Int. J. Cancer: 123, 709–715 (2008)' 2008 Wiley-Liss, Inc.

avb3 Integrin-targeting radionuclide therapy and imaging
with monomeric RGD peptide
Mitsuyoshi Yoshimoto1*, Kazuma Ogawa2, Kohshin Washiyama1, Naoto Shikano3, Hirofumi Mori2,
Ryohei Amano1 and Keiichi Kawai1,41
Division of Health Sciences, Graduate School of Medicine, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Japan
2
Advanced Science Research Center, Kanazawa University, 13-1 Takara-machi, Kanazawa, Japan3
Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, 4669-2 Ami,
Ami-machi, Inashiki-gun, Ibaraki, Japan
4
Biomedical Imaging Research Center, Fukui University, 23-3 Shimoaizuki, Matsuoka-cho, Fukui, JapanThe avb3 integrin plays a pivotal role in angiogenesis and tumor
metastasis. Angiogenic blood vessels overexpress avb3 integrin, as
in tumor neovascularization, and avb3 integrin expression in othermicrovascular beds and organs is limited. Therefore, avb3 integrin
is a suitable receptor for tumor-targeting imaging and therapy.
Recently, tetrameric and dimeric RGD peptides have been developed to enhance speciﬁcity to avb3 integrin. In comparison to thecorresponding monomeric peptide, however, these peptides showhigh levels of accumulation in kidney and liver. The purpose ofthis 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 avb3 integrin and the rapid clearance from normal tissues. These peptides were renally excreted.
At 10 min after injection of tracers, 111In-DOTA-c(RGDfK) and90
Y-DOTA-c(RGDfK) showed high uptake in tumors (7.3 6 0.6%
ID/g and 4.6 6 0.8% ID/g, respectively) and gradually decreased
over time (2.3 6 0.4% ID/g and 1.5 6 0.5% ID/g at 24 hr, respectively). High tumor-to-blood and -muscle ratios were obtained
from these peptides. In radionuclide therapeutic study, multipledose administration of 90Y-DOTA-c(RGDfK) (3 3 11.1 MBq) suppressed tumor growth in comparison to the control group and asingle-dose administration (11.1 MBq). Monomeric RGD peptides, 111In-DOTA-c(RGDfK) and 90Y-DOTA-c(RGDfK), could
be promising tracers for avb3 integrin-targeting imaging andradiotherapy.
' 2008 Wiley-Liss, Inc.
Key words: RGD peptide; radionuclide therapy; avb3 integrin; 90Y; 111In

Angiogenesis has a close relationship with tumor proliferationand metastasis. The interactions of cell–cell and cell-matrix are
implicated in both angiogenesis and metastasis. Integrins are celladhesion molecules and have basic roles in angiogenesis and metastasis. There are several isoforms of integrins consisting of achains and b chains. The avb3 integrin is highly expressed in endothelial cells in angiogenesis and tumor cells (e.g., breast cancer,
ovarian cancer, brain tumor, etc.), although the expression of avb3
integrin is not restricted to tumor cells and activated endothelial
cells.1–3
The avb3 integrin recognizes the amino acid sequence of arginine-glycine-aspartic acid (RGD peptide). On the basis of the RGD
peptide, many peptidomimetic compounds and peptides have been
designed to antagonize the avb3 integrin.4 These compounds andanti-avb3 integrin monoclonal antibodies have been reported to inhibit angiogenesis without affecting preexisting vessels.2,5,6
Because of its restricted expression, the avb3 integrin is an attractive targeting molecule for tumor imaging and therapy, leading todecreased side effects compared to conventional chemotherapy.
The expression of the avb3 integrin has been reported to be
associated with metastatic potential in melanoma, breast cancer,
and colon cancer.7–9 The development of radiopharmaceuticals fortargeting the avb3 integrin would be clinically beneﬁcial, not only
for screening and for treating patients with avb3 integrin-positive
tumors but also for monitoring therapeutic efﬁcacy.
Publication of the International Union Against Cancer

