A Thorough QT Study of the Combination Glecaprevir + Pibrentasvir on Cardiac Repolarization in Healthy Subjects

PURPOSE

Fixed-dose combination glecaprevir (GLE) 300 mg + pibrentasvir (PIB) 120 mg is an orally administered once daily antiviral regimen approved for the treatment of hepatitis C virus (HCV) infection. The objective of this study was to evaluate the potential for cardiac repolarization following GLE + PIB administration in healthy adults.

METHODS

This placebo- and active-controlled, randomized, single-dose, 4-period, 4-sequence crossover study enrolled 48 healthy subjects. The doses of GLE 400 mg + PIB 120 mg were selected to provide exposures comparable to those with the doses that are therapeutic in the HCV-infected population, GLE 300 mg + PIB 120 mg. The doses of GLE 600 mg + PIB 240 mg were selected to provide supratherapeutic exposures without exceeding the exposures of the GLE + PIB maximal tolerated doses. Moxifloxacin 400 mg (active control/open label) was used for confirming the sensitivity of the ECG assay in detecting QTc prolongation. Time-matched plasma concentrations and triplicate ECGs were obtained on treatment days -1 and 1. The primary end point was time-matched, placebo-corrected, baseline-adjusted Fridericia-corrected QT interval (ΔΔQTcF). Pharmacokinetic-pharmacodynamic analyses characterized the relationship between GLE and PIB plasma concentrations and ΔΔQTcF using a linear regression model and linear mixed-effects model. Findings from categorical analyses of ECG-interval data were also summarized. Tolerability was evaluated through adverse-events monitoring, physical examination including vital sign measurements, ECGs, and laboratory tests.

FINDINGS

A total of 48 subjects (22 women [46%], 26 men [54%]), were enrolled in the study, and 47 subjects completed all 4 periods. None of the subjects had a change from baseline in QTcF interval of >30 msec or an absolute QTcF interval of >450 msec. Peak ΔΔQTcF values observed at 5 h postdose (T_max) were 2.9 msec (upper 95% confidence limit, 4.9 msec) with the therapeutic dose and 3.1 msec (upper 95% confidence limit, 5.1 msec) with the supratherapeutic dose, with both upper 95% confidence limits well below the 10-msec threshold. Assay sensitivity was confirmed by peak ΔΔQTcF in the positive control (12.8 ms at 2 h postdose). No statistically significant GLE or PIB concentration-dependent effects on ΔΔQTcF were observed. Headache and skin irritation from ECG electrodes were the most commonly reported AEs. No clinically significant vital sign measurements, ECG findings, or laboratory measurements were observed. There were no patterns of T- and U-wave morphologic abnormalities.

IMPLICATIONS

The fixed-dose combination regimen of GLE/PIB does not prolong the QTc interval. ClinicalTrials.gov identifier.

Beta-Aminoisobutyric Acid Inhibits Hypothalamic Inflammation by Reversing Microglia Activation

Beta-aminoisobutyric acid (BAIBA), a natural thymine catabolite, is involved in the beneficial effects of exercise on metabolic disorders. In particular, it has been reported to reverse the inflammatory processes observed in the peripheral organs of animal models of obesity. Therefore, this study aimed to investigate whether BAIBA improves hypothalamic inflammation, which is also tightly coupled with the development of obesity. We observed that treatment with BAIBA effectively reversed palmitic acid-induced hypothalamic inflammation and microglial activation in vivo. Consistent with these findings, we confirmed that BAIBA reversed body weight gain and increased adiposity observed in mice fed with a high-fat diet. Collectively, the current findings evidence the beneficial impacts of BAIBA on the imbalance of energy metabolism linked to hypothalamic inflammation.

Characterization of 2-(methylamino)alkanoic acid capacity to restrict blood-brain phenylalanine transport in Pah enu2 mice: preliminary findings

BACKGROUND

Our laboratory seeks a pharmacotherapeutic intervention for PKU that utilizes non-physiological amino acids (NPAAs) to block the accumulation of phenylalanine (Phe) in the brain. In previous studies (Vogel et al. 2013), methylation of the amino group of 2-aminoisobutyrate (AIB) provided an enhanced degree of selectivity for Phe restriction into the brain of Pah(enu2) mice in comparison to unmethylated AIB, leading to the hypothesis that 2-(methylamino)alkanoic acid analogs of AIB might represent targeted inhibitors of Phe accretion into the brain.

