ACS Medicinal Chemistry Letters
Letter
Table 1. Tumor/Blood and Tumor/Muscle Ratios of
[
125I]ETB in U87MG Tumor-Bearing Mice after Injection
time after injection (min)
30
60
120
240
tumor/blood
tumor/muscle
5.6
1.4
5.6
1.8
8.4
2.6
11.7
4.2
tumor/blood and tumor/muscle ratios for each time point
(tumor/blood = 11.7 at 240 min, tumor/muscle = 4.2 at 240
min; Table 1). Compared with the previously reported
[89Zr]Zr-deferoxamine-p-NCS-DS-8895a, [125I]ETB was supe-
rior to [89Zr]Zr-deferoxamine-p-NCS-DS-8895a in tumor/
blood ratio at an early time point ([125I]ETB:11.7 at 240 min,
[89Zr]Zr-deferoxamine-p-NCS-DS-8895a:3.62 at 7 day14).
SPECT/CT imaging was conducted in U87MG tumor-
bearing mice. [123I]ETB (33.62 MBq/140 μL) was adminis-
tered intravenously to nonanesthetized U87MG tumor-bearing
mice, and the mice were maintained in a nonanesthetized
condition for 205 min after administration. A 5 min CT scan
on an X-CUBE scanner (MOLECUBES, Ghent, Belgium) was
initially performed for attenuation correction followed by a 60
min SPECT scan on γ-CUBE scanner (MOLECUBES, Ghent,
Belgium) under anesthesia using isoflurane. As shown in
Figure 9, the implanted U87MG tumors in the right limbs were
clearly visualized in both dorsal and caudal images.
Furthermore, in accordance with the ex vivo distribution
data, a high accumulation of [123I]ETB in the kidney was also
observed.
Figure 7. Cell-binding assay. [125I]ETB CUR%/mg protein in
U87MG cells. Data are represented as mean
0.05 by Student’s t test.
SD; n = 5. *: p <
We studied the ex vivo biodistribution of [125I]ETB in
U87MG tumor-bearing mice after intravenous injection of 37
kBq/100 μL [125I]ETB. [125I]ETB was administered to
U87MG tumor-bearing mice without anesthesia using a
mouse holder. The time-course accumulation of [125I]ETB in
the tissues of U87MG tumor-bearing mice is presented in
Figure 8 as % injected dose per gram of tissue (% ID/g). The
uptake of [125I]ETB by the experimental tumors was evident,
reaching 2.2 0.3% ID/g at 240 min postinjection. [125I]ETB
was cleared rapidly from the blood, and a low level of
radioactivity was observed in the heart and muscle. High renal
accumulation was also observed (27.3% ID/g at 60 min
postinjection), which decreased with time due to excretion
(18.3% ID/g at 240 min postinjection). Furthermore, high
accumulation and retention of [125I]ETB in the liver was also
confirmed, which can be attributed to the following reasons:
(1) the compound is highly lipophilic and therefore easily
taken up and retained by the liver; (2) the EphA2 receptor is
highly expressed in the liver.25 In addition to the liver,
In conclusion, we designed and synthesized an ALW-II-41-
27 derivative that can be labeled with gamma-emitting I-123,
[
123I]ETB, aiming toward the development of a potential
SPECT imaging tracer targeting EphA2 receptors in vivo.
Nonradioactive ETB is shown to inhibit EphA2 receptor kinase
activity as efficiently as its parent ALW-II-41-27. The cell-
binding assay performed in EphA2 receptor-positive U87MG
cells, along with in vitro blocking with the parent ALW-II-41-
27, demonstrated the specific binding of [125I]ETB to the
EphA2 receptor. Ex vivo biodistribution studies in U87MG
tumor-bearing mice showed that [125I]ETB is taken up by the
tumor, while SPECT/CT imaging using [123I]ETB in the same
animal model confirmed ex vivo biodistribution data with a
clear delineation of U87MG tumors at 205 min after injection.
In view of the above, [123I]ETB can be further investigated for
[
125I]ETB showed high accumulation and retention in the
pancreas, in accordance with reports confirming EphA2
receptor expression in this tissue along with the lungs.26,27
Radioactivity in the thyroid gland was found to be minimal at
all time points tested (<0.1% ID), confirming radiochemical
stability in vivo (absence of free radioiodide) and consistent
with the stability results in mouse plasma. Table 1 showed the
Figure 8. Ex vivo biodistribution data in U87MG tumor-bearing mice. Ex vivo biodistribution of [125I]ETB in U87MG tumor-bearing mice at 30,
60, 120, and 240 min after injection. [125I]ETB uptake in normal tissues and tumor. Data are represented as mean SD; n = 5.
E
ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX