esiRNAs purified with chromatography suppress homologous gene expression with high efficiency and specificity

Nanoparticle-mediated co-delivery of chemotherapeutic agent and siRNA for combination cancer therapy

INTRODUCTION

Cancer is the leading cause of death worldwide. Current cancer treatments in the clinic mainly include chemotherapy, radiotherapy and surgery, with chemotherapy being the most common. Areas covered: Cancer treatments based on the single 'magic-bullet' concept are often associated with limited therapeutic efficacy, unwanted adverse effects, and drug resistance. The combination of multiple drugs is a promising strategy for effective cancer treatment due to the synergistic or additive effects. Small interfering RNA (siRNA) has the ability to knock down the expression of carcinogenic genes or drug efflux transporter genes, paving the way for cancer treatment. Treatment with both a chemotherapeutic agent and siRNA based on nanoparticle (NP)-mediated co-delivery is a promising approach for combination cancer therapy. Expert opinion: The combination of chemotherapeutic agents and siRNAs for cancer treatment offers the potential to enhance therapeutic efficacy, decrease side effects, and overcome drug resistance. Co-delivery of chemical drug and siRNA in the same NP would be much more effective in cancer therapy than application of chemical agent or siRNA alone. With the development of material science, NPs have come to be the most widely used platform for co-delivery of chemotherapeutic drugs and siRNAs.

High-dose siRNAs upregulate mouse Eri-1 at both transcription and posttranscription levels

The eri-1 gene encodes a 3′ exonuclease that can negatively regulate RNA interference via siRNase activity. High-dose siRNAs (hd-siRNAs) can enhance Eri-1 expression, which in return degrade siRNAs and greatly reduces RNAi efficiency. Here we report that hd-siRNAs induce mouse Eri-1 (meri-1) expression through the recruitment of Sp1, Ets-1, and STAT3 to the meri-1 promoter and the formation of an Sp1-Ets-1-STAT3 complex. In addition, hd-siRNAs also abolish the 3′ untranslated region (UTR) mediated posttranscriptional repression of meri-1. Our findings demonstrate the molecular mechanism underlying the upregulation of meri-1 by hd-siRNA.

Involvement of mitochondrial permeability transition in hepatitis B virus replication

The HBx protein of human hepatitis B virus (HBV) activates a calcium-dependent kinase pathway which is essential for the viral replication. In this study, we found that HBx expression in the absence of other HBV proteins and in the context of HBV replication decreased the mitochondrial calcein-AM/CoCl(2) signals by 10% and 14% in HepG2 cells and by 15% and 10% in Huh7 cells, respectively. This indicates that HBx can induce mitochondrial permeability transition (MPT) and cause calcium effusion into the plasma. In addition, RNA interference of Cylophilin D decreased HBx-induced MPT and suppressed HBV DNA replication by 41% in HepG2 cells. Our results suggest that HBx expression can induce MPT and facilitate HBV DNA replication.

Involvement of PU.1 in mouse adar-1 gene transcription induced by high-dose esiRNA

Adar-1 gene plays an important role in the negative regulation of RNA interference. We previously showed that increased adar-1 mRNA level was associated with the rebound of gene expression after RNAi suppression. In this study, we identified a PU.1 binding site upstream from transcription start point of adar-1 gene and is essential for the promoter activity. Knockdown and over-expression of the PU.1 gene resulted in decreased and increased activity of adar-1 promoter, respectively. Our results suggest that transcription factor PU.1, could bind to the adar-1 promoter and play a key role in activating transcription of gene induced by high-dose esiRNAs.

Inhibition of hepatitis B virus gene expression and replication by artificial microRNA targeted ASGPR1

AIM: To investigate the inhibitory effects on hepatitis B virus (HBV) replication and expression by transfecting artificial microRNA targeted ASGPR1 into HepG2.2.15 cells.

METHODS: Three amiRNA-HBV plasmids were constructed and transfected into HepG2.2.15 cells via LipofectamineTM 2000 reagent. The level of ASGPR1 mRNA was measured by semi-quantitative RT-PCR. The level of ASGPR1 protein was measured by western blot. HBV antigen secretion was detected in the cells with transient and stable transfection by time-resolved fluoroimmunoassays (TRFIA). HBV DNA replication was examined by fluorescence quantitative PCR.

RESULTS: Three amiRNA significantly reduced ASGPR1 mRNA and protein expression, and the greatest reduction was seen in amiRNA-ASGPR1-610 transfected group. Expressions of ASGPR1 mRNA and protein were down-regulated by 57.3% and 49.8% at 72 h(P < 0.01). At the virus level, three amiRNA-ASGPR1 plasmids obviously inhibited the secretion of HBsAg and HBeAg with the greatest reduction seen in amiRNA-ASGPR1-610 transfected group. Expression levels of HBsAg and HBeAg were down-regulated by 31.3% and 33.6% after 72 h (P < 0.01) and HBV DNA level was down-regulated by 29.7% at 72 h (P < 0.01).

