Proof-of-Mechanism Study of the Phosphodiesterase 10 Inhibitor RG7203 in Patients With Schizophrenia and Negative Symptoms

Background

Reduced activation of dopamine D₁ receptor signaling may be implicated in reward functioning as a potential driver of negative symptoms in schizophrenia. Phosphodiesterase 10A (PDE10A), an enzyme that is highly expressed in the striatum, modulates both dopamine D₂- and D₁-dependent signaling.

Methods

We assessed whether augmentation of D₁ signaling by the PDE10 inhibitor RG7203 enhances imaging and behavioral markers of reward functions in patients with schizophrenia and negative symptoms. In a 3-period, double-blind, crossover study, we investigated the effects of RG7203 (5 mg and 15 mg doses) and placebo as adjunctive treatment to stable background antipsychotic treatment in patients with chronic schizophrenia with moderate levels of negative symptoms. Effects on reward functioning and reward-based effortful behavior were evaluated using the monetary incentive delay task during functional magnetic resonance imaging and the effort-cost-benefit and working memory reinforcement learning tasks.

Results

Patients (N = 33; 30 male, mean age ± SD 36.6 ± 7.0 years; Positive and Negative Syndrome Scale negative symptom factor score 23.0 ± 3.5 at screening) were assessed at three study centers in the United States; 24 patients completed the study. RG7203 at 5 mg significantly increased reward expectation–related activity in the monetary incentive delay task, but in the context of significantly decreased overall activity across all task conditions.

Conclusions

In contrast to our expectations, RG7203 significantly worsened reward-based effortful behavior and indices of reward learning. The results do not support the utility of RG7203 as adjunctive treatment for negative symptoms in patients with schizophrenia.

S43. A PROOF-OF-MECHANISM STUDY OF THE PDE10 INHIBITOR RG7203 IN PATIENTS WITH PROBING REWARD FUNCTIONS WITH IMAGING AND BEHAVIORAL APPROACHES

Background

The enzyme phosphodiesterase 10A (PDE10A) is highly expressed in the striatum where it modulates both dopamine D2 and D1 dependent signaling. Its inhibition leads to a suppression of D2 mediated signaling –similar to effects of D2 antagonists - and an enhancement of D1 dependent signaling. D1-dependent signaling has been implicated in reward based learning. Its deficient activation may be a key factor underlying deficient reward functions including reward anticipation and reward based learning that have been implicated as major drivers of negative symptoms of schizophrenia. Therefore, inhibition of PDE10 could be a way to ameliorate such deficits and consequently negative symptoms. In healthy volunteers the PDE10 inhibitor RG7203 indeed enhanced performance in tasks that probed reward functioning suggestive of its potential utility to treat negative symptoms in schizophrenia. We therefore tested the hypothesis that it should enhance imaging and behavioral markers of reward functions in patients with moderate negative symptoms in order to establish mechanistic proof of its utility as treatment of negative symptoms.

Methods

In a three-way cross-over study we investigated the effects of two doses of RG7203 (5 mg and 15 mg) and placebo given as adjunctive treatment to stable background antipsychotic treatment on reward functioning and reward-based effortful behavior using the monetary incentive delay (MID) task during fMRI and the effort choice task in patients with chronic schizophrenia and moderate levels of negative symptoms (PANSS negative symptom factor score ≥ 18 points). Each treatment period lasted three weeks followed by a 2 week washout period. fMRI and behavioral tasks were administered at the end of each treatment period. Key outcome measures were the differential BOLD during reward anticipation and overall BOLD activity during the MID task and the percentage of high-effort high-reward choices when the probability of reward was 100% during the effort choice task.

Results

Thirty-three patients with schizophrenia (30 male; 21 B, 9 W, 3 A; mean age 36.6 ± 7 y; PANSS NSFS = 22.8 (±1.4) at screening) were recruited at three study centers in the US. Twenty-four subjects finished the entire study. RG7203 at 5 mg significantly increased differential BOLD activity during reward anticipation in the MID task. However, this enhancement occurred in the context of a significant decrease of BOLD activity across all conditions during the MID task under treatment with RG7203. RG7203 significantly worsened reward-based effortful behavior in the effort choice task (the high-effort high-reward choice: 67% for both doses of RG7203 versus 73% for placebo). Multiple regression revealed that the decrease in effortful behavior was significantly related to the decrease in overall BOLD activity during the MID task and not related to the difference of BOLD activity during reward anticipation versus the control condition.

