RNA interference (RNAi) is an ancient biological mechanism used to defend against external invasion It theoretically can silence any disease-related genes in a sequence-specific manner, making small interfering RNA (siRNA) a promising therapeutic modality After a two-decade journey from its discovery, two approvals of siRNA therapeutics, ONPATTRO® (patisiran) and GIVLAARI™ (givosiran), have been achieved by Alnylam Pharmaceuticals Reviewing the long-term pharmaceutical history of human beings, siRNA therapy currently has set up an extraordinary milestone, as it has already changed and will continue to change the treatment and management of human diseases It can be administered quarterly, even twice-yearly, to achieve therapeutic effects, which is not the case for small molecules and antibodies The drug development process was extremely hard, aiming to surmount complex obstacles, such as how to efficiently and safely deliver siRNAs to desired tissues and cells and how to enhance the performance of siRNAs with respect to their activity, stability, specificity and potential off-target effects In this review, the evolution of siRNA chemical modifications and their biomedical performance are comprehensively reviewed All clinically explored and commercialized siRNA delivery platforms, including the GalNAc (N-acetylgalactosamine)–siRNA conjugate, and their fundamental design principles are thoroughly discussed The latest progress in siRNA therapeutic development is also summarized This review provides a comprehensive view and roadmap for general readers working in the field

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Therapeutic siRNA: state of the art.

microRNA-antagonism regulates breast cancer stemness and metastasis via TET family dependent chromatin remodeling

Rationale: The adult heart is composed primarily of terminally differentiated, mature cardiomyocytes that express signature genes related to contraction. In response to mechanical or pathological stress, the heart undergoes hypertrophic growth, a process defined as an increase in cardiomyocyte cell size without an increase in cell number. However, the molecular mechanism of cardiac hypertrophy is not fully understood.

Objective: To identify and characterize microRNAs that regulate cardiac hypertrophy and remodeling.

Methods and Results: Screening for muscle-expressed microRNAs that are dynamically regulated during muscle differentiation and hypertrophy identified microRNA-22 (miR-22) as a cardiac- and skeletal muscle–enriched microRNA that is upregulated during myocyte differentiation and cardiomyocyte hypertrophy. Overexpression of miR-22 was sufficient to induce cardiomyocyte hypertrophy. We generated mouse models with global and cardiac-specific miR-22 deletion, and we found that cardiac miR-22 was essential for hypertrophic cardiac growth in response to stress. miR-22–null hearts blunted cardiac hypertrophy and cardiac remodeling in response to 2 independent stressors: isoproterenol infusion and an activated calcineurin transgene. Loss of miR-22 sensitized mice to the development of dilated cardiomyopathy under stress conditions. We identified Sirt1 and Hdac4 as miR-22 targets in the heart.

Conclusions: Our studies uncover miR-22 as a critical regulator of cardiomyocyte hypertrophy and cardiac remodeling.

# Novelty and Significance {#article-title-30}

MicroRNA-22 Regulates Cardiac Hypertrophy and Remodeling in Response to Stress

BACKGROUND: Recently, microRNAs in cancer development have attracted much attention, but their roles in tumorigenesis are still largely unknown. In this study, a functional role of miR-22 in hepatocellular carcinoma (HCC) development has been identified. METHODS: Quantitative real-time PCR was used to determine the level of miR-22 transcript in HCC clinical samples, and its correlation with disease-free survival was determined using Kaplan–Meier method. Restoration of miR-22 expression was carried out in HCC cell lines to assess its influence on HCC cell proliferation and tumourigenicity. RESULTS: In the 160 paired HCC tissue samples, miR-22 expression was downregulated in HCC, and low miR-22 expression in HCC was predictive of poor survival in HCC patients. Functional studies indicated that ectopic expression of miR-22 significantly inhibits HCC cell proliferation and tumourigenicity. Furthermore, histone deacetylase 4 (HDAC4), known to have critical roles in cancer development, was proved to be directly targeted and regulated by miR-22. Furthermore, HDAC4 was upregulated in miR-22downregulated HCC tissues, suggesting that downregulation of miR-22 might participate in HCC carcinogenesis and progression through potentiation of HDAC4 expression. In addition, cell proliferation was also suppressed by knockdown of HDAC4 or treatment with HDAC inhibitor trichostatin A in HCC cell lines. CONCLUSION: miR-22, downregulated in HCC, has an anti-proliferative effect on HCC cells both in vitro and in vivo. Furthermore, miR-22 may have considerable potential in identification of the prognosis and application of cancer therapy for HCC patients.

