Design and Development of Theranostic Nanomedicines - Nanotechnology for Biomedical Imaging and Diagnostics - page 426

developed DoX-loaded thermally cross-linked superparamagnetic ionps (Dox@
TCl-spion) as a theranostic Mri agent and evaluated the agent in a lung cancer
mouse model [27]. Dox@TCl-spion has a hydrodynamic size of 21 nm and was
able to accumulate in the tumor region by epr effect. In vivo , Dox@TCl-spion
showed significantly larger antitumor effect than DoX alone, indicating enhanced
therapeutic efficacy with passive targeting. at the same time, the therapeutic effect
was monitored by T 2 -Mri. in an effort to develop specifically targeted theranostic
ionps, prostate-specific membrane antigen (psMa) aptamer was later on attached
to the surface of Dox@TCl-spion by the same group [28]. The resulting Dox@
apt-hybr-TCl-spion showed selective drug delivery in a prostate cancer xenograft
mouse model. Multimodal ionps have also been applied in theranostic studies of
cancers in vivo , such as Mri-optical imaging [29] and Mri/peT [30].

15.2.2 gold nanoparticles

gold-based nanoparticles represent an attractive class of theranostic nanomaterials.
This is largely due to the unique surface plasmon resonance (spr) feature of gold. a
gold nanostructure can create intense absorption and scattering peaks when illumi-
nated with an electromagnetic wave [31]. importantly, the absorption and scattering
wavelengths can be tuned based on the size and shape of gold nanoparticles (gnps),
therefore allowing in vivo imaging applications in the favorable nir optical region.
gnps have been developed in the shapes of spheres, cubes, rods, cages, and wires
[14]. although gnps are poor fluorescence emitters, they are commonly used in
photoacoustic imaging studies. in addition, the spr property renders gnps suitable
for photothermal therapy (pTT) of tumors. Moreover, bioconjugation of targeting,
imaging, and therapeutic entities to gnps surfaces is well established. as such,
gnps have been extensively investigated in theranostic studies.
The intense absorption and scattering make gnps suitable for photoacoustic and
surface-enhanced raman spectroscopy. smaller gnps also have good X-ray attenu-
ation and can serve as contrast agent for X-ray and CT [32]. in addition, the surface
functional groups of gnps allow for multimodal imaging capabilities by incorpo-
rating other techniques, such as speCT [33], peT [34, 35], CT [36], Mri [37], and
optical [38].
The strong covalent interaction between gold and sulfur is of paramount impor-
tance in stabilizing nanostructures [39]. such interaction is typically mediated
through the sulfhydryl (-sh) group in thiols; therefore, surface attachment of drug
molecules is often conducted via addition of thiolated molecules. For example, a
modified paclitaxel (pTX) drug molecule with terminal carboxyl group was attached
to surface sulfhydryl group on gnps through a 4-mercaptophenol linker [40]. in
another study, a colloidal gnp vector was developed by coupling tumor necrosis
factor (TnF) with thiol-derivatized peg on the surface [41].
as discussed earlier in this text, gnps can also serve as a cancer therapy agent
without the need of any additional drug molecules. This is because upon laser irradi-
ation, gnps are efficient in converting light to heat, which kills surrounding cancer
cells via pTT. Compared to conventional chemotherapy drugs, which have notorious