In vivo-stable bis-iminobiotin for targeted radionuclide delivery with the mutant streptavidin.

Targeted delivery of radionuclides to tumors is significant in theranostics applications for precision medicine. Pre-targeting, in which a tumor-targeting vehicle and a radionuclide-loaded effector small molecule are administered separately, holds promise since it can reduce unnecessary internal radiation exposure of healthy cells and can minimize radiation decay. The success of the pre-targeting delivery requires an in vivo-stable tumor-targeting vehicle selectively binding to tumor antigens and an in vivo-stable small molecule effector selectively binding to the vehicle accumulated on the tumor. We previously reported a drug delivery system composed of a low-immunogenic streptavidin with weakened affinity to endogenous biotin and a bis-iminobiotin with high affinity to the engineered streptavidin. It was, however, unknown whether the bis-iminobiotin is stable in vivo when administered alone for the pre-targeting applications. Here we report a new in vivo-stable bis-iminobiotin derivative. The keys to success were the identification of the degradation site of the original bis-iminobiotin treated with mouse plasma and the structural modification of the degradation site. We disclosed the successful pre-targeting delivery of astatine-211 (211At), α-particle emitter, to the CEACAM5-positive tumor in xenograft mouse models.

Optimizing the pharmacokinetics of an 211At-labeled RGD peptide with an albumin-binding moiety via the administration of an albumin-binding inhibitor.

PURPOSE: A probe for targeted alpha therapy (TAT) using the RGD peptide (Ga-DOTA-K([211At]APBA)-c(RGDfK) ([211At]1)) with albumin-binding moiety (ABM) was recently developed. [211At]1 highly accumulated in tumors and significantly inhibited tumor growth in U-87 MG tumor-bearing mice. However, high [211At]1 retention in blood may cause critical adverse events, such as hematotoxicity. Therefore, we attempted to accelerate the blood clearance of [211At]1 by competitively inhibiting the binding of [211At]1 to albumin to modulate the pharmacokinetics of the former. METHODS: To evaluate the effects of albumin-binding inhibitors in normal mice, sodium 4-(4-iodophenyl)butanoate at 2, 5, or 10 molar equivalents of blood albumin was administered at 1-h postinjection of [211At]1. The biodistribution of [211At]1, SPECT/CT imaging of [67Ga]Ga-DOTA-K(IPBA)-c(RGDfK) ([67Ga]2), and the therapeutic effects of [211At]1 were compared with or without IPBA administration in U-87 MG tumor-bearing mice. RESULTS: Blood radioactivity of [211At]1 was decreased in a dose-dependent manner with IPBA in normal mice. In U-87 MG tumor-bearing mice, the blood radioactivity and accumulation in nontarget tissues of [211At]1 were decreased by IPBA. Meanwhile, tumor [211At]1 accumulation was not changed at 3-h postinjection of IPBA. In SPECT/CT imaging of [67Ga]2, IPBA administration dramatically decreased radioactivity in nontarget tissues, and only tumor tissue was visualized. In therapeutic experiments, [211At]1 with IPBA injected-group significantly inhibited tumor growth compared to the control group. CONCLUSION: IPBA administration (as an albumin-binding inhibitor) could modulate the pharmacokinetics and enhance the therapeutic effects of [211At]1.

Development of probes for radiotheranostics with albumin binding moiety to increase the therapeutic effects of astatine-211 (211At).

