EGFP mRNA (no modification)

Fabry disease is an X-linked lysosomal storage disorder caused by loss of α-galactosidase A (α-Gal A) activity and characterized by the progressive accumulation of ceramide trihexosides and their analogs in all cells and tissues. Although enzyme replacement therapy (ERT) is considered the standard of care, the long-term effects of ERT on renal and cardiac manifestations remain uncertain, and new therapeutic approaches are needed. Here, researchers report preclinical studies evaluating systemic messenger RNA (mRNA) encoding human α-Gal A in wild-type (WT) mice, α-Gal A-deficient mice, and WT nonhuman primates (NHPs). The pharmacokinetics and distribution of h-α-Gal A mRNA-encoded protein in WT mice indicated a prolonged half-life of α-Gal A in tissues and plasma. A single intravenous injection of h-α-Gal A mRNA into Gla-deficient mice showed a dose-dependent reduction in protein activity and substrate. Furthermore, the reduction in substrate in tissues and plasma persisted for up to 6 weeks after a single injection. Repeated intravenous administration of h-α-Gal A mRNA showed sustained pharmacodynamic response and efficacy in a mouse model of Fabry disease. Finally, multiple dosing in non-human primates confirmed its safety and translatability.

To determine the duration of action of h-α-Gal A protein encoded by exogenous h-α-Gal A mRNA, LNP-encapsulated h-α-Gal A mRNA or eGFP mRNA was intravenously injected into Fabry disease mice at a dose of 0.5 mg/kg. Immunohistochemistry (IHC) analysis of heart and liver samples from Fabry disease mice treated with h-α-Gal A mRNA showed that although h-α-Gal A staining decreased over time, it was still detectable 42 days after a single dose (Figure 1A). In a pilot study, h-α-Gal A enzyme activity was detected in plasma, heart, and liver tissues at day 28 after administration. The rates of depletion and reaccumulation of Lyso-Gb3 were tissue-specific. Compared with the level of lyso-Gb3 in the control eGFP group, plasma lyso-Gb3 decreased by 80% 7 days after administration and began to reaccumulate 35 days after administration (Figure 1B). Maximum depletion of lysoglobin 3 was observed in the liver (approximately 80%) and spleen (approximately 90%) 14 days after dosing and was maintained until 42 days after dosing, when it began to increase (Figure 1B). Lysoglobin 3 in the heart and kidney decreased by approximately 60%-70% between 28 and 35 days after dosing (Figure 1B) and began to reaccumulate at 35 days after dosing (Figure 1B). Although reaccumulation occurred over time, it is noteworthy that lysoglobin 3 levels had not returned to baseline levels (as seen in eGFP-treated mice) at the completion of the study (84 days or 12 weeks after dosing).

Figure 1. Duration of Action of h-α-Gal A in Fabry Mice. (Zhu X, et al., 2019)