BIOMEDICAL APPLICATIONS II: INFLUENCE OF CARBON NANOTUBES IN CANCER THERAPY - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 47

with the cellular expression of receptors for growth factors and cell adhesion,
allow the use of multiple targeting strategies that undergo extravasation and
protracted lodging. 3 In this scenario, the reticuloendothelial system (RES),
as a part of the immune system and consisting mostly of macrophages and
monocytes localised in the lymph nodes, spleen and Kupffer cells, plays a
determinant role, and nanovectors can be designed to target or escape RES
cells by simply tuning vector size.
The approval of Abraxane™ by FDA has been a major success for cancer
nanotechnology in the last years. It consists of paclitaxel coupled with
albumin as delivery agent. This formulation has been successfully adopted
in metastatic breast cancer therapy. 4 Generally, the advantages of using
nanovectors are the possibility of overcoming poor solubility of some drugs,
which can be protected from metabolic and immune system attacks, altering
the biodistribution by tuning the nanovector size (exploiting the EPR effect)
and controlling the release proile by coupling nanovectors with enzyme-
sensitive linkers.
Nanotechnology can also be used to induce cellular damage to a speciic
target by exploiting the characteristics of the nanoparticles themselves. A
good example is the induction of hyperthermia, which involves the use of
external energy to promote a localised cytotoxic effect. 5 This non-invasive
therapy could be useful when surgery is not possible. Some nanoparticles can
act like antennas: when irradiated, they absorb energy and then release high
doses of heat. The consequent increase in the temperature of the cells where
they have been loaded promotes tumour tissue necrosis, so nanoparticles can
be used to both target and destroy cells speciically. Metallic nanoparticles
such as Au particles or Au nanoshells, oxides such as superparamagnetic
nanoparticles, and organic nanoparticles such as carbon nanotubes (CNTs)
are the most important examples in this approach (see Section 3.5) . 2 CNTs
play a major role because they can exploit the absorption of near-infrared
(NIR) radiation, combined with their excellent thermal conductivity. It is
very well known that NIR radiation can penetrate human tissues to many
centimetres without causing damage, because cellular chromophores do not
absorb NIR wavelengths. 6
Another important aspect in which nanotechnology can play a crucial
role is the enhancement of tumour imaging eficiency and resolution.
Applications of optical imaging are limited because of the low penetration
depth into tissue and lack of anatomic resolution and spatial information. 4
Although NIR wavelengths can be used to increase the penetration depth
and three-dimensional (3D) luorescence tomography could give spatial