PURPOSE: We have developed probes for multiradionuclides radiotheranostics using RGD peptide ([67Ga]Ga-DOTA-c[RGDf(4-I)K] ([67Ga]1) and Ga-DOTA-[211At]c[RGDf(4-At)K] ([211At]2)) for clinical applications. The introduction of an albumin binding moiety (ABM), such as 4-(4-iodophenyl)-butyric acid (IPBA), that has high affinity with the blood albumin and prolongs the circulation half-life can improve the pharmacokinetics of drugs. To perform more effective targeted alpha therapy (TAT), we designed and synthesized Ga-DOTA-K([211At]APBA)-c(RGDfK) ([211At]5) with 4-(4-astatophenyl)-butyric acid (APBA), which has an astato group instead of an iodo group in IPBA. We evaluated whether APBA functions as ABM and [211At]5 is effective for TAT. In addition, we prepared 67Ga-labeled RGD peptide without ABM, [67Ga]Ga-DOTA-K-c(RGDfK) ([67Ga]3), and 125I-labeled RGD peptide with ABM, Ga-DOTA-K([125I]IPBA)-c(RGDfK) ([125I]4), to compare with [211At]5. METHODS: Biodistribution experiments of [67Ga]3 without ABM, [125I]4 and [211At]5 with ABM were conducted in normal mice and U-87 MG tumor-bearing mice. In addition, two doses of [211At]5 (370 or 925 kBq) were administered to U-87 MG tumor-bearing mice to confirm the therapeutic effects. RESULTS: The blood retention of [125I]4 and [211At]5 was remarkably increased compared to [67Ga]3. Also, [125I]4 and [211At]5 showed similar biodistribution and significantly greater tumor accumulation and retention compared to [67Ga]3. In addition, [211At]5 inhibited tumor growth in a dose-dependent manner. CONCLUSION: The functionality of APBA as ABM like IPBA, and the usefulness of [211At]5 as the radionuclide therapy agent for TAT was revealed.

Astatine-211-labeled aza-vesamicol derivatives as sigma receptor ligands for targeted alpha therapy.

INTRODUCTION: As sigma receptors are abundantly expressed on different types of cancer cells, several radiolabeled sigma receptor ligands have been developed for cancer imaging and therapy. Previously, we synthesized and evaluated radioiodinated aza-vesamicol derivatives, [125I]pIC3NV, [125I]mIC2N5V, and [125I]mIC3N5V. They accumulated in tumors, and [125I]mIC2N5V and [125I]mIC3N5V showed higher tumor to non-target tissue ratios than [125I]pIC3NV. Therefore, we synthesized and evaluated the corresponding 211At-labeled compounds, [211At]mAtC2N5V and [211At]mAtC3N5V, for targeted alpha therapy (TAT). METHODS: [211At]mAtC2N5V and [211At]mAtC3N5V were prepared by the standard method of electrophilic astatodestannylation of the corresponding trimethylstannyl precursors. Cellular uptake experiments, and biodistribution experiments and therapeutic experiments in tumor-bearing mice were performed. RESULTS: The radiochemical yields of [211At]mAtC2N5V and [211At]mAtC3N5V were 45.5 ± 14.4% and 56.9 ± 13.8%, respectively. After HPLC purification, their radiochemical purities were over 95%. [211At]mAtC2N5V and [211At]mAtC3N5V showed high uptake in DU-145 cells. They demonstrated high accumulation in tumors (6.9 ± 1.4%injected dose/g and 5.1 ± 1.4%injected dose/g at 1 h, respectively) and similar biodistribution tendencies compared with the corresponding 125I-labeled compounds. A single injection of [211At]mAtC2N5V (0.48 MBq) or [211At]mAtC3N5V (0.48 MBq) significantly inhibited tumor growth. CONCLUSION: These results indicated that [211At]mAtC2N5V and [211At]mAtC3N5V could be potential candidates for TAT.

Evaluation of Aminopolycarboxylate Chelators for Whole-Body Clearance of Free 225Ac: A Feasibility Study to Reduce Unexpected Radiation Exposure during Targeted Alpha Therapy.

Actinium-225 (225Ac) is a promising radionuclide used in targeted alpha therapy (TAT). Although 225Ac labeling of bifunctional chelating ligands is effective, previous in vivo studies reported that free 225Ac can be released from the drugs and that such free 225Ac is predominantly accumulated in the liver and could cause unexpected toxicity. To accelerate the clinical development of 225Ac TAT with a variety of drugs, preparing methods to deal with any unexpected toxicity would be valuable. The aim of this study was to evaluate the feasibility of various chelators for reducing and excreting free 225Ac and compare their chemical structures. Nine candidate chelators (D-penicillamine, dimercaprol, Ca-DTPA, Ca-EDTA, CyDTA, GEDTA TTHA, Ca-TTHA, and DO3A) were evaluated in vitro and in vivo. The biodistribution and dosimetry of free 225Ac were examined in mice before an in vivo chelating study. The liver exhibited pronounced 225Ac uptake, with an estimated human absorbed dose of 4.76 SvRBE5/MBq. Aminopolycarboxylate chelators with five and six carboxylic groups, Ca-DTPA and Ca-TTHA, significantly reduced 225Ac retention in the liver (22% and 30%, respectively). Significant 225Ac reductions were observed in the heart and remainder of the body with both Ca-DTPA and Ca-TTHA, and in the lung, kidney, and spleen with Ca-TTHA. In vitro interaction analysis supported the in vivo reduction ability of Ca-DTPA and Ca-TTHA. In conclusion, aminopolycarboxylate chelators with five and six carboxylic groups, Ca-DTPA and Ca-TTHA, were effective for whole-body clearance of free 225Ac. This feasibility study provides useful information for reducing undesirable radiation exposure from free 225Ac.