METHODS

Pah(enu2) and control mice were intraperitoneally administered (500-750 mg/kg body weight, once daily; standard 19% protein diet) AIB, methyl AIB (MAIB), isovaline, and two MAIB analogs, 2-methyl-2-(methylamino)butanoic (MeVal) and 3-methyl-2-(methylamino)pentanoic (MePent) acids for one week, followed by brain and blood isolation for amino acid analyses using UPLC.

RESULTS

In the brain, AIB significantly reduced Phe accretion in Pah(enu2) mice, while MeVal significantly improved glutamine and aspartic acids. Four of five test compounds improved brain threonine and arginine levels. AIB, MAIB and IsoVal significantly reduced blood Phe, with no effect of any drug intervention on other sera amino acids.

CONCLUSIONS

Further evaluation of AIB and the 2-(methylamino)alkanoic acids as inhibitors of brain Phe accumulation in Pah(enu2) mice is warranted, with more detailed evaluations of route of administration, combinatorial intervention, and detailed toxicity studies.

Blood-brain barrier permeability during dopamine-induced hypertension in fetal sheep

Dopamine is often used as a pressor agent in sick newborn infants, but an increase in arterial blood pressure could disrupt the blood-brain barrier (BBB), especially in the preterm newborn. Using time-dated pregnant sheep, we tested the hypothesis that dopamine-induced hypertension increases fetal BBB permeability and cerebral water content. Barrier permeability was assessed in nine brain regions, including cerebral cortex, caudate, thalamus, brain stem, cerebellum, and spinal cord, by intravenous injection of the small tracer molecule [(14)C]aminoisobutyric acid at 10 min after the start of dopamine or saline infusion. We studied 23 chronically catheterized fetal sheep at 0.6 (93 days, n = 10) and 0.9 (132 days, n = 13) gestation. Intravenous infusion of dopamine increased mean arterial pressure from 38 +/- 3 to 53 +/- 5 mmHg in 93-day fetuses and from 55 +/- 5 to 77 +/- 8 mmHg in 132-day fetuses without a decrease in arterial O(2) content. These 40% increases in arterial pressure are close to the maximum hypertension reported for physiological stresses at these ages in fetal sheep. No significant increases in the brain transfer coefficient of aminoisobutyric acid were detected in any brain region in dopamine-treated fetuses compared with saline controls at 0.6 or 0.9 gestation. There was also no significant increase in cortical water content with dopamine infusion at either age. We conclude that a 40% increase in mean arterial pressure during dopamine infusion in normoxic fetal sheep does not produce substantial BBB disruption or cerebral edema even as early as 0.6 gestation.

Differential permeability of a human brain tumor xenograft in the nude rat: impact of tumor size and method of administration on optimizing delivery of biologically diverse agents

To assess how to maximize drug delivery to intracerebral tumors and surrounding brain, this study examined the effects of route and method of administration and tumor size on the distribution of three agents in a nude rat intracerebral tumor xenograft model. Aminoisobutyric acid (M(r) 103), methotrexate (M(r) 454), and dextran 70 (M(r) 70,000) were administered i.v. or intra-arterially (i.a.) with or without osmotic blood-brain barrier disruption (BBBD) at 8, 12, or 16 days after tumor cell inoculation (n = 72). A 2.2- to 2.5-fold increase in delivery to tumor and surrounding brain was observed when i.a. was compared with i.v., and a 2.5- to 7.6-fold increase was observed when BBBD was compared with the saline control. The combined effect of i.a. administration and BBBD was to increase delivery 6.3-16.7-fold. The greatest benefit of BBBD was seen in animals with 8-day tumors, whereas BBBD had less benefit in improving delivery to intracerebral tumor and brain around tumor as the tumors grew larger. Regional delivery decreased as the molecular weight of the agent increased. Based on these results, we suggest that i.a. administration of antitumor agents may be adequate to obtain initial responses in large, very permeable, intracerebral tumors. However, in smaller, less permeable tumors or after an initial response to treatment, there may be a significant therapeutic advantage to i.a. agent administration and BBBD.

Sources of amino acids for protein synthesis during early organogenesis in the rat. 3. Methionine incorporation

Rat conceptuses at 9.5 days post-conception were cultured for 27 h in whole rat serum. [3H]Methionine, or rat serum proteins containing [3H]methionine, was introduced at 24 or 6 h before the termination of the culture. The total clearance of radioactivity into the embryo and the visceral yolk sac from the two sources was measured; also the extent to which the accumulated radioactivity was acid-insoluble. Similar experiments, but using [3H]leucine, were performed for comparison. The results indicate that free amino acid and protein can both serve as sources of amino acids for incorporation into the embryo and yolk sac, and it is estimated that in vivo over 95 per cent of the methionine (and the leucine) incorporated into these tissues arises from protein captured and digested by the yolk sac. Almost all the leucine accumulated into the conceptus is present as protein, but a larger fraction of the methionine accumulated is found in acid-soluble form. When the amino acids were delivered in the form of plasma proteins, the incorporation of methionine was two to three times more efficient than that of leucine, an observation most readily explained by leucine being provided in excess of requirements. In the light of reports that an adequate concentration of free methionine is important for the normal development of rat embryos in vitro, it is concluded that, although most of the amino acid required by the embryo is supplied as protein, the small fraction supplied as free amino acid may be critical for methionine but probably not for leucine.

