UntitledBlackwell Publishing Asia Evaluation of radioiodinated vesamicol analogs for
sigma receptor imaging in tumor and radionuclide
Kazuma Ogawa,1,2,5 Kazuhiro Shiba,2 Nasima Akhter,3 Mitsuyoshi Yoshimoto,3 Kohshin Washiyama,3 Seigo Kinuya,3
Keiichi Kawai3,4 and Hirofumi Mori2
1Graduate School of Natural Science and Technology, 2Advanced Science Research Center, 3Graduate School of Medical Sciences, Kanazawa University, Kanazawa; 4Biomedical Imaging Research Center, University of Fukui, Fukui, Japan (Received May 18, 2009/Revised June 30, 2009/Accepted June 30, 2009 ation July 31, 2009) It has been reported that sigma receptors are highly expressed in
a variety of human tumors. In this study, we selected (+)-2-[4-(4-
iodophenyl)piperidino] cyclohexanol [(+)-pIV] as a sigma receptor
ligand and evaluated the potential of radioiodinated (+)-pIV for
tumor imaging and therapy. (+)-[125/131I]pIV was prepared by an
iododestannylation reaction under no-carrier-added conditions with
Chemical structure of (+)-2-[4-(4-iodophenyl)piperidino] cyclo- radiochemical purity over 99% after HPLC purification. Biodistribution
experiments were performed by the intravenous injection of
(+)-[125I]pIV into mice bearing human prostate tumors (DU-145).
being, radiolabeled sigma ligands should be useful for monitoring Blocking studies were performed by intravenous injection of (+)-
the effects of chemotherapy at an early stage when morphologic [125I]pIV mixed with an excess amount of unlabeled sigma ligand
changes are not observed.(10) into DU-145 tumor-bearing mice. For therapeutic study, (+)-[131I]pIV
Previously, we have developed several vesamicol analogs was injected at a dose of 7.4 MBq followed by measurement of the
with iodine into the 4-phenylpiperidine moiety as sigma receptor tumor size. In biodistribution experiments, (+)-[125I]pIV showed high
imaging agents for investigating the central nervous system, uptake and long residence in the tumor. High tumor to blood and
and determined the binding affinities for the sigma receptors of muscle ratios were achieved because the radioactivity levels of blood
the vesamicol analogs.(11,12) In these vesamicol analogs, the (+)- and muscle were low. However, the accumulations of radioactivity
enantiomer of 2-[4-(4-iodophenyl)piperidino] cyclohexanol in non-target tissues, such as liver and kidney, were high. The
[(+)-pIV] (Fig. 1) showed the highest affinities for the recep- radioactivity in the non-target tissues slowly decreased over time.
tors.(12) The inhibition constant (K ) of (+)-pIV to sigma-1 and Co-injection of (+)-[125I]pIV with an excess amount of unlabeled
sigma-2 was 1.3 nM and 20.4 nM, respectively. The values sigma ligand resulted in a significant decrease in the tumor/blood
mean that (+)-pIV has more than 10-times greater affinity for ratio, indicating sigma receptor-mediated tumor uptake. In therapeutic
sigma-1 than that of (+)-pentazocine (Ki = 19.9 nM), which is study, tumor growth in mice treated with (+)-[131I]pIV was significantly
known as a sigma-1 ligand, and the sigma-2 affinity of (+)-pIV is inhibited compared to that of an untreated group. These results
equivalent to that of 1,3-di(2-toyl)guanidine (DTG) (Ki = 22.5 nM), indicate that radioiodinated (+)-pIV has a high potential for sigma
which is known as a non-selective sigma ligand.
receptor imaging in tumor and radionuclide receptor therapy. (Cancer
In this study, to evaluate the potential of radioiodinated Sci 2009; 100: 2188–2192)
(+)-pIV for tumor imaging and receptor radionuclide therapy, we selected human DU-145 prostate cancer cells known to over-express sigma-1 and sigma-2 receptors(13) for preparation of It has been reported that there are at least two subtypes of tumor-bearing mice, and a biodistribution study, metabolite sigma receptors, designated sigma-1 and sigma-2.(1) Whereas analysis, and therapeutic experiments were performed.
