Enzyme replacement therapy for acute intermittent porphyria and mRNA-based rescue in a new non-human primate model developed by long-term hepatic expression of iRNA

Abstract

Acute intermittent porphyria is a rare metabolic disorder caused by autosomal dominant loss-of-function mutations leading to a decreased activity of porphobilinogen deaminase (PBGD), the third enzyme of the heme biosynthesis pathway. As consequence, when hepatic heme synthesis is activated for endogenous and or exogenous factors, there is an accumulation of the porphyrin precursors, 5-aminolevulinic acid (ALA) and porphobilinogen (PBG). The accumulation of these metabolites in addition to reduced heme bioavailability are associated with the abdomino-psychoneurlogical crises, also known as acute attacks, that characterize this disease.

Nowadays, current treatments such as carbohydrate loading, hemin and givosiran are aimed at reducing heme synthesis induction through ALAS1 inhibition, but they do not correct the enzyme deficiency that is the primary cause of the disease. Thus, the central hypothesis of this work was that increasing hepatic PBGD levels, either by enzyme replacement or mRNA-based therapy, leads to the normalization of the heme porphyrin precursors levels, preventing acute neurovisceral attacks and correcting the alterations associated with AIP. Here, we demonstrated that a recombinant protein formed by linking ApoAI to human PBGD (rhApoAI-PBGD) circulates in blood incorporated into high-density lipoprotein (HDL), penetrates into hepatocytes and increases PBGD activity in the liver. Moreover, the intravenous administration of rhApoAI-PBGD or the hyperfunctional rApoAI-PBGD-I129M N340S (rApoAI-PBGDms) variant efficiently prevented and abrogated phenobarbital-induced acute attacks in a mouse model of AIP. One month after a single intravenous dose of rApoAI-PBGDms, the protein was still detectable in the liver, and hepatic PBGD activity remained increased above control values. Consistently, a long-lasting therapeutic effect of rApoAI-PBGDms was observed after either intravenous or subcutaneous administration.

In addition, therapeutic efficacy and safety of systemic hPBGD mRNA administration was proved in a new model of AIP developed in non-human primates (NHPs). Intrahepatic overexpression of an shRNA that specifically inhibited macaque PBGD and the administration of porphyrinogenic drugs in NHPs caused ALA PBG accumulation and recapitulated clinical manifestations associated with acute attacks of AIP in humans and other animal models, such as pain, motor disturbances, altered brain glucose uptake, brain hypoperfusion, among others. Repeated administrations of hPBGD mRNA in this new model restored hepatic PBGD levels and activity, and provided successful protection against the acute attacks, apparently more effectively than hemin or givosiran, the current treatments for AIP.