CONCLUSION: In HepG2.2.15 cells, HBV replication and expression could be inhibited by artificial microRNA targeted ASGPR1. Artificial microRNA targeted ASGPR1 could be a promising therapeutic approach for chronic HBV infection.

esiRNA to eri-1 and adar-1 genes improving high doses of c-myc-directed esiRNA effect on mouse melanoma growth inhibition

Knockdown of c-myc expression via RNAi is expected to be an efficient approach to suppress tumor growth. In our preliminary study, we intraperitoneally injected different doses of c-myc-directed esiRNA (esic-MYC, c-myc-directed Escherichia coli expressed and enzyme digested siRNA) into C57BL6/6J mice with bearing B16 melanoma to investigate the inhibitory effect of esic-MYC on tumor growth. However, in high dose esic-MYC treatment groups, the tumor growth inhibition was less efficient than that of low dose treatment groups. Considering the negative regulation roles of eri-1 and adar-1 genes in RNA interference, we downregulated either/both of the two genes with c-myc gene by RNAi. Our results showed esiMERI-1 (esiRNA of mouse eri-1 gene) and esiMADAR-1 (esiRNA of mouse adar-1 gene) could rescue the tumor growth suppression in the high dose esic-MYC treatment groups obviously. The data strongly suggest that silencing of eri-1 and adar-1 homologs of human being should be concerned for cancer therapy by RNAi approach.

RNA interference against hepatitis B virus with endoribonuclease-prepared siRNA despite of the target sequence variations

RNA interference (RNAi) has proven to be very powerful in inhibiting hepatitis B virus (HBV) replication by cell culture and mouse model studies. We have previously reported that endoribonuclease-prepared short interfering RNAs (esiRNAs) were able to inhibit HBV replication more efficiently than synthesized siRNAs. Here we tested the hypothesis that esiRNAs are able to inhibit gene expression with limited mutations within the target region. Target sequences with different similarities to esiHBVP (esiRNA targeting the DNA polymerase and S antigen of Hepatitis B virus) were amplified and cloned into the 3' untranslated region of HBsAg, respectively. When the obtained expression vectors were co-transfected with esiHBVP into CHO cells, HBsAg expression was suppressed with same efficiency regardless of the target sequence similarities. In HepG2 cells, esiHP9 based on one of the amplified sequence that sharing 87% similarity to the target region suppressed HBsAg expression effectively and dose dependently. In vivo experiment showed that a single dose of 5 microg esiHP9 was able to reduce HBsAg and HBeAg level in the mouse sera by 88 and 77% despite of its 87% similarity to the target sequence, which was as good as esiHBVP that is 100% similar to the target sequence. All the data suggest that esiRNA can tolerate limited target sequence variations without losing its inhibitory capacity. It would be very helpful to suppress virus replication by RNAi despite of their high mutation rate.

Blocking c-myc and stat3 by E. coli expressed and enzyme digested siRNA in mouse melanoma

Tumour cells often show alteration in the signal-transduction pathways, leading to proliferation in response to external signals. Oncogene overexpression and constitutive expression is a common phenomenon in the development and progression of many human cancers. Therefore oncogenes provide potential targets for cancer therapy. RNA interference (RNAi), mediated by small interfering RNA (siRNA), silences genes with a high degree of specificity and potentially represents a general approach for molecularly targeted anti-cancer therapy. The data presented in this report evaluated the method of systemically administering combined esiRNAs to multiple targets as compared with the method of using a single kind of esiRNA to a single target. Our experimental data revealed that the mixed treatment of esiC-MYC and esiSTAT3 had a better inhibition effect than the single treatment of esiC-MYC or esiSTAT3 on mouse B16 melanoma.

Reversal of MDR1 gene-dependent multidrug resistance using low concentration of endonuclease-prepared small interference RNA

Multidrug resistance following initial chemotherapy is commonly associated with MDR1 gene encoding for P-glycoprotein (P-gp). RNA interference of MDR1 gene expression was used as a strategy to reverse MDR1-mediated multidrug resistance phenotypes. Here we report that endonuclease-prepared small interfering RNA (esiRNA) at concentrations as low as 10 ng/ml (about 0.7 nM) can decrease MDR1 expression and increase chemosensitivity in the Adriamycin-induced resistant MCF-7/R cells. When MCF-7/R cells were transiently transfected with esiRNA of MDR1 (esiMDR1), the MDR1 mRNA was reduced by about 50%, drug accumulation increased by about 30%, and the IC50 for daunorubicin was reduced from 4.5 to 1.2 microM. These results provide evidence that esiRNA of MDR1 could be an alternative to P-gp inhibitors with the advantage of avoiding non-specific suppression with a lower effective dosage than using a single siRNA duplex, offering a potential therapeutic application of siRNA.

EsiRNAs inhibit Hepatitis B virus replication in mice model more efficiently than synthesized siRNAs

RNA interference (RNAi) has been proved to be a promising strategy to combat Hepatitis B virus (HBV) infection by way of cell culture and animal model studies. In this work, esiRNAs (endoribonuclease-prepared siRNAs) targeting all of the four open reading frames (ORFs) of HBV genome were prepared. In vitro experiment showed that esiHBVP suppressed HBsAg expression most effectively. Its capacity to suppress HBV replication in vivo was then tested. A single dose of 1 microg esiHBVP was able to reduce HBsAg and HBeAg level in the mouse serum by 90 and 89% one day after injection, while the same amount of chemically synthesized siRNA only reduced that by 33 and 45%. Immunostaining of HBcAg showed that esiHBVP inhibited HBcAg expression more potently than chemically synthesized siRNA. Quantification of HBV DNA in the mouse serum showed 1 microg eiHBVP treatment reduced serum HBV DNA copy number to 18% that of the untreated control, while 1 microg siRNA treatment only reduced that to 63%. In conclusion, the data presented here proved that esiRNA is much more efficient in suppressing HBV replication than chemically synthesized siRNA, and it might be a better therapeutic agent to fight against HBV infection.