Synthesis and evaluation of novel technetium-99m-hydroxamamide complex based on imidazothiadiazole sulfonamide targeting carbonic anhydrase-IX for tumor imaging

Article abstract of DOI:10.1016/j.bmcl.2020.127596

Carbonic anhydrase-IX (CA-IX) is an attractive target for detecting tumors associated with a poor prognosis. We previously reported a [^99mTc]hydroxamamide complex based on ureidosulfonamide as a CA-IX ligand ([^99mTc]URB2A), which showed a favorable affinity for CA-IX high-expressing cells in vitro and tumors in vivo; however, radioactivity retention in the blood pool suggested a high background signal on imaging. To improve the pharmacokinetics of [^99mTc]URB2A, in this study, we designed and synthesized [^99mTc]ISB2 based on imidazothiadiazole sulfonamide, which exhibited greater CA-IX affinity and faster clearance from the blood pool than ureidosulfonamide in studies using corresponding ¹¹¹In-labeled compounds, and evaluated its utility for CA-IX imaging. In an in vitro cell binding assay, [^99mTc]ISB2 markedly bound to CA-IX high-expressing (HT-29) cells; moreover, its binding was greater than that of [^99mTc]URB2A. In an in vivo biodistribution assay, [^99mTc]ISB2 showed faster clearance from the blood pool than [^99mTc]URB2A; however, lower HT-29 tumor accumulation was observed. Further structural modification of [^99mTc]ISB2 to improve its stability may lead to the development of a useful [^99mTc]hydroxamamide complex for CA-IX imaging.

Full text of DOI:10.1016/j.bmcl.2020.127596

Bioorganic&MedicinalChemistryLetters30(2020)127596
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and evaluation of novel technetium-99m-hydroxamamide
complex based on imidazothiadiazole sulfonamide targeting carbonic
anhydrase-IX for tumor imaging
⁎
Shimpei Iikunia,1, Anna Kitanoa,1, Hiroyuki Watanabea, Yoichi Shimizua,b, Masahiro Onoa,
a Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida Shimoadachi-cho, Sakyo-ku, Kyoto 606-
8501, Japan
b Department of Diagnostic Imaging and Nuclear Medicine, Graduate School of Medicine, Kyoto University, 54 Shogoinkawara-cho, Sakyo-ku, Kyoto 606-8507, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords:
Carbonic anhydrase-IX (CA-IX) is an attractive target for detecting tumors associated with a poor prognosis. We
previously reported a [99mTc]hydroxamamide complex based on ureidosulfonamide as a CA-IX ligand ([99mTc]
URB2A), which showed a favorable affinity for CA-IX high-expressing cells in vitro and tumors in vivo; however,
radioactivity retention in the blood pool suggested a high background signal on imaging. To improve the
pharmacokinetics of [99mTc]URB2A, in this study, we designed and synthesized [99mTc]ISB2 based on imida-
zothiadiazole sulfonamide, which exhibited greater CA-IX affinity and faster clearance from the blood pool than
ureidosulfonamide in studies using corresponding 111In-labeled compounds, and evaluated its utility for CA-IX
imaging. In an in vitro cell binding assay, [99mTc]ISB2 markedly bound to CA-IX high-expressing (HT-29) cells;
moreover, its binding was greater than that of [99mTc]URB2A. In an in vivo biodistribution assay, [99mTc]ISB2
showed faster clearance from the blood pool than [99mTc]URB2A; however, lower HT-29 tumor accumulation
was observed. Further structural modification of [99mTc]ISB2 to improve its stability may lead to the develop-
ment of a useful [99mTc]hydroxamamide complex for CA-IX imaging.
Carbonic anhydrase-IX
Cancer
Technetium-99m
Hydroxamamide
Imidazothiadiazole sulfonamide
Sixteen α-carbonic anhydrase (CA) isozymes and CA-related pro-
teins with different subcellular localization, tissue distribution, and
catalytic activity have been reported in mammals. CA catalyzes the
reversible hydration of carbon dioxide to a bicarbonate ion and proton.1
One of the CA isozymes, CA-IX, is closely related to tumor proliferation
and resistance to various cancer therapies through the hypoxia-in-
ducible factor-1 (HIF-1) cascade, which markedly upregulates the ex-
pression of hypoxia-related proteins, such as CA-IX, glucose transpor-
ters, and vascular endothelial growth factor. HIF-1α is hydroxylated
and ultimately degraded through binding to the wild-type von Hippel
Lindau (VHL) tumor suppressor protein and subsequent ubiquitination,
reducing the expression of CA-IX.1–4 However, a deficit of VHL protein
leads to the overexpression of HIF-1α; thus, the upregulation of CA-IX
expression is found in patients with clear cell renal cell carcinoma, one
of the diseases with a deficit of VHL. CA-IX expression is markedly
increased in many kinds of tumors,5–10 while CA-IX shows limited ex-
pression in the gastrointestinal tract in normal tissues.11 In addition,
CA-IX is pathologically located on the surface of cells, while most CA
isozymes such as CA-II found in various normal tissues are located in-
side cells;1 therefore, CA-IX-targeting drugs can selectively interact
with CA-IX by restricting its cell membrane penetration. CA-IX is thus
considered to be an attractive target for in vivo imaging of tumors.
