Combination silencer RNA (siRNA) targeting Bcl-2 antagonizes siRNA against thymidylate synthase in human tumor cell lines

Thymidylate synthase predicts poor response to pemetrexed chemotherapy in patients with advanced breast cancer

Pemetrexed is a candidate chemotherapy regimen for anthracycline- and taxane-pretreated advanced breast cancer. However, to the best of our knowledge, no efficient treatment efficacy biomarkers have been identified. In the present study, the potential correlation between thymidylate synthase (TYMS) expression and clinical response to pemetrexed was examined in advanced breast cancer. A retrospective collection was performed by using 77 advanced breast cancer subjects, who received at least three cycles of pemetrexed treatment in the Second Hospital of Shandong University hospital. TYMS expression was detected using immunohistopathological staining. The correlations between TYMS and therapeutic efficacies of different chemotherapy treatment were analyzed. The objective response rate (ORR) and disease control was 31.17 and 64.94%, respectively. Immunohistochemical staining demonstrated that TYMS expression was observed in the cytoplasm and nuclei of breast cancer cells. High TYMS expression was observed in 32 specimens. Elevated TYMS expression was correlated with higher histological grade and lymph node metastasis (P<0.05). Furthermore, significantly higher TYMS expression was observed in treatment-resistant patients than response ones (P<0.05). Patients with low expression level of TYMS exhibit significantly higher ORR. Cox regression analysis indicated that elevated TYMS expression was a detrimental factor for pemetrexed treatment for advanced breast cancer patients. The present results suggested that TYMS expression levels predicts therapeutic sensitivity of pemetrexed chemotherapy in advanced breast cancer, indicating that it may be a useful biomarker to choose chemotherapy regimens.

Functionalization of the 3'-ends of DNA and RNA strands with N-ethyl-N-coupled nucleosides: a promising approach to avoid 3'-exonuclease-catalyzed hydrolysis of therapeutic oligonucleotides

The development of nucleic acid derivatives to generate novel medical treatments has become increasingly popular, but the high vulnerability of oligonucleotides to nucleases limits their practical use. We explored the possibility of increasing the stability against 3'-exonucleases by replacing the two 3'-terminal nucleotides by N-ethyl-N-coupled nucleosides. Molecular dynamics simulations of 3'-N-ethyl-N-modified DNA:Klenow fragment complexes suggested that this kind of alteration has negative effects on the correct positioning of the adjacent scissile phosphodiester bond at the active site of the enzyme, and accordingly was expected to protect the oligonucleotide from degradation. We verified that these modifications conferred complete resistance to 3'-exonucleases. Furthermore, cellular RNAi experiments with 3'-N-ethyl-N-modified siRNAs showed that these modifications were compatible with the RNAi machinery. Overall, our experimental and theoretical studies strongly suggest that these modified oligonucleotides could be valuable for therapeutic applications.

Efficient systemic delivery of siRNA by using high-density lipoprotein-mimicking peptide lipid nanoparticles

The main challenge for RNAi therapeutics lies in systemic delivery of siRNA to the correct tissues and transporting them into the cytoplasm of targeted cells, at safe, therapeutic levels. Recently, we developed a high-density lipoprotein-mimicking peptide-phospholipid scaffold (HPPS) and demonstrated its direct cytosolic delivery of siRNA in vitro, thereby bypassing endosomal trapping.

AIM

We investigate the in vivo implementation of HPPS for siRNA delivery.

METHOD & RESULTS

After systemic administration in KB tumor-bearing mice, HPPS prolonged the blood circulation time of cholesterol-modified siRNA (chol-siRNA) by a factor of four, improved its biodistribution and facilitated its uptake in scavenger receptor class B type I overexpressed tumors. For therapeutic targeting to the bcl-2 gene, the HPPS-chol-si-bcl-2 nanoparticles downregulated Bcl-2 protein, induced enhanced apoptosis (2.5-fold) in tumors when compared with controls (saline, HPPS, HPPS-chol-si-scramble and chol-si-bcl-2) and significantly inhibited tumor growth with no adverse effect.

CONCLUSION

HPPS is a safe, efficient nanocarrier for RNAi therapeutics in vivo.

