[125I]MIBG uptake and release in different regions of the rat brain

Chemical Delivery System of MIBG to the Central Nervous System: Synthesis, 11C-Radiosynthesis, and in Vivo Evaluation

The norepinephrine transporter (NET) plays an important role in neurotransmission and is involved in a multitude of psychiatric and neurodegenerative diseases. [¹²³I/¹³¹I]meta-iodobenzylguanidine (MIBG) is a widely used radiotracer in the diagnosis and follow-up of peripheral neuroendocrine tumors overexpressing the norepinephrine transporter. MIBG does not cross the blood-brain barrier (BBB), and we have demonstrated the "proof-of-concept" that 1,4-dihydroquinoline/quinolinium salt as chemical delivery system (CDS) is a promising tool to deliver MIBG to the brain. To improve BBB passage, various substituents on the 1,4-dihydroquinoline moiety and a linker between CDS and MIBG were added. A series of CDS-MIBG 1a-d was synthesized, labeled with carbon-11, and evaluated in vivo into rats. The in vivo results demonstrated that, although adding substituents on CDS in 1a-c is of no benefit for brain delivery of MIBG, the presence of a linker in CDS-MIBG 1d greatly improved both brain penetration and the release rate of MIBG in the central nervous system.

Neuroblastoma with a solitary intraventricular brain metastasis visualized on I-123 MIBG scan

BACKGROUND

Although metastatic skull lesions of neuroblastoma are not uncommon, brain involvement is infrequent and prompt diagnosis is of utmost importance in such cases. Previous studies have shown that Meta-Iodo-Benzyl-Guanidine (MIBG) scans were not always reliable in detecting central nervous system metastases, however most published reports referred to the Iodine-131 ((131)I)-MIBG scans. Herein, we report an intraventricular metastasis of neuroblastoma diagnosed using an Iodine-123 ((123)I)-MIBG scan, which is increasingly being used in clinical practice and reported as a more accurate method for detecting metastatic lesions.

CASE DESCRIPTION

An unusual case of metastatic neuroblastoma to the left lateral ventricle of the brain is presented. Planar (123)I-MIBG scintigraphy showed faint tracer activity close to the midline without asymmetric extensions or abnormal activity in the skull bones. A subsequent brain MR scan revealed an enhancing mass within the left frontal horn consistent with a metastatic lesion. The patient underwent tumor resection with pathology showing neuroblastoma.

CONCLUSIONS

Our case shows that (123) I-MIBG scintigraphy can be useful in detecting intraventricular brain metastases of neuroblastoma. Although the (123)I-MIBG scintigraphy has been reported to have a significantly superior sensitivity in monitoring asymptomatic patients with neuroblastoma compared with (131)I-MIBG scans, bone marrow histology, bone scan, CT, and urinary catecholamine levels, further studies may be necessary to evaluate its sensitivity in detecting brain lesions.

Central nervous system metastases in neuroblastoma: radiologic, clinical, and biologic features in 23 patients

BACKGROUND

Central nervous system (CNS) metastases rarely occur in patients with neuroblastoma, although recent reports suggest an increase in the rate. CNS recurrence may represent a different mechanism of spread than bone and bone marrow metastases and may be associated with unique genetic determinants. Further definition of the radiologic, clinical, and biologic features may provide clues to the predisposing factors and mechanisms of CNS dissemination.

METHODS

A retrospective analysis of all children ages 0-21 years with Stage IV neuroblastoma who were diagnosed at the Institut Curie and the Institut Gustave-Roussy between 1985 and 2000 was performed with direct review of medical records and magnetic resonance images, computed tomography scans, and iodine-123 or iodine-131 metaiodobenzylguanidine scintiscans (MIBG scans). When tumor tissue was available, genetic analysis was performed using comparative genomic hybridization (CGH).

RESULTS

Of 434 patients with Stage 4 disease, 23 children had the CNS as their site of first recurrence. The estimated risk of CNS recurrence was 8.0% at 3 years, with no significant change in risk over the 15-year period. Eleven patients had isolated CNS recurrences, and the remaining patients developed recurrences concomitantly in other sites. The sites of recurrences were parenchymal (n = 8 patients), parenchymal with meningeal (n = 7 patients), and meningeal alone (n = 8 patients). MIBG scans detected CNS lesions in only 43% of patients. Significant risk factors for CNS recurrence included lumbar puncture at diagnosis, ages 2-3 years, and MYCN gene amplification. Abnormalities that were identified using CGH, in addition to 2p24 amplification in 5/7, included gains of 17q and 18q and losses of 1p, 3p, 10q25-26, and 11q.

CONCLUSIONS

The risk of CNS recurrence in patients with neuroblastoma is 8% at 3 years after diagnosis and has not increased in the last 15 years. Because the CNS often is the sole site of recurrence, either it may be a sanctuary site, or the biologic determinants of CNS metastasis may be unique. Elucidation of risk factors and pathogenesis may allow prevention of this fatal event. Cancer 2003;98:155-65.

Effect of adrenergic receptor ligands on metaiodobenzylguanidine uptake and storage in neuroblastoma cells

The effects of adrenergic receptor ligands on uptake and storage of the radiopharmaceutical [125I]metaiodobenzylguanidine (MIBG) were studied in the human neuroblastoma cell line SK-N-SH. For uptake studies, cells were incubated for 15 min with varying concentrations of alpha-agonist (clonidine, methoxamine, and xylazine), alpha-antagonist (phentolamine, tolazoline, phenoxybenzamine, yohimbine, and prazosin), beta-antagonist (propranolol, atenolol), beta-agonist (isoprenaline and salbutamol), mixed alpha/beta antagonist (labetalol), or the neuronal blocking agent guanethidine, prior to the addition of [125I]MIBG (0.1 microM). The incubation was continued for 2 h and specific cell-associated radioactivity was measured. For the storage studies, cells were incubated with [125I]MIBG for 2 h, followed by replacement with fresh medium with or without drug (MIBG, clonidine, or yohimbine). Cell-associated radioactivity was measured at various times over the next 20 h. Propanolol reduced [125I]MIBG uptake by approximately 30% (P<0.01) at all concentrations tested, most likely due to nonspecific membrane changes. However, incubation with the other beta-agonists or antagonists failed to elicit significant reductions in uptake. In contrast, all of the alpha-agonists significantly inhibited uptake (P<0.05); guanethidine >xylazine >clonidine=methoxamine. The alpha-antagonists demonstrated a broad range of inhibition (phenoxybenzamine >>phentolamine >prazosin >>yohimbine=tolazoline)(P< 0.05). The mixed ligand, labetolol, inhibited MIBG uptake in a dose-dependent manner with an apparent IC50 of 0.65 microM. The retention studies demonstrated that unlabeled MIBG caused profound self-inhibition (P<0.01). Clonidine produced a modest inhibition of retention and yohimbine had no effect. Labetalol, phenoxybenzamine, guanethidine, and propranolol reduced uptake of [125I]MIBG by neuroblastoma cells in culture. Although only labetalol has been reported to cause false-negative MIBG scans, our results suggest that these other drugs have the potential to interfere with MIBG imaging and therapy, particularly at high doses. Adrenergic drugs did not alter cytoplasmic retention of [125I]MIBG in neuroblastoma cells but may have potential in tumors such as phenochromocytoma, where granular storage of MIBG has been observed. Inhibition of [125I]MIBG retention by unlabeled MIBG supports the use of high specific activity radioiodinated MIBG for both diagnosis and therapy.