Many RGD peptides labeled with gamma-emitting and positron-emitting nuclides (18F, 64Cu, 99mTc, 125I, etc.) have beenreported as angiogenesis-imaging agents.10 A recent trend in thedevelopment of RGD peptides is the multimerization of RGD peptides to improve the high tumor accumulation and retention of
RGD peptides.11 However, this also leads to the enhancement ofradioactive accumulation in nontargeted organs such as kidney
and liver.12 Compared with antibody or multimeric RGD peptides,
monomeric RGD peptides have a lower molecular mass. Therefore, monomeric RGD peptides labeled with 90Y are thought to bepromising radiopharmaceuticals for tumor therapy causing low radioactive exposure to normal tissues such as kidney and liver. In
this report, we describe the tumor therapeutic and imaging potential of DOTA-conjugated 90Y/111In-monomeric RGD peptide.

Material and methods
Radiolabeling of DOTA-c(RGDfK)c(RGDfK) was synthesized and conjugated with DOTA by
Thermo Electron GmbH (Ulm, Germany). 90YCl3 and 111InCl3
were kindly presented by Chiyoda Technol Corp. (Tokyo, Japan)
and Nihon Medi-Physics Co., Ltd. (Nishinomiya, Japan), respectively. Brieﬂy, 40 ll of 3 M acetate buffer (pH 6.0) was added to18.5 MBq of 111InCl3. The mixture was allowed to stand for 5 minat room temperature, and then added to 0.1 mg of DOTAc(RGDfK). The mixture was heated for 15 min at 100°C. The puriﬁcation of 111In-DOTA-c(RGDfK) was performed by RP-HPLC
using a Cosmosil 5C18-AR 300 column (4.6 3 150 mm, Nacalai
Tesque, Kyoto, Japan) eluted with 90% of 0.1% aqueous triﬂuoroacetic acid and 10% of acetonitrile with 0.1% triﬂuoroacetic acidat a ﬂow rate of 1.0 ml/min. The radiochemical purity was determined as described for the puriﬁcation. 90Y-DOTA-c(RGDfK)
was prepared as described for 111In-DOTA-c(RGDfK). The radiochemical purity of the radiolabeled DOTA-c(RGDfK) was over
99% (Fig. 1).
Cell culture
SKOV-3 human ovarian carcinoma cell line was purchasedfrom American Tissue Culture Collection (ATCC, Manassas, VA)
and maintained in DMEM (Sigma, St. Louis, MO) containing
4.5 g/l glucose and 10% FBS. Cells were cultured in a 5% CO2humidiﬁed atmosphere at 37°C.

Grant sponsor: Ministry of Education, Culture, Sports, Science andTechnology, Japan; Grant number: KAKENHI 15790657.
*Correspondence to: Division of Health Sciences, Graduate School of
Medicine, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa 9200942, Japan. Fax: 181-76-234-4366.
E-mail: myoshi@mhs.mp.kanazawa-u.ac.jp
Received 28 September 2007; Accepted after revision 20 February 2008
DOI 10.1002/ijc.23575
Published online 22 May 2008 in Wiley InterScience (www.interscience.
wiley.com).

710

YOSHIMOTO ET AL.

volume was calculated using the formula: volume 5 4/3 p (1/2
length 3 1/2 width 3 1/2 height).

FIGURE 1 – HPLC proﬁle of 111In-DOTA-c(RGDfK).

