Amplifying gene expression with RNA-targeted therapeutics

Abstract

Many diseases are caused by insufficient expression of mutated genes and would benefit from increased expression of the corresponding protein. However, in drug development, it has been historically easier to develop drugs with inhibitory or antagonistic effects. Protein replacement and gene therapy can achieve the goal of increased protein expression but have limitations. Recent discoveries of the extensive regulatory networks formed by non-coding RNAs offer alternative targets and strategies to amplify the production of a specific protein. In addition to RNA-targeting small molecules, new nucleic acid-based therapeutic modalities that allow highly specific modulation of RNA-based regulatory networks are being developed. Such approaches can directly target the stability of mRNAs or modulate non-coding RNA-mediated regulation of transcription and translation. This Review highlights emerging RNA-targeted therapeutics for gene activation, focusing on opportunities and challenges for translation to the clinic.

Chemically Modified Platforms for Better RNA Therapeutics

“…Furthermore, ASO has the capacity to reduce the expression of the targeted RNA by inhibiting the 5′ cap, inducing changes in polyadenylation, or causing translational arrest. 43 Of particular importance, compared to RNase H1-dependent ASO, steric block ASO can significantly increase the number of targeting sites within RNA sequences. They enhance the plasticity of chemical modifications and limit the formation of RNase H1 cleavage substrates through interactions with pre-mRNA, thereby reducing off-target effects.…”

“…Over the decades, substantial advancements have been achieved, leading to the approval of 10 ASO drugs for clinical use (Table ), and an additional 100 ASO drugs are currently in different stages of clinical trials (Table ). − These successes make ASO the most approved drugs in the field of small nucleic acids. Theoretically, ASOs can be designed to target sequences associated with any disease, leading to gene knockdown and expanding the potential targets for ASO drug development.…”

“…On one hand, ASO can bind to specific sequences within the target mRNA and hinder or interfere with the normal functioning of mRNA, microRNA (miRNA), or pre-mRNA. − This interference can result in both upregulation and downregulation of gene expression. , Moreover, ASO can also interrupt translation by targeting and binding to the initiation codon AUG of the target mRNA, thereby blocking the binding process between the ribosome and mRNA. , Additionally, ASO can target upstream open reading frames (uORFs) or other elements that inhibit translation to enhance RNA expression. Furthermore, ASO has the capacity to reduce the expression of the targeted RNA by inhibiting the 5′ cap, inducing changes in polyadenylation, or causing translational arrest . Of particular importance, compared to RNase H1-dependent ASO, steric block ASO can significantly increase the number of targeting sites within RNA sequences.…”

“…The RITA complex further recruits transcriptional activators such as p300 and CREB-binding protein (CBP) to the promoter region. These activators induce chromatin modifications, such as histone acetylation, and facilitate the recruitment of RNA polymerase II, the enzyme responsible for transcription, to the promoter region. , Additionally, small activating RNA-induced RNA activation can lead to epigenetic changes, including demethylation of CpG islands within the promoter region. These changes result in sustained upregulation of gene expression even beyond the exposure to small activating RNA.…”

“…The mechanism of small activating RNA-induced RNA activation holds significant potential for the development of novel gene therapies across various diseases. In 2016, MiNA Therapeutics initiated the first global clinical trial of a small activating RNA drug MTL-CEBPA, which was formulated as small activating RNA encapsulated in Smarticles lipid nanoparticles, aiming to activate the CEBPA gene encoding the CCAAT/enhancer binding protein alpha (C/EBP-α). , Promising results from the phase 1 clinical research of MTL-CEBPA in combination or sequential administration with sorafenib for advanced liver cancer were reported in 2020, leading to the advancement of the treatment into a phase 2 clinical trial. However, the intricate mechanisms of action of small activating RNA drugs present greater developmental challenges compared to other small nucleic acid therapeutics, such as siRNAs.…”