Single photon emission computed tomography (SPECT) and posi-
tron emission tomography (PET) have generally been utilized as major
in vivo imaging techniques for the noninvasive diagnosis of cancer. To
develop imaging probes for SPECT/PET targeting CA-IX, antibody-
based CA-IX imaging probes with favorable accumulation in CA-IX
high-expressing tumors in mice have been reported; however, they
showed limited pharmacokinetics such as slow clearance from the
blood and normal organs, raising concerns about a low signal-to-
background ratio at an early time-point and high radiation toxicity.12,13
In contrast, over the past few decades, many small CA-IX imaging
probes based on sulfonamide have been reported. However, probes
labeled with 99mTc, the main radioisotope used in clinical practice,
⁎ Corresponding author at: Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida
Shimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan.
E-mail address: ono@pharm.kyoto-u.ac.jp (M. Ono).
1 These authors contributed equally to this work.
https://doi.org/10.1016/j.bmcl.2020.127596
Received 17 July 2020; Received in revised form 16 September 2020; Accepted 28 September 2020
Availableonline01October2020
0960-894X/©2020ElsevierLtd.Allrightsreserved.

S. Iikuni, et al.
Bioorganic&MedicinalChemistryLetters30(2020)127596
Fig. 1. Proposed structures of [99mTc]URB2A and [99mTc]ISB2.
showed limited biodistribution including undesirable tumor/blood
ratio and low HT-29 (high level of CA-IX) tumor accumulation (< 1%
injected dose/g);14,15 therefore, the development of 99mTc-labeled CA-
IX imaging probes with fast clearance from the blood pool and favor-
able HT-29 tumor uptake is strongly needed.
bromide in EtOH. Reaction of 2 with hydroxylamine provided a Ham
compound according to a previously reported method,22 which was the
precursor for [99mTc]ISB2 (3) at a yield of 50%.
We carried out 99mTc labeling using [99mTc]pertechnetate, the Ham
precursor, and tin(II) tartrate hydrate (Scheme 2). [99mTc]ISB2 was
synthesized from precursor 3. In general, the chelation reactions of
99mTc and Ham have been confirmed only by the disappearance of the
radioactive peak derived from [99mTc]pertechnetate on reversed-phase
high-performance liquid chromatography (RP-HPLC), since corre-
sponding Ham complexes with Re, a nonradioactive surrogate metal of
99mTc, have not been obtained so far. The 99mTc-labeling reaction with
3 gave two radioactive peaks at retention times of 15.7 and 17.5 min on
Many useful chelating agents for 99mTc, such as type N2S2 diami-
dedithiols, tricarbonyl, hydrazinonicotinic acid (HYNIC), and diethy-
lenetriaminepentaacetic acid (DTPA), have been developed.16 We pre-
viously reported several imaging probes based on hydroxamamide
(Ham), a chelating agent including no thiol, which can form a 99mTc-
labeled compound with high stability and a high radiochemical
yield.17,18 Ham provides a 99mTc complex with two Ham ligands, in-
dicating that it would be useful in the synthesis of a 99mTc-labeled
compound with a bivalent targeting ligand.17,18 Recently, we reported a
RP-HPLC, as shown in previous reports on
[
99mTc]Ham com-
plexes,18,19,22 indicating the generation of two specific isomers of
[
99mTc]Ham complex based on an ureidosulfonamide (US) scaffold as a
[
99mTc]ISB2 (Fig. S1). In our previous study, we tested the biological
CA-IX binding moiety ([99mTc]URB2A) showing marked HT-29 tumor
accumulation (3.44% injected dose/g at 1 h postinjection) (Fig. 1).19
properties of each isomer of the [99mTc]Ham complex ([99mTc]URB2)
by being purified with RP-HPLC, and two isomers of [99mTc]URB2
showed similar in vitro properties, such as an affinity for the target.
