@tuinman, lijst deze passage (uit bovengenoemd artikel) maar in:
Arrowhead Pharmaceuticals uses two types of GalNAc conjugates. The first generation was a dynamic polyconjugate (DPC) that utilized an endosomolytic peptide (butyl and amino vinyl ether, PBAVE, or melittin) masked with GalNAc through a pH sensitive carboxy dimethyl maleic anhydride linkage [114,115]. The siRNA is conjugated to cholesterol and is co-injected with the DPC as combination therapy. The cholesterol-siRNA forms a large aggregate (low-density lipoprotein) in blood, which is transported to and taken up by the liver, whereas the GalNAc-DPC is taken up specifically by ASGPR in the liver. When both are present in the same endosome, the GalNAc-DPC facilitates endosomal escape of the cholesterol-siRNA conjugates [114,115].
Arrowhead's lead compound into the clinics was ARC-520 along with a related ARC-521, which contained two siRNAs targeting different regions in the X gene in Hepatitis-B infection (HBV) [116,117]. ARC-520/521 has undergone multiple phase I and phase II trials alone and in combination with the antiviral entecavir [118]. However, in late 2016, the FDA halted five ongoing clinical trials involving ARC-520 due to a NHP death in one of Arrowhead's preclinical studies, likely due to toxicity from the DPC [119]. Despite the termination of the clinical trials, results from the clinical trials showed a rapid, six log suppression (>99.9%) of HBV DNA in all Hepatitis B e-antigen positive (HBeAg) treatment naive patients.
Treatment of HBeAg-negative naive patients reduced HBV DNA below the limit of detection. Single dose treatment of ARC-520 also inhibited covalently closed circular (cccDNA)-derived mRNA expression and reduced viral protein production by 99%. In addition, some patients developed and expressed antibodies against hepatitis B surface antigen [117]. Despite the regulatory shutdown of the ARC-520/521 clinical trials, Arrowhead showed that HBV is susceptible to RNAi therapeutics and gleaned a large volume of clinical data on just how to best tackle HBV.
Arrowhead's next generation delivery platform, called Targeted RNAi Molecule (TRiM), removes the problematic active endosomal escape agent (PBAVE, melittin) in favor of direct conjugation of GalNAc targeting domains [120]. While the exact nature of the TRiM siRNAs has not been made public, Arrowhead reports that numerous tailor design chemistries have been incorporated to generate highly robust RNAi triggers. Building off of their prior RNAi clinical experience, ARO-HBV targets both the X gene and the S gene. Importantly, the X gene targeting sequence is present on all integrated forms of HBV, whereas the ARC-520 siRNAs did not.
Using multiple sequence targets present on both cccDNA and integrated HBV, ARO-HBV reduces the opportunity for HBV to develop resistance to the RNAi therapeutics and allows the drug to tackle both forms of the virus [120], which is critical for achieving a cure. Arrowhead has begun recruiting patients for phase I/II clinical trials for ARO-HBV. Arrowhead also has begun recruitment for a phase I clinical trial involving ARO-AAT to treat alpha-1 antitrypsin (AAT) related liver disease by knocking down the mutant AAT gene [121]. In addition, Arrowhead has several preclinical GalNAc TRiM programs moving toward the clinics in 2018/2019.