68Ga- and 211At-Labeled RGD Peptides for Radiotheranostics with Multiradionuclides.

Probes for radiotheranostics could be produced by introducing radionuclides with similar chemical characteristics into the same precursors. We recently developed an 211At-labeled RGD peptide and a corresponding radioiodine-labeled RGD peptide. Both labeled peptides accumulated in large quantities in the tumor with similar biodistribution, demonstrating their usefulness for radiotheranostics. In this study, we hypothesized that probes for radiotheranostics combined with multiradionuclides, such as 68Ga and 211At, have useful clinical applications. New radiolabeled RGD peptide probes were synthesized via a molecular design approach, with two labeling sites for metal and halogen. These probes were evaluated in biodistribution experiments using tumor-bearing mice. [67Ga]Ga-DOTA-c[RGDf(4-I)K] ([67Ga]4), Ga-DOTA-[125I]c[RGDf(4-I)K] ([125I]4), and Ga-DOTA-[211At]c[RGDf(4-At)K] ([211At]7) showed similar biodistribution, with high and equivalent accumulation in tumors. These results indicate the usefulness of these probes in radiotheranostics with multiradionuclides, such as a radiometal and a radiohalogen, and they could contribute to a personalized medicine regimen.

Production and Supply of α-Particle-Emitting Radionuclides for Targeted α-Therapy.

Encouraging results from targeted α-therapy have received significant attention from academia and industry. However, the limited availability of suitable radionuclides has hampered widespread translation and application. In the present review, we discuss the most promising candidates for clinical application and the state of the art of their production and supply. In this review, along with 2 forthcoming reviews on chelation and clinical application of α-emitting radionuclides, The Journal of Nuclear Medicine will provide a comprehensive assessment of the field.

Human dosimetry of free 211At and meta-[211At]astatobenzylguanidine (211At-MABG) estimated using preclinical biodistribution from normal mice.

BACKGROUND: 211At is one of the ideal nuclides for targeted radionuclide therapies (TRTs). Meta-[211At]astatobenzylguanidine (211At-MABG) has been proposed for the treatment of pheochromocytoma. To effectively use these radiopharmaceuticals, dosimetry must be performed. It is important to determine the absorbed doses of free 211At and 211At-MABG to determine the organs that may be at risk when using TRTs. The aim of this study was to estimate human dosimetry from preclinical biodistribution of free 211At and 211At-MABG in various organs in normal mice. METHODS: Male C57BL/6 N mice were administered 0.13 MBq of free 211At or 0.20 MBq of 211At-MABG by tail-vein injection. The mice were sacrificed at 5 min, and at 1, 3, 6, and 24 h after the injection (n = 5 for each group). The percentage of injected activity per mass in organs and blood (%IA/g) was determined. The human absorbed doses of free 211At and 211At-MABG were calculated using the Organ Level INternal Dose Assessment/EXponential Modeling (OLINDA/EXM) version 2.0 and IDAC-Dose 2.1. RESULTS: High uptake of free 211At was observed in the lungs, spleen, salivary glands, stomach, and thyroid. The absorbed doses of free 211At in the thyroid and several tissues were higher than those of 211At-MABG. The absorbed doses of 211At-MABG in the adrenal glands, heart wall, and liver were higher than those of free 211At. CONCLUSIONS: The absorbed doses of 211At-MABG in organs expressing the norepinephrine transporter were higher than those of free 211At. In addition, the biodistribution of free 211At was different from that of 211At-MABG. The absorbed dose of free 211At may help predict the organs potentially at risk during TRTs using 211At-MABG due to deastatination.

