq (109 mCi) itG 68Ge/68Ga generator is suitable for routinely produced 68Ga tracers used in the clinic. Up to 30% higher amount of final drug product was obtained as compared to the 1.85 GBq (50 mCi) itG generator, and as a result larger number of studies could be performed, while reducing the synthetic burden.