the sigma-1 receptor subtype has been cloned from varioustissues and species,(2,3) the sigma-2 receptor subtype has not yet Materials and Methods
been cloned. The functions of sigma receptors have not yet beenclearly defined. In the central nervous system, they have been Chemicals. [125I]Sodium iodide and [131I]sodium iodide were
shown to be involved in the regulation of neurotransmitter purchased from Perkin Elmer (Waltham, MA, USA). TLC release, modulation of neurotransmitter receptor function, learning analyses were performed with silica plates (Art 5553; Merck, and memory processes, and regulation of movement and posture.(4) Although they are expressed in peripheral tissues such phenylpropyl)piperazine (SA4503) was kindly supplied by M's as liver, kidney, and endocrine organs, their function in these Science (Kobe, Japan). Other reagents were of reagent grade tissues has been much less understood. At the same time, it has and used as received.
been reported that both sigma receptor subtypes are highly Preparation of (+)-enantiomer of (+)-pIV. The (+)-enantiomer of
expressed in a variety of human tumors such as prostate cancer, p-iodovesamicol [(+)-pIV] was prepared using a method described breast cancer, malignant melanoma, glioma, neuroblastoma, and previously.(14,15) Briefly, (+)-pIV was synthesized from the (+)- non-small-cell lung carcinoma.(5,6) The high expression of sigma enantiomer of vesamicol, which was provided from racemic receptors in tumors suggests that they are appropriate targets for vesamicol by recrystallizing the diastereoisomeric salts using developing tumor-imaging agents. Furthermore, sigma receptorsshould be potential biomarkers of tumor proliferation becausethey are highly expressed in rapidly proliferating cells and aredown-regulated when cells become quiescent.(7–9) For the time 5To whom correspondence should be addressed. E-mail: [email protected] 2188–2192
doi: 10.1111/j.1349-7006.2009.01279.x 2009 Japanese Cancer Association (–)-di-p-toluoyl-D-tartaric acid monohydrate, via a three-step 2.5 mL of 1-octanol was removed and added to 2.5 mL of new reaction of nitration, amination, and iodination.
phosphate buffer (0.02 M, pH 7.4). After repeating the same Preparation of (+)-[125I]pIV and (+)-[131I]pIV. (+)-[125I]pIV and
procedure twice, 100 μL and 1 mL of 1-octanol and phosphate (+)-[131I]pIV were prepared according to procedures described buffer were taken and their radioactivity and weight were preciously with a slight modification.(16) Briefly, [125I]sodium measured. The partition coefficient was determined by calculating iodide solution (18.5 MBq/5 μL) or [131I]sodium iodide solution the ratio of cpm/mL in 1-octanol to that in the buffer, and (74 MBq/3 μL) was added to 5 μL of 3 M formic acid. (+)-2- expressed as a common logarithm (log P).
Therapy. The mice were randomly distributed in the experi-
tributylstannylvesamicol] (3 μg), synthesized as described mental groups. When the tumors had reached a palpable size, previously,(17) in ethanol (3 μL) and 5 μL of 3% H O was added (+)-[131I]pIV was injected intravenously at a dose of 7.4 MBq. A and the reaction mixture was gently shaken. After 20 min of group of untreated mice served as a control group. After standing at room temperature, the reaction mixture was quenched injection, tumor size was measured with a slide caliper in two with 3 μL of 10 M sodium hydroxide solution and then purified dimensions, and mouse weights were measured 2–3 times per by reversed phase (RP)-HPLC performed with a Cosmosil week. Individual tumor volumes (V) were calculated by the 5C -AR 300 column (4.6 × 150 mm; Nacalai Tesque, Kyoto, formula V = [length × (width)2]/2 and compared to the values on Japan) at a flow rate of 1 mL/min with a mixture of acetonitrile, the day of treatment (relative tumor volume).
water, and ethanolamine (75:25:0.05) as a mobile phase.
