Hirofumi Mori

Biodistributions of 201Tl in tumor bearing animals and inflammatory lesion induced animals

The accumulation of 201Tl in tumor and inflammatory tissues were small. However, this nuclide showed a high concentration in viable tumor tissue, less in connective tissue (containing inflammatory tissues), and was not seen in necrotic tumor tissue regardless of the time after administration of 201Tl(I)-chloride. In inflammatory lesions, 201Tl accumulated in subcutaneous tissue infiltrated with neutrophils and macrophages, and quite large amounts of this nuclide were accumulated in subcutaneous tissue and sites where neutrophils were croeded. Most 201Tl existed in a free form in the fluid of tumor and inflammatory tissues regardless of the time after administration. A small amount of this nuclide was localized in the nuclear, mitochondrial and microsomal fractions in these tissues, and the nuclide was bound to protein in these fractions. The distribution of 201Tl(III)-chloride in tumor bearing animals was essentially the same as that of 201Tl(I)-chloride.

In vivo dopamine-D2 and serotonin-5-HT2 receptor binding study of risperidone and haloperidol

An in vivo receptor binding technique was applied to evaluate the affinities of risperidone and haloperidol for dopamine-D2 receptors (D2) and serotonin-5-HT2 receptors (5-HT2) in rat brain with [3H]YM-09151-2 and [3H]ketanserin as selective ligands. Radioactivities were obtained in the striatum frontal cortex, and cerebellum of the rats treated with the ligands. Time course study of receptor occupancy at 25 to 250 min after single doses of the drugs (1 mg/kg, IP) showed higher 5-HT2 occupancy in the frontal cortex and lower D2 occupancy in the striatum by risperidone than by haloperidol. Dose-response analysis of receptor occupancy revealed risperidone demonstrated higher binding affinity for 5-HT2 than for D2, while the reverse was observed with haloperidol. It appeared that risperidone (1 mg/kg, IP), but not haloperidol (1 mg/kg, IP), demonstrated regional selectivity in D2 occupancy favouring frontal cortex more than the striatum. That risperidone displayed a higher ratio of 5-HT2 to D2 in occupancy than haloperidol is in agreement with the previous findings obtained in vitro.

Development of [90Y]DOTA-conjugated bisphosphonate for treatment of painful bone metastases

INTRODUCTION Based on the concept of bifunctional radiopharmaceuticals, we have previously developed (186)Re-complex-conjugated bisphosphonate analogs for palliation of painful bone metastases and have demonstrated the utility of these compounds. By applying a similar concept, we hypothesized that a bone-specific directed (90)Y-labeled radiopharmaceutical could be developed. METHODS In this study, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was chosen as the chelating site, and DOTA was conjugated with 4-amino-1-hydroxybutylidene-1,1-bisphosphonate. [(90)Y]DOTA-complex-conjugated bisphosphonate ([(90)Y]DOTA-HBP) was prepared by coordination with (90)Y, and its biodistribution was studied in comparison to [(90)Y]citrate. RESULTS In biodistribution experiments, [(90)Y]DOTA-HBP and [(90)Y]citrate rapidly accumulated and resided in the bone. Although [(90)Y]citrate showed a higher level of accumulation in the bone than [(90)Y]DOTA-HBP, the clearances of [(90)Y]DOTA-HBP from the blood and from almost all soft tissues were much faster than those of [(90)Y]citrate. As a result, the estimated absorbed dose ratios of soft tissues to osteogenic cells (target organ) of [(90)Y]DOTA-HBP were lower than those of [(90)Y]citrate. CONCLUSIONS [(90)Y]DOTA-HBP showed superior biodistribution characteristics as a bone-seeking agent and led to a decrease in the level of unnecessary radiation compared to [(90)Y]citrate. Since the DOTA ligand forms a stable complex not only with (90)Y but also with lutetium ((177)Lu), indium ((111)In), gallium ((67/68)Ga), gadolinium (Gd) and so on, complexes of DOTA-conjugated bisphosphonate with various metals could be useful as agents for palliation of metastatic bone pain, bone scintigraphy and magnetic resonance imaging.

