mRNA vaccine technologies have been actively developing since the beginning of the 21st century and have received a major boost from new findings about the functioning of the immune system and the development of efficient vehicles for nucleic acid delivery. The mRNA vaccine demonstrates superior properties compared to the DNA vaccine, primarily due to accelerated mRNA vaccine development, enhanced flexibility, and the absence of integration into the genome. Artificial mRNAs have biotechnological and medical applications, including the development of antiviral and anticancer mRNA therapeutics. The effective expression of therapeutic mRNA depends upon the appropriate selection of structural elements. Along with the addition of the 5'-cap, appropriate polyadenylation, and sequence codon optimization, 5'- and 3'-untranslated regions (UTRs) play an important role in the translation efficiency of therapeutic mRNAs. In this study, new plasmids containing a novel combination of UTR pairs, namely 5'-UTR-4 and 3'-UTR AES-mtRNR1, were constructed to obtain artificial mRNAs encoding green fluorescent protein (GFP) and firefly luciferase (FLuc) with new structural elements and properties. The novel combination of the UTRs, which is described in this article for the first time, in addition to sufficient polyadenylation and pseudouridinilation of mRNA, was demonstrated to strongly increase the translation of codon-optimized sequences of reporter mRNAs. We generated lipoplexes containing the aforementioned reporter mRNAs and liposomes composed of cationic lipid 2X3 (1,26-bis(cholest-5-en-3beta-yloxycarbonylamino)-7,11,16,20-tetraazahexacosane tetrahydrochloride) and helper lipid DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine). For in vivo experiments, the liposomes were decorated with 2 % of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE- PEG2000). The translation efficiency of mRNAs was found to be superior for the novel UTR combination compared with HBB gene UTRs, both in vitro and in vivo. When mRNA is administered intramuscularly, the proposed combination of UTRs provides lasting expression for more than 4 days. The results demonstrated that the novel UTR pair combination could be useful in the development of artificial mRNAs with enhanced translation efficiency, potentially reducing the dose for mRNA-based therapeutics.