Animal model
Animal studies were performed in compliance with the guidelines for the care and use of laboratory animals of Kanazawa University. Biodistribution studies were conducted in nude mice bearing a SKOV-3 tumor. Female BALB/c nu/nu mice, 5–6 weeks old(Japan SLC, Inc. Hamamatsu, Japan), were xenografted s.c. in theright dorsum with 5 3 106 SKOV-3 cells. Two weeks after inoculation of the tumor cells, the mice were inoculated with 90YDOTA-c(RGDfK) or 111In-DOTA-c(RGDfK). SKOV-3 displayed
the avb3 integrin expression as determined by ﬂow cytometry
analysis.13
Biodistribution studies
The mice were injected via the tail vein with 370 kBq of 90YDOTA-c(RGDfK) (containing 0.5 lg of DOTA-c(RGDfK)) or
37.5 kBq of 111In-DOTA-c(RGDfK) (containing 0.5 lg of DOTAc(RGDfK)). The mice were sacriﬁced at 10 min, 1-, 4-, 24- and48-hr postinjection and tissue samples were excised. The tissue
samples were weighed and radioactivity was measured with a gcounter (ARC-360, Aloka, Tokyo, Japan). The bremsstrahlung
from the b decay of 90Y was measured. Uptake in organs was
expressed as % ID/g tissue.

Radiation dosimetry extrapolation to humans
Estimated human dosimetry was calculated from biodistribution
results of 111In-DOTA-c(RGDfK) in female BALB/c nude micewith SKOV-3 tumors, assuming that the biodistribution of the radiopharmaceuticals in mice is the same as in adult humans. Residence times were calculated by monoexponential extrapolation of
the biodistribution data. According to residence times, radiation
doses were calculated for male adults using a standard quantitation
platform, Organ Level Internal Dose Assessment (OLINDA; Vanderbilt University).14
Statistical evaluation
Mann-Whitney U test was used for the receptor speciﬁcity
study. Kruskal-Wallis test followed by Dunn’s post hoc test compared to the control group was used for the radionuclide therapy
experiment. The results were considered statistically signiﬁcant at
p < 0.05.
Results
Radiolabeling of DOTA-c(RGDfK) with 90Y and 111In
90
Y-DOTA-c(RGDfK) showed a HPLC proﬁle similar to 111InDOTA-c(RGDfK) (Fig. 1). 90Y-DOTA-c(RGDfK) and 111InDOTA-c(RGDfK) were eluted in a single peak with a retention
time of 9.7 min. Minor peaks were observed with a retention timeof 7.0 and 8.5 min. After puriﬁcation, radiochemical purity of90
Y-DOTA-c(RGDfK) and 111In-DOTA-c(RGDfK) exceeded
99%.

Receptor speciﬁcity study
The avb3 integrin-mediated uptake of 90Y-DOTA-c(RGDfK)
and 111In-DOTA-c(RGDfK) was investigated by estimating thebiodistribution of 90Y-DOTA-c(RGDfK) and 111In-DOTAc(RGDfK) in mice with SKOV-3 tumors in the presence orabsence of 100 lg of DOTA-c(RGDfK). Biodistribution wasdetermined as described above at 1-hr postinjection.

Biodistribution and animal imaging
Biodistribution and animal imaging studies were performed infemale BALB/c nude mice with SKOV-3 tumors. On scintigraphic
images made at 1- and 4-hr postinjection of 111In-DOTAc(RGDfK), kidney and bladder were the organs with high activity,
suggesting the renal excretion pattern of 111In-DOTA-c(RGDfK)(Fig. 2). Kidney was clearly visualized at 24-hr postinjection. Following the clearance of 111In-DOTA-c(RGDfK) from normal tissues, the SKOV-3 tumors were clearly delineated at 4- and 24-hr
postinjection. The images showed high tumor to nontumor rations(2.33 at 4-hr postinjection and 2.07 at 24-hr postinjection). The tumor and kidney uptake was signiﬁcantly inhibited by coinjectionof 100 lg of DOTA-c(RGDfK).
90
Y-DOTA-c(RGDfK) showed a distribution pattern similar tothat of 111In-DOTA-c(RGDfK) (Fig. 3). The tumor uptake of 90YDOTA-c(RGDfK) and 111In-DOTA-c(RGDfK) was high (2.53%
ID/g and 6.28% ID/g at 1-hr postinjection) and remained at 0.94%
ID/g and 1.86% ID/g at 48-hr postinjection, respectively. Afterinjection of both peptides, the radioactivity rapidly cleared fromthe blood and was 0.05% ID/g for 90Y-DOTA-c(RGDfK) and
0.13% ID/g for 111In-DOTA-c(RGDfK) at 1-hr postinjection. Kidney also showed the rapid clearance. In some mice, radioactivity
in the blood was not detectable at 48-hr postinjection. Various normal tissues such as muscle, liver, and pancreas had relatively
lower uptake. These resulted in high tumor-to-blood (T/B), -muscle (T/M) and -kidney (T/K) ratios (Fig. 4). The T/B ratios of bothtracers rose above 500 and the T/M ratios rose to 41 for 90YDOTA-c(RGDfK) and 50 for 111In-DOTA-c(RGDfK) at 24-hr
postinjection. The T/K ratios of both tracers were more than 1.53
after 1-hr postinjection. The highest T/K ratio for 90Y-DOTAc(RGDfK) were 2.64 at 24-hr postinjection.

