(99m)Tc-labeled SWL specific peptide for targeting EphA2 receptor.
BACKGROUND
EphA2, one member of the Eph receptor family, is widely expressed in multiple aggressive cancers. SWL, a small peptide identified by phage display, has high binding affinity to EphA2, suggesting that it could be exploited for targeted molecular imaging. Therefore, a novel peptide-based probe, (99m)Tc-HYNIC-SWL, was developed and its potential to specifically target EphA2-positive tumors was investigated.


METHODS
The SWL peptide was labeled with hydrazinonicotinic acid (HYNIC), followed by (99m)Tc labeling. Immunofluorescence staining was carried out to detect the expression of EphA2 in A549 lung cancer cells and OCM-1 melanoma cells. Saturation binding experiments were performed by incubating A549 cells with increasing concentrations of radiolabeled peptide in vitro. To test the probe in vivo, nude mice bearing either A549 or OCM-1 derived tumors were established, injected with (99m)Tc-HYNIC-SWL, and subjected to SPECT imaging. Mice injected with excess unlabeled SWL were used as a specific control. Ex vivo γ-counting of dissected tissues from the mice was also performed to evaluate biodistribution.


RESULTS
Immunofluorescence staining showed that A549 cells intensively expressed EphA2, while OCM-1 cells had little expression. (99m)Tc-HYNIC-SWL displayed high binding affinity with A549 cells (KD=2.6±0.7nM). From the SPECT images and the results of the biodistribution study, significantly higher uptake of the tracer was seen in A549 tumors (1.44±0.12 %ID/g) than in OCM-1 tumors (0.43±0.20 %ID/g) at 1h after injection. Pre-injection with excess unlabeled peptide in A549-bearing nude mice, significantly reduced tumor uptake of the radiolabeled probe (0.58±0.20 %ID/g) was seen. These data suggest that (99m)Tc-HYNIC-SWL specifically targets EphA2 in tumors.


CONCLUSIONS
The expression of EphA2 can be noninvasively investigated using (99m)Tc-HYNIC-SWL by SPECT imaging. The in vitro and in vivo characteristics of (99m)Tc-HYNIC-SWL make it a promising probe for EphA2-positive tumor imaging.
Department of Nuclear Medicine, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology, Hubei Province Key Laboratory of Molecular Imaging, Wuhan, 430022, China.
Yu
Y
Liu
Department of Nuclear Medicine, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology, Hubei Province Key Laboratory of Molecular Imaging, Wuhan, 430022, China.
Xiaoli
X
Lan
Department of Nuclear Medicine, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology, Hubei Province Key Laboratory of Molecular Imaging, Wuhan, 430022, China; Department of Nuclear Medicine, The Second People's Hospital of Wuhu, Wuhu, 241000, China.
Tao
T
Wu
Department of Nuclear Medicine, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology, Hubei Province Key Laboratory of Molecular Imaging, Wuhan, 430022, China; Department of Nuclear Medicine, Zhongshan Hospital, Fudan University, Shanghai, 200032, China.
Juntao
J
Lang
Department of Nuclear Medicine, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology, Hubei Province Key Laboratory of Molecular Imaging, Wuhan, 430022, China.
Xueyan
X
Jin
Department of Nuclear Medicine, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology, Hubei Province Key Laboratory of Molecular Imaging, Wuhan, 430022, China.
Xun
X
Sun
Department of Nuclear Medicine, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology, Hubei Province Key Laboratory of Molecular Imaging, Wuhan, 430022, China.
Qiong
Q
Wen
Department of Nuclear Medicine, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology, Hubei Province Key Laboratory of Molecular Imaging, Wuhan, 430022, China. Electronic address: anruiwh@163.com.
Rui
R
An
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D045744:Cell Line, Tumor; D006801:Humans; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics; D036104:Receptor, EphA2 / Q000378:metabolism*; D013667:Technetium; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon
D010455:Peptides; D013667:Technetium; D036104:Receptor, EphA2
(99m)Tc-HYNIC-SWL; EphA2 receptor; Molecular imaging; SPECT; SWL peptide; Tumor imaging