Biology Reference
In-Depth Information
14.2.2
Upregulation of miRNA Provided by miRNA Mimics
Certain miRNAs are known to be downregulated in cancer cells. Therefore, recov-
ering the expression of these miRNAs by the introduction of miRNA mimics into
the cell may reduce cancer progression (Fig. 14.1 ). The structure of miRNA mimic
is small, chemically modified double-stranded RNAs that mimic endogenous
miRNAs and enable miRNA functional analysis of miRNA by upregulation of
miRNA activity. Delivery, however, is a major barrier to the clinical application of
nucleic acid-based drugs.
14.2.2.1
Delivery Systems for miRNA Mimics
Atelocollagen is a cationic biomaterial used to overcome the delivery requirements
of miRNA. It is a highly purified type I collagen derived from calf dermis with
pepsin treatment [ 36 ] (Table 14.2 ). Atelocollagen is low in immunogenicity due to
the absence of telopeptides. It has been used in the clinic for a wide range of pur-
poses, including wound healing, vessel prosthesis, and as a bone cartilage substitute
and haemostatic agent. We have previously demonstrated the efficacy of atelocol-
lagen for nucleotide delivery including plasmid DNA, antisense oligonucleotides,
and siRNA both in vitro and in vivo [ 37, 38 ] . Atelocollagen complexed with siRNA
confers nuclease resistance and facilitates cellular entry and prolonged gene silenc-
ing [ 38 ]. Furthermore, we have demonstrated that systemic administration of
Atelocollagen/siRNA complexes, in addition to intratumor injection against onco-
genes (such as fibroblast growth factor 4 or EZH2), inhibited tumor growth in
orthotopic xenograft models as well as bone metastasis mouse models of human
nonseminomatous germ cell tumors and metastatic prostate cancer [ 39, 40 ] .
Importantly, no toxic side effects were exhibited. In these experiments, siRNA/ate-
locollagen complexes showed greater selective accumulation in tumor tissues, com-
pared with normal tissues, possibly due to the enhanced permeability and retention
(EPR) effect. The EPR effect facilitates extravasation of polymeric drugs more
selectively at tumor tissues, and this selective targeting to solid tumor tissues may
lead to superior therapeutic benefits with fewer systemic adverse effects. This EPR
effect is attributed to anatomical and pathophysiological alterations such as increased
vascular density due to neoangiogenesis, impaired lymphatic recovery, and lack of
smooth muscle layer in solid tumor vessels.
We have utilized the atelocollagen system for delivery of tumor-suppressive
miRNAs downregulated in cancer cells as a strategy to prevent cancer cell metasta-
sis [ 41 ]. Takeshita et al. reported that transient transfection with synthetic miR-16
expressed at lower levels in prostate cancer cells, significantly reduced cell prolif-
eration of prostate cancer cell lines in vitro [ 41 ]. In addition, mouse tail vein injec-
tion of 50 mg of miR-16 complexed with atelocollagen in a 200-m l volume
significantly inhibited the growth of prostate tumors in bone in a therapeutic bone
metastasis model. Furthermore, Osaki et al. revealed that miR-143 was the most
downregulated miRNA in metastatic human osteosarcoma cell lines relative to their
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