The REGeRNA Project started in September 2022, putting together 6 partners from 5 European countries. The project is progressing well towards its objectives.
A lead mRNA product has been identified after an extensive screening of putative factors. It is called CPY, is a single linear bicistronic mRNA coding for Cyclin D2 and YAP5SA, and it induced proliferation in vitro in cardiomyocytes, not in cardiac fibroblasts. However, in a mouse model of myocardial ischemia/reperfusion, the first set of experiments has shown that its inclusion in LNPs failed to improve function following its direct intramyocardial injections or to induce cell proliferation (regardless of cell phenotype). The assessment of fibrosis (work in progress) will be critical to confirm that at least CPY does not increase fibroblast proliferation, thereby justifying to skip engineering the mRNA with microRNAs allowing a cardiomyocyte-specific expression (as originally planned), a task which has shown to be challenging despite the careful adherence to a published protocol impossible to reproduce.
Interestingly, however, parallel biodistribution experiments performed over the reporting period and entailing the similar intramyocardial injections of either LNP or a naked mRNA, both shuttling a fluorescent reporter, have shown equivalent signals in the heart, thereby paving the way for a next set of injections of mRNA alone (only encapsulated in a polymer intended to optimize transfection of the cardiac cells).
In parallel, different LNP formulations modified to reduce liver targeting and increase cardiac homing have been performed but have not yet allowed systemic delivery to enable a substantial delivery of the vectors in heart tissue; studies on these formulations are continuing.