αvβ3 Integrin-targeting radionuclide therapy and imaging with monomeric RGD peptide

The αvβ3 integrin plays a pivotal role in angiogenesis and tumor metastasis. Angiogenic blood vessels overexpress αvβ3 integrin, as in tumor neovascularization, and αvβ3 integrin expression in other microvascular beds and organs is limited. Therefore, αvβ3 integrin is a suitable receptor for tumor‐targeting imaging and therapy. Recently, tetrameric and dimeric RGD peptides have been developed to enhance specificity to αvβ3 integrin. In comparison to the corresponding monomeric peptide, however, these peptides show high levels of accumulation in kidney and liver. The purpose of this study is to evaluate tumor‐targeting properties and the therapeutic potential of 111In‐ and 90Y‐labeled monomeric RGD peptides in BALB/c nude mice with SKOV‐3 human ovarian carcinoma tumors. DOTA‐c(RGDfK) was labeled with 111In or 90Y and purified by HPLC. A biodistribution study and scintigraphic images revealed the specific uptake to αvβ3 integrin and the rapid clearance from normal tissues. These peptides were renally excreted. At 10 min after injection of tracers, 111In‐DOTA‐c(RGDfK) and 90Y‐DOTA‐c(RGDfK) showed high uptake in tumors (7.3 ± 0.6% ID/g and 4.6 ± 0.8% ID/g, respectively) and gradually decreased over time (2.3 ± 0.4% ID/g and 1.5 ± 0.5% ID/g at 24 hr, respectively). High tumor‐to‐blood and ‐muscle ratios were obtained from these peptides. In radionuclide therapeutic study, multiple‐dose administration of 90Y‐DOTA‐c(RGDfK) (3 × 11.1 MBq) suppressed tumor growth in comparison to the control group and a single‐dose administration (11.1 MBq). Monomeric RGD peptides, 111In‐DOTA‐c(RGDfK) and 90Y‐DOTA‐c(RGDfK), could be promising tracers for αvβ3 integrin‐targeting imaging and radiotherapy.

Determination of Flow and Rate Constants in a Kinetic Model of [99mTc]-Hexamethyl-Propylene Amine Oxime in the Human Brain

The values for flow and rate constants for a kinetic model of [99mTc]–hexamethylpropyleneamine oxime (HM-PAO) distribution in the human brain were determined. The single-pass extraction ratio of HM-PAO was also determined in the rat brain by the indicator diffusion method; a value of 0.90 ± 0.02 (mean ± SEM, n = 5) was obtained. Time course data of brain activity and arterial blood activity of the tracer were fitted to a four compartment model: Values of blood flow and the firstorder rate constants for backdiffusion of the diffusible tracer from brain to blood (k2), conversion of the lipophilic tracer to the hydrophilic one in brain (k3), and conversion of the diffusible tracer to the nondiffusible one in blood (k5) were determined. Conversion of hydrophilic tracer back to a lipophilic form in both blood and brain was assumed to be negligible during the course of the experiment. The values obtained for blood flow, k2, and k3 were, respectively, 0.40 ± 0.03 ml/g/min, 0.38 ± 0.04 min−1, and 0.92 ± 0.05 min−1 in the gray matter (n = 4), and 0.23 ± 0.01 ml/g/min, 0.17 ± 0.01 min−1, and 1.01 ± 0.05 min−1 in the white matter (n = 2) in patients with cerebrovascular disorder. The k5 value was 1.14 ± 0.06 min−1 (n = 4). These experimentally determined values agree well with the theoretical ones previously reported by Lassen et al. The results suggest the relative constancy of the k3 and k5 values and the more prominent initial backdiffusion of the lipophilic HM-PAO from brain to blood in high flow regions compared to low flow regions.