Thus, both isomers of [99mTc]ISB2 were collected and used in the fol-
lowing assays. [99mTc]ISB2 was obtained at a 67% radiochemical yield
and over 95% radiochemical purity.
[
99mTc]URB2A exhibited favorable in vitro properties including stability
and affinity for the target; however, it showed limited pharmacoki-
netics. High blood retention was observed (2.07–9.52% injected dose/g
at 1–24 h postinjection), and the tumor/blood ratio was 0.4–1.0 at
1–24 h postinjection, which may cause a high background signal on in
vivo imaging.
The permeability of a cell membrane is preferably low for CA-IX-
targeting agents to selectively interact with CA-IX against other CA
isozymes inside cells (for example, most abundant CA-II). The log POW
We previously reported 111In-labeled US and imidazothiadiazole
sulfonamide (IS) derivatives ([111In]US2 and [111In]DO3A-IS1, respec-
value for [99mTc]ISB2 was 1.20
0.13 determined by the shake flask
tively) as CA-IX imaging probes.20,21
[
111In]DO3A-IS1 based on IS, our
extraction method. Meanwhile, its high molecular weight (789 Da)
suggests the limited cell membrane permeability of [99mTc]ISB2 ac-
cording to Lipinski’s rule of five (molecular weight ≥ 500).23
original CA-IX ligand, showed faster blood clearance (0.27% injected
dose/g at 1 h postinjection) and greater HT-29 tumor uptake
(3.81–8.71% injected dose/g at 1–24 h postinjection) than [111In]US2
(blood, 4.17% injected dose/g at 1 h postinjection; HT-29 tumor,
1.72–4.57% injected dose/g at 1–24 h postinjection), indicating that IS
is a more preferable CA-IX ligand than US. Therefore, the replacement
of US in [99mTc]URB2A with IS may improve its pharmacokinetics.
Here, we designed and synthesized an IS-based [99mTc]Ham complex,
To evaluate the in vitro affinity for CA-IX-expressing cells, we per-
formed a cell binding assay with HT-29 and MDA-MB-231 cells, in
which high and low CA-IX expression was observed, respectively, in our
previous report.20 The binding of
[
99mTc]ISB2 to HT-29 cells
(703
31% initial dose/mg protein) was significantly greater than
that to MDA-MB-231 cells (146
4.0% initial dose/mg protein), in-
[
99mTc]ISB2 (Fig. 1), and evaluated its utility for CA-IX imaging.
Synthesis of the precursor for [99mTc]ISB2 is shown in Scheme 1.
dicating CA-IX-selectivity of [99mTc]ISB2. Moreover, a significant re-
duction in binding to HT-29 and MDA-MB-231 cells by the addition of
acetazolamide, a well-known CA inhibitor, indicated marked specificity
Compound 1 was synthesized according to our previous report.21 IS
derivative 2 was synthesized by reacting 1 with 4-cyanophenacyl
for CA (Fig. 2). The binding of [99mTc]ISB2 to HT-29 cells (703
31%
initial dose/mg protein) was greater than that of [99mTc]URB2A and
[
99mTc]URB2B (93
14% and 83
7.6% initial dose/mg protein,
respectively),19 suggesting the enhancement of the ability to bind to
CA-IX-expressing cells by replacement of the CA-IX ligand.
To quantitatively evaluate the affinity of [99mTc]ISB2 for HT-29
cells, a cell binding assay with an increasing concentration of acet-
azolamide was performed (Fig. S2). IC50 of acetazolamide in the pre-
sence of [99mTc]ISB2 (211.6
20.0 nM) was significantly greater than
that of
(33.5
[
99mTc]URB2A (38.2
10.5 nM) and
[
99mTc]URB2B
6.8 nM),19 indicating that [99mTc]ISB2 has a higher affinity
for HT-29 cells than [99mTc]URB2 (Table 1). Replacement of the CA-IX
ligand (from US to IS) led to an increased affinity for CA-IX high-ex-
pressing cells. The results of the acetazolamide inhibition study corre-
sponded with those of the cell binding study (Fig. 2).
The stability of [99mTc]ISB2 in murine plasma was evaluated after
incubation at 37 °C. The radiochemical purities after incubation for 1, 3,
and 6 h were 79, 73, and 55%, respectively (Table 2). A time-dependent
degradation of [99mTc]ISB2 in murine plasma was suggested despite the
Fig. 2. In vitro cell binding of [99mTc]ISB2. Values are expressed as the
mean
standard error of six independent experiments. *P < 0.001 (two-
tailed Student’s t-test).