Radionuclide therapy
Mice with s.c. SKOV-3 tumors received 11.1 MBq of 90YDOTA-c(RGDfK). One group received 90Y-DOTA-c(RGDfK) for
1 day, another group for 3 days. As a control group, a third group
received saline. Tumor size was measured 3 times weekly. Tumor

Integrin speciﬁcity studies
Coinjection of 100 lg of DOTA-c(RGDfK) with 90Y-DOTAc(RGDfK) or 111In-DOTA-c(RGDfK) signiﬁcantly decreased theuptake in various tissues other than kidney and bone (Fig. 5).
Tumor uptake of 111In-DOTA-c(RGDfK) was reduced most

Scintigraphic imaging
Scintigraphic imaging was performed with a mini gamma camera (MGC1500, Acrorad Co., Ltd., Uruma, Japan) consisting of a
CdTe semiconductor detector. The ﬁeld of view was 44.6 mm 344.6 mm. The CdTe module had 1,024 pixels (32 3 32 matrix).
The size of each pixel was 1.4 mm 3 1.4 mm. Mice with s.c.
SKOV-3 tumors were anesthetized with pentobarbital. Images
were acquired for 20 min at 1-, 4- and 24-hr postinjection of 111InDOTA-c(RGDfK) (3.7 MBq) in the presence or absence of 100 lg
of DOTA-c(RGDfK). Region of interests were drawn over the tumor and the opposite side of tumor as a nontumor region. Tumor
to non-tumor (T/N) ratio was calculated as below.
T/N ratio 5 ([count of tumor/pixel] 2 [count of background/pixel])/([count of nontumor/pixel] 2 [count of background/pixel]).

TUMOR TARGETING WITH RADIOLABELED RGD PEPTIDES

711

FIGURE 2 – Scintigraphic images of SKOV-3 tumor-bearing nude mice at 1, 4 and 24 hr after injection of 111In-DOTA-c(RGDfK) in the absence (top) or presence (bottom) of 100 lg of DOTA-c(RGDfK). The tumors are indicated with arrows. Tumor was not clearly visualized inmice that received 111In-DOTA-c(RGDfK) with a blocking agent.