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microRNA-22, downregulated in hepatocellular carcinoma and correlated with prognosis, suppresses cell proliferation and tumourigenicity

Breast cancer is the most frequent malignancy diagnosed in women. Approximately 70% of breast tumors express the estrogen receptor (ER). Tamoxifen and aromatase inhibitors (AIs) are the most common and effective therapies for patients with ERα-positive breast cancer. Alone or combined with chemotherapy, tamoxifen significantly reduces disease progression and is associated with more favorable impact on survival in patients. Unfortunately, endocrine resistance occurs, either de novo or acquired during the course of the treatment. The mechanisms that contribute to hormonal resistance include loss or modification in the ERα expression, regulation of signal transduction pathways, altered expression of specific microRNAs, balance of co-regulatory proteins, and genetic polymorphisms involved in tamoxifen metabolic activity. Because of the clinical consequences of endocrine resistance, new treatment strategies are arising to make the cells sensitive to tamoxifen. Here, we will review the current knowledge on mechanisms of endocrine resistance in breast cancer cells. In addition, we will discuss novel therapeutic strategies to overcome such resistance. Undoubtedly, circumventing endocrine resistance should help to improve therapy for the benefit of breast cancer patients.

https://www.mdpi.com/1422-0067/14/1/108/pdf

Mechanisms of Resistance to Endocrine Therapy in Breast Cancer: Focus on Signaling Pathways, miRNAs and Genetically Based Resistance

Previous studies have suggested that microRNAs (miRNAs) may play important roles in tumorigenesis, but little is known about the functions of most miRNAs in cancer development. In the present study, we set up a cell-based screen using a luciferase reporter plasmid carrying the whole ∼ 4.7 kb 3′-UTR of estrogen receptor α (ERα) mRNA cotransfected with a synthetic miRNA expression library to identify potential ERα-targeting miRNAs. Among all the miRNAs, miR-22 was found to repress robustly the luciferase signal in both HEK-293T and ERα-positive MCF-7 cells. Mutation of the target site was found to abrogate this repression effect of miR-22, whereas antagonism of endogenous miR-22 in MDA-MB-231 cells resulted in elevated reporter signals. We assessed the miR-22 expression patterns in five breast cancer cell lines and 23 clinical biopsies and revealed that there is a significant inverse association between the miR-22 levels and ERα protein expression. To evaluate the potential of miR-22 as a potential therapeutic intervention, we found that reduction of endogenous ERα protein levels and suppression of cancer cell growth could be achieved in MCF-7 cells by miR-22 overexpression in a way that can be recapitulated by the introduction of specific small interfering RNA against ERα. The phenomena can be rescued by the reintroduction of ERα. Taken together, our data indicate that miR-22 was frequently downregulated in ERα-positive human breast cancer cell lines and clinical samples. Direct involvement in the regulation of ERα may be one of the mechanisms through which miR-22 could play a pivotal role in the pathogenesis of breast cancer.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1742-4658.2010.07594.x

An estrogen receptor α suppressor, microRNA-22, is downregulated in estrogen receptor α-positive human breast cancer cell lines and clinical samples

Here we report a novel electroporation microchip with great performance and compatibility with the standard multi-well plate used in biological research. The novel annular interdigitated electrode design makes it possible to achieve efficient cell transfection as high as 90% under low-strength electrical pulses, thereby circumventing the many adverse effects of conventional cuvette-type and previously reported microchip-based electroporation devices. Using this system, we demonstrated substantially improved cell transfection efficacy and viability in cultured and primary cells, for both plasmid and synthetic siRNA. Improvements of this system open new opportunities for high-throughput applications of siRNA technology in basic and biomedical research.

Tianjing Cai

Papers

An estrogen receptor α suppressor, microRNA-22, is downregulated in estrogen receptor α-positive human breast cancer cell lines and clinical samples

An efficient and high-throughput electroporation microchip applicable for siRNA delivery