Combining small interfering RNAs targeting thymidylate synthase and thymidine kinase 1 or 2 sensitizes human tumor cells to 5-fluorodeoxyuridine and pemetrexed

Thymidylate synthase (TS) is the only de novo source of thymidylate (dTMP) for DNA synthesis and repair. Drugs targeting TS protein are a mainstay in cancer treatment, but off-target effects and toxicity limit their use. Cytosolic thymidine kinase (TK1) and mitochondrial thymidine kinase (TK2) contribute to an alternative dTMP-producing pathway, by salvaging thymidine from the tumor milieu, and may modulate resistance to TS-targeting drugs. Combined down-regulation of these enzymes is an attractive strategy to enhance cancer therapy. We have shown previously that antisense-targeting TS enhanced tumor cell sensitivity to TS-targeting drugs in vitro and in vivo. Because both TS and TKs contribute to increased cellular dTMP, we hypothesized that TKs mediate resistance to the capacity of TS small interfering RNA (siRNA) to sensitize tumor cells to TS-targeting anticancer drugs. We assessed the effects of targeting TK1 or TK2 with siRNA alone and in combination with siRNA targeting TS and/or TS-protein targeting drugs on tumor cell proliferation. Down-regulation of TK with siRNA enhanced the capacity of TS siRNA to sensitize tumor cells to traditional TS protein-targeting drugs [5-fluorodeoxyuridine (5FUdR) and pemetrexed]. The sensitization was greater than that observed in response to any siRNA used alone and was specific to drugs targeting TS. Up-regulation of TK1 in response to combined 5FUdR and TS siRNA suggests that TK knockdown may be therapeutically useful in combination with these agents. TKs may be useful targets for cancer therapy when combined with molecules targeting TS mRNA and TS protein.

RAD001 shows activity against gastric cancer cells and overcomes 5-FU resistance by downregulating thymidylate synthase

We evaluated RAD001, an inhibitor of the mammalian target of rapamycin (mTOR) in human gastric cancer cell lines and determined the molecular mechanisms. RAD001 has marked growth inhibitory activity against the SNU-1 and SNU-216 cells. It inhibited phosphorylation of mTOR and S6K, and induced G1 cell cycle arrest. Synergistic growth-inhibitory effects in combination with 5-fluorouracil (5-FU) was identified. Furthermore, RAD001 conferred sensitivity to 5-FU-resistant cell lines by downregulating thymidylate synthase (TS). In conclusion, RAD001 showed growth inhibitory activity against gastric cancer cells and acted synergistically with cytotoxic agents such as 5-FU by downregulating TS.

Future of RNAi-based therapies for human papillomavirus-associated cervical cancer

Over 99% of cervical cancers are associated with infection of high-risk type human papillomaviruses (HPV). These viruses infect epithelial cells lining the cervix and express the early viral genes E6 and E7, which are oncogenes and are primarily responsible for the transformation of the epithelial cells. The continuous expression of those genes is essential for maintenance of the cancer cell phenotype and viability. These viral genes can be silenced using oligonucleotide-based techniques, for example RNAi, antisense RNA and ribozymes. In spite of promising results in vitro and in vivo, in mice, these methods have thus far proved unsuccessful in humans, owing to the lack of an effective delivery system amongst other limitations. In this review we will discuss potential gene-silencing strategies in cervical cancer that would target both viral genes such as E6 and E7, and cellular genes that become deregulated such as E2F, p53, Akt, mTor, NF-κB or Bcl-2. By investigating these approaches we may generate an effective treatment for HPV-induced cervical cancer using gene silencing.

Effective treatment of leukemic cell lines with wt1 siRNA

The expression of wt1 and bcl-2 is considered to have a proliferating and survival supporting effect in leukemia blast cells. Here we describe the use of siRNA against wt1 and bcl-2 in leukemic cell lines for successful growth inhibition. We have used two different sequences designated as siRNA-A and siRNA-B corresponding to positions within the wt1 coding sequence to downregulate wt1 and a commercially available siRNA kit to downregulate bcl-2. WT1 and bcl-2 gene expression in transfected leukemic cell lines were evaluated with RT-PCR and western blot analyses. MTT assay was used to measure the cell viability and flow cytometry using annexin V/PI-staining for apoptosis. K562 and HL-60 cell lines transfected with siRNA-A targeted to wt1 had greatly decreased levels of both wt1 mRNA and protein expression. In contrast, siRNA-B and control siRNA led almost to no effect on wt1 mRNA and protein expression. siRNA-A-reduced wt1 mRNA expression was associated with a decreased cell proliferation and increased number of apoptotic cells in K562 and HL-60 cells by 24 and 48 h after transfection. Combined treatment with wt1 siRNA and bcl-2 siRNA simultaneously was not able to override the cell growth and apoptosis effects compared to single treatment with wt1 siRNA. siRNAs targeted against human wt1 might be a valuable tool as antiproliferative agent against wt1 expressing leukemic cells.