Biomedical Engineering Reference
In-Depth Information
growth and increased the life span of xenografted animals bearing human
lung cancer, demonstrating the eficacy of siRNA delivery by means of CNTs.
This system, in fact, showed better results than that obtained by using cationic
lyposomes.
45
All examples reported in literature demonstrate that CNTs, both single-
and multi-walled, are good vectors for oligonucleotide delivery and that the
transported sequences retain their activity. These results are even more
interesting considering that a recent work by Wu
et al
. demonstrated that
CNTs exert also an important activity against enzymatic digestion. In fact
oligonucleotides, when complexed to SWCNTs, are protected from DNAase I
cleavage, increasing their stability in cells.
46
A unique approach conjugated photodynamic therapy with the use of
CNT-oligonucleotide complexes. Zhu
et al
. in fact used SWCNTs as quenchers
of singlet oxygen generation (SOG) in the presence of a photosensitiser. An
aptamer, i.e., a synthetic DNA/RNA probe able to recognise and bind speciic
target, was linked to chlorine e6 (Ce6), a well-known photosensitiser. When
the aptamer was wrapped on the nanotubes, the excitation of Ce6 did not
lead to singlet oxygen (
1
O
2
) generation because the carbon nanostructures,
physically close to the chlorine, were able to quench 98% of SOG. When
the aptamer was involved in the recognition and binding of its target, i.e.,
thrombin in the present case, it was released from the nanotubes. In these
conditions the SOG was not anymore quenched by CNTs, with the consequent
damage of cell structures (Fig. 3.10).
47
H
HN
NH
H
N
H
NH
HN
N
15
1
O
2
h
N
h
N
H
1
O
2
1
O
2
NH
HN
N
x
1
O
2
H
1
O
2
x
NH
HN
N
x
1
O
2
H
NH
= phosensitizer Ce6
= aptamer
HN
= aptamer tar
get (thrombin)
N
Figure 3.10
Selective production of singlet oxygen in PDT by compound
15
.
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