Statistical evaluation. An unpaired Student's t-test was used
Biodistribution of (+)-[125I]pIV in tumor-bearing mice. Experiments
for the therapeutic experiments. One-way anova followed by with animals were conducted in accordance with the Guidelines Dunnett's post-hoc test compared to the control group was used for the Care and Use of Laboratory Animals of Kanazawa for experiments in the blocking study. Results were considered University. The animals were housed with free access to food statistically significant at P < 0.05.
and water at 23°C with a 12-h alternating light/dark schedule.
DU-145 cells were obtained from ATCC (Manassas, VA, USA) and grown in cell culture dishes in RPMI-1640 medium withphenol red, 10% heat-inactivated fetal calf serum, 100 μg/mL Preparation of (+)-[125I]pIV. (+)-[125I]pIV and (+)-[131I]pIV were
glutamine, 100 units/mL penicillin, and 100 μg/mL streptomycin.
prepared by the iododestannylation reaction under no-carrier- The cells were cultured in a humidified atmosphere of 95% air added conditions with high radiochemical yield (87% and 83%, and 5% carbon dioxide at 37°C. They were then released from respectively). After purification by RP-HPLC, (+)-[125I]pIV and the dishes by treatment with 0.05% trypsin/EDTA. Next, the (+)-[131I]pIV showed radiochemical purities of over 99%.
mice to be inoculated were anesthetized with pentobarbital. To Biodistribution experiments of (+)-[125I]pIV in tumor-bearing
produce tumors, approximately 5 × 106 of the prepared cells mice. Table 1 lists the biodistribution of (+)-[125I]pIV in DU-145
were injected subcutaneously into the right dorsum of 4-week- tumor-bearing mice. (+)-[125I]pIV showed high uptake and long old-male BALB/c nude mice (15–19 g; Japan SLC, Hamamatsu, retention in the tumors. Since the radioactivity levels in blood Japan). Biodistribution experiments were performed at approxi- and muscle were low, high tumor to blood and muscle ratios mately 14 –21 days postinoculation, i.e. when tumors reached a were achieved. However, the accumulation of radioactivity in palpable size. Groups of four or five mice were intravenously abdominal organs such as liver and kidney was high. The administered 100 μL of (+)-[125I]pIV (37 kBq). At 1, 24, and clearance of radioactivity in these organs was faster than that in 48 h postinjection, the mice were sacrificed. Tissues of interest the tumor. At the same time, the accumulation of (+)-[125I]pIV were removed and weighed, and radioactivity counts were in the stomach was low, indicating that deiodination was not determined with an auto well gamma counter (ARC-380; Aloka, observed in vivo.
Tokyo, Japan) and corrected for background radiation.
Blocking studies. The effects of some sigma ligands on tumor
Blocking studies. For blocking studies, the above-mentioned
uptake of (+)-[125I]pIV at 1 h postinjection are shown as % DU-145 tumor-bearing mice were intravenously administered injected dose per gram in tumor in Figure 2. Co-injection of 100 μL of (+)-[125I]pIV (37 kBq) mixed with an excess of each an excess amount of haloperidol, SA4503, or (+)-pIV resulted unlabeled sigma ligand, haloperidol (10 μmol/kg), SA4503 in a significant decrease in tumor uptake after injection of (10 μmol/kg), or (+)-pIV (10 μmol/kg), respectively. At 1 h postinjection, the mice were sacrificed and biodistributionexperiments were conducted as described above.
Metabolite analysis in blood, tumor, and other tissues. For meta-
bolite analysis, the above-mentioned DU-145 tumor-bearingmice were intravenously administered 100 μL of (+)-[125I]pIV (370 kBq). At 1 and 24 h postinjection, the mice were sacrificed.
