Biomedical Engineering Reference
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larger amounts of heat than non-DNA-encased MWCNTs when irradiated
under identical conditions. Moreover, for the irst time it was demonstrated
that such complex was able to eradicate tumour xenografts in vivo in a mouse
model of human cancer, since complete tumour regression was achieved
with a single treatment and without damaging normal tissues. It is important
to notice that DNA-encased MWCNTs did not become saturated along the
investigation and, on the contrary, could be excited continuously by laser
radiation without any reduction in heat generation. In terms of safety, it
seems that the presence of DNA incorporated onto the CNTs increased the
heating eficiency, thereby suggesting that less material is required to reach
the desired effects in vivo . Additional advantages are represented by DNA's
biocompatibility, which protects from eventual immunogenicity, and the
CNT's enhanced dispersibility, which reduces the risks associated with tube
aggregation. For all these reasons, CNT-DNA complexes seem to be promising
systems that can be applied in several biomedical ields.
5.4.3 CNT-RNA complexes for biomedical applicaons
An interesting work has been published on small interfering RNA for targeted
cancer therapy. 96 The study targeted telomerase, which is an enzyme involved
in the stabilisation of chromosomes by the addition of TTAGGG units to the
telomere ends. 97 Activation of telomerase has been detected in the majority of
malignant tumours, but not in most normal cells. Therefore, small-molecule
inhibitors of telomerase activity or knockdown of telomerase expression
represents an attractive approach for targeted cancer therapy. In particular,
small interfering RNA (siRNA) seems to be a powerful tool to achieve such
goals, provided that it is stable and internalized in a suficiently high amount
inside the cells. To that purpose, SWCNTs conjugated with positively charged
-CONH-(CH 2 ) 6 -NH 3 + Cl - were shown to promote the coupling of speciic
mouse mTERT siRNA to SWCNTs. Different cancer cells, including cervical
carcinoma (TC-1), ovarian carcinoma (1H8) and lung carcinoma (LLC) cells
(which usually express high levels of mTERT m[messenger]RNA and mTERT
proteins), showed suppressed cell growth after incubation with mTERT
siRNA-SWNTs+ complex but not with nanotubes alone or mTERT siRNA
alone. The mechanism behind this result was attributed to the ability of the
complex to knock down mTERT expression, to inhibit cell proliferation and to
promote cell senescence in vitro . Analogue experiments were subsequently
performed to explore the activity with human hTERT and the effects on in
vivo tumour growth; as expected, injection of hTERT in HeLa cells and mTERT
siRNA-SWNT+ into tumour tissue also induced senescence. Noticeably, the
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