Biomedical Engineering Reference
In-Depth Information
peptides, also called Cell-Penetrating Peptides (CPPs). However, due
to the negative charge of the siRNA, conjugation of positively charged
PTDs results in aggregation, cytotoxicity, and poor delivery into cells.
This chapter describes a new delivery strategy that utilizes a PTD
fusion protein with a double-stranded RNA-binding domain (DRBD)
that binds to and masks the siRNA negative charge, allowing for PTD-
mediated delivery into cells and induction of RNAi responses.
4.1
Introduction
The hydrophobic plasma membrane of cells pose a significant barrier
in drug delivery of macromolecular therapeutics that need to cross
it in order to reach the cytoplasm or nucleus to exert its intended
therapeutic effect. Several transporters in the plasma membrane are
able to internalize small molecule therapeutics; however, for larger
macromolecules such as peptides, proteins, and oligonucleotides, a
delivery vehicle is required to transport the cargo across the cellular
membrane. Moreover, many important drug targets are difficult to
inhibit with small molecule drugs and monoclonal antibodies. One
of the most promising macromolecular drug candidates, which are
able to target the undruggable genome, is short interfering RNAs
(siRNAs). The 21 nucleotide siRNA duplex is hydrophilic, negatively
charged and can induce a natural cellular process called RNA
interference (RNAi) once it has reached inside the cytoplasm. The
process of RNAi was discovered over a decade ago, and because of
its high catalytic activity and target selectivity, RNAi has given new
hope for modern medicine to battle a wide range of diseases (Fire
et al.,
1998). However, suitable delivery vehicles have been difficult
to find because of its polyanionic nature. Although formulations
such as nanoparticles and polymers have been used both
in vitro
and
, unfortunately, many of them have suffered from toxicity
and poor efficiency (Pecot
in vivo
2011). The problems involved
in delivering siRNA into cells have slowed down the progress of
developing siRNA into a drug. Therefore, the number one priority for
RNAi has been to find a delivery vehicle that can transport the active
siRNA molecule across the cell membrane in a non-toxic manner.
et al.,
4.1.1
RNA Interference
RNAi is a post-transcriptional gene-silencing mechanism that utilizes
siRNA to bind and induce degradation of complementary mRNA,
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