2

S. Iikuni, et al.
Bioorganic&MedicinalChemistryLetters30(2020)127596
Scheme 1. Synthetic route of precursor for 99mTc-labeling.
Scheme 2. Radiolabeling route of [99mTc]ISB2.
Table 1
Half-maximal Inhibitory Concentration (IC50, nM) for the Binding of
Acetazolamide to HT-29 Cells Determined Using [99mTc]ISB2 and
[
99mTc]URB2 as Ligands.
Compound
IC50 for acetazolamide (nM)
[
[
[
99mTc]ISB2
211.6
38.2
33.5
20.0
10.5
6.8
99mTc]URB2A*
99mTc]URB2B*
Values are expressed as the mean
standard error of six in-
dependent experiments. *Data from our previous report.19
Table 2
In Vitro Stability of [99mTc]ISB2 in Murine Plasma.
Radiochemical purity (%) at given incubation times
1 h
3 h
6 h
Fig. 3. Radioactivity of extracted organs after intravenous injection of [99mTc]
ISB2 in the HT-29 tumor-bearing mice. Values are expressed as the mean
standard deviation of five mice. *Values are expressed as the % injected dose.
[
99mTc]ISB2
79.4
1.3
72.9
3.0
54.6
5.0
Values are expressed as the mean
experiments.
standard deviation of three independent
levels in the stomach were higher than those of [99mTc]URB2A
(2.41–9.21% injected dose for [99mTc]ISB2, 0.42–4.38% injected dose
for [99mTc]URB2A at 1–24 h postinjection), suggesting the conversion
of [99mTc]ISB2 to pertechnetate in vivo. Moreover, we evaluated the
radiochemical purity in the blood after injection of [99mTc]ISB2 by RP-
HPLC. The radiochemical purity of [99mTc]ISB2 in the blood at 1 h
favorable stability of [99mTc]URB2 (80% after 7-h incubation).19 One of
possible reasons for its difference of stability is electron density within
the molecule. Electron density within IS-based Ham and US-based Ham
would be different from each other, which might influence on stability
of each complex. This result suggests that the scaffold linked with Ham
is critical for the stability of the corresponding [99mTc]Ham complex.
A biodistribution study with [99mTc]ISB2 in HT-29 or MDA-MB-231
tumor-bearing mice was performed to evaluate the pharmacokinetics of
postinjection was 55.7
6.3%, suggesting the low in vivo stability.
[
99mTc]ISB2 might be partially disintegrated with time after being ad-
ministered to mice; thus, a lower amount of 99mTc activity was speci-
fically delivered to the CA-IX high-expressing tumor than [99mTc]
URB2A. An improvement of stability may lead to advanced accumula-
tion in the tumor and a more favorable tumor/blood ratio. Although
replacement of the CA-IX ligand did not enhance the tumor/blood ratio,
the HT-29 tumor accumulation of [99mTc]ISB2 at 6 h postinjection was
[
99mTc]ISB2. We previously demonstrated that high and low levels of
CA-IX expression were present in HT-29 and MDA-MB-231 tumor lysate
from model mice, respectively.20 Thus, we used HT-29 and MDA-MB-
231 tumors as CA-IX high- and low-expressing tumors in vivo, respec-
tively. The uptake of [99mTc]ISB2 in each organ or tissue is expressed as
the % injected dose/g (Fig. 3 and Table S1). The blood retention of
significantly greater than that of the MDA-MB-231 tumor (0.96
0.07
[
99mTc]ISB2 was lower at all evaluated times (5.12, 2.96, 1.22, and
and 0.66
0.09% injected dose/g, respectively), suggesting in vivo
0.81% injected dose/g at 1, 3, 6, and 24 h postinjection, respectively)
than [99mTc]URB2A (9.52, 5.40, 3.78, and 2.07% injected dose/g at 1,
3, 6, and 24 h postinjection, respectively),19 indicating the improve-
ment of blood retention by replacement of the CA-IX ligand. However,
the tumor/blood ratio of [99mTc]ISB2 was undesirable (0.36–0.85 at
1–24 h postinjection), since the tumor accumulation was also de-
creased. The HT-29 tumor uptake of [99mTc]ISB2 was 0.68–1.82% in-
jected dose/g at 1–24 h postinjection, which was lower than that of
selectivity for the CA-IX high-expressing tumor (Fig. 4 and Table S2).
