Biomedical Engineering Reference
In-Depth Information
5.2
Generation of Cell-Specific Aptamers
Developed independently by three research groups in 1990 [24-26],
aptamers (from Latin word
aptus
“to fit” and the Greek word
merus
for “piece”) are
evolved single-stranded nucleic acids that
fold into a specific three-dimensional shape to fit together with their
targets (Fig. 5.1). During the past 20 years, there has been a rapidly
increasing number of publications on the use of aptamers, and the
aptamer technique has captured the attention of scientists from
various fields, owing to their unique properties [21]. The successful
adaption of cell-specific aptamers for targeted therapy has created
excitement for generating new, more potent aptamers as well as
developing novel and facile selection approaches.
To date, by the use of either traditional purified membrane
protein-based SELEX (Systematic Evolution of Ligands by
Exponential Enrichment) or whole cell-based SELEX procedures,
researchers have successfully isolated an increasing number of
cell-specific DNA or RNA aptamers against cell surface biomarker
or receptors (Fig. 5.1A). For instance, cell-specific aptamers, raised
against PSMA (prostate-specific membrane antigen) [27], CD4
(cluster of differentiation 4) [28], CD30 (also known as TNFRSF8)
[29], CD44 [30], HIV-1 glycoprotein gp120 [31, 32], TN-C (tenascin-
C) [33], EGFR (epidermal growth factor receptor) [34], PTK7
(protein tyrosine kinase 7) [35], TfR (transferrin receptor) [36],
NCL (nucleolin) [37, 38], MUC1 (mucin protein) [39], and PDGF-
B (platelet-derived growth factor B) [40], have been successfully
harnessed for targeting delivery of various cargoes
in vitro
in vitro
as well as
in vivo
.
5.2.1
Recombinant Protein-Based SELEX Procedure
In vitro
SELEX consists of four main steps: (1) binding to the target;
(2) isolation of target-specific species; (3) recovery of target-bound
sequences; and (4) re-amplification of recovered species [25].
Through iterative selection rounds, aptamers against any given target
can be isolated from an initial combinatorial oligonucleotide library.
Numerous successful examples have been reported. In addition to
the traditional bead, resin, membrane, and chip-based segmentation
approaches, novel, powerful isolation strategies have been developed
to accelerate selection procedure and improve efficiency of aptamers,
such as, MoloLEX (so called one-step selection) [41], capillary gel
Search WWH ::




Custom Search