Biodistributions of radioactive alkaline metals in tumor bearing animals: comparison with 201Tl

The retention values for 42K, 86Rb and 134Cs in the tissues and blood were quite similar to those for 201Tl, but were very different from those for 22Na. In an experiment for subcellular fractionation of tumors, most of these nuclides were localized in the supernatant fraction, with small amounts in other fractions. The concentration ratios for these nuclides in each fraction were approximately constant regardless of the time after administration. Radioactive alkaline metals in the supernatant fraction of the tumor homogenate existed mostly as free ions and were bound to protein in other fractions of tumor tissue. These results were essentially the same as those for 201Tl. Ouabain suppression studies indicated that 201Tl is taken up into the tumor cells partly through Na+, K+-ATPase of their membranes. Ionic radii of alkaline metals and thallium were related to their blood and tumor retention values. This relationship suggested that monovalent cations whose ionic radii exceed 0.133 nm, and which exist as free ions in the tissue fluids, behave like the potassium ion. Potassium and K analogs (Tl, Rb, Cs) are avidly taken up into viable tumor cells whose Na+, K+-ATPase activity is elevated. Therefore, suitable radionuclides of K and K analogs can be excellent agents for visualization of viable tumor tissues.

Synthesis and evaluation of vesamicol analog (-)-O-[11C]methylvesamicol as a PET ligand for vesicular acetylcholine transporter.

Abstract(-)-o-Methylvesamicol ((-)-OMV) exhibitedin vitro a high affinity for vesicular acetylcholine transporter (VAChT) (Ki, 6.7 nM) and a relatively low affinity for sigmai receptor (Ki, 33.7 nM). We prepared (-)-[11C]OMV by a palladium-promoted cross-coupling reaction using [11C]methyl iodide, in a radiochemical yield of 38 ± 6.9% (n = 3), a radiochemical purity of 98 ± 2.3% (n = 5), and a specific activity of 11 ± 7.0 TBq/mmol at 30 minutes after EOB (n = 5). Then, we evaluatedin vivo whether (-)-[11C]OMV has properties as a PET radioligand for mapping VAChT. In rats, the brain uptake of (-)-[11C]OMV was 1.1%ID/g at 5 minutes postinjection, and was retained of a high level for 60 minutes. The brain uptake was significantly inhibited by the co-injection (500 nmol/kg) of cold (-)-OMV (58–66%), (-)-vesamicol (57–65%), and two sigma receptor ligands with modulate affinities for VAChTs: SA4503 (56–71%) and haloperidol (39–64%) in all of the brain regions, including the cerebellum with a low density of VAChTs, but not of sigma1-selective ligand (+)-pentazocine. However, the pretreatment with a large excess amount of (±)-pentazocine (50 μmol/kg) reduced the uptake in a different manner in the brain regions: 25% reduction in the striatum with a high density of VAChTs, and a 50–55% reduction in the other regions with a lower density of VAChTs.Ex vivo autoradiography using (-)-[11C]OMV showed a similar regional brain distribution of [3H](-)-vesamicol. In the PET study of the monkey brain, the regional brain distribution pattern of (-)-[11C]OMV was different from that of [11C]SA4503. The uptake of (-)-[11C]OMV was relatively higher in the striatum, was reversible, and an apparent equilibrium state was found at 20–40 minutes. In conclusion, (-)-[11C]OMV exhibited appropriate brain kinetics during the time frame of11C-labeled tracers and bound mainly to VAChTs; however, the binding to sigmai receptors was not disregarded. Therefore, (-)-[11C]OMV-PET together with help of [11C]SA4503-PET may evaluate VAChTs.

Characterization of radioiodinated (-)-ortho-iodovesamicol binding in rat brain preparations.

