Biomedical Engineering Reference
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H 13 C 6
C 6 H 13
CH 3
C 6 H 13
N
N
N
N
Zn
N
H 13 C 6
C 6 H 13
N
N
N
S
C 6 H 13
N
S
H 13 C 6
N
10
N
10
C 6 H 13
C 6 H 13
N
Zn
N
N
N
N
CH 3
H 13 C 6
H 13 C 6
C 6 H 13
Fig. 2 C11Pc photosensitizer
C11Pc, and that the administration of C11Pc via AuNPs is beneficial for a longer
blood circulation and a larger accumulation in most organs. As vascular damages
were identified by electron microscopy, an anti-angiogenic action promoted by the
AuNP-C11Pc conjugates was suggested to explain the efficacy of PDT.
Water-soluble AuNPs have been obtained by stabilization with polyethylene
glycol (PEG). PEG molecules are also able to shield the AuNP surface against
biomolecules. PEGylated AuNPs can preferentially accumulate in tumor tissues by
passive accumulation through the leaky vascular system of tumors. Cheng et al .
have developed the synthesis of ~5 nm diameter PEGylated AuNPs (Cheng et al.
2008 ) and studied their use as nanocarrier for the silicon phthalocyanine 4 ( Pc 4),
which is a nontoxic, hydrophobic photosensitizer approved by the FDA for clinical
trials (Fig. 3 ). They showed that 5 nm diameter PEGylated AuNPs can be loaded
with ~30 molecules of Pc 4 through N-Au bonds. Although N-Au bonds are not
very stable (6 kcal/mol), the AuNP- Pc 4 conjugates appeared to be stable for sev-
eral months in water, thanks to the PEG molecules at the surface which stabilized
the Pc 4 molecules through van der Walls interactions and protected the drug from
the aqueous media. Drug release experiments in a water-toluene two-phases system
showed that Pc 4 molecules are released within 2 h, and thus can potentially accu-
mulate in apolar cellular sites such as cell membranes. Pegylated AuNP did not
transfer into the organic phase. Cell viability experiments (HeLa cells) was greater
than 95% after incubation of the AuNP- Pc 4 conjugates (1 mM) in the dark for
24 h, and irradiation at l exc > 500 nm induced photokilling of the cells with >90%
efficiency. Uptake kinetics studies into HeLa cells showed that the pegylated
AuNP- Pc 4 conjugates were taken up within the first 2 h. Only a few AuNPs were
taken up into the cells. Pc 4 molecules were mainly localized in mitochondria and
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