main drawback of these carriers is their nonspecific interaction with cells and
proteins, leading to the drug accumulation in non-target tissues.
Chitosan has been used a carrier for DNA for gene delivery applications. The
cationically charged chitosan can form polyelectrolyte complexes with the negatively charged plasmid DNA. Chitosan–DNA complexes could be protected from
DNAse to improve the bioavailability of the plasmid DNA delivered into the body
for gene therapy. Also, chitosan could be a useful gene carrier because of its
mucoadhesive and cohesive properties in the gastrointestinal tract. The advantage
of chitosan-based vectors lies not only in avoiding cytotoxicity problems that are
inherent in most synthetic polymeric vehicles but also in their unique capability for
transcellular transport.
Chitosan–DNA nanoparticles have been prepared and the influence of several
parameters on their preparation evaluated. Transfection efficiency of the
nanoparticles were cell-type dependent. The study also developed three different
schemes to conjugate transferrin or KNOB protein to the nanoparticle surface. The
transferrin conjugation only yielded a maximum of fourfold increase in transfection
efficiency in HEK293 cells and HeLa cells, whereas KNOB-conjugated
nanoparticles could improve the gene expression level in HeLa cells by 130-fold.
The usefulness of the complex of chitosan self-aggregates and DNA for transfer of
genes into mammalian cells in vitro has also been suggested. Several transfection
studies using chemically modified chitosan have been reported. Trimethyl chitosan
oligomers, lactosylated chitosan and galactosylated chitosan were examined for
their potency as DNA carriers and transfection efficiency in in vitro systems.
Incorporation of hydrophobic moieties might considerably increase the transfection
efficiency: with longer alkyl side chains, the transfection efficiency was increased
and levelled off when the number of carbons in the side chain exceeded eight. The
higher transfection efficiency is attributed to increased entry into cells, facilitated
by hydrophobic interactions and easier unpacking of DNA from alkylated chitosan
carriers due to the weakening of electrostatic attractions between DNA and
alkylated chitosan.
Numerous studies have been conducted on prophylactic and therapeutic use of
genetic vaccines for combating a variety of infectious diseases in animal models. A
human clinical study with the gene gun has validated the concept of direct targeting
of dendritic cells in the viable epidermis of the skin. However, it is unclear whether
the gene gun technology or other needle-free devices will be commercially viable.
A very recent study, has proposed folate–chitosan–DNA nanoparticles as having
low cytotoxicity and good DNA condensation, making them a promising candidate
for nonviral gene therapy. Chitosan–DNA and folate–chitosan–DNA nanoparticles
were prepared using reductive amidation and a complex coacervation process.
The potential of gadolinium-loaded chitosan nanoparticles has been
demonstrated. The potential of gadolinium neutron-capture therapy for cancer
was evaluated using chitosan nanoparticles as a novel device. Later, the similar
gadopentectic acid-loaded chitosan nanoparticles were prepared for gadolinium
neutron-capture therapy. Their releasing properties and ability for long-term retention in the tumour indicated that these particles are useful as intratumoural
290
A.K. Anal and A. Tuladhar
proteins, leading to the drug accumulation in non-target tissues.
Chitosan has been used a carrier for DNA for gene delivery applications. The
cationically charged chitosan can form polyelectrolyte complexes with the negatively charged plasmid DNA. Chitosan–DNA complexes could be protected from
DNAse to improve the bioavailability of the plasmid DNA delivered into the body
for gene therapy. Also, chitosan could be a useful gene carrier because of its
mucoadhesive and cohesive properties in the gastrointestinal tract. The advantage
of chitosan-based vectors lies not only in avoiding cytotoxicity problems that are
inherent in most synthetic polymeric vehicles but also in their unique capability for
transcellular transport.
Chitosan–DNA nanoparticles have been prepared and the influence of several
parameters on their preparation evaluated. Transfection efficiency of the
nanoparticles were cell-type dependent. The study also developed three different
schemes to conjugate transferrin or KNOB protein to the nanoparticle surface. The
transferrin conjugation only yielded a maximum of fourfold increase in transfection
efficiency in HEK293 cells and HeLa cells, whereas KNOB-conjugated
nanoparticles could improve the gene expression level in HeLa cells by 130-fold.
The usefulness of the complex of chitosan self-aggregates and DNA for transfer of
genes into mammalian cells in vitro has also been suggested. Several transfection
studies using chemically modified chitosan have been reported. Trimethyl chitosan
oligomers, lactosylated chitosan and galactosylated chitosan were examined for
their potency as DNA carriers and transfection efficiency in in vitro systems.
Incorporation of hydrophobic moieties might considerably increase the transfection
efficiency: with longer alkyl side chains, the transfection efficiency was increased
and levelled off when the number of carbons in the side chain exceeded eight. The
higher transfection efficiency is attributed to increased entry into cells, facilitated
by hydrophobic interactions and easier unpacking of DNA from alkylated chitosan
carriers due to the weakening of electrostatic attractions between DNA and
alkylated chitosan.
Numerous studies have been conducted on prophylactic and therapeutic use of
genetic vaccines for combating a variety of infectious diseases in animal models. A
human clinical study with the gene gun has validated the concept of direct targeting
of dendritic cells in the viable epidermis of the skin. However, it is unclear whether
the gene gun technology or other needle-free devices will be commercially viable.
A very recent study, has proposed folate–chitosan–DNA nanoparticles as having
low cytotoxicity and good DNA condensation, making them a promising candidate
for nonviral gene therapy. Chitosan–DNA and folate–chitosan–DNA nanoparticles
were prepared using reductive amidation and a complex coacervation process.
The potential of gadolinium-loaded chitosan nanoparticles has been
demonstrated. The potential of gadolinium neutron-capture therapy for cancer
was evaluated using chitosan nanoparticles as a novel device. Later, the similar
gadopentectic acid-loaded chitosan nanoparticles were prepared for gadolinium
neutron-capture therapy. Their releasing properties and ability for long-term retention in the tumour indicated that these particles are useful as intratumoural
290
A.K. Anal and A. Tuladhar