Thallium-201 Imaging in Intact Olfactory Sensory Neurons with Reduced Pre-Synaptic Inhibition In Vivo.

In this study, we determined whether the 201Tl (thallium-201)-based olfactory imaging is affected if olfactory sensory neurons received reduced pre-synaptic inhibition signals from dopaminergic interneurons in the olfactory bulb in vivo. The thallium-201 migration rate to the olfactory bulb and the number of action potentials of olfactory sensory neurons were assessed 3 h following left side nasal administration of rotenone, a mitochondrial respiratory chain complex I inhibitor that decreases the number of dopaminergic interneurons without damaging the olfactory sensory neurons in the olfactory bulb, in mice (6-7 animals per group). The migration rate of thallium-201 to the olfactory bulb was significantly increased following intranasal administration of thallium-201 and rotenone (10 µg rotenone, p = 0.0012; 20 µg rotenone, p = 0.0012), compared with that in control mice. The number of action potentials was significantly reduced in the olfactory sensory neurons in the rotenone treated side of 20 µg rotenone-treated mice, compared with that in control mice (p = 0.0029). The migration rate of thallium-201 to the olfactory bulb assessed with SPECT-CT was significantly increased in rats 24 h after the left intranasal administration of thallium-201 and 100 µg rotenone, compared with that in control rats (p = 0.008, 5 rats per group). Our results suggest that thallium-201 migration to the olfactory bulb is increased in intact olfactory sensory neurons with reduced pre-synaptic inhibition from dopaminergic interneurons in olfactory bulb glomeruli.

Preliminary Evaluation of Astatine-211-Labeled Bombesin Derivatives for Targeted Alpha Therapy.

There are various diagnostic and therapeutic agents for prostate cancer using bombesin (BBN) derivatives, but astatine-211 (211At)-labeled BBN derivatives have yet to be studied. This study presented a preliminary evaluation of 211At-labeled BBN derivative. Several nonradioactive iodine-introduced BBN derivatives (IB-BBNs) with different linkers were synthesized and their binding affinities measured. Because IB-3 exhibited a comparable affinity to native BBN, [211At]AB-3 was synthesized and the radiochemical yields of [211At]AB-3 was 28.2 ± 2.4%, with a radiochemical purity of >90%. The stability studies and cell internalization/externalization experiments were performed. [211At]AB-3 was taken up by cells and internalized; however, radioactivity effluxed from cells over time. In addition, the biodistribution of [211At]AB-3, with and without excess amounts of BBN, were evaluated in PC-3 tumor-bearing mice. Despite poor stability in murine plasma, [211At]AB-3 accumulated in tumor tissue (4.05 ± 0.73%ID/g) in PC-3 tumor-bearing mice, which was inhibited by excess native BBN (2.56 ± 0.24%ID/g). Accumulated radioactivity in various organs is probably due to free 211At. Peptide degradation in murine plasma and radioactivity efflux from cells are areas of improvement. The development of 211At-labeled BBN derivatives requires modifying the BBN sequence and preventing deastatination.

Possibility of cancer-stem-cell-targeted radioimmunotherapy for acute myelogenous leukemia using 211At-CXCR4 monoclonal antibody.

To explore stem-cell-targeted radioimmunotherapy with α-particles in acute myelogenous leukemia (AML), pharmacokinetics and dosimetry of the 211At-labeled anti-C-X-C chemokine receptor type 4 monoclonal antibody (211At-CXCR4 mAb) were conducted using tumor xenografted mice. The biological half-life of 211At-CXCR4 mAb in blood was 15.0 h. The highest tumor uptake of 5.05%ID/g with the highest tumor-to-muscle ratio of 8.51 ± 6.14 was obtained at 6 h. Radiation dosimetry estimated with a human phantom showed absorbed doses of 0.512 mGy/MBq in the bone marrow, 0.287 mGy/MBq in the kidney, and <1 mGy/MBq in other major organs except bone. Sphere model analysis revealed 22.8 mGy/MBq in a tumor of 10 g; in this case, the tumor-to-bone marrow and tumor-to-kidney ratios were 44.5 and 79.4, respectively. The stem-cell-targeted α-particle therapy using 211At-CXCR4 mAb for AML appears possible and requires further therapeutic studies.