We investigated the binding characteristics of optical isomers of three iodovesamicol analogs to vesicular acetylcholine transporters (VAChT) and to sigma receptors (sigma-1, sigma-2) in rat brains. In competitive inhibition studies, (-)-enantiomers [(-)-ortho-iodovesamicol ((-)-oIV), (-)-meta-iodovesamicol ((-)-mIV), (-)-vesamicol] displayed a higher affinity for VAChT than (+)-enantiomer [(+)-oIV, (+)-mIV, (+)-vesamicol]. (-)-oIV and (-)-mIV showed the same high affinity for VAChT as (-)-vesamicol. For sigma receptors(sigma-1, sigma-2), (-)-oIV (Ki = 62.2 nM (to sigma-1) and 554 nM(to sigma-2)) showed a lower affinity than (-)-mIV (Ki = 4.5 nM (to sigma-1) and 42.9 nM (to sigma-2)). Furthermore, in a saturation binding study, (-)-[125I]-oIV exhibited a Kd of 17.4 +/- 5.1 nM with a maximum number of binding sites, Bmax, of 559 +/- 51 fmol/ mg of protein. These results showed that (-)-oIV binds to vesicular acetylcholine transporters (VAChT) more selectively than (-)-mIV, previously reported as a VAChT mapping agent, and may be suitable for VAChT imaging studies.

Time course of dopamine1,2 and serotonin2 receptor binding of antipsychotics in vivo

An in vivo receptor binding technique was applied to evaluate the affinities of clozapine (20 mg/kg), RMI-81582 (20 mg/kg), and haloperidol (1 mg/kg) for dopamine D1, D2 and serotonin 5-HT2 receptors in rat brain with [3H]-SCH23390, [3H]-YM-09151-2, and [3H]-ketanserin as selective ligands. The time course study of receptor occupancy at 25 to 250 min after intraperitoneal administration of the drugs showed higher 5-HT2 and lower D2 receptor occupancies of clozapine and RMI-81582 than those of haloperidol both in the striatum and frontal cortex. The 5-HT2/D2 ratios of receptor occupancy for clozapine and RMI-81582 were about 6 to 8 times higher than that for haloperidol. Stable occupancies of D1 receptors were observed only with RMI-81582 and clozapine, the former demonstrating the higher occupancy. These findings are in agreement with the previous findings obtained under in vitro conditions and may account for some part of the properties of atypical antipsychotic drugs.

Intraperitoneal radioimmunotherapy in treating peritoneal carcinomatosis of colon cancer in mice compared with systemic radioimmunotherapy

Peritoneal spread is one of major causes of mortality in colorectal cancer patients. In the current investigation, the efficacy of radioimmunotherapy (RIT) with i.p. administration of an anti‐colorectal cancer IgG1,131I‐A7, was compared to that with i.v. administration in BALB/c female mice bearing peritoneal nodules of LS180 human colon cancer cells, at the same toxicity level. Distribution of either i.p. or i.v. administered 131I‐A7 and i.p. administered irrelevant 131I‐HPMS‐1 was assessed. Based on the results of toxicity determination at increments of 2 MBq and estimated dosimetry, an i.p. dose of 11 MBq and an i.v. dose of 9 MBq were chosen for treatment. Mice were monitored for long‐term survival: untreated mice (n=11), mice undergoing i.p. RIT with 131I‐A7 (n=11), mice undergoing i.v. RIT with 131I‐A7 (n=11) and mice undergoing non‐specific i.p. RIT with 131I‐HPMS‐1 (n=5). Intraperitoneal injection of 131I‐A7 produced faster and greater tumor accumulation than i.v. injection: 34.2±16.5% of the injected dose per g (% ID/ g) and 11.1±3.6% ID/g at 2 h, respectively (P<0.0001). Consequently, cumulative radioactivity in tumors was 1.73‐fold higher with i.p. injection. 131I‐HPMS‐1 did not show specific accumulation. Non‐specific RIT with 131I‐HPMS‐1 (mean survival, 26.0±2.5 days) did not affect the survival as compared to no treatment (26.7±1.9 days). Intravenous RIT with 131I‐A7 prolonged the survival of mice to 32.8±1.8 days (P<0.01). Intraperitoneal RIT with 131I‐A7 improved the survival more significantly and attained cure in 2 of 11 mice (P<0.05 vs. i.v. RIT). In conclusion, i.p. RIT is more beneficial in treating peritoneal carcinomatosis of colon cancer than i.v. RIT in a murine model.