Biomedical Engineering Reference
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to the free drug, encapsulation not only improved the aqueous solubility, stability
and delivery of the drug but the PDT efficiency as well. Indeed cell viability mea-
surements on A-375 and B16-F10 melanoma cells demonstrated that the nanopar-
ticles were more photocytotoxic than the free drug. Apoptosis was the major
pathway of cell death. Evaluation of the level of intracellular protein-derived per-
oxides in A-375 melanoma cells after internalization of the nanoparticles and PDT
suggested a type II mechanism (phototoxicity through formation of
1
O
2
). Tracking
with specific markers showed that more nanoparticles were localized in mitochon-
dria and lysosomes than free PS.
Simon et al. recently published (Simon et al.
2010
) the synthesis and properties
of PpIX, (Fig.
7
) ORMOSIL nanoparticles prepared by Prasad's method, and per-
formed
in vitro
and
in vivo
studies.
In vitro
experiments showed that for the tested
NPs (10, 25 and 60 nm), no significant difference of internalization kinetic and total
amount of NPs uptake (around 200 fmol per 1,000 cells after 1 h of incubation)
could be observed. The exact mechanism of internalization remains unknown, but
both active and a high proportion of passive processes were involved, and it was
cell-dependant. PpIX silica NPs effects on cell survival were tested on the HCT 116
colon cancer cell line. The results obtained showed that 3 h incubation with PpIX
silica NPs and 20 min of illumination (50 mW.cm
−2
) gave the best results for cancer
cells destructions, i.e. EC
50
at 0.44 mM for all sizes of NPs. Moreover, in all tumor
types, PpIX silica NPs were more efficient (more than one log of difference) than
free PpIX. For both systems, a loss of efficiency was found 5 h after incubation (no
residual activity after 24 h). The cell clearance of PpIX was proved to be responsible
of the loss of efficiency and the clearance process seems to begin early, before 2 h.
There is a strong relationship between the sites of subcellular localization of the
PpIX and photodamage to nearby organelles involved in cell death. The intracel-
lular accumulation of PpIX silica NPs takes place in the cytoplasm of cells.
Quantification of cell internalization could be realized by measuring the ROS gen-
eration by fluorescence spectroscopy, since the ROS generation is correlated to the
presence of PpIX silica NPs in both HCT 116 and HT-29 colon cancer cells. Higher
ROS amounts cause larger cell damages leading to cell destruction.
In vivo
studies on nude tumor-bearing mice were performed to observe the
biodistribution of PpIX silica NPs loaded with DID (dioctadecyl tetramethyl
indodicarbocyanine chloro benzene) tracer through whole body optical imaging.
Images of the biodistribution were recorded after NPs tail vein injection (from 0 to
24 h). For the three cancer models studied (HCT 116, A 549 and glioblastoma), a
high tumor uptake of PpIX silica NPs was observed, but the maximal accumula-
tions were reached at different times: 2 h for glioblastoma, 16 h for A549 and 20 h
for HCT 116 models. A549 and HCT 116 tumor models behaved similarly, i.e. a
slow accumulation to reach a maximum until 24 h. For glioblastoma, the NPs
uptake took place quickly after the injection to reach the maximum after 2 h, while
a marked decrease was observed immediately later. NPs also accumulate in retic-
ulo-endothelial system such as liver, for which a very high accumulation was
observed (higher than that within the tumor mass), but also in spleen, lymph nodes,
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