The pharmacological properties of 3-arm or 4-arm DOTA constructs for conjugation to α-melanocyte-stimulating hormone analogues for melanoma imaging.

BACKGROUND: Although a 3-arm DOTA construct, which has three carboxylic acids, h has been applied for conjugation to many peptides, we investigated if a 4-arm DOTA construct conjugated to peptides improves chemical properties for melanoma imaging of the melanocortin 1 receptor compared to 3-arm DOTA-conjugated peptides. METHODS: Specific activities, radiolabeling efficiencies, and partition coefficients were evaluated using 111In-labeled 3-arm and 4-arm DOTA-α-melanocyte-stimulating hormone (MSH). For assessment of MC1-R affinity and accumulation in tumor cells in vitro, B16-F1 melanoma and/or 4T1 breast cancer cells were incubated with 111In-labeled 3-arm and 4-arm DOTA-α-MSH with and without α-MSH as a substrate. The stability was evaluated using mouse liver homogenates and plasma. Biological distribution and whole-body single photon emission computed tomography imaging of 111In-labeled 3-arm and 4-arm DOTA-α-MSH were obtained using B16-F1 melanoma-bearing mice. RESULTS: Specific activities and radiolabeling efficiencies of both radiotracers were about 1.2 MBq/nM and 90-95%, respectively. The partition coefficients were -0.28 ± 0.03 for 111In-labeled 3-arm DOTA-α-MSH and -0.13 ± 0.04 for 111In-labeled 4-arm DOTA-α-MSH. Although accumulation was significantly inhibited by α-MSH in B16-F1 cells, the inhibition rate of 111In-labeled 4-arm DOTA-α-MSH was lower than that of 111In-labeled 3-arm DOTA-α-MSH. 111In-labeled 4-arm DOTA-α-MSH was taken up early into B16-F1 cells and showed higher accumulation than 111In-labeled 3-arm DOTA-α-MSH after 10 min of incubation. Although these stabilities were relatively high, the stability of 111In-labeled 4-arm DOTA-α-MSH was higher than that of 111In-labeled 3-arm DOTA-α-MSH. Regarding biological distribution, 111In-labeled 4-arm DOTA-α-MSH showed significantly lower average renal accumulation (1.38-fold) and significantly higher average melanoma accumulation (1.32-fold) than 111In-labeled 3-arm DOTA-α-MSH at all acquisition times. 111In-labeled 4-arm DOTA-α-MSH showed significantly higher melanoma-to-kidney, melanoma-to-blood, and melanoma-to-muscle ratios than 111In-labeled 3-arm DOTA-α-MSH. CONCLUSIONS: The 4-arm DOTA construct has better chemical properties for peptide radiotracers than the 3-arm DOTA construct.

[Manufacture and Utilization of a Low-level Radioactive 68Ge/68Ga Generator in a Radiochemistry Laboratory Course].

The low-level radioactivity of a (68)Ge/(68)Ga generator is a suitable tool for measuring radioactive growth and decay after (68)Ga milking due to their desirable nuclear decay properties, such as the EC decay of (68)Ge with no γ-ray emission andthe ß(+) decay of (68)Ga with a weak γ-ray emission. To experience andund erstandrad ioactive equilibrium during a university laboratory course, we surveyedandtestedthe production of a small amount of (68)Ge and set up educational programs to manufacture a (68)Ge/(68)Ga generator for measuring the growth andd ecay of (68)Ga. The irradiation of natGa with 25 µA of a 30 MeV proton beam from a cyclotron for 4 h yields ca. 111 MBq of (68)Ge, which was sufficient to supply to several universities. For use as the adsorbent of the generator column, particles of hydrated tin (VI) oxide were prepared from precipitated tin hydroxide gel. Repeated elution of (68)Ga from the handmade (68)Ge/(68)Ga generator gave constant amounts of (68)Ga with acceptable breakthrough of (68)Ge. The feedback from the student's experience with the (68)Ge/(68)Ga generator was evaluatedby annual questionnaire surveys, which were given to all students taking the course every year from 2012 to 2014. It has been made clear that more than half of the students were interested in the (68)Ge/(68)Ga generator program, andthis interest increasedfrom 54.9%in 2012 to 78.6%in 2014. A low-level radioactive (68)Ge/(68)Ga generator is thus expectedto be a suitable experimental tool for demonstrating the phenomenon of radioactivity to students in an intriguing way.