The biodistribution pattern of [99mTc]ISB2 to normal organs corre-
sponded with that of [99mTc]URB2A: high accumulation in the kidney
and lung. The accumulation in these organs might be due to the ex-
pression of other membrane-related CA isozymes.24
In conclusion, we designed and synthesized a novel [99mTc]Ham
complex based on IS ([99mTc]ISB2) and evaluated its usefulness for
imaging of CA-IX high-expressing tumors. In the in vitro cell binding
assay, [99mTc]ISB2 showed greater affinity for CA-IX-expressing cells
than the [99mTc]Ham complex based on US, and specific binding to the
cells. Although improved blood clearance by the replacement of CA-IX
ligand was observed, the in vivo tumor accumulation of [99mTc]ISB2
was lower than that of [99mTc]URB2A, probably due to partial
[
99mTc]URB2A (2.18–3.44% injected dose/g at 1–24 h postinjection),19
while the in vitro study using HT-29 cells showed greater affinity of
[
99mTc]ISB2 than [99mTc]URB2A (Fig. 2 and Table 1). The lower HT-29
tumor accumulation of [99mTc]ISB2 might be due to its lower stability,
observed in the stability evaluation (Table 2). In addition, radioactivity
3

S. Iikuni, et al.
Bioorganic&MedicinalChemistryLetters30(2020)127596
hydroxyproline in HIF-1α by pVHL. Nature. 2002;417(6892):975–978.
3. Jaakkola P, Mole DR, Tian YM, et al. Targeting of HIF-α to the von Hippel-Lindau
ubiquitylation complex by O2-regulated prolyl hydroxylation. Science.
2001;292(5516):468–472.
4. Semenza GL. Hypoxia and cancer. Cancer Metastasis Rev. 2007;26(2):223–224.
5. Dorai T, Sawczuk I, Pastorek J, Wiernik PH, Dutcher JP. Role of carbonic anhydrases
in the progression of renal cell carcinoma subtypes: proposal of a unified hypothesis.
Cancer Invest. 2006;24(8):754–779.
6. Hussain SA, Ganesan R, Reynolds G, Gross L, Stevens A, Pastorek J, Murray PG,
Perunovic B, Anwar MS, Billingham L, James ND, et al. Hypoxia-regulated carbonic
anhydrase IX expression is associated with poor survival in patients with invasive
breast cancer. Br J Cancer. 2007;96(1):104–109.
7. Hutchison GJ, Valentine HR, Loncaster JA, et al. Hypoxia-inducible factor 1α ex-
pression as an intrinsic marker of hypoxia: correlation with tumor oxygen, pimoni-
dazole measurements, and outcome in locally advanced carcinoma of the cervix. Clin
Cancer Res. 2004;10(24):8405–8412.
8. Koukourakis MI, Giatromanolaki A, Sivridis E, et al. Hypoxia-activated tumor path-
ways of angiogenesis and pH regulation independent of anemia in head-and-neck
cancer. Int J Radiat Oncol Biol Phys. 2004;59(1):67–71.
9. Ord JJ, Agrawal S, Thamboo TP, Roberts I, Campo L, Turley H, Han C, et al. An
investigation into the prognostic significance of necrosis and hypoxia in high grade
and invasive bladder cancer. J Urol. 2007;178(2):677–682.
10. Swinson DEB, Jones JL, Richardson D, Wykoff C, Turley H, et al. Carbonic anhydrase
IX expression, a novel surrogate marker of tumor hypoxia, is associated with a poor
prognosis in non–small-cell lung cancer. JCO. 2003;21(3):473–482.
11. Pastorek J, Pastorekova S. Hypoxia-induced carbonic anhydrase IX as a target for
cancer therapy: from biology to clinical use. Semin Cancer Biol. 2015;31:52–64.
12. Divgi CR, Uzzo RG, Gatsonis C, Bartz R, Treutner S, Yu JQ, Chen D, et al. Positron
emission tomography/computed tomography identification of clear cell renal cell
carcinoma: results from the REDECT Trial. JCO. 2013;31(2):187–194.
13. Verhoeff SR, van Es SC, Boon E, van Helden E, Angus L, Elias SG, Oosting SF,
Aarntzen EH, Brouwers AH, Kwee TC, Heskamp S, Hoekstra OS, Verheul H, van der
Veldt AAM, de Vries EGE, et al. Lesion detection by [89Zr]Zr-DFO-girentuximab and
Fig. 4. Radioactivity of extracted tumors at 6 h postinjection of [99mTc]ISB2 in
the HT-29 or MDA-MB-231 tumor-bearing mice. Values are expressed as the
mean
test).
standard deviation of five mice. *P < 0.05 (two-tailed Student’s t-
[
18F]FDG-PET/CT in patients with newly diagnosed metastatic renal cell carcinoma.