Blood was collected by heart puncture using a heparinizedsyringe, and tissues of interest were removed. The blood wascentrifuged at 7000 g for 10 min at 4°C. After collecting the plasma, an equivalent volume of acetonitrile-water (1:1) wasadded to the plasma. The mixture was centrifuged at 7000 g for10 min at 4°C. The tissues of interest (0.2–0.5 g) were homo- genized in 1 mL of acetonitrile-water (1:1). Each homogenizedsample was centrifuged at 7000 g for 10 min at 4°C. The supernatants were analyzed by TLC with ethyl acetate, hexane,and ethanolamine (3:7:0.1) as a developing solvent.
Determination of the partition coefficient. The partition co-
efficient of (+)-[125I]pIV was measured as described previously Comparison of tumor uptake (mean ± SD) of (+)-[125I]pIV at 1 h with a slight modification.(18,19) Namely, (+)-[125I]pIV was mixed postinjection under no-carrier-added conditions and under co-injection of with 3 mL each of 1-octanol and phosphate buffer (0.02 M, haloperidol, SA4503, or (+)-2-[4-(4-iodophenyl)piperidino] cyclohexanol pH 7.4) in a test tube. The mixture was vortexed for 10 min.
[(+)-pIV]. Significance was determined using one-way ANOVA followed by After vortex, the mixture was centrifuged at 1000 g for 5 min.
Dunnett's post-hoc test (*P < 0.05, **P < 0.01 vs. control).
Ogawa et al. 2009 Japanese Cancer Association Table 1. Biodistribution of radioactivity after intravenous injection of
(+)-[125I]pIV in tumor-bearing mice
Time after injection Curves depicting inhibition of growth of DU-145 on therapy with (+)-[131I]pIV (closed circles) compared with no treatment (open circles).
Data are expressed as tumor volume relative to that on the day of treatment (mean ± SEM for four mice). Significance was determined using the Student's t-test (*P < 0.05, **P < 0.01 vs. untreated group).
Data are expressed as % injected dose per gram tissue. Each value represents the mean (SD) for four or five animals.
†Data are expressed as % injected dose.
T/B ratio, tumor : blood ratio; T/M ratio, tumor : muscle ratio.
Table 2. Analysis of metabolites after intravenous injection of (+)-
[125I]pIV in tumor-bearing mice
Time after injection Body weight of DU-145 tumor-bearing mice treated with (+)- [131I]pIV (closed circles) or with no treatment (open circles). Data are expressed as relative value to initial body weight (mean ± SEM for four postinjection, radioactivity in the tumor showed a relatively large proportion of the intact form (40.7%) compared with those in other tissues. In blood, almost no intact (+)-[125I]pIVwas observed at 1 and 24 h postinjection (3.7% and 1.4%, Data are expressed as % of intact (+)-[125I]pIV. Each value represents the mean (SD) for three samples.
Determination of the partition coefficient. The log P-value of
(+)-[125I]pIV was 2.08 ± 0.02 (mean ± SD for four samples).
Therapy. The volume of the tumors as a function of time is
Metabolite analysis in blood, tumor, and other tissues. Table 2
shown in Figure 3. As can be seen, tumor growth in the mice lists the results of the metabolite analyses after intravenous treated with (+)-[131I]pIV was significantly inhibited compared injection of (+)-[125I]pIV in DU-145 tumor-bearing mice. At 1 h to that of the untreated group. Weight could be used as a marker postinjection, large proportions of radioactivity existed as an for the general health of the mice (Fig. 4). The mice treated with intact form in almost all tissues except blood. In contrast, at 24 h (+)-[131I]pIV lost weight, which was probably caused by postinjection, the proportions of the intact form in all tissues treatment-related toxicity, but the weight loss was less than 10% were much lower than those at 1 h postinjection. At 24 h of their starting body weight.