Preparation and evaluation of an astatine-211-labeled sigma receptor ligand for alpha radionuclide therapy.

INTRODUCTION: Sigma receptors are overexpressed in a variety of human tumors, making them potential targets for radionuclide receptor therapy. We have previously synthesized and evaluated (131)I-labeled (+)-2-[4-(4-iodophenyl)piperidino]cyclohexanol [(+)-[(131)I]pIV], which has a high affinity for sigma receptors. Therefore, (+)-[(131)I]pIV significantly inhibited tumor cell proliferation in tumor-bearing mice. In the present study, we report the synthesis and the in vitro and in vivo characterization of (+)-[(211)At]pAtV, an (211)At-labeled sigma receptor ligand, that has potential use in alpha-radionuclide receptor therapy. METHODS: The radiolabeled sigma receptor ligand (+)-[(211)At]pAtV was prepared using a standard halogenation reaction generating a 91% radiochemical yield with 98% purity after HPLC purification. The partition coefficient of (+)-[(211)At]pAtV was measured. Cellular uptake experiments and in vivo biodistribution experiments were performed using a mixed solution of (+)-[(211)At]pAtV and (+)-[(125)I]pIV; the human prostate cancer cell line DU-145, which expresses high levels of the sigma receptors, and DU-145 tumor-bearing mice. RESULTS: The lipophilicity of (+)-[(211)At]pAtV was similar to that of (+)-[(125)I]pIV. DU-145 cellular uptake and the biodistribution patterns in DU-145 tumor-bearing mice at 1h post-injection were also similar between (+)-[(211)At]pAtV and (+)-[(125)I]pIV. Namely, (+)-[(211)At]pAtV demonstrated high uptake and retention in tumor via binding to sigma receptors. CONCLUSION: These results indicate that (+)-[(211)At]pAtV could function as an new agent for alpha-radionuclide receptor therapy.

Binding Affinity, Specificity and Comparative Biodistribution of the Parental Murine Monoclonal Antibody MX35 (Anti-NaPi2b) and Its Humanized Version Rebmab200.

The aim of this preclinical study was to evaluate the characteristics of the monoclonal antibody Rebmab200, which is a humanized version of the ovarian-specific murine antibody MX35. This investigation contributes to the foundation for future clinical α-radioimmunotherapy of minimal residual ovarian cancer with 211At-Rebmab200. Here, the biodistribution of 211At-Rebmab200 was evaluated, as was the utility of 99mTc-Rebmab200 for bioimaging. Rebmab200 was directly compared with its murine counterpart MX35 in terms of its in-vitro capacity for binding the immobilized NaPi2B epitope and live cells; we also assessed its biodistribution in nude mice carrying subcutaneous OVCAR-3 tumors. Tumor antigen and cell binding were similar between Rebmab200 and murine MX35, as was biodistribution, including normal tissue uptake and in-vivo tumor binding. We also demonstrated that 99mTc-Rebmab200 can be used for single-photon emission computed tomography of subcutaneous ovarian carcinomas in tumor-bearing mice. Taken together, our data support the further development of Rebmab200 for radioimmunotherapy and diagnostics.

Reduced nasal transport of insulin-like growth factor-1 to the mouse cerebrum with olfactory bulb resection.

Although the olfactory nerve is involved in nasal transport of insulin-like growth factor-1 (IGF-1) to the brain, to our knowledge there have been no direct assessments of the effects of olfactory nerve damage on this transport. To determine whether olfactory bulb resection resulted in reduced transport of nasally administered human recombinant IGF-1 (hIGF-1) to the cerebrum, we measured the uptake of nasally administered iodine-125 hIGF-1 ((125)I-hIGF-1) in the cerebrum as a percentage of that in the blood in male ICR mice subjected to left olfactory bulb resection (model mice) and in sham-operated male ICR mice (control mice). Phosphorylated extracellular signal-regulated kinase (ERK) 1/2 (Thr202/Tyr204)/(Thr185/Tyr187) as a percentage of total ERK 1/2 in the left cerebrum was also assessed by using enzyme-linked immunosorbent assay after nasal administration of hIGF-1. Uptake of nasally administered (125)I-hIGF-1 in the cerebrum as a percentage of that in the blood was significantly lower in the model group than in the control group 30min after nasal administration of hIGF-1. Unilateral olfactory bulb resection prevented nasally administered hIGF-1 from increasing the phosphorylation of ERK 1/2 in the mouse cerebrum in vivo. These findings suggest that olfactory bulb damage reduces nasal transport of hIGF-1 to the brain in vivo.