markedly from 5.76% ID/g to 0.59% ID/g. For 111In-DOTAc(RGDfK), kidney and bone showed moderate decrease from
2.97% ID/g to 1.58% ID/g and from 0.31% ID/g to 0.18% ID/g,
respectively.
Radionuclide therapy
The growth curves of the 2 groups of mice with 90Y-DOTAc(RGDfK) therapy and the control group are shown in Figure 6. Tumor volumes were 32.0 6 7.0 mm3 for the control group, 45.5 6
21.4 mm3 for the single-dose group (11.1 MBq 3 1), and 39.0 6
8.3 mm3 for the multiple-dose administration group (11.1 MBq 33) at day 0. The single-dose administration did not show signiﬁcant
inhibition to tumor growth. In contrast, the multiple-dose administration did inhibit tumor growth. At 23 days after therapy, the tumor
volume was 7.2 times greater for the multiple-dose administrationgroup compared to 9.9 times greater for the single-dose group and13.6 times greater for the control group. Throughout the experiment, no difference in body weight was found among the 3 groups.
Radiation dosimetry
Human absorbed doses to normal organs were estimated fromthe biodistribution data of 111In-DOTA-c(RGDfK) in female nude
mice, assuming that the biodistribution and pharmacokinetics of111
In-DOTA-c(RGDfK) in mice and adult human are the same
(Table I). The highest absorbed dose was to the kidneys (0.568
mGy/MBq), although all organs had a low level of radiation
doses.
Discussion
90
Y-DOTA-c(RGDfK) and 111In-DOTA-c(RGDfK) showed ahigh and retentive accumulation in the tumor tissue with a rapid
clearance from normal tissues. A trend in the biodistribution of90
Y-DOTA-c(RGDfK) was similar to that of 111In-DOTAc(RGDfK), although the amount of radioactivity in all tissues
from 90Y-DOTA-c(RGDfK) was smaller than that from 111InDOTA-c(RGDfK). This could have resulted from measuring thebremsstrahlung from 90Y because the bremsstrahlung from 90Y
contains low energy spectrum and is easily absorbed by tissues ascompared to g ray. Many studies have been reported using radiolabeled monomeric RGD peptides. In a U-87 MG glioblastoma
model, 125I-c(RGDyK) showed a high accumulation (8.97% ID/g)

at 30-min postinjection.15 However, other studies reported a low
accumulation of the RGD peptides in tumors.16,17 The tumor
uptake of 111In-DOTA-c(RGDfK) was relatively high (6.28% ID/
g at 1-hr postinjection) in our SKOV-3 model, suggesting that theexpression of avb3 integrin in tumor cells, instead of endothelial
cells, would mainly contributes to the accumulation of the RGD
peptides. Similarly to other monomeric RGD peptides, 90YDOTA-c(RGDfK) and 111In-DOTA-c(RGDfK) were rapidly
cleared from blood, resulting in remarkably high tumor-to-bloodand -muscle ratios at 24- and 48-hr postinjection.
111
In-DOTA-c(RGDfK) showed a high uptake (8.80% ID/g at
10 min postinjection) in kidney, followed by rapid clearance(2.53% ID/g at 1-hr postinjection). Furthermore, a low accumulation of 111In-DOTA-c(RGDfK) was observed in liver (1.43% ID/g
at 1-hr postinjection). This suggests that 111In-DOTA-c(RGDfK)
as well as other RGD peptides containing lysine is cleared via therenal pathway because of its hydrophilicity.15,18
Multimeric RGD peptides have been developed to increase theafﬁnity to avb3 integrin. 111In-DOTA-E-[c(RGDfK)]2 showed ahigh and retentive uptake in liver and kidney although it also
showed high tumor uptake.18 In contrast, 111In-DOTA-c(RGDfK)
was found to have a lower uptake and faster clearance in liver andkidney. This difference between monomeric and dimeric RGD
agrees with the comparison between 99mTc-HYNIC-c(RGDfK)
and 99mTc-HYNIC-E-[c(RGDfK)]2.12 Dimerization resulted inhigher uptake and prolonged retention in kidney, although it led toa higher afﬁnity for avb3 integrin as well as a longer retention in
the tumor in comparison with that of 99mTc-HYNIC-c(RGDfK). It
has been reported that T/K ratios of 99mTc-HYNIC-c(RGDfK)
were higher than that of 99mTc-HYNIC-E-[c(RGDfK)]2.12 The
enhanced renal clearance of monomeric RGD peptides may
improve the delineation of abdominal tumors.
Kidney is the dose-limiting tissue for radionuclide therapy with
RGD peptides containing lysine. However, high-dose and multiple-dose administration could be possible for 90Y-DOTAc(RGDfK) because of its rapid clearance from kidney and high T/
K ratio. Several studies have shown the successful use of alphaparticle-emitting nuclides, such as 211At, 213Bi and 227Th for radionuclide therapy due to their higher liner energy transfer andshorter path length as compared to beta particle-emitting
nuclides.19–21 However, one possible issue is the control of the712

YOSHIMOTO ET AL.

