Gerard J. Boer

[123I]FP-CIT SPECT shows a pronounced decline of striatal dopamine transporter labelling in early and advanced Parkinson's disease.

OBJECTIVES: The main neuropathological feature in Parkinsons disease is a severe degeneration of the dopaminergic neurons in the substantia nigra resulting in a loss of dopamine (DA) transporters in the striatum. [123I]beta-CIT single photon emission computed tomography (SPECT) studies have demonstrated this loss of striatal DA transporter content in Parkinsons disease in vivo. However, studies with this radioligand also showed that an adequate imaging of the striatal DA transporter content could only be performed on the day after the injection of radioligand, which is not convenient for outpatient evaluations. Recently, a new radioligand [123I]FP-CIT, with faster kinetics than beta-CIT, became available for imaging of the DA transporter with SPECT, and the applicability of this ligand was tested in patients with early and advanced Parkinsons disease, using a one day protocol. METHODS: [123I]FP-CIT SPECT was performed in six patients with early and 12 patients with advanced Parkinsons disease, and in six age matched healthy volunteers. RESULTS: Compared with an age matched control group striatal [123I]FP-CIT uptake in patients with Parkinsons disease was decreased, and this result was measurable three hours after injection of the radioligand. In the Parkinsons disease group the uptake in the putamen was reduced more than in the caudate nucleus. The contralateral striatal uptake of [123I]FP-CIT was significantly lower than the ipsilateral striatal uptake in the Parkinsons disease group. Specific to non-specific striatal uptake ratios correlated with the Hoehn and Yahr stage. A subgroup of patients with early Parkinsons disease also showed significantly lower uptake in the putamen and lower putamen:caudate ratios than controls. CONCLUSION: [123I]FP-CIT SPECT allows a significant discrimination between patients with Parkinsons disease and age matched controls with a one day protocol, which will be to great advantage in outpatient evaluations.

Practical benefit of [123I]FP-CIT SPET in the demonstration of the dopaminergic deficit in Parkinson's disease

Loss of striatal dopamine (DA) transporters in Parkinsons disease (PD) has been accurately assessed in vivo by single-photon emission tomography (SPET) studies using [123I]β-CIT. However, these studies have also shown that adequate imaging of the striatal DA transporter content can be performed only 20–30 h following the injection of [123I]β-CIT, which is not convenient for routine out-patient evaluations. Recently, a new ligand,N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)tropane (FP-CIT), became available for in vivo imaging of the DA transporter. The faster kinetics of [123I]FP-CIT have been shown to allow adequate acquisition as early as 3 h following injection. In the present study, loss of striatal DA transporters in five non-medicated PD patients was assessed on two consecutive SPET scans, one with [123I]β-CIT (24 h following injection) and one with [123I]FP-CIT (3 h following injection). The ratios of specific to non-specific [123I]FP-CIT uptake in the caudate nucleus and putamen were consistently 2.5-fold lower than those of [123I]β-CIT. However, when the uptake ratio of both ligands in these brain regions of patients was expressed as a percentage of the uptake ratio found in healthy controls, both the decrease and the variation of the data were similar. It is concluded on the basis of these findings that [123I]FP-CIT seems as good as [123I]β-CIT for the assessment of the dopaminergic deficit in PD. The faster kinetics of [123I]FP-CIT are a clear advantage.

[123I]FP-CIT binds to the dopamine transporter as assessed by biodistribution studies in rats and SPECT studies in MPTP-lesioned monkeys

[123I]FP‐CIT (N‐ω‐fluoropropyl‐2β‐carbomethoxy‐3β‐{4‐iodophenyl}tropane), a radioiodinated cocaine analogue, was evaluated as an agent for the in vivo labeling of dopamine (DA) transporters by biodistribution studies in rats and by single photon emission computed tomography (SPECT) studies in unilateral 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)–lesioned monkeys. In rats, intravenous injection of [123I]FP‐CIT resulted in high accumulation of radioactivity in the striatum. Less pronounced uptake was seen in brain areas with high densities of serotonergic uptake sites. While striatal uptake of radioactivity after injection of [123I]FP‐CIT was displaced significantly by GBR12,909 but not by fluvoxamine, the opposite was observed in brain areas known to be rich of serotonin transporters. Monkeys which were unilaterally treated with neurotoxic doses of MPTP showed severe loss of striatal [123I]FP‐CIT uptake at the side of treatment. The results of this study indicate that [123I]FP‐CIT, although not being a selective radioligand, binds specifically to the striatal DA transporter in vivo and thus suggest that [123I]FP‐CIT promises to be a suitable radioligand for SPECT imaging of DA transporters in humans. Synapse 27:183–190, 1997.

