Biomedical Engineering Reference
In-Depth Information
the low pH of the lysosomes. However, analysis of the diffraction
patterns suggested that the exposed cores retained their magnetite
structure. Nearly all the #BU48 particles appeared to remain clearly
separated. SEM showed wide variance in the surface attachment
behavior between the cell lines and nanoparticle types, which is likely
a large determinant in the observed differences in uptake behavior.
Similar results were obtained by Kalambur et al. in human
prostate tumor cells (LNCaP) (Kalambur, Longmire, and Bischof
2007). Two types of nanoparticles were studied, both with 10
nm magnetite cores. One had an anionic surfactant coating and
the other a neutral dextran coating. The cells were incubated in
medium containing concentrations of nanoparticles at 0.05, 0.1,
0.5, and 1 mg Fe per ml, and uptake was measured by magneto-
phoresis and colorimetric iron assays at 1, 6, 24, 48, and 72 hours.
The resulting uptake kinetics are included in Figure 17.9. The
surfactant-coated particles demonstrated much higher uptake than
the dextran-coated particles, with apparent saturation behavior
for both concentration and time. It was suggested that this differ-
ence in kinetics was due to differences in the uptake mechanisms.
The saturation behavior would suggest an adsorptive endocytotic
pathway for the surfactant-coated particles versus a fluid-phase
pinocytotic pathway for the dextran-coated particles, suggested by
the linear increase with external concentration. The adsorptive pro-
cess could potentially be further enhanced by specifically targeting
the nanoparticles to receptors on the cell membranes or perhaps
through cationic surfactants.
Natarajan et al. characterized the
in vivo
uptake of PEG-
coated iron-oxide nanoparticles, tagged with a breast cell tar-
geting monoclonal antibody, ChL6 (Natarajan et al. 2008).
Biodistributions for targeted and untargeted nanoparticles with
mean core diameters of 20, 30, and 100 nm were characterized in
mice bearing human breast cancer HBT 3477. The nanoparticles
were intravenously injected, and blood and tissue data were col-
lected at 4, 24, and 48 hours. The tumor uptake for the targeted
particles after two days was between 4% and 9% of the injected
dose, which was substantially higher than uptake for the untar-
geted particles, at less than 0.5% of the injected dose. This sug-
gests significant interaction between the antibodies and cancer
cell receptors, which is a promising result for prospective, clini-
cal modes of systemic delivery.
17.4.2 thermal Dose In Vitro
A large number of
in vitro
studies have demonstrated the ability
of magnetic nanoparticles to heat cells to a cytotoxic level in the
presence of an alternating magnetic field. Jordan et al. expanded
the uptake studies described in Section 17.4.1 to include heat-
ing in a magnetic field at 520 kHz and 4 to 12.5 kA/m, for times
between 5 and 120 minutes (Jordan et al. 1999). Survival rates
were compared with those of a treatment in a constant tempera-
ture water bath at 43°C and 45°C. One of the most prominent
results was the inability of the dextran-coated particles to heat
after intracellular uptake. It was expected that degradation of
the dextran coating in the lysosomes led to tight particle aggre-
gates, producing high interparticle interaction and eliminating
the superparamagnetic heating behavior. However, extracel-
lular #P6 and intra- and extracellular #BU48 produced signifi-
cant heating in the alternating magnetic field, demonstrating
cellular deactivation at levels (at least) equivalent to the water
bath hyperthermia. In addition, the iron oxide treatments also
appeared to result in some sort of sensitization effect over the
first 60 minutes, in which decreased survival occurred. It was
speculated that this might be a result of membrane disruption
or organelle-specific damage, due to localized heating of the
nanoparticles. However, the ability of magnetic nanoparticles to
produce heating rates high enough to create localized, intracel-
lular temperature increases has been questioned from an analyt-
ical perspective (Rabin 2002; Keblinski et al. 2006), and thermal
effects are more likely confined to macroscopic, bulk heating
(Qin, Etheridge, and Bischof 2011; Etheridge and Bischof 2012a).
18
1.6
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Dextran
Surfactant
16
1.4
14
1.2
12
1.0
0.0 .2 0.4 0.6 0.8 1.0 1.2
Extracellular concentration (mg Fe/ml)
10
0.8
8
0.6
6
0.4
4
0.2
2
0.0
0
0
20
40
Time (h)
60
80
0.0
0.2 0.4 0.6
Extracellular concentration (mg Fe/ml)
0.8
1.0
1.2
(a)
(b)
FIGURE 17.9
(a) Time and (b) concentration dependent uptake kinetics for surfactant and dextran coated nanoparticles in LNCaP. (From
Kalambur, V. S, E. K. Longmire, and J. C. Bischof,
Langmuir
23, 24, 2007.)
