Biomedical Engineering Reference
In-Depth Information
pathway for short, well-dispersed SWNT conjugates is mainly through clathrin-coated
pits rather than caveolae or lipid rafts. Biological systems are well known to be highly
transparent to near-infrared (NIR) light. Jones et al. [98] reported that the strong optical
absorbance of SWCNTs in this NIR spectral window, an intrinsic property of SWCNTs,
could be used for optical stimulation of nanotubes inside living cells to afford multifunc-
tional CNTs biological transporters. Their result demonstrated that if SWCNTs could be
selectively internalized into cancer cells with specific tumor markers, NIR radiation of
the CNTs in vitro can selectively activate or trigger cell death without destroying the nor-
mal cells, which would develop SWCNTs functionalization schemes with specific ligands
for the identification and targeting the tumorous cells. The ability of the functionalized
SWCNTs to conjugate with CNTs was exploited by Shao et al. [86]. According to them,
functionalization of CNTs together with the combination of optical properties of these
CNTs antibodies is capable of concomitantly targeting and destroying malignant breast
cancer cells in vitro with the aid of photodynamic therapy. The strength of this method
is that the SWCNTs constructs incorporated in the cytoplasm are able to absorb a certain
amount of energy in NIR, which is sufficient to provoke cell death. Furthermore, control
cells cultured in the presence of nonspecific antibody-SWCNTs complexes revealed a via-
bility of more than 80%. It is noteworthy that this innovative approach of multicomponent
targeting of cell surface receptors followed by subsequent NIR dosing of cancer cells using
SWCNTs will set the scene for future investigations. Based on these in vitro
results, every-
thing is available from the technical perspective to successfully translate this molecular
nanotargeting system toward related animal models and further toward the direction of
long-term clinical applications.
CNTs for Drug Delivery
To maximize the efficacy of a drug, the choice of the delivery system is of fundamental
importance. Conventional drug administration techniques often fails due to various fac-
tors such as low drug solubility, poor stability in biological environment, poor distribution
among the cells, lack of selectivity, and damage of healthy tissues. Often, drug delivery
systems are aimed and designed to minimize or avoid the drug degradation, to increase
its bioavailability, to target it to specific cells, and to reduce the amount of drug needed,
decreasing toxicity and harmful side effects. CNTs possess an enormous aspect ratio (ratio
between the length and the diameter) compared with classical drug delivery systems such
as liposomes or polymer-based carriers and are becoming a promising alternative in this
field, and they have been successfully demonstrated for their ability to penetrate into cells.
CNTs can be functionalized with antibiotics to deliver them into the cells. More specifically,
CNTs were used in the administration of amphotericin B. AmB is a potential antifungal
agent for the treatment of chronic fungal infections, but highly toxic for mammalian cells
[87] due to the formation of aggregates, which reduce the solubility in water [88]. CNTs
were also used as drug delivery systems concerns cancer therapy. Furthermore, Yinghuai
et al. [89] studied the utility of CNTs as boron delivery agents for their use in boron neutron
capture therapy. Substituted carborane cages were attached to the walls of SWCNTs via
nitrene cycloaddition followed by subsequent treatment with sodium hydroxide, obtain-
ing water-soluble carborane-appended SWCNTs. Boron tissue distribution studies indi-
cated that there exists enhanced boron uptake and retention of the carborane nanotubes in
tumor tissue compared with blood, lung, liver, or spleen. Although the mechanism of the
accumulation of carborane nanotubes in tumor is not yet clear, these results are promising
© 2011 by Taylor & Francis Group, LLC