Eur J Nucl Med Mol Imaging. 2019;46(9):1931–1939.
degradation after administration. These results provide important in-
formation on developing novel molecular imaging probes based on
14. Akurathi V, Dubois L, Celen S, et al. Development and biological evaluation of 99mTc-
sulfonamide derivatives for in vivo visualization of CA IX as surrogate tumor hypoxia
markers. Eur J Med Chem. 2014;71:374–384.
[
99mTc]Ham complexes.
15. Nakai M, Pan J, Lin K-S, Thompson JR, et al. Evaluation of 99mTc-sulfonamide and
sulfocoumarin derivatives for imaging carbonic anhydrase IX expression. J Inorg
Biochem. 2018;185:63–70.
Declaration of Competing Interest
16. Banerjee SR, Maresca KP, Francesconi L, Valliant J, Babich JW, Zubieta J. New di-
rections in the coordination chemistry of 99mTc: a reflection on technetium core
structures and a strategy for new chelate design. Nucl Med Biol. 2005;32(1):1–20.
17. Iikuni S, Ono M, Watanabe H, Matsumura K, Yoshimura M, Kimura H, et al. Imaging
of cerebral amyloid angiopathy with bivalent 99mTc-hydroxamamide complexes. Sci
Rep. 2016;6(1) https://doi.org/10.1038/srep25990.
The authors declare the following financial interests/personal re-
lationships which may be considered as potential competing interests:
Masahiro Ono received grant support from Nihon Medi-Physics Co.,
Ltd. The other authors declare no competing financial interests.
Masahiro Ono holds a patent related to imidazothiadiazole sulfonamide
(IS) derivatives with Nihon Medi-Physics Co., Ltd.
18. Iikuni S, Ono M, Watanabe H, Matsumura K, Yoshimura M, et al. Enhancement of
binding affinity for amyloid aggregates by multivalent interactions of 99mTc-hydro-
xamamide complexes. Mol Pharm. 2014;11(4):1132–1139.
19. Iikuni S, Tanimura K, Watanabe H, Shimizu Y, Saji H, Ono M. Development of the
99mTc-hydroxamamide complex as a probe targeting carbonic anhydrase IX. Mol
Pharm. 2019;16(4):1489–1497.
Acknowledgements
20. Iikuni S, Ono M, Watanabe H, Shimizu Y, Sano K, Saji H. Cancer radiotheranostics
targeting carbonic anhydrase-IX with 111In- and 90Y-labeled ureidosulfonamide
scaffold for SPECT imaging and radionuclide-based therapy. Theranostics.
2018;8(11):2992–3006.
The study was supported by AMED under Grant Number
JP19im0210819 and Nihon Medi-Physics Co., Ltd.
21. Iikuni S, Okada Y, Shimizu Y, Watanabe H, Ono M. Synthesis and evaluation of in-
dium-111-labeled imidazothiadiazole sulfonamide derivative for single photon
emission computed tomography imaging targeting carbonic anhydrase-IX. Bioorg
Med Chem Lett. 2020;30(14):127255. https://doi.org/10.1016/j.bmcl.2020.127255.
22. Nakayama M, Xu LC, Koga Y, Harada K, Sugii A, Nakayama H, Tomiguchi S, et al.
Hydroxamamide as a chelating moiety for the preparation of 99mTc-radio-
pharmaceuticals III. Characterization of various 99mTc-hydroxamamides. Appl Radiat
Isot. 1997;48(5):571–577.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.bmcl.2020.127596.
References
23. Lipinski CA, Lombardo F, Dominy BW, Feeney PJ. Experimental and computational
approaches to estimate solubility and permeability in drug discovery and develop-
ment settings. Adv Drug Deliv Rev. 1997;23(1-3):3–25.
1. Supuran CT. Carbonic anhydrases: novel therapeutic applications for inhibitors and
activators. Nat Rev Drug Discov. 2008;7(2):168–181.
24. Oosterwijk E. Carbonic anhydrase expression in kidney and renal cancer: implica-
tions for diagnosis and treatment. Subcell Biochem. 2014;75:181–198.
2. Hon WC, Wilson MI, Harlos K, et al. Structural basis for the recognition of
4