22.2.1.4 Dendrimers
Dendrimers are repetitively branched molecules. Imaging moieties can be encapsulated in the internal side or on the surface, and the degree of polymerization
control allows dendrimers to be made with diverse sizes with different weights and
chemical components. Their payload capacity and ability to form various polymer
structures mean that dendrimers are attractive probes for the construction of multimodal imaging [19]. The large number of attachment position which are accessible on a dendrimer’s surface can be exploited by various dendrimer-based
imaging probes that have been developed using novel synthetic chemistry strategies
for multimodal tumor imaging methods [20].
22.2.1.5 Liposomes
Liposome is a spherical vesicle with at least one lipid bilayer. NPs that enclose an
aqueous area that can accommodate hydrophilic/lipophilic drugs. Liposomes can
passively accumulate in tumors via cell-specific targeting or through extravasation
of abnormal leaky tumor vasculature. In addition, liposomes have versatile modifiability as they can encapsulate, insert, or attach functional molecules to the inner
membrane, the membrane bilayer, and the membrane surface, respectively. Several
ways have been made for liposome preparation with different sizes, structures, and
distributions [21]. Several liposome formulations have been approved by the FDA
or are being actively tested in clinical trials [22]. The biodistribution of liposomes is
a major concern in clinical applications. Similar to other NPs, conventional liposomes are susceptible to eliminate by the cells of the RES from systemic circulation
[23]. Many articles have verified that 50–80% of liposomes are absorbed by RES,
within first 15 min after their intravenous administration [24]. Nevertheless, it has
been found that and modulation of the surface charge and reduction of the size of
liposomes could diminish their uptake by the RES. Therefore, for imaging and
therapeutic applications, liposomes with smaller diameters (80–200 nm) that are
composed of negatively charged or neutral lipids and cholesterol have been
developed [21].
22.2.2 Targeting Groups
22.2.2.1 Antibody Molecules
Antibodies, which are commonly used in immunohistochemistry, are ideal targeting
agents. The potential of antibodies was suggested by Ehrlich [25], who described
that they could serve as “magic bullets” as they can specifically recognize epitopes
with high binding affinity. Antibody molecules have been enhanced via genetic
engineering. Furthermore, the potential of making human antibodies and antibody
22 Molecular Imaging Using Radionanomedicine
415
Dendrimers are repetitively branched molecules. Imaging moieties can be encapsulated in the internal side or on the surface, and the degree of polymerization
control allows dendrimers to be made with diverse sizes with different weights and
chemical components. Their payload capacity and ability to form various polymer
structures mean that dendrimers are attractive probes for the construction of multimodal imaging [19]. The large number of attachment position which are accessible on a dendrimer’s surface can be exploited by various dendrimer-based
imaging probes that have been developed using novel synthetic chemistry strategies
for multimodal tumor imaging methods [20].
22.2.1.5 Liposomes
Liposome is a spherical vesicle with at least one lipid bilayer. NPs that enclose an
aqueous area that can accommodate hydrophilic/lipophilic drugs. Liposomes can
passively accumulate in tumors via cell-specific targeting or through extravasation
of abnormal leaky tumor vasculature. In addition, liposomes have versatile modifiability as they can encapsulate, insert, or attach functional molecules to the inner
membrane, the membrane bilayer, and the membrane surface, respectively. Several
ways have been made for liposome preparation with different sizes, structures, and
distributions [21]. Several liposome formulations have been approved by the FDA
or are being actively tested in clinical trials [22]. The biodistribution of liposomes is
a major concern in clinical applications. Similar to other NPs, conventional liposomes are susceptible to eliminate by the cells of the RES from systemic circulation
[23]. Many articles have verified that 50–80% of liposomes are absorbed by RES,
within first 15 min after their intravenous administration [24]. Nevertheless, it has
been found that and modulation of the surface charge and reduction of the size of
liposomes could diminish their uptake by the RES. Therefore, for imaging and
therapeutic applications, liposomes with smaller diameters (80–200 nm) that are
composed of negatively charged or neutral lipids and cholesterol have been
developed [21].
22.2.2 Targeting Groups
22.2.2.1 Antibody Molecules
Antibodies, which are commonly used in immunohistochemistry, are ideal targeting
agents. The potential of antibodies was suggested by Ehrlich [25], who described
that they could serve as “magic bullets” as they can specifically recognize epitopes
with high binding affinity. Antibody molecules have been enhanced via genetic
engineering. Furthermore, the potential of making human antibodies and antibody
22 Molecular Imaging Using Radionanomedicine
415