Published online Jan 14, 2018. doi: 10.3748/wjg.v24.i2.195
Peer-review started: October 25, 2017
First decision: November 14, 2017
Revised: November 24, 2017
Accepted: December 5, 2017
Article in press: December 5, 2017
Published online: January 14, 2018
Studies within this manuscript detail the efficacy of the dual in vitro FXR/TGR5 agonist INT-767 upon multiple histological endpoints in a mouse model of diet-induced non-alcoholic steatohepatitis (NASH). Prior pharmacology studies using INT-767 had not been conducted in models of established and biopsy-confirmed NASH with sufficient fibrosis.
INT-767 is in early clinical development for NASH. These preclinical studies provide proof-of-concept for efficacy in NASH and preclinical superiority relative to obeticholic acid (OCA; an FXR agonist in late stage development for NASH). The present studies also aimed to shed light on the impact of INT-767 on morphometric features of steatosis (droplet size and number) and fibrosis (fiber density) using quantitative histological methods.
The primary objective was to characterize improvements in NASH histopathology using qualitative (e.g., NAS stage scoring for steatosis, inflammation, and ballooning and fibrosis) and quantitative (percent fractional area; %FA) endpoints. The secondary objective was to understand the relative efficacy of INT-767 to and mechanistic differences from OCA. This objective was achieved by comparing drug distribution and gene expression profiles in the liver and ileum.
Therapeutic effects in NASH were measured using blinded qualitative (HE stained sections) and quantitative (%FA of IHC-stained sections) methods. The inclusion of a biopsy at both baseline and endpoint is unique and enabled a within-subjects, repeated-measures study design. Most studies do not include a biopsy and rely on endpoint measurements only. Morphometric assessments were also performed using label-free second harmonic generation imaging (for fibrosis) and two-photon emission (for steatosis) which are novel in NASH. The rigor of measuring the same samples using multiple histological techniques also allows the reader to consider how well these methods correlate with one another. mRNA levels of FXR regulated candidate genes were measured using RNA sequencing. LC/MS/MS was used to determine compound levels in liver and ileum.
In an 8-wk monotherapy study, INT-767 significantly improved qualitative features of NASH as demonstrated by a blinded assessment of NAS and fibrosis stage scores. Quantitatively, INT-767 significantly improved %FA for steatosis, inflammation (assessed by galectin-3 immunohistochemistry; IHC), fibrosis (Col1a1 IHC) and key components of basement membrane formation (laminin IHC). In a 16-wk comparative treatment study, NASH mice treated with INT-767 (3 and 10 mg/kg) exerted greater therapeutic potency and efficacy than OCA (10 and 30 mg/kg). Mechanistically, both OCA and INT-767 accumulate to a similar extent within the liver and ileum. INT-767 drives hepatic, but not ileal, FXR gene expression profiles more strongly than OCA, implying that the liver is a key site of action for INT-767.
INT-767 improved key histological features of diet-induced and biopsy-confirmed NASH across studies using multiple methods and was shown to be more potent and efficacious than OCA. Novel insights from morphometric analyses include: (1) not only does INT-767 improve fibrosis %FA, but also the intensity of the collagen fiber signal consistent with reducing fiber density; and (2) in addition to reducing steatosis %FA, INT-767 induced a clear shift to reduce vesicular lipid droplet size believed to be more a healthful form of steatosis. Together, these preclinical findings confirm durable histological benefits with INT-767 dosing and suggest that INT-767 may exert greater efficacy than OCA.
The present studies confirm and extend upon the extant literature validating FXR as a pharmacological target for NASH. Future research should consider (1) the mechanistic contribution of TGR5 to the in vivo effects of INT-767, and (2) the necessity and sufficiency of activating hepatic vs ileal FXR when targeting NASH, as INT-767 was more efficacious than OCA yet elicited only minimal ileal FXR activation. Finally, other models of diet- or toxin-induced NASH should consider incorporating a baseline biopsy to exclude mice that did not develop the desired phenotype prior to treatment initiation and gain a deeper mechanistic understanding of any pharmacologic intervention. Ongoing research continues to elucidate the role of FXR agonism on features of the basement membrane in NASH.