2009 Japanese Cancer Association of sigma-1 receptors in tumor cells is generally less than thatpresent in normal tissues.(21) Although it was reported that rat In the case of the differential diagnosis of tumors, information liver and kidney contain high densities of sigma-1 and sigma-2 obtained from Single photon emission computed tomography receptors with sigma-2 sites comprising 75–80% of the total (SPECT) or PET imaging should be more important than that sigma receptors population,(23) Mach et al. performed biodistri- from other imaging modalities such as CT, MRI, or ultrasound.
bution experiments with a 18F-labeled compound possessing That is to say, among those imaging modalities, nuclear medicine a high affinity for both sigma-1 and sigma-2 receptors with modality is most advantageous for detecting functional changes co-injection of the unlabeled sigma-1 selective ligand and showed such as changes of receptor density, metabolism, and so on. It that the blocking of sigma-1 receptors reduced the accumula- has been reported that the density of sigma receptors affects the tion of radioactivity in non-target tissues except liver.(24) Their condition of tumors.(7,20) Therefore, nuclear imaging agents for studies indicate that labeled specific sigma-2 ligands could sigma receptors could be useful in the differential diagnosis of show less accumulation in non-target tissues compared with tumors.(9) In this study, we first examined the potential of sigma-1-specific or non-selective ligands. At the same time, radioiodine-labeled (+)-pIV, which has a very high affinity for lipophilicity might affect not only tumor uptake but also sigma receptors, as a tumor-imaging agent.
non-target tissue uptake and higher lipophilicity might lead to In the biodistribution experiments in the tumor-bearing mice, high non-specific uptake in both target and non-target tissues.(25,26) (+)-[125I]pIV showed a high uptake of radioactivity in the DU-145 Some parts of the accumulation of (+)-[125I]pIV in non-target tumor as we expected. Tu et al. described that not only receptor tissues, especially in liver, should be derived from its lipophilicity.
affinity but also optimal lipophilicity is important in the design Although the radioactivity in the non-target tissues gradually of receptor-based tumor-imaging agents.(21) The measured decreased compared to that in tumor, the clearance of the partition coefficient (log P) for (+)-[125I]pIV was 2.08. The value radioactivity in the non-target tissues was not fast. Conse- was much less than what we expected because the calculated log quently, it most likely interferes with the acquisition of clear P-value for pIV was 4.45 using CS ChemDraw Ultra software images at early times after injection of radioiodine-labeled (Cambridge Soft, Cambridge, MA, USA). A slight contamination or the presence of hydrophilic impurities could underestimate In the metabolite studies, the clearance of the intact (+)- the log P-value. Then, it might be difficult to accurately determine [125I]pIV in tumors was slower than that in any other organ the log P-value for a high lipophilicity radioactive compound (Table 2). When we calculated (% injected dose per gram) via the shake-flask method. Although it is not clear whether the × (ratio of intact (+)-[125I]pIV) at 24 h postinjection of (+)- lipophilicity of (+)-pIV is optimal for tumor uptake, part of the [125I]pIV, the values for blood, tumor, liver, kidney, lung, and high uptake in tumors might be derived from the appropriate brain were 0.01, 3.57, 1.58, 0.82, 0.42, and 0.66, respectively.
lipophilicity of (+)-[125I]pIV. Additionally, since (+)-[125I]pIV Much more intact (+)-[125I]pIV remained in tumors compared showed low radioactivity in blood and muscle, high tumor to with that in other organs. Whether these results were caused by blood and muscle ratios were achieved (Table 1). In order to differences of metabolic rate is not clear from our data. Even if determine in vivo binding of (+)-[125I]pIV to sigma receptors, more intact (+)-[125I]pIV in tumors is caused by a slow meta- (+)-[125I]pIV was co-injected with excess amounts of some types bolic rate, further studies would be needed to elucidate the of sigma ligands. The co-injection significantly decreased tumor causes. However, more intact (+)-[125I]pIV should affect the uptake of radioactivity (Fig. 2), which indicates the receptor more prolonged residence in tumors than that in other organs.
specificity of (+)-[125I]pIV uptake in DU-145 tumors in vivo.
