Pharmacological Characterization of (E)-N-(4-Fluorobut-2-enyl)-2β-carbomethoxy-3β-(4′-tolyl)nortropane (LBT-999) as a Highly Promising Fluorinated Ligand for the Dopamine Transporter

Abstract

In the aim to develop an efficient fluorinated probe for positron emission tomography (PET) exploration of the dopamine transporter (DAT), we studied several in vitro and in vivo characteristics of the phenyltropane derivative (E)-N-(4-fluorobut-2-enyl)-2␤-carbomethoxy-3␤-(4Ј-tolyl)nortropane (LBT-999). In vitro on rat striatal membrane, [3 H]LBT-999 bound to a single site with a K d of 9 nM, B max of 17 pmol/mg protein, and a very high selectivity for the DAT [IC 50 for 1-{2-[bis-(4-fluorophenyl)-methoxy]ethyl}-4-(3-phenylpropyl)piperazine (GBR 12909) and (E)-N-(3-iodoprop-2-enyl)-2␤-carbomethoxy-3␤-(4Ј-methylphenyl)nortropane (PE2I): 2.4 and 18 nM, respectively; IC 50 for paroxetine, citalopram, N,N-dimethyl-2-(2-amino-4-methylphenyl thio)benzylamine, nisoxetine, and desipramine Ͼ1 M]. In vitro on post-mortem human brain sections, LBT-999 bound with high intensity to the caudate-putamen, weakly to the thalamus, and not in the neocortex and cerebellum. This binding was totally abolished in the presence of PE2I. Ex vivo cerebral biodistribution of [11 C]LBT-999 in rats showed striatum/ cerebellum radioactivity ratios of 18 and 25 at 30 and 60 min postinjection, respectively. This accumulation was strongly prevented by preinjection of GBR 12909, whereas paroxetine and nisoxetine had no effect. An in vivo kinetic PET study in three baboons showed a fast and very high uptake in the striatum, with a plateau at 30 min postinjection and a maximal putamen/ cerebellum ratio of 30. Taken together, these findings demonstrate that LBT-999 is a highly promising agent for in vivo exploration of the DAT. This probe is currently labeled with 18 F for further characterizations.As the membrane dopamine transporter (DAT) is very involved in a number of brain functions, in vivo exploration of this molecular target could become a relevant tool for the knowledge of pathophysiological mechanisms and diagnosis and follow-up of several neurological and psychiatric conditions. In this field, scintigraphic exploration of the DAT could be very useful for the early diagnosis and follow-up of Parkinson's disease. Most of these studies have been performed using single photon emission computerized tomography with radioligands chemically derived from the cocaine structure and labeled with 123 I such as 2␤-carbomethoxy-3␤-(4-iodophenyl)tropane (Innis et al., 1993;Seibyl et al., 1998; Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.105.096792.ABBREVIATIONS: DAT, dopamine transporter; FPCIT,

Quantitative analysis of dopamine transporters in human brain using [11C]PE2I and positron emission tomography: evaluation of reference tissue models

“…One of the presynaptic functions is the dopamine reuptake mediated by dopamine transporter (DAT), a membrane-bound protein. A number of radioligands for in vivo DAT imaging have been developed for positron emission tomography (PET), such as [ 11 C]cocaine [1], [ 11 C]WIN35,428 (CFT) [2,3], [ 11 C]b-CIT (RTI-55) [4], [ 11 C] b-CIT-FE [5], [ 11 C]D-threo-methylphenidate [6], [ 18 F]FECNT [7], [ 11 C]Altropane [8], [ 11 C]PE2I [9] and most recently [ 11 C]LBT-999 [10]. Most of them are analogs of cocaine and have some degree of affinity for the serotonin transporter.…”

Imaging of the Striatal and Extrastriatal Dopamine Transporter with 18F-LBT-999: Quantification, Biodistribution, and Radiation Dosimetry in Nonhuman Primates

“…) is a tropane derivative with high affinity for the DAT (radioligand equilibrium dissociation constant [K D ], 9.15 nM) (6), and similarly to PE2I, LBT-999 is of potential interest for imaging the DAT in the striatum and extrastriatal regions (7). LBT-999 has been labeled with both 11 C and 18 F (8-10).…”

Food preferences and aversions in human health and nutrition: how can pigs help the biomedical research?

“…Some studies identified efficient radioligands and isotopes currently used to explore the dopamine transporter (DAT) because this molecular target is involved in numerous neurological diseases such as Parkinson's disease in humans. In their study, Wang et al (2007) used the 18 F-FP-CIT, a radiotracer that binds specifically to DAT, whereas Chalon et al (2006) used the 11 C-LBT-999 to investigate the DAT variations in baboons. Minuzzi et al (2006), however, reported that several usual radioligands failed to bind to DAT in the pig brain, although they revealed the presence of DAT in rat, ferret, monkey and human brains.…”