miRNAs involved in cancer, we have recently reported that PNAs
directed against miR-221-3p and miR-155-5p inhibit tumor cell
growth and induce apoptosis [34].
1.4 Delivery of PNAs
The major limit in the use of PNA for alteration of gene expression
is the low uptake by eukaryotic cells [35]. In order to solve this
drawback, several approaches have been considered, including the
delivery of PNA analogs with liposomes and microspheres [36–
41]. One of the possible strategies is to link PNAs to polyarginine
(poly-R) tails, based on the observation that these cell-membrane
penetrating oligopeptides are able to facilitate uptake of conjugated
molecules [42, 43]. Peptide-PNA conjugates have been shown to
be efficiently incorporated in cells without the need of transfecting
agents [44]. Anti-miR activity was indeed observed for instance by
conjugation of PNAs to poly-R tails [44–52] or by modification of
the PNA backbone with cationic amino acid side chains [53, 54].
As alternative to an expensive and time-consuming chemical
modification, for PNA delivery particularly convenient is the use of
carriers able to interact with the cargo in a non-covalent and
reversible way. This strategy would allow in principle to make
available a universal system effective with all native PNA sequences
that are intended to be transported into cells. In this context, it was
actually already explored the delivery of PNAs and their derivatives
or analogs with liposomes [38], polymer nanoparticles [55], and by
co-transfection with partially complementary DNA [56].
Inorganic nanocarriers, such as nanozeolites or mesoporous
silica nanoparticles (MSNPs) [57] have also been used for cellular
delivery of PNAs; for MSNPs-mediated PNA delivery, an anti-miR
activity was demonstrated [58]. However, the preparation of all
these systems and the PNA incorporation generally require special
and often time-consuming procedures. Calixarenes functionalized
with guanidinium groups were shown to be suitable for the efficient
delivery of nucleic acids [59–62]. In particular, a calix[4]arene in
cone geometry, with amphiphilic features, functionalized with a
cluster of four arginine units at the upper rim and lipophilic hexyl
chains at the lower rim resulted an efficient and low toxic non-viral
vector for cell transfection of DNA [61] and miRNA [62], more
potent than commercial transfecting agents.
The exploited parallel arrangement of the amino acid units
makes available, with respect to more classical polyarginine peptides, the primary α-amino groups that might favor the protection
of the vector–nucleic acid complex from the lysosomal degradation
and facilitate the release of cargo from the endosomes into the
cytosol through a proton sponge effect. Very recently, the same
synthetic compound was demonstrated to efficiently behave as
non-covalent vector also for PNAs [63] providing an interesting
tool for the delivery of these nucleic acid mimics with the perspective of boosting their therapeutic applications.
PNA Delivery with Argininocalix[4]arene
125
directed against miR-221-3p and miR-155-5p inhibit tumor cell
growth and induce apoptosis [34].
1.4 Delivery of PNAs
The major limit in the use of PNA for alteration of gene expression
is the low uptake by eukaryotic cells [35]. In order to solve this
drawback, several approaches have been considered, including the
delivery of PNA analogs with liposomes and microspheres [36–
41]. One of the possible strategies is to link PNAs to polyarginine
(poly-R) tails, based on the observation that these cell-membrane
penetrating oligopeptides are able to facilitate uptake of conjugated
molecules [42, 43]. Peptide-PNA conjugates have been shown to
be efficiently incorporated in cells without the need of transfecting
agents [44]. Anti-miR activity was indeed observed for instance by
conjugation of PNAs to poly-R tails [44–52] or by modification of
the PNA backbone with cationic amino acid side chains [53, 54].
As alternative to an expensive and time-consuming chemical
modification, for PNA delivery particularly convenient is the use of
carriers able to interact with the cargo in a non-covalent and
reversible way. This strategy would allow in principle to make
available a universal system effective with all native PNA sequences
that are intended to be transported into cells. In this context, it was
actually already explored the delivery of PNAs and their derivatives
or analogs with liposomes [38], polymer nanoparticles [55], and by
co-transfection with partially complementary DNA [56].
Inorganic nanocarriers, such as nanozeolites or mesoporous
silica nanoparticles (MSNPs) [57] have also been used for cellular
delivery of PNAs; for MSNPs-mediated PNA delivery, an anti-miR
activity was demonstrated [58]. However, the preparation of all
these systems and the PNA incorporation generally require special
and often time-consuming procedures. Calixarenes functionalized
with guanidinium groups were shown to be suitable for the efficient
delivery of nucleic acids [59–62]. In particular, a calix[4]arene in
cone geometry, with amphiphilic features, functionalized with a
cluster of four arginine units at the upper rim and lipophilic hexyl
chains at the lower rim resulted an efficient and low toxic non-viral
vector for cell transfection of DNA [61] and miRNA [62], more
potent than commercial transfecting agents.
The exploited parallel arrangement of the amino acid units
makes available, with respect to more classical polyarginine peptides, the primary α-amino groups that might favor the protection
of the vector–nucleic acid complex from the lysosomal degradation
and facilitate the release of cargo from the endosomes into the
cytosol through a proton sponge effect. Very recently, the same
synthetic compound was demonstrated to efficiently behave as
non-covalent vector also for PNAs [63] providing an interesting
tool for the delivery of these nucleic acid mimics with the perspective of boosting their therapeutic applications.
PNA Delivery with Argininocalix[4]arene
125