Stable suppression of gene expression by short interfering RNAs targeted to promoter in a mouse embryonal carcinoma stem cell line

Structural Basis of Targeted Imaging and Therapy in Cancer Explorations with the Epigenetic Drugs

Origin of cancer is strongly related to the unusual epigenetic regulation of gene function as indicated by recent reports. The covalent modifications to DNA or histones without affecting genomes that finally lead to phenotypical changes in cells or organisms are referred as "Epigenetics." The possibility to reprogram the epigenetics in the cancer epigenome is the most important target for cancer treatment and drug resistance. The development of epigenetic drugs holds a great potential for the current cancer therapeutic approaches. Nevertheless, targeting cancer epigenetic pathways is still exciting due to the lack of selective and effective small molecule compounds or drug molecules. Therefore, the current book chapter highlights epigenetic pathways for cancer and potential small molecule inhibitors and epidrugs targeting DNA methyltransferase, histone modification, and more new therapies with nanomaterials and imaging to improve the effectiveness of cancer treatment. The structural aspects on discovery of novel small molecules or drugs targeting epigenetic pathways in cancer exploration as promising strategies will be also discussed.

Cancer's epigenetic drugs: where are they in the cancer medicines?

Epigenetic modulation can affect the characteristics of cancers. Because it is likely to manipulate epigenetic genes, they can be considered as potential targets for cancer treatment. In this comprehensive study, epigenetic drugs are categorized according to anticancer mechanisms and phase of therapy. The relevant articles or databases were searched for epigenetic approaches to cancer therapy. Epigenetic drugs are divided according to their mechanisms and clinical phases that have been approved by the FDA or are undergoing evaluation phases. DNA methylation agents, chromatin remodelers specially HDACs, and noncoding RNAs especially microRNAs are the main epi-drugs for cancer. Despite many challenges, combination therapy using epi-drugs and routine therapies such as chemotherapy in various approaches have exhibited beneficial effects compared with each treatment alone. Cancer stem cell targeting and epigenetic editing have been confirmed as definitive pathways for cancer treatment. This paper reviewed the available epigenetic approaches to cancer therapy.

Transcriptional gene silencing in humans

It has been over a decade since the first observation that small non-coding RNAs can functionally modulate epigenetic states in human cells to achieve functional transcriptional gene silencing (TGS). TGS is mechanistically distinct from the RNA interference (RNAi) gene-silencing pathway. TGS can result in long-term stable epigenetic modifications to gene expression that can be passed on to daughter cells during cell division, whereas RNAi does not. Early studies of TGS have been largely overlooked, overshadowed by subsequent discoveries of small RNA-directed post-TGS and RNAi. A reappraisal of early work has been brought about by recent findings in human cells where endogenous long non-coding RNAs function to regulate the epigenome. There are distinct and common overlaps between the proteins involved in small and long non-coding RNA transcriptional regulatory mechanisms, suggesting that the early studies using small non-coding RNAs to modulate transcription were making use of a previously unrecognized endogenous mechanism of RNA-directed gene regulation. Here we review how non-coding RNA plays a role in regulation of transcription and epigenetic gene silencing in human cells by revisiting these earlier studies and the mechanistic insights gained to date. We also provide a list of mammalian genes that have been shown to be transcriptionally regulated by non-coding RNAs. Lastly, we explore how TGS may serve as the basis for development of future therapeutic agents.

Combined RNA interference of hexokinase II and (131)I-sodium iodide symporter gene therapy for anaplastic thyroid carcinoma

The purpose of this study was to investigate the enhanced therapeutic effect of the combined use of shRNA (small hairpin RNA) therapy for the hexokinase II (HKII) gene and (131)I human sodium iodide symporter (hNIS) as a gene therapy for in vitro and in vivo treatment of anaplastic thyroid carcinoma cells (ARO) in an animal model.

METHODS

A recombinant lentivirus containing a plasmid with the hNIS gene driven by phosphoglycerate kinase promoter and green fluorescent protein (GFP) linked with an internal ribosome entry site sequence was produced. ARO cells were transfected with the virus and sorted by fluorescent activated cell sorting using GFP (ARO-NG). The messenger RNA expression of hNIS and GFP were evaluated with reverse-transcriptase polymerase chain reaction, and the function of hNIS was verified by (125)I uptake. The lentiviral vector expressing shRNA against HKII (Lenti-HKII shRNA) was constructed and used to infect ARO-NG cells. The effect of Lenti-HKII shRNA was evaluated by reverse-transcriptase polymerase chain reaction, (18)F-FDG uptake, and HK activity. An in vitro clonogenic assay was performed after Lenti-HKII shRNA therapy, (131)I therapy, and a combined therapy. The therapies were also applied in vivo to an animal model with an ARO-NG xenograft, and the effects were assessed with caliper measurements and (18)F-FDG PET.

RESULTS

ARO-NG cells showed an (125)I uptake 76-fold higher than the parent ARO cells. Compared with the uninfected ARO-NG cells, ARO-NG cells infected with Lenti-HKII shRNA had lower HKII messenger RNA expression, lower (18)F-FDG uptake, and HK activity. The proliferation of ARO-NG cells was inhibited by (131)I and Lenti-HKII shRNA therapies and further inhibited by the combined (131)I and Lenti-HKII shRNA therapy. Both the Lenti-HKII shRNA therapy and the (131)I therapy inhibited in vivo tumor growth in the tumor xenograft model. The combined Lenti-HKII shRNA and (131)I therapy resulted in a further decrease of tumor growth.

CONCLUSION

Our results suggest that the combined HKII shRNA and (131)I therapy has a stronger antitumor effect than either the (131)I therapy or the HKII shRNA alone. Therefore, this combined therapy could be used as a powerful strategy for treating anaplastic thyroid carcinoma.