The stereoisomers of 17α-[123I]iodovinyloestradiol and its 11α-methoxy derivative evaluated for their oestrogen receptor binding in human MCF-7 cells and rat uterus, and their distribution in immature rats

We studied the potential of both stereoisomers of 17α-[123I]iodovinyloestradiol (E- andZ-[123I]IVE) and of 11β-methoxy-17α-[123I]iodovinyloestradiol (E-andZ-[123I]MIVE) as suitable radioligands for the imaging of oestrogen receptor(ER)-positive human breast tumours. The 17α-[123I]iodovinyloestradiols were prepared stereospecifically by oxidative radio-iododestannylation of the corresponding 17α-tri-n-butylstannylvi-nyloestradiol precursors. Competitive binding studies were performed in order to determine the relative binding affinity (RBA) of the unlabelled 17α-iodovinyloes-tradiols for the ER in both human MCF-7 breast tumour cells and rat uterine tissue, compared with that of diethylstilboestrol (DES). Target tissue uptake, retention and uptake selectivity of their123I-labelled analogues were studied in immature female rats. All four 17α-iodovi-nyloestradiols showed high affinity for the ER in human MCF-7 cells, as well as rat uterus. Their RBA for the ER showed the following order of decreasing potency: RBA of DES >Z-IVE >Z-MIVE >E-MIVE ≥E-IVE. Neither of these 17α-iodovinyloestradiols showed any significant binding to the sex hormone binding globulin in human plasma. The biodistribution studies showed ER-mediated uptake in the uterus, ovaries and pituitary, that ofE- andZ-[123I]MIVE being higher than that ofE- andZ-[123I]IVE. High target-to-non-target tissue uptake ratios, especially at longer periods after injection (up to 24 h), were exhibited by both isomers of [123I]MIVE. The uterus-to-blood uptake ratio was higher forE-[123I]MIVE. However, the uterus-to-fat uptake ratio appeared to be higher for theZ-isomer of [123I]MIVE, especially at 24 h after injection. Metabolic properties and temperature effects, which play a more important role in vivo, probably cause the discrepancies seen between in vitro and in vivo binding results. On the basis of their in vitro binding properties and in vivo distribution characteristics we conclude thatE- andZ-[123I]MIVE could be suitable radioligands for the diagnostic imaging of ER in human breast cancer. Therefore, further studies with these radioligands in mature normal and tumour-bearing rats are warranted.

The Z-isomer of 11β-methoxy-17α-[123I]iodovinylestradiol is a promising radioligand for estrogen receptor imaging in human breast cancer

The potential of both stereoisomers of 11 beta-methoxy-17 alpha-[123I] iodovinylestradiol (E- and Z-[123I]MIVE) as suitable radioligands for imaging of estrogen receptor (ER)-positive human breast tumours was studied. The 17 alpha-[123I]iodovinylestradiol derivatives were prepared stereospecifically by oxidative radioiododestannylation of the corresponding 17 alpha-tri-n-butylstannylvinylestradiol precursors. Both isomers of MIVE showed high in vitro affinity for dimethylbenzanthracene-induced rat and fresh human mammary tumour ER, that of Z-MIVE however being manyfold higher than that of E-MIVE. In vivo distribution studies with E- and Z-[123I]MIVE in normal and tumour-bearing female rats showed ER-mediated uptake and retention in uterus, ovaries, pituitary, hypothalamus and mammary tumours, again the highest for Z-[123I]MIVE. The uterus- and tumour-to-nontarget tissue (far, muscle) uptake ratios were also highest for Z-[123I]MIVE. Additionally, planar whole body imaging of two breast cancer patients 1-2 h after injection of Z-[123I]MIVE showed increased focal uptake at known tumour sites. Therefore, we conclude that Z-[123I]MIVE is a promising radioligand for the diagnostic imaging of ER in human breast cancer.

