Phase I study of PF‐04895162, a Kv7 channel opener, reveals unexpected hepatotoxicity in healthy subjects, but not rats or monkeys: clinical evidence of disrupted bile acid homeostasis

Abstract

During a randomized Phase 1 clinical trial the drug candidate, PF-04895162 (ICA-105665), caused transaminase elevations (≥grade 1) in six of eight healthy subjects treated at 300 mg twice daily for 2-weeks (NCT01691274). This was unexpected since studies in rats (<6 months) and cynomolgus monkeys (<9 months) treated up to 100 mg/kg/day did not identify the liver as a target organ. Mechanistic studies showed PF-04895162 had low cytotoxic potential in human hepatocytes, but inhibited liver mitochondrial function and bile salt export protein (BSEP) transport. Clinical relevance of these postulated mechanisms of liver injury was explored in three treated subjects that consented to analysis of residual pharmacokinetic plasma samples. Compared to a nonresponder, two subjects with transaminase elevations displayed higher levels of miRNA122 and total/conjugated bile acid species, whereas one demonstrated impaired postprandial clearance of systemic bile acids. Elevated taurine and glycine conjugated to unconjugated bile acid ratios were observed in two subjects, one before the onset of elevated transaminases. Based on the affinity of conjugated bile acid species for transport by BSEP, the profile of plasma conjugated/unconjugated bile acid species was consistent with inhibition of BSEP. These data collectively suggest that the human liver injury by PF-04895162 was due to alterations in bile acid handling driven by dual BSEP/mitochondrial inhibition, two important risk factors associated with drug-induced liver injury in humans. Alterations in systemic bile acid composition were more important than total bile acids in the manifestation of clinical liver injury and may be a very early biomarker of BSEP inhibition.

Keywords: BSEP inhibition; PF-04895162 (ICA-105665); bile acid conjugation status; bile acid homeostasis; hepatotoxicity.

Figure 1

Disposition of subjects

Figure 2

Individual ALT, AST, and Total Bilirubin concentrations after single dose (Period 1) and multiple dose PF‐04895162 at 300 mg BID (Period 3) after an overnight fast. Note: All subjects received PF‐04895162 in Period 1, whereas Subjects 5 and 9 received placebo in Period 3 only

Figure 3

Time‐course analysis of individual patient samples from multiple dose PF‐04895162 at 300 mg BID (Period 3) for serum alanine aminotransferase (ALT) (upper panel, data from Figure 1) and who reconsented pharmacokinetic plasma samples for miRNA122 (middle panel) and total bile acids (lower panel) analysis. Samples were obtained before dose administration under fasted conditions

Figure 4

Time course of bile acid species from individual patient samples acquired from multiple dose PF‐04895162 at 300 mg BID (Period 3). Plasma samples used for pharmacokinetic analysis were reconsented for total and fractionated bile acid analysis. (A) Differences in total bile acids between treated subjects on Day 7 and 14 during a 12 h AUC time course profile (AUC 0‐12 h). (B) Ratio of unconjugated primary/secondary bile acids (CA, cholic acid; CDCA, chenodeoxycholic acid; and DCA, deoxycholic acid) Day 14/Day 7 (AUC 0‐12 h) between treated subjects. (C) Time course of total bile acids as a function of dose (open arrow) and meal (closed arrow, B, breakfast; L, lunch; D, dinner) administration on Day 7 between treated subjects. Following an 8 h fast, study medication was administered approximately one tablet every 12 h starting at approximately 0900 h on Day 1 and concluding with a morning administration on Day 14. Subjects were dosed in the morning and evening for 14 days (morning only on Day 14). Food was withheld from subjects for 2 h post morning and evening doses in a BID schedule. Subjects were fasted overnight and for 2 h prior to evening dosing. (D) Ratio of taurine conjugated to unconjugated bile acid species (TCA, taurocholic acid; CA, cholic acid; TCDCA, taurochenodeoxycholic acid; CDCA, chenodeoxycholic acid) between treated subjects. (E) Ratio of glycine conjugated to unconjugated bile acid species (GCA, glycocholic acid; CA, cholic acid; GCDCA, glycochenodeoxycholic acid; CDCA, chenodeoxycholic acid) between treated subjects. Except for Panel C total bile acids and respective ratios are based on a 12 h AUC after the morning dose with the following unit value in μmoles.h/L. Shading in bar graphs represent specific patients (light gray = Subject 6, medium gray = Subject 10, black = Subject 8)