BIOMEDICAL APPLICATIONS II: INFLUENCE OF CARBON NANOTUBES IN CANCER THERAPY - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 58

suppose that there is a binding of the carbon nanostructures at the 5 ′ end of
the structure with a preferential positioning in the major groove. Moreover,
it seems that the presence of carboxylic residues on CNTs compensates
for the positive charges of the C-C base pairs. In fact the use of differently
funtionalised CNTs (bearing a chain with a free amino unit) did not exert the
same effect.
Figure 3.7 I-motif and G-quadruplex structures. See also Colour Insert.
The same authors reported a stabilisation effect when a poly(rA) chain
was used. This sequence has a biological relevance because it is present in all
messenger RNAs (mRNAs) at the 3 ′ end, conferring stability to the structure
and inluencing the translation and transcription processes. 36 The presence
of oxidised SWCNTs (with a diameter of 1.1 nm) induced a self-structuration
of A•A + base pairing into duplex at pH 7, where this structure is not naturally
formed, as demonstrated by melting and circular dichroism experiments.
Poly(rU) also was used in the presence of CNTs, but in this case to study
its translocation into breast cancer MCF-7 cells, successfully obtained with
SWCNTs. 37 Myc is a proto-oncogene, fundamental as sensor for mitogenic
stimuli in cells; it controls many phenotypic phenomena such as cell growth,
proliferation, transformation and apoptosis and is involved in many tumours.
Cui et al. reported the interaction between antisense-myc conjugated with
SWCNTs and HL-60 cells. Part of the complex was found to be attached on the
cell surface, but mainly reached the cytoplasm exerting an inhibition effect on
cell proliferation. 38
Oxidised SWCNTs, after activation by thionyl chloride, were allowed
to react with the monoprotected hexamethylendiammine, subsequently
deprotected. The so-obtained derivatives, bearing positive charges on the
carbon surface, were used to complex telomerase reverse transcriptase small
interfering RNA (TERT siRNA), able to silence the expression of TERT and to