In vitro and in vivo Human Metabolism of (S)-[18F]Fluspidine – A Radioligand for Imaging σ1 Receptors With Positron Emission Tomography (PET)

Abstract

S)-[ 18 F]fluspidine ((S)-[ 18 F]1) has recently been explored for positron emission tomography (PET) imaging of sigma-1 receptors in humans. In the current report, we have used plasma samples of healthy volunteers to investigate the radiometabolites of (S)-[ 18 F]1 and elucidate their structures with LC-MS/MS. For the latter purpose additional in vitro studies were conducted by incubation of (S)-[ 18 F]1 and (S)-1 with human liver microsomes (HLM). In vitro metabolites were characterized by interpretation of MS/MS fragmentation patterns from collision-induced dissociation or by use of reference compounds. Thereby, structures of corresponding radio-HPLCdetected radiometabolites, both in vitro and in vivo (human), could be identified. By incubation with HLM, mainly debenzylation and hydroxylation occurred, beside further mono-and di-oxygenations. The product hydroxylated at the fluoroethyl side chain was glucuronidated. Plasma samples (10, 20, 30 min p.i., n = 5-6), obtained from human subjects receiving 250-300 MBq (S)-[ 18 F]1 showed 97.2, 95.4, and 91.0% of unchanged radioligand, respectively. In urine samples (90 min p.i.) the fraction of unchanged radioligand was only 2.6% and three major radiometabolites were detected. The one with the highest percentage, also found in plasma, matched the glucuronide formed in vitro. Only a small amount of debenzylated metabolite was detected. In conclusion, our metabolic study, in particular the high fractions of unchanged radioligand in plasma, confirms the suitability of (S)-[ 18 F]1 as PET radioligand for sigma-1 receptor imaging.

In vitro and in vivo evaluation of fluorinated indanone derivatives as potential positron emission tomography agents for the imaging of monoamine oxidase B in the brain

“…General procedure B; tan solid; 74% yield; TLC (EA/PE, 1:1): Rf = 0.66; M. p. = 103 °C; LC-MS: tR = 11.4 min, > 99; 1 H-NMR (400 MHz, CDCl3): δ = 7.41 (dd, J = 0.9, 8.2 Hz, 1H), 7.37 (td, J = 5.9, 8.0 Hz, 1H), 7.33 -7.24 (m, 2H), 7.24 -7.20 (m, 1H), 7.17 (dt, J = 2.1, 9.7 Hz, 1H), 7.08 -6.96 (m, 1H), 5…”

“…Incubations with MLM and HLM had a final volume of 250 µL and were performed in PBS (pH 7.4) as follows, 5 with final concentrations as stated in brackets. PPS, MLM or HLM (1 mg/mL respectively), and [ 18 F]6 (~3 MBq) were mixed vigorously and pre-incubated for 3 min at 37°C.…”

“…For monitoring of metabolic depletion [ 18 F]6 the HPLC system (X-LC, JASCO) with radioactivity detection was used as previously described. 5 A ReproSil-Pur 120 C18-AQ column, (150 x 3 mm, 3 µm, incl. 10 x 3 mm pre-column -both Dr. Maisch GmbH) was used as stationary phase.…”

Evaluation of 18F-IAM6067 as a sigma-1 receptor PET tracer for neurodegeneration in vivo in rodents and in human tissue

“…18 F-FTC-146 has been used in a preclinical model 58 and in a clinical case of peripheral injury 59 although it was also found to have slow brain pharmacokinetic for its use in human 30 , 31 . Conversely, (S)- 18 F-fluspidine seems to have suitable pharmacokinetics and metabolism in human 60 , 61 and is now being used in clinical studies 62 , 63 . 18 F-IAM6067 had already been shown to have sufficient selectivity against S2R (K i σ2/σ1 = 187) and other targets (see supplementary data in 29 in which 18 F-IAM6067 is compound #30 page S3).…”

A Pharmacokinetic and Metabolism Study of the TRPC6 Inhibitor SH045 in Mice by LC-MS/MS

“…To explore metabolites of SH045 formed by microsomes, DPBS, alamethicin (25 µg/mL) [ 44 ] and MLM or HLM (1.0 mg/mL) were pre-incubated [ 45 ], further incubated with SH045 MgCl 2 , NADPH and UDPGA, terminated, and processed for LC-MS/MS analysis as described. Positive controls with testosterone and 4-nitrophenol and negative controls were analyzed too ( Supplementary Materials SM7 ).…”