Firefly Luciferase mRNA

Lipid nanoparticles (LNPs) are promising clinical siRNA drug delivery vehicles. Modified mRNA (modRNA) has attracted much attention in recent years as a cardiac regenerative therapeutic molecule. Here, researchers evaluated the functionality of LNPs in delivering mRNA to the myocardium after ischemia-reperfusion injury. By exploring the biodistribution of fluorescently labeled LNPs, they observed that LNPs accumulated in the infarcted area of the heart after reperfusion. Subsequently, the functional delivery of modRNA was evaluated by administering firefly luciferase encoding modRNA. Meanwhile, the expression of firefly luciferase in the heart after myocardial reperfusion was significantly increased compared with sham-operated animals. To characterize the target cells within the myocardium, LNPs loaded with Cre modRNA were injected into Cre reporter mice. After LNP infusion, Tdtomato+ cells derived from Cre-mediated recombination were observed in the infarcted area as well as in the epicardial layer. Within the infarcted area, most of the target cells were cardiac fibroblasts, but some cardiomyocytes and macrophages were also found. Although the expression levels were low compared to LNP-modRNA delivery to the liver, these data suggest that LNPs are capable of functionally delivering modRNA therapeutics to damaged myocardium, which holds great promise for modRNA-based cardiac therapies.

To investigate whether the increased accumulation of LNPs also affected the functional expression pattern of mRNA, the researchers injected LNPs containing 50 μg of firefly luciferase mRNA intravenously 1 hour after the start of reperfusion and compared the luciferase activity with that of the sham-operated mice. Figure 1 shows that the myocardial luciferase activity in the ischemia-reperfusion injury group was significantly higher than that in the sham-operated control group. As expected from previous observations, the cardiac luciferase activity was relatively low compared with organs where LNPs usually accumulate, such as the liver and spleen.

Figure 1. Luciferase activity in different organs lysates 4 h after LNP-mRNA fLuc administration. (Evers M J W, et al., 2022)