2 Aptamer-Based Probes for Molecular Imaging
39
aptamers assembled in the presence of thrombin, which could be detected the change
in T2 weighted MR images with 25 nM thrombin in human serum (Fig. 2.3b). Control
analytes, streptavidin, or bovine serum albumin did not show any change in the MR
image with inactive aptamer functionalized nanoparticles. It was suitable for noninvasive in vivo imaging of little molecular information, making early diagnostics and
treatment of diseases possible before the disease reaches an advanced stage by using
such an aptamer functionalized superparamagnetic iron oxide nanoparticles.
Aptamer-based activatable probes for MR imaging in several cancer models have
been evaluated. Hu et al. selected the aptamer against nucleolin and reported the
aptamer AS411 conjugated Mn 3 O 4 @SiO 2 core–shell nanoprobes (NPs) as a potential tumor-targeting agent [38]. Based on a quantitative biodistribution study, NPs
showed higher tumor accumulation in human cervical carcinoma tumor-bearing
mice in vivo MRI. NPs also exhibited the low toxicity in vivo proved by histological, hematological and biochemistry analysis. Kim et al. utilized an aptamer
binding vascular endothelial growth factor receptor type 2 (VEGFR2) that is overexpressed on angiogenic vessels [46]. Magnetic nanocrystal (MNC) was synthesized with the thermal decomposition method. Then MNC was enveloped and
surface-modified with biocompatible carboxyl polysorbate 80 and a VEGFR2specific aptamer, respectively. Apt-MNC exhibited higher magnetic resonance signal
and better VEGFR2-detecting ability than the control in U87 mice brain tumor via
MR imaging. Lim et al. developed aptamer αvß3-conjugated magnetic nanoparticles
(Aptαvß3-MNPs) to detect neovascularization and angiogenesis in cancer [39]. You
et al. selected VEGF165-aptamer as the part of nanoprobes for imaging the tumor
human vascular endothelial growth factor 165 (VEGF 165) [47].
A great deal of attention has been paid to address the problems in designing
aptamers or aptamer-based nanoparticles as MR imaging contrast agents. Many MRI
contrast agents were selected against markers exhibiting on the solid tumors or epithelial tissue instead of markers requiring extravasation from the bloodstream. These
selections might be based on the size of contrast agents, some of are more than
100 nm. Then few studies have used the aptamer comprised of a random sequence of
the same size and chemistry as the negative control. Without the control agent modified negative oligonucleotide, it is difficult to distinguish the great tumor recognition
effect is contributed to the interaction between the aptamer with its target or the
nonspecific uptake by the target position. In addition, negatively charged DNA/RNA
aptamer might disrupt substantially the biodistribution of aptamer-based nanoparticles. The effectiveness of the targeting system and the distribution of large doses of
contrast agents in vivo remain to be confirmed.
2.4 Ultrasound Imaging
Ultrasound imaging (echography) is an important medical diagnostic auxiliary tool
used in clinics for real-time anatomical and functional imaging owning to its inexpensiveness, short acquisition time, and noninvasive property. It uses a probe to
39
aptamers assembled in the presence of thrombin, which could be detected the change
in T2 weighted MR images with 25 nM thrombin in human serum (Fig. 2.3b). Control
analytes, streptavidin, or bovine serum albumin did not show any change in the MR
image with inactive aptamer functionalized nanoparticles. It was suitable for noninvasive in vivo imaging of little molecular information, making early diagnostics and
treatment of diseases possible before the disease reaches an advanced stage by using
such an aptamer functionalized superparamagnetic iron oxide nanoparticles.
Aptamer-based activatable probes for MR imaging in several cancer models have
been evaluated. Hu et al. selected the aptamer against nucleolin and reported the
aptamer AS411 conjugated Mn 3 O 4 @SiO 2 core–shell nanoprobes (NPs) as a potential tumor-targeting agent [38]. Based on a quantitative biodistribution study, NPs
showed higher tumor accumulation in human cervical carcinoma tumor-bearing
mice in vivo MRI. NPs also exhibited the low toxicity in vivo proved by histological, hematological and biochemistry analysis. Kim et al. utilized an aptamer
binding vascular endothelial growth factor receptor type 2 (VEGFR2) that is overexpressed on angiogenic vessels [46]. Magnetic nanocrystal (MNC) was synthesized with the thermal decomposition method. Then MNC was enveloped and
surface-modified with biocompatible carboxyl polysorbate 80 and a VEGFR2specific aptamer, respectively. Apt-MNC exhibited higher magnetic resonance signal
and better VEGFR2-detecting ability than the control in U87 mice brain tumor via
MR imaging. Lim et al. developed aptamer αvß3-conjugated magnetic nanoparticles
(Aptαvß3-MNPs) to detect neovascularization and angiogenesis in cancer [39]. You
et al. selected VEGF165-aptamer as the part of nanoprobes for imaging the tumor
human vascular endothelial growth factor 165 (VEGF 165) [47].
A great deal of attention has been paid to address the problems in designing
aptamers or aptamer-based nanoparticles as MR imaging contrast agents. Many MRI
contrast agents were selected against markers exhibiting on the solid tumors or epithelial tissue instead of markers requiring extravasation from the bloodstream. These
selections might be based on the size of contrast agents, some of are more than
100 nm. Then few studies have used the aptamer comprised of a random sequence of
the same size and chemistry as the negative control. Without the control agent modified negative oligonucleotide, it is difficult to distinguish the great tumor recognition
effect is contributed to the interaction between the aptamer with its target or the
nonspecific uptake by the target position. In addition, negatively charged DNA/RNA
aptamer might disrupt substantially the biodistribution of aptamer-based nanoparticles. The effectiveness of the targeting system and the distribution of large doses of
contrast agents in vivo remain to be confirmed.
2.4 Ultrasound Imaging
Ultrasound imaging (echography) is an important medical diagnostic auxiliary tool
used in clinics for real-time anatomical and functional imaging owning to its inexpensiveness, short acquisition time, and noninvasive property. It uses a probe to