Chemistry Reference
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FIGURE 16.18
TPA fluorophores in the structure of dendrimers used for biological imaging.
alternative to inorganic quantum dots [76]. The second-generation dendrimer
51-G
2
injected intravenously to a rat allowed the imaging of the vascular network in the
dorsal part of the rat olfactory bulb, at a depth of about 200
m (left image in
m
Figure 16.18) [77]. Analogously, the second-generation dendrimer
52-G
2
possessing
a green emitter TPA fluorophore as core was used for intracardiac injection in a
Xenopus tadpole, allowing imaging of the blood vessels of the tail (right image in
Figure 16.18) [78].
Concerning the use of dendrimers for treating diseases, polycationic dendrimers
have been recognized very early as useful synthetic vectors for transfection [79] and a
huge quantity of publications was generated by this topic [80]. We have shown that
the transfection efficiency of the phosphorus dendrimers having multiple ammonium
terminal groups depends on the reversibility of protonation: tertiary ammonium
groups are less toxic and more efficient than quaternary ammonium groups,
presumably due to the adaptability of tertiary ammonium groups to pH (amine/
ammonium). In addition, we have shown that the generation of the dendrimers has an
important influence on the transfection efficiency, with the fourth generation being the
best compromise between the transfection efficiency and the time needed to syn-
thesize the dendrimer. The first experiments were done with dendrimers
38-G
n
as
transfecting agents of the luciferase gene within 3T3 cells (Figure 16.19, left
part) [81], then within human cells [82], and we have recently tested the efficiency
of series of dendrimers with diverse types of ammonium terminal groups (pyrrolidine,
morpholine, methyl piperazine, or phenyl piperazine) [83].
Dendrimers
38-G
n
were also found efficient antiprion agents. Prion disorders are
fatal neurodegenerative disorders involving conformational changes from the normal
cellular form of prion protein to an infectious scrapie isoform (PrP
Sc
), leading to the
formation of fibrils (amyloid-like structures). ScN2a cells infected with the scrapie
strain 22Lwere treated with various amounts of dendrimers
38-G
n
, and analyzed after
3 days. The relative amount of PrP
Sc
measured for treated cells compared to untreated