FIGURE 3 – Biodistribution of 90Y-DOTA-c(RGDfK) (a) and 111In-DOTA-c(RGDfK) (b) in nude mice bearing SKOV-3 tumors subcutaneously (n 5 3–4). Radioactivity in tissues is expressed as % ID/g (mean 6 SD).

radiation to normal tissues (kidney or bone marrow etc.) due to its
high cytotoxicity. DOTA-c(RGDfK) would also be applicable to
the radionuclide therapy with a particle-emitting nuclides.
The coinjection of DOTA-c(RGDfK) reduced the tracer uptake
in most normal tissues such as liver and spleen. Similar resultswith regard to other peptides have been reported.18,22,23 The
expression of avb3 integrin in microvessels in rat liver and lung aswell as in osteoclast and osteoblast has been identiﬁed.24–27 This
fact suggests that there might be an expression of avb3 integrinin microvessels in normal tissues as well as in normal cells.
Therefore, these results support the suggestion that 111In-DOTAc(RGDfK) and 90Y-DOTA-c(RGDfK) could be avb3 integrintargeting tracers.

Janssen reported that 37 MBq of 90Y-DOTA-E-[c(RGDfK)]2
induced a signiﬁcant inhibition in tumor growth.18 However, 37
MBq of a scrambled sequence control peptide, 90Y-DOTA-E[c(RGKfD)]2, also elicited a delay in tumor growth in comparison
with an untreated group, suggesting that this would not only becaused by avb3 integrin-targeting therapy. Although kidney has
relative resistance to radiation, this high radiation dose might
impair kidney function. Therefore, the practicality of clinicallytreating avb3 integrin positive tumors by such a high dose injection remains in question. Injection of 11.1 MBq 90Y-DOTAc(RGDfK) did not show any signiﬁcant delay in tumor growth. A
high radiation dose of monomeric RGD peptide could be neededto adequately inhibit tumor growth because of its fast clearance.

TUMOR TARGETING WITH RADIOLABELED RGD PEPTIDES

713

FIGURE 5 – Biodistribution of 90Y-DOTA-c(RGDfK) (a) and 111InDOTA-c(RGDfK) (b) in nude mice bearing SKOV-3 tumors at 1 hrwith and without coinjection of 100 lg of DOTA-c(RGDfK) as a
blocking agent (n 5 4). Data are represented as mean 6 SD. Signiﬁcance was determined by Mann-Whitney U test (*p < 0.05 vs.
control).
FIGURE 4 – Tumor to nontumor ratios in SKOV-3 tumor-bearing
nude mice at 10 min, 1, 4, 24, and 48 hr after injection of 90Y-DOTAc(RGDfK) and 111In-DOTA-c(RGDfK) (n 5 3–4). Data are represented as mean 6 SD.

