Beyond Permanent Genome Editing: Molecular Delivery Strategies for RNA Editing and Epigenome-Editing Therapeutics.

Reversible genetic medicines are emerging as controllable alternatives to permanent genome editing by enabling programmable modulation of RNA sequence, transcript abundance, chromatin state, and gene expression without irreversible genomic alteration. However, reversibility is not a single binary property: transient editor exposure, decay of the molecular effect, recovery of cellular function, and clinical capacity to stop, redose, or counteract treatment may diverge. This review therefore distinguishes mechanistic, functional, and clinical reversibility while examining targeted delivery systems for RNA-editing and epigenome-editing therapeutics. Key payloads include ADAR-recruiting oligonucleotides, CRISPR-Cas13 RNA editors, guide RNAs, chemically modified RNAs, editor-encoding mRNAs, dCas9 transcriptional regulators, DNA methylation editors, histone-modifying systems, and CRISPRoff-like platforms. We evaluate extracellular and intracellular delivery barriers, including nuclease degradation, immune recognition, renal clearance, liver uptake, cellular entry, endosomal escape, cytoplasmic release, nuclear localization, chromatin access, editing-window duration, off-target activity, immunogenicity, repeat-dosing feasibility, manufacturing, quality control, potency assays, and regulatory translation. Overall, delivery systems for reversible genetic medicines should be judged by tissue selectivity, functional editing, duration of action, reversibility after treatment withdrawal, safety, manufacturability, and clinical controllability.