Therapeutic Application of MicroRNAs in Cancer - RNA Interference from Biology to Therapeutics - page 300

were observed. miR-122 inhibition in a diet-induced obesity mouse model resulted
in decreased plasma cholesterol levels and a significant improvement in liver steato-
sis that was accompanied by reductions in several lipogenic genes (subcutaneous
injection with 12.5 mg/kg miR-122 or control ASO twice weekly for 5 1/2 weeks).
These results suggest that miR-122 may be an attractive therapeutic target for meta-
bolic disease. Furthermore, the simple systemic delivery of a nonconjugated LNA-
antimiR in phosphate-buffered saline effectively blocked the liver-specific miR-122
in nonhuman primates [ 27 ]. Intravenous acute administration of LNA-antimiR-122
(1, 3, and 10 mg/kg) to African green monkeys resulted in depletion of mature miR-
122 and dose-dependent lowering of plasma cholesterol. In addition to its role in
metabolism, miR-122 binds two closely spaced target sites in the 5¢ noncoding
region of the hepatitis C virus (HCV) genome that are essential for HCV RNA accu-
mulation in cultured liver cells and required for modulation of HCV RNA abun-
dance [ 28 ] . Treatment of chronically infected chimpanzees with an LNA-modi fi ed
antimiR-122 (SPC3649) led to long-lasting suppression of HCV viremia, and there
was no evidence of viral resistance or side effects in the treated animals. As shown
by the lack of rebound in viremia during the 12-week treatment of SPC3649 and the
lack of adaptive mutations in the two miR-122 seed sites of HCV 5¢ noncoding
region, the prolonged virological response to SPC3649 treatment without HCV
rebound holds promise of a new antiviral therapy with a high barrier to the develop-
ment of viral resistance mutations.
Previously, Ma et al. reported that miR-10b is highly expressed in metastatic
cancer cells propagated in culture as well as in metastatic breast tumors from patients
[ 29 ]. miR-10b is also upregulated in highly metastatic and/or invasive cancers, such
as human pancreatic adenocarcinomas [ 26 ] and glioblastomas [ 30 ] . Furthermore,
miR-10b is upregulated to a higher extent in metastatic than in nonmetastatic hepa-
tocellular carcinomas [ 31 ]. To show the therapeutic potential of anti-miRNA in can-
cer treatment, the effects of miR-10b silencing in a highly metastatic mouse
mammary carcinoma cell model were examined [ 32 ]. Both in vitro and in vivo,
silencing of miR-10b with antagomirs significantly decreased miR-10b levels and
increased the levels of its target gene, Hoxd10. Intravenous administration of 50 mg/
kg miR-10b antagomirs (twice weekly for 3 weeks) to mice bearing highly meta-
static cells did not reduce primary mammary tumor growth but markedly suppressed
the formation of lung metastases in a sequence-specific manner.
As shown above, synthesized ASO can be taken into cells. The precise mecha-
nism of ASO incorporation inside cells, however, has not been clarified yet. One
possible candidate molecule that helps ASO incorporation is the mammalian homolog
of SID-1 in C. elegans [ 33, 34 ]. SID-1 is a multispan transmembrane protein that
sensitizes cells to soaking RNAi molecules with a potency that is dependent on dou-
ble-stranded RNA (dsRNA) length [ 34 ]. RNA interference (RNAi) spreads systemi-
cally in plants and nematodes to silence gene expression distant from the site of
initiation. Previous reports showed that SID-1 mediate siRNA uptake in mammalian
cells [ 35 ]. Studying the precise molecular mechanism of ASO uptake may answer
several aspects of ASO therapy, such as dosage of ASO.