BIOMEDICAL APPLICATIONS II: INFLUENCE OF CARBON NANOTUBES IN CANCER THERAPY - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 57

18% in both cases), while the drug release in PBS gave different results. The
release rates were different (faster for NHox than for NHh), and the total
amount of released cisplatin differed; it was 70% for NHh, but only 15% for
NHox. A possible explanation for this is that ions contained in PBS reacted with
the -COOH and -OH groups, forming the respective sodium salts (-COO - Na +
and -O - Na + ), with a decrease in hole diameters, thereby hindering cisplatin
release. The difference in the release rate should be due to the hydrophobic
characteristic of the NHh holes. In fact aqueous solutions should enter more
easily through the hydrophilic oxygen-containing holes of NHox. According
to this study, NHh seemed to present better drug release properties than
NHox, but the latter gave much better dispersion in PBS than NHh, so that
it was a more eficient carrier for drug delivery. Therefore another study
was carried out to deine the optimal oxidation conditions to get NHox with
enlarged hole diameters and an appropriate functionalisation degree of the
hole edges. 32 So, the new CNHs should be well dispersible and have a reduced
steric hindrance at the same time, and actually the obtained product was
able to abundantly (up to 80%) and slowly release cisplatin in PBS. Using a
PEG chain linked to a peptide, the same authors further developed this work
to coat CNHs previously loaded with cisplatin. 33 This approach was earlier
realised using a PEG-DOXO conjugate to improve dispersibility and to avoid
aggregate formation in a biological environment. 30 In this case, the complex
was used to treat human lung cancer cells, inducing apoptosis, even if at a
lower extent than doxorubicin itself.
3.4 DELIVERY OF OLIGONUCLEOTIDES MEDIATED BY
CARBON NANOTUBES
The interaction of DNA and CNTs has been studied and demonstrated using
different measurements. The condensation of the nucleic acid in the presence
of oxidised SWCNTs is dependent on the sequence, being favoured in the case
of guanine-cytosine (GC)-rich sequences, with the consequent destabilisation
of double and triple helices. From these studies it seems that the nanotubes
can induce DNA B-A transition in solution and their interaction with the GC
sequences takes place in the major groove. 34 Li et al. reported that the presence
of SWCNTs (with a diameter of 1.1 nm) induces a stabilisation of quadruplex
and of the i-motif adopted by the complementary strand, rich in C (Fig. 3.7). 35
This action can be exploited in an antitumour approach considering that the
stabilisation of those structures inhibits the action of telomerases, which
elongate and stabilise chromosomes, conferring, in the case of tumour cells,
an indeinite proliferative capacity. From some experiments it is possible to