264
Q. Lv et al.
9.6.3 Single-Photon Emission Computed Tomography
(SPECT)/Positron-Emission Tomography (PET)
SPECT and PET are two kinds of non-invasive nuclear imaging techniques, providing
the dynamical biological events and longitudinal assessment within the deep body
with high sensitivity. Aptamer-based SPECT and PET imaging strategies provide
novel specificity for a cancer diagnostic.
SPECT imaging depends on the radioisotopes derived γ-ray emission by the
gamma camera. For example, the human matrix metalloprotease-9 (hMMP-9, F3B)targeting RNA aptamers were functionalized with
111 In-DOTA to construct a cancer
cells-specific probe (
111 In-DOTA-F3B). After intravenous injection into the mice
bearing human melanoma tumors, the
111 In-DOTA-F3Bprobe can accumulate within
the tumor region and offer increased SPECT signal intensity in a tumor gradedependent manner through ex vivo imaging at 1 h. The average half-life of the
111 In-DOTA-F3Bprobe was determined as 11 min, indicating a quick clearance from
the blood [143]. Similarly, the anti-EGFRvIII DNA aptamer (U2) was conjugated
with rhenium radioisotope (
188 Re). The SPECT molecular imaging of the
188 ReU2 probe was observed within glioblastoma U87MG xenografted mice, resulting in
satisfactory tumor specificity [144].
PET technique shows ten-fold more sensitivity comparing to SPECT. For example,
the fluorine-18 radioisotope (
18 F) labeled anti-extracellular domain of protein tyrosine kinase 7 (PTK7) DNA aptamer was established as a PET probe (
18 F-Sgc8) [145].
The PTK7 is a transmembrane protein overexpressed at several types of cancer cells,
and considered as a ubiquitous cancer biomarker [146]. The
18 F-Sgc8 probe can
be visualized within the xenograft mouse model bearing human colon cancer using
PET imaging, showing highly efficient sensitivity for cancer biomarkers tracking
and early diagnosis [147].
9.6.4 Computed Tomography (CT)
CT imaging has been commonly used as a clinical examination technique for
anatomical structure visualization. Novel nanomaterial AuNPs are employed for CT
imaging. The anti-PSMA RNA aptamers were immobilized onto AuNPs to construct
a CT contrast agent. These aptamer-based AuNPs exhibit more than fourfold stronger
CT signal intensity for specific targeted LNCaP cells than that of non-targeted PC3
cells [148]. In another interesting work, a multimodal cancer-specific nanoplatform was established for CT imaging and fluorescence-guided surgery methods.
The label-free fluorescent AuNPs were functionalized with diatrizoic acid and a
tumor-targeting aptamer AS1411 to construct a tumor-specific CT contrast agent
(AS1411-DA-AuNPs). CT image can be observed at 30 min post-injection and shows
106% enhancement of signal intensity in CLI-5 tumor-bearing mice. The AS1411DA-AuNPs have an absorption peak within 300–400 nm and a visible orange-red
Q. Lv et al.
9.6.3 Single-Photon Emission Computed Tomography
(SPECT)/Positron-Emission Tomography (PET)
SPECT and PET are two kinds of non-invasive nuclear imaging techniques, providing
the dynamical biological events and longitudinal assessment within the deep body
with high sensitivity. Aptamer-based SPECT and PET imaging strategies provide
novel specificity for a cancer diagnostic.
SPECT imaging depends on the radioisotopes derived γ-ray emission by the
gamma camera. For example, the human matrix metalloprotease-9 (hMMP-9, F3B)targeting RNA aptamers were functionalized with
111 In-DOTA to construct a cancer
cells-specific probe (
111 In-DOTA-F3B). After intravenous injection into the mice
bearing human melanoma tumors, the
111 In-DOTA-F3Bprobe can accumulate within
the tumor region and offer increased SPECT signal intensity in a tumor gradedependent manner through ex vivo imaging at 1 h. The average half-life of the
111 In-DOTA-F3Bprobe was determined as 11 min, indicating a quick clearance from
the blood [143]. Similarly, the anti-EGFRvIII DNA aptamer (U2) was conjugated
with rhenium radioisotope (
188 Re). The SPECT molecular imaging of the
188 ReU2 probe was observed within glioblastoma U87MG xenografted mice, resulting in
satisfactory tumor specificity [144].
PET technique shows ten-fold more sensitivity comparing to SPECT. For example,
the fluorine-18 radioisotope (
18 F) labeled anti-extracellular domain of protein tyrosine kinase 7 (PTK7) DNA aptamer was established as a PET probe (
18 F-Sgc8) [145].
The PTK7 is a transmembrane protein overexpressed at several types of cancer cells,
and considered as a ubiquitous cancer biomarker [146]. The
18 F-Sgc8 probe can
be visualized within the xenograft mouse model bearing human colon cancer using
PET imaging, showing highly efficient sensitivity for cancer biomarkers tracking
and early diagnosis [147].
9.6.4 Computed Tomography (CT)
CT imaging has been commonly used as a clinical examination technique for
anatomical structure visualization. Novel nanomaterial AuNPs are employed for CT
imaging. The anti-PSMA RNA aptamers were immobilized onto AuNPs to construct
a CT contrast agent. These aptamer-based AuNPs exhibit more than fourfold stronger
CT signal intensity for specific targeted LNCaP cells than that of non-targeted PC3
cells [148]. In another interesting work, a multimodal cancer-specific nanoplatform was established for CT imaging and fluorescence-guided surgery methods.
The label-free fluorescent AuNPs were functionalized with diatrizoic acid and a
tumor-targeting aptamer AS1411 to construct a tumor-specific CT contrast agent
(AS1411-DA-AuNPs). CT image can be observed at 30 min post-injection and shows
106% enhancement of signal intensity in CLI-5 tumor-bearing mice. The AS1411DA-AuNPs have an absorption peak within 300–400 nm and a visible orange-red