In vitro and in vivo D2-dopamine receptor binding with [123I]S(−)iodobenzamide ([123I]IBZM) in rat and human brain

As a promising dopamine D2-receptor imaging agent for single photon emission computerized tomography (SPECT), [123I](S)-(-)-2-hydroxy-3-iodo-6-methoxy-N [(1-ethyl-2-pyrrolidinyl)methyl]benzamide ([123I]IBZM) has recently been synthesized in a modified way along with its precursor, S(-)BZM, and the stereoisomer R(+)BZM. The present study applied this new product to investigate in vitro and in vivo D2-receptor binding in rat brain and in postmortem human brain. In vitro saturation binding curves with [123I]IBZM for rat crude striatal membrane preparations yielded an affinity constant (Kd) of 0.28 nM confirming data in the literature. Displacement curves revealed an order of increasing potency as follows: R(+)BZM less than S(-)sulpiride = less than S(-)BZM less than S(-)IBZM. A similar order was obtained when [3H]spiperone was used as ligand. For human putamen and caudate nucleus membranes slightly higher Kd values (0.49 nM) were obtained. Rank order of displacing potency for the various drugs was similar to that found in the rat preparations. In vivo uptake of [123I]IBZM in rat brain following injection of 50 microCi (12-16 pmol) in the tail vein revealed an increase in the striatum-to-cerebellum ratio from 1.5 at 5 min to 6.9 at 2 h. The olfactory tubercle-to-cerebellum ratio was also raised from 1.6 to 3.3. Other brain regions tested failed to show statistically significant enhancements. Coinjection of 40 nmol S(-)IBZM, 4 mumol S(-)BZM or 200 nmol haloperidol displaced [123I]IBMZ when tested at 90 min. The use of 4 mumol R(+)BZM resulted in minor displacement only, demonstrating that stereospecificity of the displacement was present in vivo and in vitro. Displacements were also observed in substantia nigra and pons-medulla oblongata, but not in hippocampus or frontal and occipital cortex. The data provide the required background needed in order to initiate in vivo binding studies for D2-receptors in basal ganglia of human patients using [123I]IBZM in SPECT analyses.

In vitro and in vivo characterization of newly developed iodinated 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]piperazine derivatives in rats: limited value as dopamine transporter SPECT ligands

A series of 1‐{2‐[bis(4‐fluorophenyl)methoxy]ethyl}piperazines (CYD1, 2, 3, 5) with a 4‐substituent incorporating a 1‐hydroxy‐3‐iodo‐2‐propenyl moiety, except CYD2 which lacks the hydroxy, was synthesized as potential in vivo imaging ligands for the dopamine transporter. For two of the piperazine derivatives (CYD3 and 5), possible stereoselectivity was considered as well (both E‐ and Z‐form). Their in vitro potency for inhibition of [3H]dopamine uptake in rat striatal synaptosomes was 10‐fold lower than that of GBR 12909 used as a reference. The highest Ki values were 137 and 101 nM for CYD1E and CYD3E, respectively. Inhibition potency was higher for the E‐ than for the Z‐isomers. In vivo distribution of radioactivity in rats injected with the 123I‐labeled CYDs showed preferred striatal uptake for CYD1E and CYD3E as compared to the cerebellum and occipital cortex. Although the E‐isomer of CYD3 showed the best in vitro and in vivo binding characteristics, its striatal uptake ratios (maximal value: 2.7 for striatum‐to‐cerebellum at 4 h p.i.) are too low to consider application in human Single Photon Emission Computed Tomography studies.

Cardiac iodine-123 metaiodobenzylguanidine uptake in animals with diabetes mellitus and/or hypertension

The aim of the present study was to evaluate the use of the noradrenaline analogue iodine-123 metaiodobenzylguanidine ([123I]MIBG) for the assessment of cardiac sympathetic activity in the presence of diabetes mellitus and/or hypertension in animal models. One model used Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) rendered diabetic at 12 weeks of age by an intravenous injection of streptozotocin (STZ). The other model used lean and obese Zucker rats. In all groups basic haemodynamic values were established and animals received an intravenous injection of 50 μCi [123I]MIBG. Initial myocardial uptake and washout rates of [123I]MIBG were measured scintigraphically during 4 h. After sacrifice, plasma noradrenaline and left cardiac ventricular β-adrenoceptor density was determined. The diabetic state, both in STZ-treated rats (direct induction) and in obese Zucker rats (genetic induction), appeared to induce a lower cardiac density of β-adrenoceptors, indicative of increased sympathetic activity. Cardiac [123I]MIBG then showed increased washouts, thereby confirming enhanced noradrenergic activity. This parallism of results led to the conclusion that [123I]MIBG wash-out measurements could provide an excellent tool to assess cardiac sympathetic activity non-invasively. However, in hypertension (WKY vs SHR), both parameters failed to show parallelism: no changes in β-adrenoceptor density were found, whereas [123I]MIBG wash-out rate was increased. Thus, either [123I]MIBG washout or ß-adrenoceptor density may not be a reliable parameter under all circumstances to detect changes in the release of noradrenaline. Changes in the initial uptake of [123I]MIBG were observed as well. This may be a good marker for the disappearance of cardiac innervation, but it seems not to be a good parameter for distinguishing between loss of sympathetic innervation and enhanced uptake of noradrenaline in pathological conditions.

