An azide-functionalized
12-armed Buckminster fullerene has been
monosubstituted in organic media with a substoichiometric amount of
cyclooctyne-modified oligonucleotides. Exposing the intermediate products
then to the same reaction (i.e., strain-promoted alkyne–azide
cycloaddition, SPAAC) with an excess of slightly different oligonucleotide
constituents in an aqueous medium yields molecularly defined monofunctionalized
spherical nucleic acids (SNAs). This procedure offers a controlled
synthesis scheme in which one oligonucleotide arm can be functionalized
with labels or other conjugate groups (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic
acid, DOTA, and Alexa-488 demonstrated), whereas the rest of the 11
arms can be left unmodified or modified by other conjugate groups
in order to decorate the SNAs’ outer sphere. Extra attention
has been paid to the homogeneity and authenticity of the C
60
-azide scaffold used for the assembly of full-armed SNAs.
A 2-trifluoromethylaniline
C-nucleoside was synthesized, incorporated
in the middle of an oligonucleotide, and mercurated. The affinity
of the mercurated oligonucleotide toward complementary strands placing
each of the canonical nucleobases opposite to the organomercury nucleobase
analogue was examined by ultraviolet (UV), circular dichroism (CD),
and
19
F NMR spectroscopy analyses. According to the UV
melting profile analysis, the organomercury nucleobase analogue showed
increased affinities in the order T > G > C > A. The CD profiles
indicated
the typical B-type helix in each case. The
19
F resonance
signal proved sensitive for the local environmental changes, showing
clearly distinct signals for the duplexes with different opposing
nucleobases. Furthermore, valuable information on the mercurated oligonucleotide
and its binding to complementary strands at varying temperature could
be obtained by
19
F NMR spectroscopy.
Bingel cyclopropanation
between Buckminster fullerene and a heteroarmed
malonate was utilized to produce a hexakis-functionalized C
60
core, with azide and tetrazine units. This orthogonally bifunctional
C
60
scaffold can be selectively one-pot functionalized
by two pericyclic click reactions, that is, inverse electron-demand
Diels–Alder and azide–alkyne cycloaddition, which with
appropriate ligands (monosaccharides, a peptide and oligonucleotides
tested) allows one to control the assembly of heteroantennary bioconjugates.
fullerene-based molecular spherical nucleic acids (MSNAs), consisting of a human epidermal growth factor receptor 2 (HER2) mRNA antisense oligonucleotide sequence with a native phosphodiester and phosphorothioate backbone, were synthesized, site-specifically labeled with a positron emitting fluorine-18 and intravenously administrated via tail vein to HER2 expressing HCC1954 tumor-bearing mice. The biodistribution of the MSNAs was monitored in vivo by positron emission tomography/computed tomography (PET/CT) imaging. MSNA with a native phosphodiester backbone (MSNA-PO) was prone to rapid nuclease-mediated degradation, whereas the corresponding phosphorothioate analogue (MSNA-PS) with improved enzymatic stability showed an interesting biodistribution profile in vivo. One hour after the injection, majority of the radioactivity was observed in spleen and liver but also in blood with an average tumor-tomuscle ratio of 2. The prolonged radioactivity in blood circulation may open possibilities to the targeted delivery of the MSNAs.
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