Discussion

In contrast to our expectation and previous results in healthy volunteers, RG7203 worsened indices of reward functions which we hypothesize may be due to a further enhancement of D2 antagonistic activity. The results do not support the utility of a PDE10 inhibitor as adjunctive treatment for negative symptoms in patients with schizophrenia. Given the previous observation that RG7203 enhanced reward functions in healthy volunteers who were not treated with D2 antagonist, the results of our study point to potentially deleterious effects of D2 blockade on reward functions and by extension on negative symptoms of schizophrenia. They raise the question if the presence of D2 antagonistic treatment curtails the potential effects of any adjunctive treatment for negative symptoms.

Evaluation of the Tolerability of Switching Patients on Chronic Full μ-Opioid Agonist Therapy to Buccal Buprenorphine

Objective Assess whether patients with chronic pain receiving 80 to 220 mg oral morphine sulfate equivalent of a full μ-opioid agonist could be transitioned to buccal buprenorphine at approximately 50% of their full dose without inducing opioid withdrawal or sacrificing analgesic efficacy.

Methods. A randomized, double-blind, double-dummy, active-controlled, two-period crossover study in adult patients receiving around-the-clock full opioid agonist therapy and confirmed to be opioid dependent by naloxone challenge. Study doses were substituted at the time of the regular dose schedule for each patient. The primary endpoint was the proportion of patients with a maximum Clinical Opiate Withdrawal Scale score ≥ 13 (moderate withdrawal) or use of rescue medication.

Results. 35 subjects on ≥ 80 mg morphine sulfate equivalent per day were evaluable for opioid withdrawal. One patient during buccal buprenorphine treatment and two during 50% full μ-opioid agonist treatment experienced opioid withdrawal of at least moderate intensity. The mean maximum Clinical Opiate Withdrawal Scale scores were similar, and numerically lower on buccal buprenorphine. There were no significant differences in pain ratings between treatments. The most frequent adverse events with buccal buprenorphine were headache (19%), vomiting (13%), nausea, diarrhea, and drug withdrawal syndrome (each 9%), and with full μ-opioid agonist were headache (16%), drug withdrawal syndrome (13%), and nausea (6%).

Conclusions. Chronic pain patients treated with around-the-clock full μ-opioid agonist therapy can be switched to buccal buprenorphine (a partial μ-opioid agonist) at approximately 50% of the full μ-opioid agonist dose without an increased risk of opioid withdrawal or loss of pain control.

Safety, pharmacokinetics and pharmacodynamics of the oral toll-like receptor 7 agonist GS-9620 in treatment-naive patients with chronic hepatitis C

BACKGROUND

GS-9620 is a potent oral agonist of toll-like receptor 7, a key modulator of the innate immune response. In healthy volunteers, low doses of GS-9620 (2, 4 and 6 mg) induced significant expression of peripheral interferon-stimulated-gene (ISG) mRNA in the absence of detectable serum interferon-α and systemic adverse events (AEs). We evaluated the safety, pharmacokinetics and pharmacodynamics of GS-9620 in treatment-naive patients chronically infected with HCV genotype 1.

METHODS

In this double-blind, placebo-controlled study, 51 patients were randomized 5:1 (active:placebo) to receive either a single dose or two once-weekly doses of GS-9620 at four dose levels (0.3, 1, 2 and 4 mg) or placebo. Pharmacodynamic assessments included peripheral ISG15 mRNA expression, serum interferon-α and interferon-γ-inducible protein (IP)-10 levels and HCV RNA quantification.

RESULTS

GS-9620 was well-tolerated at all doses. Most AEs were mild or moderate in severity. GS-9620 exhibited dose-linear pharmacokinetics with a median half-life in plasma of 18 h. Transient, dose-dependent ISG15 induction was observed at 1, 2 and 4 mg, with peak mean fold change within 48 h followed by a decline to baseline levels within 7 days of dosing. Serum interferon-α induction post-baseline was detected in 16.7% (8/48) of patients. No clinically significant reductions in HCV RNA were observed.