Sources of amino acids for protein synthesis during early organogenesis in the rat. 4. Mechanisms before envelopment of the embryo by the yolk sac

It was previously shown that uptake and digestion of protein by the visceral yolk sac supplies almost all of the amino acid needed by the 9.5-11.5-day rat conceptus cultured in vitro. Our aim was to test the hypothesis that protein uptake and digestion may not be as important as an amino acid source in the 8.5-9.5-day period, a stage of development before the yolk sac placenta envelops the embryo and before the vitelline circulation is established. Eight and a half-day rat conceptuses were cultured in serum supplemented with trace amounts of free [3H]leucine, [3H]leucine-containing serum proteins, free [3H]methionine or [3H]methionine-containing serum proteins. The incorporation of radiolabelled amino acid into acid-soluble and acid-insoluble fractions of the conceptus was determined. Leucine from either source was incorporated principally into proteins of the conceptus, but a greater proportion of the methionine incorporated was found in the low molecular weight fraction. It is estimated that 88 per cent of the leucine and 96 per cent of the methionine used by the conceptus was derived from protein in the culture serum; free amino acid comprised a minor supply source. We conclude that, despite the different anatomic relationships, the majority of amino acid incorporated into newly synthesized proteins of the conceptus very early in organogenesis is supplied by the digestion of protein in extraembryonic tissue, most likely the visceral yolk sac.

In vivo release of neuroactive amino acids from the inferior colliculus of the guinea pig using brain microdialysis

Microdialysis techniques were used to measure in vivo release of neuroactive amino acids from the central nucleus of the inferior colliculus (ICC) in anesthetized guinea pigs. Concentric dialysis probes were implanted in the ICC and perfused with Ringer solution of various compositions at a flow rate of 2.0 microliters/min. Consecutive 10-min fractions of the dialysate were collected for up to 3 h under different experimental conditions, frozen and assayed for amino acid content by high performance liquid chromatography (HPLC). There was an initial high outflow of amino acids which declined to stable baseline levels after 2 h. Following this stabilization period, perfusion with a medium containing 100 mM KCl produced an increase in the extracellular levels of aspartate (Asp), glutamate (Glu), gamma-aminobutyric acid (GABA) and glycine (Gly). Only the increases in GABA and Gly were statistically significant. None of the increases occurred in the presence of 2.0 mM cobalt suggesting the release of amino acids is calcium dependent. Histological examination revealed that tissue damage was minimal and largely confined to the immediate vicinity of the probes. We were also able to show that the blood brain barrier (BBB) appeared to heal 2 h after probe implantation. Thus, following intravenous injection of [3H]alpha-aminoisobutyric acid (AIB), which does not cross the intact BBB, no isotope was recovered in the dialysate. These results demonstrate that microdialysis is a unique and suitable method to monitor changes in the extracellular levels of amino acid neurotransmitters in a central auditory structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of two model amino acids from cerebrospinal fluid to brain and blood

Ventriculocisternal perfusions of anesthetized rabbits were performed for 1-3 h with solutions containing radioactively labeled alpha-aminoisobutyric acid (AIB), cycloleucine (CYCL), and sucrose. Serial brain samples were taken at the conclusion of the perfusion period and assayed for radioactivity. Tissue concentration profiles were constructed from these data; tissue distribution spaces and diffusion coefficients (Dt) plus brain capillary transfer constants were estimated from the profiles. The Dt of sucrose was somewhat larger at 1 h than at 2 and 3 h. Tissue distribution spaces of 300-400% were found with AIB after 3 h. Inclusion of 5 mM AIB in the perfusate produced markedly lower tracer AIB spaces. The tissue distribution spaces of CYCL ranged from 100 to 400% and depended on the concentration of CYCL in the perfusate. A brain-to-blood transfer half time of 7.5 min was measured for CYCL. These findings demonstrate that sizable cellular uptake of CYCL and AIB occurs, that these processes are concentration dependent, and that the rates of influx and efflux across brain capillaries are similar.