Arrowhead Pharmaceuticals (Nasdaq: ARWR) announced an exclusive worldwide license agreement with Madrigal Pharmaceuticals (Nasdaq: MDGL) for ARO-PNPLA3 (formerly JNJ-75220795), Arrowhead's Phase I-stage RNAi therapeutic targeting the PNPLA3 I148M genetic variant, in a deal that could reach USD 1 billion. Under the agreement, Madrigal assumes full global responsibility for development, manufacturing, and commercialization of the siRNA candidate in metabolic dysfunction-associated steatohepatitis (MASH). The transaction entails a USD 25 million upfront payment from Madrigal to Arrowhead, with up to USD 975 million in development, regulatory, and sales milestones, plus tiered royalties on net commercial sales ranging from high-single digits to the mid-teens.
ARO-PNPLA3 was developed using Arrowhead's proprietary TRiM (Targeted RNAi Molecule) platform, which uses covalently linked targeting ligands to direct siRNA conjugates to specific cell types via subcutaneous injection. For this asset, the platform directs the molecule to hepatocytes through the asialoglycoprotein receptor, where it silences expression of the PNPLA3 gene. The I148M variant of PNPLA3, described by the company as a well-established genetic contributor to MASH progression, causes accumulation of a catalytically inactive protein on hepatocyte lipid droplets, driving fat accumulation, inflammation, and fibrotic progression.
The molecule was previously licensed to Johnson & Johnson in a 2018 deal, before the multinational handed back rights to Arrowhead in 2023 during a portfolio shuffle. Phase I data published in The New England Journal of Medicine showed that ARO-PNPLA3 produced a 46% reduction in liver fat, as measured by MRI-PDFF, at 12 weeks following a single dose in patients homozygous for the I148M variant, with effects observed as early as six weeks and sustained through at least 24 weeks. No clinically meaningful adverse events were reported. A 55-patient, double-blind, placebo-controlled Phase I trial conducted in the US enrolled participants who were either homozygous or heterozygous I148M carriers, approximately 93% of whom identified as Hispanic or Latino. A separate nine-patient Phase I study conducted in Japan produced consistent findings. No liver fat reduction was observed in heterozygous participants at any dose level studied.
Deal context
The transaction positions Madrigal to pursue a genetically stratified approach to MASH alongside its existing approved therapy, Rezdiffra (resmetirom), which targets a broader patient population through thyroid hormone receptor-beta agonism. ARO-PNPLA3 would address a distinct, genetically defined subset of MASH patients — those carrying the PNPLA3 I148M variant — rather than the general MASH population, creating a potential complementary positioning within Madrigal's portfolio. The PNPLA3 I148M variant is particularly prevalent among Hispanic patients, a population with elevated rates of MASH and historically underrepresented in clinical development programs.