CONCLUSIONS

GS-9620 was safe, well-tolerated and biologically active in patients with HCV infection. Induction of ISG15 occurred in the absence of detectable serum interferon-α or systemic AEs in most patients, supporting a pre-systemic mechanism of action. ClinicalTrials.gov identifier: NCT01591668.

Clinical outcomes from an open-label study of edivoxetine use in pediatric patients with attention-deficit/hyperactivity disorder

OBJECTIVE

The purpose of this study was to assess the clinical outcomes from an open label study of edivoxetine, a selective norepinephrine reuptake inhibitor, in pediatric patients with attention-deficit/hyperactivity disorder (ADHD).

METHODS

This was a multi-cohort open-label study of edivoxetine consisting of a single-dose administration period (Part 1) and an open-label once daily (QD) dose long-term period (Part 2). Adolescents ages 12-17 years and children ages 6-11 years were enrolled in Part 1 and continued to Part 2 where they received 0.05 to 0.3 mg/kg edivoxetine QD for ≤12 months. Safety was assessed by adverse events, vital signs, weight, electrocardiograms, and laboratory tests. In Part 2, Attention-Deficit/Hyperactivity Disorder Rating Scale-Version IV-Parent Reported: Investigator Scored (ADHDRS-IV) and Clinical Global Impressions-ADHD-Severity (CGI-ADHD-S) scores were determined.

RESULTS

Fifty-three patients enrolled in Part 1, and 49 continued to Part 2 with a mean exposure duration of 22 weeks. The 31 patients completing Part 2 then entered another long-term open-label study. One serious adverse event of mania was reported; all other treatment-emergent adverse events were mild or moderate in severity. Nausea, decreased appetite, somnolence, increased blood pressure, and upper respiratory tract infection were most frequently reported (three events each). No clinically relevant changes were noted in the laboratory parameters. ADHDRS-IV total score, inattention and hyperactivity/impulsivity subscores, and CGI-ADHD-S scores were statistically significantly improved at endpoint compared with baseline.

CONCLUSIONS

This study provides preliminary evidence to suggest that edivoxetine at doses ≤0.3 mg/kg/day is safe and may improve ADHD symptoms in pediatric patients. These results require confirmation in larger, double-blind, placebo-controlled trials.

A phase 1, randomized, placebo-controlled, 3-day, dose-ranging study of GS-5885, an NS5A inhibitor, in patients with genotype 1 hepatitis C

BACKGROUND & AIMS

GS-5885 is an inhibitor of the hepatitis C virus (HCV) NS5A protein and exhibits potent suppression of genotype 1 HCV replicons. The safety, tolerability, pharmacokinetics, antiviral activity, and resistance profile of once-daily GS-5885 doses of 1-90 mg were evaluated in patients with chronic genotype 1 HCV.

METHODS

Genotype 1 HCV-infected patients were randomized to 3 days of once-daily (QD) dosing with placebo (n=12) or GS-5885 1 mg (n=10), 3 mg (n=10), 10 mg (n=20), 30 mg (n=10), or 90 mg (n=10). Plasma samples for pharmacokinetics, HCV RNA, and NS5A sequencing were collected through day 14.

RESULTS

GS-5885 was well tolerated and resulted in median maximal reductions in HCV RNA ranging from 2.3 log(10) IU/ml (1 mg QD) to 3.3 log(10) IU/ml (10 mg QD in genotype 1b and 30 mg QD). E(max) modeling indicated GS-5885 30 mg was associated with>95% of maximal antiviral response to HCV genotype 1a. HCV RNA reductions were generally more sustained among patients with genotype 1b vs. 1a. Three of 60 patients had a reduced response and harbored NS5A-resistant virus at baseline. NS5A sequencing identified residues 30 and 31 in genotype 1a, and 93 in genotype 1b as the predominant sites of mutation following GS-5885 dosing. Plasma pharmacokinetics was consistent with QD dosing.

CONCLUSIONS

During 3 days of monotherapy, low doses of GS-5885 demonstrated significant antiviral activity in genotype 1a and 1b HCV-infected patients. GS-5885 is currently being evaluated in combination with direct antiviral regimens with and without peginterferon.