Iron Oxide Nanoparticles and Derivatives for Biomedical Imaging and Application in Cancer Diagnosis and Therapy - Bioanalysis Advanced Materials Methods and Devices - page 9

delivery, it is important to image the bioavailability of the siRNA noninvasively.
There are several examples of probes synthesized and tested to address this goal.
In one example, the probe consists of magnetic nanoparticles (for MRI) tagged
with Cy5.5 dye (for NIRF imaging) and conjugated to a synthetic siRNA duplex
targeting green fluorescent protein (GFP). The probe was tested in GFP-expressing
tumors as a model system [ 21 ]. The probe was further conjugated to myristoylated
polyarginine peptide (MPAP), which acts as a membrane translocation vector for
increased uptake in tumor cells. First, in vitro experiments using green fluorescent
protein (GFP) or control red fluorescent protein (RFP)-expressing tumor cells
confirmed that GFP was down-regulated, whereas RFP expression remained con-
stant. The in vivo studies showed that after systematic intravenous administration of
the probe, accumulation was observed in tumors. Tumor uptake was confirmed by
MRI and in vivo optical imaging (Fig. 1.4 ). The expression of GFP in the GFP-
expressing tumor cells was reduced, whereas RFP expression was not affected in
the RFP-expressing tumors, indicating that the effect was specific. These results
were confirmed by in vivo optical imaging and quantitative RT-PCR.
In a more clinically relevant scenario, the nanoparticles carried siRNA to the
antiapoptotic gene birc5 , which encodes Survivin. Survivin is an important thera-
peutic target because it is a member of the inhibitor of apoptosis protein family,
which shows tumor-restricted expression in most human neoplasms. The
synthesized probe was administered intravenously into breast tumor-bearing mice
twice a week for 2 weeks. MRI studies before and after probe administration
revealed that the probe accumulated in tumor cells, which was also confirmed by
in vivo optical imaging.
The specific silencing of birc5 was confirmed by RT-PCR. As a result, a
noticeable increase in tumor-associated levels of apoptosis and necrosis was
observed. These results demonstrated the applicability of the siRNA-conjugated
nanoparticles as multifunctional therapeutic and imaging agents (Fig. 1.5 ).
In a similar scenario, in order to improve the bioavailability of the siRNA
complex to tumor cells, the nanoparticles were conjugated to the MUC-1 specific
EPPT peptide, instead of MPAP. This modification increases the overall nanoparti-
cle availability in tumor cells [ 17 ]. Studies with the targeted probe revealed that the
contrast agents were taken up by tumor cells in vivo resulting in an overall slower
tumor growth due to specific silencing of birc5 by the siRNA-functionalized probe.
This technology has far-reaching implications. By bringing imaging and therapy
together, it can be applied to a wide range of diseases, which can be treated using
intervention at the level of gene expression.
1.6 Magnetic Fluid Hyperthermia
Magnetic fluid hyperthermia (MFH) is based on the following principle: the
superparamagnetic core absorbs the energy from an alternating external magnetic
field and converts it into thermal energy. This causes the nanoparticles to heat up
by magnetic hysteresis losses or N ´ el relaxation. The cells containing these