New iodinated progestins as potential ligands for progesterone receptor imaging in breast cancer. part 2: in vivo pharmacological characterization

On the basis of the observed high selective binding to both the human and rat progesterone receptor (PR) in vitro, three 17alpha-iodovinyl-substituted nortestosterone derivatives, i.e., the Z-isomer of 17alpha-iodovinyl-19-nortestosterone (Z-IVNT; Z-IPG1) and both the stereoisomers of 17alpha-iodovinyl-18-methyl-11-methylene-19-nortestosterone (E- and Z-IPG2), were selected for radio-iodination and subsequently evaluated as potential radioligands for PR imaging in human breast cancer. Their target tissue uptake, retention, and uptake selectivity were studied in female rats. The distribution studies revealed that PR-mediated uptake in the uterus and ovaries could only be demonstrated for Z-[123I]IPG2. The target tissue uptake selectivity was, however, low, with the highest uterus-to-nontarget tissue uptake ratios observed at 2-4 h postinjection (p.i.), being 4.4, 1.8, and 7.4 for the uterus-to-blood, -fat, and -muscle ratio, respectively. For Z-[123I]IPG2, distribution was also studied in dimethylbenzanthracene (DMBA)-induced mammary tumour-bearing rats and in normal rabbits. Mammary tumour uptake of Z-[123I]IPG2 in the mammary tumour-bearing rat was also found to be PR-specific. In rabbits, higher selective target tissue uptake of Z-[123I]IPG2 was observed than in rats, resulting in uterus-to-blood, -fat, and -muscle ratios of 6.6, 2.2, and 21.3 at 2-4 h p.i., respectively. In conclusion, Z-[123I]IPG2, which displayed high binding affinity for both the human and rat PR in vitro, showed specific PR-mediated target tissue uptake in rats and rabbits in vivo, the uptake selectivity being highest in the latter. Because the binding characteristics appeared to vary between species, a pilot study in breast cancer patients may be needed to decide whether Z-[123I]IPG2 can be of potential use as PR imaging agent in breast cancer.

Synthesis, Estrogen Receptor Binding, and Tissue Distribution of a New Iodovinylestradiol Derivative (17α,20E)-21-[123I]Iodo-11β-Nitrato-19-Norpregna-1,3,5(10),20-Tetraene-3,17-Diol (E-[123I]NIVE)

We have synthesized and evaluated E-11beta-nitrato-17alpha-iodovinylestradiol (E-NIVE; E-3c) and its 123I-labelled form, as a new potential radioligand for imaging of estrogen receptor (ER)-positive human breast tumors. E-[123I]NIVE was prepared by stereospecific iododestannylation of the E-tri-n-butylstannylvinyl precursor (E-2c), obtained from reaction of 11beta-nitrato-estrone (8) with E-tributylstannylvinyllithium. In competitive binding studies, E-NIVE proved to have high binding affinity for both the rat and the human ER (Ki 280-730 pM), without significant binding to human sex hormone binding globulin. Distribution studies in normal and mammary tumor-bearing rats showed specific ER-mediated uptake of E-[123I]NIVE in the estrogen target tissues, i.e., uterus, ovaries, pituitary, and hypothalamus, but not in the mammary tumors. Selective retention in these target tissues, including tumor tissue, resulted in significant increases over time for the target tissue-to-muscle uptake ratios, but not for the target tissue-to-fat uptake ratios. The tumor-to-fat uptake ratio even appeared constantly below 1. In the primary estrogen target tissues, E-[123I]NIVE displayed high specific ER-mediated uptake and retention, which resulted in moderate target-to-nontarget tissue uptake ratios. In contrast, in tumor tissue, E-[123I]NIVE uptake appeared to be rather low and not ER-specific. As a consequence, E-[123I]NIVE appears to be a less favorable radioligand for ER imaging in breast cancer than the previously studied stereoisomers of 11beta-methoxy-17alpha-[123I]iodovinylestradiol (E- and Z-[123I]MIVE; [123I]E- and [123I]Z-3b).