BIOMEDICAL APPLICATIONS II: INFLUENCE OF CARBON NANOTUBES IN CANCER THERAPY - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 56

Another interesting approach for the functionalisation of CNTs, studied
also for potential oncology applications, is the illing of the nanotubes. This
method was irst investigated by Green's group in 1994 and involves the
opening of multi-walled nanotube caps by nitric acid treatment and the illing
of the inner cavity through a wet chemistry approach. 27 It has been applied
to ill the tubes with different materials, including carboplatin. 28 After the
cutting procedure, MWCNTs were illed with carboplatin, sonicating them
in a solution containing the drug, at different temperatures, and eventually
washed in water and ethanol to get rid of the particles deposited on the outer
surface. Derivative 12 was characterised through different techniques to
conirm the presence of the drug inside the tubes and to identify the best
preparation methodology. It was shown that the optimal temperature was
90°C, with a drug loading of 30% (wt). This derivative was then tested on
human bladder cancer cells to evaluate its cytotoxicity, showing a decreased
cell viability compared with the treatment with the drug alone. Moreover,
a synergistic effect in increasing the mortality rate was reported for the
simultaneous administration of empty CNTs and carboplatin, while the
empty CNTs themselves did not exert any lethal effect. A possible explanation
could be an alteration of membrane permeability induced by nanotubes, with
a consequent increased uptake of carboplatin.
Not only MWCNTs have been illed with a Pt-based anticancer drug, but also
carbon nanohorns (CNHs). They are another class of carbon nanomaterials
that appear as spherical aggregates of SWCNTs, with an average diameter of
80-100 nm, and they have the very interesting characteristic of being void
of metal particles. Moreover, they are capable of containing molecules. 29,30
Nanometer-size holes can be generated in their walls by oxidation, and drugs
can be then incorporated via nanoprecipitation. Ajima et al . prepared CNHs
containing cisplatin, inding a platinum-to-carbon mole ratio of about 1:120,
and spectroscopic data suggested that the cisplatin structure was retained
during incorporation. 29 Drug release studies performed in phosphate buffer
solution (PBS) and in culture medium have shown a decreased dissolution
rate with respect to free cisplatin, this being a positive achievement in drug
delivery because a slow release reduces the loss of the drug before it reaches
the target. Finally, the cisplatin-loaded nanohorns have been proved to reduce
the viability of human lung cancer cells, while CNHs alone do not inluence
the growth of cancer cells.
The same authors performed also a study to compare the effect of the
presence of different functional groups at hole edges on drug incorporation
and release. 31 CNHs having holes with hydrogen-terminated edges (NHh) and
with oxygen-containing groups at the edges (NHox) were prepared, and the
two types showed almost no differences in cisplatin incorporation (about