Multiple-dose administration (11.1 MBq 3 3) induced signiﬁcant inhibition of tumor growth. Although the therapeutic effectby single-dose administration of 33.3 MBq 90Y-DOTA-c(RGDfK)
was not investigated in this study, dose fractionation-like effects
in addition to an increase in the total radiation dose would enhance
the growth inhibition. Some studies have revealed the potential
and advantage of dose fractionation in radionuclide therapy.28–30
Anderson et al. reported that dose fractionation of 15 mCi 64CuTETA-octreotide into 2 doses (1 or 2 days apart) showed signiﬁcantly longer inhibition of tumor growth and lower toxicity than asingle-dose administration.31 Therefore, it is thought that multiple-dose administration rather than single-dose administration ofhigh radiation might achieve the therapeutic effect while regulating the exposure of normal tissues to radiation.
In radionuclide therapy, radiation exposure to normal tissues aswell as the absolute accumulated dose in the tumor is an importantfactor. Kidney is the dose-limiting tissue for radionuclide therapy
with 90Y-DOTA-c(RGDfK) or peptides such as octreotide. There
are some reports of kidney absorbed dose for 90Y-DOTA-octreotide. Jamar et al. and Joerster et al. showed that the kidney
absorbed dose are 4.4 and 2.73 Gy/GBq, respectively.32,33 Lewis
et al. showed kidney absorbed dose (0.670 mGy/MBq) from
177
Lu-DOTA-octreotate dose not indicate any probability of ﬁnding radiation damage in the rats kidneys with an injected activityof 555 MBq, leading to a renal dose of 0.37 Gy.34 Compared tothose results, 90Y-DOTA-c(RGDfK) has the lower kidney
absorbed dosimetry (0.568 mGy/MBq). In our radionuclide therapy, a maximum administrated activity were 33.3 MBq (11.1
MBq 3 3), leading to a renal dose of 0.019 Gy. In view of a differ-

714

YOSHIMOTO ET AL.
TABLE I – HUMAN ABSORBED DOSE ESTIMATES OF 90Y-DOTA-c(RGDFK)IN SKOV-3 TUMOR-BEARING NUDE MICE
Organ

mGy/MBq

StomachHeart
Kidneys
Liver
Lungs
Pancreas
Red Marrow
Osteogenic Cells
SpleenEffective Dose1

0.10000.00690.56800.16900.01440.06700.03710.07420.32800.24701

Expressed as mSv/MBq.

FIGURE 6 – Relative growth curves of the s.c. SKOV-3 tumors in
the three groups of mice after injection of 11.1 MBq of 90Y-DOTAc(RGDfK), 11.1 MBq of 90Y-DOTA-c(RGDfK) (3 days), or saline(untreated controls). Data are represented as mean 6 SD for 5–6
mice. Signiﬁcance was determined using Kruskal-Wallis test followedby the Dunn’s post hoc test (*p < 0.01 vs. control).

ence in animal models (rats and mice), this renal dose from90
Y-DOTA-c(RGDfK) would not induce any probability of nephrotoxicity. It is reported that the 5% of probability threshold forradiation nephropathy by 90Y-DOTA-octreotide is 35 6 7 Gy,
indicating the higher threshold than that by external beam therapy.35 For clinical use, therefore, precise absorbed doses inpatients should be estimated with 86Y-DOTA-c(RGDfK) or 111InDOTA-c(RGDfK) and administrated activity of 90Y-DOTAc(RGDfK) should be decided.
avb3 integrin is very abundant in bone-residing breast cancer
metastase, malignant ovarian carcinoma, metastatic melanoma
and invasive prostate cancer.13,36–38 Our results indicated that theradionuclide therapy with 90Y-DOTA-c(RGDfK) would be suc-cessful in tumors with high expression of avb3 integrin. Therefore,
avb3 integrin is suitable target for the radionuclide therapy when
it is highly expressed on tumor cells. However, the relationshipbetween the expression level of avb3 integrin and the therapeutic
efﬁcacy is still not unclear. Further studies in various tumor models are needed to investigate the relationship between tumor
uptake of 86Y-DOTA-c(RGDfK) or 111In-DOTA-c(RGDfK) as
surrogate markers and the therapeutic efﬁcacy.

Conclusion
Our research indicates the potential of 90Y-DOTA-c(RGDfK)
and 111In-DOTA-c(RGDfK) as radionuclide therapy and imaging
agents. We require further optimization of the therapy by theamount of radiation dose, the number of administrations, and theselection of radionuclide (a emitters as well as auger emitters).
These optimizations would lead to an improvement of the therapeutic effect while reducing radiation toxicity to normal tissues.
Acknowledgement
Authors thank Ms. Yoko Kawai for assistance in the animal
experiments.

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