Actually, previous studies have reported that the clearance of the These results indicate that (+)-pIV labeled with I-123 and I-124 sigma ligands from the brain was faster than those from instead of I-125 as a radionuclide could be useful as sigma tumors.(13,24,27,28) The long residence of radiotracer in tumors is receptor-imaging agents in tumors for SPECT and PET, respec- convenient for internal radiotherapy. Accordingly, we supposed tively. Meanwhile, from our previous in vitro experiments,(12) we that radioiodinated (+)-pIV could also be used as an internal assume that (+)-[125I]pIV prefers sigma-1, but could bind to not radionuclide therapy by using I-131, which emits middle energy only sigma-1 but also sigma-2. Sigma-1 and sigma-2 receptors of beta particles for therapy, instead of I-125. We examined the are highly expressed in DU-145 cells.(13) In this study, SA4503 potential of (+)-[131I]pIV as a therapeutic agent. As a result, a inhibited tumor uptake of (+)-[125I]pIV more strongly than with single treatment with (+)-[131I]pIV (7.4 MBq/mice) achieved haloperidol. SA4503 binds mainly to sigma-1, and haloperidol significant inhibition of tumor growth in tumor-bearing mice is a non-selective sigma ligand.(22) Therefore, the results from compared with a control group (Fig. 3). As far as we know, this the in vivo experiments in this study suggest that (+)-[125I]pIV was the first trial to use a radiolabeled sigma ligand for receptor binds to sigma-1 receptors, but it is not clear whether (+)-[125I]pIV radionuclide therapy. Although the data are insufficient, these also binds to sigma-2 receptors.
results indicate that (+)-[131I]pIV has potential as an agent for The problem of the tracer was high accumulations of radi- radionuclide receptor therapy.
oactivity in non-target tissues, such as liver and kidney. As In conclusion, radioiodinated (+)-pIV has a high potential described in the introduction section, since sigma receptors are for sigma receptor imaging in tumor and radionuclide receptor expressed in not only tumor but also non-target tissues such as therapy because of its high tumor uptake via sigma receptor in in the liver and kidney, some parts of the accumulation of the an animal model. However, further studies are needed in order radioactivity in non-target tissues should be sigma receptor– to reduce the radioactivity levels in non-target tissues.
specific. It may be difficult to avoid some uptakes in non-targettissues for labeled sigma ligands. Tu et al. mentioned that sigma-1-selective or sigma-1/sigma-2-non-selective compoundsmight not be ideal candidates for imaging tumors because many This work was supported in part by Grants-in-Aid for Scientific Research kinds of tumors possess a higher density of sigma-2 receptors from the Ministry of Education, Culture, Sports, Science and Technology than the surrounding normal tissue. On the other hand, the density 2 Hanner M, Moebius FF, Flandorfer A et al. Purification, molecular cloning, and expression of the mammalian sigma1-binding site. Proc Natl Acad Sci 1 Quirion R, Bowen WD, Itzhak Y et al. A proposal for the classification of USA 1996; 93: 8072 –7.
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2009 Japanese Cancer Association
Prof. Dr. Thomas Koller II VORLESUNG ZUM OBLIGATIOENRECHT BT 1. TEIL: VORBEMERKUNGEN UND INNOMINATKONTRAKTE A Aufbau und Funktion des OR BT I. Aufbau II. Funktion • Rationalisierung Die meisten Verträge passen in einen der gesetzlichen Vertragstypen, dies trotz der Vertragstypenfreiheit. Es ist möglich, einen Vertrag bewusst oder unbewusst lücken-haft zu belassen, weil man darauf vertrauen kann, dass Detailfragen bereits im Ge-setz geregelt sind. Der Aufwand bei Vertragsschluss kann so erheblich gesenkt wer-den.
Review Article Types of Hair Loss and Treatment Options,Including the Novel Low-Level Light Therapyand Its Proposed MechanismMahyar Ghanaat, MD evaluated based on the Ludwig scale, which ranges from I-III Abstract: Androgenetic alopecia (AGA) is the most common form (Fig. 2).4 These classification systems differ based on the fact of hair loss in men, and female pattern hair loss (FPHL) is the most