Assessment of olfactory nerve by SPECT-MRI image with nasal thallium-201 administration in patients with olfactory impairments in comparison to healthy volunteers.

PURPOSE: The aim of this study was to assess whether migration of thallium-201 ((201)Tl) to the olfactory bulb were reduced in patients with olfactory impairments in comparison to healthy volunteers after nasal administration of (201)Tl. PROCEDURES: 10 healthy volunteers and 21 patients enrolled in the study (19 males and 12 females; 26-71 years old). The causes of olfactory dysfunction in the patients were head trauma (n = 7), upper respiratory tract infection (n = 7), and chronic rhinosinusitis (n = 7). (201)TlCl was administered unilaterally to the olfactory cleft, and SPECT-CT was conducted 24 h later. Separate MRI images were merged with the SPECT images. (201)Tl olfactory migration was also correlated with the volume of the olfactory bulb determined from MRI images, as well as with odor recognition thresholds measured by using T&T olfactometry. RESULTS: Nasal (201)Tl migration to the olfactory bulb was significantly lower in the olfactory-impaired patients than in healthy volunteers. The migration of (201)Tl to the olfactory bulb was significantly correlated with odor recognition thresholds obtained with T&T olfactometry and correlated with the volume of the olfactory bulb determined from MRI images when all subjects were included. CONCLUSIONS: Assessment of the (201)Tl migration to the olfactory bulb was the new method for the evaluation of the olfactory nerve connectivity in patients with impaired olfaction.

Evaluation of the olfactory nerve transport function by SPECT-MRI fusion image with nasal thallium-201 administration.

PURPOSE: The aim of this study was to visualize the human olfactory transport pathway to the brain by performing imaging after nasal thallium-201 ((201)Tl) administration. PROCEDURES: Healthy volunteers were enrolled in this study after giving informed consent (five males, 35-51 years old). The subjects were nasally administered (201)TlCl into either the olfactory cleft. Twenty-four hours later, uptake of (201)Tl was detected by a single photon emission computed tomography (SPECT)/X-ray computed tomography hybrid system. For each subject, an MRI image was obtained and merged with the SPECT image. RESULTS: The peak of the (201)Tl uptake entered into the olfactory bulb in the anterior skull base through the cribriform lamina 24 h after nasal administration of (201)Tl. No participant had olfactory disturbance after treatment. CONCLUSIONS: Nasal (201)Tl administration was safely used to assess the direct pathway to the brain via the nose in healthy volunteers with normal olfactory threshold.

Use of thallium transport to visualize functional olfactory nerve regeneration in vivo.

OBJECTIVE: To image olfactory nerve regeneration in vivo using a high-resolution gamma cam- era and radiography after nasal administration of thallium-201 (olfacto-scintigraphy). METHODS: Six Wistar rats were trained to avoid the smell of cycloheximide as a test of olfactory function. The olfactory nerve fibers of 3 rats were then carefully transected bilaterally with a Teflon knife, avoiding damage to the olfactory bulbs. The remaining 3 rats underwent sham operations and were used as controls. Steel wires were implanted in the left olfactory bulb of each rat for locating the bulbs with plain X-rays. The rats were assessed 2, 14, 28, and 42 d after the olfactory nerve transection or sham operation for their ability to detect odours and for transport of 201Tl to the olfactory bulb area 8 h after nasal administration of 201Tl. RESULTS: Both transport of 201Tl to the olfactory bulb area (p < 0.04) and ability to detect odours (p < 0.04) significantly increased with a time course after olfactory nerve transection. CONCLUSION: 201Tl transport to the olfactory bulb may be useful to visually assess olfactory ability in vivo. We plan to test olfacto-scintigraphy clinically by nasal administration of 201Tl in patients with posttraumatic olfactory loss.