BIOMEDICAL APPLICATIONS IV: CARBON NANOTUBE-NUCLEIC ACID COMPLEXES FOR BIOSENSORS, GENE DELIVERY AND SELECTIVE CANCER THERAPY - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 136

authors deduced that because of the rapid response of the cell lines to TERT
knockdown, it was possible that other mechanisms were involved in cell
growth arrest besides the telomeric shortening, but further studies need to
be conducted on this aspect.
An interesting target in gene therapy is represented by cyclin A 2 , a protein
often over-expressed in many types of cancers, including leukemia. Since it was
demonstrated to play a critical role in DNA replication, transcription and cell
cycle regulation, it has been hypothesised that its selective inhibition through
siRNA can be beneicial against tumour progression. To that purpose, Wang
et al. condensed ammonium-functionalised SWCNTs with cyclin A 2 siRNA
and incubated the complex in human myelogenous leukaemia (K562) cells. 98
Results showed reduced cellular levels through blockage of cell proliferation
in S phase as well as promotion of apoptosis. No analogous effects were
measured with the controls. Similarly to Dai, the authors demonstrated that
CNT transporters can eficiently deliver siRNA into cells and offer remarkable
advantages with respect to conventional transfection vectors, which showed
little effect in the internalisation of siRNA. On the basis of these encouraging
results, together with the evidence that normal cells are less sensitive than
transformed cells to siRNA, 99 it could be envisaged that the delivery of siRNA
against cyclin A 2 mediated by functionalised SWCNTs is a useful therapeutic
strategy for cancer therapy.
A very recent article adopted a similar approach, demonstrating
that pegylated CNTs could be coupled with thiol-modiied siRNA via
sulfosuccinimidyl 6-[3 ′ -(2-pyridyldithio)-propionamido] hexanoate (SPDP-
S) to successfully knock down the transient receptor potential channel 3
(TRPC3) involved in insulin-resistant conditions. 100 In the experiments,
isolated muscle ibres were transfected with the luorescent siRNA bond to
CNTs. The results obtained disproved the initial hypothesis that inhibition
of TRPC3 affected Ca 2+ inlux through such channels. On the contrary, Ca 2+
inlux was not signiicantly different between muscle ibres cultured with
(55±5 nM, n = 9) or without (49±1 nM, n = 9) TRPC3-siRNA for 48 h. However,
the knockdown of TRPC3 expression decreased insulin-mediated glucose
uptake (Fig. 5.29) . It was also suggested that there exist two pools of TRPC3,
one constitutively present in the plasma membrane and the other located
in the insulin-sensitive glucose transporter 4 ( GLUT4)-containing vesicles,
which moves to the plasma membrane in response to insulin stimulation.
Thus, it was concluded that TRPC3 is a potential target for the treatment of
insulin resistance and type II diabetes and that the combination of CNTs with
siRNA can represent a valuable therapeutic approach.